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  • 1.
    Abdellah, Mohamed
    et al.
    Uppsala universitet, Teknisk-naturvetenskapliga vetenskapsområdet, Kemiska sektionen, Institutionen för kemi - Ångström, Fysikalisk kemi. South Valley Univ, Qena Fac Sci, Dept Chem, Qena 83523, Egypt..
    El-Zohry, Ahmed M.
    Uppsala universitet, Teknisk-naturvetenskapliga vetenskapsområdet, Kemiska sektionen, Institutionen för kemi - Ångström, Fysikalisk kemi.
    Antila, Liisa J.
    Uppsala universitet, Teknisk-naturvetenskapliga vetenskapsområdet, Kemiska sektionen, Institutionen för kemi - Ångström, Fysikalisk kemi.
    Windle, Christopher D.
    Univ Cambridge, Dept Chem, Christian Doppler Lab Sustainable SynGas Chem, Lensfield Rd, Cambridge CB2 1EW, England..
    Reisner, Erwin
    Univ Cambridge, Dept Chem, Christian Doppler Lab Sustainable SynGas Chem, Lensfield Rd, Cambridge CB2 1EW, England..
    Hammarström, Leif
    Uppsala universitet, Teknisk-naturvetenskapliga vetenskapsområdet, Kemiska sektionen, Institutionen för kemi - Ångström, Fysikalisk kemi.
    Time-Resolved IR Spectroscopy Reveals a. Mechanism with TiO2 as a Reversible Electron Acceptor in a TiO2-Re Catalyst System for CO2 Photoreduction2017Inngår i: Journal of the American Chemical Society, ISSN 0002-7863, E-ISSN 1520-5126, Vol. 139, nr 3, s. 1226-1232Artikkel i tidsskrift (Fagfellevurdert)
    Abstract [en]

    Attaching the phosphonated molecular catalyst [(ReBr)-Br-I(bpy)-(CO)(3)](0) to the wide-bandgap semiconductor TiO2 strongly enhances the rate of visible-light-driven reduction of CO2 to CO in dimethylformamide with triethanolamine (TEOA) as sacrificial electron donor. Herein, we show by transient mid-IR spectroscopy that the mechanism of catalyst photoreduction is initiated by ultrafast electron injection into TiO2, followed by rapid (ps-ns) and sequential two-electron oxidation of TEOA that is coordinated to the Re center. The injected electrons can be stored in the conduction band of TiO2 on an ms-s time scale, and we propose that they lead to further reduction of the Re catalyst and completion of the catalytic cycle. Thus, the excited Re catalyst gives away one electron and would eventually get three electrons back. The function of an electron reservoir would represent a role for TiO2 in photocatalytic CO2 reduction that has previously not been considered. We propose that the increase in photocatalytic activity upon heterogenization of the catalyst to TiO2 is due to the slow charge recombination and the high oxidative power of the Re-II species after electron injection as compared to the excited MLCT state of the unbound Re catalyst or when immobilized on ZrO2, which results in a more efficient reaction with TEOA.

    Fulltekst (pdf)
    fulltext
  • 2.
    Abelein, Axel
    et al.
    Stockholms universitet, Naturvetenskapliga fakulteten, Institutionen för biokemi och biofysik.
    Jarvet, Jüri
    Stockholms universitet, Naturvetenskapliga fakulteten, Institutionen för biokemi och biofysik. The National Institute of Chemical Physics and Biophysics, Estonia.
    Barth, Andreas
    Stockholms universitet, Naturvetenskapliga fakulteten, Institutionen för biokemi och biofysik.
    Gräslund, Astrid
    Stockholms universitet, Naturvetenskapliga fakulteten, Institutionen för biokemi och biofysik.
    Danielsson, Jens
    Stockholms universitet, Naturvetenskapliga fakulteten, Institutionen för biokemi och biofysik.
    Ionic Strength Modulation of the Free Energy Landscape of A beta(40) Peptide Fibril Formation2016Inngår i: Journal of the American Chemical Society, ISSN 0002-7863, E-ISSN 1520-5126, Vol. 138, nr 21, s. 6893-6902Artikkel i tidsskrift (Fagfellevurdert)
    Abstract [en]

    Protein misfolding and formation of cross-beta structured amyloid fibrils are linked to, many neurodegenerative disorders. Although recently developed,quantitative approaches have started to reveal the molecular nature of self-assembly and fibril formation of proteins and peptides, it is yet unclear how these self-organization events are precisely modulated by microenvironmental factors, which are known to strongly affect the macroscopic aggregation properties. Here, we characterize the explicit effect of ionic strength on the microscopic aggregation rates of amyloid beta peptide (A beta 40) self-association, implicated in Alzheimer's disease. We found that physiological ionic strength accelerates A beta 40 aggregation kinetics by promoting surface-catalyzed secondary nucleation reactions. This promoted catalytic effect can be assigned to shielding of electrostatic repulsion between Monomers on the fibril surface or between the fibril surface itself and monomeric peptides. Furthermore, we observe the formation of two different beta-structured states with =similar but distinct spectroscopic features, which can be assigned to an off-pathway immature state (F-beta*) and a mature stable State (F-beta), where salt favors formation of the F-beta fibril morphology. Addition of salt to preformed F-beta* accelerates transition to F-beta, underlining the dynamic nature of A beta 40 fibrils in solution. On the basis of,these results we suggest a model where salt decreases the free-energy barrier for A beta 40 folding to the F-beta state, favoring the buildup of the mature fibril morphology while omitting competing, energetically less favorable structural states.

  • 3.
    Abrahamsson, Maria
    et al.
    Uppsala universitet, Teknisk-naturvetenskapliga vetenskapsområdet, För teknisk-naturvetenskapliga fakulteten gemensamma enheter, Acceleratormasspektrometrigruppen. Uppsala universitet, Teknisk-naturvetenskapliga vetenskapsområdet, Kemiska sektionen, Institutionen för fotokemi och molekylärvetenskap.
    Jäger, Michael
    Uppsala universitet, Teknisk-naturvetenskapliga vetenskapsområdet, Kemiska sektionen, Institutionen för fotokemi och molekylärvetenskap.
    Kumar, Rohan J.
    Uppsala universitet, Teknisk-naturvetenskapliga vetenskapsområdet, Kemiska sektionen, Institutionen för fotokemi och molekylärvetenskap.
    Österman, Tomas
    Uppsala universitet, Teknisk-naturvetenskapliga vetenskapsområdet, Kemiska sektionen, Institutionen för kvantkemi.
    Persson, Petter
    Uppsala universitet, Teknisk-naturvetenskapliga vetenskapsområdet, Kemiska sektionen, Institutionen för kvantkemi.
    Becker, Hans-Christian
    Uppsala universitet, Teknisk-naturvetenskapliga vetenskapsområdet, Kemiska sektionen, Institutionen för fotokemi och molekylärvetenskap.
    Johansson, Olof
    Uppsala universitet, Teknisk-naturvetenskapliga vetenskapsområdet, Kemiska sektionen, Institutionen för kvantkemi.
    Hammarström, Leif
    Uppsala universitet, Teknisk-naturvetenskapliga vetenskapsområdet, Kemiska sektionen, Institutionen för fotokemi och molekylärvetenskap.
    Bistridentate Ruthenium(II)polypyridyl-Type Complexes with Microsecond 3MLCT State Lifetimes: Sensitizers for Rod-Like Molecular Arrays2008Inngår i: Journal of the American Chemical Society, ISSN 0002-7863, E-ISSN 1520-5126, Vol. 130, nr 46, s. 15533-15542Artikkel i tidsskrift (Fagfellevurdert)
    Abstract [en]

    A series of bistridentate ruthenium(II) polypyridyl-type complexes based on the novel 2,6-di(quinolin-8-yl)pyridine (dqp) ligand have been synthesized and their photophysical properties have been studied. The complexes are amenable to substitution in the 4-position of the central pyridine with conserved quasi-C2v symmetry, which allows for extension to isomer-free, rod-like molecular arrays for vectorial control of electron and energy transfer. DFT calculations performed on the parent [Ru(dqp) 2](2+) complex (1) predicted a more octahedral structure than in the typical bistridentate complex [Ru(tpy)2](2+) (tpy is 2,2':6',2"-terpyridine) thanks to the larger ligand bite angle, which was confirmed by X-ray crystallography. A strong visible absorption band, with a maximum at 491 nm was assigned to a metal-to-ligand charge transfer (MLCT) transition, based on time-dependent DFT calculations. 1 shows room temperature emission (Phi = 0.02) from its lowest excited ((3)MLCT) state that has a very long lifetime (tau = 3 micros). The long lifetime is due to a stronger ligand field, because of the more octahedral structure, which makes the often dominant activated decay via short-lived metal-centered states insignificant also at elevated temperatures. A series of complexes based on dqp with electron donating and/or accepting substituents in the 4-position of the pyridine was prepared and the properties were compared to those of 1. An unprecedented (3)MLCT state lifetime of 5.5 micros was demonstrated for the homoleptic complex based on dqpCO2Et. The favorable photosensitizer properties of 1, such as a high extinction coefficient, high excited-state energy and long lifetime, and tunable redox potentials, are maintained upon substitution. In addition, the parent complex 1 is shown to be remarkably photostable and displays a high reactivity in light-induced electron and energy transfer reactions with typical energy and electron acceptors and donors: methylviologen, tetrathiofulvalene, and 9,10-diphenylanthracene. This new class of complexes constitutes a promising starting point for the construction of linear, rod-like molecular arrays for photosensitized reactions and applications in artificial photosynthesis and molecular electronics.

  • 4.
    Abrahamsson, Maria
    et al.
    Uppsala universitet, Teknisk-naturvetenskapliga vetenskapsområdet, För teknisk-naturvetenskapliga fakulteten gemensamma enheter, Acceleratormasspektrometrigruppen. Uppsala universitet, Teknisk-naturvetenskapliga vetenskapsområdet, Kemiska sektionen, Institutionen för fotokemi och molekylärvetenskap.
    Jäger, Michael
    Uppsala universitet, Teknisk-naturvetenskapliga vetenskapsområdet, Kemiska sektionen, Institutionen för fotokemi och molekylärvetenskap.
    Österman, Tomas
    Uppsala universitet, Teknisk-naturvetenskapliga vetenskapsområdet, Kemiska sektionen, Institutionen för fotokemi och molekylärvetenskap. Uppsala universitet, Teknisk-naturvetenskapliga vetenskapsområdet, Kemiska sektionen, Institutionen för kvantkemi.
    Eriksson, Lars
    Persson, Petter
    Uppsala universitet, Teknisk-naturvetenskapliga vetenskapsområdet, Kemiska sektionen, Institutionen för kvantkemi.
    Becker, Hans-Christian
    Uppsala universitet, Teknisk-naturvetenskapliga vetenskapsområdet, Kemiska sektionen, Institutionen för fotokemi och molekylärvetenskap.
    Johansson, Olof
    Uppsala universitet, Teknisk-naturvetenskapliga vetenskapsområdet, Kemiska sektionen, Institutionen för fotokemi och molekylärvetenskap.
    Hammarström, Leif
    Uppsala universitet, Teknisk-naturvetenskapliga vetenskapsområdet, Kemiska sektionen, Institutionen för fotokemi och molekylärvetenskap.
    A 3.0 mu s room temperature excited state lifetime of a bistridentate Ru-II-polypyridine complex for rod-like molecular arrays2006Inngår i: Journal of the American Chemical Society, ISSN 0002-7863, E-ISSN 1520-5126, Vol. 128, nr 39, s. 12616-12617Artikkel i tidsskrift (Fagfellevurdert)
    Abstract [en]

    A bistridentate RuII-polypyridine complex [Ru(bqp)2]2+ (bqp = 2,6-bis(8'-quinolinyl)pyridine) has been prepared, which has a coordination geometry much closer to a perfect octahedron than the typical Ru(terpyridine)2-type complex. Thus, the complex displays a 3.0 mus lifetime of the lowest excited metal-to-ligand charge transfer (3MLCT) state at room temperature. This is, to the best of our knowledge, the longest MLCT state lifetime reported for a RuII-polypyridyl complex at room temperature. The structure allows for the future construction of rod-like, isomer-free molecular arrays by substitution of donor and acceptor moieties on the central pyridine units. This makes it a promising photosensitizer for applications in molecular devices for artificial photosynthesis and molecular electronics.

  • 5.
    Acharya, P
    et al.
    Uppsala universitet, Teknisk-naturvetenskapliga vetenskapsområdet, Biologiska sektionen, Institutionen för bioorganisk kemi.
    Cheruku, P
    Uppsala universitet, Teknisk-naturvetenskapliga vetenskapsområdet, Biologiska sektionen, Institutionen för bioorganisk kemi.
    Chatterjee, Sunanda
    Uppsala universitet, Teknisk-naturvetenskapliga vetenskapsområdet, Biologiska sektionen, Institutionen för bioorganisk kemi.
    Karthick Babu, S
    Uppsala universitet, Teknisk-naturvetenskapliga vetenskapsområdet, Biologiska sektionen, Institutionen för bioorganisk kemi.
    Acharya, S
    Uppsala universitet, Teknisk-naturvetenskapliga vetenskapsområdet, Biologiska sektionen, Institutionen för bioorganisk kemi.
    Measurement of nucleobase pKa values in model mononucleotides shows RNA-RNA duplexes to be more stable than DNA-DNA duplexes2004Inngår i: Journal of the American Chemical Society, ISSN 0002-7863, E-ISSN 1520-5126, Vol. 126, nr 9, s. 2862-2869Artikkel i tidsskrift (Fagfellevurdert)
    Abstract [en]

    To understand why the RNA-RNA duplexes in general has a higher thermodynamic stability over the corresponding DNA-DNA duplexes, we have measured the pK(a) values of both nucleoside 3',5'-bis-ethyl phosphates [Etp(d/rN)pEt] and nucleoside 3'-ethyl phosphates [(d/rN)pEt] (N = A, G, C, or T/U), modeling as donors and acceptors of base pairs in duplexes. While the 3',5'-bis-phosphates, Etp(d/rN)pEt, mimic the internucleotidic monomeric units of DNA and RNA, in which the stacking contribution is completely absent, the 3'-ethyl phosphates, (d/rN)pEt, mimic the nucleotide at the 5'-end. The pK(a) values of the nucleobase in each of these model nucleoside phosphates have been determined with low pK(a) error (sigma = +/-0.01 to 0.02) by (1)H NMR (at 500 MHz) with 20-33 different pH measurements for each compound. This study has led us to show the following: (1) All monomeric DNA nucleobases are more basic than the corresponding RNA nucleobases in their respective Etp(d/rN)pEt and (d/rN)pEt. (2) The pK(a) values of the monomeric nucleotide blocks as well as Delta pK(a) values between the donor and acceptor can be used to understand the relative base-pairing strength in the oligomeric duplexes in the RNA and DNA series. (3) The Delta G*(pKa) of the donor and acceptor of the base pair in duplexes enables a qualitative dissection of the relative strength of the base-pairing and stacking in the RNA-RNA over the DNA-DNA duplexes. (4) It is also found that the relative contribution of base-pairing strength and nucleobase stacking in RNA-RNA over DNA-DNA is mutually compensating as the % A-T/U content increases or decreases. This interdependency of stacking and hydrogen bonding can be potentially important in the molecular design of the base-pair mimics to expand the alphabet of the genetic code.

  • 6.
    Acharya, Parag
    et al.
    Uppsala universitet, Teknisk-naturvetenskapliga vetenskapsområdet, Biologiska sektionen, Institutionen för bioorganisk kemi.
    Acharya, Sandipta
    Uppsala universitet, Teknisk-naturvetenskapliga vetenskapsområdet, Biologiska sektionen, Institutionen för bioorganisk kemi.
    Cheruku, P
    Uppsala universitet, Teknisk-naturvetenskapliga vetenskapsområdet, Biologiska sektionen, Institutionen för bioorganisk kemi.
    Amirkhanov, N. V.
    Uppsala universitet, Teknisk-naturvetenskapliga vetenskapsområdet, Biologiska sektionen, Institutionen för bioorganisk kemi.
    Földesi, A
    Uppsala universitet, Teknisk-naturvetenskapliga vetenskapsområdet, Biologiska sektionen, Institutionen för bioorganisk kemi.
    Chattopadhyaya, J
    Uppsala universitet, Teknisk-naturvetenskapliga vetenskapsområdet, Biologiska sektionen, Institutionen för bioorganisk kemi.
    Cross-Modulation of the pKa of Nucleobases in a Single-Stranded Hexameric-RNA Due to Tandem Electrostatic Nearest-Neighbor Interactions2003Inngår i: Journal of the American Chemical Society, ISSN 0002-7863, E-ISSN 1520-5126, Vol. 125, nr 33, s. 9948-9961Artikkel i tidsskrift (Fagfellevurdert)
    Abstract [en]

    The pH titration studies (pH 6.7-12.1) in a series of dimeric, trimeric, tetrameric, pentameric, and hexameric oligo-RNA molecules [GpA (2a), GpC (3a), GpApC (5), GpA(1)pA(2)pC (6), GpA(1)pA(2)pA(3)pC (7), GpA(1)pA(2)pA(3)pA(4)pC (8)] have shown that the pK(a) of N(1)-H of 9-guaninyl could be measured not only from its own deltaH8G, but also from the aromatic marker protons of other constituent nucleobases. The relative chemical shift differences [Deltadelta((N)(-)(D))] between the protons in various nucleotide residues in the oligo-RNAs at the neutral (N) and deprotonated (D) states of the guanine moiety show that the generation of the 5'-(9-guanylate ion) in oligo-RNAs 2-8 reduces the stability of the stacked helical RNA conformation owing to the destabilizing anion(G(-))-pi/dipole(Im(delta)(-)) interaction. This destabilizing effect in the deprotonated RNA is, however, opposed by the electrostatically attractive atom-pisigma (major) as well as the anion(G(-))-pi/dipole(Py(delta)(+)) (minor) interactions. Our studies have demonstrated that the electrostatically repulsive anion(G(-))-pi/dipole(Im(delta)(-)) interaction propagates from the first to the third nucleobase quite strongly in the oligo-RNAs 6-8, causing destacking of the helix, and then its effect is gradually reduced, although it is clearly NMR detectable along the RNA chain. Thus, such specific generation of a charge at a single nucleobase moiety allows us to explore the relative strength of stacking within a single-stranded helix. The pK(a) of 5'-Gp residue from its own deltaH8G in the hexameric RNA 8 is found to be 9.76 +/- 0.01; it, however, varies from 9.65 +/- 0.01 to 10.5 +/- 0.07 along the RNA chain as measured from the other marker protons (H2, H8, H5, and H6) of 9-adeninyl and 1-cytosinyl residues. This nucleobase-dependent modulation of pK(a)s (DeltapK(a) +/- 0.9) of 9-guaninyl obtained from other nucleobases in the hexameric RNA 8 represents a difference of ca. 5.1 kJ mol(-)(1), which has been attributed to the variable strength of electrostatic interactions between the electron densities of the involved atoms in the offset stacked nucleobases as well as with that of the phosphates. The chemical implication of this variable pK(a) for guanin-9-yl deprotonation as obtained from all other marker protons of each nucleotide residue within a ssRNA molecule is that it enables us to experimentally understand the variation of the electronic microenvironment around each constituent nucleobase along the RNA chain in a stepwise manner with very high accuracy without having to make any assumption. This means that the pseudoaromaticity of neighboring 9-adeninyl and next-neighbor nucleobases within a polyanionic sugar-phosphate backbone of a ssRNA can vary from one case to another due to cross-modulation of an electronically coupled pi system by a neighboring nucleobase. This modulation may depend on the sequence context, spatial proximity of the negatively charged phosphates, as well as whether the offset stacking is ON or OFF. The net outcome of this electrostatic interaction between the neighbors is creation of new sequence-dependent hybrid nucleobases in an oligo- or polynucleotide whose properties are unlike the monomeric counterpart, which may have considerable biological implications.

  • 7.
    Acharya, Sandipta
    et al.
    Uppsala universitet, Teknisk-naturvetenskapliga vetenskapsområdet, Biologiska sektionen, Institutionen för bioorganisk kemi.
    Barman, Jharna
    Uppsala universitet, Teknisk-naturvetenskapliga vetenskapsområdet, Biologiska sektionen, Institutionen för bioorganisk kemi.
    Cheruku, Pradeep
    Uppsala universitet, Teknisk-naturvetenskapliga vetenskapsområdet, Biologiska sektionen, Institutionen för bioorganisk kemi.
    Chatterjee, Subhrangsu
    Uppsala universitet, Teknisk-naturvetenskapliga vetenskapsområdet, Biologiska sektionen, Institutionen för bioorganisk kemi.
    Acharya, Parag
    Uppsala universitet, Teknisk-naturvetenskapliga vetenskapsområdet, Biologiska sektionen, Institutionen för bioorganisk kemi.
    Isaksson, Johan
    Uppsala universitet, Teknisk-naturvetenskapliga vetenskapsområdet, Biologiska sektionen, Institutionen för bioorganisk kemi.
    Chattopadhyaya, Jyoti
    Uppsala universitet, Teknisk-naturvetenskapliga vetenskapsområdet, Biologiska sektionen, Institutionen för bioorganisk kemi.
    Significant pKa Perturbation of Nucleobases Is an Intrinsic Property of the Sequence Context in DNA and RNA2004Inngår i: Journal of the American Chemical Society, ISSN 0002-7863, E-ISSN 1520-5126, Vol. 126, nr 28, s. 8674-8681Artikkel i tidsskrift (Fagfellevurdert)
  • 8.
    Ahlquist, Mårten
    et al.
    KTH, Skolan för bioteknologi (BIO), Teoretisk kemi och biologi.
    Fabrizi, Giancarlo
    Cacchi, Sandro
    Norrby, Per-Ola
    Technical Univeristy of Denmark.
    The mechanism of the phosphine-free palladium-catalyzed hydroarylation of alkynes2006Inngår i: Journal of the American Chemical Society, ISSN 0002-7863, E-ISSN 1520-5126, Vol. 128, nr 39, s. 12785-12793Artikkel i tidsskrift (Fagfellevurdert)
    Abstract [en]

    The mechanism of the Pd-catalyzed hydroarylation and hydrovinylation reaction of alkynes has been studied by a combination of experimental and theoretical methods (B3LYP), with an emphasis on the phosphine-free version. The regioselectivity of the hydroarylation and hydrovinylation shows unexpected differences, which could be attributed mainly to the higher steric demand of the cyclohexenyl group as compared to the phenyl group. Hydroarylation of alpha,beta-acetylenic carbonyl substrates yields a very unusual anti-Michael selectivity, which is shown to result from reaction of the nonconjugated double bond, leaving the conjugation intact. In all cases were the regioselectivities reproduced by the calculations.

  • 9.
    Ahlquist, Mårten
    et al.
    Technical University of Denmark.
    Nielsen, Robert J.
    Periana, Roy A.
    Goddard, William A., III
    Product Protection, the Key to Developing High Performance Methane Selective Oxidation Catalysts2009Inngår i: Journal of the American Chemical Society, ISSN 0002-7863, E-ISSN 1520-5126, Vol. 131, nr 47, s. 17110-17115Artikkel i tidsskrift (Fagfellevurdert)
    Abstract [en]

    Selective, direct conversion of methane to methanol might seem an impossible task since the C-H bond energy of methane is 105 kcal mol(-1) compared to the C-H bond energy for methanol of 94. We show here that the Catalytica catalyst is successful because the methanol is protected as methyl bisulfate, which is substantially less reactive than methanol toward the catalyst. This analysis suggests a limiting performance for systems that operate by this type of protection that is well above the Catalytica system.

  • 10.
    Ahmed, Md Estak
    et al.
    Indian Assoc Cultivat Sci, Sch Chem Sci, Kolkata 700032, India..
    Nayek, Abhijit
    Indian Assoc Cultivat Sci, Sch Chem Sci, Kolkata 700032, India..
    Krizan, Alenka
    Uppsala universitet, Teknisk-naturvetenskapliga vetenskapsområdet, Kemiska sektionen, Institutionen för kemi - Ångström.
    Coutard, Nathan
    Univ Grenoble Alpes, Lab Chim & Biol Metaux, IRIG, CEA,CNRS, F-38000 Grenoble, France..
    Morozan, Adina
    Univ Grenoble Alpes, Lab Chim & Biol Metaux, IRIG, CEA,CNRS, F-38000 Grenoble, France..
    Dey, Somdatta Ghosh
    Indian Assoc Cultivat Sci, Sch Chem Sci, Kolkata 700032, India..
    Lomoth, Reiner
    Uppsala universitet, Teknisk-naturvetenskapliga vetenskapsområdet, Kemiska sektionen, Institutionen för kemi - Ångström, Fysikalisk kemi.
    Hammarström, Leif
    Uppsala universitet, Teknisk-naturvetenskapliga vetenskapsområdet, Kemiska sektionen, Institutionen för kemi - Ångström, Fysikalisk kemi.
    Artero, Vincent
    Univ Grenoble Alpes, Lab Chim & Biol Metaux, IRIG, CEA,CNRS, F-38000 Grenoble, France..
    Dey, Abhishek
    Indian Assoc Cultivat Sci, Sch Chem Sci, Kolkata 700032, India..
    A Bidirectional Bioinspired [FeFe]-Hydrogenase Model2022Inngår i: Journal of the American Chemical Society, ISSN 0002-7863, E-ISSN 1520-5126, Vol. 144, nr 8, s. 3614-3625Artikkel i tidsskrift (Fagfellevurdert)
    Abstract [en]

    With the price-competitiveness of solar and wind power, hydrogen technologies may be game changers for a cleaner, defossilized, and sustainable energy future. H-2 can indeed be produced in electrolyzers from water, stored for long periods, and converted back into power, on demand, in fuel cells. The feasibility of the latter process critically depends on the discovery of cheap and efficient catalysts able to replace platinum group metals at the anode and cathode of fuel cells. Bioinspiration can be key for designing such alternative catalysts. Here we show that a novel class of iron-based catalysts inspired from the active site of [FeFe]-hydrogenase behave as unprecedented bidirectional electrocatalysts for interconverting H-2 and protons efficiently under near-neutral aqueous conditions. Such bioinspired catalysts have been implemented at the anode of a functional membrane-less H-2/O-2 fuel cell device.

  • 11.
    Aili, Daniel
    et al.
    Linköpings universitet, Institutionen för fysik, kemi och biologi, Sensorvetenskap och Molekylfysik. Linköpings universitet, Tekniska högskolan.
    Enander, Karin
    Linköpings universitet, Institutionen för fysik, kemi och biologi, Sensorvetenskap och Molekylfysik. Linköpings universitet, Tekniska högskolan.
    Rydberg, Johan
    Linköpings universitet, Institutionen för fysik, kemi och biologi. Linköpings universitet, Tekniska högskolan.
    Nesterenko, Irina
    Linköpings universitet, Institutionen för fysik, kemi och biologi. Linköpings universitet, Tekniska högskolan.
    Björefors, Fredrik
    Linköpings universitet, Institutionen för fysik, kemi och biologi, Sensorvetenskap och Molekylfysik. Linköpings universitet, Tekniska högskolan.
    Baltzer, Lars
    Department of Biochemistry and Organic Chemistry, BMC, Box 599, Uppsala UniVersity, SE-751 24 Uppsala, Sweden.
    Liedberg, Bo
    Linköpings universitet, Institutionen för fysik, kemi och biologi, Sensorvetenskap och Molekylfysik. Linköpings universitet, Tekniska högskolan.
    Folding Induced Assembly of Polypeptide Decorated Gold Nanoparticles2008Inngår i: Journal of the American Chemical Society, ISSN 0002-7863, E-ISSN 1520-5126, Vol. 130, nr 17, s. 5780-5788Artikkel i tidsskrift (Fagfellevurdert)
    Abstract [en]

    Reversible assembly of gold nanoparticles controlled by the homodimerization and folding of an immobilized de novo designed synthetic polypeptide is described. In solution at neutral pH, the polypeptide folds into a helix–loop–helix four-helix bundle in the presence of zinc ions. When immobilized on gold nanoparticles, the addition of zinc ions induces dimerization and folding between peptide monomers located on separate particles, resulting in rapid particle aggregation. The particles can be completely redispersed by removal of the zinc ions from the peptide upon addition of EDTA. Calcium ions, which do not induce folding in solution, have no effect on the stability of the peptide decorated particles. The contribution from folding on particle assembly was further determined utilizing a reference peptide with the same primary sequence but containing both D and L amino acids. Particles functionalized with the reference peptide do not aggregate, as the peptides are unable to fold. The two peptides, linked to the nanoparticle surface via a cysteine residue located in the loop region, form submonolayers on planar gold with comparable properties regarding surface density, orientation, and ability to interact with zinc ions. These results demonstrate that nanoparticle assembly can be induced, controlled, and to some extent tuned, by exploiting specific molecular interactions involved in polypeptide folding.

  • 12.
    Aili, Daniel
    et al.
    Linköpings universitet, Institutionen för fysik, kemi och biologi, Sensorvetenskap och Molekylfysik. Linköpings universitet, Tekniska högskolan.
    Enander, Karin
    Linköpings universitet, Institutionen för fysik, kemi och biologi, Sensorvetenskap och Molekylfysik. Linköpings universitet, Tekniska högskolan.
    Rydberg, Johan
    Linköpings universitet, Institutionen för fysik, kemi och biologi. Linköpings universitet, Tekniska högskolan.
    Lundström, Ingemar
    Linköpings universitet, Institutionen för fysik, kemi och biologi, Tillämpad Fysik. Linköpings universitet, Tekniska högskolan.
    Baltzer, Lars
    Linköpings universitet, Institutionen för fysik, kemi och biologi. Linköpings universitet, Tekniska högskolan.
    Liedberg, Bo
    Linköpings universitet, Institutionen för fysik, kemi och biologi, Sensorvetenskap och Molekylfysik. Linköpings universitet, Tekniska högskolan.
    Aggregation-Induced Folding of a de novo Designed Polypeptide Immobilized on Gold Nanoparticles2006Inngår i: Journal of the American Chemical Society, ISSN 0002-7863, E-ISSN 1520-5126, Vol. 128, nr 7, s. 2194 -2195Artikkel i tidsskrift (Fagfellevurdert)
    Abstract [en]

    This communication reports the first steps in the construction of a novel, nanoparticle-based hybrid material for biomimetic and biosensor applications. Gold nanoparticles were modified with synthetic polypeptides to enable control of the particle aggregation state in a switchable manner, and particle aggregation was, in turn, found to induce folding of the immobilized peptides.

  • 13. Aili, Daniel
    et al.
    Enander, Karin
    Rydberg, Johan
    Uppsala universitet, Teknisk-naturvetenskapliga vetenskapsområdet, Kemiska sektionen, Institutionen för biokemi och organisk kemi, Organisk kemi II.
    Nesterenko, Irina
    Björefors, Fredrik
    Baltzer, Lars
    Uppsala universitet, Teknisk-naturvetenskapliga vetenskapsområdet, Kemiska sektionen, Institutionen för biokemi och organisk kemi, Organisk kemi II.
    Liedberg, Bo
    Folding Induced Assembly of Polypeptide Decorated Gold Nanoparticles2008Inngår i: Journal of the American Chemical Society, ISSN 0002-7863, E-ISSN 1520-5126, Vol. 130, nr 17, s. 5780-5788Artikkel i tidsskrift (Fagfellevurdert)
    Abstract [en]

    Reversible assembly of gold nanoparticles controlled by the homodimerization and folding of an immobilized de novo designed synthetic polypeptide is described. In solution at neutral pH, the polypeptide folds into a helix-loop-helix four-helix bundle in the presence of zinc ions. When immobilized on gold nanoparticles, the addition of zinc ions induces dimerization and folding between peptide monomers located on separate particles, resulting in rapid particle aggregation. The particles can be completely redispersed by removal of the zinc ions from the peptide upon addition of EDTA. Calcium ions, which do not induce folding in solution, have no effect on the stability of the peptide decorated particles. The contribution from folding on particle assembly was further determined utilizing a reference peptide with the same primary sequence but containing both D and L amino acids. Particles functionalized with the reference peptide do not aggregate, as the peptides are unable to fold. The two peptides, linked to the nanoparticle surface via a cysteine residue located in the loop region, form submonolayers on planar gold with comparable properties regarding surface density, orientation, and ability to interact with zinc ions. These results demonstrate that nanoparticle assembly can be induced, controlled, and to some extent tuned, by exploiting specific molecular interactions involved in polypeptide folding.

  • 14.
    Alam, Rauful
    et al.
    Stockholms universitet, Naturvetenskapliga fakulteten, Institutionen för organisk kemi.
    Pilarski, Lukasz T.
    Stockholms universitet, Naturvetenskapliga fakulteten, Institutionen för organisk kemi.
    Pershagen, Elias
    Stockholms universitet, Naturvetenskapliga fakulteten, Institutionen för organisk kemi.
    Szabó, Kálmán J.
    Stockholms universitet, Naturvetenskapliga fakulteten, Institutionen för organisk kemi.
    Stereoselective intermolecular allylic C-H trifluoroacetoxylation of functionalized alkenes2012Inngår i: Journal of the American Chemical Society, ISSN 0002-7863, E-ISSN 1520-5126, Vol. 134, nr 21, s. 8778-8781Artikkel i tidsskrift (Fagfellevurdert)
    Abstract [en]

    Pd-catalyzed allylic C-H trifluoroacetoxylation of substituted alkenes was performed using PhI(OCOCF3)(2) as the oxidant and acyloxy source. Trifluoroacetoxylation of monosubstituted cyclopentenes and cyclohexenes proceeds with excellent regio- and diastereoselectivity. Studies with one of the possible (eta(3)-allyl)Pd(II) intermediates suggest that the reaction proceeds via stereoselective formation of Pd(IV) intermediates and subsequent stereo- and regioselective reductive elimination of the product.

  • 15.
    Alam, Rauful
    et al.
    Stockholms universitet, Naturvetenskapliga fakulteten, Institutionen för organisk kemi.
    Vollgraff, Tobias
    Stockholms universitet, Naturvetenskapliga fakulteten, Institutionen för organisk kemi.
    Eriksson, Lars
    Stockholms universitet, Naturvetenskapliga fakulteten, Institutionen för material- och miljökemi (MMK).
    Szabó, Kálmán J.
    Stockholms universitet, Naturvetenskapliga fakulteten, Institutionen för organisk kemi.
    Synthesis of Adjacent Quaternary Stereocenters by Catalytic Asymmetric Allylboration2015Inngår i: Journal of the American Chemical Society, ISSN 0002-7863, E-ISSN 1520-5126, Vol. 137, nr 35, s. 11262-11265Artikkel i tidsskrift (Fagfellevurdert)
    Abstract [en]

    Allylboration of ketones with gamma-disubstituted allylboronic acids is performed in the presence of chiral BINOL derivatives. The reaction is suitable for single-step creation of adjacent quaternary stereocenters with high selectivity. We show that, with an appropriate choice of the chiral catalyst and the stereoisomeric prenyl substrate, full control of the stereo- and enantioselectivity is possible in the reaction.

  • 16.
    Allardice, Jesse R.
    et al.
    Univ Cambridge, Cavendish Lab, JJ Thomson Ave, Cambridge CB3 OHE, England.
    Thampi, Arya
    Univ Cambridge, Cavendish Lab, JJ Thomson Ave, Cambridge CB3 OHE, England.
    Dowland, Simon
    Univ Cambridge, Cavendish Lab, JJ Thomson Ave, Cambridge CB3 OHE, England.
    Xiao, James
    Univ Cambridge, Cavendish Lab, JJ Thomson Ave, Cambridge CB3 OHE, England.
    Gray, Victor
    Uppsala universitet, Teknisk-naturvetenskapliga vetenskapsområdet, Kemiska sektionen, Institutionen för kemi - Ångström, Fysikalisk kemi. Univ Cambridge, Cavendish Lab, JJ Thomson Ave, Cambridge CB3 OHE, England.
    Zhang, Zhilong
    Univ Cambridge, Cavendish Lab, JJ Thomson Ave, Cambridge CB3 OHE, England.
    Budden, Peter
    Univ Cambridge, Cavendish Lab, JJ Thomson Ave, Cambridge CB3 OHE, England.
    Petty, Anthony J., II
    Univ Kentucky, Ctr Appl Energy Res, Res Pk Dr, Lexington, KY 40511 USA.
    Davis, Nathaniel J. L. K.
    Univ Cambridge, Cavendish Lab, JJ Thomson Ave, Cambridge CB3 OHE, England;Victoria Univ Wellington, MacDiarmid Inst Adv Mat & Nanotechnol, Dodd Walls Ctr Photon & Quantum Technol, Sch Chem & Phys Sci, Wellington 6140, New Zealand.
    Greenham, Neil C.
    Univ Cambridge, Cavendish Lab, JJ Thomson Ave, Cambridge CB3 OHE, England.
    Anthony, John E.
    Univ Kentucky, Ctr Appl Energy Res, Res Pk Dr, Lexington, KY 40511 USA.
    Rao, Akshay
    Univ Cambridge, Cavendish Lab, JJ Thomson Ave, Cambridge CB3 OHE, England.
    Engineering Molecular Ligand Shells on Quantum Dots for Quantitative Harvesting of Triplet Excitons Generated by Singlet Fission2019Inngår i: Journal of the American Chemical Society, ISSN 0002-7863, E-ISSN 1520-5126, Vol. 141, nr 32, s. 12907-12915Artikkel i tidsskrift (Fagfellevurdert)
    Abstract [en]

    Singlet fission is an exciton multiplication process in organic molecules in which a photogenerated spin-singlet exciton is rapidly and efficiently converted to two spin-triplet excitons. This process offers a mechanism to break the Shockley-Queisser limit by overcoming the thermalization losses inherent to all single-junction photovoltaics. One of the most promising methods to harness the singlet fission process is via the efficient extraction of the dark triplet excitons into quantum dots (QDs) where they can recombine radiatively, thereby converting high-energy photons to pairs of low-energy photons, which can then be captured in traditional inorganic PVs such as Si. Such a singlet fission photon multiplication (SF-PM) process could increase the efficiency of the best Si cells from 26.7% to 32.5%, breaking the Shockley-Queisser limit. However, there has been no demonstration of such a singlet fission photon multiplication (SF-PM) process in a bulk system to date. Here, we demonstrate a solution-based bulk SF-PM system based on the singlet fission material TIPS-Tc combined with PbS QDs. Using a range of steady-state and time-resolved measurements combined with analytical modeling we study the dynamics and mechanism of the triplet harvesting process. We show that the system absorbs >95% of incident photons within the singlet fission material to form singlet excitons, which then undergo efficient singlet fission in the solution phase (135 +/- 5%) before quantitative harvesting of the triplet excitons (95 +/- 5%) via a low concentration of QD acceptors, followed by the emission of IR photons. We find that in order to achieve efficient triplet harvesting it is critical to engineer the surface of the QD with a triplet transfer ligand and that bimolecular decay of triplets is potentially a major loss pathway which can be controlled via tuning the concentration of QD acceptors. We demonstrate that the photon multiplication efficiency is maintained up to solar fluence. Our results establish the solution-based SF-PM system as a simple and highly tunable platform to understand the dynamics of a triplet energy transfer process between organic semiconductors and QDs, one that can provide clear design rules for new materials.

    Fulltekst (pdf)
    fulltext
  • 17.
    Allgöwer, Friederike
    et al.
    Stockholms universitet, Naturvetenskapliga fakulteten, Institutionen för biokemi och biofysik.
    Gamiz-Hernandez, Ana P.
    Stockholms universitet, Naturvetenskapliga fakulteten, Institutionen för biokemi och biofysik.
    Rutherford, A. William
    Kaila, Ville R. I.
    Stockholms universitet, Naturvetenskapliga fakulteten, Institutionen för biokemi och biofysik.
    Molecular Principles of Redox-Coupled Protonation Dynamics in Photosystem II2022Inngår i: Journal of the American Chemical Society, ISSN 0002-7863, E-ISSN 1520-5126, Vol. 144, nr 16, s. 7171-7180Artikkel i tidsskrift (Fagfellevurdert)
    Abstract [en]

    Photosystem II (PSII) catalyzes light-driven water oxidization, releasing O2 into the atmosphere and transferring the electrons for the synthesis of biomass. However, despite decades of structural and functional studies, the water oxidation mechanism of PSII has remained puzzling and a major challenge for modern chemical research. Here, we show that PSII catalyzes redox-triggered proton transfer between its oxygen-evolving Mn4O5Ca cluster and a nearby cluster of conserved buried ion-pairs, which are connected to the bulk solvent via a proton pathway. By using multi-scale quantum and classical simulations, we find that oxidation of a redox-active Tyrz (Tyr161) lowers the reaction barrier for the water-mediated proton transfer from a Ca2+-bound water molecule (W3) to Asp61 via conformational changes in a nearby ion-pair (Asp61/Lys317). Deprotonation of this W3 substrate water triggers its migration toward Mn1 to a position identified in recent X-ray free-electron laser (XFEL) experiments [Ibrahim et al. Proc. Natl. Acad. Sci. USA 2020, 117, 12,624–12,635]. Further oxidation of the Mn4O5Ca cluster lowers the proton transfer barrier through the water ligand sphere of the Mn4O5Ca cluster to Asp61 via a similar ion-pair dissociation process, while the resulting Mn-bound oxo/oxyl species leads to O2 formation by a radical coupling mechanism. The proposed redox-coupled protonation mechanism shows a striking resemblance to functional motifs in other enzymes involved in biological energy conversion, with an interplay between hydration changes, ion-pair dynamics, and electric fields that modulate the catalytic barriers. 

  • 18.
    Alonso, Diego A
    et al.
    Uppsala universitet, Teknisk-naturvetenskapliga vetenskapsområdet, Kemiska sektionen, Kemiska institutionen, Avdelningen för organisk kemi.
    Brandt, P
    Nordin, Sofia J M
    Uppsala universitet, Teknisk-naturvetenskapliga vetenskapsområdet, Kemiska sektionen, Kemiska institutionen, Avdelningen för organisk kemi.
    Andersson, Pher G
    Uppsala universitet, Teknisk-naturvetenskapliga vetenskapsområdet, Kemiska sektionen, Kemiska institutionen, Avdelningen för organisk kemi.
    Ru(arene)(amino alcohol)-Catalyzed Transfer Hydrogenation of Ketones: Mechanism and Origin of Enantioselectivity1999Inngår i: Journal of the American Chemical Society, ISSN 0002-7863, E-ISSN 1520-5126, Vol. 121, nr 41, s. 9580-9588Artikkel i tidsskrift (Fagfellevurdert)
    Abstract [en]

    The mechanism of the Ru(arene)(amino alcohol)-catalyzed transfer hydrogenation of ketones using isopropyl alcohol as the hydrogen source has been studied by means of hybrid density functional methods (B3PW91). Three mechanistic alternatives were evaluated, and it was shown that the reaction takes place via a six-membered transition state, where a metal-bound hydride and a proton of a coordinated amine are transferred simultaneously to the ketone. Further calculations provided a general rationale for the rate of the reaction by comparison of steric effects in the ground and transition states of the ruthenium hydride complex. It was found that the TS has a strong preference for planarity, and this in turn is dependent on the conformational behavior of the O,N-linkage of the amino alcohol ligand. Finally, a general model, rationalizing the enantioselectivity of the reaction, was developed. Experimental studies of both rate and enantioselectivity were used in order to support the computational results.

  • 19. Ames, William
    et al.
    Pantazis, Dimitrios A
    Krewald, Vera
    Cox, Nicholas
    Messinger, Johannes
    Umeå universitet, Teknisk-naturvetenskapliga fakulteten, Kemiska institutionen.
    Lubitz, Wolfgang
    Neese, Frank
    Theoretical Evaluation of Structural Models of the S(2) State in the Oxygen Evolving Complex of Photosystem II: Protonation States and Magnetic Interactions2011Inngår i: Journal of the American Chemical Society, ISSN 0002-7863, E-ISSN 1520-5126, Vol. 133, nr 49, s. 19743-19757Artikkel i tidsskrift (Fagfellevurdert)
    Abstract [en]

    Protonation states of water ligands and oxo bridges are intimately involved in tuning the electronic structures and oxidation potentials of the oxygen evolving complex (OEC) in Photosystem II, steering the mechanistic pathway, which involves at least five redox state intermediates S(n) (n = 0-4) resulting in the oxidation of water to molecular oxygen. Although protons are practically invisible in protein crystallography, their effects on the electronic structure and magnetic properties of metal active sites can be probed using spectroscopy. With the twin purpose of aiding the interpretation of the complex electron paramagnetic resonance (EPR) spectroscopic data of the OEC and of improving the view of the cluster at the atomic level, a complete set of protonation configurations for the S(2) state of the OEC were investigated, and their distinctive effects on magnetic properties of the cluster were evaluated. The most recent X-ray structure of Photosystem II at 1.9 Å resolution was used and refined to obtain the optimum structure for the Mn(4)O(5)Ca core within the protein pocket. Employing this model, a set of 26 structures was constructed that tested various protonation scenarios of the water ligands and oxo bridges. Our results suggest that one of the two water molecules that are proposed to coordinate the outer Mn ion (Mn(A)) of the cluster is deprotonated in the S(2) state, as this leads to optimal experimental agreement, reproducing the correct ground state spin multiplicity (S = 1/2), spin expectation values, and EXAFS-derived metal-metal distances. Deprotonation of Ca(2+)-bound water molecules is strongly disfavored in the S(2) state, but dissociation of one of the two water ligands appears to be facile. The computed isotropic hyperfine couplings presented here allow distinctions between models to be made and call into question the assumption that the largest coupling is always attributable to Mn(III). The present results impose limits for the total charge and the proton configuration of the OEC in the S(2) state, with implications for the cascade of events in the Kok cycle and for the water splitting mechanism.

  • 20.
    Ames, William
    et al.
    Max Planck Inst Bioanorgan Chem, D-45470 Mulheim, Germany..
    Pantazis, Dimitrios A.
    Max Planck Inst Bioanorgan Chem, D-45470 Mulheim, Germany..
    Krewald, Vera
    Max Planck Inst Bioanorgan Chem, D-45470 Mulheim, Germany..
    Cox, Nicholas
    Max Planck Inst Bioanorgan Chem, D-45470 Mulheim, Germany..
    Messinger, Johannes
    Umea Univ, Inst Kemi, Kemiskt Biol Ctr, S-90187 Umea, Sweden..
    Lubitz, Wolfgang
    Max Planck Inst Bioanorgan Chem, D-45470 Mulheim, Germany..
    Neese, Frank
    Max Planck Inst Bioanorgan Chem, D-45470 Mulheim, Germany..
    Theoretical Evaluation of Structural Models of the S2 State in the Oxygen Evolving Complex of Photosystem II: Protonation States and Magnetic Interactions2011Inngår i: Journal of the American Chemical Society, ISSN 0002-7863, E-ISSN 1520-5126, Vol. 133, nr 49, s. 19743-19757Artikkel i tidsskrift (Fagfellevurdert)
    Abstract [en]

    Protonation states of water ligands and oxo bridges are intimately involved in tuning the electronic structures and oxidation potentials of the oxygen evolving complex (OEC) in Photosystem II, steering the mechanistic pathway, which involves at least five redox state intermediates S-n (n = 0-4) resulting in the oxidation of water to molecular oxygen. Although protons are practically invisible in protein crystallography, their effects on the electronic structure and magnetic properties of metal active sites can be probed using spectroscopy. With the twin purpose of aiding the interpretation of the complex electron paramagnetic resonance (EPR) spectroscopic data of the OEC and of improving the view of the cluster at the atomic level, a complete set of protonation configurations for the S-2 state of the OEC were investigated, and their distinctive effects on magnetic properties of the cluster were evaluated. The most recent X-ray structure of Photosystem II at 1.9 angstrom resolution was used and refined to obtain the optimum structure for the Mn4O5Ca core within the protein pocket. Employing this model, a set of 26 structures was constructed that tested various protonation scenarios of the water ligands and oxo bridges. Our results suggest that one of the two water molecules that are proposed to coordinate the outer Mn ion (Mn-A) of the cluster is deprotonated in the S-2 state, as this leads to optimal experimental agreement, reproducing the correct ground state spin multiplicity (S = 1/2), spin expectation values, and EXAFS-derived metal-metal distances. Deprotonation of Ca2+-bound water molecules is strongly disfavored in the S-2 state, but dissociation of one of the two water ligands appears to be facile. The computed isotropic hyperfine couplings presented here allow distinctions between models to be made and call into question the assumption that the largest coupling is always attributable to Mn-III. The present results impose limits for the total charge and the proton configuration of the OEC in the S-2 state, with implications for the cascade of events in the Kok cycle and for the water splitting mechanism.

  • 21.
    Amft, Martin
    et al.
    Uppsala universitet, Teknisk-naturvetenskapliga vetenskapsområdet, Fysiska sektionen, Institutionen för fysik och astronomi, Materialteori.
    Edvinsson, Tomas
    Uppsala universitet, Teknisk-naturvetenskapliga vetenskapsområdet, Kemiska sektionen, Institutionen för materialkemi, Oorganisk kemi.
    Skorodumova, Natalia V.
    Uppsala universitet, Teknisk-naturvetenskapliga vetenskapsområdet, Fysiska sektionen, Institutionen för fysik och astronomi, Materialteori.
    Thermally Excited Vibrations in Copper, Silver, and Gold Trimers and Enhanced Binding of CO2010Inngår i: Journal of the American Chemical Society, ISSN 0002-7863, E-ISSN 1520-5126Artikkel i tidsskrift (Annet vitenskapelig)
  • 22.
    Amombo Noa, Francoise M.
    et al.
    Chalmers Univ Technol, Dept Chem & Chem Engn, Chem & Biochem, SE-41296 Gothenburg, Sweden.
    Svensson Grape, Erik
    Stockholm Univ, Dept Mat & Environm Chem, SE-10691 Stockholm, Sweden.
    Brülls, Steffen Marc
    Chalmers Univ Technol, Dept Chem & Chem Engn, Chem & Biochem, SE-41296 Gothenburg, Sweden.
    Cheung, Ocean
    Uppsala universitet, Teknisk-naturvetenskapliga vetenskapsområdet, Tekniska sektionen, Institutionen för materialvetenskap, Nanoteknologi och funktionella material.
    Malmberg, Per
    Chalmers Univ Technol, Dept Chem & Chem Engn, Chem & Biochem, SE-41296 Gothenburg, Sweden.
    Inge, A. Ken
    Stockholm Univ, Dept Mat & Environm Chem, SE-10691 Stockholm, Sweden.
    McKenzie, Christine J.
    Univ Southern Denmark, Dept Phys Chem & Pharm, DK-5230 Odense M, Denmark.
    Mårtensson, Jerker
    Chalmers Univ Technol, Dept Chem & Chem Engn, Chem & Biochem, SE-41296 Gothenburg, Sweden.
    Öhrström, Lars
    Chalmers Univ Technol, Dept Chem & Chem Engn, Chem & Biochem, SE-41296 Gothenburg, Sweden.
    Metal-Organic Frameworks with Hexakis(4-carboxyphenyl)benzene: Extensions to Reticular Chemistry and Introducing Foldable Nets2020Inngår i: Journal of the American Chemical Society, ISSN 0002-7863, E-ISSN 1520-5126, Vol. 142, nr 20, s. 9471-9481Artikkel i tidsskrift (Fagfellevurdert)
    Abstract [en]

    Nine metal–organic frameworks have been prepared with the hexagon-shaped linker 1,2,3,4,5,6-hexakis(4-carboxyphenyl)benzene (H6cpb) by solvothermal reactions in dimethylformamide (dmf) or dimethylacetamide (dmac) with acetic acid or formic acid as modulators: [Bi2(cpb)(acetato)2(dmf)2]·2dmf CTH-6 forms a rtl-net; 2(H2NMe2)[Cu2(cpb)] CTH-7 forms a kgd-net; [Fe4(cpb)(acetato)2(dmf)4] CTH-8 and [Co4(cpb)(acetato)2(dmf)4] CTH-9 are isostructural and form yav-nets; 2(HNEt3)[Fe2(cpb)] CTH-10 and the two polymorphs of 2(H2NMe2)[Zn2(cpb)]·1.5dmac, Zn-MOF-888 and CTH-11, show kgd-nets; [Cu2(cpb)(acetato)2(dmf)2]·2dmf, CTH-12, forms a mixed coordination and hydrogen-bonded sql-net; and 2(H2NMe2)[Zn2(cpb)] CTH-13, a similarly mixed yav-net. Surface area values (Brunauer–Emmett–Teller, BET) range from 34 m2 g–1 for CTH-12 to 303 m2 g–1 for CTH-9 for samples activated at 120 °C in dynamic vacuum. All compounds show normal (10-fold higher) molar CO2 versus N2 uptake at 298 K, except the 19-fold CO2 uptake for CTH-12 containing Cu(II) dinuclear paddle-wheels. We also show how perfect hexagons and triangles can combine to a new 3D topology laf, a model of which gave us the idea of foldable network topologies, as the laf-net can fold into a 2D form while retaining the local geometry around each vertex. Other foldable nets identified are cds, cds-a, ths, sqc163, clh, jem, and tfc covering the basic polygons and their combinations. The impact of this concept on “breathing” MOFs is discussed. I2 sorption, both from gas phase and from MeOH solution, into CTH-7 were studied by time of flight secondary ion mass spectrometry (ToF-SIMS) on dried crystals. I2 was shown to have penetrated the crystals, as layers were consecutively peeled off by the ion beam. We suggest ToF-SIMS to be a method for studying sorption depth profiles of MOFs.

    Fulltekst (pdf)
    FULLTEXT01
  • 23. Amombo Noa, Francoise M.
    et al.
    Svensson Grape, Erik
    Stockholms universitet, Naturvetenskapliga fakulteten, Institutionen för material- och miljökemi (MMK).
    Åhlén, Michelle
    Reinholdsson, William E.
    Göb, Christian R.
    Coudert, François-Xavier
    Cheung, Ocean
    Inge, A. Ken
    Stockholms universitet, Naturvetenskapliga fakulteten, Institutionen för material- och miljökemi (MMK).
    Öhrström, Lars
    Chiral Lanthanum Metal–Organic Framework with Gated CO2 Sorption and Concerted Framework Flexibility2022Inngår i: Journal of the American Chemical Society, ISSN 0002-7863, E-ISSN 1520-5126, Vol. 144, nr 19, s. 8725-8733Artikkel i tidsskrift (Fagfellevurdert)
    Abstract [en]

    A metal–organic framework (MOF) CTH-17 based on lanthanum(III) and the conformationally chiral linker 1,2,3,4,5,6-hexakis(4-carboxyphenyl)benzene, cpb6–: [La2(cpb)]·1.5dmf was prepared by the solvothermal method in dimethylformamide (dmf) and characterized by variable-temperature X-ray powder diffraction (VTPXRD), variable-temperature X-ray single-crystal diffraction (SCXRD), and thermogravimetric analysis (TGA). CTH-17 is a rod-MOF with new topology och. It has high-temperature stability with Sohncke space groups P6122/P6522 at 90 K and P622 at 300 and 500 K, all phases characterized with SCXRD and at 293 K also with three-dimensional (3D) electron diffraction. VTPXRD indicates a third phase appearing after 620 K and stable up to 770 K. Gas sorption isotherms with N2 indicate a modest surface area of 231 m2 g–1 for CTH-17, roughly in agreement with the crystal structure. Carbon dioxide sorption reveals a gate-opening effect of CTH-17 where the structure opens up when the loading of CO2 reaches approximately ∼0.45 mmol g–1 or 1 molecule per unit cell. Based on the SCXRD data, this is interpreted as flexibility based on the concerted movements of the propeller-like hexatopic cpb linkers, the movement intramolecularly transmitted by the π–π stacking of the cpb linkers and helped by the fluidity of the LaO6 coordination sphere. This was corroborated by density functional theory (DFT) calculations yielding the chiral phase (P622) as the energy minimum and a completely racemic phase (P6/mmm), with symmetric cpb linkers representing a saddle point in a racemization process.

  • 24.
    An, Xiaoqiang
    et al.
    Tsinghua Univ, Peoples R China.
    Wei, Tingcha
    Tsinghua Univ, Peoples R China; Nanjing Univ Aeronaut & Astronaut, Peoples R China.
    Ding, Peijia
    Beihang Univ, Peoples R China.
    Liu, Li-Min
    Beihang Univ, Peoples R China.
    Xiong, Lunqiao
    UCL, England.
    Tang, Junwang
    UCL, England.
    Ma, Jiani
    Shanxi Normal Univ, Peoples R China.
    Wang, Feng
    Linköpings universitet, Institutionen för fysik, kemi och biologi, Elektroniska och fotoniska material. Linköpings universitet, Tekniska fakulteten.
    Liu, Huijuan
    Tsinghua Univ, Peoples R China.
    Qu, Jiuhui
    Tsinghua Univ, Peoples R China.
    Sodium-Directed Photon-Induced Assembly Strategy for Preparing Multisite Catalysts with High Atomic Utilization Efficiency2023Inngår i: Journal of the American Chemical Society, ISSN 0002-7863, E-ISSN 1520-5126, Vol. 145, nr 3, s. 1759-1768Artikkel i tidsskrift (Fagfellevurdert)
    Abstract [en]

    Integrating different reaction sites offers new prospects to address the difficulties in single-atom catalysis, but the precise regulation of active sites at the atomic level remains challenging. Here, we demonstrate a sodium-directed photon-induced assembly (SPA) strategy for boosting the atomic utilization efficiency of single-atom catalysts (SACs) by constructing multifarious Au sites on TiO2 substrate. Na+ was employed as the crucial cement to direct Au single atoms onto TiO2, while the light-induced electron transfer from excited TiO2 to Au(Na+) ensembles contributed to the self-assembly formation of Au nanoclusters. The synergism between plasmonic near-field and Schottky junction enabled the cascade electron transfer for charge separation, which was further enhanced by oxygen vacancies in TiO2. Our dual-site photocatalysts exhibited a nearly 2 orders of magnitude improvement in the hydrogen evolution activity under simulated solar light, with a striking turnover frequency (TOF) value of 1533 h(-1) that exceeded other Au/TiO2-based photocatalysts reported. Our SPA strategy can be easily extended to prepare a wide range of metal-coupled nanostructures with enhanced performance for diverse catalytic reactions. Thus, this study provides a well-defined platform to extend the boundaries of SACs for multisite catalysis through harnessing metal-support interactions.

    Fulltekst (pdf)
    fulltext
  • 25. Andersen, Thomas L.
    et al.
    Friis, Stig D.
    Audrain, Helene
    Nordeman, Patrik
    Uppsala universitet, Medicinska och farmaceutiska vetenskapsområdet, Farmaceutiska fakulteten, Institutionen för läkemedelskemi, Plattformen för preklinisk PET.
    Antoni, Gunnar
    Uppsala universitet, Medicinska och farmaceutiska vetenskapsområdet, Farmaceutiska fakulteten, Institutionen för läkemedelskemi, Plattformen för preklinisk PET.
    Skrydstrup, Troels
    Efficient C-11-Carbonylation of Isolated Aryl Palladium Complexes for PET: Application to Challenging Radiopharmaceutical Synthesis2015Inngår i: Journal of the American Chemical Society, ISSN 0002-7863, E-ISSN 1520-5126, Vol. 137, nr 4, s. 1548-1555Artikkel i tidsskrift (Fagfellevurdert)
    Abstract [en]

    We describe the successful implementation of palladium-aryl oxidative addition complexes as stoichiometric reagents in carbonylation reactions with (CO)-C-11 to produce structurally challenging, pharmaceutically relevant compounds. This method enables the first C-11-carbonyl labeling of an approved PET tracer, [C-11]raclopride, for the dopamine D2/D3 receptor by carbonylation with excellent radiochemical purity and yield. Two other molecules, [C-11]olaparib and [C-11]JNJ 31020028, were efficiently labeled in this manner. The technique distinguishes itself from existing methods by the markedly improved purity profiles of the tracer molecules produced and provides access to complex structures in synthetically useful yields, hereby offering a viable alternative to other C-11-labeling strategies.

  • 26.
    Andersson, August
    et al.
    Stockholms universitet, Naturvetenskapliga fakulteten, Institutionen för biokemi och biofysik.
    Mäler, Lena
    Stockholms universitet, Naturvetenskapliga fakulteten, Institutionen för biokemi och biofysik.
    Magnetic resonance investigations of lipid motion in isotropic bicelles2005Inngår i: Journal of the American Chemical Society, ISSN 0002-7863, E-ISSN 1520-5126, Vol. 21, nr 7, s. 7702-7709Artikkel i tidsskrift (Fagfellevurdert)
    Abstract [en]

    The dynamics of DMPC in different isotropic bicelles have been investigated by NMR and EPR methods. The local dynamics were obtained by interpretation of 13C NMR relaxation measurements of DMPC in the bicelles, and these results were compared to EPR spectra of spin-labeled lipids. The overall size of the bicelles was investigated by PFG NMR translational diffusion measurements. The dynamics and relative sizes were compared among three different bicelles: [DMPC]/[DHPC] = 0.25, [DMPC]/[DHPC] = 0.5, and [DMPC]/[CHAPS] = 0.5. The local motion is found to depend much more strongly on the choice of the detergent, rather than the overall size of the bicelle. The results provide an explanation for differences in apparent dynamics for different peptides, which are bound to bicelles. This in turn determines under what conditions reasonable NMR spectra can be observed. A model is presented in which extensive local motion, in conjunction with the overall size, affects the spectral properties. An analytical expression for the size dependence of the bicelles, relating the radius of the bilayer region with physical properties of the detergent and the lipid, is also presented.

  • 27.
    Andersson, Charlotta S.
    et al.
    Stockholms universitet, Naturvetenskapliga fakulteten, Institutionen för biokemi och biofysik.
    Öhrström, Maria
    Stockholms universitet, Naturvetenskapliga fakulteten, Institutionen för biokemi och biofysik.
    Popović-Bijelić, Ana
    Stockholms universitet, Naturvetenskapliga fakulteten, Institutionen för biokemi och biofysik.
    Gräslund, Astrid
    Stockholms universitet, Naturvetenskapliga fakulteten, Institutionen för biokemi och biofysik.
    Stenmark, Pål
    Stockholms universitet, Naturvetenskapliga fakulteten, Institutionen för biokemi och biofysik.
    Högbom, Martin
    Stockholms universitet, Naturvetenskapliga fakulteten, Institutionen för biokemi och biofysik.
    The manganese ion of the heterodinuclear Mn/Fe cofactor in Chlamydia trachomatis ribonucleotide reductase R2c is located at metal position 1.2012Inngår i: Journal of the American Chemical Society, ISSN 0002-7863, E-ISSN 1520-5126, Vol. 134, nr 1, s. 123-125Artikkel i tidsskrift (Fagfellevurdert)
    Abstract [en]

    The essential catalytic radical of Class-I ribonucleotide reductase is generated and delivered by protein R2, carrying a dinuclear metal cofactor. A new R2 subclass, R2c, prototyped by the Chlamydia trachomatis protein was recently discovered. This protein carries an oxygen-activating heterodinuclear Mn(II)/Fe(II) metal cofactor and generates a radical-equivalent Mn(IV)/Fe(III) oxidation state of the metal site, as opposed to the tyrosyl radical generated by other R2 subclasses. The metal arrangement of the heterodinuclear cofactor remains unknown. Is the metal positioning specific, and if so, where is which ion located? Here we use X-ray crystallography with anomalous scattering to show that the metal arrangement of this cofactor is specific with the manganese ion occupying metal position 1. This is the position proximal to the tyrosyl radical site in other R2 proteins and consistent with the assumption that the high-valent Mn(IV) species functions as a direct substitute for the tyrosyl radical.

    Fulltekst (pdf)
    fulltext
  • 28.
    Andersson, Ida E.
    et al.
    Umeå universitet, Teknisk-naturvetenskapliga fakulteten, Kemiska institutionen.
    Batsalova, Tsvetelina
    Medical Inflammation Research, Department of Medical Biochemistry and Biophysics, Karolinska Institutet.
    Haag, Sabrina
    Medical Inflammation Research, Department of Medical Biochemistry and Biophysics, Karolinska Institutet.
    Dzhambazov, Balik
    Medical Inflammation Research, Department of Medical Biochemistry and Biophysics, Karolinska Institutet.
    Holmdahl, Rikard
    Medical Inflammation Research, Department of Medical Biochemistry and Biophysics, Karolinska Institutet.
    Kihlberg, Jan
    Umeå universitet, Teknisk-naturvetenskapliga fakulteten, Kemiska institutionen.
    Linusson, Anna
    Umeå universitet, Teknisk-naturvetenskapliga fakulteten, Kemiska institutionen.
    (E)-Alkene and Ethylene Isosteres Substantially Alter the Hydrogen-Bonding Network in Class II MHC Aq/Glycopeptide Complexes and Affect T-Cell Recognition2011Inngår i: Journal of the American Chemical Society, ISSN 0002-7863, E-ISSN 1520-5126, Vol. 133, nr 36, s. 14368-14378Artikkel i tidsskrift (Fagfellevurdert)
    Abstract [en]

    The structural basis for antigen presentation by class II major histocompatibility complex (MHC) proteins to CD4(+) T-cells is important for understanding and possibly treating autoimmune diseases. In the work described in this paper, (E)-alkene and ethylene amide-bond isosteres were used to investigate the effect of removing hydrogen-bonding possibilities from the CII259-270 glycopeptide, which is bound by the arthritis-associated murine A(q) class II MHC protein. The isostere-modified glycopeptides showed varying and unexpectedly large losses of A(q) binding that could be linked to the dynamics of the system. Molecular dynamics (MD) simulations revealed that the backbone of CII259-270 and the A(q) protein are able to form up to 11 hydrogen bonds, but fewer than this number are present at any one time. Most of the strong hydrogen-bond interactions were formed by the N-terminal part of the glycopeptide, i.e., in the region where the isosteric replacements were made. The structural dynamics also revealed that hydrogen bonds were strongly coupled to each other; the loss of one hydrogen-bond interaction had a profound effect on the entire hydrogen-bonding network. The A(q) binding data revealed that an ethylene isostere glycopeptide unexpectedly bound more strongly to A(q) than the corresponding (E)-alkene, which is in contrast to the trend observed for the other isosteres. Analysis of the MD trajectories revealed that the complex conformation of this ethylene isostere was structurally different and had an altered molecular interaction pattern compared to the other A(q)/glycopeptide complexes. The introduced amide-bond isosteres also affected the interactions of the glycopeptide/A(q) complexes with T-cell receptors. The dynamic variation of the patterns and strengths of the hydrogen-bond interactions in the class II MHC system is of critical importance for the class II MHC/peptide/TCR signaling system.

  • 29.
    Andrén, Oliver C. J.
    et al.
    KTH, Skolan för kemivetenskap (CHE), Fiber- och polymerteknologi, Ytbehandlingsteknik.
    Fernandes, Aristi P.
    Malkoch, Michael
    KTH, Skolan för kemivetenskap (CHE), Fiber- och polymerteknologi, Ytbehandlingsteknik.
    Heterogeneous Rupturing Dendrimers2017Inngår i: Journal of the American Chemical Society, ISSN 0002-7863, E-ISSN 1520-5126Artikkel i tidsskrift (Fagfellevurdert)
    Abstract [en]

    Utilizing macromolecular scaffolds as templates for the production of small molecules that are distinctively different from the original monomer feedstock has many potential applications. Herein, as a proof-of-concept, a family of dendrimers displaying internally queued disulfide bridges were synthesized and exploited as flawless macromolecular templates that selectively rupture into a set of monomeric mercaptans. Disassembly was accomplished in a reducing environment, using DTT as an external stimulus, and the thiol constituents were successfully isolated. Their composition was dictated by three dendritic regions, i.e., (i) the symmetrical trithiol of the core (C3), (ii) the interior-asymmetric trithiols (CD2), and (iii) the periphery-asymmetric monothiols (DB2), in which B functionality is of an orthogonal nature. Taking into account the steady state between disulfides and thiols in all living cells, the collapse of the dendrimers to a multitude of smaller thiols was intracellularly assessed as a means to disrupt the balance of reactive oxygen species (ROS) often elevated in cancer cells. Indeed, the fragmentation induced a significant increase of ROS in human lung carcinoma A549 cells. These findings can potentially alter the perception of dendrimers being limited to carriers to being prodrugs for intracellular delivery of ROS with the potential to fight cancer.

  • 30.
    Atluri, Rambabu
    et al.
    Uppsala universitet, Teknisk-naturvetenskapliga vetenskapsområdet, Tekniska sektionen, Institutionen för teknikvetenskaper, Nanoteknologi och funktionella material.
    Garcia-Bennett, Alfonso
    Uppsala universitet, Teknisk-naturvetenskapliga vetenskapsområdet, Tekniska sektionen, Institutionen för teknikvetenskaper, Nanoteknologi och funktionella material.
    Hedin, Niklas
    Uppsala universitet, Teknisk-naturvetenskapliga vetenskapsområdet, Tekniska sektionen, Institutionen för teknikvetenskaper, Nanoteknologi och funktionella material.
    Nonsurfactant Supramolecular Synthesis of Ordered Mesoporous Silica2009Inngår i: Journal of the American Chemical Society, ISSN 0002-7863, E-ISSN 1520-5126, Vol. 131, nr 9, s. 3189-3191Artikkel i tidsskrift (Fagfellevurdert)
    Abstract [en]

    Hoogsteen-bonded tetrads and pentamers are formed by a large variety of organic molecules through H-donor and acceptor groups capable of inducing self-organization to form columnar and hexagonal mesophases. The biological importance of such macromolecular structures is exemplified by the assembly of guanosine-rich groups of telomere units and their implication in chromosomal replication. Folic acid is composed of a pterin group, chemically and structurally similar to guanine, conjugated to an l-glutamate moiety via a p-amino benzoic acid. Our aim has been to develop a delivery vehicle for folic acid and at the same time provide a novel synthetic route for ordered mesoporous materials without the use of amphiphilic surfactants. We present a new nonsurfactant route for the synthesis of highly ordered mesoporous materials, based on the supramolecular templating of stacked arrays of the tetramer-forming pterin groups of folic acid under a variety of synthetic conditions. This method leads to hexagonally ordered mesoporous structures with gyroid, spherical, and chiral morphologies with pores on the order of 25−30 Å in diameter and surface areas above 1000 m2/g. More importantly circular dichroism studies reveal that the folate template possesses a chiral signature within the pores in the as-synthesized solid and that chirality is transferred from the folate template to the pore surface via the aminopropyl triethoxysilane costructure directing agent used in the supramolecular assembly. This novel templating approach for ordered mesoporous materials breaks the hegemony of surfactant micellar systems for the preparation of these exciting high surface area solids and opens new opportunities for structural control, design of pore geometry, and novel applications.

  • 31.
    Atluri, Rambabu
    et al.
    Stockholms universitet, Naturvetenskapliga fakulteten, Institutionen för fysikalisk kemi, oorganisk kemi och strukturkemi.
    Hedin, Niklas
    Stockholms universitet, Naturvetenskapliga fakulteten, Institutionen för fysikalisk kemi, oorganisk kemi och strukturkemi.
    Garcia-Bennett, Alfonso E.
    Non-Surfactant Supramolecular Templating Synthesis of Ordered Mesoporous Silica2009Inngår i: Journal of the American Chemical Society, ISSN 0002-7863, E-ISSN 1520-5126, Vol. 131, nr 9, s. 3189-3191Artikkel i tidsskrift (Fagfellevurdert)
    Abstract [en]

    Hoogsteen-bonded tetrads and pentamers are formed by a large variety of organic molecules through H-donor and acceptor groups capable of inducing self-organization to form columnar and hexagonal mesophases. The biological importance of such macromolecular structures is exemplified by the assembly of guanosine-rich groups of telomere units and their implication in chromosomal replication. Folic acid is composed of a pterin group, chemically and structurally similar to guanine, conjugated to an l-glutamate moiety via a p-amino benzoic acid. Our aim has been to develop a delivery vehicle for folic acid and at the same time provide a novel synthetic route for ordered mesoporous materials without the use of amphiphilic surfactants. We present a new nonsurfactant route for the synthesis of highly ordered mesoporous materials, based on the supramolecular templating of stacked arrays of the tetramer-forming pterin groups of folic acid under a variety of synthetic conditions. This method leads to hexagonally ordered mesoporous structures with gyroid, spherical, and chiral morphologies with pores on the order of 25−30 Å in diameter and surface areas above 1000 m2/g. More importantly circular dichroism studies reveal that the folate template possesses a chiral signature within the pores in the as-synthesized solid and that chirality is transferred from the folate template to the pore surface via the aminopropyl triethoxysilane costructure directing agent used in the supramolecular assembly. This novel templating approach for ordered mesoporous materials breaks the hegemony of surfactant micellar systems for the preparation of these exciting high surface area solids and opens new opportunities for structural control, design of pore geometry, and novel applications.

  • 32.
    Auman, Dirk
    et al.
    Stockholms universitet, Naturvetenskapliga fakulteten, Institutionen för biokemi och biofysik.
    Ecker, Felix
    Mader, Sophie L.
    Stockholms universitet, Naturvetenskapliga fakulteten, Institutionen för biokemi och biofysik.
    Dorst, Kevin M.
    Stockholms universitet, Naturvetenskapliga fakulteten, Institutionen för organisk kemi.
    Bräuer, Alois
    Widmalm, Göran
    Stockholms universitet, Naturvetenskapliga fakulteten, Institutionen för organisk kemi.
    Groll, Michael
    Kaila, Ville R. I.
    Stockholms universitet, Naturvetenskapliga fakulteten, Institutionen för biokemi och biofysik.
    Peroxy Intermediate Drives Carbon Bond Activation in the Dioxygenase AsqJ2022Inngår i: Journal of the American Chemical Society, ISSN 0002-7863, E-ISSN 1520-5126, Vol. 144, nr 34, s. 15622-15632Artikkel i tidsskrift (Fagfellevurdert)
    Abstract [en]

    Dioxygenases catalyze stereoselective oxygen atom transfer in metabolic pathways of biological, industrial, and pharmaceutical importance, but their precise chemical principles remain controversial. The α-ketoglutarate (αKG)-dependent dioxygenase AsqJ synthesizes biomedically active quinolone alkaloids via desaturation and subsequent epoxidation of a carbon–carbon bond in the cyclopeptin substrate. Here, we combine high-resolution X-ray crystallography with enzyme engineering, quantum-classical (QM/MM) simulations, and biochemical assays to describe a peroxidic intermediate that bridges the substrate and active site metal ion in AsqJ. Homolytic cleavage of this moiety during substrate epoxidation generates an activated high-valent ferryl (FeIV = O) species that mediates the next catalytic cycle, possibly without the consumption of the metabolically valuable αKG cosubstrate. Our combined findings provide an important understanding of chemical bond activation principles in complex enzymatic reaction networks and molecular mechanisms of dioxygenases. 

  • 33.
    Axelsson, Martin
    et al.
    Uppsala universitet, Teknisk-naturvetenskapliga vetenskapsområdet, Kemiska sektionen, Institutionen för kemi - Ångström, Fysikalisk kemi.
    Marchiori, Cleber F. N.
    Karlstad Univ, Dept Engn & Phys, S-65188 Karlstad, Sweden..
    Huang, Ping
    Uppsala universitet, Teknisk-naturvetenskapliga vetenskapsområdet, Kemiska sektionen, Institutionen för kemi - Ångström, Molekylär biomimetik.
    Araujo, C. Moyses
    Uppsala universitet, Teknisk-naturvetenskapliga vetenskapsområdet, Fysiska sektionen, Institutionen för fysik och astronomi, Materialteori. Karlstad Univ, Dept Engn & Phys, S-65188 Karlstad, Sweden..
    Tian, Haining
    Uppsala universitet, Teknisk-naturvetenskapliga vetenskapsområdet, Kemiska sektionen, Institutionen för kemi - Ångström, Fysikalisk kemi.
    Small Organic Molecule Based on Benzothiadiazole for Electrocatalytic Hydrogen Production2021Inngår i: Journal of the American Chemical Society, ISSN 0002-7863, E-ISSN 1520-5126, Vol. 143, nr 50, s. 21229-21233Artikkel i tidsskrift (Fagfellevurdert)
    Abstract [en]

    A small organic molecule 2,1,3-benzothiadiazole-4, 7-dicarbonitrile (BTDN) is assessed for electrocatalytic hydrogen evolution on glassy carbon electrode and shows a hydrogen production Faradaic efficiency of 82% in the presence of salicylic acid. The key catalytic intermediates of reduced species BTDN-center dot and protonated intermediates are characterized or hypothesized by using various spectroscopic methods and density functional theory (DFT)-based calculations. With the experimental and theoretical results, a catalytic mechanism of BTDN for electrocatalytic H-2 evolution is proposed.

    Fulltekst (pdf)
    FULLTEXT01
  • 34.
    Axelsson, Martin
    et al.
    Uppsala University.
    Marchiori, Cleber
    Karlstads universitet, Fakulteten för hälsa, natur- och teknikvetenskap (from 2013), Institutionen för ingenjörsvetenskap och fysik (from 2013).
    Huang, Ping
    Uppsala University.
    Araujo, C. Moyses
    Karlstad University.
    Tian, Haining
    Uppsala University.
    Small Organic Molecule Based on Benzothiadiazole for Electrocatalytic Hydrogen Production2021Inngår i: Journal of the American Chemical Society, ISSN 0002-7863, E-ISSN 1520-5126, Vol. 143, nr 50, s. 21229-21233Artikkel i tidsskrift (Fagfellevurdert)
    Abstract [en]

    A small organic molecule 2,1,3-benzothiadiazole-4, 7-dicarbonitrile (BTDN) is assessed for electrocatalytic hydrogen evolution on glassy carbon electrode and shows a hydrogen production Faradaic efficiency of 82% in the presence of salicylic acid. The key catalytic intermediates of reduced species BTDN-. and protonated intermediates are characterized or hypothesized by using various spectroscopic methods and density functional theory (DFT)-based calculations. With the experimental and theoretical results, a catalytic mechanism of BTDN for electrocatalytic H-2 evolution is proposed.

  • 35.
    Aydin, Juhanes
    et al.
    Stockholms universitet, Naturvetenskapliga fakulteten, Institutionen för organisk kemi.
    Larsson, Johanna M.
    Stockholms universitet, Naturvetenskapliga fakulteten, Institutionen för organisk kemi.
    Szabó, Kálmán J.
    Stockholms universitet, Naturvetenskapliga fakulteten, Institutionen för organisk kemi.
    Pincer Complex-Catalyzed Coupling Reactions via Palladium (IV) Intermediates2009Inngår i: Journal of the American Chemical Society, ISSN 0002-7863, E-ISSN 1520-5126, Vol. 11, nr 13, s. 2852-2854Artikkel i tidsskrift (Fagfellevurdert)
    Abstract [en]

    Palladium pincer complexes directly catalyze the redox coupling reactions of functionalized alkenes and iodonium salts. The catalytic process, which is suitable for mild catalytic functionalization of allylic acetates and electron-rich alkenes, probably occurs through Pd(IV) intermediates. Due to the strong metal−ligand interactions, the oxidation of phosphine and amine ligands of the pincer complexes can be avoided in the presented reactions.

  • 36. Azam, M. S.
    et al.
    Cai, C.
    Gibbs, J. M.
    Tyrode, Eric
    KTH, Skolan för kemi, bioteknologi och hälsa (CBH), Kemi, Yt- och korrosionsvetenskap.
    Hore, D. K.
    Silica Surface Charge Enhancement at Elevated Temperatures Revealed by Interfacial Water Signals2020Inngår i: Journal of the American Chemical Society, ISSN 0002-7863, E-ISSN 1520-5126, Vol. 142, nr 2, s. 669-673Artikkel i tidsskrift (Fagfellevurdert)
    Abstract [en]

    The structure of water adjacent to silica is sensitive to the degree of deprotonation of surface silanol groups. As a result, close inspection of signals originating from these water molecules can be used to reveal the surface charge density. We have used nonlinear vibrational spectroscopy of the water O-H stretching band over a temperature range of 10-75 °C to account for the increase in surface potential from deprotonation. We demonstrate that the behavior at the silica surface is a balance between increasing surface charge and a decreasing contribution of water molecules aligned by the surface charge. Together with a model that accounts for two different types of silanol sites, we use our data to report the changes in enthalpy and entropy for deprotonation at each site. This is the first experimental determination of these thermodynamic parameters for hydrated silanol groups at the silica surface, critical to a wide range of geochemical and technological applications.

  • 37.
    Baber, Ashleigh E.
    et al.
    Brookhaven National Laboratory, USA.
    Xu, Fang
    Brookhaven National Laboratory, USA.
    Dvorak, Filip
    Charles University, Czech Republic.
    Mudiyanselage, Kumudu
    Brookhaven National Laboratory, USA.
    Soldemo, Markus
    KTH.
    Weissenrieder, Jonas
    KTH.
    Senanayake, Sanjaya D.
    Brookhaven National Laboratory, USA.
    Sadowski, Jerzy T.
    Rodriguez, José A.
    Brookhaven National Laboratory, USA.
    Matolín, Vladimír
    Charles University, Czech Republic.
    White, Michael G.
    Brookhaven National Laboratory, USA; Brookhaven National Laboratory, USA.
    Stacchiola, Darío J.
    Brookhaven National Laboratory, USA.
    In Situ Imaging of Cu2O under Reducing Conditions: Formation of Metallic Fronts by Mass Transfer2013Inngår i: Journal of the American Chemical Society, ISSN 0002-7863, E-ISSN 1520-5126, Vol. 135, nr 45, s. 16781-16784Artikkel i tidsskrift (Fagfellevurdert)
    Abstract [en]

    Active catalytic sites have traditionally been analyzed based on static representations of surface structures and characterization of materials before or after reactions. We show here by a combination of in situ microscopy and spectroscopy techniques that, in the presence of reactants, an oxide catalyst's chemical state and morphology are dynamically modified. The reduction of Cu2O films is studied under ambient pressures (AP) of CO. The use of complementary techniques allows us to identify intermediate surface oxide phases and determine how reaction fronts propagate across the surface by massive mass transfer of Cu atoms released during the reduction of the oxide phase in the presence of CO. High resolution in situ imaging by AP scanning tunneling microscopy (AP-STM) shows that the reduction of the oxide films is initiated at defects both on step edges and the center of oxide terraces.

  • 38. Baber, Ashleigh E.
    et al.
    Xu, Fang
    Dvorak, Filip
    Mudiyanselage, Kumudu
    Soldemo, Markus
    KTH, Skolan för informations- och kommunikationsteknik (ICT), Material- och nanofysik, Materialfysik, MF.
    Weissenrieder, Jonas
    KTH, Skolan för informations- och kommunikationsteknik (ICT), Material- och nanofysik, Materialfysik, MF.
    Senanayake, Sanjaya D.
    Sadowski, Jerzy T.
    Rodriguez, José A.
    Matolín, Vladimír
    White, Michael G.
    Stacchiola, Darío J.
    In Situ Imaging of Cu2O under Reducing Conditions: Formation of Metallic Fronts by Mass Transfer2013Inngår i: Journal of the American Chemical Society, ISSN 0002-7863, E-ISSN 1520-5126, Vol. 135, nr 45, s. 16781-16784Artikkel i tidsskrift (Fagfellevurdert)
    Abstract [en]

    Active catalytic sites have traditionally been analyzed based on static representations of surface structures and characterization of materials before or after reactions. We show here by a combination of in situ microscopy and spectroscopy techniques that, in the presence of reactants, an oxide catalyst's chemical state and morphology are dynamically modified. The reduction of Cu2O films is studied under ambient pressures (AP) of CO. The use of complementary techniques allows us to identify intermediate surface oxide phases and determine how reaction fronts propagate across the surface by massive mass transfer of Cu atoms released during the reduction of the oxide phase in the presence of CO. High resolution in situ imaging by AP scanning tunneling microscopy (AP-STM) shows that the reduction of the oxide films is initiated at defects both on step edges and the center of oxide terraces.

  • 39.
    Baias, Maria
    et al.
    Universite de Lyon, France.
    Dumez, Jean Nicolas
    Universite de Lyon, France.
    Svensson, Per H.
    RISE., SP – Sveriges Tekniska Forskningsinstitut, SP Process Development, Analys och fastfas. KTH Royal Institute of Technology, Sweden.
    Schantz, Staffan
    AstraZeneca, Sweden.
    Day, Graeme M.
    University of Southampton, United Kingdom.
    Emsley, Lyndon
    Universite de Lyon, France.
    De novo determination of the crystal structure of a large drug molecule by crystal structure prediction-based powder NMR crystallography2013Inngår i: Journal of the American Chemical Society, ISSN 0002-7863, E-ISSN 1520-5126, Vol. 135, nr 46, s. 17501-17507Artikkel i tidsskrift (Fagfellevurdert)
    Abstract [en]

    The crystal structure of form 4 of the drug 4-[4-(2-adamantylcarbamoyl)-5-tert-butyl-pyrazol-1-yl]benzoic acid is determined using a protocol for NMR powder crystallography at natural isotopic abundance combining solid-state (1)H NMR spectroscopy, crystal structure prediction, and density functional theory chemical shift calculations. This is the first example of NMR crystal structure determination for a molecular compound of previously unknown structure, and at 422 g/mol this is the largest compound to which this method has been applied so far.

  • 40. Baias, Maria
    et al.
    Dumez, Jean-Nicolas
    Svensson, Per Henrik
    KTH, Skolan för kemivetenskap (CHE), Kemi, Tillämpad fysikalisk kemi.
    Schantz, Staffan
    Day, Graeme M.
    Emsley, Lyndon
    De Novo Determination of the Crystal Structure of a Large Drug Molecule by Crystal Structure Prediction-Based Powder NMR Crystallography2013Inngår i: Journal of the American Chemical Society, ISSN 0002-7863, E-ISSN 1520-5126, Vol. 135, nr 46, s. 17501-17507Artikkel i tidsskrift (Fagfellevurdert)
    Abstract [en]

    The crystal structure of form 4 of the drug 4-[4-(2-adamantylcarbamoyl)-5-tert-butyl-pyrazol-1-yl]benzoic acid is determined using a protocol for NMR powder crystallography at natural isotopic abundance combining solid-state H-1 NMR spectroscopy, crystal structure prediction, and density functional theory chemical shift calculations. This is the first example of NMR crystal structure determination for a molecular compound of previously unknown structure, and at 422 g/mol this is the largest compound to which this method has been applied so far.

  • 41. Baranov, A. I.
    et al.
    Kloo, Lars A.
    KTH, Tidigare Institutioner (före 2005), Kemi.
    Olenev, A. V.
    Popovkin, B. A.
    Romanenko, A. I.
    Shevelkov, A. V.
    Unique (infinity Ni8Bi8S)-Ni-1 metallic wires in a novel quasi-1D compound. Synthesis, crystal and electronic structure, and properties of Ni8Bi8SI2001Inngår i: Journal of the American Chemical Society, ISSN 0002-7863, E-ISSN 1520-5126, Vol. 123, nr 49, s. 12375-12379Artikkel i tidsskrift (Fagfellevurdert)
    Abstract [en]

    A new quasi-one-dimensional compound Ni8Bi8SI has been synthesized and its crystal structure determined from single-crystal X-ray diffraction data. The structure of Ni8Bi8SI consists of [(infinityNi8Bi8S)-Ni-1] columns separated by iodine atoms. Conductivity and magnetic susceptibility measurements (down to 4.2 K) show that Ni8Bi8SI is a one-dimensional metal and exhibits Pauli paramagnetic properties. These observations are in good agreement with the results from electronic structure calculations. An analysis of the chemical bonding employing difference electron charge density maps reveals strong multicenter Ni-Bi bonds and pair Ni-S interactions within the [(infinityNi8Bi8S)-Ni-1] columns. Only electrostatic interactions are inferred between the columns and iodine atoms.

  • 42.
    Barrozo, Alexandre
    et al.
    Uppsala universitet, Teknisk-naturvetenskapliga vetenskapsområdet, Biologiska sektionen, Institutionen för cell- och molekylärbiologi, Struktur- och molekylärbiologi. Uppsala universitet, Science for Life Laboratory, SciLifeLab.
    Duarte, Fernanda
    Uppsala universitet, Teknisk-naturvetenskapliga vetenskapsområdet, Biologiska sektionen, Institutionen för cell- och molekylärbiologi, Struktur- och molekylärbiologi. Uppsala universitet, Science for Life Laboratory, SciLifeLab.
    Bauer, Paul
    Uppsala universitet, Teknisk-naturvetenskapliga vetenskapsområdet, Biologiska sektionen, Institutionen för cell- och molekylärbiologi, Struktur- och molekylärbiologi. Uppsala universitet, Science for Life Laboratory, SciLifeLab.
    Carvalho, Alexandra T. P.
    Uppsala universitet, Teknisk-naturvetenskapliga vetenskapsområdet, Biologiska sektionen, Institutionen för cell- och molekylärbiologi, Struktur- och molekylärbiologi. Uppsala universitet, Science for Life Laboratory, SciLifeLab.
    Kamerlin, Shina C. Lynn
    Uppsala universitet, Teknisk-naturvetenskapliga vetenskapsområdet, Biologiska sektionen, Institutionen för cell- och molekylärbiologi, Struktur- och molekylärbiologi. Uppsala universitet, Science for Life Laboratory, SciLifeLab.
    Cooperative Electrostatic Interactions Drive Functional Evolution in the Alkaline Phosphatase Superfamily2015Inngår i: Journal of the American Chemical Society, ISSN 0002-7863, E-ISSN 1520-5126, Vol. 137, nr 28, s. 9061-9076Artikkel i tidsskrift (Fagfellevurdert)
    Abstract [en]

    It is becoming widely accepted that catalytic promiscuity, i.e., the ability of a single enzyme to catalyze the turnover of multiple, chemically distinct substrates, plays a key role in the evolution of new enzyme functions. In this context, the members of the alkaline phosphatase superfamily have been extensively studied as model systems in order to understand the phenomenon of enzyme multifunctionality. In the present work, we model the selectivity of two multiply promiscuous members of this superfamily, namely the phosphonate monoester hydrolases from Burkholderia caryophylli and Rhizobium leguminosarum. We have performed extensive simulations of the enzymatic reaction of both wild-type enzymes and several experimentally characterized mutants. Our computational models are in agreement with key experimental observables, such as the observed activities of the wild-type enzymes, qualitative interpretations of experimental pH-rate profiles, and activity trends among several active site mutants. In all cases the substrates of interest bind to the enzyme in similar conformations, with largely unperturbed transition states from their corresponding analogues in aqueous solution. Examination of transition-state geometries and the contribution of individual residues to the calculated activation barriers suggest that the broad promiscuity of these enzymes arises from cooperative electrostatic interactions in the active site, allowing each enzyme to adapt to the electrostatic needs of different substrates. By comparing the structural and electrostatic features of several alkaline phosphatases, we suggest that this phenomenon is a generalized feature driving selectivity and promiscuity within this superfamily and can be in turn used for artificial enzyme design.

    Fulltekst (pdf)
    fulltext
  • 43.
    Bartholomeyzik, Teresa
    et al.
    Stockholms universitet, Naturvetenskapliga fakulteten, Institutionen för organisk kemi.
    Pendrill, Robert
    Stockholms universitet, Naturvetenskapliga fakulteten, Institutionen för organisk kemi.
    Lihammar, Richard
    Stockholms universitet, Naturvetenskapliga fakulteten, Institutionen för organisk kemi.
    Jiang, Tuo
    Stockholms universitet, Naturvetenskapliga fakulteten, Institutionen för organisk kemi.
    Widmalm, Göran
    Stockholms universitet, Naturvetenskapliga fakulteten, Institutionen för organisk kemi.
    Bäckvall, Jan-E.
    Stockholms universitet, Naturvetenskapliga fakulteten, Institutionen för organisk kemi.
    Kinetics and Mechanism of the Palladium-Catalyzed Oxidative Arylating Carbocyclization of Allenynes2018Inngår i: Journal of the American Chemical Society, ISSN 0002-7863, E-ISSN 1520-5126, Vol. 140, nr 1, s. 298-309Artikkel i tidsskrift (Fagfellevurdert)
    Abstract [en]

    Pd-catalyzed C-C bond-forming reactions under oxidative conditions constitute a class of important and widely used synthetic protocols. This Article describes a mechanistic investigation of the arylating carbocyclization of allenynes using boronic acids and focuses on the correlation between reaction conditions and product selectivity. Isotope effects confirm that either allenic or propargylic C-H activation occurs directly after substrate binding. With an excess of H2O, a triene product is selectively formed via allenic C-H activation. The latter C-H activation was found to be turnover-limiting and the reaction zeroth order in reactants as well as the oxidant. A dominant feature is continuous catalyst activation, which was shown to occur even in the absence of substrate. Smaller amounts of H2O lead to mixtures of triene and vinylallene products, where the latter is formed via propargylic C-H activation. The formation of triene occurs only in the presence of ArB(OH)(2). Vinylallene, on the other hand, was shown to be formed by consumption of (ArBO)(3) as a first-order reactant. Conditions with sub-stoichiometric BF3 center dot OEt2 gave selectively the vinylallene product, and the reaction is first order in PhB(OH)(2). Both C-H activation and transmetalation influence the reaction rate. However, with electron-deficient ArB(OH)(2), C-H activation is turnover-limiting. It was difficult to establish the order of transmetalation vs C-H activation with certainty, but the results suggest that BF3 center dot OEt2 promotes an early transmetalation. The catalytically active species were found to be dependent on the reaction conditions, and H2O is a crucial parameter in the control of selectivity.

  • 44.
    Barz, Bogdan
    et al.
    Forschungszentrum Jülich GmbH, Institute of Complex Systems: Structural Biochemistry (ICS-6), Jülich; Heinrich Heine University Düsseldorf, Institute of Theoretical and Computational Chemistry, Düsseldorf.
    Liao, Qinghua
    Uppsala universitet, Teknisk-naturvetenskapliga vetenskapsområdet, Biologiska sektionen, Institutionen för cell- och molekylärbiologi, Strukturbiologi. Forschungszentrum Jülich GmbH, Institute of Complex Systems: Structural Biochemistry (ICS-6), Jülich.
    Strodel, Birgit
    Forschungszentrum Jülich GmbH, Institute of Complex Systems: Structural Biochemistry (ICS-6), Jülich; Heinrich Heine University Düsseldorf, Institute of Theoretical and Computational Chemistry, Düsseldorf.
    Pathways of Amyloid-β Aggregation Depend on Oligomer Shape2018Inngår i: Journal of the American Chemical Society, ISSN 0002-7863, E-ISSN 1520-5126, Vol. 140, nr 1, s. 319-327Artikkel i tidsskrift (Fagfellevurdert)
    Abstract [en]

    One of the main research topics related to Alzheimer’s disease is the aggregation of the amyloid-β peptide, which was shown to follow different pathways for the two major alloforms of the peptide, Aβ40 and the more toxic Aβ42. Experimental studies emphasized that oligomers of specific sizes appear in the early aggregation process in different quantities and might be the key toxic agents for each of the two alloforms. We use transition networks derived from all-atom molecular dynamics simulations to show that the oligomers leading to the type of oligomer distributions observed in experiments originate from compact conformations. Extended oligomers, on the other hand, contribute more to the production of larger aggregates thus driving the aggregation process. We further demonstrate that differences in the aggregation pathways of the two Aβ alloforms occur as early as during the dimer stage. The higher solvent-exposure of hydrophobic residues in Aβ42 oligomers contributes to the different aggregation pathways of both alloforms and also to the increased cytotoxicity of Aβ42.

  • 45.
    Bassan, Arianna
    et al.
    Stockholms universitet, Naturvetenskapliga fakulteten, Fysikum.
    Blomberg, Margareta R. A.
    Stockholms universitet, Naturvetenskapliga fakulteten, Fysikum.
    Siegbahn, Per E. M.
    Stockholms universitet, Naturvetenskapliga fakulteten, Fysikum.
    Que, Jr., Lawrence
    A Density Functional Study of O-O Bond Cleavage for a Biomimetic Non-Heme Iron Complex Demonstrating an Fe(V)-Intermediate2002Inngår i: Journal of the American Chemical Society, ISSN 0002-7863, E-ISSN 1520-5126, Vol. 124, nr 37, s. 11056-11063Artikkel i tidsskrift (Fagfellevurdert)
  • 46.
    Berglund, Per
    et al.
    University of Toronto, Canada.
    DeSantis, Grace
    Stabile, Michele R.
    Shang, Xiao
    Gold, Marvin
    Bott, Richard R.
    Graycar, Thomas P.
    Lau, Tony Hing
    Mitchinson, Colin
    Jones, J. Bryan
    Chemical Modification of Cysteine Mutants of Subtilisin Bacillus lentus Can Create Better Catalysts Than the Wild-Type Enzyme1997Inngår i: Journal of the American Chemical Society, ISSN 0002-7863, E-ISSN 1520-5126, Vol. 119, nr 22, s. 5265-5266Artikkel i tidsskrift (Fagfellevurdert)
  • 47. Bergström, Fredrik
    et al.
    Mikhalyov, Ilya
    Hägglöf, Peter
    Wortmann, Rüdiger
    Ny, Tor
    Umeå universitet, Medicinska fakulteten, Institutionen för medicinsk kemi och biofysik.
    Johansson, Lennart B A
    Dimers of dipyrrometheneboron difluoride (BODIPY) with light spectroscopic applications in chemistry and biology.2002Inngår i: Journal of the American Chemical Society, ISSN 0002-7863, E-ISSN 1520-5126, Vol. 124, nr 2, s. 196-204Artikkel i tidsskrift (Fagfellevurdert)
    Abstract [en]

    A ground-state dimer (denoted D(I)) exhibiting a strong absorption maximum at 477 nm (epsilon = 97 000 M(-1)cm(-1)) can form between adjacent BODIPY groups attached to mutant forms of the protein, plasminogen activator inhibitor type 1 (PAI-1). No fluorescence from excited D(I) was detected. A locally high concentration of BODIPY groups was also achieved by doping lipid phases (micelles, vesicles) with BODIPY-labeled lipids. In addition to an absorption band located at about 480 nm, a new weak absorption band is also observed at ca. 570 nm. Both bands are ascribed to the formation of BODIPY dimers of different conformation (D(I) and D(II)). Contrary to D(I) in PAI-1, the D(II) aggregates absorbing at 570 nm are emitting light observed as a broad band centered at about 630 nm. The integrated absorption band of D(I) is about twice that of the monomer, which is compatible with exciton coupling within a dimer. The Förster radius of electronic energy transfer between a BODIPY excited monomer and the ground-state dimer (D(I)()) is 57 +/- 2 A. A simple model of exciton coupling suggests that in D(I) two BODIPY groups are stacked on top of each other in a sandwich-like configuration with parallel electronic transition dipoles. For D(II) the model suggests that the S(0) --> S(1) transition dipoles are colinear. An explanation for the previously reported (J. Am. Chem. Soc. 1994, 116, 7801) exceptional light spectroscopic properties of BODIPY is also presented. These are ascribed to the extraordinary electric properties of the BODIPY chromophore. First, changes of the permanent electric dipole moment (Delta(mu) approximately -0.05 D) and polarizability (-26 x 10(-40) C m(2) V(-1)) between the ground and the first excited states are small. Second, the S(0) <--> S(1) electronic transition dipole moments are perpendicular to Delta(mu).

  • 48.
    Berry, Bruce W.
    et al.
    Stockholms universitet, Naturvetenskapliga fakulteten, Institutionen för biokemi och biofysik. University of Pennsylvania, USA.
    Elvekrog, Margaret M.
    Stockholms universitet, Naturvetenskapliga fakulteten, Institutionen för biokemi och biofysik. University of Pennsylvania, USA.
    Tommos, Cecilia
    Stockholms universitet, Naturvetenskapliga fakulteten, Institutionen för biokemi och biofysik. University of Pennsylvania, USA.
    Environmental modulation of protein cation-pi interactions2007Inngår i: Journal of the American Chemical Society, ISSN 0002-7863, E-ISSN 1520-5126, Vol. 129, nr 17, s. 5308+-Artikkel i tidsskrift (Fagfellevurdert)
    Abstract [en]

    Protein cation-pi interactions are frequently found near the protein surface with their interacting residues partly solvent exposed. The structurally characterized alpha W-3 model protein contains the W32/K36 cation-pi interaction which has properties similar to those of naturally occurring protein cation-pi interactions. alpha W-3 was studied with the following results: Cation-pi interactions formed by a buried tryptophan and a partly solvated lysine, arginine, or histidine range from -0.8 to -0.5 kcal mol(-1) and rank as: W32/K36 approximate to W32/R36 > W32/H36. The W32/K36 pair in alpha W-3 represents the first W/K cation-pi interaction for which both the structure and the bond energy have been experimentally determined. Upon increasing the solvent exposure of the cation-pi pair, the W/K interaction energy drops from -0.73 to -0.06 and +0.15 kcal mol(-1). These results suggest that solvent exposure can tune the interaction energy between a tryptophan and a lysine by at least 0.9 kcal mol(-1).

  • 49. Bertelsen, Søren
    et al.
    Dinér, Peter
    Center for Catalysis, Department of Chemistry, Aarhus University.
    Johansen, Rasmus Lyng
    Jørgensen, Karl Anker
    Asymmetric organocatalytic beta-hydroxylation of alpha, beta-unsaturated aldehydes2007Inngår i: Journal of the American Chemical Society, ISSN 0002-7863, E-ISSN 1520-5126, Vol. 129, nr 6, s. 1536-1537Artikkel i tidsskrift (Fagfellevurdert)
    Abstract [en]

    The first catalytic enantioselective beta-hydroxylation of alpha,beta-unsaturated aldehydes is presented. Using commercially available (E)-benzaldehyde oxime in the presence of 2-[bis(3,5-bis-trifluoromethyl-phenyl)trimethyl-silanyloxymethyl]pyrrolidine as organocatalyst, the corresponding chiral carbonyl beta-oxime ethers are obtained in high yields and with excellent enantioselectivities. These optically active carbonyl and hydroxy beta-oxime ethers are highly interesting biological compounds in, e.g., sex pheromone analogues, highly potent antiinflammatory agents, and penicillin and cephalosporin analogues. The chiral carbonyl beta-oxime ethers can be reduced to the corresponding 1,3-diols in high yields. Furthermore, the organocatalytic enantioselective beta-hydroxylation of alpha,beta-unsaturated aldehydes could be performed on gram scale without loss of enantioselectivity.

  • 50. Bertelsen, Søren
    et al.
    Dinér, Peter
    Johansen, Rasmus Lyng
    Jørgensen, Karl Anker
    Asymmetric organocatalytic beta-hydroxylation of alpha, beta-unsaturated aldehydes2007Inngår i: Journal of the American Chemical Society, ISSN 0002-7863, E-ISSN 1520-5126, Vol. 129 1536-1537, nr 6, s. 1536-1537Artikkel i tidsskrift (Fagfellevurdert)
    Abstract [en]

    The first catalytic enantioselective β-hydroxylation of α,β-unsaturated aldehydes is presented. Using commercially available (E)-benzaldehyde oxime in the presence of 2-[bis(3,5-bis-trifluoromethyl-phenyl)trimethyl-silanyloxymethyl]pyrrolidine as organocatalyst, the corresponding chiral carbonyl β-oxime ethers are obtained in high yields and with excellent enantioselectivities. These optically active carbonyl and hydroxy β-oxime ethers are highly interesting biological compounds in, e.g., sex pheromone analogues, highly potent antiinflammatory agents, and penicillin and cephalosporin analogues. The chiral carbonyl β-oxime ethers can be reduced to the corresponding 1,3-diols in high yields. Furthermore, the organocatalytic enantioselective β-hydroxylation of α,β-unsaturated aldehydes could be performed on gram scale without loss of enantioselectivity.

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