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  • 1.
    Afewerki, Samson
    et al.
    Mid Sweden University, Faculty of Science, Technology and Media, Department of Natural Sciences. Stockholm Univ, Berzelii Ctr EXSELENT, SE-10691 Stockholm, Sweden.
    Ma, Guangning
    Mid Sweden University, Faculty of Science, Technology and Media, Department of Natural Sciences.
    Ibrahem, Ismail
    Mid Sweden University, Faculty of Science, Technology and Media, Department of Chemical Engineering.
    Liu, Leifeng
    Department of Materials and Environmental Chemistry, Stockholm University, Stockholm, Sweden .
    Sun, Junliang
    Department of Materials and Environmental Chemistry, Stockholm University, Stockholm, Sweden .
    Cordova, Armando
    Mid Sweden University, Faculty of Science, Technology and Media, Department of Natural Sciences. Department of Materials and Environmental Chemistry, Stockholm University, Stockholm, Sweden .
    Highly Enantioselective Control of Dynamic Cascade Transformations by Dual Catalysis: Asymmetric Synthesis of Polysubstituted Spirocyclic Oxindoles2015In: ACS Catalysis, ISSN 2155-5435, E-ISSN 2155-5435, Vol. 5, no 2, p. 1266-1272Article in journal (Refereed)
    Abstract [en]

    The highly enantioselective (up to >99.5:0.5 er) synthesis of polysubstituted spirocyclic oxindoles with four new contiguous stereocenters, including the spiro all-carbon quaternary center, is disclosed. It is accomplished by the highly stereoselective control of a dynamic conjugate/intramolecular allylic alkylation relay sequence based on the synergistic cooperation of metal and chiral amine catalysts in which the careful selection of organic Nand, metal complex, and chiral amine is essential. The intermolecular C-C bond-forming step occurred only when both the metal and chiral amine catalysts were present.

  • 2.
    Afewerki, Samson
    et al.
    Stockholm University, Faculty of Science, Department of Materials and Environmental Chemistry (MMK). Mid-Sweden University, Sweden.
    Ma, Guangning
    Ibrahem, Ismail
    Liu, Leifeng
    Stockholm University, Faculty of Science, Department of Materials and Environmental Chemistry (MMK).
    Sun, Junliang
    Stockholm University, Faculty of Science, Department of Materials and Environmental Chemistry (MMK).
    Córdova, Armando
    Stockholm University, Faculty of Science, Department of Materials and Environmental Chemistry (MMK). Mid-Sweden University, Sweden.
    Highly Enantioselective Control of Dynamic Cascade Transformations by Dual Catalysis: Asymmetric Synthesis of Polysubstituted Spirocyclic Oxindoles2015In: ACS Catalysis, ISSN 2155-5435, E-ISSN 2155-5435, Vol. 5, no 2, p. 1266-1272Article in journal (Refereed)
    Abstract [en]

    The highly enantioselective (up to >99.5:0.5 er) synthesis of polysubstituted spirocyclic oxindoles with four new contiguous stereocenters, including the spiro all-carbon quaternary center, is disclosed. It is accomplished by the highly stereoselective control of a dynamic conjugate/intramolecular allylic alkylation relay sequence based on the synergistic cooperation of metal and chiral amine catalysts in which the careful selection of organic Nand, metal complex, and chiral amine is essential. The intermolecular C-C bond-forming step occurred only when both the metal and chiral amine catalysts were present.

  • 3.
    Amrein, Beat A.
    et al.
    Uppsala University, Disciplinary Domain of Science and Technology, Biology, Department of Cell and Molecular Biology, Structure and Molecular Biology. Uppsala University, Science for Life Laboratory, SciLifeLab.
    Bauer, Paul
    Uppsala University, Disciplinary Domain of Science and Technology, Biology, Department of Cell and Molecular Biology, Structure and Molecular Biology. Uppsala University, Science for Life Laboratory, SciLifeLab.
    Duarte, Fernanda
    Uppsala University, Disciplinary Domain of Science and Technology, Biology, Department of Cell and Molecular Biology, Structure and Molecular Biology. Uppsala University, Science for Life Laboratory, SciLifeLab.
    Janfalk Carlsson, Åsa
    Uppsala University, Disciplinary Domain of Science and Technology, Chemistry, Department of Chemistry - BMC, Biochemistry.
    Naworyta, Agata
    Uppsala University, Disciplinary Domain of Science and Technology, Biology, Department of Cell and Molecular Biology. Uppsala University, Science for Life Laboratory, SciLifeLab.
    Mowbray, Sherry L.
    Uppsala University, Disciplinary Domain of Science and Technology, Biology, Department of Cell and Molecular Biology, Structure and Molecular Biology. Uppsala University, Science for Life Laboratory, SciLifeLab.
    Widersten, Mikael
    Uppsala University, Disciplinary Domain of Science and Technology, Chemistry, Department of Chemistry - BMC, Biochemistry.
    Kamerlin, Shina C. L.
    Uppsala University, Disciplinary Domain of Science and Technology, Biology, Department of Cell and Molecular Biology, Structure and Molecular Biology. Uppsala University, Science for Life Laboratory, SciLifeLab.
    Expanding the catalytic triad in epoxide hydrolases and related enzymes2015In: ACS Catalysis, ISSN 2155-5435, E-ISSN 2155-5435, Vol. 5, no 10, p. 5702-5713Article in journal (Refereed)
    Abstract [en]

    Potato epoxide hydrolase 1 exhibits rich enantio- and regioselectivity in the hydrolysis of a broadrange of substrates. The enzyme can be engineered to increase the yield of optically pureproducts, as a result of changes in both enantio- and regioselectivity. It is thus highly attractive inbiocatalysis, particularly for the generation of enantiopure fine chemicals and pharmaceuticals.The present work aims to establish the principles underlying the activity and selectivity of theenzyme through a combined computational, structural, and kinetic study, using the substratetrans-stilbene oxide as a model system. Extensive empirical valence bond simulations have beenperformed on the wild-type enzyme together with several experimentally characterized mutants.We are able to computationally reproduce the differences in activities between differentstereoisomers of the substrate, and the effects of mutations in several active-site residues. Inaddition, our results indicate the involvement of a previously neglected residue, H104, which iselectrostatically linked to the general base, H300. We find that this residue, which is highlyconserved in epoxide hydrolases and related hydrolytic enzymes, needs to be in its protonatedform in order to provide charge balance in an otherwise negatively-charged active site. Our datashow that unless the active-site charge balance is correctly treated in simulations, it is notpossible to generate a physically meaningful model for the enzyme that can accurately reproduceactivity and selectivity trends. We also expand our understanding of other catalytic residues,demonstrating in particular the role of a non-canonical residue, E35, as a “backup-base” in theabsence of H300. Our results provide a detailed view of the main factors driving catalysis andregioselectivity in this enzyme, and identify targets for subsequent enzyme design efforts.

  • 4.
    Aqvist, Johan
    et al.
    Uppsala University, Disciplinary Domain of Science and Technology, Biology, Department of Cell and Molecular Biology.
    Kamerlin, Shina C. L.
    Uppsala University, Disciplinary Domain of Science and Technology, Biology, Department of Cell and Molecular Biology.
    Conserved Motifs in Different Classes of GTPases Dictate their Specific Modes of Catalysis2016In: ACS Catalysis, ISSN 2155-5435, E-ISSN 2155-5435, Vol. 6, no 3, p. 1737-1743Article in journal (Refereed)
    Abstract [en]

    The GTPase superfamily of enzymes that hydrolyze GTP have a number of conserved sequence regions (the so-called "G-motifs"), and several of the subfamilies also require catalytic activation by specific GTPase-activating proteins. In the translational GTPases involved in protein synthesis, this activating function is instead accomplished by their interaction with the ribosome. Despite these similarities, there are distinct differences regarding some of the amino acid residues making up the GTPase active sites. This raises the question of whether or not the catalytic mechanisms of different types of GTPases are identical. We report herein extensive computer simulations of both the intrinsic GTP hydrolysis reaction of Ras and the considerably faster reaction activated by the interaction with RasGAP. The results of these calculations are compared to earlier simulations of GTP hydrolysis by EF-Tu on the ribosome and show that the favored reaction pathways are strongly dependent on the composition of the active site. By computing Arrhenius plots for the temperature dependence of the calculated free energy profiles, we further show that different mechanistic pathways are associated with distinct differences in activation entropies and enthalpies. The activation parameters are in good agreement with experimental data, and we conclude that calculations of Arrhenius plots from computer simulations can be very useful for dissecting the energetics of enzyme catalysis.

  • 5.
    Bartoszewicz, Agnieszka
    et al.
    Stockholm University, Faculty of Science, Department of Organic Chemistry.
    González Miera, Greco
    Stockholm University, Faculty of Science, Department of Organic Chemistry.
    Marcos, Rocio
    Stockholm University, Faculty of Science, Department of Organic Chemistry.
    Norrby, Per-Ola
    Martín-Matute, Belén
    Stockholm University, Faculty of Science, Department of Organic Chemistry.
    Mechanistic Studies on the Alkylation of Amines with Alcohols Catalyzed by a Bifunctional Iridium Complex2015In: ACS Catalysis, ISSN 2155-5435, E-ISSN 2155-5435, Vol. 5, no 6, p. 3704-3716Article in journal (Refereed)
    Abstract [en]

    The mechanism of the N-alkylation of amines with alcohols catalyzed by an iridium complex containing an N-heterocyclic carbene (NHC) ligand with a tethered alcohol/alkoxide functionality was investigated by a combination of experimental and computational methods. The catalyst resting state is an iridium hydride species containing the amine substrate as a ligand, and decoordination of the amine, followed by coordination of the imine intermediate to the iridium center, constitute the rate-determining step (rds) of the catalytic process. The alcohol/alkoxide that is tethered to the NHC participates in every step of the catalytic cycle by accepting or releasing protons and forming hydrogen bonds with the reacting species. Thus, the iridium complex with the alcohol/alkoxide tethered to the N-heterocyclic carbene ligand acts as a bifunctional catalyst.

  • 6.
    Bellini, Rosalba
    et al.
    KTH, School of Chemical Science and Engineering (CHE), Chemistry, Organic Chemistry.
    Magre, Marc
    Biosca, Maria
    Norrby, Per-Ola
    Pamies, Oscar
    Dieguez, Montserrat
    Moberg, Christina
    KTH, School of Chemical Science and Engineering (CHE), Chemistry, Organic Chemistry.
    Conformational Preferences of a Tropos Biphenyl Phosphinooxazoline-a Ligand with Wide Substrate Scope2016In: ACS Catalysis, ISSN 2155-5435, E-ISSN 2155-5435, Vol. 6, no 3, p. 1701-1712Article in journal (Refereed)
    Abstract [en]

    Excellent enantioselectivities are observed in palladium-catalyzed allylic substitutions of a wide range of substrate types and nucleophiles using a bidentate ligand composed of oxazoline and chirally flexible biaryl phosphite elements. This unusually wide substrate scope is shown by experimental and theoretical studies of its eta(3)-allyl and eta(2)-olefin complexes not to be a result of configurational interconversion of the biaryl unit, since the ligand in all reactions adopts an S-a,S configuration on coordination to palladium, but rather the ability of the ligand to adapt the size of the substrate-binding pocket to the reacting substrate. This ability also serves as an explanation to its excellent performance in other types of catalytic processes.

  • 7. Bersani, Marco
    et al.
    Gupta, Kalyani
    Mishra, Abhishek Kumar
    Lanza, Roberto
    KTH, School of Chemical Science and Engineering (CHE), Chemical Engineering and Technology, Chemical Technology.
    Taylor, S. F. Rebecca
    Islam, Husn-Ubayda
    Hollingsworth, Nathan
    Hardacre, Christopher
    de Leeuw, Nora H.
    Darr, Jawwad A.
    Combined EXAFS, XRD, DRIFTS, and DFT Study of Nano Copper Based Catalysts for CO2 Hydrogenation2016In: ACS Catalysis, ISSN 2155-5435, E-ISSN 2155-5435, Vol. 6, no 9, p. 5823-5833Article in journal (Refereed)
    Abstract [en]

    Highly monodispersed CuO nanoparticles (NPs) were synthesized via continuous hydrothermal flow synthesis (CHFS) and then tested as catalysts for CO2 hydrogenation. The catalytic behavior of unsupported 11 nm sized nanoparticles from the same batch was characterized by diffuse reflectance infrared fourier transform spectroscopy (DRIFTS), extended X-ray absorption fine structure (EXAFS), X-ray diffraction (XRD), and catalytic testing, under CO2/H-2 in the temperature range 25-500 degrees C in consistent experimental conditions. This was done to highlight the relationship among structural evolution, surface products, and reaction yields; the experimental results were compared with modeling predictions based on density functional theory (DFT) simulations of the CuO system. In situ DRIFTS revealed the formation of surface formate species at temperatures as low as 70 degrees C. DFT calculations of CO2 hydrogenation on the CuO surface suggested that hydrogenation reduced the CuO surface to Cu2O, which facilitated the formation of formate. In situ EXAFS supported a strong correlation between the Cu2O phase fraction and the formate peak intensity, with the maxima corresponding to where Cu2O was the only detectable phase at 170 degrees C, before the onset of reduction to Cu at 190 degrees C. The concurrent phase and crystallite size evolution were monitored by in situ XRD, which suggested that the CuO NPs were stable in size before the onset of reduction, with smaller Cu2O crystallites being observed from 130 degrees C. Further reduction to Cu from 190 C was followed by a rapid decrease of surface formate and the detection of adsorbed CO from 250 degrees C; these results are in agreement with heterogeneous catalytic tests where surface CO was observed over the same temperature range. Furthermore, CH4 was detected in correspondence with the decomposition of formate and formation of the Cu phase, with a maximum conversion rate of 2.8% measured at 470 degrees C (on completely reduced copper), supporting the indication of independent reaction pathways for the conversion of CO2 to CH4 and CO that was suggested by catalytic tests. The resulting Cu NPs had a final crystallite size of ca. 44 nm at 500 degrees C and retained a significantly active surface.

  • 8.
    Cortina, George A.
    et al.
    Univ Virginia, Dept Mol Physiol & Biol Phys, Box 800886, Charlottesville, VA 22908 USA;Univ Virginia, Dept Biomed Engn, Box 800886, Charlottesville, VA 22908 USA.
    Hays, Jennifer M.
    Univ Virginia, Dept Mol Physiol & Biol Phys, Box 800886, Charlottesville, VA 22908 USA;Univ Virginia, Dept Biomed Engn, Box 800886, Charlottesville, VA 22908 USA.
    Kasson, P. M.
    Uppsala University, Disciplinary Domain of Science and Technology, Biology, Department of Cell and Molecular Biology, Molecular biophysics. Uppsala University, Science for Life Laboratory, SciLifeLab. Univ Virginia, Dept Mol Physiol & Biol Phys, Box 800886, Charlottesville, VA 22908 USA;Univ Virginia, Dept Biomed Engn, Box 800886, Charlottesville, VA 22908 USA.
    Conformational Intermediate That Controls KPC-2 Catalysis and Beta-Lactam Drug Resistance2018In: ACS Catalysis, ISSN 2155-5435, E-ISSN 2155-5435, Vol. 8, no 4, p. 2741-2747Article in journal (Refereed)
    Abstract [en]

    The KPC-2 carbapenemase enzyme is responsible for drug resistance in the majority of carbapenem-resistant Gram-negative bacterial infections in the United States. A better understanding of what permits KPC-2 to hydrolyze carbapenem antibiotics and how this might be inhibited is thus of fundamental interest and great practical importance to development of better anti-infectives. By correlating molecular dynamics simulations with experimental enzyme kinetics, we identified conformational changes that control KPC-2's ability to hydrolyze carbapenem antibiotics. Related beta-lactamase enzymes can interconvert between catalytically permissive and catalytically nonpermissive forms of an acylenzyme intermediate critical to drug hydrolysis. identify a similar equilibrium in KPC-2 and analyze the determinants of this conformational change. Because the conformational dynamics of KPC-2 are complex and sensitive to allosteric changes, we develop an information-theoretic approach to identify key determinants of this change. We measure unbiased estimators of the reaction coordinate between catalytically permissive and nonpermissive states, perform information-theoretic feature selection, and, using restrained molecular dynamics simulations, validate the protein conformational changes predicted to control catalytically permissive geometry. We identify two binding pocket residues that control the conformational transitions between catalytically active and inactive forms of KPC-2. Mutations to one of these residues, Trp105, lower the stability of the catalytically permissive state in simulations and have reduced experimental k(cat) values that show a strong linear correlation with the simulated catalytically permissive state lifetimes. This understanding can be leveraged to predict the drug resistance of further KPC-2 mutants and help design inhibitors to combat extreme drug resistance.

  • 9.
    Daniel, Quentin
    et al.
    KTH, School of Chemical Science and Engineering (CHE), Chemistry, Organic Chemistry.
    Anabre, Ram B.
    KTH, School of Chemical Science and Engineering (CHE), Chemistry.
    Zhang, Biaobiao
    KTH, School of Chemical Science and Engineering (CHE), Chemistry, Organic Chemistry.
    Philippe, Bertrand
    Chen, Hong
    KTH, School of Chemical Science and Engineering (CHE), Chemistry.
    Li, Fusheng
    KTH, School of Chemical Science and Engineering (CHE), Chemistry.
    Fan, Ke
    KTH, School of Chemical Science and Engineering (CHE), Chemistry.
    Ahmadi, Sareh
    Rensmo, Hakan
    Sun, Licheng
    KTH, School of Chemical Science and Engineering (CHE), Chemistry, Organic Chemistry. Dalian University of Technology (DUT), China.
    Re-Investigation of Cobalt Porphyrin for Electrochemical Water Oxidation on FTO Surface: Formation of CoOx as Active Species2017In: ACS Catalysis, ISSN 2155-5435, E-ISSN 2155-5435, Vol. 7, no 2, p. 1143-1149Article in journal (Refereed)
    Abstract [en]

    The use of cobalt porphyrin complexes as efficient and cost-effective molecular catalysts for water oxidation has been investigated previously. However, by combining a set of analytical techniques (electrochemistry, ultraviolet-visible spectroscopy (UV-vis), scanning electron microscopy (SEM), energy-dispersive X-ray spectroscopy (EDS), and synchrotron-based photoelectron spectroscopy (SOXPES and HAXPES)), we have demonstrated that three different cobalt porphyrins, deposited on FTO glasses, decompose promptly into a thin film of CoOx on the surface of the electrode during water oxidation under certain conditions (borate buffer pH 9.2). It is presumed that the film is composed of CoO, only detectable by SOXPES, as conventional techniques are ineffective. This newly formed film has a high turnover frequency (TOF), while the high transparency of the CoOx-based electrode is very promising for future application in photoelectrochemical cells.

  • 10.
    Daniel, Quentin
    et al.
    KTH Royal Inst Technol, Sch Chem Sci & Engn, Dept Chem, S-10044 Stockholm, Sweden..
    Anabre, Ram B.
    KTH Royal Inst Technol, Sch Chem Sci & Engn, Dept Chem, S-10044 Stockholm, Sweden..
    Zhang, Biaobiao
    KTH Royal Inst Technol, Sch Chem Sci & Engn, Dept Chem, S-10044 Stockholm, Sweden..
    Philippe, Bertrand
    Uppsala University, Disciplinary Domain of Science and Technology, Physics, Department of Physics and Astronomy, Molecular and Condensed Matter Physics.
    Chen, Hong
    KTH Royal Inst Technol, Sch Chem Sci & Engn, Dept Chem, S-10044 Stockholm, Sweden..
    Li, Fusheng
    KTH Royal Inst Technol, Sch Chem Sci & Engn, Dept Chem, S-10044 Stockholm, Sweden..
    Fan, Ke
    KTH Royal Inst Technol, Sch Chem Sci & Engn, Dept Chem, S-10044 Stockholm, Sweden..
    Ahmadi, Sareh
    Uppsala University, Disciplinary Domain of Science and Technology, Physics, Department of Physics and Astronomy, Molecular and Condensed Matter Physics.
    Rensmo, Håkan
    Uppsala University, Disciplinary Domain of Science and Technology, Physics, Department of Physics and Astronomy, Molecular and Condensed Matter Physics.
    Sun, Licheng
    KTH Royal Inst Technol, Sch Chem Sci & Engn, Dept Chem, S-10044 Stockholm, Sweden.;Dalian Univ Technol, State Key Lab Fine Chem, DUT KTH Joint Educ & Res Ctr Mol Devices, Dalian 116024, Peoples R China..
    Re-Investigation of Cobalt Porphyrin for Electrochemical Water Oxidation on FTO Surface: Formation of CoOx as Active Species2017In: ACS Catalysis, ISSN 2155-5435, E-ISSN 2155-5435, Vol. 7, no 2, p. 1143-1149Article in journal (Refereed)
    Abstract [en]

    The use of cobalt porphyrin complexes as efficient and cost-effective molecular catalysts for water oxidation has been investigated previously. However, by combining a set of analytical techniques (electrochemistry, ultraviolet-visible spectroscopy (UV-vis), scanning electron microscopy (SEM), energy-dispersive X-ray spectroscopy (EDS), and synchrotron-based photoelectron spectroscopy (SOXPES and HAXPES)), we have demonstrated that three different cobalt porphyrins, deposited on FTO glasses, decompose promptly into a thin film of CoOx on the surface of the electrode during water oxidation under certain conditions (borate buffer pH 9.2). It is presumed that the film is composed of CoO, only detectable by SOXPES, as conventional techniques are ineffective. This newly formed film has a high turnover frequency (TOF), while the high transparency of the CoOx-based electrode is very promising for future application in photoelectrochemical cells.

  • 11.
    Daniel, Quentin
    et al.
    KTH, School of Engineering Sciences in Chemistry, Biotechnology and Health (CBH).
    Duan, Lele
    KTH, School of Chemical Science and Engineering (CHE), Centres, Centre of Molecular Devices, CMD.
    Timmer, Brian J. J.
    KTH, School of Engineering Sciences in Chemistry, Biotechnology and Health (CBH).
    Chen, Hong
    KTH, School of Engineering Sciences in Chemistry, Biotechnology and Health (CBH).
    Luo, Xiaodan
    Peking Univ, Coll Chem & Mol Engn, Beijing 100871, Peoples R China..
    Ambre, Ram
    KTH, School of Engineering Sciences in Chemistry, Biotechnology and Health (CBH).
    Wang, Ying
    KTH, School of Engineering Sciences in Chemistry, Biotechnology and Health (CBH).
    Zhang, Biaobiao
    KTH, School of Engineering Sciences in Chemistry, Biotechnology and Health (CBH).
    Zhang, Peili
    KTH, School of Engineering Sciences in Chemistry, Biotechnology and Health (CBH), Chemistry.
    Wang, Lei
    KTH, School of Engineering Sciences in Chemistry, Biotechnology and Health (CBH).
    Li, Fusheng
    KTH, School of Chemical Science and Engineering (CHE), Centres, Centre of Molecular Devices, CMD.
    Sun, Junliang
    Peking Univ, Coll Chem & Mol Engn, Beijing 100871, Peoples R China..
    Ahlquist, Mårten S. G.
    KTH, School of Engineering Sciences in Chemistry, Biotechnology and Health (CBH), Theoretical Chemistry and Biology.
    Sun, Licheng
    KTH, School of Chemical Science and Engineering (CHE), Centres, Centre of Molecular Devices, CMD. KTH, School of Engineering Sciences in Chemistry, Biotechnology and Health (CBH), Chemistry.
    Water Oxidation Initiated by In Situ Dimerization of the Molecular Ru(pdc) Catalyst2018In: ACS Catalysis, ISSN 2155-5435, E-ISSN 2155-5435, Vol. 8, no 5, p. 4375-4382Article in journal (Refereed)
    Abstract [en]

    The mononuclear ruthenium complex [Ru(pdc)L-3] (H(2)pdc = 2,6-pyridinedicarboxylic acid, L = N-heterocycles such as 4-picoline) has previously shown promising catalytic efficiency toward water oxidation, both in homogeneous solutions and anchored on electrode surfaces. However, the detailed water oxidation mechanism catalyzed by this type of complex has remained unclear. In order to deepen understanding of this type of catalyst, in the present study, [Ru(pdc)(py)(3)] (py = pyridine) has been synthesized, and the detailed catalytic mechanism has been studied by electrochemistry, UV-vis, NMR, MS, and X-ray crystallography. Interestingly, it was found that once having reached the Ru-IV state, this complex promptly formed a stable ruthenium dimer [Ru-III(pdc)(py)(2)-O-Ru-IV(pdc)(py)(2)](+). Further investigations suggested that the present dimer, after one pyridine ligand exchange with water to form [Ru-III(pdc)(py)(2)-O-Ru-IV(pdc)(py)(H2O)](+), was the true active species to catalyze water oxidation in homogeneous solutions.

  • 12. Ding, Xin
    et al.
    Gao, Yan
    Zhang, Linlin
    Yu, Ze
    Liu, Jianhui
    Sun, Licheng
    KTH, School of Chemical Science and Engineering (CHE), Chemistry, Organic Chemistry.
    Visible Light-Driven Water Splitting in Photoelectrochemical Cells with Supramolecular Catalysts on Photoanodes2014In: ACS Catalysis, ISSN 2155-5435, E-ISSN 2155-5435, Vol. 4, no 7, p. 2347-2350Article in journal (Refereed)
    Abstract [en]

    By using a supramolecular self-assembly method, a functional water splitting device based on a photoactive anode TiO2(1+2) has been successfully assembled with a molecular photosensitizer 1 and a molecular catalyst 2 connected by coordination of 1 and 2 with Zr4+ ions on the surface of nanostructured TiO2. On the basis of this photoanode in a three-electrode photoelectrochemical cell, a maximal incident photon to current conversion efficiency of 4.1% at similar to 450 nm and a photocurrent density of similar to 0.48 mA cm(-2) were successfully obtained.

  • 13.
    Erbing, Elis
    et al.
    Stockholm University, Faculty of Science, Department of Organic Chemistry.
    Sanz-Marco, Amparo
    Stockholm University, Faculty of Science, Department of Organic Chemistry.
    Vazquez-Romero, Ana
    Stockholm University, Faculty of Science, Department of Organic Chemistry.
    Malmberg, Jesper
    Johansson, Magnus J.
    Gomez-Bengoa, Enrique
    Martín-Matute, Belén
    Stockholm University, Faculty of Science, Department of Organic Chemistry.
    Base- and Additive-Free Ir-Catalyzed ortho-Iodination of Benzoic Acids: Scope and Mechanistic Investigations2018In: ACS Catalysis, ISSN 2155-5435, E-ISSN 2155-5435, Vol. 8, no 2, p. 920-925Article in journal (Refereed)
    Abstract [en]

    A protocol for the C-H activation/iodination of benzoic acids catalyzed by a simple iridium complex has been developed. The method described in this paper allows the ortho-selective iodination of a variety of benzoic acids under extraordinarily mild conditions in the absence of any additive or base in 1,1,1,3,3,3-hexafluoroisopropanol as the solvent. The iridium catalyst used tolerates air and moisture, and selectively gives ortho-iodobenzoic acids with high conversions. Mechanistic investigations revealed that an Ir(III)/Ir(V) catalytic cycle operates, and that the unique properties of HFIP enables the C-H iodination using the carboxylic moiety as a directing group.

  • 14.
    Fan, Ting
    et al.
    KTH Royal Inst Technol, Sch Biotechnol, Div Theoret Chem & Biol, S-10691 Stockholm, Sweden..
    Duan, Lele
    KTH Royal Inst Technol, Dept Chem, S-10044 Stockholm, Sweden.;Southern Univ Sci & Technol, Dept Chem, Shenzhen 518055, Peoples R China..
    Huang, Ping
    Uppsala University, Disciplinary Domain of Science and Technology, Chemistry, Department of Chemistry - Ångström, Molecular Biomimetics.
    Chen, Hong
    KTH Royal Inst Technol, Dept Chem, S-10044 Stockholm, Sweden..
    Daniel, Quentin
    KTH Royal Inst Technol, Dept Chem, S-10044 Stockholm, Sweden..
    Ahlquist, Marten S. G.
    KTH Royal Inst Technol, Sch Biotechnol, Div Theoret Chem & Biol, S-10691 Stockholm, Sweden..
    Sun, Licheng
    KTH Royal Inst Technol, Dept Chem, S-10044 Stockholm, Sweden.;Dalian Univ Technol, DUT KTH Joint Educ & Res Ctr Mol Devices, State Key Lab Fine Chem, Dalian 116012, Peoples R China..
    The Ru-tpc Water Oxidation Catalyst and Beyond: Water Nucleophilic Attack Pathway versus Radical Coupling Pathway.2017In: ACS Catalysis, ISSN 2155-5435, E-ISSN 2155-5435, Vol. 7, no 4, p. 2956-2966Article in journal (Refereed)
    Abstract [en]

    Many Ru water oxidation catalysts have been documented in the literature. However, only a few can catalyze the O-O bond formation via the radical coupling pathway, while most go through the water nucleophilic attack pathway. Understanding the electronic effect on the reaction pathway is of importance in design of active water oxidation catalysts. The Ru-bda (bda = 2,2'-bipyridine-6,6'-dicarboxylate) catalyst is one example that catalyzes the 0-0 bond formation via the radical coupling pathway. Herein, we manipulate the equatorial backbone ligand, change the doubly charged bda(2-) ligand to a singly charged tpc- (2,2':6',2 ''-terpyridine-6-carboxylate) ligand, and study the structure activity relationship. Surprisingly, kinetics measurements revealed that the resulting Ru-tpc catalyst catalyzes water oxidation via the water nucleophilic attack pathway, which is different from the Ru-bda catalyst. The O-O bond formation Gibbs free energy of activation (AGO) at T = 298.15 K was 20.2 +/- 1.7 kcal mol(-1). The electronic structures of a series of Ru-v=O species were studied by density function theory calculations, revealing that the spin density of O-Ru=O of Ru-v=O is largely dependent on the surrounding ligands. Seven coordination configuration significantly enhances the radical character of Ru-v=O.

  • 15.
    Fan, Ting
    et al.
    KTH, School of Biotechnology (BIO), Theoretical Chemistry and Biology.
    Duan, Lele
    KTH, School of Chemical Science and Engineering (CHE), Chemistry.
    Huang, Ping
    Chen, Hong
    KTH, School of Chemical Science and Engineering (CHE), Chemistry.
    Daniel, Quentin
    KTH, School of Chemical Science and Engineering (CHE), Chemistry.
    Ahlquist, Mårten S. G.
    KTH, School of Biotechnology (BIO), Theoretical Chemistry and Biology.
    Sun, Licheng
    KTH, School of Chemical Science and Engineering (CHE), Chemistry.
    The Ru-tpc Water Oxidation Catalyst and Beyond: Water Nucleophilic Attack Pathway versus Radical Coupling Pathway.2017In: ACS Catalysis, ISSN 2155-5435, E-ISSN 2155-5435, Vol. 7, no 4, p. 2956-2966Article in journal (Refereed)
    Abstract [en]

    Many Ru water oxidation catalysts have been documented in the literature. However, only a few can catalyze the O-O bond formation via the radical coupling pathway, while most go through the water nucleophilic attack pathway. Understanding the electronic effect on the reaction pathway is of importance in design of active water oxidation catalysts. The Ru-bda (bda = 2,2'-bipyridine-6,6'-dicarboxylate) catalyst is one example that catalyzes the 0-0 bond formation via the radical coupling pathway. Herein, we manipulate the equatorial backbone ligand, change the doubly charged bda(2-) ligand to a singly charged tpc- (2,2':6',2 ''-terpyridine-6-carboxylate) ligand, and study the structure activity relationship. Surprisingly, kinetics measurements revealed that the resulting Ru-tpc catalyst catalyzes water oxidation via the water nucleophilic attack pathway, which is different from the Ru-bda catalyst. The O-O bond formation Gibbs free energy of activation (AGO) at T = 298.15 K was 20.2 +/- 1.7 kcal mol(-1). The electronic structures of a series of Ru-v=O species were studied by density function theory calculations, revealing that the spin density of O-Ru=O of Ru-v=O is largely dependent on the surrounding ligands. Seven coordination configuration significantly enhances the radical character of Ru-v=O.

  • 16.
    Fan, Ting
    et al.
    KTH, School of Biotechnology (BIO), Theoretical Chemistry and Biology.
    Zhan, Shaoqi
    KTH, School of Biotechnology (BIO), Theoretical Chemistry and Biology.
    Ahlquist, Mårten S. G.
    KTH, School of Biotechnology (BIO), Theoretical Chemistry and Biology.
    Why Is There a Barrier in the Coupling of Two Radicals in the Water Oxidation Reaction?2016In: ACS Catalysis, ISSN 2155-5435, E-ISSN 2155-5435, Vol. 6, no 12, p. 8308-8312Article in journal (Refereed)
    Abstract [en]

    Two radicals can form a bond without an energetic barrier. However, the radical coupling mechanism in ruthenium catalyzed water oxidation has been found to be associated with substantial activation energies. Here we have investigated the coupling reaction of [Ru=O(bda)L-2](+) catalysts with different axial L ligands. The interaction between the two oxo radical moieties at the Ru(V) state was found to have a favorable interaction in the transition state in comparison to the prereactive complex. To further understand the existence of the activation energy, the activation energy has been decomposed into distortion energy and interaction energy. No correlation between the experimental rates and the calculated coupling barriers of different axial L was found, showing that more aspects such as solvation, supramolecular properties, and solvent dynamics likely play important roles in the equilibrium between the free Ru-v=0 monomer and the [Ru-v=O center dot center dot center dot O=Ru-v] dimer. On the basis of our findings, we give general guidelines for the design of catalysts that operate by the radical coupling mechanism.

  • 17. Genoni, Andrea
    et al.
    Chirdon, Danielle N.
    Boniolo, Manuel
    Umeå University, Faculty of Science and Technology, Department of Chemistry. Univ Padua, Padua, Italy ; UoS Padova, Padua, Italy.
    Sartorel, Andrea
    Bernhard, Stefan
    Bonchio, Marcella
    Tuning Iridium Photocatalysts and Light Irradiation for Enhanced CO2 Reduction2017In: ACS Catalysis, ISSN 2155-5435, E-ISSN 2155-5435, Vol. 7, no 1, p. 154-160Article in journal (Refereed)
    Abstract [en]

    Efficient photocatalytic conversion of carbon dioxide into valuable reduction products is a priority goal for artificial photosynthesis. Iridium(III) photocatalysts with a combined 2-phenylpyridine (ppy) and 2,2':6',2 ''-terpyridine (tpy) ligand set have been shown to selectively reduce CO, to CO. Here, terpyridine modifications have been investigated that yield a turnover number (TON) of up to 265, a quantum yield of 0.10, and a photocatalyst lifespan of over 10 days. The key to success is the combined effect of adding aromatic substituents to the tpy ligand 4'-position and optimizing lighting conditions. Insights into the photocatalyst fate are provided by kinetics analysis and spectroelectrochemistry, which point out the critical role of the reductively quenched catalyst and its evolution to a spent "green" state via a dark deactivation pathway. The stereoelectronic effect of adding a 9-anthryl substituent together with the use of low-energy blue light proves instrumental in the management of excited and reduced species, dictating the overall performance of the molecular photocatalyst.

  • 18.
    Gudmundsson, Arnar
    et al.
    Stockholm University, Faculty of Science, Department of Organic Chemistry.
    Gustafson, Karl P. J.
    Stockholm University, Faculty of Science, Department of Organic Chemistry.
    Yang, Bin
    Stockholm University, Faculty of Science, Department of Organic Chemistry.
    Himo, Fahmi
    Stockholm University, Faculty of Science, Department of Organic Chemistry.
    Bäckvall, Jan-E.
    Stockholm University, Faculty of Science, Department of Organic Chemistry.
    Efficient Formation of 2,3-Dihydrofurans via Iron-Catalyzed Cycloisomerization of alpha-Allenols2018In: ACS Catalysis, ISSN 2155-5435, E-ISSN 2155-5435, Vol. 8, no 1, p. 12-16Article in journal (Refereed)
    Abstract [en]

    Herein, we report a highly efficient iron-catalyzed intramolecular nucleophilic cyclization of alpha-allenols to furnish substituted 2,3-dihydrofurans under mild reaction conditions. A highly diastereoselective variant of the reaction was developed as well, giving diastereomeric ratios of up to 98:2. The combination of the iron-catalyzed cycloisomerization with enzymatic resolution afforded the 2,3-dihydrofuran in high ee. A detailed DFT study provides insight into the reaction mechanism and gives a rationalization for the high chemo-and diastereoselectivity.

  • 19.
    Guha, Anku
    et al.
    Tata Inst Fundamental Res Hyderabad, Sy 36-P, Hyderabad 500107, India.
    Vineesh, Thazhe Veettil
    Tata Inst Fundamental Res Hyderabad, Sy 36-P, Hyderabad 500107, India.
    Sekar, Archana
    Tata Inst Fundamental Res Hyderabad, Sy 36-P, Hyderabad 500107, India.
    Narayanaru, Sreekanth
    Tata Inst Fundamental Res Hyderabad, Sy 36-P, Hyderabad 500107, India.
    Sahoo, Mihir
    Indian Inst Technol, Sch Basic Sci, Bhubaneswar 751013, Odisha, India.
    Nayak, Saroj
    Indian Inst Technol, Sch Basic Sci, Bhubaneswar 751013, Odisha, India.
    Chakraborty, Sudip
    Uppsala University, Disciplinary Domain of Science and Technology, Physics, Department of Physics and Astronomy, Materials Theory.
    Narayanan, Tharangattu N.
    Tata Inst Fundamental Res Hyderabad, Sy 36-P, Hyderabad 500107, India.
    Mechanistic Insight into Enhanced Hydrogen Evolution Reaction Activity of Ultrathin Hexagonal Boron Nitride-Modified Pt Electrodes2018In: ACS Catalysis, ISSN 2155-5435, E-ISSN 2155-5435, Vol. 8, no 7, p. 6636-6644Article in journal (Refereed)
    Abstract [en]

    Enhancing the intrinsic activity of a benchmarked electrocatalyst such as platinum (Pt) is highly intriguing from fundamental as well as applied perspectives. In this work, hydrogen evolution reaction (HER) activity of Pt electrodes, benchmarked HER catalysts, modified with ultrathin sheets of hexagonal boron nitride (h-BN) is studied in acidic medium (Pt/h-BN), and augmented HER performance, in terms of the overpotential at a 10 mA cm(-2) current density (10 mV lower than that of Pt nanoparticles) and a lower Tafel slope (29 +/- 1 mV/decade), of the Pt/h-BN system is demonstrated. The effects of h-BN surface modification of bulk Pt as well as Pt nanoparticles are studied, and the origin of such an enhanced HER activity is probed using density functional theory-based calculations. The HER charge transfer resistance of h-BN-modified Pt is found to be drastically reduced, and this enhances the charge transfer kinetics of the Pt/h-BN system because of the synergistic interaction between h-BN and Pt. An enormous reduction in the hydrogen adsorption energy on h-BN monolayers is also found when they are placed over the Pt electrode [-2.51 eV (h-BN) to -0.25 eV (h-BN over Pt)]. Corrosion preventive atomic layers such as h-BN-protected Pt electrodes that perform better than Pt electrodes do open possibilities of benchmarked catalysts by simple modification of a surface via atomic layers.

  • 20. Gustafson, Johan
    et al.
    Balmes, Olivier
    Zhang, Chu
    Shipilin, Mikhail
    Stockholm University, Faculty of Science, Department of Physics.
    Schaefer, Andreas
    Hagman, Benjamin
    Merte, Lindsay R.
    Martin, Natalia M.
    Carlsson, Per-Anders
    Jankowski, Maciej
    Crumlin, Ethan J.
    Lundgren, Edvin
    The Role of Oxides in Catalytic CO Oxidation over Rhodium and Palladium2018In: ACS Catalysis, ISSN 2155-5435, E-ISSN 2155-5435, Vol. 8, no 5, p. 4438-4445Article in journal (Refereed)
    Abstract [en]

    Catalytic CO oxidation is a seemingly simple reaction between CO and O-2 molecules, one of the reactions in automotive catalytic converters, and the fruit-fly reaction in model catalysis. Surprisingly, the phase responsible for the catalytic activity is still under debate, despite decades of investigations. We have performed a simple but yet conclusive study of single crystal Rh and Pd model catalysts, resolving this controversy. For Rh, the oxygen-covered metallic surface is more active than the oxide, while for Pd, thin oxide films are at least as active as the metallic surface, but a thicker oxide is less active. Apart from resolving a long-standing debate, our results pinpoint important design principles for oxidation catalysts as to prevent catalytic extinction at high oxygen exposures.

  • 21.
    Guđmundsson, Arnar
    et al.
    Stockholm University, Faculty of Science, Department of Organic Chemistry.
    Gustafson, Karl P. J.
    Stockholm University, Faculty of Science, Department of Organic Chemistry.
    Mai, Binh Khanh
    Stockholm University, Faculty of Science, Department of Organic Chemistry.
    Hobiger, Viola
    Stockholm University, Faculty of Science, Department of Organic Chemistry.
    Himo, Fahmi
    Stockholm University, Faculty of Science, Department of Organic Chemistry.
    Bäckvall, Jan-E.
    Stockholm University, Faculty of Science, Department of Organic Chemistry.
    Diastereoselective Synthesis of N-Protected 2,3-Dihydropyrroles via Iron-Catalyzed Cycloisomerization of alpha-Allenic Sulfonamides2019In: ACS Catalysis, ISSN 2155-5435, E-ISSN 2155-5435, Vol. 9, no 3, p. 1733-1737Article in journal (Refereed)
    Abstract [en]

    Herein, we report the synthesis of 2,3-dihydropyrroles via an iron-catalyzed intramolecular nucleophilic cyclization of alpha-allenic sulfonamides. A highly diastereoselective variant of the reaction was also developed with the use of 1,2-disubstituted allenamides, which afforded 2,3-dihydropyrroles with diastereomeric ratios of >98:2. Insight into the mechanism was gained through a detailed DFT study, which elucidates the reaction mechanism and rationalizes the high chemoselectivity and diastereoselectivity.

  • 22.
    Görbe, Tamás
    et al.
    Stockholm University, Faculty of Science, Department of Organic Chemistry.
    Gustafson, Karl P. J.
    Stockholm University, Faculty of Science, Department of Organic Chemistry.
    Verho, Oscar
    Stockholm University, Faculty of Science, Department of Organic Chemistry.
    Kervefors, Gabriella
    Stockholm University, Faculty of Science, Department of Organic Chemistry.
    Zheng, Haoquan
    Stockholm University, Faculty of Science, Department of Materials and Environmental Chemistry (MMK).
    Zou, Xiaodong
    Stockholm University, Faculty of Science, Department of Materials and Environmental Chemistry (MMK).
    Johnston, Eric V.
    Stockholm University, Faculty of Science, Department of Organic Chemistry.
    Bäckvall, Jan-E.
    Stockholm University, Faculty of Science, Department of Organic Chemistry.
    Design of a Pd(0)-CalB CLEA Biohybrid Catalyst and Its Application in a One-Pot Cascade Reaction2017In: ACS Catalysis, ISSN 2155-5435, E-ISSN 2155-5435, Vol. 7, no 3, p. 1601-1605Article in journal (Refereed)
    Abstract [en]

    Herein, a design of a biohybrid catalyst is described, consisting of Pd nanoparticles and a cross-linked network of aggregated lipase B enzyme of Candida antarctica (CalB CLEA) functioning as an active support for the Pd nanoparticles. Both entities of the hybrid catalyst showed good catalytic activity. The applicability was demonstrated in a one-pot reaction, where the Pd-catalyzed cycloisomerization of 4-pentynoic acid afforded a lactone that serves as an acyl donor in a subsequent selective enzymatic kinetic resolution of a set of sec-alcohols. The catalyst proved to be robust and could be recycled five times without a significant loss of activity.

  • 23. Harvey, Jeremy N.
    et al.
    Himo, Fahmi
    Stockholm University, Faculty of Science, Department of Organic Chemistry.
    Maseras, Feliu
    Perrin, Lionel
    Scope and Challenge of Computational Methods for Studying Mechanism and Reactivity in Homogeneous Catalysis2019In: ACS Catalysis, ISSN 2155-5435, E-ISSN 2155-5435, Vol. 9, no 8, p. 6803-6813Article in journal (Refereed)
    Abstract [en]

    Computational methods based on quantum mechanical modeling are increasingly used to provide insight into mechanistic aspects of homogeneous catalysis. While the potential and value of such methods are obvious, it is also clear that it remains challenging to obtain reliable and predictive mechanistic insights from modeling. In this Perspective, we assess the various factors influencing the quality of computational studies. While the type of electronic structure theory methodology used is of course of great importance, we argue that many other aspects can play a large role also. The other factors emphasized here include the treatment of entropic effects, solvation, the choice of the structural model, conformational complexity, the translation of computed relative Gibbs energies into a kinetic model, and the high demands required for the prediction of selectivity.

  • 24.
    Hou, Jungang
    et al.
    DUT, Inst Energy Sci & Technol, KTH Joint Educ & Res Ctr Mol Devices, State Key Lab Fine Chem, Dalian 116024, Peoples R China..
    Zhang, Bo
    DUT, Inst Energy Sci & Technol, KTH Joint Educ & Res Ctr Mol Devices, State Key Lab Fine Chem, Dalian 116024, Peoples R China..
    Li, Zhuwei
    DUT, Inst Energy Sci & Technol, KTH Joint Educ & Res Ctr Mol Devices, State Key Lab Fine Chem, Dalian 116024, Peoples R China..
    Cao, Shuyan
    DUT, Inst Energy Sci & Technol, KTH Joint Educ & Res Ctr Mol Devices, State Key Lab Fine Chem, Dalian 116024, Peoples R China..
    Sun, Yiqing
    DUT, Inst Energy Sci & Technol, KTH Joint Educ & Res Ctr Mol Devices, State Key Lab Fine Chem, Dalian 116024, Peoples R China..
    Wu, Yunzhen
    DUT, Inst Energy Sci & Technol, KTH Joint Educ & Res Ctr Mol Devices, State Key Lab Fine Chem, Dalian 116024, Peoples R China..
    Gao, Zhanming
    DUT, Inst Energy Sci & Technol, KTH Joint Educ & Res Ctr Mol Devices, State Key Lab Fine Chem, Dalian 116024, Peoples R China..
    Sun, Licheng
    KTH, School of Chemical Science and Engineering (CHE), Centres, Centre of Molecular Devices, CMD. KTH, School of Engineering Sciences in Chemistry, Biotechnology and Health (CBH), Chemistry.
    Vertically Aligned Oxygenated-CoS2-MoS2 Heteronanosheet Architecture from Polyoxometalate for Efficient and Stable Overall Water Splitting2018In: ACS Catalysis, ISSN 2155-5435, E-ISSN 2155-5435, Vol. 8, no 5, p. 4612-4621Article in journal (Refereed)
    Abstract [en]

    To achieve efficient conversion of renewable energy sources through water splitting, low-cost, earth-abundant, and robust electrocatalysts for the oxygen evolution reaction (OER) and hydrogen evolution reaction (HER) are required. Herein, vertically aligned oxygenated-CoS2-MoS2 (O-CoMoS) heteronanosheets grown on flexible carbon fiber cloth as bifunctional electrocatalysts have been produced by use of the Anderson-type (NH4)(4)[CoIIMo(6)O(2)4H(6)]center dot 6H(2)O polyoxometalate as bimetal precursor. In comparison to different O-FeMoS, O-NiMoS, and MoS2 nanosheet arrays, the O-CoMoS heteronanosheet array exhibited low overpotentials of 97 and 272 mV to reach a current density of 10 mA cm(-2) in alkaline solution for the HER and OER, respectively. Assembled as an electrolyzer for overall water splitting, O-CoMoS heteronanosheets as both the anode and cathode deliver a current density of 10 mA cm(-2) at a quite low cell voltage of 1.6 V. This O-CoMoS architecture is highly advantageous for a disordered structure, exposure of active heterointerfaces, a "highway" of charge transport on two-dimensional conductive channels, and abundant active catalytic sites from the synergistic effect of the heterostructures, accomplishing a dramatically enhanced performance for the OER, HER, and overall water splitting. This work represents a feasible strategy to explore efficient and stable bifunctional bimetal sulfide electrocatalysts for renewable energy applications.

  • 25.
    Ilchenko, Nadia O.
    et al.
    Stockholm University, Faculty of Science, Department of Organic Chemistry.
    Cortes, Miguel Angel
    Stockholm University, Faculty of Science, Department of Organic Chemistry.
    Szabó, Kálmán J.
    Stockholm University, Faculty of Science, Department of Organic Chemistry.
    Palladium-Catalyzed lodofluorination of Alkenes Using Fluorolodoxole Reagent2016In: ACS Catalysis, ISSN 2155-5435, E-ISSN 2155-5435, Vol. 6, no 1, p. 447-450Article in journal (Refereed)
    Abstract [en]

    The application of an air- and moisture-stable fluoroiodane reagent was investigated in the palladium-catalyzed iodofluorination reaction of alkenes. Both the iodo and fluoro substituents arise from the fluoroiodane reagent. In the case of certain palladium catalysts, the alkene substrates undergo allylic rearrangement prior to the iodofluorination process. The reaction is faster for electron-rich alkenes than for electron-deficient ones.

  • 26.
    Ji, Yongfei
    et al.
    KTH, School of Biotechnology (BIO), Theoretical Chemistry and Biology.
    Luo, Yi
    KTH, School of Biotechnology (BIO), Theoretical Chemistry and Biology. University of Science and Technology of China, Anhui, China.
    Theoretical Study on the Mechanism of Photoreduction of CO2 to CH4 on the Anatase TiO2(101) Surface2016In: ACS Catalysis, ISSN 2155-5435, E-ISSN 2155-5435, Vol. 6, no 3, p. 2018-2025Article in journal (Refereed)
    Abstract [en]

    Artificial photosynthesis of CO, has recently attracted intense attention as a potential solution for the energy crisis and global warming. However, the molecular mechanism of the reaction is quite complicated and is far from understood. We performed a first-principles calculation on the thermodynamically feasible formaldehyde pathway: CO2 -> HCOOH -> H2CO -> CH3OH -> CH4. The interconversion of the Cl molecules has been systematically investigated. We find that a two-electron process has a lower barrier than a one-electron process for the photoreduction of all of the molecules under investigation except for methanol. On the basis of the full potential energy surface for photoreduction of CO, to methane, the rate-limiting step is found to be the photoreduction of formic acid to formaldehyde, which contains the elementary step that has the largest kinetic barrier. It will be more efficient if CO instead of formic acid is the precursor of formaldehyde. Then the rate-limiting step becomes the photoreduction of CO, to CO. However, the barriers for the photoreduction of the organic molecules are all higher than the barriers for their photodecomposition reaction, which suggests that all of the Cl organic molecules are more easily oxidized than reduced. Thus, charge separation is crucial for improving the efficiency and selectivity of the reaction. The intertwining of photoreduction and photooxidation reactions might be one of the major reasons for the complexity and low efficiency of the reaction. On the basis of the calculations, a new mechanism for the reaction is proposed.

  • 27. Kagalwala, Husain N.
    et al.
    Tong, Lianpeng
    Zong, Ruifa
    Kohler, Lars
    Ahlquist, Mårten S. G.
    KTH, School of Biotechnology (BIO), Theoretical Chemistry and Biology.
    Fan, Ting
    KTH, School of Biotechnology (BIO), Theoretical Chemistry and Biology.
    Gagnon, Kevin J.
    Thummel, Randolph P.
    Evidence for Oxidative Decay of a Ru-Bound Ligand during Catalyzed Water Oxidation2017In: ACS Catalysis, ISSN 2155-5435, E-ISSN 2155-5435, Vol. 7, no 4, p. 2607-2615Article in journal (Refereed)
    Abstract [en]

    In the evaluation of systems designed for 800 catalytic water oxidation, ceric ammonium nitrate (CAN) is often used as a sacrificial electron acceptor. One of the sources of failure for such systems is oxidative decay of the catalyst in the presence of the strong oxidant CAN (E-ox = +1.71 V). Little progress has been made in understanding the circumstances behind this decay. In this study we show that a 2-(2'-hydroxphenyl) derivative (LH) of 1,10-phenanthroline (phen) in the complex [Ru(L)(tpy)](+) (tpy = 2,2';6',2 ''-terpyridine) can be oxidized by CAN to a 2-carboxy-phen while still bound to the metal. This complex is, in fact, a very active water oxidation catalyst. The incorporation of a methyl substituent on the phenol ring of LH slows down the oxidative decay and consequently slows down the catalytic oxidation. An analogous system based on bpy (2,2'-bipyridine) instead of phen shows much lower activity under the same conditions. Water molecule association to the Ru center of [Ru(L)(tpy)](+) and carboxylate donor dissociation were proposed to occur at the trivalent state. The resulting [Ru-III-OH2] was further oxidized to [Ru-IV=O] via a PCET process.

  • 28. Kartusch, Christiane
    et al.
    Krumeich, Frank
    Safonova, Olga
    Hartfelder, Urs
    Makosch, Martin
    Sa, Jacinto
    van Bokhoven, Jeroen A.
    Redispersion of Gold Multiple-Twinned Particles during Liquid-Phase Hydrogenation2012In: ACS Catalysis, ISSN 2155-5435, E-ISSN 2155-5435, Vol. 2, no 7, p. 1394-1403Article in journal (Refereed)
  • 29. Kazemi, Masoud
    et al.
    Himo, Fahmi
    Stockholm University, Faculty of Science, Department of Organic Chemistry.
    Aqvist, Johan
    Peptide Release on the Ribosome Involves Substrate-Assisted Base Catalysis2016In: ACS Catalysis, ISSN 2155-5435, E-ISSN 2155-5435, Vol. 6, no 12, p. 8432-8439Article in journal (Refereed)
    Abstract [en]

    Termination of protein synthesis on the ribosome involves hydrolysis of the ester bond between the P-site tRNA and the nascent peptide chain. This reaction occurs in the peptidyl transferase center and is triggered by the class I release factors RF1 and RF2 in prokaryotes. Peptidyl-tRNA hydrolysis is pH-dependent, and experimental results suggest that an ionizable group with pK(a) > 9 is involved in the reaction. The nature of this group is, however, unknown. To resolve this problem, we conducted density functional theory calculations using a large cluster model of the peptidyl transferase center. Our calculations reveal that peptidyl-tRNA hydrolysis occurs via a base-catalyzed mechanism with a predicted activation energy of 15.8 kcal mol(-1), which is in good agreement with experimental data. In this mechanism, the P-site A76 2'-OH group is deprotonated and acts as the general base by activating the nucleophilic water molecule. The energy cost of deprotonating the 2'-hydroxyl group at pH 7.5 is estimated to be about 8 kcal mo1(-1), on the basis of its experimental plc in aqueous solution, and this step is predicted to be the source of the observed pH dependence. The proposed mechanism is consistent not only with experimentally derived activation energies but also with the observed kinetic solvent isotope effect.

  • 30.
    Kazemi, Masoud
    et al.
    Uppsala University, Disciplinary Domain of Science and Technology, Biology, Department of Cell and Molecular Biology, Computational Biology and Bioinformatics.
    Himo, Fahmi
    Stockholm Univ, Arrhenius Lab, Dept Organ Chem, SE-10691 Stockholm, Sweden..
    Åqvist, Johan
    Uppsala University, Disciplinary Domain of Science and Technology, Biology, Department of Cell and Molecular Biology, Computational Biology and Bioinformatics.
    Peptide Release on the Ribosome Involves Substrate-Assisted Base Catalysis2016In: ACS Catalysis, ISSN 2155-5435, E-ISSN 2155-5435, Vol. 6, no 12, p. 8432-8439Article in journal (Refereed)
    Abstract [en]

    Termination of protein synthesis on the ribosome involves hydrolysis of the ester bond between the P-site tRNA and the nascent peptide chain. This reaction occurs in the peptidyl transferase center and is triggered by the class I release factors RF1 and RF2 in prokaryotes. Peptidyl-tRNA hydrolysis is pH-dependent, and experimental results suggest that an ionizable group with pK(a) > 9 is involved in the reaction. The nature of this group is, however, unknown. To resolve this problem, we conducted density functional theory calculations using a large cluster model of the peptidyl transferase center. Our calculations reveal that peptidyl-tRNA hydrolysis occurs via a base-catalyzed mechanism with a predicted activation energy of 15.8 kcal mol(-1), which is in good agreement with experimental data. In this mechanism, the P-site A76 2'-OH group is deprotonated and acts as the general base by activating the nucleophilic water molecule. The energy cost of deprotonating the 2'-hydroxyl group at pH 7.5 is estimated to be about 8 kcal mo1(-1), on the basis of its experimental plc in aqueous solution, and this step is predicted to be the source of the observed pH dependence. The proposed mechanism is consistent not only with experimentally derived activation energies but also with the observed kinetic solvent isotope effect.

  • 31.
    Kazemi, Masoud
    et al.
    Stockholm University, Faculty of Science, Department of Organic Chemistry.
    Sheng, Xiang
    Stockholm University, Faculty of Science, Department of Organic Chemistry.
    Kroutil, Wolfgang
    Himo, Fahmi
    Stockholm University, Faculty of Science, Department of Organic Chemistry.
    Computational Study of Mycobacterium smegmatis Acyl Transferase Reaction Mechanism and Specificity2018In: ACS Catalysis, ISSN 2155-5435, E-ISSN 2155-5435, Vol. 8, no 11, p. 10698-10706Article in journal (Refereed)
    Abstract [en]

    The acyl transferase from Mycobacterium smegmatis (MsAcT) catalyzes the acyl transfer between a range of primary and secondary alcohols, whereby its outstanding ability is to perform this reaction in aqueous solution. Therefore, MsAcT opens different options for acylation reactions enabling alternatives for many conventionally hydrolytic enzymes used in biocatalysis. Nevertheless, hydrolysis is still a major side reaction of this enzyme. To provide a detailed understanding of the competition between hydrolysis and transesterification reactions, a combination of density functional theory and free energy perturbation methods have been employed. The relative binding free energies and the energy profiles of the chemical steps involved in the reaction were calculated for a number of substrates. The calculations show that the enzyme active site exhibits a higher affinity for substrates with an aromatic ring. The rate-determining step corresponds to the collapse of a negatively charged tetrahedral intermediate in the substrate acylation half-reaction. The intrinsic barriers of the transesterification and hydrolysis half-reactions are calculated to be of similar heights, suggesting that the determining factor in the MsAcT specificity is the higher binding affinity of the active site for the alcohol substrates relative to water. Finally, the influence of the acyl donor on the MsAcT-catalyzed reaction is also investigated by considering different esters in the calculations.

  • 32.
    Kerdphon, Sutthichat
    et al.
    Stockholm University, Faculty of Science, Department of Organic Chemistry.
    Ponra, Sudipta
    Stockholm University, Faculty of Science, Department of Organic Chemistry.
    Yang, Jianping
    Stockholm University, Faculty of Science, Department of Organic Chemistry.
    Wu, Haibo
    Stockholm University, Faculty of Science, Department of Organic Chemistry.
    Eriksson, Lars
    Stockholm University, Faculty of Science, Department of Materials and Environmental Chemistry (MMK).
    Andersson, Pher G.
    Stockholm University, Faculty of Science, Department of Organic Chemistry. University of KwaZulu-Natal, South Africa.
    Diastereo- and Enantioselective Synthesis of Structurally Diverse Succinate, Butyrolactone, and Trifluoromethyl Derivatives by Iridium-Catalyzed Hydrogenation of Tetrasubstituted Olefins2019In: ACS Catalysis, ISSN 2155-5435, E-ISSN 2155-5435, Vol. 9, no 7, p. 6169-6176Article in journal (Refereed)
    Abstract [en]

    A highly efficient iridium N,P-ligand-catalyzed asymmetric hydrogenation of functionalized tetrasubstituted olefins lacking a directing group has been developed. Various structural diverse chiral succinate derivatives were obtained in high yields and excellent enantio- and diastereoselectivities (up to 99% ee) using 0.5-1.0 mol % catalyst loadings. This stereoselective reaction is applicable for the synthesis of chiral acyclic molecules (up to >99% ee) having two contiguous stereogenic centers and is compatible with various aromatic, aliphatic, and heterocyclic systems, a variety of functional groups of different electronic nature. Furthermore, this asymmetric protocol allows a short enantioselective route to the butyrolactone building block, an intermediate in the synthesis of anticancer agent BMS-871 and pharmaceuticals (2S)-(-)-Verapamil and (2S)-(-)-Gallopamil.

  • 33.
    Kessler, Simon N.
    et al.
    Stockholm University, Faculty of Science, Department of Organic Chemistry.
    Hundemer, Fabian
    Stockholm University, Faculty of Science, Department of Organic Chemistry. Stockholm Univ, Arrhenius Lab, Dept Organ Chem, SE-10691 Stockholm, Sweden.
    Bäckvall, Jan-E.
    Stockholm University, Faculty of Science, Department of Organic Chemistry.
    A Synthesis of Substituted alpha-Allenols via Iron-Catalyzed Cross-Coupling of Propargyl Carboxylates with Grignard Reagents2016In: ACS Catalysis, ISSN 2155-5435, E-ISSN 2155-5435, Vol. 6, no 11, p. 7448-7451Article in journal (Refereed)
    Abstract [en]

    alpha-Allenols are attractive and versatile compounds whose preparation can be a nontrivial task. In this Letter, we provide a method for the prompt synthesis of substituted alpha-allenols via a catalytic cross-coupling reaction which makes use of a nontoxic and cost-effective iron catalyst. The catalyst loading is typically as low as 1-5 mol %. The mild reaction conditions (-20 degrees C) and the short reaction time (15 min) allow for the presence of a variety of functional groups. Moreover, the reaction was shown to be scalable up to gram scale and the propargyl substrates are readily accessible by a one-pot synthesis.

  • 34.
    Khanh Mai, Binh
    et al.
    Stockholm University, Faculty of Science, Department of Organic Chemistry.
    Szabó, Kálmán J.
    Stockholm University, Faculty of Science, Department of Organic Chemistry.
    Himo, Fahmi
    Stockholm University, Faculty of Science, Department of Organic Chemistry.
    Mechanisms of Rh-Catalyzed Oxyfluorination and Oxytrifluoromethylation of Diazocarbonyl Compounds with Hypervalent Fluoroiodine2018In: ACS Catalysis, ISSN 2155-5435, E-ISSN 2155-5435, Vol. 8, no 5, p. 4483-4492Article in journal (Refereed)
    Abstract [en]

    The reaction mechanisms of rhodium-catalyzed geminal oxyfluorination and oxytrifluoromethylation of diazo-carbonyl compounds with fluoro-benziodoxole and Togni reagents are investigated by means of density functional theory calculations. It is shown that the two reactions follow very similar mechanisms, involving N-2 dissociation to form a Rh-carbene intermediate, alcohol insertion and proton transfer resulting in a stable Rh-enol intermediate, and concerted proton transfer/electrophilic addition of the hypervalent iodine reagent to the enol. Isomerization of the hypervalent iodine takes then place before a ligand coupling affords the final product. The role of the dirhodium catalyst in facilitating the various steps of the reaction is discussed. The presented mechanisms are consistent with available experimental information, and the obtained insights allow for extension to other reactions involving hypervalent iodine reagents.

  • 35.
    Kottwitz, Matthew
    et al.
    Univ Illinois, Dept Chem, 1209 W Calif St, Urbana, IL 61801 USA..
    Li, Yuanyuan
    SUNY Stony Brook, Dept Mat Sci & Chem Engn, Stony Brook, NY 11794 USA..
    Palomino, Robert M.
    Brookhaven Natl Lab, Div Chem, Upton, NY 11973 USA..
    Liu, Zongyuan
    Brookhaven Natl Lab, Div Chem, Upton, NY 11973 USA..
    Wang, Guangjin
    Hubei Engn Univ, Coll Chem & Mat Sci, Xiaogan 432000, Peoples R China.;Foshan Univ, Sch Mat Sci & Energy Engn, Foshan 528000, Peoples R China..
    Wu, Qin
    Brookhaven Natl Lab, Ctr Funct Nanomat, Upton, NY 11973 USA..
    Huang, Jiahao
    SUNY Stony Brook, Dept Mat Sci & Chem Engn, Stony Brook, NY 11794 USA..
    Timoshenko, Janis
    SUNY Stony Brook, Dept Mat Sci & Chem Engn, Stony Brook, NY 11794 USA..
    Senanayake, Sanjaya D.
    Brookhaven Natl Lab, Div Chem, Upton, NY 11973 USA..
    Balasubramanian, Mahalingam
    Argonne Natl Lab, Adv Photon Source, Lemont, IL 60439 USA..
    Lu, Deyu
    Brookhaven Natl Lab, Ctr Funct Nanomat, Upton, NY 11973 USA..
    Nuzzo, Ralph G.
    KTH, School of Engineering Sciences in Chemistry, Biotechnology and Health (CBH), Chemistry, Surface and Corrosion Science. Univ Illinois, Dept Chem, 1209 W Calif St, Urbana, IL 61801 USA..
    Frenkel, Anatoly I.
    SUNY Stony Brook, Dept Mat Sci & Chem Engn, Stony Brook, NY 11794 USA.;Brookhaven Natl Lab, Div Chem, Upton, NY 11973 USA..
    Local Structure and Electronic State of Atomically Dispersed Pt Supported on Nanosized CeO22019In: ACS Catalysis, ISSN 2155-5435, E-ISSN 2155-5435, Vol. 9, no 9, p. 8738-8748Article in journal (Refereed)
    Abstract [en]

    Single atom catalysts (SACs) have shown high activity and selectivity in a growing number of chemical reactions. Many efforts aimed at unveiling the structure-property relationships underpinning these activities and developing synthesis methods for obtaining SACs with the desired structures are hindered by the paucity of experimental methods capable of probing the attributes of local structure, electronic properties, and interaction with support-features that comprise key descriptors of their activity. In this work, we describe a combination of experimental and theoretical approaches that include photon and electron spectroscopy, scattering, and imaging methods, linked by density functional theory calculations, for providing detailed and comprehensive information on the atomic structure and electronic properties of SACs. This characterization toolbox is demonstrated here using a model single atom Pt/CeO2 catalyst prepared via a sol-gel-based synthesis method. Isolated Pt atoms together with extra oxygen atoms passivate the (100) surface of nanosized ceria. A detailed picture of the local structure of Pt nearest environment emerges from this work involving the bonding of isolated Pt2+ ions at the hollow sites of perturbed (100) surface planes of the CeO2 support, as well as a substantial (and heretofore unrecognized) strain within the CeO2 lattice in the immediate vicinity of the Pt centers. The detailed information on structural attributes provided by our approach is the key for understanding and improving the properties of SACs.

  • 36.
    Kärkäs, Markus D.
    Stockholm University, Faculty of Science, Department of Organic Chemistry.
    Photochemical Generation of Nitrogen-Centered Amidyl, Hydrazonyl, and Imidyl Radicals: Methodology Developments and Catalytic Applications2017In: ACS Catalysis, ISSN 2155-5435, E-ISSN 2155-5435, Vol. 7, no 8, p. 4999-5022Article in journal (Refereed)
    Abstract [en]

    During the past decade, visible light photo catalysis has become a powerful synthetic platform for promoting challenging bond constructions under mild reaction conditions. These photocatalytic systems rely on harnessing visible light energy for synthetic purposes through the generation of reactive but controllable free radical species. Recent progress in the area of visible light photocatalysis has established it as an enabling catalytic strategy for the mild and selective generation of nitrogen-centered radicals. The application of visible light for photocatalytic activation of amides, hydrazones, and imides represents a valuable approach for facilitating the formation of nitrogen-centered radicals. Within the span of only a couple of years, significant progress has been made for expediting the generation of amidyl, hydrazonyl, and imidyl radicals from a variety of precursors. This Perspective highlights the recent advances in visible light-mediated generation of these radicals. A particular emphasis is placed on the unique ability of visible light photocatalysis in accessing elusive reaction manifolds for the construction of diversely functionalized nitrogen-containing motifs and as a platform for nontraditional bond disconnections in contemporary synthetic chemistry.

  • 37.
    Kärkäs, Markus D.
    KTH, School of Engineering Sciences in Chemistry, Biotechnology and Health (CBH), Chemistry, Organic chemistry. Department of Organic Chemistry, Arrhenius Laboratory, Stockholm University, Svante Arrhenius väg 16C, SE-106 91 Stockholm, Sweden.
    Photochemical Generation of Nitrogen-Centered Amidyl, Hydrazonyl, and Imidyl Radicals: Methodology Developments and Catalytic Applications2017In: ACS Catalysis, ISSN 2155-5435, E-ISSN 2155-5435, Vol. 7, p. 4999-5022Article, review/survey (Refereed)
    Abstract [en]

    During the past decade, visible light photocatalysis has become a powerful synthetic platform for promoting challenging bond constructions under mild reaction conditions. These photocatalytic systems rely on harnessing visible light energy for synthetic purposes through the generation of reactive but controllable free radical species. Recent progress in the area of visible light photocatalysis has established it as an enabling catalytic strategy for the mild and selective generation of nitrogen-centered radicals. The application of visible light for photocatalytic activation of amides, hydrazones, and imides represents a valuable approach for facilitating the formation of nitrogen-centered radicals. Within the span of only a couple of years, significant progress has been made for expediting the generation of amidyl, hydrazonyl, and imidyl radicals from a variety of precursors. This Perspective highlights the recent advances in visible light-mediated generation of these radicals. A particular emphasis is placed on the unique ability of visible light photocatalysis in accessing elusive reaction manifolds for the construction of diversely functionalized nitrogen-containing motifs and as a platform for nontraditional bond disconnections in contemporary synthetic chemistry.

  • 38.
    Li, Fusheng
    et al.
    KTH, School of Chemical Science and Engineering (CHE), Chemistry, Organic Chemistry.
    Fan, Ke
    KTH, School of Chemical Science and Engineering (CHE), Chemistry, Organic Chemistry.
    Wang, Lei
    KTH, School of Chemical Science and Engineering (CHE), Chemistry, Organic Chemistry.
    Daniel, Quentin
    Duan, Lele
    KTH, School of Chemical Science and Engineering (CHE), Chemistry, Organic Chemistry.
    Sun, Licheng
    KTH, School of Chemical Science and Engineering (CHE), Chemistry, Organic Chemistry. State Key Laboratory of Fine Chemicals, Research Center on Molecular Devices, Dalian University of Technology (DUT), Dalian, China .
    Immobilizing Ru(bda) Catalyst on a Photoanode via Electrochemical Polymerization for Light-Driven Water Splitting2015In: ACS Catalysis, ISSN 2155-5435, E-ISSN 2155-5435, Vol. 5, no 6, p. 3786-3790Article in journal (Refereed)
    Abstract [en]

    The molecular water oxidation catalyst 1 was electrochemically polymerized on a dye-sensitized TiO2 electrode and an Fe2O3 nanorod electrode. High photocurrent densities of ca. 1.4 mA cm(-2) for poly-1+RuP@TiO2 and ca. 0.4 mA cm(-2) for poly-1@Fe2O3 were achieved under pH-neutral conditions. A kinetic isotope effect (KIE) study on poly-1+RuP@TiO2 shows that poly-1 catalyzes water oxidation on the surface of TiO2 via a radical coupling mechanism.

  • 39. Li, Jia-Qi
    et al.
    Liu, Jianguo
    Stockholm University, Faculty of Science, Department of Organic Chemistry.
    Krajangsri, Suppachai
    Stockholm University, Faculty of Science, Department of Organic Chemistry.
    Chumnanvej, Napasawan
    Stockholm University, Faculty of Science, Department of Organic Chemistry.
    Singh, Thishana
    Stockholm University, Faculty of Science, Department of Organic Chemistry.
    Andersson, Pher G.
    Stockholm University, Faculty of Science, Department of Organic Chemistry.
    Asymmetric Hydrogenation of Allylic Alcohols Using Ir-N,P-Complexes2016In: ACS Catalysis, ISSN 2155-5435, E-ISSN 2155-5435, Vol. 6, no 12, p. 8342-8349Article in journal (Refereed)
    Abstract [en]

    In this study, a series of gamma,gamma-disubstituted and beta,gamma-disubstituted allylic alcohols were prepared and successfully hydrogenated using suitable N,P-based Ir complexes. High yields and excellent enantioselectivities were obtained for most of the substrates studied. This investigation also revealed the effect of the acidity of the N,P-Ir-complexes on the acid sensitive allylic alcohols. DFT Delta pK(a) calculations were used to explain the effect of the N,P-ligand on the acidity of the corresponding Ir-complex. The selectivity model of the reaction was used to accurately predict the absolute configuration of the hydrogenated alcohols.

  • 40.
    Li, Man-Bo
    et al.
    Stockholm University, Faculty of Science, Department of Organic Chemistry.
    Svensson Grape, Erik
    Stockholm University, Faculty of Science, Department of Materials and Environmental Chemistry (MMK).
    Bäckvall, Jan-E.
    Stockholm University, Faculty of Science, Department of Organic Chemistry.
    Palladium-Catalyzed Stereospecific Oxidative Cascade Reaction of Allenes for the Construction of Pyrrole Rings: Control of Reactivity and Selectivity2019In: ACS Catalysis, ISSN 2155-5435, E-ISSN 2155-5435, Vol. 9, no 6, p. 5184-5190Article in journal (Refereed)
    Abstract [en]

    A palladium-catalyzed oxidative cascade reaction of alpha-tosylamide allenes has been developed. The reactivity of the allenes is controlled by the tosylamide group. In the presence of terminal alkynes the reaction proceeds via a pathway leading to a one-pot construction of pyrrole rings. Moreover, a solvent-controlled chemoselectivity of the cascade reaction was realized, leading to a stereospecific and divergent synthesis of (Z)-tetrasubstituted olefins, 2,5-dihydropyrroles, and pyrroles. Enantioenriched (Z)-tetrasubstituted olefins and 2,5-dihydropyrroles are readily synthesized by chirality transfer using this approach.

  • 41. Liao, Rong-Zhen
    et al.
    Chen, Shi-Lu
    Siegbahn, Per E. M.
    Stockholm University, Faculty of Science, Department of Organic Chemistry.
    Which Oxidation State Initiates Dehalogenation in the B12-Dependent Enzyme NpRdhA: Co-II, COI or Co-0?2015In: ACS Catalysis, ISSN 2155-5435, E-ISSN 2155-5435, Vol. 5, no 12, p. 7350-7358Article in journal (Refereed)
    Abstract [en]

    The quantum chemical cluster approach was used to elucidate the reaction mechanism of debromination catalyzed by the B12-dependent reductive dehalogenase NpRdliA. Various pathways, involving different oxidation states of the cobalt ion and different protonation states of the model, have been analyzed in order to find the most favorable one. We find that the reductive C Br cleavage takes place exclusively at the Co' state via a heterolytic pathway in the singlet state. Importantly, the C-H bond formation and the C Br bond cleavage proceeds via a concerted transition state, as opposed to the stepwise pathway suggested before. C Br cleavage at the Coll state has a very high barrier, and the reduction of Co' to Co is associated with a very negative potential; thus, reductive dehalogenation at Coll and Co can be safely ruled out. Examination of substrate with different halogen substitutions (F, Cl, Br, I) shows that the dehalogenation reactivity follows the order C I > C Br > C-C1 > C-F, and the barrier for defluorination is so high that NpRdhA cannot catalyze that reaction.

  • 42. Liao, Rong-Zhen
    et al.
    Masaoka, Shigeyuki
    Siegbahn, Per E. M.
    Stockholm University, Faculty of Science, Department of Organic Chemistry.
    Metal Oxidation States for the O-O Bond Formation in the Water Oxidation Catalyzed by a Pentanuclear Iron Complex2018In: ACS Catalysis, ISSN 2155-5435, E-ISSN 2155-5435, Vol. 8, no 12, p. 11671-11678Article in journal (Refereed)
    Abstract [en]

    Understanding the water oxidation mechanism, especially how the O-O bond formation takes place, provides crucial implication for the design of more efficient molecular catalysts for water oxidation in artificial photosynthesis. Density functional calculations have here been used to revisit the mechanism of O-O bond formation catalyzed by a pentanuclear iron complex. By comparing energetics for O-O bond formation at different oxidation states, it is suggested that the formally Fe-5(III,III,III,IV,IV) state is the best candidate for the coupling of two oxo groups, with a barrier of 17.3 kcal/mol, rather than the previously suggested lower oxidation state of Fe-5(II,II,III,IV,IV). Importantly, the first water insertion into the Fe-5(III,III,III,III,III) complex is associated with a barrier of 18.8 kcal/mol. The calculated barrier is somewhat overestimated as discussed in the text. Other possible reaction pathways, including water attack at the Fe-5(III,III,III,IV,IV) state, coupling of oxo and hydroxide at the Fe-5(III,III,III,III,IV) state, and coupling of two oxo groups at the Fe-5(III,III,IV,IV,IV) state, were found to have much higher barriers.

  • 43. Liao, Rong-Zhen
    et al.
    Santoro, Stefano
    Gotsev, Martin
    Stockholm University, Faculty of Science, Department of Organic Chemistry.
    Marcelli, Tommaso
    Stockholm University, Faculty of Science, Department of Organic Chemistry.
    Himo, Fahmi
    Stockholm University, Faculty of Science, Department of Organic Chemistry.
    Origins of Stereoselectivity in Peptide-Catalyzed Kinetic Resolution of Alcohols2016In: ACS Catalysis, ISSN 2155-5435, E-ISSN 2155-5435, Vol. 6, no 2, p. 1165-1171Article in journal (Refereed)
    Abstract [en]

    The origin of the stereoselectivity of the tetrapeptide-catalyzed kinetic resolution of trans-2-N-acetamidocyclohexanol is investigated by means of density functional theory calculations. Transition states for the functionalization of both (R,R) and (S,S) substrates were optimized considering all possible conformers. Due to the flexibility of the peptidic catalyst, a large number of transition states had to be located, and analysis of the geometries and energies allowed for the identification of the main factors that control the stereo selectivity.

  • 44.
    Liao, Rong-Zhen
    et al.
    Stockholm University, Faculty of Science, Department of Organic Chemistry.
    Siegbahn, Per E. M.
    Stockholm University, Faculty of Science, Department of Organic Chemistry.
    Which Oxidation State Leads to O-O Bond Formation in Cp*Ir(bpy)CI-Catalyzed Water Oxidation, Ir(V), Ir(VI), or Ir(VII)?2014In: ACS Catalysis, ISSN 2155-5435, E-ISSN 2155-5435, Vol. 4, no 11, p. 3937-3949Article in journal (Refereed)
    Abstract [en]

    Density functional calculations are used to revisit the reaction mechanism of water oxidation catalyzed by the Cp*Ir(bpy)Cl (Cp* = pentamethylcyclopentadienyl, bpy = 2,2'-bipyridine) complex. One of the experimentally suggested active species [(bpy)Ir(H2O)(2)(HCOO)Cl](+) can undergo very facile intramolecular formate oxidation at higher oxidation state even though it can also promote OO bond formation. Therefore, [(bpy)Ir(H2O)(2)(CH3COO)Cl](+) is here proposed to be the most likely precatalyst as acetate was also experimentally observed after Cp* oxidation. OO bond formation takes place at the high formal oxidation states of IrVI and IrVII, rather than that of IrV, as suggested before. Three sequential proton-coupled electron transfer oxidations result in the formation of a highly oxidized intermediate, [(bpy)IrVIO(OH)(CH3COO)Cl](+). From this formal IrVI intermediate, OO bond formation takes place by a water attack on the IrVI=O moiety assisted by the acetate ligand, which abstracts a proton during the attack. The barrier was calculated to be very facile, being 14.7 kcal/mol, in good agreement with experimental kinetic results, which gave a barrier of around 18 kcal/mol. The attack leads to the formation of an IrIV-peroxide intermediate, which undergoes proton-coupled electron transfer to form an IrIIIO2 intermediate. Finally, O2 can be released, coupled with the binding of another water molecule, to regenerate the catalytic Ir-III species. Water oxidation at IrVII has a slightly higher barrier, but it may also contribute to the activity. However, water oxidation at IrV has a significantly higher barrier. Acetate oxidation by CH activation was found to have a much higher barrier, suggesting that [(bpy)Ir(H2O)(2)(CH3COO)Cl](+) is a remarkably stable catalyst. The possible catalytic species [(bpy-dc)IrIII(H2O)(3)Cl](2+) without acetate coordination has also been considered and also gave a reasonably feasible barrier for the water oxidation. OO bond formation at IrVII is slightly preferred compared with at IrVI, which is different from the case with acetate.

  • 45.
    Lind, Maria E. S.
    et al.
    Stockholm University, Faculty of Science, Department of Organic Chemistry.
    Himo, Fahmi
    Stockholm University, Faculty of Science, Department of Organic Chemistry.
    Theoretical Study of Reaction Mechanism and Stereoselectivity of Arylmalonate Decarboxylase2014In: ACS Catalysis, ISSN 2155-5435, E-ISSN 2155-5435, Vol. 4, no 11, p. 4153-4160Article in journal (Refereed)
    Abstract [en]

    The reaction mechanism of arylmalonate decarboxylase is investigated using density functional theory calculations. This enzyme catalyzes the asymmetric decarboxylation of prochiral disubstituted malonic acids to yield the corresponding enantiopure carboxylic acids. The quantum chemical cluster approach is employed, and two different models of the active site are designed: a small one to study the mechanism and characterize the stationary points and a large one to study the enantioselectivity. The reactions of both α-methyl-α-phenylmalonate and α-methyl-α-vinylmalonate are considered, and different substrate binding modes are assessed. The calculations overall give strong support to the suggested mechanism in which decarboxylation of the substrate first takes place, followed by a stereoselective protonation by a cysteine residue. The enediolate intermediate and the transition states are stabilized by a number of hydrogen bonds that make up the dioxyanion hole, resulting in feasible energy barriers. It is further demonstrated that the enantioselectivity in the case of α-methyl-α-phenylmalonate substrate is dictated already in the substrate binding, because only one binding mode is energetically accessible, whereas in the case of the smaller α-methyl-α-vinylmalonate substrate, both the binding and the following transition states contribute to the enantioselectivity.

  • 46.
    Lind, Maria E.S.
    et al.
    Stockholm University, Faculty of Science, Department of Organic Chemistry.
    Himo, Fahmi
    Stockholm University, Faculty of Science, Department of Organic Chemistry.
    Quantum Chemical Modeling of Enantioconvergency in Soluble Epoxide Hydrolase2016In: ACS Catalysis, ISSN 2155-5435, E-ISSN 2155-5435, Vol. 6, no 12, p. 8145-8155Article in journal (Refereed)
    Abstract [en]

    Soluble epoxide hydrolases (sEHs) catalyze the hydrolysis of epoxides to their corresponding vicinal diols. One property of a number of these enzymes is that they can catalyze the hydrolysis of some racemic substrates in an enantioconvergent one-enzyme fashion. Here, we have used the dispersion-corrected B3LYP-D3 density functional theory method to investigate the enantioconvergent conversion of styrene oxide (SO) by sEH from Solanum tuberosum (StEH1). A large cluster model of the active site, consisting of 279 atoms, is designed on the basis of the X-ray crystal structure of StEH1 in complex with the competitive inhibitor valpromide. Different substrate orientations of the two enantiomers of SO are examined, and the full reaction mechanisms for epoxide opening at the two carbons are calculated, including both the alkylation and hydrolysis half-reactions. The calculated overall reaction energy profiles show that the rate-determining step is associated with the dissociation of the covalent intermediate, which is the second step of the hydrolysis half-reaction. The calculations reproduce the experimentally observed regioselectivities for the two enantiomers of the substrate, in that both (S)-SO and (R)-SO are calculated to yield the same (R)-diol product. The obtained energy profiles indicate that the transition states for both the alkylation and hydrolysis half-reactions have to be taken into account in order to understand the stereochemical outcome of the reaction. The transition state structures are analyzed in detail, and several factors that contribute to the selectivity control are identified. In addition, the mechanistic scenario in which the active site His300 residue is in the protonated form is also considered and the implications on the energies and enantioselection are discussed. The current calculations demonstrate the applicability of the quantum chemical cluster methodology in reproducing and rationalizing experimental enantioselectivities, lending further support to its usefulness as a tool in asymmetric biocatalysis. The results presented here can be helpful in the rational engineering of sEHs to obtain variants with refined biocatalytic properties.

  • 47. Liu, Xue
    et al.
    Xu, Hao
    Zhang, Lin
    Han, Lu
    Jiang, Jingang
    Oleynikov, Peter
    Stockholm University, Faculty of Science, Department of Materials and Environmental Chemistry (MMK).
    Chen, Li
    Wu, Peng
    Isomorphous Incorporation of Tin Ions into Germanosilicate Framework Assisted by Local Structural Rearrangement2016In: ACS Catalysis, ISSN 2155-5435, E-ISSN 2155-5435, Vol. 6, no 12, p. 8420-8431Article in journal (Refereed)
    Abstract [en]

    The crystalline structure of UTL zeolite experienced an unusual orientated collapse and reconstruction within an extremely narrow time window during the structural stabilization process by nitric acid treatment at elevated temperature. Taking full advantage of this unique structural change, extra-large pore Sn-UTL zeolites were postsynthesized via the reaction between the SnCl4 molecules and the silanols in the hydroxyl nests, which occurred concomitantly with the removal of Ge and/or Si species from the dense layer. The original UTL topology was restored thereafter, leading to a Sn-incorporated analogue. The usage of the most seriously collapsed intermediate structure, which was captured by timing during the precisely controlled acid treatment, was vital for achieving Sn-UTL zeolites with a larger amount of isolated Sn species effectively incorporated. With tetrahedrally coordinated Sn ions in the highly stabilized UTL topology consisting of intersecting 12- and 14-membered ring (MR) pore channels, Sn-UTL showed promising catalytic performance in the Meerwein-Pondorf-Verley reaction as well as in the Baeyer-Villiger oxidation reactions of ketones using H2O2 or even bulky tert-butyl hydroperoxide (TBHP) as an oxidant.

  • 48.
    Lundberg, Helena
    et al.
    Stockholm University, Faculty of Science, Department of Organic Chemistry.
    Hans, Adolfsson
    Stockholm University, Faculty of Science, Department of Organic Chemistry.
    Hafnium-Catalyzed Direct Amide Formation at Room Temperature2015In: ACS Catalysis, ISSN 2155-5435, E-ISSN 2155-5435, Vol. 5, no 6, p. 3271-3277Article in journal (Refereed)
    Abstract [en]

    Herein, the first example of a metal-catalyzed protocol for direct amidation of non-activated carboxylic acids at ambient temperature (26 °C) is presented. The mild reaction conditions give rise to high yields of a range of amides in reaction times as short as 90 minutes, employing a commercial hafnium complex, [Hf(Cp)2Cl2], as catalyst. Amino acids are transformed into their corresponding amides without racemization, and the catalyst displays full selectivity for the amidation of carboxylic acids over esters. Electronic properties of the carboxylic acids were found to have a strong influence on the rate of the amidation reaction, and the need for a balanced amount of molecular sieves was observed to be highly important for optimal reaction outcome.

  • 49.
    Magallanes, Gabriel
    et al.
    Univ Michigan, Dept Chem, Willard Henry Dow Lab, 930 North Univ Ave, Ann Arbor, MI 48109 USA..
    Kärkäs, Markus D.
    KTH, School of Engineering Sciences in Chemistry, Biotechnology and Health (CBH), Chemistry, Organic chemistry. Univ Michigan, Dept Chem, Willard Henry Dow Lab, 930 North Univ Ave, Ann Arbor, MI 48109 USA..
    Bosque, Irene
    Univ Michigan, Dept Chem, Willard Henry Dow Lab, 930 North Univ Ave, Ann Arbor, MI 48109 USA..
    Lee, Sudarat
    Univ Michigan, Dept Chem, Willard Henry Dow Lab, 930 North Univ Ave, Ann Arbor, MI 48109 USA..
    Maldonado, Stephen
    Univ Michigan, Dept Chem, Willard Henry Dow Lab, 930 North Univ Ave, Ann Arbor, MI 48109 USA.;Univ Michigan, Program Appl Phys, Ann Arbor, MI 48109 USA..
    Stephenson, Corey R. J.
    Univ Michigan, Dept Chem, Willard Henry Dow Lab, 930 North Univ Ave, Ann Arbor, MI 48109 USA..
    Selective C-O Bond Cleavage of Lignin Systems and Polymers Enabled by Sequential Palladium-Catalyzed Aerobic Oxidation and Visible-Light Photoredox Catalysis2019In: ACS Catalysis, ISSN 2155-5435, E-ISSN 2155-5435, Vol. 9, no 3, p. 2252-2260Article in journal (Refereed)
    Abstract [en]

    Lignin, which is a highly cross-linked and irregular biopolymer, is nature's most abundant source of aromatic compounds and constitutes an attractive renewable resource for the production of aromatic commodity chemicals. Herein, we demonstrate a practical and operationally simple two-step degradation approach involving Pd-catalyzed aerobic oxidation and visible-light photoredox-catalyzed reductive fragmentation for the chemoselective cleavage of the beta-O-4 linkage-the predominant linkage in lignin for the generation of lower-molecular-weight aromatic building blocks. The developed strategy affords the beta-O-4 bond cleaved products with high chemoselectivity and in high yields, is amenable to continuous flow processing, operates at ambient temperature and pressure, and is moisture- and oxygen-tolerant.

  • 50. Makosch, Martin
    et al.
    Lin, Wan-Ing
    Bumbalek, Viclav
    Sa, Jacinto
    Medlin, J. Will
    Hungerbuehler, Konrad
    van Bokhoven, Jeroen A.
    Organic Thiol Modified Pt/TiO2 Catalysts to Control Chemoselective Hydrogenation of Substituted Nitroarenes2012In: ACS Catalysis, ISSN 2155-5435, E-ISSN 2155-5435, Vol. 2, no 10, p. 2079-2081Article in journal (Refereed)
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