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  • 1.
    Aydin, Juhanes
    et al.
    Stockholms universitet, Naturvetenskapliga fakulteten, Institutionen för organisk kemi.
    Senthil, Kumar K
    Stockholms universitet, Naturvetenskapliga fakulteten, Institutionen för organisk kemi.
    Sayah, Mahmoud J
    Stockholms universitet, Naturvetenskapliga fakulteten, Institutionen för organisk kemi.
    Wallner, Olov A
    Stockholms universitet, Naturvetenskapliga fakulteten, Institutionen för organisk kemi.
    Szabó, Kálmán J
    Synthesis and catalytic application of chiral 1,1'-Bi-2-naphthol- and biphenanthrol-based pincer complexes: selective allylation of sulfonimines with allyl stannane and allyl trifluoroborate.2007Ingår i: Journal of Organic Chemistry, Vol. 72, nr 13, s. 4689-4697Artikel i tidskrift (Refereegranskat)
    Abstract [en]

    New easily accessible 1,1'-bi-2-naphthol- (BINOL-) and biphenanthrol-based chiral pincer complex catalysts were prepared for selective (up to 85% enantiomeric excess) allylation of sulfonimines. The chiral pincer complexes were prepared by a flexible modular approach allowing an efficient tuning of the selectivity of the catalysts. By employment of the different enantiomeric forms of the catalysts, both enantiomers of the homoallylic amines could be selectively obtained. Both allyl stannanes and allyl trifluoroborates can be employed as allyl sources in the reactions. The biphenanthrol-based complexes gave higher selectivity than the substituted BINOL-based analogues, probably because of the well-shaped chiral pocket generated by employment of the biphenanthrol complexes. The enantioselective allylation of sulfonimines presented in this study has important implications for the mechanism given for the pincer complex-catalyzed allylation reactions, confirming that this process takes place without involvement of palladium(0) species.

  • 2.
    Aydin, Juhanes
    et al.
    Stockholms universitet, Naturvetenskapliga fakulteten, Institutionen för organisk kemi.
    Szabó, Kálmán
    Stockholms universitet, Naturvetenskapliga fakulteten, Institutionen för organisk kemi.
    Palladium-pincer complex catalyzed C-C coupling of allyl nitriles with tosyl imines via regioselective allylic C-H bond functionalization2008Ingår i: Organic Letters, ISSN 1523-7060, Vol. 10, nr 13, s. 2881-2884Artikel i tidskrift (Refereegranskat)
    Abstract [en]

    A mechanistically new palladium-pincer complex catalyzed allylation of sulfonimines is presented. This reaction involves C-H bond functionalization of allyl nitriles under mild conditions. The reaction proceeds with a high regioselectivity, without allyl rearrangement of the product. Modeling studies indicate that the carbon-carbon bond formation process proceeds via (η1-allyl)palladium pincer complex intermediates.

  • 3.
    Bielawski, Marcin
    et al.
    Stockholms universitet, Naturvetenskapliga fakulteten, Institutionen för organisk kemi.
    Olofsson, Berit
    Stockholms universitet, Naturvetenskapliga fakulteten, Institutionen för organisk kemi.
    Efficient one-pot synthesis of bis(4-tert-butylphenyl)iodonium triflate2009Ingår i: Organic Syntheses, ISSN 0078-6209, Vol. 86, s. 308-314Artikel i tidskrift (Refereegranskat)
  • 4. Cribiù, Riccardo
    et al.
    Borbas, K. Eszter
    Stockholms universitet, Naturvetenskapliga fakulteten, Institutionen för organisk kemi.
    Cumpstey, Ian
    Stockholms universitet, Naturvetenskapliga fakulteten, Institutionen för organisk kemi.
    On the synthesis of vinyl and phenyl C-furanosides by stereospecific debenzylative cycloetherification2009Ingår i: Tetrahedron, ISSN 0040-4020, E-ISSN 1464-5416, Vol. 65, nr 10, s. 2022-2031Artikel i tidskrift (Refereegranskat)
  • 5.
    Córdova, Armando
    et al.
    Stockholms universitet, Naturvetenskapliga fakulteten, Institutionen för organisk kemi.
    Ibrahem, Ismail
    Casas, Jesús
    Sundén, Henrik
    Engqvist, Magnus
    Stockholms universitet, Naturvetenskapliga fakulteten, Institutionen för organisk kemi.
    Reyes, Efraim
    Amino Acid-Catalyzed Neogenesis of Carbohydrates: A Plausible Ancient Transformation2005Ingår i: Chemistry - A European Journal, ISSN 0947-6539, E-ISSN 1521-3765, Vol. 11, nr 16, s. 4772-4784Artikel i tidskrift (Refereegranskat)
    Abstract [en]

    Hexose sugars play a fundamental role in vital biochemical processes and their biosynthesis is achieved through enzyme-catalyzed pathways. Herein we disclose the ability of amino acids to catalyze the asymmetric neogenesis of carbohydrates by sequential cross-aldol reactions. The amino acids mediate the asymmetric de novo synthesis of natural L- and D-hexoses and their analogues with excellent stereoselectivity in organic solvents. In some cases, the four new stereocenters are assembled with almost absolute stereocontrol. The unique feature of these results is that, when an amino acid is employed as the catalyst, a single reaction sequence can convert a protected glycol aldehyde into a hexose in one step. For example, proline and its derivatives catalyze the asymmetric neogenesis of allose with >99 % ee in one chemical manipulation. Furthermore, all amino acids tested catalyzed the asymmetric formation of natural sugars under prebiotic conditions, with alanine being the smallest catalyst. The inherent simplicity of this catalytic process suggests that a catalytic prebiotic “gluconeogenesis” may occur, in which amino acids transfer their stereochemical information to sugars. In addition, the amino acid catalyzed stereoselective sequential cross-aldol reactions were performed as a two-step procedure with different aldehydes as acceptors and nucleophiles. The employment of two different amino acids as catalysts for the iterative direct aldol reactions enabled the asymmetric synthesis of deoxysugars with >99 % ee. In addition, the direct amino acid catalyzed C2+C2+C2 methodology is a new entry for the short, highly enantioselective de novo synthesis of carbohydrate derivatives, isotope-labeled sugars, and polyketide natural products. The one-pot asymmetric de novo syntheses of deoxy and polyketide carbohydrates involved a novel dynamic kinetic asymmetric transformation (DYKAT) mediated by an amino acid.

  • 6.
    Dziedzic, Pawel
    Stockholms universitet, Naturvetenskapliga fakulteten, Institutionen för organisk kemi.
    Amino acid-catalyzed synthesis of amino acid derivatives: Application and semi-synthesis of Paclitaxel, Docetaxel and their derivatives2010Doktorsavhandling, sammanläggning (Övrigt vetenskapligt)
    Abstract [en]

    This thesis deals with different applications of organocatalysis, where amino acid derivatives and small peptides are applied as catalysts. First, the development of environmentally friendly aldol reactions, carried out in aqueous media is illustrated. The corresponding β-hydroxy ketones are formed with ee´s up to 99%. Chapter 3 describes the ability of β3-amino acids to selectively catalyze Mannich-type reactions and govern the formation of products with high anti-selectivity (up to >19:1) and ee´s up to 99%. In the following chapter, an amino acid-catalyzed one-pot three component Mannich reaction between dihydroxyacetone and PMP-protected imines, is presented. The corresponding a,a’-dihydroxy-b-aminoketones are obtained in high yields and with 82-95% ee. Next, an aza-Morita-Baylis-Hillman reaction was investigated where L-proline is the catalyst. The reaction proceeds with excellent chemo- and enantioselectivity to give the corresponding compounds in good yields and with 97-99% ee. Finally, the last part describes development of a proline-catalyzed Mannich reation between N-acyl imines and protected α-hydroxyaldehyes, providing access to different α-hydroxy-β-amino acids in good yields and high enantioselctivity (92-99% ee). The obtained amino acids were further applied in the semisynthesis of paclitaxel and docetaxel derivatives.

  • 7.
    Dziedzic, Pawel
    et al.
    Stockholms universitet, Naturvetenskapliga fakulteten, Institutionen för organisk kemi.
    Weibiao, Zou
    Hafrén, Jonas
    Córdova, Armando
    Stockholms universitet, Naturvetenskapliga fakulteten, Institutionen för organisk kemi.
    The small peptide-catalyzed direct asymmetric aldol reaction in water2006Ingår i: Organic and biomolecular chemistry, ISSN 1477-0520, E-ISSN 1477-0539, Vol. 4, s. 38-40Artikel i tidskrift (Refereegranskat)
  • 8.
    Dziedzic, Pawel
    et al.
    Stockholms universitet, Naturvetenskapliga fakulteten, Institutionen för organisk kemi.
    Zhao, Gui-ling
    Stockholms universitet, Naturvetenskapliga fakulteten, Institutionen för organisk kemi.
    Córdova, Armando
    Stockholms universitet, Naturvetenskapliga fakulteten, Institutionen för organisk kemi.
    Practical amino acid-catalyzed asymmetric synthesis pf protected α-hydroxy-amino aldehydes and acidsManuskript (preprint) (Övrigt vetenskapligt)
  • 9.
    Jonsson, Hanna
    et al.
    Stockholms universitet, Naturvetenskapliga fakulteten, Institutionen för organisk kemi.
    Säwén, Elin
    Stockholms universitet, Naturvetenskapliga fakulteten, Institutionen för organisk kemi.
    Widmalm, Göran
    Stockholms universitet, Naturvetenskapliga fakulteten, Institutionen för organisk kemi.
    Studies on the conformational flexibility of α-L-Rhap-(1→2)-α-L-Rhap-OMe using molecular simulation and 13C-site-specific labeling: a model for a commonly occurring disaccharide in bacterial polysaccharidesManuskript (preprint) (Övrigt vetenskapligt)
    Abstract [en]

    Bacterial polysaccharides are comprised of a variety of monosaccharides, L-rhamnose (6-deoxy-Lmannose) being one of them. This sugar is often part of α-(1→2)- and/or α-(1→3)-linkages and wehave therefore studied the disaccharide α-L-Rhap-(1→2)-α-L-Rhap-OMe to obtain information onconformational preferences at this glycosidic linkage. The target disaccharide was synthesized with 13C site-specific labeling at C1' and at C2', i.e., in the terminal group. 2D 1H,13C-HSQC-HECADE and 1H,13C-J-HMBC NMR experiments, 1D 13C and 1H NMR spectra together with total line-shape analysis were used to extract conformationally dependent hetero- and homonuclear spin-spincoupling constants. This resulted in the determination of 2JC2',H1' , 3JC1',C1 , 3JC1',C3 , 3JC2',C2 , 2JC1',C2 ,1JC1',C2' , and 1JC1',H1' . These data together with previously determined JC,H and 1H,1H NOEs result in fourteen conformationally dependent NMR parameters that are available for analysis of glycosidiclinkage flexibility and conformational preferences. A molecular dynamics simulation of the disaccharide with explicit water molecules as solvent showed a major conformational state at ΦH =40° and ψH = –35°, consistent with experimental NMR data.

  • 10.
    Jonsson, Hanna
    et al.
    Stockholms universitet, Naturvetenskapliga fakulteten, Institutionen för organisk kemi.
    Widmalm, Göran
    Stockholms universitet, Naturvetenskapliga fakulteten, Institutionen för organisk kemi.
    NMR analysis of conformationally dependent nJCH and nJCC in the trisaccharide α-L-Rhap-(1→2)[α-L-Rhap-(1→3)]-α-L-Rhap-OMe and a site-specifically labeled isotopologue thereofManuskript (preprint) (Övrigt vetenskapligt)
    Abstract [en]

    An array of NMR spectroscopy experiments have been carried out to obtain conformationallydependent 1H,13C- and 13C,13C-spin-spin coupling constants in the trisaccharide a-L-Rhap-(1®2)[a-LRhap-(1®3)]-a-L-Rhap-OMe. The trisaccharide was synthesized with 13C site-specific labeling at C2'and C2'', i.e., in the rhamnosyl groups in order to alleviate 1H spectral overlap. Using both the naturalabundance compound and the 13C-labeled sample 2D 1H,13C-J-HMBC and 1H,13C-HSQC-HECADENMR experiments, total line-shape analysis of 1H NMR spectra and 1D 13C NMR experiments wereemployed to extract 3C,H J , 2C,H J , 3C,C J , and1C,C J . The 13C site-specific labeling facilitates straightforward determination of nC,C J as the splitting of the 13C natural abundance resonances. This studyresulted in seven conformationally dependent coupling constants for the trisaccharide and illustrates theuse of 13C site-specific labeling as a valuable tool that extends the 1D and 2D NMR methods in currentuse to attain both hetero- and homonuclear spin-spin coupling constants.

  • 11.
    Jonsson, K. Hanna M.
    et al.
    Stockholms universitet, Naturvetenskapliga fakulteten, Institutionen för organisk kemi.
    Weintraub, Andrej
    Widmalm, Göran
    Stockholms universitet, Naturvetenskapliga fakulteten, Institutionen för organisk kemi.
    Structural determination of the O-antigenic polysaccharide from Escherichia coli O742009Ingår i: Carbohydrate Research, ISSN 0008-6215, E-ISSN 1873-426X, Vol. 344, nr 12, s. 1592-1595Artikel i tidskrift (Refereegranskat)
    Abstract [en]

    The structure of the O-antigen polysaccharide (PS) from Escherichia coli O74 has been determined. Component analysis, together with 1H and 13C NMR spectroscopy as well as 1H,15N-HSQC experiments were employed to elucidate the structure. Inter-residue correlations were determined by 1H,1H-NOESY and 1H,13C-heteronuclear multiple-bond correlation experiments. The PS is composed of tetrasaccharide repeating units with the following structure:

    Full-size image (5K)

    Cross-peaks of low intensity from an α-linked N-acetylglucosamine residue were present in the NMR spectra, and spectral analysis indicates that they originate from the penultimate residue in the polysaccharide. Consequently, the biological repeating unit has a 3-substituted N-acetyl-d-glucosamine residue at its reducing end. The 1H, 13C and 15N NMR chemical shifts of the α- and β-anomeric forms of d-Fucp3NAc are also reported. The repeating unit of the E. coli O74 O-antigen is identical to that of the capsular polysaccharide from E. coli K45.

  • 12.
    Kjellberg, Alexandra
    Stockholms universitet, Naturvetenskapliga fakulteten, Institutionen för organisk kemi.
    Studies of oligosaccharides and carbon-13 enriched bacterial polysaccharides using NMR spectroscopy and computer simulations1998Doktorsavhandling, sammanläggning (Övrigt vetenskapligt)
    Abstract [en]

    The conformation and dynamics of the trisaccharide methyl β-D-Glcp-(1--> 2)[β-D-Glcp-(1 --> 3)] α-D-Manp and its constituent disaccharides methyl β-D-Glcp-(1 --> 2) α-D-Manp and methyl β-D-Glcp-(1 --> 3) α-D-Manp have been studied using computer simulations and NMR spectroscopy. The computer simulations applied were Metropolis Monte Carlo simulations employing the HSEA force field and Langevin dynamics simulations using the PARM22 and CHEAT95 force fileds. The NMR methods used were measurement of long-range heteronuclear coupling constants across the glycosidic linkages, measurement of carbon-13 nuclear relaxation rates for the determination of dynamical parameters according the Lipari-Szabo "model free" approach and measurements of homonuclear NOE and TROE cross relaxation rates for the determination of proton-proton distances. Experimental data were then compared to the corresponding parameters extracted from the various computer simulations.

    Studies of the carbon-13 labelled O-polysaccharides from Escherichia coli O25 and O91 have also been performed. 13C-13C TOCSY experiments, with the spin-lock on the carbon-13 nuclei, were applied to sugar residues of different geometries. This circumvented the problem of hampered magnetisation transfer encountered in residues with 3JHH < 2Hz when the spin-lock is applied on the protons.The carbon-13 labelling was also used to demonstrate the biosynthesis of one of the substituents in the Escherichia coli O91 O-polysaccharide.

  • 13.
    Lavén, Gaston
    et al.
    Stockholms universitet, Naturvetenskapliga fakulteten, Institutionen för organisk kemi.
    Stawinski, Jacek
    Stockholms universitet, Naturvetenskapliga fakulteten, Institutionen för organisk kemi.
    Palladium(0)-catalyzed benzylation of H-phosphonate diesters: An efficient entry to benzylphosphonates2009Ingår i: Synlett: Accounts and Rapid Communications in Synthetic Organic Chemistry, ISSN 0936-5214, E-ISSN 1437-2096, nr 2, s. 225-228Artikel i tidskrift (Refereegranskat)
    Abstract [en]

    A new, efficient method for the synthesis of benzylphosphonate diesters via a palladium(0)-catalyzed cross-coupling reaction between benzyl halides and H-phosphonate diesters, using Pd(OAc)2 as a palladium source and Xantphos as a supporting ligand, has been developed.

  • 14.
    Lavén, Gaston
    et al.
    Stockholms universitet, Naturvetenskapliga fakulteten, Institutionen för organisk kemi.
    Stawinski, Jacek
    Stockholms universitet, Naturvetenskapliga fakulteten, Institutionen för organisk kemi.
    Synthetic Studies on the Preparation of Dinucleoside Phenyl-Phosphonates and Phenyl-Phosphonothioates via Palladium(0) Catalyzed Cross-Coupling2005Ingår i: / [ed] Michal Hocek, 2005, s. 195-199Konferensbidrag (Refereegranskat)
    Abstract [en]

    Separate diastereomers of protected dithymidine (3'-5')-phenylphosphonates and dithymidine (3'-5')phenylphosphonothioate were obtained via a palladium(0) catalysed stereo-specific cross-coupling reaction of separate diastereomers of corresponding dinucleoside H-phosphonate and dinucleoside H-phosphonothioate with halobenzenes.

  • 15.
    Liao, Rong-Zhen
    et al.
    Stockholms universitet, Naturvetenskapliga fakulteten, Institutionen för organisk kemi.
    Himo, Fahmi
    Stockholms universitet, Naturvetenskapliga fakulteten, Institutionen för organisk kemi.
    Yu, Jian-Guo
    Liu, Ruo-Zhuang
    Theoretical study of the RNA hydrolysis mechanism of the dinuclear zinc enzyme RNase Z2009Ingår i: European Journal of Inorganic Chemistry, ISSN 1434-1948, E-ISSN 1099-1948, Vol. 2009, nr 20, s. 2967-2972Artikel i tidskrift (Refereegranskat)
    Abstract [en]

    RNase Z is a dinuclear zinc enzyme that catalyzes the removal of the tRNA 3'-end trailer. Density functional theory is used to investigate the phosphodiester hydrolysis mechanism of this enzyme with a model of the active site constructed on the basis of the crystal structure. The calculations imply that the reaction proceeds through two steps. The first step is a nucleophihc attack by a bridging hydroxide coupled with protonation of the leaving group by a Glu-His diad. Subsequently, a water molecule activated by the same Glu-His diad makes a reverse attack, regenerating the bridging hydroxide. The second step is calculated to be the rate-limiting step with a barrier of 18 kcal/mol, in good agreement with experimental kinetic studies. Both zinc ions participate in substrate binding and orientation, facilitating nucleophilic attack. In addition, they act as electrophilic catalysts to stabilize the pentacoordinate trigonal-bipyramidal transition states.

  • 16.
    Merritt, Eleanor A.
    et al.
    Stockholms universitet, Naturvetenskapliga fakulteten, Institutionen för organisk kemi.
    Malmgren, Joel
    Stockholms universitet, Naturvetenskapliga fakulteten, Institutionen för organisk kemi.
    Klinke, Felix J.
    Stockholms universitet, Naturvetenskapliga fakulteten, Institutionen för organisk kemi.
    Olofsson, Berit
    Stockholms universitet, Naturvetenskapliga fakulteten, Institutionen för organisk kemi.
    Synthesis of diaryliodonium triflates using environmentally benign oxidizing agents2009Ingår i: Synlett: Accounts and Rapid Communications in Synthetic Organic Chemistry, ISSN 0936-5214, E-ISSN 1437-2096, nr 14, s. 2277-2280Artikel i tidskrift (Refereegranskat)
  • 17.
    Olsson, Vilhelm
    Stockholms universitet, Naturvetenskapliga fakulteten, Institutionen för organisk kemi.
    Functionalization of Unactivated Alkenes trough Iridium-Catalyzed Borylation of Carbon-Hydrogen Bonds. Mechanism and Synthetic ApplicationsManuskript (Övrigt vetenskapligt)
  • 18.
    Olsson, Vilhelm
    et al.
    Stockholms universitet, Naturvetenskapliga fakulteten, Institutionen för organisk kemi.
    Sebelius, Sara
    Stockholms universitet, Naturvetenskapliga fakulteten, Institutionen för organisk kemi.
    Selander, Nicklas
    Stockholms universitet, Naturvetenskapliga fakulteten, Institutionen för organisk kemi.
    Szabó, Kálmán
    Stockholms universitet, Naturvetenskapliga fakulteten, Institutionen för organisk kemi.
    Direct Boronation of Allyl Alcohols with Diboronic Acid Using Palladium Pincer-Complex Catalysis. A Remarkably Facile Allylic Displacement of the Hydroxy Group under Mild Reaction Conditions2006Ingår i: Journal of the American Chemical Society, ISSN 0002-7863, E-ISSN 1520-5126, Vol. 128, nr 14, s. 4588-4589Artikel i tidskrift (Refereegranskat)
    Abstract [en]

    Allyl alcohols were converted to allyl boronic acids and subsequently to trifluoro(allyl)borates with tetrahydroxy diboron using palladium pincer-complex catalysis. These reactions are regio- and stereoselective proceeding with high isolated yields. Competitive boronation experiments indicate that under the applied reaction conditions the allylic displacement of a hydroxy group is faster than the displacement of an acetate leaving group. It is assumed that the hydroxy group of the allyl alcohol is converted to a diboronic acid ester functionality, which can easily be substituted.

  • 19.
    Privalov, Timofei
    et al.
    Stockholms universitet, Naturvetenskapliga fakulteten, Institutionen för organisk kemi.
    Boschloo, Gerrit
    Hagfeldt, Anders
    Svensson, Per H.
    Kloo, Lars
    A study of the interactions between I-/I3- redox , mediators amd organometallic sensitizing dyes in solar cells2009Ingår i: The Journal of Physical Chemistry C, ISSN 1932-7447, E-ISSN 1932-7455, Vol. 113, nr 2, s. 783-790Artikel i tidskrift (Refereegranskat)
  • 20.
    Samec, Joseph S M
    et al.
    Stockholms universitet, Naturvetenskapliga fakulteten, Institutionen för organisk kemi.
    Mony, Laetitia
    Bäckvall, Jan-E
    Efficient Ruthenium-Catalyzed Transfer Hydrogenation of Functionalized Imines by Isopropanol under Controlled Microwave Heating2005Ingår i: Canadian journal of chemistry (Print), ISSN 0008-4042, E-ISSN 1480-3291, Vol. 83, nr 6, s. 909-916Artikel i tidskrift (Refereegranskat)
    Abstract [en]

    Transfer hydrogenation of various functionalized imines by isopropanol catalyzed by [Ru(CO)(2)(Ph4C4CO)](2) (3) has been studied. The use of either an oil bath or controlled microwave heating in toluene led to an efficient procedure with high turnover frequencies and the product amines were obtained in high yields. An advantage with catalyst 3 over the conventional [Ru-2(CO)(4)(mu-H)(Ph4C4COHOCC4Ph4)] (1) is the absence of an initiation period, which results in a faster reaction with 3 as compared to 1.

  • 21. Sjödin, Martin
    et al.
    Styring, Stenbjörn
    Wolpher, Henriette
    Stockholms universitet, Naturvetenskapliga fakulteten, Institutionen för organisk kemi.
    Xu, Yunhua
    Sun, Licheng
    Hammarström, Leif
    Switching the redox mechanism: Models for proton coupled electron transfer from tyrosine and tryptophan2005Ingår i: Journal of the American Chemical Society, ISSN 0002-7863, E-ISSN 1520-5126, Vol. 127, nr 11, s. 3855-3863Artikel i tidskrift (Refereegranskat)
    Abstract [en]

    The coupling of electron and proton transfer is an important controlling factor in radical proteins, such as photosystem II, ribinucleotide reductase, cytochrome oxidases, and DNA photolyase. This was investigated in model complexes in which a tyrosine or tryptophan residue was oxidized by a laser-flash generated trisbipyridine-Ru-III moiety in an intramolecular, proton-coupled electron transfer (PCET) reaction. The PCET was found to proceed in a competition between a stepwise reaction, in which electron transfer is followed by deprotonation of the amino acid radical (ETPT), and a concerted reaction, in which both the electron and proton are transferred in a single reaction step (CEP). Moreover, we found that we could analyze the kinetic data for PCET by Marcus' theory for electron transfer. By altering the solution pH, the strength of the Ru-III oxidant, or the identity of the amino acid, we could induce a switch between the two mechanisms and obtain quantitative data for the parameters that control which one will dominate. The characteristic pH-dependence of the CEP rate (M. Sjodin et al. J. Am. Chem. Soc. 2000, 122, 3932) reflects the pH-dependence of the driving force caused by proton release to the bulk. For the pH-independent ETPT on the other hand, the driving force of the rate-determining ET step is pH-independent and smaller. On the other hand, temperature-dependent data showed that the reorganization energy was higher for CEP, while the pre-exponential factors showed no significant difference between the mechanisms. Thus, the opposing effect of the differences in driving force and reorganization energy determines which of the mechanisms will dominate. Our results show that a concerted mechanism is in general quite likely and provides a low-barrier reaction pathway for weakly exoergonic reactions. In addition, the kinetic isotope effect was much higher for CEP (k(H)/k(D) &GT; 10) than for ETPT (k(H)/k(D) = 2), consistent with significant changes along the proton reaction coordinate in the rate-determining step of CEP.

  • 22.
    Stenutz, Roland
    Stockholms universitet, Naturvetenskapliga fakulteten, Institutionen för organisk kemi.
    The structure and conformation of saccharides determined by experiment and simulation1997Doktorsavhandling, sammanläggning (Övrigt vetenskapligt)
    Abstract [en]

    A computer program, CASPER, for sequence determination of oligosaccharides and regular polysaccharides using NMR-data, has been extended to support multiply branched structures. The program has been modified to allow the use of incomplete experimental data since spectral overlap can be a problem even at high fields. The resulting program was tested and used in the structure determination of the capsular polysaccharide from Klebsiella type K52.

    Four carboxyethyl-substituted sugars, methyl 4-O-[(R)- and (S)-1-carboxyethyl]-a-L-rhamnopyranoside and methyl 6-O-[(R)- and (S)-1-carboxyethyl]-a-D-galactopyranoside have been synthesized. The conformational properties of the latter two have been investigated by both NMR spectroscopy and molecular modelling studies. For the NMR-studies stereospecifically deuterated compounds were prepared.

  • 23. Zerbetto, Mirco
    et al.
    Polimeno, Antonino
    Kotsyubynskyy, Dmytro
    Stockholms universitet, Naturvetenskapliga fakulteten, Institutionen för fysikalisk kemi, oorganisk kemi och strukturkemi.
    Ghalebani, Leila
    Stockholms universitet, Naturvetenskapliga fakulteten, Institutionen för fysikalisk kemi, oorganisk kemi och strukturkemi.
    Kowalewski, Jozef
    Stockholms universitet, Naturvetenskapliga fakulteten, Institutionen för fysikalisk kemi, oorganisk kemi och strukturkemi, Avdelningen för fysikalisk kemi.
    Meirovitch, Eva
    Olsson, Ulrika
    Stockholms universitet, Naturvetenskapliga fakulteten, Institutionen för organisk kemi.
    Widmalm, Göran
    Stockholms universitet, Naturvetenskapliga fakulteten, Institutionen för organisk kemi.
    An integrated approach to NMR spin relaxation in flexible biomolecules: Application to β-D-glucopyranosyl-(1→6)-α-D-mannopyranosyl-OMe2009Ingår i: Journal of Chemical Physics, ISSN 0021-9606, E-ISSN 1089-7690, Vol. 131, nr 23, s. p234501-Artikel i tidskrift (Refereegranskat)
    Abstract [en]

    The description of the reorientational dynamics of flexible molecules is a challenging task, in particular when the rates of internal and global motions are comparable. The commonly used simple mode-decoupling models are based on the assumption of statistical independence between these motions. This assumption is not valid when the time scale separation between their rates is small, a situation that was found to arise in oligosaccharides in the context of certain internal motions. To make possible the interpretation of NMR spin relaxation data from such molecules, we developed a comprehensive approach generally applicable to flexible rotators with one internal degree of freedom. This approach integrates a stochastic description of coupled global tumbling and internal torsional motion, quantum chemical calculations of the local potential and the local geometry at the site of the restricted torsion, and hydrodynamics-based calculations of the diffusive properties. The method is applied to the disaccharide -D-Glcp-(16)--D-[6-13C]-Manp-OMe dissolved in a DMSO-d6/D2O cryosolvent. The experimental NMR relaxation parameters, associated with the 13CH2 probe residing at the glycosidic linkage, include 13C T1 and T2 and 13C-{1H} nuclear Overhauser enhancement (NOE) as well as longitudinal and transverse dipole-dipole cross-correlated relaxation rates, acquired in the temperature range of 253–293 K. These data are predicted successfully by the new theory with only the H–C–H angle allowed to vary. Previous attempts to fit these data using mode-decoupling models failed.

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