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  • 1. An, Wei
    et al.
    Baber, Ashleigh E.
    Xu, Fang
    Soldemo, Markus
    KTH, School of Information and Communication Technology (ICT), Materials- and Nano Physics, Material Physics, MF.
    Weissenrieder, Jonas
    KTH, School of Information and Communication Technology (ICT), Materials- and Nano Physics, Material Physics, MF.
    Stacchiola, Dario
    Liu, Ping
    Mechanistic Study of CO Titration on CuxO/Cu(111) (x <= 2) Surfaces2014In: ChemCatChem, ISSN 1867-3880, E-ISSN 1867-3899, Vol. 6, no 8, p. 2364-2372Article in journal (Refereed)
    Abstract [en]

    The reducibility of metal oxides is of great importance to their catalytic behavior. Herein, we combined ambient-pressure scanning tunneling microscopy (AP-STM), X-ray photoemission spectroscopy (AP-XPS), and DFT calculations to study the CO titration of CuxO thin films supported on Cu(111) (CuxO/Cu(111)) aiming to gain a better understanding of the roles that the Cu(111) support and surface defects play in tuning catalytic performances. Different conformations have been observed during the reduction, namely, the 44 structure and a recently identified (5-7-7-5) Stone-Wales defects (5-7 structure). The DFT calculations revealed that the Cu(111) support is important to the reducibility of supported CuxO thin films. Compared with the case for the Cu2O(111) bulk surface, at the initial stage CO titration is less favorable on both the 44 and 5-7 structures. The strong CuxO <-> Cu interaction accompanied with the charge transfer from Cu to CuxO is able to stabilize the oxide film and hinder the removal of O. However, with the formation of more oxygen vacancies, the binding between CuxO and Cu(111) is weakened and the oxide film is destabilized, and Cu2O(111) is likely to become the most stable system under the reaction conditions. In addition, the surface defects also play an essential role. With the proceeding of the CO titration reaction, the 5-7 structure displays the highest activity among all three systems. Stone-Wales defects on the surface of the 5-7 structure exhibit a large difference from the 44 structure and Cu2O(111) in CO binding energy, stability of lattice oxygen, and, therefore, the reduction activity. The DFT results agree well with the experimental measurements, demonstrating that by adopting the unique conformation, the 5-7 structure is the active phase of CuxO, which is able to facilitate the redox reaction and the Cu2O/Cu(111)<-> Cu transition.

  • 2. Chen, Hu
    et al.
    Gao, Yan
    Sun, Licheng
    KTH, School of Chemical Science and Engineering (CHE), Chemistry, Organic Chemistry. Dalian University of Technology (DUT), China.
    A Cobalt-Based Film for Highly Efficient Electrocatalytic Water Oxidation in Neutral Aqueous Solution2016In: ChemCatChem, ISSN 1867-3880, E-ISSN 1867-3899, Vol. 8, no 17, p. 2757-2760Article in journal (Refereed)
    Abstract [en]

    A cobalt-based film (Co-Hi) for water oxidation was prepared in 2-[4-(2-hydroxyethyl) piperazin-1-yl]ethanesulfonic acid buffer at pH 7.0 through a unique cyclic voltammetry electrodeposition method by applying a wide scan range from 1.40 to -1.00 V versus normal hydrogen electrode (NHE). This catalyst film displayed highly efficient activity during oxygen evolution in neutral aqueous solution. An impressive current density of more than 1.5 mAcm(-2) that was stable over a prolonged time period was obtained with a remarkably low onset overpotential of 230 mV in 0.1 M phosphate buffer (pH 7.0).

  • 3.
    Dinér, Peter
    et al.
    KTH, School of Chemical Science and Engineering (CHE), Chemistry.
    Sadhukhan, Arghya
    KTH, School of Chemical Science and Engineering (CHE), Chemistry.
    Blomkvist, Björn
    KTH, School of Chemical Science and Engineering (CHE), Chemistry.
    Chiral Sulfinamides as Highly Enantioselective Organocatalysts2014In: ChemCatChem, ISSN 1867-3880, E-ISSN 1867-3899, Vol. 6, no 11, p. 3063-3066Article in journal (Refereed)
  • 4.
    Fatih Polat, Muhammed
    et al.
    KTH, School of Chemical Science and Engineering (CHE), Chemistry, Organic Chemistry.
    Hettmanczyk, Lara
    KTH, School of Chemical Science and Engineering (CHE), Chemistry, Organic Chemistry.
    Zhang, Wei
    KTH, School of Chemical Science and Engineering (CHE), Chemistry, Organic Chemistry.
    Szabo, Zoltan
    KTH, School of Chemical Science and Engineering (CHE), Chemistry, Organic Chemistry.
    Franzén, Johan
    KTH, School of Chemical Science and Engineering (CHE), Chemistry, Organic Chemistry.
    One-Pot, Two-Step Protocol for the Catalytic Asymmetric Synthesis of Optically Active N,O- and O,O-Acetals2013In: ChemCatChem, ISSN 1867-3880, E-ISSN 1867-3899, Vol. 5, no 6, p. 1334-1339Article in journal (Refereed)
  • 5.
    Fransson, Linda
    et al.
    KTH, School of Chemical Science and Engineering (CHE), Chemistry, Organic Chemistry. KTH, School of Biotechnology (BIO), Biochemistry. KTH, School of Biotechnology (BIO), Centres, Albanova VinnExcellence Center for Protein Technology, ProNova.
    Laurell, Anna
    KTH, School of Chemical Science and Engineering (CHE), Chemistry, Organic Chemistry.
    Widyan, Khalid
    KTH, School of Chemical Science and Engineering (CHE), Chemistry, Organic Chemistry.
    Wingstrand, Erica
    KTH, School of Chemical Science and Engineering (CHE), Chemistry, Organic Chemistry.
    Hult, Karl
    KTH, School of Biotechnology (BIO), Biochemistry. KTH, School of Biotechnology (BIO), Centres, Albanova VinnExcellence Center for Protein Technology, ProNova.
    Moberg, Christina
    KTH, School of Chemical Science and Engineering (CHE), Chemistry, Organic Chemistry.
    Minor Enantiomer Recycling-Effect of Two Reinforcing Catalysts on Product Yield and Enantiomeric Excess2010In: ChemCatChem, ISSN 1867-3880, E-ISSN 1867-3899, Vol. 2, no 6, p. 683-693Article in journal (Refereed)
    Abstract [en]

    Kinetic modeling of a recycling procedure in which the minor product enantiomer from an enantioselective catalytic reaction is selectively retransformed to starting material by a second chiral catalyst demonstrates that the enantiomeric excess of the product is not affected by the relative amounts of the two catalysts, but that the yield increases when the amount of the catalyst for the product-forming reaction is increased. The yield, but not the enantiomeric excess, is also affected by the initial substrate concentration. The recycling process is compared to sequential processes in which either the second catalyst is added after completion of the first reaction or in which the two catalysts are added simultaneously. In the sequential processes, high enantioselectivity can be obtained at the expense of product yield, whereas under recycling conditions both high enantiomeric excess and high yield can be achieved. Experimental data from a recycling procedure providing qualitative support for results from kinetic modeling are presented.

  • 6.
    Hamberg, Anders
    et al.
    KTH, School of Biotechnology (BIO), Biochemistry.
    Magnusson, Anders
    KTH, School of Biotechnology (BIO), Biochemistry.
    Hu, Francis J.
    KTH, School of Biotechnology (BIO), Biochemistry.
    Hult, Karl
    KTH, School of Biotechnology (BIO), Biochemistry.
    Selective Monoacylation of Diols by Substrate Assisted Catalysis in T40A Candida antarctica Lipase B2013In: ChemCatChem, ISSN 1867-3880, E-ISSN 1867-3899, Vol. 5, no 3, p. 743-747Article in journal (Refereed)
    Abstract [en]

    The selectivity towards diols over monoesters in the esterification of diols catalysed by lipase B from Candida antarctica (CALB) was improved by the single point mutation T40A in the enzyme's oxyanion hole. Substrate-assisted catalysis was suggested from molecular modelling of the tetrahedral intermediate in esterification of 1,2-ethanediol catalysed by T40A CALB. The non-reacting hydroxyl group of the diol forms a hydrogen bond to the oxyanion in the transition state, replacing that deleted in mutation. Monoester yields in transacylation reactions were monitored over time to compare the selectivities for wild-type and T40A CALB. The results showed increased selectivities towards the diols tested over their corresponding monoesters as a result of the T40A mutation with substrate-assisted catalysis as a plausible explanation.

  • 7.
    Laurell Nash, Anna
    et al.
    KTH, School of Chemical Science and Engineering (CHE), Chemistry, Organic Chemistry.
    Widyan, Khalid
    KTH, School of Chemical Science and Engineering (CHE), Chemistry, Organic Chemistry.
    Moberg, Christina
    KTH, School of Chemical Science and Engineering (CHE), Chemistry, Organic Chemistry.
    Recycling Powered by Release of Carbon Dioxide2014In: ChemCatChem, ISSN 1867-3880, E-ISSN 1867-3899, Vol. 6, no 12, p. 3314-3317Article in journal (Refereed)
    Abstract [en]

    In a cyclic process, fed with external chemical energy generated by the transformation of a compound with high chemical potential to carbon dioxide, the undesired enantiomer from a catalytic asymmetric reaction is continuously recycled to starting reagent. This minor enantiomer recycling is characterized by gradually increasing yields and product enantiomeric ratios. The requirements for maintaining a cyclic procedure are discussed; the necessity of a coupled exergonic process is demonstrated experimentally.

  • 8.
    Naidu, Veluru Ramesh
    et al.
    KTH, School of Chemical Science and Engineering (CHE), Chemistry, Organic Chemistry.
    Ni, Shengjun
    KTH, School of Chemical Science and Engineering (CHE), Chemistry, Organic Chemistry.
    Franzén, Johan
    KTH, School of Chemical Science and Engineering (CHE), Chemistry, Organic Chemistry.
    The Carbocation: A Forgotten Lewis Acid Catalyst2015In: ChemCatChem, ISSN 1867-3880, E-ISSN 1867-3899, Vol. 7, no 13, p. 1896-1905Article in journal (Refereed)
    Abstract [en]

    A Lewis acid that has received negligible attention as a catalyst is the carbocation. The carbocation is isoelectronic to boron and owes its Lewis acidity to a low-lying empty p(C) orbital. In terms of reactivity and stability carbocations are very versatile Lewis acids, from the extremely unstable methylium cation to the water-stable tris(N,N-dimethylaniline) methylium ion (crystal violet). Although the Lewis acid properties of carbocations have been extensively studied since the discovery of the tropolium ion more than 130years ago there is only a handful examples on the application of carbocations as Lewis acid catalysts. Herein, the research on triarylmethylium (trityl)-cation catalysis is summarized. In light of the reports the trityl ion emerges as a highly efficient and highly versatile Lewis acid catalyst capable of catalyzing different classes of reactions often with high selectivity and low catalyst loadings (for some reactions down to ppm levels).

  • 9. Nobili, Alberto
    et al.
    Steffen-Munsberg, Fabian
    KTH, School of Biotechnology (BIO), Industrial Biotechnology. University of Greifswald, Germany .
    Kohls, Hannes
    Trentin, Ivan
    Schulzke, Carola
    Höhne, Matthias
    Bornscheuer, Uwe T.
    Engineering the Active Site of the Amine Transaminase from Vibrio fluvialis for the Asymmetric Synthesis of Aryl-Alkyl Amines and Amino Alcohols2015In: ChemCatChem, ISSN 1867-3880, E-ISSN 1867-3899, Vol. 7, no 5, p. 757-760Article in journal (Refereed)
    Abstract [en]

    Although the amine transaminase from Vibrio fluvialis has often been applied as a catalyst for the biocatalytic preparation of various chiral primary amines, it is not suitable for the transamination of a-hydroxy ketones and aryl-alkyl ketones bearing an alkyl substituent larger than a methyl group. We addressed this problem through a systematic mutagenesis study of active site residues to expand its substrate scope towards two bulky ketones. We identified two mutants (F85L/V153A and Y150F/V153A) showing 30-fold increased activity in the conversion of (S)-phenylbutylamine and (R)-phenylglycinol, respectively. Notably, they facilitated asymmetric synthesis of these amines with excellent enantiomeric purities of 98% ee.

  • 10. Sjöblom, Magnus
    et al.
    Risberg, Per
    KTH, School of Industrial Engineering and Management (ITM), Machine Design (Dept.), Internal Combustion Engines.
    Filippova, Alfia
    Öhrman, Olov G. W.
    Rova, Ulrika
    Christakopoulos, Paul
    In Situ Biocatalytic Synthesis of Butyl Butyrate in Diesel and Engine Evaluations2017In: ChemCatChem, ISSN 1867-3880, E-ISSN 1867-3899, Vol. 9, no 24, p. 4529-4537Article in journal (Refereed)
    Abstract [en]

    Blending petroleum fuels with biofuels is likely to become increasingly important over the years to come. Butyl butyrate has promising characteristics as a blend component in diesel and can be synthesized by lipase-catalyzed esterification of 1-butanol and butyric acid, which both can be derived from fermentation technologies. In the current study, the enzyme load and reaction temperature were optimized for the production of butyl butyrate with Novozyme 435 ( immobilized Candida antarctica lipase B) directly in diesel at a substrate concentration of 1m using a molar ratio of 1:1 between n-butanol and butyric acid. Optimum conditions were found by using a central composite design at an enzyme load of 12% of substrate weight and a temperature of 57 degrees C, giving 90% yield conversion in 30 min, corresponding to a butyl butyrate productivity of 1.8 mol L(-1)h(-1). Diesel blended with 5, 10, and 30% butyl butyrate was tested in a heavy-duty diesel engine under two load cases. The ignition properties of the blended fuels were very similar to pure diesel, making butyl butyrate an interesting diesel substitute. The emission analysis demonstrated lower soot and CO emissions, similar hydrocarbons levels and slightly increased NOx levels compared with using pure diesel. The high activity of lipase in diesel and the compatibility between diesel and butyl butyrate opens up the possibility to develop fuel blending systems where the synthesis of the blendin component occurs directly in the fuel.

  • 11. Steffen-Munsberg, F.
    et al.
    Vickers, C.
    Thontowi, A.
    Schätzle, S.
    Meinhardt, T.
    Svedendahl Humble, M.
    Land, Henrik
    KTH, School of Biotechnology (BIO), Biochemistry.
    Berglund, Per
    KTH, School of Biotechnology (BIO), Biochemistry.
    Bornscheuer, U. T.
    Höhne, M.
    Revealing the Structural Basis of Promiscuous Amine Transaminase Activity2013In: ChemCatChem, ISSN 1867-3880, E-ISSN 1867-3899, Vol. 5, no 1, p. 154-157Article in journal (Refereed)
  • 12. Steffen-Munsberg, F.
    et al.
    Vickers, C.
    Thontowi, A.
    Schätzle, S.
    Tumlirsch, T.
    Svedendahl Humble, M.
    Land, Henrik
    KTH, School of Biotechnology (BIO), Biochemistry.
    Berglund, Per
    KTH, School of Biotechnology (BIO), Biochemistry.
    Bornscheuer, U. T.
    Höhne, M.
    Connecting Unexplored Protein Crystal Structures to Enzymatic Function2013In: ChemCatChem, ISSN 1867-3880, E-ISSN 1867-3899, Vol. 5, no 1, p. 150-153Article in journal (Refereed)
  • 13.
    Svedendahl Humble, Maria
    et al.
    KTH, School of Biotechnology (BIO), Biochemistry.
    Engelmark Cassimjee, Karim
    KTH, School of Biotechnology (BIO), Biochemistry.
    Abedu, Vahak
    Federsel, Hans-Jürgen
    Berglund, Per
    KTH, School of Biotechnology (BIO), Biochemistry.
    Key Amino Acid Residues for Reversed or Improved Enantiospecificity of an omega-Transaminase2012In: ChemCatChem, ISSN 1867-3880, E-ISSN 1867-3899, Vol. 4, no 8, p. 1167-1172Article in journal (Refereed)
    Abstract [en]

    Transaminases inherently possess high enantiospecificity and are valuable tools for stereoselective synthesis of chiral amines in high yield from a ketone and a simple amino donor such as 2-propylamine. Most known ?-transaminases are (S)-selective and there is, therefore, a need of (R)-selective enzymes. We report the successful rational design of an (S)-selective ?-transaminase for reversed and improved enantioselectivity. Previously, engineering performed on this enzyme group was mainly based on directed evolution, with few exceptions. One reason for this is the current lack of 3D structures. We have explored the ?-transaminase from Chromobacterium violaceum and have used a homology modeling/rational design approach to create enzyme variants for which the activity was increased and the enantioselectivity reversed. This work led to the identification of key amino acid residues that control the activity and enantiomeric preference. To increase the enantiospecificity of the C. violaceum ?-transaminase, a possible single point mutation (W60C) in the active site was identified by homology modeling. By site-directed mutagenesis this enzyme variant was created and it displayed an E value improved up to 15-fold. In addition, to reverse the enantiomeric preference of the enzyme, two other point mutations (F88A/A231F) were identified. This double mutation created an enzyme variant, which displayed substrate dependent reversed enantiomeric preference with an E value shifted from 3.9 (S) to 63 (R) for 2-aminotetralin.

  • 14.
    Syrén, Per-Olof
    et al.
    KTH, School of Biotechnology (BIO), Biochemistry.
    Le Joubioux, Florian
    Ben Henda, Yesmine
    Maugard, Thierry
    Hult, Karl
    KTH, School of Biotechnology (BIO), Biochemistry.
    Graber, Marianne
    Proton Shuttle Mechanism in the Transition State of Lipase-Catalyzed N-Acylation of Amino Alcohols2013In: ChemCatChem, ISSN 1867-3880, E-ISSN 1867-3899, Vol. 5, no 7, p. 1842-1853Article in journal (Refereed)
    Abstract [en]

    An increased reaction rate for lipase-catalyzed N-acylation of amino alcohols relative to that of monofunctionalized amines can be explained by a hydrogen shuttling mechanism that avoids nitrogen inversion in the transition state. The mechanism does not involve acyl migration from an ester intermediate that would be formed first, an explanation that permeates the literature. Our suggested reaction mechanism is dependent on the preference of amino alcohols to form intramolecular hydrogen bonds and the capability of the enzyme to accommodate and exploit the specific hydrogen bonding pattern provided by the ligand during catalysis. Our proposed proton shuttle mechanism involves the transfer of two protons in the transition state concomitant with a nucleophilic attack on the acyl enzyme and provides an explanation for the high reaction rate and chemoselectivity for lipase-catalyzed N-acylation of amino alcohols. Moreover, the proton shuttle mechanism explains the increased reaction rate for the enzyme-catalyzed N-acylation of diamines and of methoxy-2-propylamine, for which O- to N-acyl migration is impossible. A linear free-energy relationship analysis based on the experimental results showed that all of our investigated difunctionalized amine substrates afforded a substrate-assisted rate acceleration of the N-acylation by the same reaction mechanism. Furthermore, the results of the analysis were consistent with partial proton transfer in the rate-limiting transition state, which further supports our suggested proton shuttle mechanism.

  • 15. Verendel, J. Johan
    et al.
    Dinér, Peter
    Department of Chemistry – BMC, Uppsala university.
    Efficient, Low Temperature Production of Hydrogen from Methanol2013In: ChemCatChem, ISSN 1867-3880, E-ISSN 1867-3899, Vol. 5, no 10, p. 2795-2797Article, review/survey (Refereed)
1 - 15 of 15
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