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  • 1.
    Li, Xichen
    et al.
    Stockholm University, Faculty of Science, Department of Physics. Stockholm University, Faculty of Science, Department of Biochemistry and Biophysics.
    Chen, Guangju
    Schinzel, Sandra
    Stockholm University, Faculty of Science, Department of Physics. Stockholm University, Faculty of Science, Department of Biochemistry and Biophysics.
    Siegbahn, Per E. M.
    Stockholm University, Faculty of Science, Department of Physics. Stockholm University, Faculty of Science, Department of Biochemistry and Biophysics.
    A comparison between artificial and natural water oxidation2011In: Dalton Transactions, ISSN 1477-9226, E-ISSN 1477-9234, Vol. 40, no 42, p. 11296-11307Article in journal (Refereed)
    Abstract [en]

    Two artificial water oxidation catalysts, the blue dimer and the Llobet catalyst, have been studied using hybrid DFT methods. The results are compared to those for water oxidation in the natural photosystem II enzyme. Studies on the latter system have now reached a high level of understanding, at present much higher than the one for the artificial systems. A recent high resolution X-ray structural investigation of PSII has confirmed the main features of the structure of the oxygen evolving complex (OEC) suggested by previous DFT cluster studies. The O-O bond formation mechanism suggested is of direct coupling (DC) type between an oxygen radical and a bridging oxo ligand. A similar DC mechanism is found for the Llobet catalyst, while an acid-base (AB) mechanism is preferred for the blue dimer. All of them require at least one oxygen radical. Full energy diagrams, including both redox and chemical steps, have been constructed illustrating similarities and differences to the natural system. Unlike previous DFT studies, the results of the present study suggest that the blue dimer is rate-limited by the initial redox steps, and the Llobet catalyst by O(2) release. The results could be useful for further improvement of the artificial systems.

  • 2.
    Noack, Holger
    et al.
    Stockholm University, Faculty of Science, Department of Physics.
    Valentin, Georgiev
    Stockholm University, Faculty of Science, Department of Physics.
    Johansson, Adam Johannes
    Stockholm University, Faculty of Science, Department of Physics.
    Blomberg, Margareta R.A.
    Stockholm University, Faculty of Science, Department of Physics.
    Siegbahn, Per E,M.
    Stockholm University, Faculty of Science, Department of Physics.
    Theoretical Insights into Heme Catalysed Oxidation of Cyclohexane to Adipic Acid Article in journal (Refereed)
    Abstract [en]

    Adipic acid is a key compound in the chemical industry, where it is mainly used in the production of polymers. The conventional process of its generation requires vast amounts of energy, and moreover, pro- duces environmentally deleterious substances. Thus, there is interest in alternative ways to gain adequate amounts of adipic acid. Experimental reports on a one-pot iron catalyzed conversion of cyclohexane to adipic acid motivated a theoretical investigation based on DFT calculations. The process investigated is interesting because it requires less energy than contemporary methods and does not produce environmentally harmful side products. The aim of the present contribution is to gain insight into the mechanism of the iron catalyzed cyclohexane conversion to provide a basis for further development of this process. The rate limiting step along the reaction path is discussed. Furthermore, it is shown that the C-C bond breaks spontaneously after an initial hydrogen atom abstraction from one of the cylohexane-1,2-diol hydroxides.

  • 3.
    Siegbahn, Per E. M.
    et al.
    Stockholm University, Faculty of Science, Department of Biochemistry and Biophysics. Stockholm University, Faculty of Science, Department of Physics.
    Himo, Fahmi
    Stockholm University, Faculty of Science, Department of Organic Chemistry.
    The quantum chemical clusterapproach for modeling enzymereactions2011In: Wiley Interdisciplinary Reviews. Computational Molecular Science, ISSN 1759-0876, E-ISSN 1759-0884, Vol. 1, no 3, p. 323-356Article in journal (Refereed)
    Abstract [en]

    This Overview describes the general concepts behind the quantum chemical clusterapproach formodeling enzyme active sites and reaction mechanisms. First, theunderlying density functional electronic structure method is briefly recapitulated.The cluster methodology is then discussed, including the important observationon the convergence of the solvation effects. The concepts are illustrated usingexamples from recent applications, such as the discrimination between differentreaction mechanisms in phosphotriesterase, the elucidation of origins of regioselectivityin the epoxide-opening reaction of haloalcohol dehalogenase, and finallythe use of the cluster methodology to establish the detailed structure of theoxygen-evolving complex in photosystem II.

1 - 3 of 3
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