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Analysis of the primary photocycle reactions occurring in the light, oxygen, and voltage blue−light receptor by multiconfigurational quantum−chemical methods

MPS-Authors
http://pubman.mpdl.mpg.de/cone/persons/resource/persons92695

Domratcheva,  Tatiana
Department of Biomolecular Mechanisms, Max Planck Institute for Medical Research, Max Planck Society;

http://pubman.mpdl.mpg.de/cone/persons/resource/persons92867

Fedorov,  Roman
Department of Biomolecular Mechanisms, Max Planck Institute for Medical Research, Max Planck Society;

http://pubman.mpdl.mpg.de/cone/persons/resource/persons95189

Schlichting,  Ilme
Department of Biomolecular Mechanisms, Max Planck Institute for Medical Research, Max Planck Society;

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Citation

Domratcheva, T., Fedorov, R., & Schlichting, I. (2006). Analysis of the primary photocycle reactions occurring in the light, oxygen, and voltage blue−light receptor by multiconfigurational quantum−chemical methods. Journal of Chemical Theory and Computation, 2(6), 1565-1574. doi:10.1021/ct0600114.


Cite as: http://hdl.handle.net/11858/00-001M-0000-0019-9A4E-D
Abstract
The photocycle reactions occurring between the flavin mononucleotide cofactor and the reactive cysteine residue in the blue−light photoreceptor domain light, oxygen, and voltage (LOV) were modeled for a system consisting of lumiflavin and thiomethanol. The electronic structure and energies of the reactive species were estimated using the CASSCF and MCQDPT2 quantum−chemical methods. The reaction pathway for the S−C4a covalent adduct formation in the triplet state was determined. Concerted electron and proton transfer from the thiol to the flavin in the triplet electronic state results in a biradical complex that is, however, unstable because its structure corresponds to a triplet−singlet crossing. The covalent adduct dissociation in the ground electronic state is a reverse of the photoreaction proceeding via a single energy barrier for hydrogen transfer. Thus, both photo− and dark reactions were found to be single−step chemical transformations occurring without stable intermediates. The photoreaction yielding the S−C4a covalent adduct is an intrinsic property of the isoalloxazine−thiol complex in the specific geometry arranged by the protein in LOV. The S−C4a covalent adduct between lumiflavin and thiomethanol is rather stable implying that in LOV its dissociation is facilitated by the protein