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Geometric Structure and 57Fe Mössbauer Parameters of Antiferromagnetic Reaction Intermediate of MMOH

11-21-2011

Prof. Jorge H. Rodriguez and his team use methods of computational quantum mechanics to investigate the biochemical function and structure of metal containing enzymes. Metalloenzymes catalyze many important biochemical reactions. Rodriguez and his team realize that metal-mediated biochemical reactions are related to the interaction between valence electrons of the reactant species. Such valence electrons are microscopic particles properly described by quantum mechanics. Taking advantage of powerful parallel-processing supercomputers, Rodriguez and his group solve the fundamental equations of quantum mechanics to elucidate physico-chemical properties and reactivities of metal centers in enzymes. The quantum effects are incorporated via Kohn-Sham spin density functional theory (SDFT) and, when appropriate, its relativistic extensions.

Rodriguez and his group pioneer the emerging field of "Quantum Biochemistry". As an example, Rodriguez and his team have predicted the electronic and geometric structures of a key peroxo reaction intermediate in the catalytic cycle of the enzyme methane monooxygenase hydroxylase (MMOH). This enzyme catalyzes an important reaction, namely the conversion of methane (CH4) to methanol (CH3OH). During such catalytic process, the di-iron center of MMOH must pass through various key stages known as reaction intermediates. Often, there are serious difficulties that prevent obtaining structures of reaction intermediates from experiment. However, it may be possible to obtain other types of experimental information based on spectroscopic techniques such as 57Fe Mössbauer spectroscopy. By using algorithms developed in his group, able to accurately predict 57Fe Mössbauer spectral parameters, Rodriguez and his team have been able to predict the geometric structure of a key reaction intermediate of MMOH for which there is no experimental crystallographic structure. In an article published in Dalton Transactions [Dalton Trans., 2012, DOI: 10.1039/C1DT11656H], Rodriguez and his former graduate student Dr. Teepanis Chachiyo present the predicted structural and electronic details of a key peroxo intermediate of MMOH. Rodriguez and Chachiyo started this project several years ago. The main structural results on the MMOH intermediate and its consistency with 57Fe Mössbauer spectral parameters were reported in Chachiyo's PhD thesis in 2005. Later, to further support their findings, the coauthors computed optical (UV-vis) parameters of the same intermediate and Raman parameters of other structuraly-related intermediates since, currently, there are no reliable Raman parameters for MMOH peroxo. In their Dalton publication, the coauthors show that the predicted structure is consistent with several experimental parameters. In particular, the predicted structure is fully consistent with experimental 57Fe Mössbauer spectral parameters. Mössbauer isomer shifts and quadrupole splittings computed with the algorithm developed at Purdue are, within experimental error, in excellent agreement with experiment.

diagram

Predicted structure of MMOH peroxo reaction intermediate.