Chemical Sciences Journal

Theoretical Comparison of O, S, Se and Te Terminal Active Site of Molybdo-Enzymes, In Terms of Their Property upon Reaction with Acetaldehyde

Abstract

Sofani Tafesse Gebreyesus

Previous researches show that all members of chalcogene family could be a terminal in the molybdo-enzymes. But their structure as well as catalytic mechanism has not been studied much. In this paper, Density functional calculations have been performed on a model for the reductive half-reaction of the molybdo- enzymes containing Oxo, sulfido, sellenido and tellurido terminals, enabling a discussion of structural details of the Mo coordination sphere involved in the reaction with acetaldehyde.The reductive half reaction active sites, with oxo, sufido, sellenido and tellerido terminal truncated structures, were modeled using GaussView software. Energy, Mullikens charge, single negative frequency and bond descriptions of the complexes were among the very important tools obtained from the transition state structures, to study the properties of the active sites. In this work it has been found that the normalized energies for complexes with oxo, sulfido, sellenido and tellerido terminals were 433.923, 421.742, 419.284 and 403.0578 kcal/mol respectively. The decreasing trend found was the same, though the magnitudes of the energies differ significantly. The complex with oxo terminal shows considerably maximum energy barrier of 433.923 kcal in addition to its highest frequency. These are the evidence for its poor catalytic activity towards hydroxylation reaction. As a result of this and additional evidences from mulliken charge and bond length values, the reactivity of the active site towards acetaldehyde for its oxidation increases from active site with oxo to tellurido terminal. Besides, these findings give a clue for the possible natural existence of a molybdo-enzyme with Te-terminal.