A promiscuous dicopper(II) system promoting the hydrolysis of bis(2,4-dinitrophenyl)phosphate: Gaining mechanistic insight by means of structural and spectroscopic DFT studies

摘要

Catechol oxidases (COs) are plant enzymes that belong to the oxidoreductases class. They contain a dinuclear copper center in their active site. In this article, we have investigated the dicopper(II) model complex [Cu_2(μ-OH)(C_(21)H_(33)ON_6)] ~(2+) (Complex-A) under a computational perspective, using the DFT method, since this approach has been very useful in the treatment of bimetallic copper systems. The structural and spectroscopic study of Complex-A as well as the structural analysis of the BDNPP/Complex-A (Complex-B) adduct have been carried out. The calculated parameters for Complex-A are in good accordance with the experimental Xray data. Some remarkable points can be observed from the calculated UV-vis relative excitations. The Complex-B computed structure verifies its identity as a key intermediate species in the BDNPP hydrolysis mechanism. The Cu~(II)?Cu~(II) calculated distance in Complex-B (3.026 ?) is shorter than the calculated for Complex-A (3.080 ?); one copper atom is bonded to the oxygen of phosphate [Cu (2)?O64-P] at 2.511 ?. These arguments clearly suggest a monodentate interaction and lead to a new mechanism involving terminal substrate coordination and subsequent intramolecular nucleophilic attack by a bridging hydroxide. Such a hypothesis is completely new in terms of homobimetallic copper systems, and may have important implications regarding the chemistry of several biological dinuclear catalytic sites.