Estudo computacional da reação da cisteína desprotonada com o ozônio em fase gás

Abstract

In this work, calculations were performed using the density functional theory with the functional UB2PLYP and the base function aug-cc-PVDZ to map the reaction mechanism of the deprotonated cysteine with the ozone in gaseous phase. In the description of the reaction mechanism, it was taken into account the change of the spin state along the reaction using of the potential energy curve in the singlet and triplet spin states. The results showed that the method UB2PLYP/aug-cc- pVDZ is suitable to describe and predict the intersystem crossing, providing a good description for the formation of the products formed with the spin state different from the reagents. The reaction between deprotonated cysteine and ozone implies an electron transfer, however, this intra-complexo transfer occurs after an initial complexation. Initially the reaction takes place on the singlet spin potential energy curve and the MECP (minimum energy crossing point) called the minimum energy crossing point, which is the lowest energy point at the intersection of potential energy there is a change from the singlet spin state to the triplet, leading to the formation of: i) anions cysteine sulfenate, sulfinate and sulphonate, (ii) radical anions of sulfenates formed by the ejection of a hydroperoxyl radical, and (iii) production of anions: Alanine (C3H6NO2)^- and C2H4NS^- . and - C2H4NS . This change is configured by the lower energy crossover point that leads to two competitive reaction paths. As the products - radical anion sulfenate and the hydroperoxyl - formed radical have different spin states of the reagents, on the path of reaction that leads to their formation is the type prohibited by spin.