No abstract

In this work, the cleavage activity of the metal complex [Cu(C(21)H(21)N(3)O(2))(OH(2))(2)](2+) is demonstrated to occur toward double-stranded DNA, in addition to its previously described amide bond cleavage activity, thus suggesting catalytic promiscuity for this complex.

A reação da hidroxilamina com acetato de fenila foi investigada teoricamente para se obter uma melhor compreensão do efeito alfa nas reações de nucleófilos neutros. Os cálculos foram feitos em nível B3LYP/6-311+G(2df,2p)//HF/6-31G(d) incluindo o solvente (água) em nível PCM/HF/6-31G(d). Os resultados mostram que um ataque direto da hidroxilamina leva a uma barreira de energia livre de ativação DG ‡ muito alta, em torno de 50 kcal mol -1. Uma segunda molécula de hidroxilamina pode catalisar o processo através de catálise bifuncional usando ambos os grupos NH 2 e OH simultaneamente. Esta catálise bifuncional reduz o DG ‡ para 19 kcal mol -1 e é capaz de explicar a relação de produtos cinético e termodinâmico observada experimentalmente.The reaction of hydroxylamine with phenyl acetate was theoretically investigated to shed light on the role of catalysis and the origin of the a-effect in this system. Calculations at the B3LYP/6-311+G(2df,2p)//HF/6-31G(d) level and the solvent effect included at the PCM/HF/6-31G(d) level predict that the direct attack of hydroxylamine to the carbonyl centre has a high DG ‡ barrier, close to 50 kcal mol -1. A second hydroxylamine molecule can catalyse the process through bifunctional catalysis using both the NH 2 and OH groups simultaneously. This dual bifunctional catalysis decreases the DG ‡ to 19 kcal mol -1 and is able to explain the experimentally observed kinetics and product ratio.

The reaction of aryl acetates and hydroxylamine produces O-acylhydroxylamine and Nacylhydroxylamine, the latter being essentially observed for good leaving group esters and the former for poor leaving esters. For both acylation reactions, kinetics studies suggested a tetrahedral intermediate intervention for nucleofuges in a pKa range of 1 to 9. Esters having leaving groups with a pKa value less than 7 react by a rate-determining step inferred to be the tetrahedral intermediate formation, while for esters having leaving groups with a pKa value equal to or higher than 7, the rate-limiting step has been proposed to be the tetrahedral intermediate decomposition. General bifunctional acid-base catalysis by a second hydroxylamine molecule was identified as one of the components of the reaction for the intermediate collapse to products in the poor leaving group ester