QM/MM Study on the Mechanism of Aminophenol Oxidation by Functionalized beta-Cyclodextrin as Oxidase Nanomimic

In this study, functionalized beta-cyclodextrin (beta-CD) by aldehyde group was investigated as an oxidase enzyme mimic for the amino phenol oxidation. All calculations were performed by GAUSSIAN 09 package using two layers ONIOM method at the ONIOM (MPW1PW91/6-311++G(d,p)/UFF) level. In the first step, H2O2 is encapsulated in the hydrophobic cavity. In the second step, H2O2 molecule oxidized the aldehyde group of the functionalized beta-CD, through the wide edge of beta-CD. This step is the Rate Determining Step (RDS) with the activation energy of 54.4 kcal mol(-1). Natural population analysis has been performed for calculation of the global electron density transfer of the atoms involved at the center of the reaction. In order to have a knowledge of the intermolecular interactions, HOMO-LUMO analysis has been done and showed a reduction in the chemical hardness during the reaction. Topological analysis of the structures at the RDS confirmed that the ratio of the potential to the kinetic energy density for the O-O bond at the transition state is covalent in nature.