Metallo-vesicular catalysis: A mixture of vesicular cysteine/iron mediates oxidative pH switchable catalysis

The design of heme and non-heme active centers, which resemble peroxidase enzymes, has recently received a significant attention. Herein, a cysteine-metal complex was designed and encapsulated in a vesicular mixture (1:4; SDS/DTAB) in order to imitate a chloroperoxidase (CLP) enzyme via chlorination of thionine at pH 3. This artificial enzyme behaved both as a catalase and CLP at pH 3, and as a peroxidase at pH 1. The shape of the metallo-vesicular catalyst at each pH value was obtained by dynamic light scattering, and was confirmed by transmission electron microscopy (TEM). The different fluidities as interior structure property of catalyst aggregates at pH 3 and 1 were obtained by differential scanning calorimetry (DSC). IR, H-1 and C-13 NMR spectroscopies were utilized to investigate the structural properties of the vesicular catalyst. These studies demonstrated that the cysteine/iron (III) center acted as a multifunctional catalyst. In addition, the sulfur and ammonium moieties of L-Cys interacted in the presence of metal ion at pH 1. However, the ammonium side chain was replaced with the carboxylate group at pH 3. Collectively, we engineered two distinct vesicular cysteinate-Fe3+/(2+) complexes, which functioned as a pH-switchable catalyst. (C) 2016 Elsevier B.V. All rights reserved.