Catalytic activity of poly(amino-organosiloxane)s

Abstract

The poly(amino-organosiloxane)s (PAOS) form PAOS-Cu( ii) complexes. The copper catalysed oxidation of ascorbate and hydroquinone by molecular oxygen was studied in the presence of PAOS. It was found that the addition of PAOS enhances the catalytic efficiency of Cu( ii). The PAOS-Cu( ii) catalysed reaction, unlike the Cu( ii) catalysed reaction, becomes zero-order in the substrate concentration at relatively low concentration of substrate and exhibits Michaelis-Menten kinetics, which indicates the existence of a catalyst-substrate complex. This catalytic activity is similar to the poly( l-histidine)-Cu( ii) catalysed reaction described by Pecht and Levitski. The specific effect of PAOS on the Cu( ii) catalysed reactions is interpreted by the conformation of PAOS in aqueous solution, which is dependent on the flexibility and hydrophobicity of the PAOS main chain. In order to investigate the conformation of PAOS in aqueous solution, the decarboxylation of 6-nitrobenzisoxazole-3-carboxylate anion was studied, and it was found that the conformation of PAOS is easily controlled by altering the pH, the coordination to Cu( ii) ions and the hydrophobicity of PAOS.