Abstract:

The pH effect on the oxidation of (+)-catechin was investigated in B-R buffers at pH range from 1.8 to 11.5. During the potentiostatic oxidation, the dynamic UV-Vis spectra were recorded in a long-optical-path thin-layer cell. The natural chemical oxidation of (+)-catechin in alkaline media was also examined in the same cell for the purpose of comparison. The results showed that the electro-oxidation of (+)-catechin abides by transformation polymerization mechanism, in which the following polymerization steps are accelerated and the electro-oxidation steps are inhibited at higher pH. Moreover, the oxidation products of (+)-catechin vary markedly with pH values of media. In acidic media the products are catechin dimmers, whereas in alkaline media they are possible oligomers with different degrees of polymerization. Controlled by O2 concentration, the natural oxidation of (+)-catechin is slower than the electro-oxidation in the same alkaline medium but they lead to the same products.

Key words: catechin, antioxidant, spectroelectrochemistry, oxidation product, pH effect