CHEMI-LUMINESCENCE IN THE PEROXIDATION OF TANNIC-ACID

Abstract— Peroxidation of tannins with alkaline H2O2 is accompanied by weak chemiluminescence in the spectral region 480–800 nm. o‐Di and tri‐hydroxy groups of polyphenols undergo oxidation by a free‐radical mechanism and a green intermediate anion‐radical with absorption Δmax= 600 nm is formed. The radical mechanism is supported by the low activation energy 14–20 kJ/mol and the quenching effect of radical scavengers. The reaction of the green intermediate with peroxy anions is the chemiluminescence rate limiting step. In the presence of a‐hydroxy‐methylperoxide formed from H2O2 and formaldehyde, the alkaline peroxidation of tannins is accompanied by strong red luminescence (420–800 nm). The base catalyzed decomposition of peroxides gives only a weak red emission (460–800 nm). Light intensity is enhanced in D2O by a factor 6.5. Quenchers of O2(1Δg) and 1,3‐di‐phenylisobenzofurane diminish light intensity in non‐aqueous solutions. The data suggest 1O2 participation in the observed chemiluminescence. Thermo‐chemical calculations give —ΔH values from 250–1000 kJ/mol for one elementary reaction step which limits the mechanism of chemi‐enereization. Chemiexcitation of tannins is relevant to biochemical mechanisms of aerobic degradation of aromatic compounds, energy utilization as well as to defense and resistance processes in plants. Copyright © 1979, Wiley Blackwell. All rights reserved