VISIBLE-LIGHT PROMOTED PHOTOPROCESSES ON AQUEOUS GALLIC ACID IN THE PRESENCE OF RIBOFLAVIN. KINETICS AND MECHANISM

PAJARES A.; BREGLIANI M.; MONTAÑA M.P.; CRIADO S.; MASSAD W.A.; GIANOTTI J.; GUTIERREZ I.; GARCÍA N. A.

JOURNAL OF PHOTOCHEMISTRY AND PHOTOBIOLOGY A-CHEMISTRY

ELSEVIER SCIENCE SA

Año: 2010 vol. 209 p. 89 - 94

1010-6030

Within the frame of possible precursory photoreactions in the generation of humic substances, the visiblelight promoted interaction between riboflavin (Rf), a native photosensitizer in aqueous systems, and gallic acid (GA), a polyphenol naturally formed after lignin degradation, was investigated. A systematic kinetic and mechanistic studywasconducted under aerobic conditions in aqueous media, through visiblelight continuous photolysis, polarographic detection of oxygen uptake, stationary and time resolved fluorescence spectroscopy, time resolved near-IR phosphorescence detection and laser flash photolysis techniques. GA is degraded relatively fast in pH 7 aqueous solutions, where singlet molecular oxygen (O2(1Δg)), superoxide radical anion (O2•-) and hydrogen peroxide (H2O2) – all three species photogenerated from triplet excited Rf – participate in the photoprocess. The general conclusion is that in natural waters GA can undergo spontaneous phototodegradation under environmental conditions. Radical species generated in the presence of Rf can participate in condensation or polymerization reactions promoting the natural synthesis of humic products.