| The photochemistry of several model plant derived compounds has been studied in aqueous solution. The purpose of this study was to investigate the reactions of catechin as a model tannin and methoxy-substituted hydroxybenzyl alcohols as model lignins. Tannins and lignins constitute a significant portion of the humic substances in aquatic systems, which are themselves the main component of dissolved organic matter thought to be responsible for the absorption and attenuation of light in these environments. Using photochemical product studies, UV-Vis spectroscopy, fluorescence spectroscopy, and laser flash photolysis, these compounds were investigated to determine if they exhibit light attenuating functions, and if they did, to elucidate their possible mechanisms.; Catechin was found to undergo an efficient reversible photoisomerization reaction. Such a reaction is an explicit example of a photon absorbing process that enables catechin and its derivatives to act as natural sunscreens by attenuating light energy through non-destructive reactions. Catechin was also found to generate phenoxyl radicals that are thought to play a role in the apparent antioxidant abilities of these compounds, the reactions of which are of both environmental and medicinal significance.; The methoxy-substituted hydroxybenzyl alcohols were found to undergo photosolvolysis reactions in the presence of nucleophiles via efficient generation of quinone methide intermediates. The resulting quinone methides were observed to be longer lived, and thus more stable, than their previously studied non-methoxylated derivatives. In particular, the para quinone methide was found to have a lifetime in 1:1 CH3CN/H2O of 110 minutes. The meta substituted hydroxybenzhydrol was found to undergo additional chemistry leading to the production of a ring-closed fluorene via the quinone methide intermediate. These reactions are examples of how such compounds photoreact in aqueous environments. |
