ELECTRONIC-STRUCTURES AND SPECTRA OF 2 ANTIOXIDANTS - URIC-ACID AND ASCORBIC-ACID

Electronic absorption and fluorescence spectra of aqueous solutions of two well known antioxidants, uric acid and ascorbic acid (vitamin C), have been studied at different pH. The observed spectra have been int erpreted in terms of neutral and anionic forms of the molecules with t he help of molecular orbital calculations. The N-3 Site of uric acid h as been shown to be the most acidic. Fluorescence of uric acid seems t o originate from an anion of the molecule in a wide pH range. Around p H 3, both the neutral and anionic forms of ascorbic acid appear to be present in aqueous solutions. In aqueous media, ascorbic acid appears to get converted easily to its dehydro form and this conversion does n ot seem to be reversible. An anion of dehydroascorbic acid seems to be formed on heating dehydroascorbic acid in aqueous solutions.