Electronic spectra and structures of some biologically important xanthines

摘要: Abstract Electronic absorption and fluorescence spectra of aqueous solutions xanthine, caffeine, theophylline theobromine have been studied at different pH. The observed interpreted in terms neutral ionic forms the molecules with help molecular orbital calculations. At acidic pH, can be assigned to corresponding most stable forms, exception that xanthine pH appears originate from lowest singlet excited state a cation molecule. alkaline exist mainly as their monoanions. In originates anion. However, caffeine theobromine, even belongs species. On whole, properties are quite those methyl xanthines.