A NEW FLUORESCENT PHOTOPRODUCT OF TRYPTOPHAN EVIDENCED BY LONG WAVELENGTH EXCITATION OF FLUORESCENCE

Abstract— Besides the normal tryptophan (Trp) fluorescence in aqueous solution (emission maximum at 350 nm), a new emission, peaking around 380 nm, appears by long wavelength excitation. Its fluorescence yield (φ s 0.24) is higher than that of tryptophan (φ Trp = 0.13). The growth of this emission is observed under different experimental conditions, mainly under UV anaerobic irradiation. To explain this observation, the formation of a C 3 ‐hydroxylated derivative is tentatively suggested.