Polymer Photochemistry 3 (1983) 421-434 The Photochemistry o| Tyrosine and Tyrosine Derivatives in Solid Polymer Films Richard Sakurovs, C. H. Nicholls and M. T. Pailthorpe School of Textile Technology, University of New South Wales, PO Box 1, Kensington, New South Wales 2033, Australia (Received: 13 August, 1982) ABSTRACT A study of the photochemistry of tyrosine and its derivatives in poly(vinyl alcohol) and methyl cellulose films found no evidence for photoejection of electrons, dimerisation or DOPA production, reac- tions known to occur in aqueous solution. The fluorescence quantum yields of tyrosine and derivatives were found to be within the range 0-17 + 0.02, implying that the charge transfer quenching mechanisms of tyrosine fluorescence postulated to occur in aqueous solution does not occur in solid films. Tyrosine derivatives could be classified into three groups by their photochemical behaviour: (1) tyrosine and tyramine degraded without generating absorption at wavelengths above 260 nm; (2) the C-substituted derivatives deaminated to form p-coumaryl derivatives; and (3) the N-substituted derivatives de- graded with phenol ring breakdown to produce labile products which had maximum UV absorbances near 280 nm. INTRODUCTION Tryptophan, tyrosine and cystine are the amino acid residues thought to be most responsible for the degradation and yellowing of proteins exposed to UV light. 1"2 Although tryptophan has been shown to contribute to the UV-initiated yellowing of proteins such as wool and silk 3 and its photochemistry has been well-investigated, *-7 the role of 421