Photodegradative changes in chemical structures of silk studied by pyrolysis-gas chromatography with sulfur chemiluminescence detection

A novel approach to trace photodegradation processes of silk was developed by means of pyrolysis-gas chromatography (Py-GC) with sulfur chemiluminesce nce detection (Py-GC/SCD). A series of photodegraded silk fabric samples pr epared by exposure to artificial sunlight were investigated in this work. V arious sulfur-containing amino acid related compounds such as H2S, COS, CH3 SH, CH3SCH3, CS2 and CH2=CHSCH3 were detected on the pyrograms of samples, a weighing about 200 mu g, pyrolyzed at 600 degrees C under the flow of He carrier gas and separated using temperature programmed fused silica capilla ry column followed by selective SCD. The yields of the characteristic produ cts proved to decrease as a function of irradiation time. This change was q uantitatively evaluated by use of three calibration curves prepared for met hionine (Met), cysteine (Cys) and cystine (Cys-Cys) residues where aliquot amounts of four different kinds of protein enzyme solutions with known resi due distributions were used as standard reference materials, and CH3SH, H2S and CS2 were used as the key components for Met, Cys and Cys-Cys residues in protein, respectively. Thus obtained results revealed that among three d ifferent sulfur-containing residues in silk fibroin, the S-S bonds in Cys-C ys residues were cleaved preferentially at the very initial stage and that Met residues in silk were slightly stabler than Cys residues. (C) 2000 Else vier Science Ltd. All rights reserved.