Pyrolysis of poly-glycine and poly-L-alanine: analysis of less-volatile products by gas chromatography/Fourier transform infrared spectroscopy/mass spectrometry

Pyrolysis of poly-glycine and poly-L-alanine at 500 degrees C under nitroge n atmosphere gives rise to volatile low-molecular-mass decomposition produc ts, as well as to less-volatile compounds which have been analyzed by the c oupled technique of gas chromatography/Fourier transform infrared spectrosc opy/mass spectrometry. All identified products are nitrogen compounds, 5-me mbered mono-N-heterocycles bring the most frequently encountered ones. In t he case of poly-glycine, we found acetamide, a dimethyl 2-pyrrolidinone, N- methyl succinimide, piperazine-2,5-dione derived from glycine, and barbitur ic acid. In the case of poly-L-alanine pyrolysis, the compounds identified were N-methyl, 2,3,5-trimethyl, 2-ethyl-4-methyl and 3-ethyl-2,5-dimethyl p yrrole, 4-methyl and 2,6-dimethyl pyridine, propanamide, a trimethyl 2-pyrr olidinone, 3-ethyl-5-methylhydantoin, and piperazine-2,5-dione derived from alanine. The formation of piperazine-2,5-diones (diketopiperazines) is one of the major pyrolytic pathways. (C) 2000 Elsevier Science B.V. All rights reserved.