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 °C under nitrogen atmosphere gives rise to volatile low-molecular-mass decomposition products, as well as to less-volatile compounds which have been analyzed by the coupled technique of gas chromatography/Fourier transform infrared spectroscopy/mass spectrometry. All identified products are nitrogen compounds, 5-membered mono-N-heterocycles being the most frequently encountered ones. In the case of poly-glycine, we found acetamide, a dimethyl 2-pyrrolidinone, N-methyl succinimide, piperazine-2,5-dione derived from glycine, and barbituric 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 pyrrole, 4-methyl and 2,6-dimethyl pyridine, propanamide, a trimethyl 2-pyrrolidinone, 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.