COPOLYMERIZATION OF SARCOSINE-NCA AND L-LEUCINE-NCA OR L-PHENYLALANINE-NCA

Copolymerizations of sarcosine-NCA (Sar-NCA) with leucine-NCA (Leu-NCA) or phenylalanine NCA (Phe-NCA) were conducted under five different reaction conditions. Benzylamine, triethylamine, pyridine and sodium methoxide (NaOMe) were used as initiators. Molar compositions of the resulting copolypeptides were determined by H-1 or C-13 NMR spectroscopy and reactivity ratios were calculated from copolymerizations stopped at low conversions. Sequence analyses of copolypeptides isolated at high conversions were conducted by means of C-13 or N-15 NMR spectroscopy. Blocky sequences were found due to a higher reactivity of Sar-NCA under all reaction conditions. The secondary structure of the solid copolypeptides was characterized by C-13 NMR CP/MAS spectroscopy and WAXS powder patterns. The secondary structures are kinetically controlled and change into thermodynamically stable ones upon reprecipitation.