INCORPORATION OF DIACIDS INTO THE POLYGLYCINE-II STRUCTURE - MODEL STUDIES

Aliphatic diacids are often incorporated into polypeptide structures i n order to obtain model compounds for hormones, protein turns, etc. Th ey are also fundamental components of many commercial polyamides. On t he other hand glycine, the simplest amino acid, shows unique conformat ional features. In order to better understand the structure of such co mpounds, we have synthetized and determined the molecular structure of three models represented by the general formula -CH2-NH-CO-(CH2)(n-2) -CO-NH-CH2-CO-NH-CH2-CH2-CH3, with n = 3, 4, or 6. Conformational diff erences have been found in the dicarboxylic moiety, whereas glycine al ways has the polyglycine II conformation. The -CO-(CH2)(n-2)-CO- segme nt adapts a folded conformation: SS, TGT, and <S(G)over bar TG(S)over bar> for n = 3, 4, and 6, respectively. Molecular packing is always ps eudohexagonal and a network of hydrogen bonds oriented in three direct ions at 120 degrees is formed. The results are of interest in order to provide information about polyamides in which glycine residues are in corporated. Our results confirm the tendency of glycine residues to ad opt the polyglycine II conformation in its copolymers with aliphatic c ompounds. (C) 1995 John Wiley & Sons, Inc.