Conformational studies of multichain copoly(α-amino acids)s in solution

The conformational transition of multichain copoly(-amino acid)s consisting of copoly(-methyl-L-glutamyl-L-lysine) as backbone molecule and poly(-benzyl-L-glutamate) as branch molecules was studied in chloroform and DCA mixtures. The helix stability of backbone molecule is strongly affected by the length of branch molecules. In the case of the multichain copolymer having short branch molecular chains, i.e.,DP_br<10, the helix conformation of the backbone molecule is strictly affected by some interferences among the randomly coiled molecular chains. In the case of water-soluble multichain copolymer having poly(L-glutamic acid) or poly(L-lysine) as branch molecules, the transitional process from coil to helix is observed by depressing hydrostatic repulsion among the ionized side chain of branch molecules. However, such conformational transition is depressed to a considerable extent by interferences among the branch molecules.Abbreviations used (shown alphabetically) A/I molar ratio of NCA to initiator - Cbz carbobenzyloxy - DCA dichloroacetic acid - DMF N,N-dimethylformamide - DP_br number-average degree of polymerization of branches of multichain copolymer - Fw_br weight fraction of-benzyl-L-glutamyl residues of multichain copolymer - Mn number-average molecular weight - NCA N-carboxy anhydride of-amino acid - ORD optical rotatory dispersion