Stereocomplex organized by chiral recognition between l- and d-enantiomers of poly(γ-alkyl glutamate) with short alkyl side chain

Stereocomplex formation based on chiral recognition was examined in racemic mixtures (PnG) of α-helical poly(γ-alkyl l-glutamate) (PnLG) and poly(γ-alkyl d-glutamate) (PnDG), where n, the carbon number of the side-chain alkyl groups, was varied from 1 to 6. When enantiomorphic solutions of PnG with relatively short side chains of n = 1-3 were mixed in DMF, precipitation occurred as fine fibrils with an equimolar content of PnLG and PnDG, demonstrating the formation of a stereocomplex of l and d molecules. The precipitates included 10-12 vol% of DMF solvent and possessed tetragonal packing structure of α-helices. The tetragonal packing symmetry, which is unusual in the α-helical polypeptide system, was considered to be produced by “knobs-into-holes” packing of side chains between l and d helices regularly arrayed in a lattice.