Helical superstructures from a poly(γ-benzyl-L-glutamate)-poly(L-glutamic acid) amphiphilic diblock copolymer:: Monolayer formation on water and its specific binding of amino acids

This study examines the monolayer properties of a novel amphiphilic diblock polymer of poly(gamma-benzyl-L-glutamate) (PBLG)-block-poly(L-glutamic acid) (PLGA) (PBLG-b-PLGA) at the air-water interface and the binding of alpha-amino acids such as tryptophan, tyrosine, and phenylalanine to the monolayer surfaces. The block polymer, PBLG-6-PLGA, was synthesized via two steps: at first the PLGA block was prepared by polymerization of gamma-benzyl-L-glutamate-N-carboxylic anhydride (BLG-NCA) with propylamine and then by removal of benzyl group, and subsequently the polymerization of BLG-NCA initiated with the amino group at the chain end of the PLGA was performed and gave a final product. PBLG-b-PLGA formed stable monolayers, in which the PLGA segment took an alpha-helix structure with above 95% helicity over the wide range of surface pressures and pi-Is. The helix orientaion was in almost perpendicular to the surface, being variable slightly by changing the surface pressure. These helix assemblies were found to have the ability to capture D-isomers of alpha-amino acids enantiomerically, and the enantioselectivity depended strongly on the hydrophobicity of the side groups of the amino acids.