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(γ-benzyl- l -glutamate) (PBLG)- block -poly( l -glutamic acid) (PLGA) (PBLG- b -PLGA) at the air−water interface and the binding of α-amino acids such as tryptophan, tyrosine, and phenylalanine to the monolayer surfaces. The block polymer, PBLG- b -PLGA, was synthesized via two steps: at first the PLGA block was prepared by polymerization of γ-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 α-helix structure with above 95% helicity over the wide range of surface pressures and pHs. 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 α-amino acids enantiomerically, and the enantioselectivity depended strongly on the hydrophobicity of the side groups of the amino acids.