Synthesis of Hydrophobic Poly(γ-Glutamic Acid) Derivatives by Enzymatic Grafting of Partially 2-Deoxygenated Amyloses

We have previously found that a partially 2-deoxygenated (P2D)-amylose, produced by glucan phosphorylase (GP)-catalyzed enzymatic copolymerization, shows hydrophobic nature. Based on this finding, the present study demonstrates hydrophobization of a strong hydrophilic polypeptide, i.e., poly(γ-glutamic acid) (PGA), by grafting of the P2D-amylose chains via GP-catalyzed enzymatic approach. After maltooligosaccharide primers for the enzymatic reaction were modified on the PGA chain, we performed GP-catalyzed copolymerization of d-glucan with α-d-glucose 1-phosphate as comonomers in different feed ratios from the primers to produce P2D-amylose-grafted PGAs. We analyzed the structures (chemical and crystalline) of the products, precipitated from reaction mixtures, by 1H NMR and powder X-ray diffraction measurements, respectively. The values of the water contact angle of the cast films, prepared from DMSO solutions of the products with different 2-deoxyglucose/glucose unit ratios, were greater than 100°, indicating efficient hydrophobization of the hydrophilic polypeptide by the present approach.