NMR Study of Poly(γ-Glutamic Acid) Hydrogels Prepared by γ-Irradiation : Characterization of Bond Formation and Scission

Hydrogels were prepared from poly(γ-glutamic acid) (PGA) solution by γ-irradiation of 90 kGy and 170 kGy. The hydrogels were more cross-linked with a higher dosage γ-irradiation and completely hydrolyzed at 85 oC within 4 hours resulting in homogeneous solution. NMR techniques were employed to clarify chemical bond formation and scission involved during γ-irradiation and hydrolysis. Characterization of these samples was carried out by taking both liquid state and solid state NMR spectra of PGA and hydrolyzed hydrogels and comparison of these spectra with the solid state NMR spectra of hydrogels. Our results indicate that complicated chemical bond formation and scission have occurred during hydrolysis and γ-irradiation. The samples prepared with higher dosage of γ irradiation showed more diverse chemical bond formation and scission.