NMR Study of Poly(γ-Glutamic Acid) and Partially Benzylated Poly(γ-Glutamic Acid): Nanoparticles in Solution

Poly(gamma-glutamic acid) (gamma-PGA) and its partially benzylamidated (hydrophobized) derivatives were prepared and studied in solution by means of dynamic light scattering (DLS), I D, 2D and PGSE NMR in order to determine the structure, size and aggregation in solution. By pH potentiometric titrations in aqueous solution the apparent pK approximate to 4 of gamma-PGA was determined. The measured diffusion coefficients as a function of pH showed the swelling of gamma-PGA by deprotonation of carboxyls. DLS measurements showed a certain degree of aggregation even in dilute solution. The degree of aggregation is increased in the presence H2PO4- and H2PO42- buffer anions. Benzylamidation of 30-50% of caboxylates resulted in folded structure of the BzPGA, probably spherical like nanoparticles, verified by NMR diffusiometry and 2D NOE spectroscopy.