Non-Covalent Adducts of Sodium Poly(α,L-glutamate) with Poly(N-vinyl pyrrolidone): Methods of Preparation and Characterization of Structure

Abstract

Non-covalent adducts of poly(N-vinyl pyrrolidone) (PVP) (mol. wt. 10 K & 29 K) with sodium poly(α,L-glutamate)(PGNA) (mol. wt. 32 K) are prepared by evaporation of aqueous mixtures (EAM), ultra-centrifugation (UC) and dehydration of reverse micelles (DRM). The EAM and UC adducts contain nearly equal amounts of PVP while the DRM adduct has lower amounts. Higher-molecular-weight PVP favored greater PVP content in the adducts regardless of the method of preparation. DSC thermograms, and FT-IR and CD spectra of the three adducts in the solid state revealed that PVP and PGNA are intimately mixed and the PGNA is in a random conformation. Hydrophobic interactions between PGNA and PVP are evident in dilute aqueous solutions of all three adducts, while Na+ ions of PGNA remain as free ions. 2D-NOESY 1H NMR spectra of the EAM and UC adducts are very similar and show a strong correlation between the α-proton of PGNA with a pyrrolidone ring (no. 3 and no. 4 protons) and β-protons of PGNA with a pyrrolidone ring (no. 5 proton). In contrast, regarding the DRM adduct, only the α-proton of PGNA interacts with the pyrrolidone ring (no. 3 and no. 4 protons), presumably due to the orientation of the pyrrolidone ring at the organic phase–water interface of the reverse micelle, which causes the proton in position 5 of the ring to be buried in the organic phase. All three adducts dissociate in water to form free PVP and PGNA. However, the DRM adduct dissociates faster than other two, presumably due to reduced hydrophobic interactions. Differences in composition and properties observed for the non-covalent adducts may be attributed to the differences in intermolecular (hydrophobic) interactions imposed on the two components, PGNA and PVP, during each method of preparation.