Preparation of Water-Soluble Tocopherol Compositions Based on N-Vinylpyrrolidone Polymers and Exploration of the Molecular Exchange Process in Aqueous Solutions Using High-Resolution and Pulsed Field Gradient NMR Techniques

Abstract

Water-soluble compositions of D-α-tocopherol (TP) as an effective antioxidant obtained by its encapsulation into amphiphilic copolymer of N-vinylpyrrolidone with hexyl methacrylate and triethylene glycol dimethacrylate (VP–HMA–TEGDM) and linear polyvinylpyrrolidone (PVP) were studied by electron absorption spectroscopy, dynamic light scattering and by ¹H high-resolution and pulsed field gradient (PFG) NMR. TP absorption band was at 292 nm in the absorption spectra of TP–VP–HMA–TEGDM and TP–PVP solutions, and the TP-loaded nanoparticles in water solution had average hydrodynamic radii, R_h, values about 65 and 57 nm, and diffusion coefficient, D_t, values were 3.7 × 10^–8 and 4.3 × 10^–8 cm²/s, respectively. The investigation of the self-diffusion by PFG NMR technique in addition reveals the presence of the phases of small sizes containing TP, which are invisible in DLS measurements. The investigation of the exchange between these phases shows that the retention time of TP in large associates is longer for TP–VP–HMA–TEGDM water solution compared to TP–PVP.