Characterization of low molecular-weight gelator methyl-4,6- O-( p-nitrobenzylidene)- α- d-glucopyranoside hydrogels and water diffusion in their networks

Abstract

This paper focuses on the thermal properties, the microstructure, and the molecular dynamics of water in the hydrogels (1.5, 2, 3, 4, and 5% [g mL −1]) formed by sugar-based low molecular-weight gelator methyl-4,6- O-( p-nitrobenzylidene)- α- d-glucopyranoside. The energy needed to break the non-covalent interactions such as the hydrophobic, dipole–dipole, and π–π stacking interactions responsible for the gel formation was calculated to be 43 kJ mol −1. The microstructure of the 4% [g mL −1] hydrogel shows a characteristic fibril structure of the gel network with individual gel fibers, the junction points of thicker fibers, and pores occupied by water. The single mode diffusion of water molecules inside the gel network was detected irrespective of the diffusion time Δ (8–75 ms) and hydrogel concentration. For Δ of 10 ms the water diffusion is almost free and characterized by the diffusion coefficient in the range from 2.17×10 −9 to 1.84×10 −9 m 2 s −1 for studied hydrogels. For larger Δ values, so-called restricted diffusions are observed and manifested in the linear decreases of the diffusion coefficient with diffusing time Δ, as shown for 5% gel. Only the one average proton spin-lattice relaxation time T 1 of water was determined for the studied hydrogels, irrespective of gelator concentration.