A correlation study between hydrogen-bonded network and gelation ability of three galactose derivatives

Abstract

A correlation study between gelling/non-gelling behaviour and the presence (or absence) of a one-dimensional (1D) hydrogen-bonded network in single crystal structures of three galactose derivatives (p-methoxyphenyl-β-D-galactopyranoside (1), p-methoxyphenyl-3,4-O-isopropylidene-β-D-galactopyranoside (2) and p-methoxyphenyl-6-O-benzoyl-3,4-O-isopropylidene-β-D-galactopyranoside (3)) is attempted. Structure–property correlation studies in the literature suggest that the presence of a 1D hydrogen-bonded network promotes efficient gelation in hydrogen-bond-based gelators. Unexpectedly, saccharide 1 having a 2D hydrogen-bonded network (HBN) showed efficient gelation ability in various solvents, while saccharide 3 with a 1D HBN failed to show gelation. Failure of the latter could be due to unsuitable surface compatibility of self-assembled fibrillar networks (SAFiNs) and solvent molecules. On the other hand, saccharide 2 with a 2D HBN was found to be a non-gelator as expected. Importantly, saccharide 1, which is a simple, small and eco-friendly LMWG and can be easily prepared from cheaply available D-galactose, is an efficient gelator for 1,2-dichlorobenzene with a critical gelation concentration of only 0.25% w/v. FT-IR spectroscopy showed the involvement of intermolecular hydrogen bonding in the gelation process, and rheological experimental results confirmed its true gel behaviour. SEM and AFM studies revealed the fibrous entanglement of the molecules in the gel state.