Water content thresholds in glycerol/water system: Low- and high-wavenumber Raman spectroscopy study

Abstract

Water structure is the key in such diverse processes as protein folding, catalysis of chemical reactions, and stability of pharmaceuticals and biopharmaceuticals. In the current investigation, glycerol-water mixtures are studied by low- and high-wavenumber Raman spectroscopy. Three water content regions, which are separated by two water content thresholds (WT), WT1 at 6.1 ± 0.7 wt% water and WT2 at 18.6 ± 4.4 wt% water, are identified, based on the trends in the hydrogen bond strength and the cage effect. It is hypothesized that WT1 corresponds to a transition from predominantly unclustered water molecules to small water clusters, and is associated with facilitation of proton transfer as water content exceeds WT1. The WT2 is proposed to mark formation of large (>100 molecules) water clusters, which can form stable nucleus of hexagonal ice at lower temperatures. These findings, if confirmed for other polyhydroxycompounds, could facilitate development of novel pharmaceuticals and vaccines, and also contribute to fundamental understanding of mechanisms of cryo- and lyo-protection of proteins, viruses, and cells.