Preferential solvation of carbohydrates in water–trifluoroethanol mixtures: a solvent detected heteronuclear NMR approach

Abstract

The present study aims to establish a simple approach involving multi-field multinuclear longitudinal relaxation (R₁) analysis of the solvents to decipher solute–solvent interactions during the solvation of model carbohydrates in aqueous trifluoroethanol (TFE) co-solvent systems (TFE:D₂O). The behavior of D₂O and TFE is monitored around β-CD (β-cyclodextrin) and glucose through R_1D (²H) and R_1F (¹⁹F), respectively. Correlation times (τ_c) are estimated for D₂O and TFE for various % (v/v) compositions of TFE:D₂O mixtures. The differential trends of the R₁ or τ_c ratio for D₂O and TFE (in the presence and absence of carbohydrates) revealed that both β-CD and glucose undergo selective solvation by TFE in comparison to D₂O. Owing to its encapsulation properties, β-CD exhibited a comparatively higher tendency to undergo solvation by TFE than glucose. The maximum transfer of solute bound water to bulk solvent appears in the 20–30% (v/v) TFE range. The current approach emerges as being straightforward in contrast to traditional methods that primarily focus on solute behavior to unravel the preferential solvation dynamics.