Molecular Interactions of Saccharides and Their Derivatives with Thiamine HCl and Pyridoxine HCl Vitamins in Aqueous Solutions: Calorimetric, Viscometric, and NMR Spectroscopic Studies

Limiting standard enthalpies of dilution (Δ_dil<i>H</i>°) and Jones–Dole viscosity <i>B</i>-coefficients of various polyhydroxy solutes, viz., saccharides, their methyl and deoxy derivatives, and sugar alcohol in 0.05, 0.15, 0.25, and 0.35 mol·kg^–1 thiamine HCl_(aq) and pyridoxine HCl_(aq) solutions have been determined from heat change (<i>q</i>) and viscosity (η) data at <i>T</i> = 288.15–318.15 K and pressure <i>p</i> = 0.1 MPa. The corresponding transfer parameters (Δ_trΔ_dil<i>H</i>°, Δ_tr<i>B</i>), change in heat capacity (Δ_dil<i>C</i>°_{<i>p</i>,2,<i>m</i>}), and enthalpic (<i>h</i>_AB and <i>h</i>_ABB) and viscometric (η_AB and η_ABB) pair and triplet interaction coefficients have also been derived. The d<i>B</i>/d<i>T</i> coefficients have been calculated and discussed in terms of the kosmotropic or chaotropic nature of solutes in aqueous solutions of vitamins. The present results have also been compared with previously reported studies carried out in l-ascorbic acid. Further, NMR spectroscopy has been employed to understand the nature of interactions occurring in ternary solution {polyhydroxy solute + vitamins + 9:1 (w/w) H₂O–D₂O} at molality <i>m</i>_B = 0.15 mol·kg^–1 and <i>T</i> = 300.15 K. The results have been explained in terms of contributions due to hydrophilic–hydrophilic/hydrophobic interactions and H-bonding between solute–solute/cosolute molecules. The effect of stereochemistry and molecular conformations of both polyhydroxy solutes and cosolutes (vitamins) have also been discussed