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 (Delta H-dil degrees) and Jones-Dole viscosity B-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 (q) and viscosity (eta) data at T = 288.15-318.15 K and pressure p = 0.1 MPa. The corresponding transfer parameters (Delta(tr)Delta H-dil degrees, Delta B-tr), change in heat capacity (Delta C-dil degrees(p,2,m)), and enthalpic (h(AB) and h(ABB)) and viscometric (eta(AB) and eta(ABB)) pair and triplet interaction coefficients have also been derived. The dB/dT 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.(17) 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 m(B) = 0.15 mol.kg(-1) and T = 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.