Investigations to explore interactions in (polyhydroxy solute + l-ascorbic acid + H2O) solutions at different temperatures: Calorimetric and viscometric approach

• The hydrophilic-hydrophilic interactions predominate at low temperatures.
• Enthalpy change for polyol is less exothermic than its parent saccharide.
• ΔdilCop,2,m values suggest structural increase in presence of l-ascorbic acid.
• Solutes act as kosmotropes in l-ascorbic acid(aq) solutions as indicated by dB/dT.

Isothermal titration micro-calorimeter has been used to measure the enthalpy change (q) of polyhydroxy solutes [(+)-d-xylose, xylitol, (+)-d-glucose, 2-deoxy-d-glucose, (+)-methyl-α-d-glucopyranoside, and (+)-maltose monohydrate] in water and in (0.05, 0.15, and 0.25) mol·kg−1l-ascorbic acid(aq) solutions at (288.15, 298.15, 308.15, and 318.15) K. Limiting enthalpies of dilution (ΔdilH°) of these solutes were calculated from heat evolved/absorbed during calorimetric experiments. Further thermodynamic quantities such as limiting enthalpies of dilution of transfer (ΔtrΔdilH°), change in heat capacity (ΔdilCop,2,m), and pair (hAB) and triplet (hABB) enthalpic interaction coefficients were also calculated and used to explore the nature of interactions of solutes with cosolute (l-ascorbic acid). The Jones-Dole viscosity B-coefficients for (+)-d-xylose, xylitol, (+)-d-galactose, galactitol, (+)-d-glucose, 2-deoxy-d-glucose, (+)-methyl-α-d-glucopyranoside, and (+)-maltose monohydrate in water and in (0.05, 0.15, 0.25, and 0.35) mol·kg−1l-ascorbic acid(aq) solutions have been determined from viscosity (η) data measured over temperature range (288.15–318.15) K and at pressure, P = 101.3 kPa. The temperature dependence of B-coefficients (dB/dT), and viscosity B-coefficients of transfer (ΔtrB) of solutes from water to cosolute have also been estimated. These parameters have been discussed in terms of structure-making (kosmotropic) or -breaking (chaotropic) behavior of solutes.

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