Understanding the interactions of polyhydroxy solutes with ammonium salts in aqueous solutions via calorimetric and spectroscopic studies at different temperatures

Enthalpy change, q of polyhydroxy solutes; (+)-o-xylose, xylitol, (-)-L-sorbose, D-sorbitol, (+)-D-glucose, and (+)-D-maltose monohydrate have been measured in water and in aqueous (0.10, 0.15, 0.25, and 0.35) mol.kg(-1) ammonium bromide (NH4Br) and (0.15, 0.25, and 035) mol.kg(-1) tetraethylammonium bromide (Et4NBr) solutions at T = (288.15, 298.15, 308.15, and 318.15) K by using isothermal titration microcalorimeter. From the data q, the limiting standard enthalpies of dilution (Delta H-dil degrees) and their corresponding transfer parameters (Delta(t)Delta H-dil degrees) have been evaluated. The enthalpic interaction coefficients that characterize the interactions of polyhydroxy solutes with ammonium salts in aqueous solutions were determined from Delta(t)Delta H-dil degrees values. Proton (H-1) NMR spectra were recorded for ms = (0.15, 025 and 035) mol.kg(-1) tetraethylammonium bromide solutions and in ternary solutions {polyhydroxy solute + Et4NBr + 9:1 (w/w) H2O + D(2)0}, where the molality of solute has been fixed as m(A) = 025 mol.kg(-1). The comparison of NMR results shows more upfield shift in ternary solutions than in pure alkyl ammonium salt solution, thereby suggesting the predominance of hydrophobic-ionic interactions over hydrophilic-ionic interactions. (C) 2017 Published by Elsevier B.V.