Temperature-dependent thermodynamic and physicochemical studies of glycols in aqueous biotin solutions

Abstract

The current study deals with the analysis of the molecular interactions among the glycols (propylene glycol, PG and hexylene glycol, HG) molecules in (0.000, 0.001, 0.002 and 0.003) mol·Kg-1 aqueous solutions of biotin at constant experimental pressure 0.1 MPa and temperature range (288.15 K, 298.15 K, 308.15 K and 318.15 K). The speed of sound and the density for the liquid mixtures is measured with Anton Paar DSA 5000 M. Numerous thermodynamic and acoustic parameters are determined using these experimental data. The apparent molar volume (Vϕ), partial molar volume (Vϕ0), partial molar volume of transfer (ΔVϕ0), apparent molar isentropic compression (Kϕ,S), partial molar isentropic compression (Kϕ,S0), partial molar isentropic compression of transfer (ΔKϕ,S0) were estimated using the experimentally obtained density and speed of sound respectively along with the partial molar expansibility(Eϕ0), its first-order derivative ∂Eϕ0/∂TP and pair-triplet interaction coefficients (VAB,KAB,VABB; KABB). The apparent molar properties recommend the existence of strong (solute and solvent) interactions in the ternary mixture which is also justified by the positive partial molar expansibility values, while the partial molar properties suggest the formation of the hydrogen bond in the mixture. With Passynski's equation the hydration number (nh) for PG/HG in aqueous solutions of biotin is calculated utilizing the compressibility data and the obtained results are explained in terms of combined hydration effects and hydrophobic effect.