Single-ion enthalpies and entropies of transfer from water to aqueous urea solutions at 298.15 K

Abstract

In this paper we report enthalpies of solution at infinite dilution [Formula: see text] at 298.15 K for tetraphenylarsonium chloride (Ph4AsCl), sodium tetraphenylborate (NaBPh4), sodium chloride (NaCl), sodium bromide (NaBr), and sodium iodide (NaI) in water and aqueous solutions containing 5, 10, 20, and 30% urea by weight. Enthalpies of transfer from water to aqueous urea solutions are reported. Single-ion enthalpies of transfer [Formula: see text] have been calculated using the tetraphenylarsonium tetraphenylborate, (TATB) reference electrolyte assumption. These single-ion enthalpy data have been combined with single-ion Gibbs functions of transfer [Formula: see text] reported in the literature to obtain single-ion entropies of transfer [Formula: see text] for the urea + water mixed solvent system. The results of this single-ion analysis are discussed in terms of the impact of electrolytes on the structure of aqueous urea solutions.

Enthalpies and Entropies of Transfer of Electrolytes and Ions from Water to Mixed Aqueous Organic Solvents

“…An alternative route suggested by Hakin and Beswick 289 is to combine ∆ t H°(ion) values with ∆ t G°values calculated from the solubility products reported by Talukdar et al 194 This is preferred since the solubility products are inherently more precise than their temperature coefficients. Thus, the values reported in Table 55 are taken from the work of Hakin and Beswick 289 or calculated from them using data in Table 53. With the exception of the values for Pi -, the ∆ t S°(ion) values seem reasonable.…”

Thermodynamics of Micellization of β-Sheet Forming Poly(acrylic acid)-block-poly(l-valine) Hybrids

“…It can be thought that this negative enthalpy came from the remaining β sheet that cannot be completely removed by urea (approx 30% for all three polymers) and also from the random hydrogen bonds within the core. Another possible contribution to this negative ∆H 0 m was the enthalpy of transfer of ionic or hydrophilic groups from water to aqueous urea solution, which was exothermic as reported by Hakin et al 39 It can be seen that the ∆H 0 urea of PAA 40 -PLVAL 100 was still the most negative of the three polymers, which indicated a higher average strength of hydrogen bonds in this system (since the three polymers were observed to have the same β-sheet content). It can be hypothesized that the extreme hydrophobicity of this polymer enhanced the association of PLVAL segments compared to the other two systems.…”