ISSN:
1572-8927
Keywords:
Aqueous nonelectrolyte solutions
;
hydrophobic hydration
;
Isotope effects
;
thermodynamics
;
water
;
water-d2
Source:
Springer Online Journal Archives 1860-2000
Topics:
Chemistry and Pharmacology
Notes:
Abstract A recently introduced modified hydration shell hydrogen bond model for rationalizing the thermodynamic consequences of hydrophobic hydration is adapted for use with heavy water. The required adjustment of parameters employs the assumption that breaking hydrogen bonds in water-d2 involves a greater enthalpy change and a larger entropy increase than bond breaking in ordinary water. It also makes some use of information derived from studies of gas solubilities in the two solvents, although a review of the data leads to serious questions about the reliability of results obtained in this way. The model permits calculations of hydrogen bonding contributions to the changes, ΔG t o , ΔH t o , ΔS t o , and ΔC p,t o , for transfer of nonpolar solutes from water to water-d2 and implies that such data should show regular trends. Although some of the numerical results depend strongly on the values chosen for the parameters, the pattern defined by these trends is nearly independent of parameters. Predicted values of ΔC p,t o are large and positive for all nonpolar solutes, while ΔS t o is expected to be negative near 0°C, becoming progressively less negative on warming and eventually positive. Both of these quantities should be proportional to the molecular surface area of the solute. Analogous predictions regarding ΔG t o and ΔH t o can also be made, but only if it is permissible to neglect possible contributions to these quantities from van der Waals interactions.
Type of Medium:
Electronic Resource
URL:
http://dx.doi.org/10.1007/BF00650715
Permalink
