Incollection,
A Physical Mechanism Underlying the Increase of Aqueous Solubility of Nonpolar Compounds and the Denaturation of Proteins upon Cooling
Abstract Book of the XXIII IUPAP International Conference on Statistical Physics, Genova, Italy, (9-13 July 2007)
Abstract
The increase of aqueous solubility of nonpolar compounds upon cooling
and the cold denaturation of proteins are established experimental
facts. Both phenomena have been hypothesized to be related to
restructuring of the hydrogen bond network of water around small
nonpolar solutes or hydrophobic amino acid side chains. However, an
underlying physical mechanism has yet to be identified. We assume
the solute particles and the monomers of a polymer interact via a hard
sphere potential. We further assume that the solvent molecules
interact via the two-scale spherically symmetric Jagla potential,
which qualitatively reproduces the anomalies of water, such as
expansion on cooling. We find that this model correctly predicts the
increase in solubility of nonpolar compounds and the swelling of
polymers on cooling. Our findings are consistent with the possibility
that the presence of two length scales in the Jagla potential---a rigid hard
core and a more flexible soft core---is responsible for both
phenomena. At low temperatures, the solvent particles prefer to
remain at the soft core distance, leaving enough space for small
nonpolar solutes to enter the solvent thus increasing solubility. We
support this hypothesized mechanism by molecular dynamic simulations.
For details see http://lanl.arxiv.org/abs/cond-mat/0701485
