On the solubility of long n-alkanes in water at room temperature

Ferguson et al. [A. L. Ferguson, P. G. Debenedetti, A.Z. Panagiotopoulos, J. Phys. Chem. B 113 (2009) 6405] did not find any evidence of a water-induced chain collapse for n-alkanes smaller than n-docosane: extended conformations are thermodynamically preferred. Using a simple geometric description of the different conformations of n-eicosane, reliable values of the reversible work to create a suitable cavity in water and to switch on alkane-water van der Waals attractions have been calculated. There is no chain collapse because the gain of attractive alkane-water interactions overwhelms in magnitude the loss in configurational/translational entropy of water molecules associated with the increase in the solvent-excluded volume on passing from a spherical shape to an elongated spherocylindrical one. (C) 2011 Elsevier B. V. All rights reserved.