Solvation Thermodynamics of Water in Nonpolar Organic Solvents Indicate the Occurrence of Nontraditional Hydrogen Bonds

A review about nothing: are apolar cavities in proteins really empty?

Cavities within proteins that are strictly apolar typically appear to be empty. It has been suggested, however, that water molecules may be present within such cavities but are too disordered to be seen in conventional crystallographic analyses. In contrast, it is argued here that solvent mobility will be limited by the size of the cavity and for this reason high-occupancy solvent in cavities of typical volume should be readily detectable using X-ray crystallography. Recent experimental studies of cavity hydration are reviewed. Such studies are consistent with theoretical predictions that it is energetically unfavorable to have a single water molecule in an apolar cavity. As apolar cavities become larger, a point is reached where it is favorable to have the cavity occupied by a cluster of mutually H-bonded water molecules. The exact size of such a cavity in a protein is yet to be verified.

Water solubility in linear fluoroalkanes used in blood substitute formulations

The interactions between water and n-perfluoroalkanes or substituted alpha-(omega-)fluoroalkanes used in blood substitute formulations were investigated experimentally and using ab initio calculations. The solubility of water in C(6)-C(9) perfluoroalkanes and five C(8) analogues of substituted fluoroalkanes was measured in the temperature range between 288 and 318 K at atmospheric pressure, using a Karl Fischer coulometer. From these data, the thermodynamic functions and partial molar solvation quantities such as Gibbs energy, enthalpy, and entropy were determined and compared with the interaction energies in 1:1 water-fluoroalkane complexes in vacuum, obtained using B3LYP/6-311++G(d,p). The experimental solubility data indicates a significant specific interaction between the water and the alpha-(omega-)substitute atom (H, I, Br, or Cl) in the fluoroalkanes.