Intrinsic volumetric properties of trialanine isomers in aqueous solution.

The intrinsic volume and the intrinsic coefficient of thermal expansion of alanine tripeptides of different chirality are obtained from densimetric and pressure-perturbation calorimetric measurements by using the volumetric properties of water of hydration obtained from computer simulations. The aim of this study is to provide better understanding of the different contributions to the volumetric properties of peptides in solution. Water of hydration makes a major contribution to the volumetric properties measured experimentally. The intrinsic thermal expansivity of the peptides is found to be negative despite positive apparent values of thermal expansivity due to the large positive expansivity of the water of hydration, which notably exceeds the bulk value. The different volumetric behavior of the isomers is discussed in relation to their structural characteristics.