Time-dependent heat capacity of aqueous solutions of biomolecules

Abstract

We present heat capacity (C _p) and thermal conductivity measurements on water-lysozyme solution in the water-rich region versus both time and protein concentration. The aim is to prove the occurrence of structural rearrangements vs. time in water-lysozyme solutions already observed in the high-concentration region (10 + 15 wt%) using different techniques. — The observed increase of heat capacity in time occurs independently of the lysozyme concentration and the pH value of the solvent. The characteristic time to reach equilibrium can change from a few minutes to hours, and it seems to be independent of pH values of the solution. Evolution of a spatial order of lysozyme in water and/or of water molecules interacting with the protein is considered as a possible explanation for the observed phenomenon, which is absent when the solute ris an amino acid (alanine, glycine, etc.). — The thermal conductivity of these solutions does not show the time dependence observed for the heat capacity.