Thermal properties and hydration structure of poly-l-lysine, polyglycine, and lysozyme

Abstract

Differential scanning calorimetry (DSC) and X-ray diffraction (XRD) measurements of hydrated poly-l-lysine, polyglycine and lysozyme at hydration levels (mass of water/mass of peptide and protein)=0.30–0.82, 0.27–0.49, and 0.30–0.81, respectively, were performed in the temperature range of 180–298K. The DSC data showed that the interfacial hydration water of the polypeptides and the protein is not frozen even at 180K. The X-ray radial distribution functions revealed that with decreasing temperature the interactions of the polypeptides and the protein with hydration water molecules gradually become remarkable, resulting in the development of the structure of their hydration water. The structure change of the hydration water with lowering temperature is monotonous and could not be the origin of dynamic transition (glass transition and fragile-to-strong crossover) for hydrated proteins as previously observed by neutron scattering.