Two dynamical crossovers in protein hydration water revealed by the NMR spin-spin relaxation time

Hydration water is essential in determining the optimal conditions for the development of the biological activity of biological systems. Indeed the physical properties of hydration water are responsible for and determine the region of biological stability of proteins. By means of Nuclear Magnetic Resonance, we probe some thermodynamical properties of the first hydration shell of lysozyme from 200K to 360 K. In particular, we study the thermal behavior of the nuclear magnetization and of the apparent spin-spin relaxation time (T∗2 ). We find the existence of two thermal borders with two corresponding evident crossovers at low and high temperatures signaling the thresholds of the native state of lysozyme and therefore of its functionality.