Temperature-dependent femtosecond-resolved hydration dynamics of water in aqueous guanidinium hydrochloride solution.

The influence of ion dissolution in water is still controversial. The challenge posed to the existing concept of dissolved ions acting as water structure makers and structure breakers through recent studies calls for more experimental evidence. The temperature-dependent relaxation dynamics of water in bulk and in ionic salt solutions can give an idea about the hydrogen-bonded network and hence the perturbation induced in the tetrahedral structure of bulk water subsequent to ion dissolution. In our study, the temperature dependence of the observed relaxation dynamics in bulk water and guanidinium hydrochloride reveals the activation energy needed to convert water from hydrogen bonded to the free forms and hence the difference in the hydrogen-bonded network in the close vicinity of the probe molecule. The results might prove helpful to understand the interaction of hydrophobic amino acid residues with guanidinium hydrochloride during protein denaturation.