[Water: nanostructure and fluctuations]

Recently a model of local organization of water was experimentally justified, in which tetrahedrally coordinated water clusters of 1-2 nanometers arise and disappear in liquid composed of H2O molecules with partially broken hydrogen bonds [1, 2]. Here we show that the clusters can oscillate between two structural forms, of which one is common hexagonal ice Ih whereas another is formed of the modules participating in formation of hydration shells of biomolecules. It is suggested that such self-oscillations are responsible for observable fluctuations of various physical and chemical parameters of water.