Percolation transition of hydration water in biosystems

Hydration water at the surface of a biomolecule may exist as an ensemble of small clusters or as a hydrogen-bonded spanning network, which homogeneously envelopes the biomolecule. The formation of this spanning water network occurs via an intrinsically rounded quasi-two-dimensional percolation transition. We propose methods to study the percolation transition of hydration water at the surface of a finite object, including the surface of a biomolecule. Application of the developed methods to the various model biosystems demonstrates the percolation transition of hydration water when the hydration level, temperature or pressure is varied. We show that the percolation transition of hydration water is closely related to the conformational transitions of hydrated biomolecules and to the qualitative changes of their dynamics. The nature of this coupling may be clarified by the analysis of the various physical properties when crossing the percolation threshold.