Interfacial Water Compartments on Tendon/Collagen and in Cells

Bulk water exists in three phase states: crystalline solid, liquid and vapor. Phase transitions between these states are brought about by changes in the physical environment such as temperature and pressure. Each phase of water is characterized by differences in translational and rotational motion of the water molecule. For example, water molecules in ice move one million times slower than in the liquid state. Does this adequately describe behavior of water at the multitude of surfaces in the cell? A molecular model of four water of hydration subcompartments on tendon/collagen, on globular proteins and in a cell is presented. Each subcompartment is defined in terms of compartmental protein hydration capacities, compartmental water motional restrictions and related descriptors. The range of water molecule motional activity in biological systems are described by correlation times that range from that of ice at 10-6 s to bulk water at 10-12 s. The existence and size of water subcompartments with intermediate motional and other properties has been measured by proton NMR titration, differential scanning calorimetry, centrifugal dehydration force flow rate, isotherm rehydration and osmotic behavior. In addition sub-compartment capacities can be predicted by molecular modeling. The molecular model of water subcompartments first developed for tendon/collagen appears generally applicable for globular proteins and for human erythrocytes. However, changes in protein conformation and aggregation cause changes in the size of the outer-most sub-compartments. Such changes bring about changes in the physical and physiological properties of cellular water. This growing awareness of the role of water subcompartments in explaining cellular activities is predicted to have a revolutionary effect on cell biology.