| Popis: |
Water in its liquid state is known for possessing properties that run contrary to those of most liquids. These properties arise from a change in distance of the non-hydrogen bonded neighbor. The changes in distance are a result of changes in local structure from a tetrahedral structure (type-I bonding) to a collapsed tetrahedral structure (type-II bonding). The two bonding types are used as endpoints in a linear combination of structural types and is the cornerstone of the two-state representation of water, as developed by Wilse Robinson and co-workers. Experimental diffraction studies have confirmed the presence of these outer structural features and their transformation from type-I to type-II with increasing temperature or pressure. This picture leads to a molecular level description of all the anomalies of water. For example, the density maxima near 4.0°C for H2O arises because of transformations from the low density type-I bonding to the more dense, type-II bonding, in competition with normal thermal expansion. The minimum in the isothermal compressibility near 47°C (H2O) is caused by the fact that the open —• dense transformation creates a contribution to the compressibility which decreases rapidly with increasing temperature. The decrease in viscosity with increasing temperature and pressure, the prediction of hot and cold denaturation temperatures for proteins, and an explanation of the anomalous isotope effect can all be explained by this structural transformation. Presented in this work is a quantitative explanation of the anomalous properties of water based on the structural transformation as explained by the two-state representation. This explanation acts as a connecting thread which serves to unify the properties of water. |
