Dynamic Simulations of Biowater

So far there have been few in-depth MD simulations of water at the interfaces of cells. As indicated earlier, the results of general studies and Spectroscopic data suggest that much of the water in biological cells is affected by the interface. The fact that the 

SOME DIRECTIONS OF FUTURE RESEARCH IN ION-SOLVENT INTERACTIONS 

Traditionally, the interaction between particles in chemistry has been based upon empirical laws, principally on Coulomb s law. This law is also the basis of the attractive part of the potential energy used in the Schrodinger equation, but the resultant 

A quantum mechanical approach to ion-water interactions has the up side that it is the kind of development one might think of as inevitable. On the other hand, there is a fundamental difficulty that attends all quantum mechanical approaches to reactions in chemistry. It is that they concern potential energy and do not account for the entropic aspects of the situation. The importance of the latter (cf. the basic thermodynamic equation AG = AH - TAS) depends on temperature, so that at T = 0, the change in entropy in a reaction, AS, has no effect. However, in calculations of solvation at ordinary temperatures, the inaease in order brought about by the effect of the ion on the water molecules is an essential feature of the situation. Thus, a quantum mechanical approach to solvation can provide information on the energy of individual ion-water interactions (clusters in the gas phase have also been calculated), but one has to ask whether it is relevant to solution chemistry. 

Another problem in the quantal approach is that ions in solution are not stationary as pictured in the quantum mechanical calculations. Depending on the time scale considered, they can be seen as darting about or shuffling around. At any rate, they move and therefore the reorientation time of the water when an ion approaches is of vital concern and affects what is a solvation number (waters moving with the ion) and what is a coordination number (Fig. 2.23). However, the Clementi calculations concerned stationary models and cannot have much to do with dynamic solvation numbers. 

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