Computational Study of Proline - Water Cluster

Our present results have clearly shown that the water molecule interacting with proline may profoundly affect the relative energies of proline, providing an excellent example of the influence of microsolvation on biomolecules. We hope that the present work would stimulate experimental studies on this interesting system. The effects of solvation on amino acids may be easily appreciated when it is noted that the canonical forms are much more stable in the gas phase, while the zwitterionic (that is, charge-separated) forms are only observed in the aqueous solution phase. One very interesting question concerned is: How many water molecules are needed to stabilize the zwitterionic conformers? Although the PCM type methods were able to elucidate some features of the property of amino acid in aqueous solution phase (for example, the relative stability of the neutral and the zwitterion amino acid in the solution phase), other more important physicochemical properties depend on the nature of the solute - solvent interactions on the molecular level. One example is the solvent-mediated chemical reaction, and in this case the cluster model would be much more helpful. In this latter approach, the solvent molecules are treated by quantum chemical methods explicitly as molecules, and one examines the effects of 'microsolvation' as a function of the number of solvent molecules by analyzing the detailed interactions between the solute and the solvent molecule(s) affecting the structure and reaction of the solute