We have completed our gas phase work on NAD analogs. Currently we are exploring the effects of specific solvation by water on the reactions and stabilities of oxocarbenium ions. Of particular note are the following findings: The stability of the diol anion of NAD+ is related to specific solvation of the 2' alkoxy; without solvation, computed enthalpies of reacition fail to correlate with the kinetics of either solution or enzyme reactions. Solvation of other 2' substituents have little or no effect on the enthalpies of reaction. The putative Baker-Nathan order found for the hydration reactions of simple dioxolenium ions was found to be independent of solvation and to be a property of the relative geometries of 2-substituents to the entering group. Specific solvation of NAD+ during the bo nd-breaking reaction shows that closure of the diol anion to the epoxide is less favorable than substitution at the C1' carbon, contrary to the gas-phase behavior. This rules out several suggested mechanisms for product distributions in solution, and furthermore sets limits on suppositions regarding selectivities as a function merely of ion stability.
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