Studies of solvent effects

The effect of water on the conformational preferences of acetylcholine has been studied within the discrete, the continuum and the combined discrete-continuum models described in parts I and II of this series. All the models lead to the conclusion that the trans-gauche form which is, following refined quantum-mechanical computations, the intrinsically preferred one and the one observed in the crystal of acetylcholine and of a number of analogues should remain also the preferred conformation in water. This result agrees with NMR studies. The results of the empirical discrete model used here compare favorably to those obtained by an ab initio super-molecule treatment. The continuum model utilized here represents a net improvement above such models utilized in other works.     

Purine–water interactions in base stacking

The intermolecular energy of two conformations of stacked hydrated purine dimers is computed for a varying number of molecules of water around the stacks. The results obtained show that hydration can modify the relative stability of the dimers as calculated in vacuo. In addition, the optimized arrangements of the molecules of water around the dimers depict that purine molecules strongly interact with the solvent and that bridges made of water dimers or trimers are formed between the stacked bases.