Solvation of hydrogen bonded systems

Bopp, P. (1987). Molecular dynamics computer simulations of solvation in hydrogen bonded systems. Pure Appl. Chem. 59, 1071-82. 

Sometimes the problem of solvation may be reduced to the investigation of hydrogen-bonded systems of the type (AH "A) , that represent an important entity in aqueous solutions of electrolytes. These systems possess double-well proton potential curves, if the A-A distance is larger than about 2.4 x 10 m. Such a hydrogen bond is... 

Not only it is difficult to distinguish between a co-crystal and a solvate (as a matter of fact all molecules are solid and form crystals at sufficiently low temperature) but it is also often difficult to distinguish between a crystal and a salt. As discussed above in the case of hydrogen-bonded systems between acids and bases the transition between a salt and a co-crystal may be a very semantic issue depending exclusively on the position of a proton along a N O supramolecular link [90]. 

C. S. Callam, S. J. Singer, T. F. Fowary, and C. M. Hadad, Computational analysis of the potential energy surfaces of glycerol in the gas and aqueous phases Effects of level of theory, basis set, and solvation on strongly intramolecularly hydrogen bonded systems. J. Am. Chem. Soc. 123, 11743 11754 (2001). 

Solvent KIEs for MeCl + Cl in the presence of 1—4 molecules of water were examined by ab initio calculations.70 The ratio h/ d was <1 for the monohydrated system and > 1 for the dihydrated system it increased with the number of micro solvating water molecules, owing to breakage of hydrogen bonds in attaining the transition state. 

The understanding of chemical reaction mechanisms in solution is often based on the nature of the interactions between reactants and solvent, which are governed by the physical properties of molecules, such as polarity, or by the possibility of bonds formation (e.g., hydrogen-bonding) and their dynamical evolution. The goal of the majority of works on molecular clusters is to try to fill the gap between the gas phase reaction and the condensed phase reaction by a step-by-step solvation of the reactive system. This approach will give useful... 

Accurate predictions of solute interactions with a limited number of solvent molecules are possible using the supermolecular approximation. This is an approach based on the consideration of the dissolved molecule together with the limited number of solvent molecules as the unified system. The quantum-chemical calculations are performed on the complex of the solute molecule surrounded by as many solvent molecules as possible. The main advantage of the supermolecular approximation is the ability to take into account such specific effects of solvation as hydrogen bonding between the selected sites of the solvated molecules and the molecules of the solvent. In principle there are only two restrictions for the supermolecular approximation. One of them is the internal limitations of the quantum-chemical methods. The second restriction is the limitation of the current computer technology. Because of such restrictions this approximation coupled with ab initio molecular dynamics is possible only for small model systems.46-50... 

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