NMR and DFT Studies on Solvation Phenomena in Bioorganic Molecules, Natural Products and Model Compounds: Current and Future Perspectives for Atomic-Level Structures and Mechanistic Catalytic Reactions.

The structural role of solvation phenomena in bioorganic compounds has been documented sporadically over the last two decades, although they are of fundamental importance in a variety of chemical, physical, and biological processes. NMR chemical shifts depend on the electron densities around the nuclei, which can be influenced by the surrounding environment. Solvent-dependent chemical shift variations, therefore, can provide important structural information on solute-solvent interactions, especially nuclei, which belong to polar groups, such as OH, NH, CONH, COOH, etc. Recent developments in quantum chemical methods for calculating NMR chemical shifts, especially those incorporating explicit solvent effects, and the exponential advances in computer power can provide an excellent methodology for the accurate calculation of chemical shifts in solution. Furthermore, comparison of density functional theory (DFT) calculated activation free energies with NMR experimentally determined values can provide a reliable method for investigating the role of solvents in various atomistic reaction mechanisms. It has been demonstrated that the combined use of NMR and DFT calculations represents the new frontier of our understanding of the role of solvents, at the atomic level, in molecular structures and in catalytic reactions of bioorganic molecules, natural products and model compounds.