PREFERENTIAL FORMATION OF THE DIFFERENT HYDROGEN BOND DURING THE MICROHYDRATION OF CYCLOETHER

VALLEJOS, MARGARITA; PERUCHENA, N. M.

Riviera Maya

Congreso; XXXVII Congreso Internacional de Químicos Teóricos de Expresión Latina; 2011

QUIMICOS TEORICOS DE EXPRESION LATINA

Hydration is a universal phenomenon in nature, many chemical and biological processes occur in aqueous media. In the hydration of organic compounds which have polar groups, water molecules interact with them through both hydrophilic and hydrophobic hydration. One of the most important intermolecular interactions that occurs in this type of hydration is the hydrogen bond (H–bond). In the present work we have explored the microhydration of tetrahydrofuran (THF) and tetrahydropyran (THP) compounds considering the complexes THF/(H2O)n and THP(H2O)n (with n = 1–4) in order to gain insight about which intermolecular interactions, either cycloether–water or water–water, are dominant and what type of hydrogen bonding patterns are involved in the most stable microhydrated structures of n–size. Geometry optimizations for the microhydrated complexes were carried out with various possible initial guess structures using the density functional approach. The changes in the different properties due to the increase of n were also discussed. In addition, an analysis based on atom in molecule (AIM) theory has also been carried out to understand the charge distribution and to pinpoint the atoms or regions that experiencing the larger changes in electron population, and in energy, upon the microhydration. For the most favorable microhydrated complexes, two different hydrogen bonding patterns were found. In one of them, a chain of water molecules engaged by Ow–Hw···Ow H–bonds is simultaneously bonded to both hydrophilic and hydrophobic portion of the cycloether by Ow–Hw··O1 and C–H···Ow H–bonds, respectively. In the other one, the water molecules are self–associated forming a close–loop and one of them also forms a Ow–Hw···O1 H–bond. A linear correlation is obtained for the sum of electron density at the bond critical points (rb) with the interaction energy (DE) and with the solute–solvent interaction energy (DEs–w) of the microhydrated complexes. In addition, a new way to estimate the energetic contribution as well as the preferential formation of the cycloether–water and water–water H–bonds based completely on charge density was found. Even more, it allows to differentiate the contribution from cycloether–water interactions in both hydrophilic and hydrophobic contributions, it is therefore a useful tool for studying the hydration of large biomolecules. It was revealed that as n raises, the water–water contribution also increases whereas the cycloether–water contribution decreases but it is not negligible. During the microhydration the changes in atomic properties occur on the whole system, particularly in the water groups wherein it was identified that the remarkable stabilization of their oxygen atoms is crucial for the stabilization of the complexes.