Exploration of the (ethanol)₄–water heteropentamers potential energy surface by simulated annealing and Ab initio molecular dynamics

Abstract

A DFT electronic structure study of the (ethanol) 4 -water heteropentamers at the B3LYP/6-31þG(d) model chemistry was carried out. To get determine possible configurations, the potential energy surface (PES) was explored with two methods: simulated annealing and ab initio molecular dynamics. The results suggest that the PES is very flat. A total of 81 stable structures were determined. These structures were classified into 16 different geometric patterns according to geometric criteria like the number of hydrogen bonds and their spatial arrangement: cyclic, bicyclic, or lineal patterns. Thermodynamic stability was used for defining the order of such classification. Hydrogen bonds are mutually disturbed due to the existence of cooperative effects. Cooperativity affects the nature of the hydrogen bonds and the overall stability of the ethanol-water system given that the strongest interactions are markedly covalent and the most stable geometric pattern corresponds to the pentagonal arrangement. These observations were supported by the analysis of the loss of atomic charge of the hydrogen atoms involved in hydrogen bonds. These hydrogen bonds were classified as primary and secondary hydrogen bonds: OAHÁÁÁO and CAHÁÁÁO, respectively. For comparative purposes, some (ethanol) 5 , (methanol) 5 , and (methanol) 4 -water clusters were characterized in this study.

Looking for the Azeotrope: A Computational Study of (Ethanol)6–Water, (Methanol)6–Water, (Ethanol)7, and (Methanol)7 Heptamers

“…For the particular case of (ethanol) n –water structures with respect to analogous structures of the same size, the decreasing stability order that has been reported is (methanol) n –water > (methanol) n +1 > (ethanol) n –water > (ethanol) n +1 , for n = 4, 5. , However, to the best of our knowledge, no results were reported for n > 5, and therefore, previous studies do not allow us to explain why ethanol forms an azeotrope with water while methanol does not present this phenomenological deviation with respect to Raoult’s law. The special stability of the ethanol–water in comparison to methanol–water systems could be the effect of the other van der Waals interactions that appear when the size of the interacting units increases.…”

“…This is the first time that the stability order locates the (ethanol) n and (ethanol) n −water systems as more stable than their analogues: (methanol) n and (methanol) n − water. 5,14,15 This remarkable energetic stabilization of the ethanol-containing systems in comparison to methanolcontaining systems could contribute to a possible explanation in energy terms why methanol does not form an azeotrope with water as ethanol does.…”

“…The large values of the association enthalpies, above 60 kcal/mol for the two most stable conformers, are not only the result of a large number of HBs but also of cooperative effects also called secondary interactions, 34 as found for smaller heteroclusters. 5,14,15 As indicated in the Introduction section, cooperativity is already responsible for the stability and structure of water timer, 12 but ethanol−water heteroclusters 5,14,15 or certain acetamide clusters with up to 15 molecules 35 are also typical examples.…”

Adaptive Aggregation and Chirality Recognition of Neuroactive Substances and their Building Blocks: A Vibrational Spectroscopic and Microscopic Study

“…see Refs. [116,[121][122][123]). In the present work, some of these calculations had to be repeated and complemented in order to obtain all the information relevant for this study.…”