Quantum Mechanical Study of the Nonbonded Forces in Water−Methanol Complexes

Abstract

The water-methanol dimer can adopt two possible configurations (WdM or MdW) depending on whether the water or the methanol acts as the hydrogen bond donor. The relative stability between the two configurations is less than 1 kcal/mol, and as a result, this dimer has been a challenging system to investigate using either theoretical or experimental techniques. In this paper, we present a systematic study of the dependence of the geometries, interaction energies, and harmonic frequencies on basis sets and treatment of electron correlation for the two configurations. At the highest theory level, MP2/aug-cc-pVQZ//MP2/aug-cc-pVTZ, interaction energies of −5.72 and −4.95 kcal/mol were determined for the WdM and MdW configurations, respectively, after correcting for basis set superposition error using the Boys-Bernardi counterpoise scheme. Extrapolating to the complete basis set limit resulted in interaction energies of −5.87 for WdM and −5.16 kcal/mol for MdW. The energy difference between the two configurations is larger than the majority of previously reported values, confirming that the WdM complex is preferred, in agreement with experimental observations. The effects that electron correlation have on the geometry were investigated by performing optimization at the MP2(full), MP4, and CCSD levels of theory. The approach trajectories for the formation of each dimer configuration are presented and the importance of these trajectories in the development of parameters for use in classical force fields is discussed.

Ab initio NMR study of the isomeric hydrogen‐bonded methanol–water complexes

“…O distances for the complexes where the methanol molecule is the proton acceptor and proton donor are calculated as 2.860 Å and 2.913 Å, respectively. An early theoretical study by Kirschner and Woods [43] found the results of 2.845 Å and 2.912 Å, respectively, in good agreement with our results. The experimental result for the proton acceptor case has been inferred as 2.997 Ϯ 0.009 Å [15], but this experimental value could not be reproduced theoretically, even at a very high level of calculation [43].…”

Ab initio molecular dynamics study of aqueous solvation of ethanol and ethylene

“…It should be noted that in the same study the methanol-water complex with the methanol as hydrogen bond donor is found to be the most stable, in contradiction with the MP2 basis-set limit result of Ref. [74]. This suggests that in the Ref.…”

“…Switching to the other ethanol conformer within either complex destabilizes the complex by 0.07 and 0.4 kcal/mol, respectively. The relative stability of the ethanol donor and acceptor complexes is similar to that for the methanol-water complex where CPMD-BLYP [53] and the complete-basis-set MP2 estimate [74] yields the methanol acceptor complex stable by 0.74 and 0.35 kcal/mol, respectively. There are no experimental data for the structure and energetics of the ethanol-water dimer.…”

Extension of the GLYCAM06 biomolecular force field to lipids, lipid bilayers and glycolipids

“…To remain consistent with the GLYCAM06 formalism, the following criteria were used to guide its extension: 1) the new parameters should be transferable to the most common and biologically relevant lipids, lipid bilayers, and glycolipids, 2) they should be self-contained and therefore readily transferable to many quadratic force fields, 3) as few new atom types as possible should be introduced, 4) the new parameters should be compatible with all existing parameters and molecular classes in GLYCAM06, 5) the accuracy of the parameters should be rigorously assessed by application to developmental and test molecules through comparison with theoretical and experimental data, and 6) the use of 1-4 non-bonded electrostatic or van der Waals (vdW) scale factors should be avoided [15].…”