Title

Ability of the PM3 quantum-mechanical method to model intermolecular hydrogen bonding between neutral molecules

ACS Citation

Jurema, M. W.; Shields, G. C. Ability of the PM3 Quantum-Mechanical Method to Model Intermolecular Hydrogen Bonding between Neutral Molecules. J. Comput. Chem. 1993, 14 (1), 89-€“104.

Abstract

The PM3 semiempirical quantum-mechanical method was found to systematically describe intermolecular hydrogen bonding in small polar molecules. PM3 shows charge transfer from the donor to acceptor molecules on the order of 0.02-0.06 units of charge when strong hydrogen bonds are formed. The PM3 method is predictive; calculated hydrogen bond energies with an absolute magnitude greater than 2 kcal mol-1 suggest that the global minimum is a hydrogen bonded complex; absolute energies less than 2 kcal mol-1 imply that other van der Waals complexes are more stable. The geometries of the PM3 hydrogen bonded complexes agree with high-resolution spectroscopic observations, gas electron diffraction data, and high-level ab initio calculations. The main limitations in the PM3 method are the underestimation of hydrogen bond lengths by 0.1-0.2 angstrom for some systems and the underestimation of reliable experimental hydrogen bond energies by approximately 1-2 kcal mol-1. The PM3 method predicts that ammonia is a good hydrogen bond acceptor and a poor hydrogen donor when interacting with neutral molecules. Electronegativity differences between F, N, and O predict that donor strength follows the order F {\textgreater} O {\textgreater} N and acceptor strength follows the order N {\textgreater} O {\textgreater} F. In the calculations presented in this article, the PM3 method mirrors these electronegativity differences, predicting the F-H---N bond to be the strongest and the N-H---F bond the weakest. It appears that the PM3 Hamiltonian is able to model hydrogen bonding because of the reduction of two-center repulsive forces brought about by the parameterization of the Gaussian core-core interactions. The ability of the PM3 method to model intermolecular hydrogen bonding means reasonably accurate quantum-mechanical calculations can be applied to small biologic systems.

Source Name

Journal of Computational Chemistry

Publication Date

1993

Volume

14

Issue

1

Page(s)

89-104

Document Type

Citation

Citation Type

Article