UNIVERSITY OF ARKANSAS CHEMIST’S PAPER ON MOLECULAR STRUCTURE ONE OF TOP 100 CITED IN CHEMICAL JOURNAL

FAYETTEVILLE, Ark. - The basis of modern-day understanding of molecular structure can be attributed, in part, to University of Arkansas chemistry professor Peter Pulay. One of Pulay's pioneering papers in the field has been recognized by the American Chemical Society as one of the top 125 most cited papers from the Journal of the American Chemical Society. The ACS is celebrating its 125th anniversary this year.

The paper originally appeared in the journal in 1979, and was ranked as the 64th most cited paper in the history of the journal. It built on work published in a 1969 paper, which was cited in the 1998 Nobel Prize awarded in chemistry,

  "The paper showed how to calculate molecular structures using theoretical techniques," Pulay said. The research built on contributions to the field that Pulay had made 10 years before, when he showed how to use theoretical calculations to determine the structure of a molecule.

Structure determines function in most molecules. You can't drive a truck if the wheels are perched on the hood, and the same philosophy applies to atom placement. Change a molecule's shape, and you get different properties and different reactions Thus, structure serves as the basis for determining how a molecule will react in a given environment.

Molecules tend to act like lazy people--they like to be at the lowest energy state. The lowest energy state determines the arrangement of atoms in a molecule. Therefore the distances between atoms within the molecule--and the molecule's shape--can be determined by determining the lowest energy state for a given molecule. Moving the atoms around until the arrangement having the lowest energy is found works for a few atoms, Pulay said, "but with, say, 12 atoms it already becomes a taxing problem."

Pulay realized that calculating the forces on the atoms would tell which direction the atoms must be moved to minimize the energy within the molecule. He also realized that these forces are also useful to calculate the infrared spectra. Infrared spectra are caused by the atoms vibrating at different frequencies, depending upon the rigidity of the molecule. This rigidity is proportional to the restoring forces, which arise when the molecule is distorted from its lowest energy state.

Pulay used small molecules to determine molecular structures both theoretically and experimentally using infrared spectrometry. His work served as a basis for the most popular computer program available for calculating molecular geometries, developed by 1998 Nobel Prize-winning chemist John Pople.

His methods made it easier to determine large molecular structures containing hundreds of atoms. His work helped to elevate theoretical research from its position as a stepchild of chemistry to an essential function that is applied hand in hand with experimentation.

Pulay has continued to push the boundaries in this field, using complex computer programs and large computers to solve challenging molecular structural mysteries. With inexpensive, powerful computers and improved computer programs a calculation which took a week 20 years ago can be performed in a minute today. This has contributed greatly to the popularity of the computational determination of molecular structures. Computed molecular structures are now routinely used by thousands of academic and industrial researchers.