Comparison of methods of density functional theory modeling of the specific rotation of amino acid solutions

COMP 215

Matthew D. Kundrat, Department of Chemistry, SUNY at Buffalo, 345 Natural Sciences Complex, Buffalo, NY 14260-3000 and Jochen Autschbach, jochena@buffalo.edu, Department of Chemistry, State University of New York at Buffalo, 312 Natural Sciences Complex, Buffalo, NY 14260-3000.
When chemists measure the specific rotation of a chiral compound in solution they measure a phenomenon caused by the interaction of polarized light with a large number of molecules which undergo conformational changes, vibrate and interact with the solvent. Computational chemists must simulate this effect by looking at a comparatively small number of configurations of isolated molecules. Most often computational models are built by first generating a set of a set of local minimum molecular geometries of the compound, next computing a specific rotation for each conformer, then Boltzmann averaging the results. We use this method to calculate the specific rotation for a few small amino acid molecules. We also consider an alternative approach in which molecular dynamics are used to generate a large number of non-minimized conformers, next calculating the specific rotation of each as before then computing a straight average. Results from the various methods are compared.