Atomic charges in conformers of gaseous glycine

The potential energy surface of gaseous glycine determined years ago in ab initio MP2/6-311 ++ G** calculations (A. Csas-zar, J. Am. Chem. Soc., 114 ( 1992) 9568) is composed of 13 stable conformers with relative energies with in 11 kcal/mol. Glycine being the simplest amino acid and having a large nu mber of conformers with close energies, it offers a stringent benchmark to explore the conformational dependences of properties of interest for furthe r studies on peptides or proteins. The conformational behavior of atomic ch arges computed with the MP2/6-311 ++ G** electron density using population analyses and partition approaches of different nature are analyzed. The beh avior of every atom as well as that of molecular fragments COOH, CH2 and NH 2 show that atoms in molecules (AIM) and natural population analysis (NPA) charges exhibit not only a good conformational independence but also provid e a meaningful picture of the electron charge distribution in this system. (C) 2001 Elsevier Science B.V. All rights reserved.