Very large scale computations of the free energies of eight low-lying structures of arginine in the gas phase

To assess the relative energies and free energies of five canonical and three zwitterionic low-lying structures of the arginine molecule, modem basis set extrapolation techniques and high-level ab initio treatments of electron correlation have been used on state-of-the-art parallel computers. The electronic energy and Gibbs free energy orderings of these eight species turn out to be consistent with previous findings [Rak, J.; Skurski, P.; Simons, J.; Gutowski M. J. Am. Chem. Soc. 2001, 123, 11695] obtained using smaller basis sets and lower level treatments of electron correlation. Nevertheless, the results presented here represent what the current state of the art can achieve for a molecule of this size and complexity and they offer the best available estimates of the relative stabilities of the eight structures.