8th Liquid Matter Conference September 6-10, 2011 Wien, Austria ...

P2.84Tue 611:23-14:00Guanidinium in aqueous solution studied by quantummechanical charge field - molecular dynamics(QMCF-MD)Alexander Weiss, 1 Thomas Hofer, 1 Bernhard Randolf, 1 Anirban Bhattacharjee, 1and Bernd Rode 11 Leopold Franzens University of Innsbruck, Innrain 52, A-6020 Innsbruck 6020, Innsbruck,AustriaStructure and dynamics of guanidinium in aqueous solution were examined via double zeta HFlevel Quantum Mechanical Charge Field - Molecular Dynamics (QMCF-MD) simulation as wellas two Molecular Mechanics - Molecular Dynamics (MM-MD) simulations, parametrized via thestandard AMBER-99-SB Force-Field parameters, employing the arginine+ side chain force constantsand equilibrium geometry. Coulombic parameters were fitted via Mulliken population dataof the QM simulation, as well as via the commonly employed electrostatic potential (RESP) fit.Even though this species is one of the most weakly hydrated cations yet characterized, its hydrationpattern is quite complex and advanced analysis techniques have been employed to characterizethe spatial arrangement of ligands. The positive charge is mainly located at the central carbon, resultingin a strong solute oxygen coordination. Hydrogen bonds are mainly donored by the amidehydrogens, but are also accepted via the nitrogen atoms to a certain extent. Comparison of theapplied QM and MM models provides evidence that the arginine+ parametrization leads to highlydifferent results than the quantum mechanical treatment.84