Berlin 2015 – scientific programme
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CPP: Fachverband Chemische Physik und Polymerphysik
CPP 32: P4: Computational Physics of Soft Matter
CPP 32.2: Poster
Tuesday, March 17, 2015, 14:00–16:00, Poster B
Water Dynamics in Aqueous TMAO Solutions: a DFT-MD Study — •Kota Usui1, Marialore Sulpizi2, Johannes Hunger1, Mischa Bonn1, and Yuki Nagata1 — 1Max-Planck Institute for Polymer Research, Mainz, Germany — 2Johannes Gutenberg University Mainz, Mainz, Germany
Trimethylamine N-oxide (TMAO) is one of the most effective agents to stabilize proteins. It has been found that TMAO is excluded from the protein's surface, which indicates that stabilization occurs via interaction of TMAO with the solvent, i.e. water. We investigate the mechanism behind the interaction of TMAO with water using DFT and force field molecular dynamics (MD) simulations. Our DFT-MD simulation reproduces the experimentally observed ~200 cm-1 red-shift of the O-D stretch vibrational peak, in contrast to force field MD. The water reorientational motion, reflected by the anisotropy decay, is significantly retarded in the vicinity of the hydrophilic O atom of TMAO (OTMAO) for our DFT-MD simulations, which is not observed in force field MD simulations. This slow-down of the anisotropy decay is found not only for the O-D group bound to OTMAO but also for the other O-D group of the same D2O molecule. Sequentially, we elucidated why force field MD predicts significantly different dynamics from the DFT-MD. To this end, we selectively calculated the anisotropy decay of those O-D groups which remain hydrogen bonded to OTMAO, which reveals the same time scale of the anisotropy decay of TMAO, indicating that the TMAO-bound D2O loses its reorientational information by following the TMAO rotational motion.