Authors:	Usui, Kota
Title:	Molecular dynamics simulations of aqueous Trimethylamine N-oxide solution and room temperature ionic liquids to reveal their microscopic dynamics
Online publication date:	1-Feb-2018
Year of first publication:	2018
Language:	english
Abstract:	In this thesis I investigated, using molecular dynamics simulations, the structure and dynamics of complex molecular systems, where strong, specific intermolecular interactions are responsible for structural and dynamical heterogeneity. The aim of my work was twofold. On one side, it was to unravel the molecular mechanism behind experimental observations, in particular time resolved vibrational spectroscopy, and on the other side, it was to develop new, accurate force fields capable of extending the power of atomistic simulations to larger size systems and longer time scales. I specifically investigated two systems: trimethylamine N-oxide (TMAO) and a series of alkylammonium nitrates, room temperature ionic liquids (RTILs). TMAO is a biomolecule known as osmolyte and chemical chaperone. These functions are supposed to stem from the strong intermolecular interaction between TMAO and water, via the hydrophilic oxygen (OTMAO) atom of TMAO. To reveal those mechanisms, the dynamics of water molecules around TMAO has been experimentally investigated, though the extent and molecular origin of the experimentally observed slowdown remained unclear. I performed ab initio MD (AIMD) simulations to understand the effect of TMAO on the rotational dynamics of water molecules. My simulations revealed that the water rotation is strongly slowed down near the hydrophilic OTMAO atom, due to a long-lived and highly-directional hydrogen bond between TMAO and water. As a further step, I also developed a new force field for TMAO, which captures the directionality of the TMAO-water hydrogen bonds, providing a better description of water structure and dynamics and structure around the OTMAO atom, which closely resembles the AIMD simulations results. The new force field will permit to investigate larger scale TMAO solutions, also including proteins, capturing the local water dynamics. In the second part of my thesis I investigated, using molecular dynamics simulations, the dynamics of a series of RTILs (specifically a series of alkylammonium nitrates), which are promising new green solvents. I revealed that the dynamics of the constituent ions is heterogeneous in two different aspects. Specifically, the rotational dynamics of the two ends of cationic chains differ, as a result of the asymmetry of the charge distribution on the cations. Additionally, the rotational dynamics of the charged group of cations (Nhead-H groups) has a broad distribution, which originates from the different local inter-ionic environment.
DDC:	540 Chemie 540 Chemistry and allied sciences
Institution:	Johannes Gutenberg-Universität Mainz
Department:	FB 09 Chemie, Pharmazie u. Geowissensch.
Place:	Mainz
ROR:	https://ror.org/023b0x485
DOI:	http://doi.org/10.25358/openscience-2844
URN:	urn:nbn:de:hebis:77-diss-1000018908
Version:	Original work
Publication type:	Dissertation
License:	In Copyright
Information on rights of use:	https://rightsstatements.org/vocab/InC/1.0/
Extent:	vi, 91 Seiten
Appears in collections:	JGU-Publikationen