S.T. van der Post
- Love and fear of water: Water dynamics around charged and apolar solutes
- Award date
- 7 February 2014
- Number of pages
- Document type
- PhD thesis
- Faculty of Science (FNWI)
- Van 't Hoff Institute for Molecular Sciences (HIMS)
Water molecules are deceptively simple considering their importance to many (biological) processes. The interesting properties of water and its role in these processes can be attributed to the ability of water molecules to form up to four hydrogen-bonds. This hydrogen-bond network is altered in the vicinity of electric charges and hydrophobic (apolar) groups. In this thesis we describe a number of studies on the vibrational relaxation and reorientation dynamics of water molecules in aqueous solutions. These processes take place on a picosecond timescale and have been found to be sensitive probes of the hydrogen-bond network. The experimental technique that we used is polarization resolved femtosecond infrared pump-probe spectroscopy. This technique uses extremely short laser pulses (100 femtoseconds) to excite a molecular vibration in a small subset of the water molecules. A second laser pulse probes the induced molecular changes after waiting times that vary between 100 femtoseconds and 100 picoseconds. The thus obtained time dependent data provide information on dynamical parameters of the system like hydrogen-bond dynamics and molecular reorientation. Specifically we studied the reorientation of water molecules around various negatively charged ions and how the type of positively charged counterions affect these dynamics. In addition we studied the strong retardation effect of hydrophobic groups on the dynamics of water. First in a single amphiphilic molecule, later as a part of salts of which the cations contain hydrophobic chains.
- Research conducted at: Universiteit van Amsterdam
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