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Title: Molecular models of hydration in methanol-water mixtures
Author: Dixit, Sanhita
Awarding Body: University of Edinburgh
Current Institution: University of Edinburgh
Date of Award: 2002
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The work presented in this thesis addresses the issue of hydration of a simple amphiphile-like molecule; methanol. High-resolution Raman spectroscopy is used to study methanol-water mixtures over the whole concentration range. A highly non-linear dependence of the carbon-oxygen and carbon-hydrogen stretching frequencies with composition is observed. The data suggest the first global picture of the progressive hydration of methanol: water first breaks up the molecular chains which exist in pure methanol, and then completely hydrates the hydroxyl groups before solvating in hydrophobic methyl groups. In order to corroborate this proposed picture, neutron diffraction experiments using hydrogen/deuterium substitution were performed on a concentrated methanol in water mixture (70 mole% methanol : 30 mole% water) and a dilute methanol in water mixture (5 mole% methanol : 95 mole% water). The diffraction data were modelled using the Empirical Potential Structural Refinement technique. In the concentrated mixture, although there is insufficient water for the classical hydrophobic mechanism to operate, the structural effects observed are consistent with those that might be expected in a hydrophobically driven system. An unexpected reduction is found in the methyl-methyl contact distance compared to pure methanol, which corresponds to an overall compressive effect apparently driven by hydrogen bonding of the added water to the alcohol hydroxyl groups. Surprisingly, the water structure is largely preserved in this mixture. The results obtained provide unambiguous evidence for the preferential interaction of the methanol hydroxyl group with water and suggest that hydrogen bonding interactions between water and polar groups of amphiphilic molecules may be more important than previously thought.
Supervisor: Not available Sponsor: Not available
Qualification Name: Thesis (Ph.D.) Qualification Level: Doctoral
EThOS ID:  DOI: Not available