A study of inter- and intramolecular interactions through neutron compton scattering and low temperature matrix isolation infrared spectroscopy

Matrix Isolation Infrared Spectroscopy has been proposed as an alternative for detection and quantification of site-specific isotopic signals. 4-hydroxy-3-methoxy benzaldehyde (vanillin) is used in an attempt to make use of its asymmetry and distinguish between the vibrations of its three functional groups, assigning structural effects to specific locations in the molecule. After achieving an apparent near-isolated state, the role of isotopic signals in the resulting splitting effects of the predicted isolated-peak structure are discussed, as well as possible significant contributions from conformational, aggregation and steric effects from the matrix on the guest molecule. Density Functional Theory is considered as a method of simulating and predicting the behaviour of the molecule in the isolated phase, and simulated spectra are produced to attempt to replicate and assign the observed phenomena, predicting the positions and intensities of isotopic peaks based on natural isotopic abundances, and estimated conformer populations calculated from the energy levels of each structure. In a novel experiment to observe changes in momentum distributions in a solution of poly-N-isopropyl acrylamide (pNIPAAm) passing through a temperature-induced phase change, deuterated polymer/ solvent mixtures were studied on the VESUVIO instrument at the ISIS RAL facility, and the analysis of that data is presented. pNIPAAm and related compounds display a critical temperature for solvation above which they precipitate due to competition between solvent-polymer H-bonding verses internal H-bonding structure; though better stabilised by the additional hydrophobic effects of methanol, pure water solvation shows this behaviour. It is additionally seen that the mixture of water and methanol results in a depression of this Lower Critical Solution Temperature (LCST) relative to the pure solvents, thought to be due to solvent-solvent interactions limiting solvent availability to the polymer. Deuterium labels were introduced in neutron scattering experiments, and expected to show significant momentum change with this collapse of hydrogen bonding.

Name dc:type.qualificationname

phd

Level dc:type.qualificationlevel

doctoral

Grantor dc:publisher.institution

University of East Anglia

Year dc:date.issued

2014

Author dc:creator

• Iverson, Lee

Language dc:language

en