Analysis of solution-phase macromolecular materials by diffusion NMR

Eden, EG
(2017) Analysis of solution-phase macromolecular materials by diffusion NMR. PhD thesis, University of Liverpool.

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Molecules such as covalent cages can adopt several shapes, in which the ratio of starting materials is the same, but the number of starting materials, and the shape of the resulting molecule is different. However, determining this in the absence of a crystal structure can be challenging. Pulsed field gradient (PFG) NMR has been used for two decades to characterise large macromolecules in solution, but it is still difficult to determine precise structural information, because of the rotational-averaging experienced in experimental measurements. Here, we develop experimental techniques for collecting PFG-NMR data that break this barrier, and allow characterisation of several useful molecular descriptors. By measuring the diffusion coefficients of molecules in a range of solvents, incurvate surfaces are probed to map the outer surface of nanometre-sized molecular species. This technique allows details about the geometrical shape of covalent cages to be determined without the need for isolation. Furthermore, we compare experimental PFG-NMR data to structures produced by computational modelling and produce a new molecular descriptor, ρr, which describes the isotropy of covalent cages. This descriptor is used to determine the quality of agreement between proposed structures and experimental PFG-NMR data. In analysing polymers, we develop a new mathematical model for determining the molar-mass dispersity (ÐM) by PFG-NMR. We find a single parameter is sufficient to determine the dispersity of a system, which eliminates the need for data modelling and enhances the reliability of analysis. We hope this will make the technique more accessible to polymer scientists, and will help test the validity of molar-mass dispersity measurements made by other means. Finally, we synthesise five novel dodecaamide cages, which contain functional groups that offer the opportunity to extend functionality beyond the cage via further reaction. We take significant steps towards producing singly functionalised species, which could be incorporated into polymeric materials for the development of robust membranes and coatings.

Item Type: Thesis (PhD)
Additional Information:
Divisions: Faculty of Science and Engineering > School of Physical Sciences > Chemistry
Depositing User: Symplectic Admin
Date Deposited: 08 Sep 2017 14:07
Last Modified: 19 Jan 2023 07:09
DOI: 10.17638/03006567