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Cresswell, Rosalie J (2020) New Applications and Methods in Solid-state NMR. PhD thesis, University of Nottingham.

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Abstract

Solid-state NMR is a powerful, non-destructive, technique which can probe the local chemical structure of both crystalline and amorphous materials. In this thesis several different practical applications and methods of solid- state NMR have been studied.

Solid-state NMR, has been shown to be an effective technique for char- acterising changes in the molecular architecture of plants during a potential pretreatment process for the production of biofuels. Carbon-13 labelled wheat straw was fermented over 5 days with a fungus, Aspergilus niger. Quantitative analysis of 1D 13C MAS spectra over the fermentation time revealed the production of the cellulase enzymes in the first 24 hours and the steady decrease of the cellulose by 25% over the 5 day period. The 2D analysis also showed clear changes in the xylan shift from a 2-fold conforma- tion, which binds to cellulose microfibrils, to a 3-fold conformation which cannot. It also showed a gradual broadening of the cellulose peaks indicting the cellulose becomes more amorphous throughout the fermentation.

High-field DNP-enhanced NMR has recently become commercially avail- able due to the production of high powered microwave sources such as the gyrotron. DNP-enhanced NMR has been used to study the structure of a pharmaceutical, naloxone where an enhancement of 18 meant a 2D 13C -13C refocused INADEQUATE could be acquired in 16 hours using a 13C natural abundance sample rather than 216 days using standard NMR. The 2D spectrum was then used to make a complete assignment of the naloxone alkaloid 13C NMR shifts.

Finally, improvements have been made to a two-dimensional anisotropic- isotropic experiment which uses an R-sequence to recouple chemical shift anisotropy (CSA) of fluorine sites. The basic R element in the R-sequence was replaced with the 270090180 composite pulse which has been shown to make the experiment significantly more robust to B1 inhomogeneity. This experiment was the used to extract the CSA parameters for two inseparable polymorphs of casopitant.

Item Type:	Thesis (University of Nottingham only) (PhD)
Supervisors:	Titman, Jeremy
Keywords:	Solid-state NMR, wheat straw, crystalline pharmaceuticals, nuclear magnetic resonance spectroscopy
Subjects:	Q Science > QD Chemistry > QD450 Physical and theoretical chemistry
Faculties/Schools:	UK Campuses > Faculty of Science > School of Chemistry
Item ID:	60386
Depositing User:	Cresswell, Rosalie
Date Deposited:	15 Jan 2025 11:11
Last Modified:	15 Jan 2025 11:11
URI:	https://eprints.nottingham.ac.uk/id/eprint/60386

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