Menakath, Anjali (2019) Characterisation of organic solids using solid-state NMR spectroscopy. PhD thesis, University of Warwick.

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Abstract

This thesis utilizes high-resolution solid-state magic angle spinning (MAS) NMR technique for the characterisation of various organic compounds, specifically pharmaceutical APIs, mesoporous silica loaded with iPMPA, and solid electrolyte interphase layer (SEI) components of lithium-ion batteries. Solid-state NMR is highly sensitive to the local environment, and hence MAS experiments in particular two-dimensional experiments can be used to probe 1H ̶1H and 1H ̶X (X=7Li, 13C, 14N, 29Si, 31P) proximities. Some of the presented results have used an NMR crystallography approach, whereby chemical shifts are calculated using the gauge-including projector augmented wave (GIPAW) method for structures usually obtained from diffraction. Moreover, intermolecular hydrogen bonding motifs can be probed by a comparison of chemical shifts calculated for the full crystal to those calculated chemical shift for an isolated molecule.

The first application concerns conformational polymorphism, which is the existence in distinct solid-state forms of the same molecule in different conformations due to variation in torsion angle and has importance for the development of pharmaceutical products. 1H− 1H homonuclear and 13C− 1H and 14N− 1H heteronuclear correlation solid-state NMR approaches are used to elucidate crystal packing and internuclear proximities between nuclei. This Chapter considers the development of a scoring function for evaluating crystal structures of tolfenamic acid (TFA) using solution- and solid-state NMR data. To build this scoring function, we experimentally measured (Form I and Form II) and calculated (Form I, II, III, and IV) 1H and 13C chemical shifts in both the solid state and in solution. The implementation of solid-state NMR chemical shift data in conjunction with both experimental and calculated changes in solution NMR chemical shifts allowed the scoring function to discriminate amongst four similar TFA polymorphs. This approach has the potential to improve the efficiency and accuracy of crystal structure prediction (CSP) by incorporating solution-state NMR conformational and chemical shift data into solid-state NMR based NMR crystallography approaches. Importantly, this novel approach provides a way to predict the conformation of a new polymorphic form for which experimental NMR data is accessible but there is no crystal structure.

In a second application, a range of isopropyl methyl (iPMPA, a degradation product of the chemical warfare agent Sarin) loaded mesoporous silica samples are investigated through multinuclear solid-state NMR. 13C cross polarisation (CP) MAS NMR spectra confirmed the presence of iPMPA molecules in the silica matrix. 1H, 31P, and two-dimensional heteronuclear experiments are applied to probe the number of phosphorous sites and hydrogen bonding motifs. xvi Variable-temperature 1H and 31P MAS NMR experiments provided information about the mobility of acidic protons involved in hydrogen bonding. A structural model for the iPMPA loading in the pores of the mesoporous silica is presented.

In a third application, a series of standard components of an solid-electrolyte interphase (SEI) layer along with the SEI generated on graphite electrode was investigated using fast MAS NMR. Specifically, high-resolution 1H, 7Li, 1H-1H DQ/MAS, 7Li-1H HMQC, and 13C CP MAS techniques are used, in conjunction with GIPAW calculated NMR chemical shifts to provide an understanding about likely components in the SEI layer. Specifically, a solid-state NMR characterisation of lithium ethylene dicarbonate (LEDC) and lithium mono carbonate (LMC) is presented.

Item Type:	Thesis (PhD)
Subjects:	Q Science > QC Physics Q Science > QD Chemistry
Library of Congress Subject Headings (LCSH):	Nuclear magnetic resonance spectroscopy, Organic compounds -- Spectroscopic imaging, Organic compounds -- Analysis, X-ray crystallography
Official Date:	September 2019
Dates:	Date Event September 2019 UNSPECIFIED
Institution:	University of Warwick
Theses Department:	Department of Physics
Thesis Type:	PhD
Publication Status:	Unpublished
Supervisor(s)/Advisor:	Brown, Steven P.
Sponsors:	University of Warwick
Format of File:	pdf
Extent:	xix, 215 leaves : illustrations (some colour)
Language:	eng

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