Terahertz spectroscopy to explore the role of vibrational dynamics in systems with varying structural order and disorder

Understanding the processes occurring in materials with varying structural order and disorder, such as pharmaceutical mixtures, has profound implications for drug formulation and delivery. Pharmaceutically active biological molecules such as peptides, proteins, and antibodies need to be formulated and processed into dry powder form that can be reconstituted quickly in order to achieve long-term storage stability. The biomolecules retain their functional properties by embedding them into an amorphous matrix of suitable small organic molecular glass formers. Degradation mechanisms catalysed by water clusters, the influence of the solvation shell in solution upon reconstitution, and crystallisation processes are important aspects to consider in this context, and this thesis investigates these points using terahertz time-domain spectroscopy (THz-TDS). Glycerol is commonly used to protect proteins during cryo-preservation and its interactions with small amounts of water are important to understand. The onset of molecular mobility, as measured by the infrared active dipoles in glycerol-water mixtures, resulted in increased anharmonic effects, obscured the boson peak, and influenced the vibrational density of states. The effect of the relative water content in aqueous mixtures of glycerol at room temperature was also explored. By utilising four different model biopharmaceuticals, the effect of size on the dynamics of one-component lyophilised products was studied with THz-TDS and differential scanning calorimetry. Anharmonic effects were identified in the spectra and linked to protein jamming in high molecular-weight samples, hindering the increase in molecular mobility with temperature. Two-component lyophilisates of varying sucrose to monoclonal antibody ratio were assessed with terahertz spectroscopy and it was shown that protein jamming at a critical temperature must be associated with the macromolecular structure of the protein itself, that it is not dependent on the presence of any excipient, and that it is not dependent on the presence of water molecules. Even if proteins are stored in dry form, they have to be rehydrated before use without losing their functionality due to misfolding or aggregation. Using terahertz spectroscopy and structural techniques, an increased aggregation rate of α-synuclein (aSyn), a protein associated with Parkinson’s disease, in the presence of NaCl compared to CsI was found to be not due to a change in the structural conformations of aSyn, but due to a reduction in both the water mobility and subsequently the protein mobility. The same method was applied to two other proteins, namely β-lactoglobulin and bovine serum albumin, and the interactions with the surrounding salt solution were found to strongly depend on the protein characteristics. Crystallisation dynamics in aqueous solution were studied using THz-TDS in a transmission geometry on the example of magnesium sulfate heptahydrate. A novel method was developed to perform temperature and concentration calibrations of liquid samples at terahertz frequencies, enabling the studies of local concentration of semicrystalline systems.

Name dc:type.qualificationname

Doctor of Philosophy (PhD)

Level dc:type.qualificationlevel

Doctoral

Grantor dc:publisher.institution

University of Cambridge

Year dc:date.issued

2022

Author dc:creator

• Kölbel, Johanna

Advisor dc:contributor.advisor

• Zeitler, J Axel

• THz-TDS
• spectroscopy
• crystallisation
• water clustering

Licence

• https://www.rioxx.net/licenses/all-rights-reserved/

Language dc:language

eng

DOI dc:identifier.doi

https://doi.org/10.17863/CAM.92778

OAI identifier oai:identifier

oai:www.repository.cam.ac.uk:1810/345355