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Title: Hydration phenomena in concentrated protein solutions
Author: Jahn, Niklas Henning
ISNI:       0000 0004 5994 2051
Awarding Body: Imperial College London
Current Institution: Imperial College London
Date of Award: 2015
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The transport of water in glassy polymers is important in many fields but an underappreciated topic in protein science; though proteins are of rising importance in many industries. Similar to water transport in synthetic polymers, glassy proteins suffer from non-equilibrium effects during water sorption. However, the presence (or absence) of these phenomena is unclear. Here and for the first time, experimental evidence is reported for the presence and consequences of non-equilibrium relaxations during water sorption in proteins over long time scales based on gravimetric and calorimetric experiments. Non-Fickian water sorption kinetics were found in all experiments. It is demonstrated how water solubility in a glassy protein is highly dependent on experimental design and time scales. The apparent sorption kinetics were attributed to the convolution of two processes: one that is controlled by the concentration gradient; one that is driven by a slow relaxation of the protein. A relaxation-diffusion model was employed to model sorption kinetics and the respective time constants were estimated. Exothermic heats of mixing, that were both temperature and concentration dependent, were measured. Enthalpy of mixing time evolution data was in excellent agreement with gravimetric sorption kinetics. The plasticising effect of water onto the protein was further shown by differential scanning calorimetry of concentrated protein solutions. All this demonstrates the unsuitability of long established surface and lattice approaches to model or predict water sorption in proteins. Protein pressure-volume isotherms were obtained and used to model a protein's water sorption isotherms by the non-equilibrium lattice fluid theory for the first time. It is anticipated that this work stimulates a revaluation of the design of water sorption experiments in glassy proteins and the interpretation of such data. This in turn is expected to profoundly affect formulation engineering and Quality-by-Design approaches for a wide range of protein-based products.
Supervisor: Williams, Daryl ; Heng, Jerry Sponsor: Biotechnology and Biological Sciences Research Council
Qualification Name: Thesis (Ph.D.) Qualification Level: Doctoral