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Title: The structure and activity of enzymes in ionic liquids
Author: Sate, Daniel
ISNI:       0000 0001 3553 4924
Awarding Body: University of Manchester
Current Institution: University of Manchester
Date of Award: 2008
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Ionic Liquids are a potentially new and exciting solvent for biocatalysis. Initial studies have shown enzymes to exhibit increased activity, stability and enantioselectivity in this solvent, with many interesting and industrially relevant reactions able to be performed that were previously impossible in the aqueous environment. However, while some enzyme and ionic liquid combinations have proven successful, many ionic liquids are seemingly incapable of supporting enzyme activity with negligible activity observed - in particular in those ionic liquids which are capable ofdissolving the enzyme or protein. In this study, the techniques of Small Angle Neutron Scattering (SANS), Dynamic Light Scattering (DLS), Circular Dichorism (CD), Differential Scanning Calorimetry (DSC) and classical enzyme assays are applied to investigate the underlying mechanisms of enzyme activity and deactivation in this novel solvent class. The effect of several structurally varied water miscible ionic liquids on the activity and subsequent structure of both enzymatic and non-enzymatic proteins was observed, both in anhydrous form and in aqueous solution. It was shown that properties such as the electron density associated with the anion and the hydrophobic nature of the cation were key factors in dictating the fate of proteins in the presence of ionic liquids. Ionic liquids which possessed anions of high charge density, such as [C2MIM] [N(CN)2], were found to not only dissolve enzymes but also caused large scale unfolding, which was reflected in the formation of large enzyme aggregates of non-native dimensions and obliteration of enzyme activity. Furthermore, the observed changes in tertiary structure and enzyme activity were correlated to concomitant changes in secondary structure, suggesting that the solvent was interacting with the polypeptide backbone and compromising the delicate innate hydrogen bonding of the protein. It was subsequently shown that by varying the electron density ofthe anion the extent of unfolding could be reduced, though not completely negated, and that the effect of the cation on protein structure could also not be disregarded, especially in the aqueous environment.
Supervisor: Not available Sponsor: Not available
Qualification Name: Thesis (Ph.D.) Qualification Level: Doctoral
EThOS ID:  DOI: Not available