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Title: Biotransformation of alkenes by Rhodococcus OU
Author: Hunt, Jonathan Ralph
ISNI:       0000 0001 3584 5474
Awarding Body: University of Warwick
Current Institution: University of Warwick
Date of Award: 1991
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Epoxides are an important class of synthons, produced in large quantities (notably epoxyethane and epoxypropane) for the manufacture of polymers. Reaction of epoxides with nucleophiles is stereospecific, offering a route to homochiral pharmaceuticals and agrochemicals from homochiral epoxides. With few exceptions, production of homochiral epoxides is difficult to achieve by chemical syntheses alone. However, alkene epoxidation by monooxygenase enzymes has been shown to proceed with a high degree of stereoselectivity in many instances. The aims of this project were to isolate microorganisms capable of converting alkenes to epoxides and to select the most suitable isolate for further characterization. Two Gram positive bacteria were isolated using α-methylstyrene (αMeS-1) and octane (Rhodococcus OU). The latter isolate was subjected to a more detailed study. Rhodococcus OU were shown to convert a range of structurally diverse alkenes to their corresponding epoxides: aliphatic (1-alkenes from propene to 1-tetradecene and cis-2- butene), alicyclic (cyclopentene and cyclohexene) and aromatic (styrene, allylbenzene and allylphenylether) alkenes. Alcohols, aldehydes and ketones were produced from alkenes with sub-terminal double bonds, in addition to epoxides. The stereoselectivity of alkene epoxidation was investigated by chiral HPLC. Partial resolution of (±)-1,2-epoxy-3-phenoxypropane was achieved, although assignment of the two peaks was not possible. Biotransformation of allyl phenyl ether to 1,2-epoxy-3- phenoxypropane was shown to proceed in a stereoselective manner. Problems associated with the chiral analysis of styrene oxide were not overcome, but preliminary results suggest that Rhodococcus OU is completely stereoselective for (R)-(+)-styrene oxide. Alkene epoxidation was shown to occur by one or more monooxygenase enzymes, expression of which is inducible by growth on n-alkanes but not by growth on 1-hexanol or glucose. Catalytic activity was retained after freezing in liquid nitrogen and storage at -70°C, only diminishing after being stored in excess of two months. Optimization of 1-alkene epoxidation was investigated, with particular reference to 1-hexene epoxidation. The specific rate of 1-alkene epoxidation (qp) was shown to increase as chain length decreased, correlating with an increase in 1-alkene solubility in water. Increasing the biocatalyst concentration resulted in an increase in volumetric productivity, but a decrease in qp. Epoxidation of 1-hexene showed saturable kinetics, qp being maximal between 0.05% to 0.10% (v/v) 1-hexene, whilst the final concentration of 1,2-epoxyhexane attained was concentration-dependant up to 0.40% (v/v) 1-hexene (the maximum concentration tested). Addition of co-substrates was not shown to enhance qp.
Supervisor: Not available Sponsor: Science and Engineering Research Council
Qualification Name: Thesis (Ph.D.) Qualification Level: Doctoral
EThOS ID:  DOI: Not available
Keywords: QD Chemistry