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Title: Spin trapping and lyoluminescence
Author: Hunter, Charles John
Awarding Body: University of Aberdeen
Current Institution: University of Aberdeen
Date of Award: 1981
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Lyoluminescence, which is the emission of light on dissolution of a previously gamma-irradiated solid, is known to depend critically on the concentrations of free radicals generated in the solid. The identity of these and the final emitting species is not yet known with certainty. The present study uses spin trapping to identify the radicals which are present on dissolution of irradiated amino acids and carbohydrates in water. The synthesis and trial of several water soluble nitroso and nitrone spin traps was carried out. 2-Methyl-2-nitrosopropane (MNP), 2-methyl-2-nitroso-4'(4'-pyridyl-1'-oxide)-butane (MNPOB) and 3,5-dibromo-4-nitrosobenzenesulphonic acid (DBNSA) were found to be the most useful. Using these traps, radicals present in solution after dissolution of gamma-irradiated amino acids were identified as (a), deaminated radicals or (b), hydrogen abstraction radicals. The e.s.r. spectra obtained in the same way with irradiated carbohydrates were more complex than those with the amino acids. The trapped radicals were identified mainly as secondary alkyl radicals which were produced in the solid by rearrangement or fragmentation of the initially formed, mainly tertiary alkyl radicals. Radicals trapped from model systems, in which the initially-formed radicals were produced by hydrogen abstraction from carbohydrates and polyhydric alcohols, usually arise via acid-catalysed dehydration. Hydrogen abstraction from cyclic ethers in the presence of spin traps also gave results that could be explained in terms of rearrangement or fragmentation of the initially formed radicals. However, none of the above systems was found to model the gamma-irradiation of carbohydrates in the solid state. The final emitting species was investigated by recording the transient emmission spectra of lyoluminescence. Evidence was obtained for the involvement of triplet carbonyls in amino acid lyoluminescence and in carbohydrate lyoluminescence at high pH, and for singlet oxygen in carbohydrate lyoluminescence in water. In the presence of sensitisers, the lyoluminescence spectrum became characteristic of the sensitiser. Correlations were obtained between light yield, solid state radical concentration and trapped radical concentration for L-glutamine and L-alpha-alanime. The effects of annealing on glutamine were explained in terms of destruction of a particular type of radical which led to a reduction in the proportion of radical-radical reactions in solution and for alanine by a diffusion of oxygen into the crystal lattice. No evidence for the formation of peroxyl radicals in the solid was obtained.
Supervisor: Not available Sponsor: Not available
Qualification Name: Thesis (Ph.D.) Qualification Level: Doctoral
EThOS ID:  DOI: Not available