Peter J. Baugh

γ-Irradiation-induced ring-opening of polycrystalline cycloamylose hydrates

Abstract The chemical modifications induced in polycrystalline cycloamylose hydrates during γ-irradiation have been investigated by using g.l.c-m.s. to analyse the monosaccharide mixtures formed on hydrolysis. Unchanged substrate and material retaining the original cyclic structure were removed by precipitation prior to hydrolysis, and the products therefore reflect the effect of the radical-induced opening of the cycloamylose ring structure. The following products were identified: glucose and glucono-1, 5-lactone ( 1 ), 4-deoxy- xylo -hexose ( 2 ), arabinose ( 3 ), ribose ( 4 ), 2-deoxy- erythro -pentose ( 5 ), 3-deoxy- erythro -hexos-4-ulose ( 6 ), xylo -hexos-5-ulose ( 7 ), 6-deoxy- xylo -hexos-5-ulose ( 8 ), 5-deoxy- xylo -hexodialdose ( 9 ), 2,6-dideoxyhexos-5-ulose ( 10 ), xylose ( 11 ), 5-deoxypentose ( 12 ), 3-deoxypentulose ( 13 ), erythrose ( 14 ), and threose ( 15 ). Products 1 - 9 appear to be terminals of the “anhydroglucose” chain. Established free-radical reactions, typical for carbohydrates. are invoked to account for these products.

Physical and chemical characteristics of the species responsible for the lyoluminescent behaviour of irradiated carbohydrates

Abstract When irradiated solid carbohydrates are dissolved in water, light is emitted which maximizes in the 480–550 nm region. The emission is enhanced in water saturated with oxygen and reduced in argon- or nitrogen-saturated water, and is not affected by changing the solvent to D2O, or when a singlet molecular oxygen (1Δg) quencher, such as β-carotene, is present. The emission is extremely weak, consistent with the low quantum yields found for singlet oxygen species. Addition of eosin, an acceptor of excitation energy corresponding to that of a 1Σg. 1Δg molecular pair state, leads to the observation of a fluorescence with a maximum in the 550 nm region, which is indicative of energy transfer. The difficulties in proposing singlet oxygen as the species responsible for the light emission are discussed.

Lyoluminescence of irradiated carbohydrates— The role of dissolution rate and oxygen

Abstract The lyoluminescent emission from γ-irradiated carbohydrates is shown to be strictly controlled by the rate of dissolution of the solid and the availability of oxygen for reaction during dissolution. These effects are explained in terms of oxidation of trapped radicals diffusing from the dissolving carbohydrate which react in an “active volume” set up at the onset of dissolution at the crystal-water interface. At irradiation doses greater than 82.5 krad for mannose there is a suppression of the emission which results from an incomplete oxidation of the diffusing radicals due to insufficient O2 in the active volume leading to a reaction involving unoxidised radicals and peroxyl radicals which are believed to be the precursors of the emission. This reaction is suppressed when the oxygen supply to the “active volume” is increased. This can be achieved by increasing the oxygen content of the injector gas and indirectly by decreasing the solubility of the carbohydrate. Under these conditions the linear dose range of the lyoluminescence response is extended to ca. 330 krad close to the dose at which trapped radicals saturate in the irradiated solid carbohydrate. Although lyoluminescence is a liquid surface-layer effect as expected the generation of the emission is greatly influenced by oxygen present in the injection atmosphere. Quenching of lyoluminescence by adding peroxyl radical quenchers Cu(II) ions and hydroquinone, suggests that the reaction involving these quenchers also occurs in the “active volume”. The results generally can be interpreted in terms of a diffusion model.

γ-Radiolysis of N2O-saturated aqueous glycerol solutions: Product yields and free radical mechanism

Abstract The yields of products, glyceraldehyde (I), dihydroxyacetone (II), 3-hydroxypropanal (III), hydroxyacetone (IV), 2,3-bis(hydroxymethyl)-1,4-butandial (V), 1,2-bis(glycolyl)ethane (VI), 3-(glycolyl)-2-(hydroxymethyl)-propanal (VII), 2-(hydroxymethyl)-3, 4, 5-trihydroxy pentanal (VIII), 3-deoxyhexulose (IX), hexitol (X), 2-(hydroxymethyl)-pentitol (XI) and trimer (XII) formed during the γ-radiolysis of N2O-saturated aqueous solutions containing glycerol have been quantitatively determined by gas liquid chromatography. It is evident that four radicals generated from the initial substrate participate in disproportionation, dimerisation and hydrogen abstraction reactions leading to these products. These radicals comprise two hydroxyalkyl radicals and their corresponding carbonyl-conjugated product radicals formed after water elimination. The initial radicals lead directly to products I, II, X and XI and the water-eliminated radicals to products III, IV, VI and VII. Products VIII and IX result from combination of the hydroxy-alkyl and carbonyl-conjugated radicals. Dimerisation and disproportionation of the hydroxy-alkyl radicals are favoured at higher dose rates while there is a reduction in water elemination and the products resulting. Hydrogen abstraction from glycerol by carbonyl-conjugated radicals in a chain mechanism is responsible for the large increase in yields of products III and IV when the initial substrate concentration is increased.

Electron spin resonance study of hydrogen adduct radicals generated from indole and its derivatives in γ-irradiated methanolic glasses at 77 K

The structures of radiation-induced radicals generated from indole and a selected number of its derivatives in methanolic glasses at 77 K have been investigated by e.s.r. spectroscopy. From the spectral characteristics [tt, aHCH2(2) 38.5, and aHCH(2) 12.0 G for indole], which are identical in almost all instances to the parent compound, it can be deduced that the radicals are formed primarily by hydrogen addition at the benzene nucleus. The α-carbon position, C-7, is favoured from the e.s.r. results obtained for selective blocking of reactive sites and by comparison with e.s.r. spectra obtained for benzene, indoline, and pyrrole in irradiated methanolic glasses and pyrrolidine irradiated in the pure state at 77 K. In the polycrystalline state only indole exhibits an e.s.r. spectrum which is indicative of the formation of a hydrogen adduct. Although there is some doubt about the homogeneity of these protic glasses containing >1M-solute it is clear that a significant contribution to the mechanism of formation of hydrogen adduct radicals comes from a process involving solvent protonation of an intermediate indole anion.

Radiation studies of aryl glycosides : Part VI. Radicals derived from Phenyl β-d-glucopyranosides

Abstract Radicals formed by γ-irradiation of o -, m -, and p -substituted-phenyl β- d -glucopyranosides have been studied in the polycrystalline state, in glassy methanol, and in frozen, aqueous solution. Substituted cyclohexadienyl radicals and radicals derived from the d -glucopyranosyl group are evident after irradiation of the compounds in the solid state and in frozen, aqueous solutions. Cyclohexadienyl radicals are the more stable during thermal annealing and are present in 2–3 times greater yield than the sugar radicals. p -Hydroxy- and methoxy-phenyl β- d -glucopyranosides yield phenoxy radicals, which can be transformed into substituted cyclohexadienyl radicals by thermal annealing. Hydrogen abstraction and inter- and intra-molecular hydrogen-transfer are the most likely processes leading to the radicals which have been identified.

Organic guest radical and radical anion trapping in cycloamylose host matrices induced by γ-irradiation at 77 K

The e.s.r. spectra of a number of organic radicals and radical anions generated from organic ‘guest’ in cycloamylose matrices by γ-irradiation at 77 K have been investigated. Both hydrogen addition to and hydrogen removal from guest molecules occurs, depending on the nature of the guest. Electron addition is observed only in certain instances, i.e. for highly electron affinic molecules, viz. hexafluorobenzene. The ability of these systems to stabilise organic radicals for the purpose of observing isotropic e.s.r. spectra at well below room temperature compares favourably with the extensively used adamantane systems. Furthermore, since the host void dimensions can be varied to a greater extent enhanced spectral resolution is observed in certain instances and the variations in line width with void size can be studied.

Nitroxide and nitro-anion radicals derived from nitrophenyl β-D-glycosides

Abstract Photolysis of m - and p -nitrophenyl β- D -glycopyranosides in methanol yields the corresponding nitroxide radical under neutral conditions and the nitro-anion radical in the presence of alkali. No stable radicals are produced from the o -isomer, due to facile hydrolysis of the glycosidic bond. From the e.s.r. spectra, it is clear that the glycosidic bond remains intact in these radicals, and m -proton couplings, not previously resolved, can be identified ( a H 1.0 gauss). For the nitro-anion from the p -isomer, a N = 15.28 gauss, which is larger than for other p -substituted ether nitro-anions. Radical anions from o -, m -, and p -isomers can be produced electrochemically in acetonitrile, and coupling to H-1 of the glycosyl group, not previously found, is evident ( a N = 0.3–0.4 gauss) in the nitro-anion from the p -isomers, but not from the o - and m -isomers. A Hammett-type correlation for p -substituents gives σ values of −0.15 for the galactoside and −0.13 for glucoside groups.

Methylation as a means of location of anionic groups in some cellulose phosphates

Abstract The distribution of methyl groups after methylation of celluloses containing phosphate groups is quite different from that obtained after methylation of cellulose. The results indicate a probable high level of phosphorylation at positions 2 and 6 of d -glucopyranosyl units, and give supporting evidence for the recognised fibrillar models for cotton.

Hydrogen adduct radical formation in γ-irradiated α-, β-, and γ-cycloamylose–benzene complexes

α-, β-, and γ-Cycloamyloses are suitable ‘host’ matrices for stabilising hydrogen adduct radicals formed by hydrogen atom addition to the benzene ‘guest’ during γ-irradiation and compare favourably with the extensively used adamantane matrix for the observation of extremely well resolved e.s.r. spectra.