ESR studies of radical reaction kinetics in γ-irradiated α-glycine single crystals

Syutkin, V. M.; Tolkatchev, V.A.

doi:10.1016/0146-5724(82)90038-3

Cited by 6 publications

(5 citation statements)

References 26 publications

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“…Two species have been suggested, the σ-radical NH 2 CH 2 COO species 8 (K1) by deprotonation from the amino group, and the electronically rearranged nitrogen centered π-radical species N CH 2 COO - (K2). , The latter seems to relax slowly into a conformational slightly different product K2‘. , Upon 77 K photolysis using various wavelengths of the light, the products HṄCH 2 COO - and N CH 2 were detected . Upon thermal annealing from 77 K, Product K2 or K2‘ has been suggested to convert directly into N CHCOO - (radical I) by intramolecular hydrogen transfer, , but several authors also have suggested an alternative decay route, involving decarboxylation of K2 or K2‘ as an intermediate step. , Thermochemical properties of glycine radicals 40 as well as detectable amounts of CO 2 upon chemical analysis of stable radiation products may support this suggestion. ,, It should be noted that Armstrong et al points out that the radical NH 2 ĊHCOO(H) as detected in aqueous solution 31 are expected products from K2 by spontaneous deprotonation.…”

Section: Mechanistic Aspectsmentioning

confidence: 99%

“…Following the primary reduction event by capturing an electron, the glycine anion protonates at the carboxy group 7 by proton transfer from a hydrogen-bonded neighboring molecule. This is followed by deamination yielding the C ˙H2 COOH radical (A2) 6 which has been suggested to deprotonated (A2′). A major part of the A2 or A2′ radicals transform by H-abstraction from a neighboring molecule 34 into the NH 3 + CHCOOproduct, radical I, above 200 K, but a fraction of the C ˙H2 COO(H) species remain stable at room temperature and has been analyzed by various authors.…”

Section: Mechanistic Aspectsmentioning

confidence: 99%

“…8,10 Upon 77 K photolysis using various wavelengths of the light, the products HN ˙CH 2 COOand N H 3 + CH 2 were detected. 37 Upon thermal annealing from 77 K, Product K2 or K2′ has been suggested to convert directly into NH 3 + CHCOO -(radical I) by intramolecular hydrogen transfer, 6,38 but several authors also have suggested an alternative decay route, involving decarboxylation of K2 or K2′ as an intermediate step. 10,39 Thermochemical properties of glycine radicals 40 as well as detectable amounts of CO 2 upon chemical analysis of stable radiation products may support this suggestion.…”

Section: Mechanistic Aspectsmentioning

confidence: 99%

Section: Introductionmentioning

confidence: 99%

“…The low-temperature irradiation and EPR/ENDOR analysis of glycine crystals have shown that even for this simple amino acid, the radiation chemistry is complex . Iwasaki and co-workers − discussed the radicals formed after 4 K irradiation and measurement, and several other authors ,− have analyzed sequences of reactions taking place and products formed from the initially formed anion and cation radical species. The bulk of experimental data may suggest possible schemes of radical reactions, but even after many years of intensive studies, pieces still are missing in the complex puzzle of mechanistically connecting the various radical products stabilized at different temperatures.…”

Section: Introductionmentioning

confidence: 99%

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EPR and ENDOR Studies of Single Crystals of α-Glycine X-ray Irradiated at 295 K

and

Sagstuen

1998

J. Phys. Chem. B

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Single crystals of the amino acid α-glycine N−CH2−COO- were X-ray irradiated at 280 K and studied at 295 K and at 100 K using EPR, ENDOR, and EIE techniques. Five radicals were detected and characterized. Two of these are well known from previous studies, the oxidation product N−ĊH−COO- (radical I) and the reduction product ĊH2−COO- (radical II). It is shown that at 295 K the ENDOR and EIE spectra from radical I are characteristic of efficient W1 x cross relaxation induced by rapid rotation of the amino group. This allows for the determination of the absolute signs of the hyperfine coupling constants of radical I. The other three radicals are two geometrical conformations of the product H2N−ĊH−COOH (radicals III and IV) and a species suggested to be the dimer product N−CH2−CO−ĊH−COO- (radical V). Radical III exhibits spectral parameters related to those previously reported by M. Brustolon et al. (J. Phys. Chem. 1997, 101, 4887). However, on the basis of our analysis of ENDOR and EIE spectra from normal as well as from partially deuterated crystals, the structural assignment for radical III is different from that suggested by these authors. A comparison with a new radical species recently observed and characterized in irradiated crystals of the amino acid l-α-alanine indicates that the new alanine radical and radical III presented here have similar structures. A review of the mechanistic aspects of radical formation in glycine is given, and the newly detected species (radicals III−V) are tentatively fitted into this scheme.

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