Environmental Effects on Primary Radical Formation in Guanine: Solid-State ESR and ENDOR of Guanine Hydrobromide Monohydrate

Single crystals of guanine hydrobromide monohydrate, in which the guanine base is protonated at N7, were X-irradiated at 8 and 65 K. Using K-band ESR, ENDOR, and field-swept-ENDOR (FSE) techniques, the crystals were studied between 8 K and room temperature. There was evidence for five different radi...

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Bibliographic Details
Published in:Radiation research 1991-02, Vol.125 (2), p.119-128
Main Authors: Hole, Eli O., Sagstuen, Einar, Nelson, William H., Close, David M.
Format: Article
Language:English
Subjects:
Anions
Biological and medical sciences
Chemical bases
Crystallization
Crystals
Electron paramagnetic resonance
Electron Spin Resonance Spectroscopy
Free Radicals
Freezing
Guanine - radiation effects
Hydrochlorides
Magnetic fields
Medical sciences
Protons
Radiotherapy. Instrumental treatment. Physiotherapy. Reeducation. Rehabilitation, orthophony, crenotherapy. Diet therapy and various other treatments (general aspects)
Single crystals
Space life sciences
Tensors
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Summary:Single crystals of guanine hydrobromide monohydrate, in which the guanine base is protonated at N7, were X-irradiated at 8 and 65 K. Using K-band ESR, ENDOR, and field-swept-ENDOR (FSE) techniques, the crystals were studied between 8 K and room temperature. There was evidence for five different radicals, RI-RV, immediately following irradiation at 8 or 65 K. RI was identified as the O6-protonated anion. It decayed near room temperature with no detectible successor. RII was identified as the N7-deprotonated cation, and decayed near 130 K. RIII is thought to be a ring-opened product formed by C8-N9 bond rupture; upon warming, it decayed at 150 K. RIV is the well-known C8 H-addition radical. These four radicals have been observed previously in the hydrochloride salt of guanine monohydrate. RV is novel, however, with magnetic characteristics consistent with those of the product formed by net OH addition to C5 of the unsaturated C4-C5 bond. It is characterized by four α-proton couplings indicating π-electron spin as follows: 13% at C8; 11% at N7; and 12% at N10. RV decayed between 240 and 255 K with no detectable successor. Upon further warming, very weak resonance lines due to additional, unidentified radicals were observed. A comparison of these results with those obtained from other systems containing N7-protonated guanine bases demonstrates the effect of the environment on the primary radical formation.
ISSN:0033-7587
1938-5404
DOI:10.2307/3577878