The Triplet State of 6-thio-2'-deoxyguanosine: Intrinsic Properties and Reactivity Toward Molecular Oxygen.
Photochem Photobiol
; 92(2): 286-292, 2016 03.
Article
em En
| MEDLINE
| ID: mdl-26757207
ABSTRACT
Thiopurine prodrugs are currently among the leading treatment options for leukemia, immunosuppression, and arthritis. Patients undergoing long-term thiopurine treatment are at a higher risk of developing sunlight-induced skin cancers than the general population. This side effect originates from the cellular metabolization of thiopurine prodrugs to form 6-thio-2'-deoxyguanosine, which can absorb UVA radiation, populating its reactive triplet state and leading to oxidatively generated damage. However, the photo-oxidation mechanism is not fully understood. In this contribution, the oxidation potential and the adiabatic triplet energy of 6-thio-2'-deoxyguanosine are estimated computationally, whereas the intrinsic rate of triple-state decay and the rate constant for triplet quenching by molecular oxygen are determined using time-resolved spectroscopic techniques. A singlet oxygen quantum yield of 0.24 ± 0.02 is measured in aqueous solution (0.29 ± 0.02 in acetonitrile). Its magnitude correlates with the relatively low percentage of triplet-O2 collision events that generate singlet oxygen (SΔ = 37%). This behavior is rationalized as being due to the exergonic driving force for electron transfer between the triplet state of 6-thio-2'-deoxyguanosine and molecular oxygen (ΔGET = -69.7 kJ mol-1 ), resulting in the formation of a charge-transfer complex that favors nonradiative decay to the ground state over triplet energy transfer.
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1
Coleções:
01-internacional
Base de dados:
MEDLINE
Assunto principal:
Oxigênio
Idioma:
En
Revista:
Photochem Photobiol
Ano de publicação:
2016
Tipo de documento:
Article