Theoretical study of photoreactions between oxidized pterins and molecular oxygen

• Published in: Journal of photochemistry and photobiology. A, Chemistry. Chemistry., 2019-03, Vol.372, p.254-259
• Main Authors: Buglak, Andrey A., Telegina, Taisiya A., Vorotelyak, Ekaterina A., Kononov, Alexei I.
• Format: Article
• Language: English
• Subjects: Atomic energy levels; Autoionization; Cancer; Density functional theory; Deoxyribonucleic acid; DFT; DNA; Electron transfer; Electronegativity; Heterocyclic compounds; Ionization; Ionization potentials; Irradiation; Low molecular weights; Molecular weight; Molecular weight distribution; Oxidation; Oxidative stress; Oxygen; Photodynamic therapy; Photosensitization; Pterins; Singlet oxygen; Skin; Solvation; Superoxide; TDDFT; Time dependence; Triplet states; Ultraviolet radiation; Vitiligo
• ISSN: 1010-6030; 1873-2666
• DOI: 10.1016/j.jphotochem.2018.12.002

[Display omitted] •Reactions between pterins and molecular oxygen were explored using DFT.•Pterins participate in reaction with O2 and are able to generate singlet oxygen.•Pterins may produce superoxide-anion radicals through autoionization reactions.•More electronegative molecules have higher ionization potential of both S0 and T1. Pterins are low molecular weight heterocyclic compounds that are widely distributed in living organisms, primarily in the form of reduced coenzyme forms. Oxidized pterins are present in the cells for the most part as oxidation products of tetrahydropterins and dihydropterins. Oxidized pterins are known to cause DNA photodamage under UV-irradiation. Photosensitization of oxidized pterins may cause oxidative stress in the human skin depigmentation disorder vitiligo. There have been made attempts to use oxidized pterins as sensitizers in photodynamic therapy (PDT) of cancer. The photoreactions between a set of six pterin compounds and molecular oxygen were explored using density functional theory, a time-dependent formalism for excited states (TD-DFT) and a continuum COSMO model to include the effects of H2O solvation. Both acid and base forms of pterins were taken into consideration. The computed singlet and triplet excitation energies are in agreement with the experimental data. We showed that compounds with the most electronegative lateral substituent (formyl, carboxyl) at C6 position have the highest value of both S0 and T1 state ionization potential. We conclude that pterin molecules do participate in photoreactions with molecular oxygen. Oxidized pterins are able to generate singlet oxygen and may also produce superoxide-anion radicals indirectly through autoionization reactions. Direct electron transfer reactions between pterins and oxygen were also studied.