Electronic relaxation mechanism of 9‐methyl‐2,6‐diaminopurine and 2,6‐diaminopurine‐2′‐deoxyribose in solution
Prolonged ultraviolet exposure results in the formation of cyclobutane pyrimidine dimers (CPDs) in RNA. Consequently, prebiotic photolesion repair mechanisms should have played an important role in the maintenance of the structural integrity of primitive nucleic acids. 2,6‐Diaminopurine is a prebiot...
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| Published in: | Photochemistry and photobiology Vol. 100; no. 2; pp. 393 - 403 |
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| Main Authors: | , , , , |
| Format: | Journal Article |
| Language: | English |
| Published: |
United States
Blackwell Publishing Ltd
01-03-2024
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| Subjects: | |
| Online Access: | Get full text |
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| Summary: | Prolonged ultraviolet exposure results in the formation of cyclobutane pyrimidine dimers (CPDs) in RNA. Consequently, prebiotic photolesion repair mechanisms should have played an important role in the maintenance of the structural integrity of primitive nucleic acids. 2,6‐Diaminopurine is a prebiotic nucleobase that repairs CPDs with high efficiency when incorporated into polymers. We investigate the electronic deactivation pathways of 2,6‐diaminopurine‐2′‐deoxyribose and 9‐methyl‐2,6‐diaminopurine in acetonitrile and aqueous solution to shed light on the photophysical and excited state properties of the 2,6‐diaminopurine chromophore. Evidence is presented that both are photostable compounds exhibiting similar deactivation mechanisms upon the population of the S1(ππ* La) state at 290 nm. The mechanism involves deactivation through the C2‐ and C6‐reaction coordinates and >99% of the excited state population decays through nonradiative pathways involving two conical intersections with the ground state. The radiative and nonradiative lifetimes are longer in aqueous solution compared to acetonitrile. While τ1 is similar in both derivatives, τ2 is ca. 1.5‐fold longer in 2,6‐diaminopurine‐2′‐deoxyribose due to a more efficient trapping in the S1(ππ* La) minimum. Therefore, 2,6‐diaminopurine could have accumulated in significant quantities during prebiotic times to be incorporated into non‐canonical RNA and play a significant role in its photoprotection.
The photophysics and electronic relaxation mechanism of 2,6‐diaminopurine‐2′‐deoxyribose and 9‐methyl‐2,6‐diaminopurine is experimentally and computationally investigated in acetonitrile and aqueous solution. The relaxation mechanism includes deactivation through C2‐ and C6‐reaction coordinates and involves two conical intersections. Longer lifetimes are observed in aqueous solution than in acetonitrile and trapping of the population in the S1(ππ*) is more efficient in 2,6‐diaminopurine‐2′‐deoxyribose than in 9‐methyl‐2,6‐diaminopurine. Collectively, it is demonstrated that prebiotic 2,6‐diaminopurine could have accumulated in significant quantities during the prebiotic era to be incorporated into non‐canonical RNA and play a significant role in the photoprotection of primitive nucleic acids. |
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| Bibliography: | This article is part of a Special Issue dedicated to the topic of Nucleic Acid Photophysics. ObjectType-Article-1 SourceType-Scholarly Journals-1 ObjectType-Feature-2 content type line 23 |
| ISSN: | 0031-8655 1751-1097 |
| DOI: | 10.1111/php.13887 |