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Zhou Q, Guo W, Hu Z, Yan S, Jie J, Su H. Can methylated purine bases act as photoionization hotspots? Photochem Photobiol 2024; 100:368-379. [PMID: 37792888 DOI: 10.1111/php.13862] [Citation(s) in RCA: 0] [Impact Index Per Article: 0] [Reference Citation Analysis] [Abstract] [Key Words] [MESH Headings] [Grants] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 05/29/2023] [Revised: 09/12/2023] [Accepted: 09/12/2023] [Indexed: 10/06/2023]
Abstract
The direct photoionization of DNA canonical bases under ultraviolet radiation is difficult due to the high ionization potentials. According to previous quantum chemical calculations, methylation can have great influence on the ionization potential. Are methylated nucleobases prone to photoionization and cause DNA damage? As an important epigenetic modification in transcription, expression, and regulation of genes, it is of great biological significance to explore the effect of methylation on base photoionization from the experimental perspective. Herein, we study the photoionization behavior of methylated purines 6 mA and 6mG at 266 nm using a nanosecond transient UV-Vis spectroscopy. The hydrated electron and methylated base radicals are observed, indicating the occurrence of photoionization for both 6mG and 6 mA. We measured one-photon ionization yields to be (5.0 ± 0.2) × 10-3 and (1.4 ± 0.2) × 10-3 for 6mG and 6 mA, respectively. These are higher than those of (dA)20 and (dA20 )·(dT20 ) previously reported, indicating that methylation significantly promotes base photoionization with a stronger effect than base stacking, consistent with calculations in literature. Given that the hydrated electrons and methylated base radicals from photoionization can trigger a cascade of deleterious reactions, the methylated purine bases may act as hotspots of DNA photoionization damage of living organisms.
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Affiliation(s)
- Qian Zhou
- College of Chemistry, Beijing Normal University, Beijing, China
| | - Wenwen Guo
- College of Chemistry, Beijing Normal University, Beijing, China
| | - Zheng Hu
- College of Chemistry, Beijing Normal University, Beijing, China
| | - Shuyi Yan
- College of Chemistry, Beijing Normal University, Beijing, China
| | - Jialong Jie
- College of Chemistry, Beijing Normal University, Beijing, China
| | - Hongmei Su
- College of Chemistry, Beijing Normal University, Beijing, China
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2
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Zhou Q, Hao Y, Jie J, Wang S, Xia Y, Yang C, Liu L, Fang WH, Su H. Dual Functionality of 6-Methylthioguanine: Synergistic Effects Enhancing the Photolability of DNA Nucleobases. JACS AU 2024; 4:441-453. [PMID: 38425924 PMCID: PMC10900203 DOI: 10.1021/jacsau.3c00575] [Citation(s) in RCA: 0] [Impact Index Per Article: 0] [Reference Citation Analysis] [Abstract] [Key Words] [Grants] [Track Full Text] [Download PDF] [Figures] [Subscribe] [Scholar Register] [Received: 09/28/2023] [Revised: 01/05/2024] [Accepted: 01/05/2024] [Indexed: 03/02/2024]
Abstract
A small chemical modification of the nucleobase structure can significantly enhance the photoactivity of DNA, which may incur DNA damage, thus holding promising applications in photochemotherapy treatment of cancers or pathogens. However, single substitution confers only limited phototoxicity to DNA. Herein, we combine femtosecond and nanosecond time-resolved spectroscopy with high-level ab initio calculations to disentangle the excited-state dynamics of 6-methylthioguanine (me6-TG) under variable wavelength UVA excitation (310-330 nm). We find that double substitution of nucleobases (thionation and methylation) boosts the photoactivity by introducing more reactive channels. Intriguingly, 1nNπ*, rather than 1nSπ*, acts as the doorway state engendering the formation of the long-lived reactive triplet state in me6-TG. The 1nNπ* induces a low spin-orbit coupling of 8.3 cm-1, which increases the intersystem crossing (ISC) time (2.91 ± 0.14 ns). Despite the slowed ISC, the triplet quantum yield (ΦT) still accounts for a large fraction (0.6 ± 0.1), consistent with the potential energy surface that favors excited-state bifurcation to 1nNπ*min (3.36 ± 0.15 ps) rather than 1ππ*min (5.05 ± 0.26 ps), such that the subsequent ISC to triplet via 1nNπ*min constitutes the main relaxation pathway in me6-TG. Although this ΦT is inferior to its single-substituted predecessor 6-thioguanine (6-TG, 0.8 ± 0.2), the effect of thionation in synergy with methylation opens a unique C-S bond cleavage pathway through crossing to a repulsive 1πσ* state, generating thiyl radicals as highly reactive intermediates that may invoke biological damage. This photodissociation channel is extremely difficult for conventional nucleobases. These findings demonstrate the synergistic effects of double functionality substitution in modulating excited-state dynamics and enhancing the photolabile character of DNA nucleobases, providing inspirations for the rational design of advanced photodynamic and photochemotherapy approaches.
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Affiliation(s)
| | | | - Jialong Jie
- College of Chemistry, Beijing Normal University, Beijing 100875, China
| | - Shuo Wang
- College of Chemistry, Beijing Normal University, Beijing 100875, China
| | - Ye Xia
- College of Chemistry, Beijing Normal University, Beijing 100875, China
| | - Chunfan Yang
- College of Chemistry, Beijing Normal University, Beijing 100875, China
| | - Lihong Liu
- College of Chemistry, Beijing Normal University, Beijing 100875, China
| | - Wei-Hai Fang
- College of Chemistry, Beijing Normal University, Beijing 100875, China
| | - Hongmei Su
- College of Chemistry, Beijing Normal University, Beijing 100875, China
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Caldero-Rodríguez NE, Crespo-Hernández CE. Excited state dynamics of 2'-deoxyisoguanosine and isoguanosine in aqueous solution. Phys Chem Chem Phys 2022; 24:6769-6781. [PMID: 35244114 DOI: 10.1039/d1cp05795b] [Citation(s) in RCA: 0] [Impact Index Per Article: 0] [Reference Citation Analysis] [Abstract] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/21/2022]
Abstract
Photostability is thought to be an inherent property of nucleobases required to survive the extreme ultraviolet radiation conditions of the prebiotic era. Previous studies have shown that absorption of ultraviolet radiation by the canonical nucleosides results in ultrafast internal conversion to the ground state, demonstrating that these nucleosides efficiently dissipate the excess electronic energy to the environment. In recent years, studies on the photophysical and photochemical properties of nucleobase derivatives have revealed that chemical substitution influences the electronic relaxation pathways of purine and pyrimidine nucleobases. It has been suggested that amino or carbonyl substitution at the C6 position could increase the photostability of the purine derivatives more than the substitution at the C2 position. This investigation aims to elucidate the excited state dynamics of 2'-deoxyisoguanosine (dIsoGuo) and isoguanosine (IsoGuo) in aqueous solution at pH 7.4 and 1.4, which contain an amino group at the C6 position and a carbonyl group at the C2 position of the purine chromophore. The study of these derivatives is performed using absorption and emission spectroscopies, broadband transient absorption spectroscopy, and density functional and time-dependent density functional levels of theory. It is shown that the primary relaxation mechanism of dIsoGuo and IsoGuo involves nonradiative decay pathways, where the population decays from the S1(ππ*) state through internal conversion to the ground state via two relaxation pathways with lifetimes of hundreds of femtoseconds and less than 2 ps, making these purine nucleosides photostable in aqueous solution.
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Wang D, Wang X, Jiang Y, Cao S, Jin P, Pan H, Sun H, Sun Z, Chen J. Excited State Dynamics of Methylated Guanosine Derivatives Revealed by Femtosecond Time-resolved Spectroscopy. Photochem Photobiol 2022; 98:1008-1016. [PMID: 35203108 DOI: 10.1111/php.13612] [Citation(s) in RCA: 0] [Impact Index Per Article: 0] [Reference Citation Analysis] [Abstract] [Key Words] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 11/29/2021] [Accepted: 02/20/2022] [Indexed: 11/28/2022]
Abstract
Methylated DNA/RNA nucleobases are important epigenetic marks in living species and play an important role for targeted therapies. Moreover, they could bring significant changes to the photo-stability of nucleic acid, leading these sites become mutational hotspots for disease such as skin cancer. While a number of studies have demonstrated the relationship between excited state dynamics and the biological function of methylated cytosine in DNA, investigations aimed at unraveling the excited state dynamics of methylated guanosine in RNA have been largely overlooked. In this work, influence of methylation on the excited state dynamics of guanosine is studied by using femtosecond time-resolved spectroscopy. Our results suggest that the effect of methyl substitution on the photophysical properties of guanosine is position sensitive. N1-methylguanosine shows very similar excited state dynamics as that in guanosine, while almost one order of magnitude longer lifetime of the La state is observed in N2, N2-dimethylguanosine. Notably, N7-methylation can lead to a new minimum on the La state, which shows a two orders of magnitude longer excited state lifetime compared with guanosine. These findings not only help understanding excited state dynamics of methylated guanosines, but also lay the foundation for further studying DNA/RNA strands incorporated with these bases.
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Affiliation(s)
- Danhong Wang
- State Key Laboratory of Precision Spectroscopy, East China Normal University, Shanghai, 200062, China
| | - Xueli Wang
- State Key Laboratory of Precision Spectroscopy, East China Normal University, Shanghai, 200062, China
| | - Yanrong Jiang
- State Key Laboratory of Precision Spectroscopy, East China Normal University, Shanghai, 200062, China
| | - Simin Cao
- State Key Laboratory of Precision Spectroscopy, East China Normal University, Shanghai, 200062, China
| | - Peipei Jin
- State Key Laboratory of Precision Spectroscopy, East China Normal University, Shanghai, 200062, China
| | - Haifeng Pan
- State Key Laboratory of Precision Spectroscopy, East China Normal University, Shanghai, 200062, China
| | - Haitao Sun
- State Key Laboratory of Precision Spectroscopy, East China Normal University, Shanghai, 200062, China
| | - Zhenrong Sun
- State Key Laboratory of Precision Spectroscopy, East China Normal University, Shanghai, 200062, China
| | - Jinquan Chen
- State Key Laboratory of Precision Spectroscopy, East China Normal University, Shanghai, 200062, China.,Collaborative Innovation Center of Extreme Optics, Shanxi University, Taiyuan, Shanxi, 030006, China
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Caldero-Rodríguez NE, Ortiz-Rodríguez LA, Gonzalez AA, Crespo-Hernández CE. Photostability of 2,6-diaminopurine and its 2'-deoxyriboside investigated by femtosecond transient absorption spectroscopy. Phys Chem Chem Phys 2022; 24:4204-4211. [PMID: 35119441 DOI: 10.1039/d1cp05269a] [Citation(s) in RCA: 2] [Impact Index Per Article: 1.0] [Reference Citation Analysis] [Abstract] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/21/2022]
Abstract
Ultraviolet radiation (UVR) from the sun is essential for the prebiotic syntheses of nucleotides, but it can also induce photolesions such as the cyclobutane pyrimidine dimers (CPDs) to RNA or DNA oligonucleotide in prebiotic Earth. 2,6-Diaminopurine (26DAP) has been proposed to repair CPDs in high yield under prebiotic conditions and be a key component in enhancing the photostability of higher-order prebiotic DNA structures. However, its electronic relaxation pathways have not been studied, which is necessary to know whether 26DAP could have survived the intense UV fluxes of the prebiotic Earth. We investigate the electronic relaxation mechanism of both 26DAP and its 2'-deoxyribonucleoside (26DAP-d) in aqueous solution using steady-state and femtosecond transient absorption measurements that are complemented with electronic-structure calculations. The results demonstrate that both purine derivatives are significantly photostable to UVR. It is shown that upon excitation at 287 nm, the lowest energy 1ππ* state is initially populated. The population then branches following two relaxation coordinates in the 1ππ* potential energy surface, which are identified as the C2- and C6-relaxation coordinates. The population following the C6-coordinate internally converts to the ground state nonradiatively through a nearly barrierless conical intersection within 0.7 ps in 26DAP or within 1.1 ps in 26DAP-d. The population that follows the C2-relaxation coordinate decays back to the ground state by a combination of nonradiative internal conversion via a conical intersection and fluorescence emission from the 1ππ* minimum in 43 ps and 1.8 ns for the N9 and N7 tautomers of 26DAP, respectively, or in 70 ps for 26DAP-d. Fluorescence quantum yields of 0.037 and 0.008 are determined for 26DAP and 26DAP-d, respectively. Collectively, it is demonstrated that most of the excited state population in 26DAP and 26DAP-d decays back to the ground state via both nonradiative and radiative relaxation pathways. This result lends support to the idea that 26DAP could have accumulated in large enough quantities during the prebiotic era to participate in the formation of prebiotic RNA or DNA oligomers and act as a key component in the protection of the prebiotic genetic alphabet.
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Affiliation(s)
| | | | - Andres A Gonzalez
- Department of Chemistry, Case Western Reserve University, Cleveland, OH 44106, USA.
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Maiti S, Kim J, Park JH, Nam D, Lee JB, Kim YJ, Kee JM, Seo JK, Myung K, Rohde JU, Choe W, Kwon OH, Hong SY. Chemoselective Trifluoroethylation Reactions of Quinazolinones and Identification of Photostability. J Org Chem 2019; 84:6737-6751. [DOI: 10.1021/acs.joc.9b00470] [Citation(s) in RCA: 23] [Impact Index Per Article: 4.6] [Reference Citation Analysis] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 12/14/2022]
Affiliation(s)
- Saikat Maiti
- School of Energy and Chemical Engineering, Ulsan National Institute of Science and Technology (UNIST), 50 UNIST-gil, Ulsan 44919, Republic of Korea
- Center for Genomic Integrity (CGI), Institute for Basic Science (IBS), 50 UNIST-gil, Ulsan 44919, Republic of Korea
| | - Jaeshin Kim
- School of Energy and Chemical Engineering, Ulsan National Institute of Science and Technology (UNIST), 50 UNIST-gil, Ulsan 44919, Republic of Korea
| | - Jae-Heon Park
- Center for Soft and Living Matter, IBS, 50 UNIST-gil, Ulsan 44919, Republic of Korea
| | | | - Jae Bin Lee
- School of Energy and Chemical Engineering, Ulsan National Institute of Science and Technology (UNIST), 50 UNIST-gil, Ulsan 44919, Republic of Korea
| | - Ye-Jin Kim
- Center for Soft and Living Matter, IBS, 50 UNIST-gil, Ulsan 44919, Republic of Korea
| | | | | | - Kyungjae Myung
- Center for Genomic Integrity (CGI), Institute for Basic Science (IBS), 50 UNIST-gil, Ulsan 44919, Republic of Korea
| | | | | | - Oh-Hoon Kwon
- Center for Soft and Living Matter, IBS, 50 UNIST-gil, Ulsan 44919, Republic of Korea
| | - Sung You Hong
- School of Energy and Chemical Engineering, Ulsan National Institute of Science and Technology (UNIST), 50 UNIST-gil, Ulsan 44919, Republic of Korea
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A theoretical investigation of sugar and phosphate contributions to the activation barriers of guanine methylation by carcinogenic methane diazonium ion. Chem Phys Lett 2019. [DOI: 10.1016/j.cplett.2018.10.063] [Citation(s) in RCA: 2] [Impact Index Per Article: 0.4] [Reference Citation Analysis] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 01/22/2023]
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Zhou P, Zhao L. How Does the O6-Methylation Regulate the Excited-State Decay of Guanine Monomers. J Phys Chem B 2018; 123:201-206. [DOI: 10.1021/acs.jpcb.8b08606] [Citation(s) in RCA: 5] [Impact Index Per Article: 0.8] [Reference Citation Analysis] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/29/2022]
Affiliation(s)
- Panwang Zhou
- State Key Laboratory of Molecular Reaction Dynamics, Dalian Institute of Chemical Physics, Chinese Academy of Science, Dalian 116023, Liaoning, China
| | - Li Zhao
- School of Science, China University of Petroleum, Qingdao 266580, Shandong, China
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Ashwood B, Ortiz-Rodríguez LA, Crespo-Hernández CE. Photochemical relaxation pathways of S 6-methylthioinosine and O 6-methylguanosine in solution. Faraday Discuss 2018; 207:351-374. [PMID: 29372193 DOI: 10.1039/c7fd00193b] [Citation(s) in RCA: 7] [Impact Index Per Article: 1.2] [Reference Citation Analysis] [Abstract] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/21/2022]
Abstract
S6-Methylthioinosine and O6-methylguanosine are byproducts resulting from the enzymatic reactions of sulfur-substituted prodrugs in cells and from the interaction of alkylating agents with cellular DNA, respectively. Their photochemistry has not been investigated, and it is currently unknown whether light absorption by these byproducts may pose any threat to the cell. In this contribution, their photoinduced processes upon absorption of UVB radiation are reported using broadband transient absorption spectroscopy. Plausible electronic relaxation mechanisms are proposed for both biological molecules, which are supported by steady-state absorption and emission measurements, and by singlet and triplet vertical excitation energies performed on a large subset of ground-state optimized conformational isomers in solution. The results are compared to the body of knowledge gathered in the scientific literature about the light-induced processes in the sulfur-substituted and canonical purine monomers. In particular, it is shown that S6-methylation decreases the rate to populate the lowest-energy triplet state and blueshifts the ground-state absorption spectrum compared to those for the sulfur-substituted prodrugs and for the 6-thioguanosine metabolite. Similarly, O6-methylation decreases the rate of internal conversion to the ground state observed in the guanine monomers by more than 10-fold in acetonitrile and 40-fold in aqueous solution, while it redshifts the ground-state absorption spectrum. Collectively, this investigation provides relevant new insights about the relationship between structural modifications of the purine chromophore and the electronic relaxation mechanisms in this important group of biological molecules.
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Affiliation(s)
- Brennan Ashwood
- Department of Chemistry, Center for Chemical Dynamics, Case Western Reserve University, 10900 Euclid Avenue, Cleveland, Ohio 44106, USA.
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Eichler DR, Papadantonakis GA. Activation barriers for methylation of DNA bases by dimethyl sulfate. Chem Phys Lett 2017. [DOI: 10.1016/j.cplett.2017.10.003] [Citation(s) in RCA: 7] [Impact Index Per Article: 1.0] [Reference Citation Analysis] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/28/2022]
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