Relaxation of the T1 excited state of 2-thiothymine, its riboside and deoxyriboside-enhanced nonradiative decay rate induced by sugar substituent

Taras-Goślińska, Katarzyna; Burdziński, Gotard; Wenska, G.

doi:10.1016/j.jphotochem.2013.11.003

Cited by 43 publications

(85 citation statements)

References 42 publications

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“…Its magnitude depends on the solvent and concentration used, as has previously been reported for 4-thiodeoxythymidine [18,19]. This pathway only accounts for a small fraction of the T 1 (ππ*) state decay in 2-thiothymine and 2-thiouracil, while most of the triplet state population decays nonradiatively to the ground state on the microsecond time scale [31].…”

Section: Excited-state Deactivation Mechanism In 2-thiouracil Derivatmentioning

confidence: 64%

“…As described below, the key role of the S 1 (nπ*) state in the efficient and ultrafast population of the T 1 (ππ*) state has been corroborated recently by experimental [32] and computational methods [29]. Taras-Goślińska et al [31] investigated the radiative and nonradiative decay pathways of the T 1 (ππ*) state in 2-thiothymine and of its DNA and RNA nucleosides in acetonitrile. The authors used absorption, emission, and circular dichroism spectroscopic techniques, as well as nanosecond (λ exc ¼ 266 nm) and femtosecond As suggested by Suzuki and co-workers for 2-thiothymine earlier [16], the authors proposed that intersystem crossing occurs on an ultrafast time scale and with nearunity quantum yields, independent of the substituent in the N1 position (i.e., H, riboside, or deoxyriboside).…”

Section: Excited-state Deactivation Mechanism In 2-thiouracil Derivatmentioning

confidence: 88%

“…The absorption spectra shift from the UVC region in the nucleic acid monomers out to the UVA region in the thiobases. Furthermore, sulfur substitution inhibits ultrafast internal conversion to the ground state and dramatically increases the rate of intersystem crossing to the triplet manifold by enhanced spin-orbit coupling [11,17,18,27,33], which leads to near-unity triplet yields in these nucleic acid base analogues [11,16,18,22,31,144,195,196].…”

Section: Thiobasesmentioning

confidence: 99%

“…The enhanced nonradiative decay of the T 1 (ππ*) state hinders phosphorescence emission in the nucleosides, whereas a weak phosphorescence was detected in 2-thiothymine at room temperature (Table 14). It was suggested that addition of the sugar results in an increased number of vibrational and torsional modes in the nucleosides, which increases the Franck-Condon factors for nonradiative decay [31]. However, it is not clear if covalent addition of a sugar group at position 1 of 4-thiouracil or 4-thiothymine also reduces the phosphorescence emission because the values reported in Table 10 were obtained by different groups and under different experimental conditions.…”

Section: Excited-state Deactivation Mechanism In 2-thiouracil Derivatmentioning

confidence: 99%

“…2.4 for the nucleic acid bases, but more work is needed before making direct comparisons or arriving at any major conclusion. The femtosecond laser experiments performed by Taras-Goślińska et al were unable to determine the intersystem crossing rate of 2-thiothymine because of their limited time resolution [31], but did reveal small changes in the transient absorption spectra over a 1-20 ps time window in acetonitrile. The amplitude of the absorption bands from~350 nm to 600 nm decreases during this time window, whereas the amplitude of the absorption band from~600 nm to 650 nm (the highest probe wavelength used) increases during the same time scale.…”

Section: Excited-state Deactivation Mechanism In 2-thiouracil Derivatmentioning

confidence: 99%

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Photochemistry of Nucleic Acid Bases and Their Thio- and Aza-Analogues in Solution

Pollum

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Crespo‐Hernández

2014

Topics in Current Chemistry

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The steady-state and time-resolved photochemistry of the natural nucleic acid bases and their sulfur- and nitrogen-substituted analogues in solution is reviewed. Emphasis is given to the experimental studies performed over the last 3-5 years that showcase topical areas of scientific inquiry and those that require further scrutiny. Significant progress has been made toward mapping the radiative and nonradiative decay pathways of nucleic acid bases. There is a consensus that ultrafast internal conversion to the ground state is the primary relaxation pathway in the nucleic acid bases, whereas the mechanism of this relaxation and the level of participation of the (1)πσ*, (1) nπ*, and (3)ππ* states are still matters of debate. Although impressive research has been performed in recent years, the microscopic mechanism(s) by which the nucleic acid bases dissipate excess vibrational energy to their environment, and the role of the N-glycosidic group in this and in other nonradiative decay pathways, are still poorly understood. The simple replacement of a single atom in a nucleobase with a sulfur or nitrogen atom severely restricts access to the conical intersections responsible for the intrinsic internal conversion pathways to the ground state in the nucleic acid bases. It also enhances access to ultrafast and efficient inter-system crossing pathways that populate the triplet manifold in yields close to unity. Determining the coupled nuclear and electronic pathways responsible for the significantly different photochemistry in these nucleic acid base analogues serves as a convenient platform to examine the current state of knowledge regarding the photodynamic properties of the DNA and RNA bases from both experimental and computational perspectives. Further investigations should also aid in forecasting the prospective use of sulfur- and nitrogen-substituted base analogues in photochemotherapeutic applications.

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Section: Excited-state Deactivation Mechanism In 2-thiouracil Derivatmentioning

confidence: 64%

Section: Excited-state Deactivation Mechanism In 2-thiouracil Derivatmentioning

confidence: 88%

Section: Thiobasesmentioning

confidence: 99%

Section: Excited-state Deactivation Mechanism In 2-thiouracil Derivatmentioning

confidence: 99%

Section: Excited-state Deactivation Mechanism In 2-thiouracil Derivatmentioning

confidence: 99%

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Photochemistry of Nucleic Acid Bases and Their Thio- and Aza-Analogues in Solution

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2014

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Photoinduced Processes in Nucleic Acids

Barbatti

Borin

Ullrich

2014

Topics in Current Chemistry

103

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Photoinduced processes in nucleic acids are phenomena of fundamental interest in diverse fields, from prebiotic studies, through medical research on carcinogenesis, to the development of bioorganic photodevices. In this contribution we survey many aspects of the research across the boundaries. Starting from a historical background, where the main milestones are identified, we review the main findings of the physical-chemical research of photoinduced processes on several types of nucleic-acid fragments, from monomers to duplexes. We also discuss a number of different issues which are still under debate.

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Solvation effects alter the photochemistry of 2-thiocytosine

et al. 2018

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Radiationless deactivation channels of 2-thiocytosine in aqueous environment are revisited by means of quantum-chemical simulations of excited-state absorption spectra, and investigations of potential energy surfaces of the chromophore clustered with two water molecules using the algebraic diagrammatic construction method to the second-order (ADC(2)), and multireference configuration interaction with single and double excitations (MR-CISD) methods. We argue that interactions of explicit water molecules with thiocarbonyl group might enable water-chromophore electron transfer (WCET) which leads to formation of intersystem crossing that was not considered previously. This is the first example of a WCET process occurring in the triplet manifold of electronic states. This phenomenon might explain nonradiative decay of the triplet state population observed in thiopyrimidines in the absence of molecular oxygen. According to our calculations this WCET process might also entail a subsequent, virtually barrierless, electron-driven proton transfer (EDPT) resulting in the formation of hydroxyl radical which could further participate in photohydration or deamination reactions.

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Relaxation of the T1 excited state of 2-thiothymine, its riboside and deoxyriboside-enhanced nonradiative decay rate induced by sugar substituent

Cited by 43 publications

References 42 publications

Photochemistry of Nucleic Acid Bases and Their Thio- and Aza-Analogues in Solution

Photochemistry of Nucleic Acid Bases and Their Thio- and Aza-Analogues in Solution

Photoinduced Processes in Nucleic Acids

Solvation effects alter the photochemistry of 2-thiocytosine

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