An ab initio mechanism for efficient population of triplet states in cytotoxic sulfur substituted DNA bases: the case of 6-thioguanine

Martínez‐Fernández, Lara; González, Leticia; Corral, Inés

doi:10.1039/c2cc15775f

Cited by 78 publications

(136 citation statements)

References 21 publications

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“…As has now been shown in a few thiobases [18,19,32], intersystem crossing on the femtosecond time scale is an intrinsic property also observed in other 6-thiopurine derivatives. The ultrafast intersystem crossing dynamics, together with the lack of any significant internal conversion process to the ground state (see below) [22,27,33], explains the near unity triplet yield and the high yield of singlet oxygen generation reported for several 6-thiopurine derivatives in Tables 12 and 6, respectively [13,195].…”

Section: Excited-state Deactivation Mechanism In 6-thiopurine Derivatmentioning

confidence: 89%

“…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%

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

Pollum

Martínez‐Fernández

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 6-thiopurine Derivatmentioning

confidence: 89%

Section: Thiobasesmentioning

confidence: 99%

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

Pollum

Martínez‐Fernández

Crespo‐Hernández

2014

Topics in Current Chemistry

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114

200

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“…Examples of molecules where ISC is important range from aldehydes [37] and small aromatic compounds like benzene, [38] naphthalene, anthracene, and their carbonylic derivatives [39][40][41][42][43][44][45][46][47][48][49][50][51] to nitrocompounds. [43,[52][53][54][55][56][57][58][59][60][61] Furthermore, ISC has been reported for thio-substituted, [62][63][64][65][66][67][68] aza-substituted, [69] bromo-substituted, [70] and canonical nucleobases. [71][72][73] From a theoretical point of view, ISC can be explained by the interaction of states of different multiplicity by spin-orbit coupling (SOC), which is a relativistic effect.…”

Section: Introductionmentioning

confidence: 99%

A general method to describe intersystem crossing dynamics in trajectory surface hopping

Mai

Marquetand

González

2015

Int J of Quantum Chemistry

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Intersystem crossing is a radiationless process that can take place in a molecule irradiated by UV‐Vis light, thereby playing an important role in many environmental, biological and technological processes. This paper reviews different methods to describe intersystem crossing dynamics, paying attention to semiclassical trajectory theories, which are especially interesting because they can be applied to large systems with many degrees of freedom. In particular, a general trajectory surface hopping methodology recently developed by the authors, which is able to include nonadiabatic and spin‐orbit couplings in excited‐state dynamics simulations, is explained in detail. This method, termed SHARC, can in principle include any arbitrary coupling, what makes it generally applicable to photophysical and photochemical problems, also those including explicit laser fields. A step‐by‐step derivation of the main equations of motion employed in surface hopping based on the fewest‐switches method of Tully, adapted for the inclusion of spin‐orbit interactions, is provided. Special emphasis is put on describing the different possible choices of the electronic bases in which spin‐orbit can be included in surface hopping, highlighting the advantages and inconsistencies of the different approaches. © 2015 Wiley Periodicals, Inc.

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“…Despite their similar structure, the presence of a thiocarbonyl group results in a red-shift of the UV absorption spectrum and an increase of intersystem crossing. [8][9][10] These differences have prompted a large number of studies with focus on their electronic structure [11][12][13][14] and excited-state dynamics, both from the theoretical 15 experimental points of view, in particular by means of transient absorption spectroscopy. 9,10,[16][17][18][19] Among thiobases, the series of thiouracils, i.e., 2-thiouracil (2TU), 4-thiouracil (4TU) and 2,4-dithiouracil (DTU), are particularly interesting.…”

Section: Introductionmentioning

confidence: 99%

Photoelectron spectra of 2-thiouracil, 4-thiouracil, and 2,4-dithiouracil

Ruckenbauer

Mai

Marquetand

et al. 2016

The Journal of Chemical Physics

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Ground-and excited-state UV photoelectron spectra of thiouracils (2-thiouracil, 4-thiouracil and 2,4-dithiouracil) have been simulated using multireference configuration interaction calculations and Dyson norms as measure for the photoionization intensity. Except for a constant shift, the calculated spectrum of 2-thiouracil agrees very well with experiment, while no experimental spectra are available for the two other compounds. For all three molecules, the photoelectron spectra show distinct bands due to ionization of the sulphur and oxygen lone pairs and the pyrimidine π system. The excited-state photoelectron spectra of 2-thiouracil show bands at much lower energies than in the ground state spectrum, allowing to monitor the excited-state population in time-resolved UV photoelectron spectroscopy (TRPES) experiments. However, the results also reveal that single-photon ionization probe schemes alone will not allow monitoring all photodynamic processes existing in 2-thiouracil. Especially, due to overlapping bands of singlet and triplet states the clear observation of intersystem crossing will be hampered.

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An ab initio mechanism for efficient population of triplet states in cytotoxic sulfur substituted DNA bases: the case of 6-thioguanine

Cited by 78 publications

References 21 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

A general method to describe intersystem crossing dynamics in trajectory surface hopping

Photoelectron spectra of 2-thiouracil, 4-thiouracil, and 2,4-dithiouracil

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