Early Events of DNA Photodamage

Schreier, Wolfgang; Gilch, Peter; Zinth, Wolfgang

doi:10.1146/annurev-physchem-040214-121821

Cited by 199 publications

(273 citation statements)

References 134 publications

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“…In fact, the region of low E exc probed in our experiments and calculations corresponds to the long-wavelength "red edge" absorption of cytosine in solution. 5,73 This is the primary region of photobiological and -medical interest with respect to UV lesions and skin cancer, 73 and not the vertical excitation to the absorption band maximum at ∼260 nm. 32,33 In summary, we show that upon exciting gas-phase S 1 state keto-amino cytosine from the 0 0 0 band up to E exc ∼ 440 cm −1 , neither S 1 S 0 internal conversion 16 nor S 1 T 1 intersystem crossing are ultrafast.…”

Section: Discussionmentioning

confidence: 99%

Intersystem crossing rates of S1 state keto-amino cytosine at low excess energy

Lobsiger

Etinski

Blaser

et al. 2015

The Journal of Chemical Physics

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Intersystem crossing rates of S 1 state keto-amino cytosine at low excess energy The amino-keto tautomer of supersonic jet-cooled cytosine undergoes intersystem crossing (ISC) from the v = 0 and low-lying vibronic levels of its S 1 ( 1 ππ * ) state. We investigate these ISC rates experimentally and theoretically as a function of S 1 state vibrational excess energy E exc . The S 1 vibronic levels are pumped with a ∼5 ns UV laser, the S 1 and triplet state ion signals are separated by prompt or delayed ionization with a second UV laser pulse. After correcting the raw ISC yields for the relative S 1 and T 1 ionization cross sections, we obtain energy dependent ISC quantum yields Q corr ISC = 1%-5%. These are combined with previously measured vibronic state-specific decay rates, giving ISC rates k ISC = 0.4-1.5 · 10 9 s −1 , the corresponding S 1 S 0 internal conversion (IC) rates are 30-100 times larger. Theoretical ISC rates are computed using SCS-CC2 methods, which predict rapid ISC from the S 1 ; v = 0 state with k ISC = 3 · 10 9 s −1 to the T 1 ( 3 ππ * ) triplet state. The surprisingly high rate of this El Sayed-forbidden transition is caused by a substantial admixture of 1 n O π * character into the S 1 ( 1 ππ * ) wave function at its non-planar minimum geometry. The combination of experiment and theory implies that (1) below E exc = 550 cm −1 in the S 1 state, S 1 S 0 internal conversion dominates the nonradiative decay with k IC ≥ 2 · 10 10 s −1 , (2) the calculated S 1 T 1 ( 1 ππ * 3 ππ * ) ISC rate is in good agreement with experiment, (3) being El-Sayed forbidden, the S 1 T 1 ISC is moderately fast (k ISC = 3 · 10 9 s −1 ), and not ultrafast, as claimed by other calculations, and (4) at E exc ∼ 550 cm −1 the IC rate increases by ∼50 times, probably by accessing the lowest conical intersection (the C5-twist CI) and thereby effectively switching off the ISC decay channels. C 2015 AIP Publishing LLC. [http://dx

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Section: Discussionmentioning

confidence: 99%

Intersystem crossing rates of S1 state keto-amino cytosine at low excess energy

Lobsiger

Etinski

Blaser

et al. 2015

The Journal of Chemical Physics

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“…The Empire State Building provides a sense of scale. UVC excites a single base or a delocalized quantum state of 2–3 bases to the singlet state at E S = 4.2–4.4 eV (center) [22, 24, 61]. UVB does this weakly.…”

Section: Figmentioning

confidence: 99%

Chemical excitation of electrons: A dark path to melanoma

Premi

Brash

2016

DNA Repair

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Sunlight’s ultraviolet wavelengths induce cyclobutane pyrimidine dimers (CPDs), which then cause mutations that lead to melanoma or to cancers of skin keratinocytes. In pigmented melanocytes, we found that CPDs arise both instantaneously and for hours after UV exposure ends. Remarkably, the CPDs arising in the dark originate by a novel pathway that resembles bioluminescence but does not end in light: First, UV activates the enzymes nitric oxide synthase (NOS) and NADPH oxidase (NOX), which generate the radicals nitric oxide (NO•) and superoxide (O2•−); these combine to form the powerful oxidant peroxynitrite (ONOO−). A fragment of the skin pigment melanin is then oxidized, exciting an electron to an energy level so high that it is rarely seen in biology. This process of chemically exciting electrons, termed “chemiexcitation”, is used by fireflies to generate light but it had never been seen in mammalian cells. In melanocytes, the energy transfers radiationlessly to DNA, inducing CPDs. Chemiexcitation is a new source of genome instability, and it calls attention to endogenous mechanisms of genome maintenance that prevent electronic excitation or dissipate the energy of excited states. Chemiexcitation may also trigger pathogenesis in internal tissues because the same chemistry should arise wherever superoxide and nitric oxide arise near cells that contain melanin.

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“…[7] Between these two states, the triplet states represent a minor reaction channel and only contribute to < 10% of CPDs formed in single-stranded DNA under UVC (100 -290 nm) and UVB (290 -320 nm) irradiation. [8] Surprisingly, the long-wavelength UVA light (320 -400 nm) was also found to induce CPD formation potentially through triplet energy transfer.…”

Section: Introductionmentioning

confidence: 99%

Indications of 5′ to 3′ Interbase Electron Transfer as the First Step of Pyrimidine Dimer Formation Probed by a Dinucleotide Analog

Jian

Maximowitsch

Liu

et al. 2017

Chemistry A European J

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Pyrimidine dimers are the most common DNA lesions generated under UV radiation. To reveal the molecular mechanisms behind their formation, it is of significance to reveal the roles of each pyrimidine residue. We thus replaced the 5'-pyrimidine residue with a photochemically inert xylene moiety (X). The electron-rich X can be readily oxidized but not reduced defining the direction of interbase electron transfer (ET). Irradiation of the XpT dinucleotide under 254 nm UV light generates two major photoproducts: a pyrimidine (6-4) pyrimidone (6-4PP) analog and an analog of the socalled spore photoproduct (SP). Both products are formed via reaction at C4=O of the photo-excited 3'-T, which indicates that excitation of a single "driver" residue is sufficient to trigger pyrimidine dimerization. Our quantum-chemical calculations demonstrated that photo-excited 3'-T accepts an electron from 5′-X. The resulting charge-separated radical pair lowers its energy upon formation of interbase covalent bonds eventually yielding 6-4PP and SP.

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Early Events of DNA Photodamage

Cited by 199 publications

References 134 publications

Intersystem crossing rates of S1 state keto-amino cytosine at low excess energy

Intersystem crossing rates of S1 state keto-amino cytosine at low excess energy

Chemical excitation of electrons: A dark path to melanoma

Indications of 5′ to 3′ Interbase Electron Transfer as the First Step of Pyrimidine Dimer Formation Probed by a Dinucleotide Analog

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