ENDOR study of a thiocytosine oxidation product in cytosine monohydrate crystals doped with 2-thiocytosine, X-irradiated at 15 K

Herak, Janko N.; Sanković, Krešimir; Hole, Eli O.; Sagstuen, Einar

doi:10.1039/b004639f

Cited by 18 publications

(26 citation statements)

References 22 publications

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“…A series of papers was published in recent five years addressing the dissociative electron attachment to 2-thiouracil (2-TU) and 2-thiothymine in gas-phase and showing that the fragmentation of these molecules arises mainly at the sulfur site [35,36,37,38,39,40]. Some attention was also paid to electron paramagnetic resonance (EPR) studies [41,42,43,44,45,46,47,48,49] combined with DFT calculations [50,51,52] of radicals derived from γ-irradiated single crystals of sulfur-substituted nucleobases.…”

Section: Introductionmentioning

confidence: 99%

Radiation Induced One-Electron Oxidation of 2-Thiouracil in Aqueous Solutions

et al. 2019

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Oxidative damage to 2-thiouracil (2-TU) by hydroxyl (•OH) and azide (●N3) radicals produces various primary reactive intermediates. Their optical absorption spectra and kinetic characteristics were studied by pulse radiolysis with UV-vis spectrophotometric and conductivity detection and by time-dependent density functional theory (TD-DFT) method. The transient absorption spectra recorded in the reactions of •OH with 2-TU depend on the concentration of 2-TU, however, only slightly on pH. At low concentrations, they are characterized by a broad absorption band with a weakly pronounced maxima located at λ = 325, 340 and 385 nm, whereas for high concentrations, they are dominated by an absorption band with λmax ≈ 425 nm. Based on calculations using TD-DFT method, the transient absorption spectra at low concentration of 2-TU were assigned to the ●OH-adducts to the double bond at C5 and C6 carbon atoms (3●, 4●) and 2c-3e bonded ●OH adduct to sulfur atom (1…●OH) and at high concentration of 2-TU also to the dimeric 2c-3e S-S-bonded radical in neutral form (2●). The dimeric radical (2●) is formed in the reaction of thiyl-type radical (6●) with 2-TU and both radicals are in an equilibrium with Keq = 4.2 × 103 M−1. Similar equilibrium (with Keq = 4.3 × 103 M−1) was found for pH above the pKa of 2-TU which involves admittedly the same radical (6●) but with the dimeric 2c-3e S-S bonded radical in anionic form (2●−). In turn, ●N3-induced oxidation of 2-TU occurs via radical cation with maximum spin location on the sulfur atom which subsequently undergoes deprotonation at N1 atom leading again to thiyl-type radical (6●). This radical is a direct precursor of dimeric radical (2●).

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Section: Introductionmentioning

confidence: 99%

Radiation Induced One-Electron Oxidation of 2-Thiouracil in Aqueous Solutions

et al. 2019

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“…The thio-analogues of nucleic acid bases absorb light at long wavelengths and can be selectively photoactivated into the electronic triplet state, which leads to their high af®nity for crosslinking to other nucleic acid bases and amino acid residues with which they are in contact. It has also been shown that the thio-analogues of nucleic acid bases behave as good traps for the excess energy emitted by ionizing radiation (Sankovic Â et al, 1991;Herak & Hu È ttermann, 1991;Herak et al, 1999Herak et al, , 2000.…”

Section: Commentmentioning

confidence: 99%

5-Methyl-2-thiouracil

2002

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The molecular structure of the title compound, also known as 2-thiothymine [systematic name: 2,3-dihydro-5-methyl-2-thioxopyrimidin-4(1H)-one], C(5)H(6)N(2)OS, is similar to that of thymine, with only small changes in the ring structure, apart from a significant difference at the substitution site [S=C = 1.674 (1) A]. The molecules are connected by hydrogen bonds, with N-H.O = 2.755 (2) A and N-H.S = 3.352 (1) A. The hydrogen-bond network is different from that in thymine, since it involves all the donor and acceptor atoms.

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“…The transfer of electrons/holes over considerable distances in single crystals of purine or pyrimidine bases was researched in our previous experiments using the EPR spectroscopic properties of sulfur-centred radicals. We hypothesized that charge transfer occurs either by the overlapping of -orbitals (base stacking) or by the ions potentially present in the environment of the DNA bases (Kabiljo et al, 1990;Herak et al, 1994Herak et al, , 1997Herak et al, , 1999Herak et al, , 2000Herak et al, , 2001; ISSN 2053ISSN -2296 # 2017 International Union of Crystallography Sanković et al, 1996Sanković et al, , 2003. The ring stacking of a DNA base in a single crystal resembles the base stacking in natural DNA (Jeffrey & Kinoshita, 1963;McClure & Craven, 1973;Mandel, 1977;Padmaja et al, 1987;Grainger & Bailey, 1981;Bugg & Thewalt, 1970;Iball & Wilson, 1965;Matković-Č alogović & Sanković, 1999Prugovečki et al, 2005;Sanković et al, 2005).…”

Section: Introductionmentioning

confidence: 99%

Structural and computational analysis of intermolecular interactions in a new 2-thiouracil polymorph

et al. 2017

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The crystallization and characterization of a new polymorph of 2-thiouracil by single-crystal X-ray diffraction, Hirshfeld surface analysis and periodic density functional theory (DFT) calculations are described. The previously published polymorph (A) crystallizes in the triclinic space group P\overline{1}, while that described herein (B) crystallizes in the monoclinic space group P2/c. Periodic DFT calculations showed that the energies of polymorphs A and B, compared to the gas-phase geometry, were -108.8 and -29.4 kJ mol, respectively. The two polymorphs have different intermolecular contacts that were analyzed and are discussed in detail. Significant differences in the molecular structure were found only in the bond lengths and angles involving heteroatoms that are involved in hydrogen bonds. Decomposition of the Hirshfeld fingerprint plots revealed that O...H and S...H contacts cover over 50% of the noncovalent contacts in both of the polymorphs; however, they are quite different in strength. Hydrogen bonds of the N-H...O and N-H...S types were found in polymorph A, whereas in polymorph B, only those of the N-H...O type are present, resulting in a different packing in the unit cell. QTAIM (quantum theory of atoms in molecules) computational analysis showed that the interaction energies for these weak-to-medium strength hydrogen bonds with a noncovalent or mixed interaction character were estimated to fall within the ranges 5.4-10.2 and 4.9-9.2 kJ mol for polymorphs A and B, respectively. Also, the NCI (noncovalent interaction) plots revealed weak stacking interactions. The interaction energies for these interactions were in the ranges 3.5-4.1 and 3.1-5.5 kJ mol for polymorphs A and B, respectively, as shown by QTAIM analysis.

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ENDOR study of a thiocytosine oxidation product in cytosine monohydrate crystals doped with 2-thiocytosine, X-irradiated at 15 K

Cited by 18 publications

References 22 publications

Radiation Induced One-Electron Oxidation of 2-Thiouracil in Aqueous Solutions

Radiation Induced One-Electron Oxidation of 2-Thiouracil in Aqueous Solutions

5-Methyl-2-thiouracil

Structural and computational analysis of intermolecular interactions in a new 2-thiouracil polymorph

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