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

Molecules ◽  
2019 ◽  
Vol 24 (23) ◽  
pp. 4402
Author(s):  
Skotnicki ◽  
Taras-Goslinska ◽  
Janik ◽  
Bobrowski
Keyword(s):  
Absorption Band ◽  
Absorption Spectra ◽  
Sulfur Atom ◽  
Density Functional ◽  
Transient Absorption ◽  
Dft Method ◽  
Broad Absorption Band ◽  
Transient Absorption Spectra ◽  
Td Dft ◽  
Type Radical

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●).

scholarly journals Radiation-Induced Oxidation Reactions of 2-Selenouracil in Aqueous Solutions: Comparison with Sulfur Analog of Uracil

Molecules ◽  
2021 ◽  
Vol 27 (1) ◽  
pp. 133
Author(s):  
Konrad Skotnicki ◽  
Ireneusz Janik ◽  
Klaudia Sadowska ◽  
Grazyna Leszczynska ◽  
Krzysztof Bobrowski
Keyword(s):  
Absorption Band ◽  
Absorption Spectra ◽  
Density Functional ◽  
Transient Absorption ◽  
Dft Method ◽  
Transient Absorption Spectrum ◽  
Oxidation Reactions ◽  
Radiation Induced ◽  
High Concentrations ◽  
The Stability

One-electron oxidation of 2-selenouracil (2-SeU) by hydroxyl (●OH) and azide (●N3) radicals leads to 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 the density functional theory (DFT) method. The transient absorption spectra recorded in the reactions of ●OH with 2-SeU are dominated by an absorption band with an λmax = 440 nm, the intensity of which depends on the concentration of 2-SeU and pH. Based on the combination of conductometric and DFT studies, the transient absorption band observed both at low and high concentrations of 2-SeU was assigned to the dimeric 2c-3e Se-Se-bonded radical in neutral form (2●). The dimeric radical (2●) is formed in the reaction of a selenyl-type radical (6●) with 2-SeU, and both radicals are in equilibrium with Keq = 1.3 × 104 M−1 at pH 4 (below the pKa of 2-SeU). Similar equilibrium with Keq = 4.4 × 103 M−1 was determined for pH 10 (above the pKa of 2-SeU), which admittedly involves the same radical (6●) but with a dimeric 2c-3e Se-Se bonded radical in anionic form (2●−). In turn, at the lowest concentration of 2-SeU (0.05 mM) and pH 10, the transient absorption spectrum is dominated by an absorption band with an λmax = 390 nm, which was assigned to the ●OH adduct to the double bond at C5 carbon atom (3●) based on DFT calculations. Similar spectral and kinetic features were also observed during the ●N3-induced oxidation of 2-SeU. In principle, our results mostly revealed similarities in one-electron oxidation pathways of 2-SeU and 2-thiouracil (2-TU). The major difference concerns the stability of dimeric radicals with a 2c-3e chalcogen-chalcogen bond in favor of 2-SeU.

scholarly journals ABSORPTION OF SOME SMALL SILVER CLUSTERS: DFT AND CASPT2 CALCULATIONS

2018 ◽  
Vol 55 (6A) ◽  
pp. 72
Author(s):  
Ngo Tuan Cuong
Keyword(s):  
Absorption Spectra ◽  
Density Functional ◽  
Noble Gas ◽  
Silver Cluster ◽  
Dft Method ◽  
Basis Sets ◽  
Silver Clusters ◽  
Excitation Energies ◽  
Complete Active Space ◽  
Td Dft

Two quantum chemical methods which are the time-dependent density functional theory (TD-DFT) and the complete active space CASPT2/CASSCF have been used in modeling absorption spectra of silver clusters Agn (n = 2, 3, 4, 6, 8). There is an overall good agreement between TD-DFT and CASPT2 results for transition energies. The absorption spectra of the Agn clusters examined can reasonably be simulated using the excitation energies obtained by either TD-DFT or CASPT2 method.  The main result emerged from this calculation is that the TD-DFT method is suitable for treatment of excited states of Ag clusters. The choice of specific functionals and basis sets to be used in some cases induces important effects on the calculated spectra. It is also noteworthy to mention that for some clusters, the neutral Ag6 for instance, the effect of noble gas environment is significant, while for some others such as the neutral Ag8, it is not. Therefore, carrying out TD-DFT calculations to reproduce and to assign a given structure to an experimental absorption spectrum of a silver cluster, it is not only to select suitable functionals but also to take enough effects of environments into account. 

Successful Application of TD-DFT in Transient Absorption Spectra Assignment

2005 ◽  
Vol 7 (2) ◽  
pp. 243-246 ◽  
Author(s):  
Liang Shen ◽  
Hong-Yu Zhang ◽  
Hong-Fang Ji
Keyword(s):  
Absorption Spectra ◽  
Transient Absorption ◽  
Transient Absorption Spectra ◽  
Td Dft

Kinetic-Model-Free Analysis of Transient Absorption Spectra Enabled by 2D Correlation Analysis

2021 ◽  
pp. 4148-4153
Author(s):  
Julian Hniopek ◽  
Carolin Müller ◽  
Thomas Bocklitz ◽  
Michael Schmitt ◽  
Benjamin Dietzek ◽  
...  
Keyword(s):  
Kinetic Model ◽  
Correlation Analysis ◽  
Absorption Spectra ◽  
Transient Absorption ◽  
Transient Absorption Spectra ◽  
Model Free ◽  
2D Correlation Analysis

Graphical analysis of transient absorption spectra using the phasor approach

2015 ◽  
Vol 32 (8) ◽  
pp. 1693
Author(s):  
Hong Liu ◽  
Yulei Bai ◽  
Yun Zhang ◽  
Shuangli Ye ◽  
Weichao Xu ◽  
...  
Keyword(s):  
Absorption Spectra ◽  
Transient Absorption ◽  
Graphical Analysis ◽  
Transient Absorption Spectra

scholarly journals Spectral properties of coumarin derivatives in various environments

2013 ◽  
Vol 11 (4) ◽  
pp. 492-501 ◽  
Author(s):  
Alzbeta Holubekova ◽  
Pavel Mach ◽  
Jan Urban
Keyword(s):  
Gas Phase ◽  
Absorption Spectra ◽  
Spectral Properties ◽  
Density Functional ◽  
Water Solution ◽  
Blue Shift ◽  
Coumarin Derivatives ◽  
Complex Environments ◽  
Td Dft ◽  
Solvent Environment

AbstractThe structural and spectral properties of coumarin derivatives in complex environments were investigated within the time-dependent density functional theory (TD DFT). Absorption spectra calculations were obtained at TD PBE0/6-31+G(d,p) level of theory for coumarin47 in the gas-phase and in various polar and non-polar organic solvents. The geometries of coumarins 6, 30, 47 and 522 in the gas phase and in inclusion complexes with the β-cyclodextrin (βCD) were determined by PM3 and DFT (HCTH/6-31G) calculations. Encapsulation of coumarin in βCD and associated changes in electronic structure produced either a red or blue shift in the absorption spectra of coumarins. A proposed cavity model for βCD-coumarin complex in water solution allowed identification of various contributions to the overall shift in the absorption spectra of coumarin upon complex formation in a solvent environment

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