scholarly journals Spectral Probe for Electron Transfer and Addition Reactions of Azide Radicals with Substituted Quinoxalin-2-Ones in Aqueous Solutions

2021 ◽  
Vol 22 (2) ◽  
pp. 633
Author(s):  
Konrad Skotnicki ◽  
Slawomir Ostrowski ◽  
Jan Cz. Dobrowolski ◽  
Julio R. De la Fuente ◽  
Alvaro Cañete ◽  
...  
Keyword(s):  
Electron Transfer ◽  
Aqueous Solutions ◽  
Absorption Spectra ◽  
Density Functional ◽  
Reduction Potential ◽  
Biological Significance ◽  
Radical Cations ◽  
Basis Sets ◽  
Double Bonds ◽  
Reduction Potentials

The azide radical (N3●) is one of the most important one-electron oxidants used extensively in radiation chemistry studies involving molecules of biological significance. Generally, it was assumed that N3● reacts in aqueous solutions only by electron transfer. However, there were several reports indicating the possibility of N3● addition in aqueous solutions to organic compounds containing double bonds. The main purpose of this study was to find an experimental approach that allows a clear assignment of the nature of obtained products either to its one-electron oxidation or its addition products. Radiolysis of water provides a convenient source of one-electron oxidizing radicals characterized by a very broad range of reduction potentials. Two inorganic radicals (SO4●−, CO3●−) and Tl2+ ions with the reduction potentials higher, and one radical (SCN)2●− with the reduction potential slightly lower than the reduction potential of N3● were selected as dominant electron-acceptors. Transient absorption spectra formed in their reactions with a series of quinoxalin-2-one derivatives were confronted with absorption spectra formed from reactions of N3● with the same series of compounds. Cases, in which the absorption spectra formed in reactions involving N3● differ from the absorption spectra formed in the reactions involving other one-electron oxidants, strongly indicate that N3● is involved in the other reaction channel such as addition to double bonds. Moreover, it was shown that high-rate constants of reactions of N3● with quinoxalin-2-ones do not ultimately prove that they are electron transfer reactions. The optimized structures of the radical cations (7-R-3-MeQ)●+, radicals (7-R-3-MeQ)● and N3● adducts at the C2 carbon atom in pyrazine moiety and their absorption spectra are reasonably well reproduced by density functional theory quantum mechanics calculations employing the ωB97XD functional combined with the Dunning’s aug-cc-pVTZ correlation-consistent polarized basis sets augmented with diffuse functions.

scholarly journals Density functional theory (DFT) calculations of VI/V reduction potentials of uranyl coordination complexes in non-aqueous solutions

2019 ◽  
Vol 21 (6) ◽  
pp. 3227-3241 ◽  
Author(s):  
Krishnamoorthy Arumugam ◽  
Neil A. Burton
Keyword(s):  
Density Functional Theory ◽  
Dft Calculations ◽  
Aqueous Solutions ◽  
Density Functional ◽  
Coordination Complexes ◽  
Dft Study ◽  
Redox Behavior ◽  
Functional Theory ◽  
Reduction Potentials ◽  
Uranium Complexes

Of particular interest within the +6 uranium complexes is the linear uranyl(vi) cation and it forms numerous coordination complexes in solution and exhibits incongruent redox behavior depending on coordinating ligands. This DFT study predicts VI/V reduction potentials of a range of uranyl(vi) complexes in non-aqueous solutions within ∼0.10−0.20 eV of experiment.

Theoretical investigation of [Ru(tpy)2]2+, [Ru(tpy)(bpy)(H2O)]2+ and [Ru(tpy)(bpy)(Cl)]+ complexes in acetone revisited: Inclusion of strong spin–orbit couplings to quantum chemistry calculations

2016 ◽  
Vol 15 (01) ◽  
pp. 1650001
Author(s):  
Kenji Mishima ◽  
Takumi Kinoshita ◽  
Michitoshi Hayashi ◽  
Ryota Jono ◽  
Hiroshi Segawa ◽  
...  
Keyword(s):  
Experimental Data ◽  
Quantum Chemistry ◽  
Absorption Spectra ◽  
Density Functional ◽  
Order Perturbation ◽  
Basis Sets ◽  
Spin Orbit ◽  
First Order ◽  
Quantum Chemistry Calculations ◽  
First Order Perturbation

In the present paper, we theoretically reinvestigate structural properties, and photo-physical and chemical characteristics and electronic absorption spectra of three kinds of ruthenium polypyridyl complexes [Ru(tpy)[Formula: see text], [Ru(tpy)(bpy)(H2O)][Formula: see text], and [Ru(tpy)(bpy)(Cl)][Formula: see text] complexes in acetone (tpy[Formula: see text]2,2[Formula: see text],2[Formula: see text]-terpyridine and bpy[Formula: see text]2,2[Formula: see text]-bipyridine). In particular, the experimental absorption spectra of these complexes are revisited theoretically in detail and are simulated using the first-order perturbation theory based on time-dependent density functional theory (TD-DFT) where the first-order perturbation term is the spin–orbit (SO) coupling Hamiltonian, and quantum chemistry calculations based on various functionals and basis sets. It was found that in general the theory including SO coupling can reproduce experimental data better than the simple quantum chemistry calculation neglecting SO coupling, which indicates that SO coupling is very important to understand the optical features of these complexes and that therefore the mixing between singlet and triplet states is strong due to the large SO coupling constant of Ru atom involved in these complexes. This suggests the fact that the disagreement between the experimental and calculated absorption spectra was found in TDB3LYP/(SDD with triple-[Formula: see text] for Ru and 6-31G* for others) [Jakubikova EJ et al., Inorg Chem 48:10720, 2009] can be tracked down to the neglect of SO couplings. It was also found that the choice of the DFT functionals and basis sets is crucial for a good theoretical reproduction of experimental data.

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. 

What Silicon Nanocluster is Most Likely Formed in Etching Experiments? Theoretical DFT Study

2008 ◽  
Vol 8 (7) ◽  
pp. 3478-3482
Author(s):  
Nurbosyn U. Zhanpeisov ◽  
Hiroshi Fukumura
Keyword(s):  
Absorption Spectra ◽  
Density Functional Calculations ◽  
Density Functional ◽  
Electrochemical Etching ◽  
Time Dependent ◽  
Cluster Models ◽  
Dft Study ◽  
Basis Sets ◽  
Self Healing ◽  
Tddft Calculations

Density functional calculations at the B3LYP/6-31G* level were performed for Si nanoclusters of ca.1 nm in size. The structural, energetic, electronic as well as the estimated absorption spectra by the time-dependent DFT (TDDFT) calculations using varied functionals and basis sets for the representative cluster models are all in favor of the formation of most probable Si35H36 nanocluster in recent electrochemical etching experiments. The nanostructure has a complete H-termination at the borderline regions and lacks from the presence of any defects like surface Si—Si dimer units formed via self-healing of dangling Si—Si bonds or from any relatively short H…H contacts.

scholarly journals ANALYSIS OF DIFFERENT DATASETS FOR IONIZATION POTENTIAL AND ELECTRON AFFINITY OF QUINONES ON THE BASIS OF DFT CALCULATIONS

2017 ◽  
Vol 60 (8) ◽  
pp. 4
Author(s):  
Li Sun ◽  
Jianhua Ran ◽  
Cong Zhang ◽  
Felix Yu. Telegin
Keyword(s):  
Electron Transfer ◽  
Dft Calculations ◽  
Ionization Potential ◽  
Electron Affinity ◽  
Density Functional ◽  
Basis Sets ◽  
Electron Affinities ◽  
Linear Quadratic ◽  
Equilibrium Studies ◽  
Chemical Catalysis

The idea of this research deals with theoretical problems of studying quinones as representatives of natural and synthetic compounds with a huge variety of applications in chemical catalysis, biomedical and technical sciences. For this purpose computational chemistry is chosen as an advanced tool for evaluating electronic energies in gase phase for a series of simple quinones, naphthoquinones and anthraquinones as parent compounds for more complicated ones. Ionization potentials and electron affinities (IPs and EAs) of 88 quinones are calculated by the use of B3LYP level of density functional theory (DFT) with different basis sets, and on this base the validation of several databases for electronic energies of quinones is done. The databases for EAs include published results of measurements of absolute electron affinities of pi charge transfer complex acceptors and those determined as relative values from electron transfer equilibrium studies. Non-linear quadratic correlation was found for relationship between calculated and experiment values of electron affinities. Analysis of the relative deviation between obtained calculated results and the three experimental databases indicated the high quality of the database proposed by Hilal et al. based on electron transfer equilibrium studies. The results found in the research are applicable for validation of computational methods and experimental data for electronic energies of quinones.Forcitation:Li Sun, Jianhua Ran, Cong Zhang, Telegin F.Yu. Analysis of different datasets for ionization potential and electron affinity of quinones on the basis of DFT calculations. Izv. Vyssh. Uchebn. Zaved. Khim. Khim. Tekhnol. 2017. V. 60. N 8. P. 4-12.

scholarly journals Voltammetric detection of hydrochlorothiazide at molybdenum oxide modified screen-printed electrodes

2019 ◽  
Vol 51 (3) ◽  
pp. 305-311
Author(s):  
M. F. Khanfar ◽  
E. S. M. Abu-Nameh ◽  
A. T. Afaneh ◽  
M. M. Saket ◽  
A. Ahmad ◽  
...  
Keyword(s):  
Molybdenum Oxide ◽  
Density Functional ◽  
Reduction Potential ◽  
Oxidation Potential ◽  
Basis Sets ◽  
Drug Products ◽  
Screen Printed Electrodes ◽  
Voltammetric Detection ◽  
Deposition Density ◽  
Screen Printed

Electrochemical oxidation of hydrochlorothiazide (HCT) was investigated both experimentally and theoretically to explore the connection between thermodynamics and the oxidation potential. In this work, screen printed carbon electrodes were modified with molybdenum oxide by means of voltammetry. The modified surfaces demonstrated significant sensitivity toward hydrochlorothiazide detection in pH 2.00–buffered aqueous solutions. The employed method was validated and used for hydrochlorothiazide quantification in commercial drug products. In this work, we presented results of density functional calculations for the standard reduction potential of the HCT (H)2|HCT couple in aqueous solution. After consideration of 20 density functionals with 4 different basis sets, it was found that the hybrid meta functionals provide the most accurate prediction of the reduction potential in comparison with the available experimental data. The reported reduction potential is underestimated with GGA and MGGA and is overestimated with hybrid and meta hybrid functionals. Our results highlighted the importance of including solute-solvent hydrogen bonding effects in the theoretical modeling of redox processes. Keywords: Molybdenum oxide, Hydrochlorothiazide, Screen-printed electrodes, Electrochemical deposition, Density functional theory (DFT).

Comparative Interpretation of Absorption Spectra of Technetium (IV) and Rhenium (IV) Hexahalides

1965 ◽  
Vol 20 (1) ◽  
pp. 65-75 ◽  
Author(s):  
Chr. Klixbüll Jørgensen ◽  
Klaus Schwochau
Keyword(s):  
Electron Transfer ◽  
Aqueous Solutions ◽  
Absorption Spectra ◽  
Vibrational Structure ◽  
Octahedral Symmetry ◽  
Absorption Bands ◽  
Nephelauxetic Effect

Absorption spectra of aqueous solutions of TcX6- and ReX6- (X = F, Cl, Br, I) are measured between 8 000 and ∼ 50 000 cm-1 and theoretically discussed. The electron transfer spectra indicate the optical electronegativity xopt= 2.25 for Tc (IV) and 2.05 for the less oxidizing Re (IV). The spectrochemical parameter Δ is determined to 28 400 cm-1 in TcF6 and 32 800 cm-1 in ReF6-. The nephelauxetic effect is evaluated from the spin-forbidden intra-sub-shell transitions in all eight species, and from the two spin-allowed bands of TcF6- The vibrational structure of the narrow absorption bands and the possible weak distortion from octahedral symmetry of Tc (IV) hexahalides are discussed.

Elektronentransfer und Ionenpaar-Bildung, 18 [1 -3] / Electron Transfer and Ion Pairing, 18 [ 1 - 3]

1991 ◽  
Vol 46 (3) ◽  
pp. 326-338 ◽  
Author(s):  
H. Bock ◽  
P. Dickmann ◽  
H.-F. Herrmann
Keyword(s):  
Electron Transfer ◽  
Metal Cation ◽  
Reduction Potential ◽  
Ion Pairs ◽  
Radical Cations ◽  
Membered Ring ◽  
Cation Complexation ◽  
Metal Cation Complexation ◽  
Contact Ion Pairs ◽  
Triple Ion

The redox behaviour of aza-substituted naphtho- and anthraquinones, which offer O=C–C=N– chelate tongs for an advantageous five-membered ring metal cation complexation, is investigated by a combination of cyclovoltammetric and ESR/ENDOR spectroscopic measurements. The formation of paramagnetic contact ion pairs like [(quinoline-5,8-semiquinone)·⊖Me⨁]·, with Me⨁ = Li⨁, Na⨁, Tl⨁, or of triple ion radical cations like [(1,4-diazo-9,10-anthrasemiquinone)eMe⨁]·⨁, with Me⨁ = Li⨁, Na⨁ is corroborated both by shifts of the second reduction potential of up to 0,67 V for e.g. quinoline 5,8-quinone upon addition of Li⨁[B(C6H5)4]⊖ to its DMF solution and by the observation of ESR/ENDOR metal couplings.

scholarly journals Broadband X-Ray Absorption Spectra from Time-Dependent Kohn-Sham Calculations

2021 ◽  
Author(s):  
Ying Zhu ◽  
Bushra Alam ◽  
John Herbert
Keyword(s):  
Absorption Spectra ◽  
Density Functional ◽  
Time Dependent ◽  
Basis Set ◽  
Basis Sets ◽  
Propagation Time ◽  
Edge Structure ◽  
X Ray ◽  
The Cost ◽  
X Ray Absorption

We present a protocol for calculation of K-edge x-ray absorption spectra using time-dependent Kohn-Sham (TDKS) calculations, also known as "real-time" time-dependent density functional theory (TDDFT). In principle, the entire absorption spectrum (at all wavelengths) can be computed via Fourier transform of the time-dependent dipole moment function, following a perturbation of the ground-state density and propagation of time-dependent Kohn-Sham molecular orbitals. In practice, very short time steps are required to obtain an accurate spectrum, which increases the cost, but the use of Pade approximants significantly reduces the length of time propagation that is required. Spectra that are well converged with respect to the corresponding linear-response (LR-)TDDFT result can be obtained with < 10 fs of propagation time. Use of complex absorbing potentials helps to remove artifacts at high energies that otherwise result from the use of a finite atom-centered Gaussian basis set. Benchmark results, comparing TDKS to LR-TDDFT, are presented for several small molecules at the carbon and oxygen K-edges, demonstrating good agreement with experiment without the need for specialized basis sets. Whereas LR-TDDFT is a reasonable approach to obtain the near-edge structure, that approach requires hundreds of states and quickly becomes cost prohibitive for large systems, even when the core\slash valence separation approximation is used to remove most of the occupied states from the excitation manifold. We demonstrate the cost-effective TDKS approach by application to a copper dithiolene complex, where binding of a ligand is detectable via shifts in the sulfur K-edge.

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