Wave Reduction Potentials Research Articles

Improved Computational Prediction of the Electrochemical Reduction Potential of Twenty 3-Aryl-Quinoxaline-2-Carbonitrile 1,4-Di-N-Oxide Derivatives

The ability of density functional theory (DFT) using the functional B3LYP with the cc-pVTZ basis set to accurately predict the electrochemical properties of 20 3-aryl-quinoxaline-2-carbonitrile 1,4-di-N-oxide derivatives in dimethylformamide (DMF) was investigated and compared to previous predictions from B3LYP/6-31G and B3LYP/lanl2dz. The B3LYP/cc-pVTZ method was an improvement over the B3LYP/6-31G and B3LYP/lanl2dz methods as it was able to predict the first reduction potential of the diazine ring (wave 1) for all of the 3-aryl-quinoxaline-2-carbonitrile 1,4-di-N-oxide derivatives accurately. The B3LYP/cc-pVTZ predicted electrochemical potentials had a strong correlation to experimental values for wave 1. None of the methods demonstrated the ability to predict the nitro wave reduction potential for derivatives containing a nitro group. B3LYP/cc-pVTZ predicted electrochemical potentials for the second reduction of the diazine ring (wave 2) had a low correlation to the experimental values for the derivatives without a nitro group and no correlation of the derivatives when the nitro group was included in the analysis.

Relationship between Electrochemical Parameters, Cytotoxicity Data against Cancer Cells of 3-Thio-Substituted Nor-Beta-Lapachone Derivatives. Implications for Cancer Therapy

Electrochemical methods are powerful in the characterization and design of redox-modulating agents. We, herein, report the electrochemical investigation, in aprotic medium, of eleven synthetic 3-thio-substituted-nor-beta-lapachones, along with the determination of cytotoxic activity and correspondent selectivity index, against several cancer cell lines and one normal cell. Four of the quinones are novel compounds. The redox behavior is representative of two independent systems: the easy reduction of the quinone moiety and, at far more negative potential, the reductive cleavage of the C-S-C bonding; and the anodic part controlled by the oxidation of the sulfur moiety. The compounds have shown relevant cytotoxic activity, with emphasis on 3-phenyl-thio-2,2-dimethyl-2,3-dihydronaphtho[1,2-b]furan-4,5-dione (compound 2), which mechanism of molecular action was shown to be related to reactive oxygen species (ROS) release. Despite the absence of a linear correlation, there is a trend: the majority of the thionaphthoquinones, with values of first wave reduction potential, less negative than -0.65 V, were active. The less electrophilic compound (3-(cyclohexylthio)-2,2-dimethyl-2,3-dihydronaphtho[1,2-b]furan-4,5-dione, cyclohexyl derivative) is also the less cytotoxic toward cancer cells. Agents containing chalcogens and quinones can be used to attack entities with a disturbed redox balance.

Characterization, antibacterial, anticarbonic anhydrase II isoenzyme, anticancer, electrochemical and computational studies of sulfonic acid hydrazide derivative and its Cu(II) complex

A new N′-acetyl butane sulfonic acid hydrazide, C4H9-SO2-NH-NH-COCH3 (Absh, an sulfonamide compound), and its Cu(II) complex [Cu(Absh)2(CH3COO)2], have been synthesized and characterized by elemental analysis, spectrometric methods (1H–13C NMR, FT-IR, LC–MS), thermal analysis, magnetic susceptibility and conductivity measurements. In addition, molecular structure of the ligand, Absh was determined by single crystal X-ray diffraction technique and found that the compound crystallizes in monoclinic, space group P21/c. To gain information about the structure of the ligand and its complex, we have performed computational studies using density functional theory (DFT) for optimized geometries of the compounds. Electrochemical studies showed that, the complex is electrochemically active and has one irreversible reduction and one irreversible oxidation potentials, and the half wave reduction potentials are −1.15 and 0.45 volt respectively, versus ferrocene/ferrocenium internal reference electrode. The antibacterial activities of synthesized compounds were studied against Gram positive bacteria; Staphylococcus aureus ATCC 6538, Bacillus subtilis ATCC 6633, Bacillus cereus NRRL-B-3711, Enterococcus faecalis ATCC 29212 and Gram negative bacteria; Escherichia coli ATCC 11230, Pseudomonas aeruginosa ATCC 15442, Klebsiella pneumonia ATCC 70063 by using the disc diffusion and micro dilution methods. The inhibition activities of these compounds on carbonic anhydrase II enzyme (hCA II) have been investigated by comparing IC50 and Ki values. The anticancer activities of these compounds on MCF-7 cell line investigated by comparing IC50 values. The biological activity screening showed that Cu(II) complex has more activity than ligand against the tested bacteria, hCA II enzyme and breast cancer cell lines MCF-7.

Theoretical prediction for the half wave reduction potential of organic molecules

A quantitative structure-property relationship (QSPR) was developed using partial least square (PLS) and Levenberg-Marquardt artificial neural network (L-M ANN) modeling to study of half-wave reduction potential (E1/2) of some organic compounds. A set of 67 organic compounds were selected and suitable sets of molecular descriptors were calculated. The genetic algorithm was used as descriptor selection and model development method. Then selected descriptors were used as inputs for artificial neural network model. The stability and prediction ability of these models were validated using Leave-Group-out cross-validation (LGO CV) and external test set techniques. The described model does not parameters require experimental and potentially provides useful prediction for E1/2 of new organic compounds.

Electrochemical and spectrophotometrical investigation of the electron-accepting strength of organic superelectrophiles: X-ray structure of their charge transfer complexes with tetrathiafulvalene

Nitro Benzoxadiazoles (benzofurazans), benzoxadiazoles-N-oxide (benzofuroxans) and benzothiadiazoles are ranked amongst the strongest electrophiles known to date. In the past twenty years, their propensity to act as electron organic acceptors has been less studied. In this paper, we report on the study of their electrochemical behavior and on the structural characterization of charge transfer complexes (CTC) deriving from their interaction with tetrathiafulvalene (TTF) derivatives, both in solution and in the solid state. The first half wave reduction potentials (E(1/2)(I)) associated with a reversible monoelectronic transfer process of a large set of nitro substituted benzoxadiazoles (benzofurazans), benzoxadiazoles-N-oxide (benzofuroxans) and benzothiadiazoles have been determined through a detailed electrochemical approach in acetonitrile with a microelectrode network using the ferrocene as an internal reference potential in this electrochemical study. Determination of the electron affinity (EA(CT)) of this series of substituted electrodeficient heteroaromatics as well as their LUMO energy was performed using the Charge Transfer Spectroscopic (CTS) method in solution and by DFT calculations, respectively. The use of the correlation EA(CT) versus the reversible half wave potential (E(1/2)(I)) appears to be a useful tool to estimate readily the E(1/2)(I) or EA(CT) values when they cannot be experimentally determined. The diffusion coefficient of these electrophiles has, for the first time, been determined in acetonitrile. These air stable electrodeficient heteroaromatics have been explored as potential new organic acceptors in the formation of charge transfer (CT) complexes with TTF derivatives. Crystallographic data of two CT complexes with TTF (especially the C-C and C-S bond lengths of the TTF moieties) indicate that these complexes exhibit weak electron delocalization and that both molecules remain neutral. Their resulting levels of charge transfer were probed using UV-visible, IR spectroscopy and by DFT calculations.

Influence of landscape restoration and degradation on storm surge and waves in southern Louisiana

The purpose of this investigation was to examine storm surge and wave reduction benefits of different environmental restoration features (marsh restoration and barrier island changes), as well as the impact of future wetland degradation on local surge and wave conditions. Storm surge simulations of two representative hurricanes were performed using the ADCIRC storm surge model with the inclusion of radiation stress gradients from the STWAVE nearshore wave model. Coupled model simulations were made for a number of landscape configurations that involved both restored and degraded wetland features. The impact of barrier island condition on hurricane surge and waves was also evaluated. Effects of landscape features were represented by changes in elevation and frictional resistance. Restoration and degradation of marsh resulted in decreases (for restoration cases) and increases (for degradation cases) in both surge and waves. The magnitude of change was correlated with the magnitude of the horizontal extent and elevation changes in the marsh. In general, the wave change patterns are consistent with the water level changes. Deflation of the Chandeleur Islands (barrier island chain) resulted in slightly increased surge. Results suggest that coastal marsh does have surge and wave reduction potential. Results also indicate that the impact of the landscape features is amplified in areas where there are levee “pockets.” Barrier islands and coastal ridges reduce wave heights, even if in a degraded condition and thus can reduce wave energy in wetland areas, protecting them from erosion.

Molecular Electron Affinities and the Calculation of the Temperature Dependence of the Electron‐Capture Detector Response

AbstractFor Abstract see ChemInform Abstract in Full Text.

Molluscicidal hydroxynaphthoquinones and derivatives: correlation between their redox potentials and activity against Biomphalaria glabrata

Several 2-hydroxy-3-alkyl-1,4-naphthoquinones have been submitted to molluscicidal bioassays against the snail Biomphalaria glabrata, intermediate host of Schistosoma mansoni. Cyclic voltammetric studies in aprotic medium (N,N-dimethylformamide plus tetrabutylammonium perchlorate) on Hg and glassy carbon electrodes have been performed on these compounds in order to obtain information about their biological mechanism of action. Several of the quinones assayed showed significant molluscicidal activities, and correlation of their activities and electrochemical parameters showed that the first wave reduction potential is an important parameter. The easily reduced quinones (>Ep1c) were more active against adult snails and against their egg masses, whilst the 3-methylamino-2-hydroxy derivatives presented higher negative reduction potentials and were not active as molluscicides.

Substituent effects in reductions of heteroaromatic cations

AbstractA set of 11 each of 2,4,6‐triphenylpyrylium, ‐thiopyrylium and ‐N‐methylpyridinium tetrafluoroborates carrying a range of substituents in the phenyl rings were prepared. First and second wave reduction potentials were determined. For the thiopyrylium series there are linear correlations between scaled potentials (E°/0.05915) and summed Hammett constants for substituents in the pendant phenyl groups (σ = 2.29 and 3.38 for first and second waves respectively). For the pyrylium series, a good linear relationship (σ = 2.79) is obtained for all substituent patterns for the first wave reduction potentials, but for the second wave there are separate correlations for salts carrying substituents in the 4‐phenyl and for those carrying substituents in 2‐ and 6‐phenyls. For the pyridinium series, the first wave potentials show separate correlations for salts carrying substituents in the 4‐phenyl and for those carrying substituents in 2‐and 6‐phenyls, but a single linear relationship for the second wave potentials. These are related to particular structural features in the cations, radicals and anions in each series. Rates and products were determined for reductions of the pyrylium and thiopyrylium cations by sodium cyanoborohydride and of all cations by sodium borohydride in acetonitrile solution. Reactions are first order in reducing agent and cation. Primary kinetic isotope effects were determined for borohydride reduction of the least reactive of each of the series of cations. Plots of logarithms of second‐order rate constants against summed Hammett constants for substituents in the pendant phenyl groups are linear for all combinations of reagent and cation with 0.91 < σ < 1.50 across all substituent patterns. For parent pyrylium and thiopyryliums, kBH4/kCNBH3 = 8.4 × 104 and 1.5 × 104, respectively, and for reductions by borohydride the reactivities of the pyrylium, thiopyrylium and pyridinium, series decrease in the order 1.4 × 105:8.8 × 103:1. Constant selectivities are not observed. Comparison of the correlations for electrochemical reduction and for hydride addition leads to the conclusion that charge neutralization in the hydride addition transition states runs ahead of bonding changes at the originating B—H bond. Copyright © 2002 John Wiley & Sons, Ltd.

Synthesis, spectroscopic, photophysical and electrochemical behaviour of ruthenium(II) and copper(I) isocyano-bridged complexes with polypyridine ligands: 2,2′-bipyridine and 1,10-phenanthroline

New binuclear complexes with [Cu(PPh3)3]+ and [Cu(PPh3)(N—N)]+ (N—N – 2,2′-bipyridine, 1,10-phenanthroline) moieties connected via the isocyanide group to [Ru(bpy)2(py)]+ and [Ru(phen)2(py)]+ have been prepared and isolated as PF6 − salts. In addition, new trinuclear complexes, [{(PPh3)3Cu(μ-NC)}2Ru(bpy)2](PF6)2 and [{(N—N)-(PPh3)Cu(μ-NC)}2Ru(bpy)2](PF6)2, have been synthesized using [Ru(bpy)2(CN)2]. The complexes have been characterized by elemental analyses, i.r., n.m.r., u.v.–vis., FAB mass spectra and by conductivity measurements. The i.r. spectra reveal an increase in v;(CN) in the isocyano-bridged complexes compared to the mononuclear parent complexes. The complexes are luminescent with emission wavelengths in the 458–550 and 600–636 nm ranges. The half wave reduction potentials in MeCN are always more positive than those of the parent complexes. It is observed that the isocyano-bridged complexes are more powerful excited state reductants than the cyano-bridged, Cu(I)(μ-CN)Ru(II) complexes.

Synthesis, electrochemistry, and molluscicidal activity of nitroaromatic compounds: effects of substituents and the role of redox potential

Molluscicidal bioassays and electrochemical studies (measurement of first wave reduction potential, Epc1) were performed on several synthetic nitroaromatics, in relation to possible correlation between biological activity, redox potential and structural effects. Five of them presented a significant molluscicidal activity on Biomphalaria glabrata (LD 50<20 ppm). The Epc1 values ranged from −0.532 to −0.857 V versus Ag/AgCl (0.1 M) (−0.260 to −0.585 V versus NHE), all of them, in the favorable range for reduction in vivo. Data comparison between Epc1 and molluscicidal activity indicates that the presence of the electroactive nitro group is important for the biological activity. Correlation with redox potential, however, was not evident. Structural effects seem to be the most important parameter. Higher activity is noticeable for phenols, including the para-nitro azo or hydrazo-containing compounds. No activity was observed for compounds having the benzylic substituent in meta position to the nitro group. These results suggest that activity undoubtedly involves more than reduction characteristics and that the possible formation of electrophilic species, after nitro reduction, can play an important role in molluscicidal activity against B. glabrata.

Classification of organic molecules to obtain electron affinities from half wave reduction potentials: The aromatic hydrocarbons

Adiabatic absolute electron affinities (EA) of about 80 aromatic hydrocarbons are calculated from literature values of half wave reduction potentials in aprotic solvents. Solution energy differences are estimated by grouping the molecules based on experimental and theoretical values, chemical logic and statistical analysis. The electronegativity values, (IP+EA)/2, calculated using literature data for ionization potentials, are constant for many of the compounds. Others vary in a systematic manner, such as benzene, 4.26±0.05; naphthalene, 4.14±0.02; anthracene, 4.06±0.02; tetracene, 4.03±0.03; pentacene, 3.98±0.03, in eV. Theoretical values, recalculated from the beginning, compare favorably with the literature values. Three independent methods for obtaining absolute EA’s are summarized and verified; the calibration of reduction potentials, the combination of ionization potentials with electronegativities and the use of semiempirical methods.

A proposed model for electron conduction in DNA based upon pairwise anion π stacking: electron affinities and ionization potentials of the hydrogen bonded base pairs

The values of the electron affinities (EAs) and ionization potentials (IPs) of the Watson–Crick hydrogen-bonded base pairs were calculated using the AM1-multiconfiguration configuration interaction (AM1-MCCI) method. This procedure was previously used to verify the electron affinities of the monomers determined from half wave reduction potentials. The electron affinities of the DNA base pairs differ by only 180 meV (4 kcal/mol). This makes rapid electron transport in DNA thermodynamically feasible in biological systems. During anion formation, calculations show geometry changes which affect the noncovalent hydrogen bonds and π stacking interactions. A model for rapid electron transfer through the π-system inherent in the base pairs is postulated. This mechanism is based upon the separation of the system into two distinct portions: a tunneling down the backbone and a pairwise donor–acceptor process through the π-way.

Experimental Determination of Electron Affinities of Organic Molecules

Abstract The electron affinity of a molecule is the definitive measure of its ability to act as an electron acceptor. During the past twenty years, experimental methods for the determination of this quantity have been developed. While the magnetron procedure and the electron capture detector method were introduced in the 1960s, only recently have confirmatory gas phase measurements been made. In this review, the experimental procedures and their limitations will be summarized, the available experimental results (about 200 values) will be critically evaluated, and the gas phase measurements will be compared with half wave reduction potentials. A method for estimating electron affinities from substituent effects will be presented.

Correlation and prediction of electron-capture response from molecular parameters

The kinetic model of the electron-capture detector (ECD) relates the response to the fundamental properties of the capturing species. In the case of molecules which undergo reversible reactions, the important properties are the electron affinity, the rate constant for thermal electron attachment and the rate constant for ionic recombination. The direct calculation of the response has not been carried out because of the limited number of experimental values. In this paper, the available molecular electron affinities are correlated with the reversible half wave reduction potentials in aprotic solvents for these compounds in order to provide additional electron affinities to calculate ECD response factors. Examples of this procedure are given for data on aromatic hydrocarbons, aldehydes and ketones determined in this laboratory; and data on substituted benzophenones, aromatic hydrocarbons and heterocyclic compounds taken from the literature. Both the magnitude and the temperature dependence are predicted. The success with these compounds suggests that the effect of substituents on half wave reduction potentials can be extended to the prediction of electron affinities and in some cases, the ECD response from the structure of these molecules.

An electron spin resonance and polarographic study of the sulphone group

The electron spin resonance spectra of the radical anions of diphenyl sulphone, dibenzothiophene S, S-dioxide and thianthrene S, S, S′, S′-tetroxide have been measured and the proton hyperfine splitting constants assigned to the various protons by measurement of the spectra of deuterio and methyl derivatives. The experimentally determined spin populations were correlated by molecular orbital calculations, using the formalism of Koch and Moffit to describe the sulphone group, and it is shown that irrespective of the mutual orientation of this group and the conjugated system it may be described as far as the electron spin resonance spectra are concerned as contributing a vacant symmetric orbital to the conjugated system whose coulomb integral (αSO2 ) and sulphur carbon resonance integral (βC-SO2 ) are given by αSO2 =αC – 2·0β, βC-SO2 =0·8β where α and β are the carbon coulomb integral and carbon-carbon resonance integrals respectively. The polarographic half wave reduction potentials of these compounds and some of their methyl derivatives dissolved in anhydrous dimethylformamide were also determined and the effect of methyl substitution on this quanttiy is also well described by the above parameters for the sulphone group. Finally a difference between the results obtained here and those previously obtained by Vincow from the electron spin resonance spectrum of thioxanthone S, S-dioxide radical anion is noted and discussed.