Half-wave Oxidation Potentials Research Articles

Synthesis, Crystal Structure, and Electrochemistry of Mono- and Bis-Homoannular Ferrocene Derivatives

Two ferrocene derivatives, namely, 1,2-(tetramethylene)-ferrocene and 1,2,1′,2′-bis(tetramethylene)-ferrocene, were synthesized in a four-step reaction sequence starting from ferrocene. Friedel–Crafts acylation of ferrocene using succinic anhydride gave mono- or bis(3-carboxypropinoyl)-ferrocene depending on the stoichiometry of succinic anhydride. The reduction of the keto groups to methylene followed by ring-closing using trifluoroacetic anhydride gave 1,2-(α-ketotetramethylene)-ferrocene or 1,2,1′,2′-bis(α-ketotetramethylene)-ferrocene. The diastereomeric mixture of the latter diketones was separated using column chromatography, characterized via single-crystal X-ray analysis, and assigned its stereochemistry. Reduction of the keto groups to methylene under Clemmensen conditions gave homoannular mono- or bis(tetramethylene)-ferrocene derivatives. The molecular structure of 1,2-(tetramethylene)-ferrocene revealed that the ipso carbon atoms of the cyclopentadienyl group are 0.023(3) Å farther away from Fe(II) compared to the remaining three carbon atoms. Both complexes exhibit lower half-wave oxidation potentials than ferrocene, possibly due to the electron-releasing effects of the tetramethylene bridges.

QSER modeling of half-wave oxidation potential of indolizines by theoretical descriptors

Indolizine derivatives hold essential biological functions and have been researched for hypoglycemic, antibacterial, anti-inflammatory, analgesic, and anti-tumor actions. Indolizine scaffold has intrigued conjecture and continuous attention and has become an effective parent system for generating powerful novel medication candidates. This research focused on applying the quantitative structure-electrochemistry relationship (QSER) approach to the half-wave potential (E1/2) for Indolizine derivatives using theoretical molecular descriptors. After calculating the descriptors and splitting the data into both sets, training and prediction. The QSER model was constructed using the Genetic Algorithm/Multiple Linear Regression (GA/MLR) technique, which was used to choose the optimal descriptors for the model. A four-parameter model has been established. Many assessment procedures, including cross-validation, external validation, and Y-scrambling testing, were used to assess the model's performance. Furthermore, the applicability domain (AD) was investigated using the Williams and Insubria graphs to assess the correctness of the established model's predictions. The constructed model exhibits great goodness-of-fit to experimental data, as well as high stability (R²=0.893, Q²LOO= 0.851, Q²LMO=0.843 RMSEtr= 0.052, s= 0.056). Prediction results show a good agreement with the experimental data of E1/2 (R²ext= 0.912, Q²F1= 0.883, Q²F2= 0.883, Q²F3= 0.919, CCCext= 0.942, RMSEext=0.045).

Chlorogenic acids protect organic dyes against self-catalyzed photobleaching

An environmentally benign method for preventing the photofading of organic dyes was developed using chlorogenic acids, also known as caffeoylquinic acids (CQAs), which can be obtained in large quantities from agricultural wastes. In this study, 5-caffeoylquinic acid (5-CQA) and 4,5-dicaffeolyquinic acid (4,5-diCQA) were used as singlet oxygen (1O2) quenchers, and their suppression mechanisms were evaluated by the self-catalyzed photobleaching reactions of methylene blue (MB) and rose bengal (RB) in aqueous solutions at different pH values. Light irradiation experiments, half-wave oxidation potentials measurements, LC-MS, and NMR demonstrated that CQAs effectively inhibited the photofading of the dyes in the pH range of 4–9 with two independent reaction mechanisms. 4,5-diCQA was more effective in preventing the photofading than 5-CQA. The kinetic analysis estimated the 1O2 quenching constants of CQAs (kq = 7.22 × 107 M−1 s−1 and 9.33 × 107 M−1 s−1 for 5-CQA and 4,5-diCQA) and the bimolecular rate constant for the chemical quenching of 1O2 by MB (kf = 2.88 × 104 M−1 s−1). Comparing these rate constants revealed that the quenching reactions of 1O2 by CQAs were more predominantly than the photofading reaction of MB.

Air Stable Chalcogen-Doped Rubicenes with Diradical Character

Air Stable Chalcogen-Doped Rubicenes with Diradical Character

How the Ancillary Ligand X Drives the Redox Properties of Biscyclopentadienyl Pentavalent Uranium Cp2U(═N-Ar)X Complexes.

Relativistic zero order regular approximation (ZORA) density functional theory computations, coupled with the conductor-like screening model for solvation effects, are used to investigate the redox properties of a series of biscyclopentadienyl pentavalent uranium(V) complexes Cp2U(═N-Ar)X (Ar = 2,6-Me2-C6H3; X = OTf, C6F5, SPh, C═CPh, NPh2, Ph, Me, OPh, N(TMS)2, N═CPh2). Regarding the UV/UIV and UVI/UV couple systems, a linear correlation (R2 ∼ 0.99) is obtained at the ZORA/BP86/TZP level, between the calculated ionization energies and the measured experimental E1/2 half-wave oxidation potentials (UVI/UV) and between the electron affinities and the reduction potentials E1/2 (UV/UIV). The study brings to light the importance of solvation effects that are needed in order to achieve a good agreement between the theory and experiment. Introducing spin-orbit coupling corrections slightly improves this agreement. Both the singly occupied molecular orbital and the lowest unoccupied molecular orbital of the neutral UV complexes exhibit a majority 5f orbital character. The frontier molecular orbitals show a substantial ancillary ligand X σ and/or π character that drives the redox properties. Moreover, our investigations allow estimating the redox potentials of the X = Ph, X = C6F5, and N(TMS)2 UV complexes for which no experimental electrochemical data exist.

Tuning of Persulfate Activation from a Free Radical to a Nonradical Pathway through the Incorporation of Non-Redox Magnesium Oxide.

Nonradical-based advanced oxidation processes for pollutant removal have attracted much attention due to their inherent advantages. Herein we report that magnesium oxides (MgO) in CuOMgO/Fe3O4 not only enhanced the catalytic properties but also switched the free radical peroxymonosulfate (PMS)-activated process into the 1O2 based nonradical process. CuOMgO/Fe3O4 catalyst exhibited consistent performance in a wide pH range from 5.0 to 10.0, and the degradation kinetics were not inhibited by the common free radical scavengers, anions, or natural organic matter. Quantitative structure-activity relationships (QSARs) revealed the relationship between the degradation rate constant of 14 substituted phenols and their conventional descriptor variables (i.e., Hammett constants σ, σ-, σ+), half-wave oxidation potential (E1/2), and pKa values. QSARs together with the kinetic isotopic effect (KIE) recognized the electron transfer as the dominant oxidation process. Characterizations and DFT calculation indicated that the incorporated MgO alters the copper sites to highly oxidized metal centers, offering a more suitable platform for PMS to generate metastable copper intermediates. These highly oxidized metals centers of copper played the key role in producing O2•- after accepting an electron from another PMS molecule, and finally 1O2 as sole reactive species was generated from the direct oxidation of O2•- through thermodynamically feasible reactions.

Electrochemical, Spectroelectrochemical, Mößbauer, and EPR Spectroscopic Studies on Ferrocenyl-Substituted Tritylium Dyes.

Four monoferrocenyl tritylium derivatives with donor-substituted (OMe, NMe2 ) aryl rings are reported, along with their spectroscopic and electrochemical properties. All the complexes show a one-electron reduction and a quasi-reversible ferrocene oxidation at a very positive potential. Small quadrupole splittings, ΔEQ , in Mößbauer spectra agree with highly electron-deficient ferrocenes. Comparison of the experimental half-wave potentials for ferrocene oxidation, E1/2 (Fc/Fc+ ), with those estimated from established correlations of E1/2 (Fc/Fc+ ) with ΔEQ indicates that the E1/2 values of the anisyl-substituted congeners FcOMe+ and FcMeOMe+ are affected by Coulombic repulsion between the positive charges at the Fe ion and the neighboring methylium site. Electronic spectra are recorded and interpreted with the aid of quantum chemical calculations. UV/Vis spectroelectrochemical measurements as well as chemical reduction provide insight into the redox-induced color changes upon ferrocene oxidation or upon reduction to the neutral trityl radicals. The neutral radicals reversibly form EPR-silent dimers. This process is studied by temperature-dependent EPR spectroscopy, and thermodynamic data for their dimerization are determined. Experimental and quantum chemical data suggest that the dimers assume classical hexaarylethane structures as opposed to normal or "offset" Jacobson-Nauta-type structures.

New fluorinated aromatic polyamides based on N,N-bis(4-carboxyphenyl)-4-trifluoromethylaniline

A new aromatic diacid monomer, N, N-bis(4-carboxyphenyl)-4-trifluoromethylaniline, was synthesized by the substitution reaction of 4-trifluoromethylaniline with 4-fluorobenzonitrile, followed by alkaline hydrolysis of the dinitrile intermediate. Several polyamides with 4-trifluoromethyltriphenylamine moieties were prepared from the diacid and various aromatic diamines via the direct phosphorylation polycondensation. All the polyamides were amorphous and readily soluble in many polar organic solvents such as N, N-dimethylacetamide and N-methyl-2-pyrrolidone, and could be solution-cast into transparent, tough, and flexible films with good mechanical properties. They exhibited good thermal stability with glass transition temperatures of 260–330°C, 10% weight-loss temperatures above 500°C, and char yields higher than 60% at 800°C in nitrogen. These polymers had low dielectric constants of 3.35–3.72 (100 Hz), low water uptake of 1.80–2.60%, and high transparency with an ultraviolet–visible absorption cutoff wavelength in the range of 378–390 nm. Cyclic voltammograms of the polyamide films cast onto an indium-tin oxide–coated glass substrate exhibited a reversible oxidation redox coupled with oxidation half-wave potentials ( E 1/2) of 0.95–1.04 V versus silver/silver chloride in an acetonitrile solution.

Experimental and computational study on the electrochemistry of meso-tetrasubstituted porphyrins: Effects of resonance and inductive substituents

Meso-tetrasubstituted free base porphyrins with six-membered rings, which exhibit inductive or resonance effects between the substituents and the porphyrin rings, were synthesized and their electrochemical behavior was examined by employing cyclic voltammetry (CV) and density functional theory (DFT). The experimental results show that the free-base porphyrin with 4-hexoxy-biphenyl substituents (H2TBoC6P) has the smallest half-wave oxidation potential splitting (∆E = 2nd E1/2 − 1st E1/2), compared to that with tetra-naphthalene (TNP) or tetra-phenyl (TPP) substituents. The ∆E values follow the trend of H2TBoC6P < H2T(2 − N)P < H2T(1 − N)P < H2TPP. The DFT results show that sterically controlled inter π-conjugation between the porphyrin ring and meso-substituents, defined by dihedral angles (ψ), mainly contributes to the half-wave oxidation potentials of free-base porphyrins rather than the saddle deformation of the porphyrin rings. Furthermore, the half-wave oxidation potential splitting ∆E is related to the highest spin density (HSD) distribution on porphyrin rings and HOMO-LUMO energy gaps of free-base porphyrin cationic radicals. A good agreement between calculated and experimental results indicates that steric hindrance between the porphyrin ring and meso-substituents is more important than substituent effects in determining the electrochemistry of free-base porphyrins.

Redox Properties of Monocyclooctatetraenyl Uranium(IV) and (V) Complexes: Experimental and Relativistic DFT Studies

The redox properties of a series of mono(cyclooctatetraenyl) uranium(IV) and (V) complexes [(Cot)(Cp)U(NEt2)2] (1) (Cot = η-C8H8, Cp = η-C5H5) [(Cot)U(OiPr)3] (2), [(Cot)U(NMe2)3] (3), [(Cot)U(N{SiMe3}2)2] (4), [(Cot)U(NEt2)3]– (5), and the cyclopentadienyl compound [(C5Me5)U(NEt2)3] (6) have been investigated using cyclic voltammetry and relativistic density functional theory (DFT). Electrochemical measurements of half-wave potentials in tetrahydrofuran were carried out under strictly anaerobic conditions. The calculations of ionization energies (IE) and electron affinities (EA) of these compounds, related to the UIII/UIV, UIV/UV, and UV/UVI redox systems, revealed a very good linear correlation (r2 = 0.99) between calculated ionization energies at the ZORA/BP86/TZP level and the measured E1/2 half-wave oxidation potentials. A similar good linear correlation between the computed electron affinities and the electrochemical reduction potentials (r2 = 0.98) was obtained. It was found to be crucial to take i...

Effect of Imidazole on the Electrochemistry of Zinc Porphyrins: An Electrochemical and Computational Study.

In this study, the electrochemical behavior of zinc meso-substituted porphyrins in the presence of imidazole is examined by using both cyclic voltammetry (CV) and density functional theory (DFT) methods. The results show that the first half-wave oxidation potentials (1st E1/2) of zinc porphyrins complexed with imidazole all move to the negative side, while the second ones (2nd E1/2) move to the positive side, resulting in larger half-wave oxidation potential splittings of the two oxidation states (ΔE = second E1/2 - first E1/2) comparing with the zinc porphyrins. By employing DFT calculations, we have found that both sterically controlled inter π-conjugation between porphyrin rings and meso-substituted phenyl groups and deformation of porphyrin rings do play important roles in contributing to the half-wave oxidation potentials. Imidazole exhibits strong effects on the deformation of porphyrin rings which is dominant in determining the first E1/2 while the inter π-conjugation between porphyrin rings and meso-substituted phenyl groups mainly contributes to the second E1/2. Without imidazole, the inter π-conjugation between porphyrin rings and meso-substituted phenyl groups is the only important criterion which effects both first E1/2 and second E1/2 of zinc porphyrins.

Synthesis and characterization of novel aromatic polyamides containing 3-trifluoromethyl-substituted triphenylamine

ABSTRACTA new 3-trifluoromethyl-substituted triphenylamine-containing aromatic diacid monomer, N,N-bis(4-carboxyphenyl)-3-trifluoromethylaniline, was prepared by the substitution reaction of 3-trifluoromethylaniline with 4-fluorobenzonitrile, followed by alkaline hydrolysis of the dinitrile intermediate. Novel aromatic polyamides with 3-trifluoromethyl-substituted triphenylamine moieties were prepared from the diacid and various aromatic diamines via the direct phosphorylation polycondensation. All the polyamides were amorphous and readily soluble in many polar organic solvents such as N,N-dimethylacetamide and N-methyl-2-pyrrolidone, and could be solution-cast into transparent, tough, and flexible films with good mechanical properties. They exhibited good thermal stability with relatively high glass-transition temperatures (258–327°C), 10% weight-loss temperatures above 500°C, and char yields higher than 60% at 800°C in nitrogen. These polymers had low dielectric constants of 3.22–3.70 (100 Hz), low moisture absorption in the range of 1.75–2.58%, and high transparency with an ultraviolet–visible absorption cut-off wavelength in the 375–395 nm range. Cyclic voltammograms of the polyamide films cast onto an indium tin oxide coated glass substrate exhibited a reversible oxidation redox couple with oxidation half-wave potentials (E1/2) of 0.95–1.00 V vs. Ag/AgCl in an acetonitrile solution.

Binding Interactions between a Ferrocenylguanidinium Guest and Cucurbit[n]uril Hosts.

The binding interactions between a novel ferrocenylguanidinium derivative (FcG+) and the macrocyclic hosts cucurbit[7]uril (CB7) and cucurbit[8]uril (CB8) were investigated in aqueous solution. 1H NMR spectroscopic experiments indicated that both hosts form stable 1:1 inclusion complexes with FcG+, in which the ferrocenyl group is engulfed by the host cavity. The stoichiometry of the CB7·FcG+ complex was also confirmed by electrospray mass spectrometric (ESI MS) experiments. The association equilibrium constants (K) were determined from NMR competition experiments. The measured K values were 3.5 × 109 and 2.5 × 108 M-1 for CB7 and CB8, respectively, in 50 mM sodium acetate-d3 D2O solution (pD 4.7). DFT computational studies confirmed the 1:1 stoichiometry and the inclusion character of both complexes. Voltammetric experiments were carried out to measure the complexation-induced shifts on the half-wave potentials for the one-electron oxidation of the ferrocenyl moiety. Complexation by CB7 led to a 12 mV anodic shift, while CB8 caused a larger 32 mV shift also in the positive direction. These potential shifts suggest that the delocalization of the positive charge on the side arm over the three nitrogens in the guanidinium unit results in electrochemical behavior similar to that observed with neutral ferrocene derivatives.

SYNTHESIS OF FUNCTIONALIZED PROPYLAMINEPOLYANILINES AND INVESTIGATION OF THEIR PROPERTIES

In present investigation, N-substituted propylaminepolyaniline ( N -PAPANI) was prepared by reaction of dimethylsulfoxide solution of polyaniline (emeraldine) base with sodium hydride, then reacted with 3-chloropropylaminehydrochloride. The N -PAPANI was characterized using reflectance Fourier transformation infrared (FTIR), cyclic voltammetry, UV-vis spectroscopy and chemical analysis. Polyaniline (PANI) was also subjected to a reaction with 3-chloropropylaminehydrochloride and ferric chloride in acetonitrile as solvent under refluxing temperature (85-90 oC) (Friedel-Craft synthetic method) to produce ring substituted functionalized PAPANI. Characterization of PAPANI was carried out using various aforementioned techniques. PANI and N -PAPANI polymers exhibited strong UV-vis absorption maxima at 273-294 nm in solution. Cyclic voltammograms of the polymers on an indium-tin oxide (ITO)-coated glass substrate exhibited one pair of reversible redox couples at half-wave oxidation potentials ( E 1/2) around 0.84-0.86 V and 0.88 V, respectively, versus Ag/AgCl in an acetonitrile solution. The obtained polymers showed good solubility in common organic solvents such as tetrahydrofuran and chloroform compared with emeraldine which is difficult to process due to lack of solubility. Furthermore, these polymers are air stable.

Synthesis and properties of electroactive aromatic polyimides with methyl- or trifluoromethyl-protecting triphenylamine units

Two series of new redox-active aromatic polyimides with methyl- (–CH3) or trifluoromethyl (–CF3)-protecting triphenylamine moieties were prepared from 4,4′-diamino-4″-methyltriphenylamine and 4,4′-diamino-4″-(trifluoromethyl)triphenylamine with aromatic tetracarboxylic dianhydrides via the conventional two-step polycondensation technique. Flexible and strong polyimide films could be obtained via the thermal curing of their precursor poly(amic acid) films or direct solution cast from some organosoluble polyimides. The polyimides showed high glass-transition temperatures between 269°C and 312°C, and they did not show significant decomposition before 500°C in air or under nitrogen atmosphere. Cyclic voltammograms of the polyimide films on the indium–tin oxide-coated glass substrate exhibited a pair of reversible redox waves with half-wave oxidation potentials of 1.08–1.10 V (for the –CH3 series) and 1.23–1.26 V (vs. silver/silver chloride; for the –CF3 series) in acetonitrile solution. The polyimide films showed anodic electrochromism from pale yellow neutral state to purplish blue (for the –CH3 series) and chrome yellow (for the –CF3 series) when oxidized.

Synthesis and properties of poly(amine-amide)s and poly(amine-imide)s based on 4,4′-diamino-4″-fluorotriphenylamine

Abstract Novel electroactive aromatic poly(amine-amide)s and poly(amine-imide)s with 4-fluorotriphenylamine units in the backbone were prepared from a newly synthesized diamine monomer, 4,4′-diamino-4″-fluorotriphenylamine, with aromatic dicarboxylic acids and tetracarboxylic dianhydrides via the phosphorylation technique and conventional two-step polycondensation technique, respectively. All the synthesized polymers could afford flexible and tough films with moderately high thermal stability. Cyclic voltammograms of the poly(amine-amide) and poly(amine-imide) films on the indium-tin oxide (ITO)-coated glass substrate exhibited a pair of reversible oxidation waves with oxidation half-wave potentials ( E 1/2 ) of 0.91–0.99 V and 1.19–1.23 V ( vs . Ag/AgCl), respectively, in an electrolyte/acetonitrile solution. They also exhibited obvious electrochromic behavior between their neutral and oxidized states changing from pale yellow to green or blue.

Catalytic activity of unsupported Pd-Pt nanoalloys with low Pt content towards formic acid oxidation

We present the results of systematic investigation of catalytic activity of unsupported Pd-Pt nanoparticles towards formic acid oxidation. Investigation of unsupported nanoparticles allowed us to address the changes in catalytic activity caused by interactions between Pt and Pd and to exclude the possible influence of the support. While full range of Pt concentration in Pd was covered, we focused on the role of small amounts of Pt on the catalytic activity of Pd nanoparticles. We determined that formic acid oxidation half-wave potential was lower on Pd-Pt nanoparticles containing small amounts of Pt as compared to pure Pd nanoparticles. In comparison to pure Pd, Pd-Pt nanoparticles also exhibited higher formic acid electrooxidation current density observed in cathodic scans during voltammetric experiments. We attribute the changes in the half-wave potential mostly to the changes of surface electronic properties due to interactions between Pt and Pd, and the changes in catalytic current density to interplay between modified electronic properties and changes in surface morphology.

Model for electrochemical parameters for 4-(benzylsulfanyl)pyridines calculated from the molecular structure

As the half-wave potential is an important electrochemical property used for the characterization of organic compounds, this study is aimed to build up a QSPR model of half-wave oxidation potential of 4-(benzylsulfanyl)pyridines. Firstly, mechanism of electrochemical oxidation of 4-(benzylsulfanyl)pyridines as a model of their possible metabolic degradation was elucidated by preparative electrolysis and GC–MS analysis of oxidative products. Secondly, the QSPR of a half-wave potential of 4-(benzylsulfanyl)pyridines has been performed by two computational approaches: (i) optimal descriptors calculated with Simplified Molecular Input Line Entry System (SMILES), and (ii) classical Hammett constants. Both models have been proved to be statistically significant, and the statistical qualities of both computational approaches are comparable. The mechanistic interpretations of both approaches have been given, and their results gave complementary views on effect of structure of molecular fragments of substituents on the half-wave potential of examined compounds.

Electrochemical Properties of a New Class of Europium Sandwich Triple-Decker Complexes with Corrole and Phthalocyanine Macrocycles

The electrochemical properties of a new class of sandwich (phthalocyaninato)(corrolato) europium triple-decker complexes were synthesized and characterized by cyclic voltammetry in CH2Cl2 containing 0.1 M tetrabutylammonium perchlorate (TBAP) as supporting electrolyte. Two of the compounds described in the current paper are shown in the figure, and represented by HEu2[Pc(R)8]2[Cor(ClPh)3], where R = OC5H11 or OC8H17, Pc represents the dianion of phthalocyanine and Cor represents the trianion of corrole. Both triple-decker complexes exhibit five reversible oxidations and three reversible reductions, all of which are attributed to ligand-based redox processes. The half-wave potentials for the first oxidation and first and second reduction of the two europium triple-deckers are close to E 1/2 values for the double-decker species Eu[Pc(OC8H17)8]2, while half-wave potentials for the second to fifth oxidations are close to E 1/2 values for the triple-decker Eu2[Pc][Pc(OC8H17)8]2. The synthesis and electrochemical properties of the new compounds will be described. Acknowledgment: This work was supported by the Natural Science Foundation of China (No. 21001054, 21071067) and the Robert A. Welch Foundation (K.M.K., Grant E-680). Figure 1

Redox properties of biscyclopentadienyl uranium(V) imido-halide complexes: a relativistic DFT study

Calculations of ionization energies (IE) and electron affinities (EA) of a series of biscyclopentadienyl imido-halide uranium(V) complexes Cp*2U(=N-2,6-(i)Pr2-C6H3)(X) with X = F, Cl, Br, and I, related to the U(IV)/U(V) and U(V)/U(VI) redox systems, were carried out, for the first time, using density functional theory (DFT) in the framework of the relativistic zeroth order regular approximation (ZORA) coupled with the conductor-like screening model (COSMO) solvation approach. A very good linear correlation (R(2) = 0.993) was obtained, between calculated ionization energies at the ZORA/BP86/TZP level, and the experimental half-wave oxidation potentials E1/2. A similar linear correlation between the computed electron affinities and the electrochemical reduction U(IV)/U(III) potentials (R(2) = 0.996) is obtained. The importance of solvent effects and of spin-orbit coupling is definitively confirmed. The molecular orbital analysis underlines the crucial role played by the 5f orbitals of the central metal whereas the Nalewajski-Mrozek (N-M) bond indices explain well the bond distances variations following the redox processes. The IE variation of the complexes, i.e., IE(F) < IE(Cl) < IE(Br) < IE(I) is also well rationalized considering the frontier MO diagrams of these species. Finally, this work confirms the relevance of the Hirshfeld charges analysis which bring to light an excellent linear correlation (R(2) = 0.999) between the variations of the uranium charges and E1/2 in the reduction process of the U(V) species.