Monoelectronic Transfer Research Articles

Synthesis, Characterization, Cyclic Voltammetry, and Biological Studies of Co(II), Ni(II), and Cu(II) Complexes of a Tridentate Schiff Base, 1-((E)-(2-Mercaptophenylimino) Methyl) Naphthalen-2-ol (H2L1)

A novel tridentate Schiff base, 1-((E)-(2-mercaptophenylimino) methyl) naphthalen-2-ol (H2L1), was synthesized by the condensation reaction of 2-hydroxy-1-naphthaldehyde with 2-aminothiophenol in absolute ethanol. The resulting ligand was reacted with Co(II), Ni(II), and Cu(II) ions to obtain tetrahedral CoL1, NiL1, and square planar CuL1 complexes. The Schiff base and its metal complexes were characterized using 1H-NMR, microanalysis, FT-IR, UV-visible, and mass spectroscopy (ESI-MS). All the compounds are soluble in DMSO and DMF. Spectroscopic studies show that the ligand coordinates to the metal center through the azomethine nitrogen, naphthoxide oxygen, and thiophenoxide sulfur to form a tridentate chelate system. Conductance measurements show that these compounds are molecular in solution. Cyclic voltammetry studies show Co(III)/Co(II) and Cu(II)/Cu(I) redox systems to be quasi-reversible involving a monoelectronic transfer while Ni(III)/Ni(II) was irreversible. In vitro antibacterial and antifungal activity against five bacterial strains (Escherichia coli, Staphylococcus aureus, Pseudomonas aeruginosa, Enterococcus faecalis, and Proteus mirabilis) and five fungal strains (Candida albicans, Candida glabrata, Candida tropicalis, Candida krusei, and Candida parapsilosis) showed no antifungal activity but moderate antibacterial activity on E. coli, S. aureus, P. aeruginosa, and P. mirabilis bacterial strains. Antioxidant studies reveal that the ligand and its Cu(II) complex are more potent than Co(II) and Ni(II) complexes to eliminate free radicals.

The Proven Versatility of Cp2TiCl.

In the last two decades, titanocene monochloride has been postulated as a monoelectronic transfer reagent capable of catalyzing an important variety of chemical transformations. In this Perspective, our contributions to this growing field of research are summarized and analyzed. Especially known have been our contributions in C-C bond formation reactions, hydrogen-atom transfer from water to radicals, and isomerization reactions, as well as the development of a catalytic cycle that has subsequently allowed the preparation of a great variety of natural terpenes. It is also worth mentioning our contribution in the postulation of this single-electron transfer agent (SET) as a new green catalyst with a broad range of applications in organic and organometallic chemistry. The most significant catalytic processes developed by other research groups are also briefly described, with special emphasis on the reaction mechanisms involved. Finally, a reflection is made on the future trends in the research of this SET, aimed at consolidating this chemical as a new green reagent that will be widely used in fine chemistry, green chemistry, and industrial chemical processes.

On mechanism of reduction on DME of some compounds with local anesthetic activity N-oxides containing tertiary amine

It has been shown for the first time the obtaining of N-oxides of dymedrol (DMD) and bupivacaine (BVK). Bupivacaine is a local anesthetic of amide group. Dymedrol (diphenhydramine hydrochloride) is an antihistamine that reduces the effects of natural chemical histamine in the body. The N-oxides of DMD and BVK are formed during chemical oxidation with potassium peroxymonosulfate (KPMS). The first step was investigation of the optimal conditions for oxidation reaction to reach the maximum yield of final products (N-oxides). The investigated conditions were pH, time of oxidation and ratio of reagents. The needed time for oxidation of DMD and BVK is 10 min. At least two-fold excess of KPMS must be in the solution in recount to analyte concentration, but not higher than 10 -4 M. The maximum concentration of BVK and DMD N-oxides was obtained in weakly basic medium (pH 8.5–9.3). The second step was optimization of conditions for polarographic reduction of BVK and DMD N-oxides on the dropping mercury electrode (DME). The best medium for electrochemical reduction was the medium of phosphate buffer solution with pH in the range 5–6. On polarogramms it was observed only one irreversible peak in full pH range studied. The rate of electrochemical reaction is diffusion-controlled with weak adsorption of BVK, other local anesthetics (LA) (lidocaine, mepivacaine and trimecaine) and DMD N-oxides on DME surface confirmed by studying of effect of scan rates on polarogramms characteristics. The reduction potentials of peak linearly depend on solution pH. Thus, the electrochemical reduction of LA and DMD N-oxides includes protonation reaction stage. Based on literature survey and our calculations it was suggested that reduction mechanism of BVK and DMD N-oxides consist in monoelectron transfer resulting in anion-radical formation proceeding one proton adjunction. Keywords : polarography, N-oxides, local anesthetics, dymedrol, bupivacaine.

Electroreduction of Nitrobenzene: Nominal Simulation of Voltammogram

For the electrochemical reduction of nitrobenzene in aqueous cationic micellar solution of cetyltrimethylammonium bromide [CTAB] at platinum electrode using cyclic voltammetry, a reversible/quasi reversible charge transfer reaction pertaining to one electron couple of ArNO2/ArNO2.- was indicated (1). Digital simulation was used to evaluate electrochemical kinetic parameters for the mono-electron transfer step (1). An ECE mechanism, Scheme-1 and Figures 1 and 2 and Table-1, is suggested for the previously reported voltammograms (2) featuring nitrobenzene reduction on a coated platinum electrode partially covered by a thin film of dioctadecyldimethylammonium chloride [DODAC]. Table-1: Diffusion coefficients for nitrobenzene (2) Diffusion coefficient (cm2/s) 6.11×10-5 1.09×10-4 Bare Pt DODAC covered Pt, this work References (1) Tariq, M.; Haque, I. U., Science International (Lahore), 2016, 28, 361 (2) Haque, I. U.; Tariq, M., Journal of the Chemical Society of Pakistan, 2011, 33, 529 Figure 1

Electrochemical and theoretical analysis of the reactivity of shikonin derivatives: dissociative electron transfer in esterified compounds

An electrochemical and theoretical analysis of a series of shikonin derivatives in aprotic media is presented. Results showed that the first electrochemical reduction signal is a reversible monoelectronic transfer, generating a stable semiquinone intermediate; the corresponding E(I)⁰ values were correlated with calculated values of electroaccepting power (ω(+)) and adiabatic electron affinities (A(Ad)), obtained with BH and HLYP/6-311++G(2d,2p) and considering the solvent effect, revealing the influence of intramolecular hydrogen bonding and the substituting group at position C-2 in the experimental reduction potential. For the second reduction step, esterified compounds isobutyryl and isovalerylshikonin presented a coupled chemical reaction following dianion formation. Analysis of the variation of the dimensionless cathodic peak potential values (ξ(p)) as a function of the scan rate (v) functions and complementary experiments in benzonitrile suggested that this process follows a dissociative electron transfer, in which the rate of heterogeneous electron transfer is slow (~0.2 cm s(-1)), and the rate constant of the chemical process is at least 10(5) larger.

Formation of zinc–oxianion complex adlayer by underpotential deposition of Zn on Au(1 1 1) electrode: Preferential formation of zinc monohydrogen phosphate complex in weakly acidic solutions

The underpotential deposition (upd) of zinc was studied on Au(111) electrode in weakly acidic solutions by voltammetry. The difference of anion co-adsorption strength was investigated on upd Zn in the solutions containing phosphate, sulfate, perchlorate, and halides. The order of anion co-adsorption strength was found to be phosphate>sulfate, phosphate≫perchlorate, and phosphate≫halides. We present the electrochemical evidence that no co-adsorption of halide progresses on upd Zn at E>−0.7V (vs. SCE) in spite of the relatively high adsorbability of halide on Au(111). In 0.1M KH2PO4 (pH=4.4), the amount of charge density of the upd Zn stripping corresponded to that of 1/3 monolayer of the Zn adlayer formed as a result of mono-electron transfer between −0.35V and −0.6V. The coverage was coincident with that inferred from the (√3×√3)R30° STM image reported by us in the same condition. The formation of zinc–oxianion (phosphate and sulfate) surface complexes by Zn upd was proposed base on the difference of complex formation constants among the related zinc–anion complexes. Identification of the zinc–phosphate surface complex was thermodynamically carried out around pH=4 with a Nernst equation, where the shifts of Zn upd peak potential were investigated with the concentration changes of Zn2+, H2PO4−, and H+ under an imaginarily reversible condition. The formation of ZnHPO4 surface complex was concluded in the Zn upd with mono-electron transfer and explained a recent XAS analysis, which demonstrate each phosphate anion bridging three upd Zn atoms.

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.

From polysubstituted 1,5-dihydro- s-indacene lithium derivatives to polysubstituted hydro- s-indacenyl radicals by a new method involving a single electron transfer from an electron rich olefin

Polyalkyl-hydro- s-indacenyl radicals were obtained from the corresponding polyalkyl-hydro- s-indacenylmonolithium derivatives using a monoelectronic transfer from an electron rich olefin: 1,1′,3,3′-tetramethyl-2,2′-bisimidazolidine (ERO). The reaction involves the transient formation of a polyalkyl-hydro- s-indacenylimidazolidinium salt. The same salt was obtained by another way, reacting imidazolidinium chloride with polyalkyl-hydro- s-indacenyl lithium, and also generates the corresponding polyalkyl-hydro- s-indacenyl radical. All polyalkyl-hydro- s-indacenyl radicals studied present an unsymmetrical spin distribution and, in ESR, hyperfine couplings smaller than those usually observed in similar aromatic radical anions. They were identified from their dimerization products and also by trapping on 2,4,6-tri-tert-butylnitrosobenzene. A rhodium complex radical analog was also studied.

Synthesis of samarium(ii) borohydrides and their behaviour as initiators in styrene and ε-caprolactone polymerisation

The bisborohydrido samarium compound Sm(BH(4))(2)(THF)(2) (1) was prepared in high yield by comproportionation between Sm and 2 equivalents of Sm(BH(4))(3)(THF)(3). Reaction of 1 with KCp* (Cp* = C(5)Me(5)) afforded the half-sandwich Cp*Sm(BH(4))(THF)(2) (2). The (1)H NMR borohydride resonances of both complexes, observed at very high field, are typical of divalent Sm compounds. X-Ray single crystal analysis revealed polymeric and dimeric molecular arrangements for 1 and 2, respectively. Complex 1 was found moderately active towards styrene polymerisation when activated with Al((i)Bu)(3), or with a borate/Al combination, whereas 2 showed no activity. Ring-opening polymerisation of epsilon-caprolactone could be performed rapidly at room temperature with both initiators. Complex 2 leads to narrow polydispersities and higher activity. Two different mechanisms, by monoelectronic transfer or by insertion into the Sm-(BH(4)) bond can be proposed.

Stratégie TDAE appliquée à la synthèse de candidats–médicaments

Research, developed at the Laboratory of Organic Pharmaceutical Chemistry of the School of Pharmacy, UMR-CNRS 6517, is centred on the synthesis of novel therapeutic compounds using monoelectronic transfer reactions. Tetrakis(dimethylamino)ethylene (TDAE) is a powerful electron donor which has the specific property of activating the carbon-halogen bond leading to the formation of a stable electrophilic radical and a stable neutrophilic anion. Since 2002, our team has developed a program using monoelectronic transfer reactions initiated by TDAE of nitroaromatic, nitroheterocyclic and quinonic bioreducible alkylating agents. The goal is to synthesize new therapeutic compounds for use as anti-infectious agents, anticancer agents, and agents active on the central nervous system. In this context, we present the first pharmacochemical tools obtained with this strategy during reactions between diverse electrophilic compounds (aldehydes, ketones, alpha-keto-esters, ketomalonates, alpha-ketolactames, ...) and benzylic anions formed in situ by the action of TDAE. We illustrate the usefulness of this strategy by describing the preparation of new compounds of biological interest and the associated pharmacomodulation work.

On the electrochemistry of dopamine in aqueous solution. Part I: The role of [SDS] on the voltammetric behavior of dopamine on a carbon paste electrode

Abstract From CV and HPLC experiments, the influence of [SDS] on the dopamine electrochemical behavior was determined in aqueous solution. It is shown that in the absence of SDS the dopamine electrochemical oxidation at a carbon paste electrode is a quasi-reversible process, mass transfer controlled that is coupled to a slow chemical reaction (EC mechanism), however, as the [SDS] in solution is increased, the heterogeneous standard rate constant, k 0 , drastically increases. When [SDS] reaches a value of 5 mM, which is higher than the corresponding critical micellar concentration (CMC), the dopamine electrooxidation reaction becomes adsorption controlled and the chemical reaction is avoided. In all these cases, it was found that, the electrode reaction involves a monoelectronic transfer step. From HPLC experiments it was found that, after imposing a macroelectrolysis (oxidation) of dopamine, two products were detected except when the [SDS] in solution was 5 mM. In this case, just one product was formed corresponding to that having the highest retention time, which can be associated to dopamine semiquinone.

Convenient Preparation of Original Vinylic Chlorides with Antiparasitic Potential in Quinoline Series

The synthesis of various original vinylic chlorides from trichloromethylated substrates in the quinoline series is described herein. This reaction takes place under mild operating conditions via a monoelectronic transfer mechanism and presents elevated yields.

Electrochemical Quartz Crystal Microbalance Study of Copper Electrochemical Reaction in Acid Medium Containing Chlorides

Copper electrodissolution and electrodeposition were studied by means of gravimetric quartz crystal microbalance and electric (cyclic voltammetry) combined measurements. Relevant information on the mechanism of these electrochemical processes is provided by the analysis of experimental data and particularly of the mass change per charge unit. The copper electrodeposition and electrodissolution take place by means of two consecutive monoelectronic transfers where the anion participation in the reaction mechanism is specified. Besides, it is proved that the presence of molecular oxygen in the solution contributes to the formation of a passive layer on the surface of the metallic copper deposit.

Influence of the Cr Content on the Electrochemical Behavior of the LiCryMn2 − y O 4 ( 0 ⩽ y ⩽ 1 ) Compounds: II. Cyclovoltammetric Study of Bulk and Superficial Processes

In the 3.8-4.3 V range, deintercalation of Li from the title compounds, occurs in one or two well resolved steps (depending on y) which are single-phase phenomena for For the first step capacity is constant, whereas the second decreases rapidly. For larger y values, the only remaining step is the first, whose capacity decreases linearly with y, down to zero for An interpretation based on Li-Li repulsive interactions which play a role when and disappear when is proposed. In the 4.3-5.2 V range, deintercalation of Li occurs in two steps (at ∼4.55 and ∼4.92 V for and at ∼4.75 V and ∼4.92 V for which are single-phase phenomena. For the cyclable capacity increases with y while the irreversible capacity remains low. On the other hand, for an important capacity loss is observed at the second cycle, and a catalytic effect of the Cr content on the electrolyte oxidation is observed. Above 5.5 V, the kinetics of electronic transfer, associated to the electrolyte oxidation, remains about three times slower than expected for a standard monoelectronic transfer. This oxidation begins ∼0.2 V below, and its kinetics is faster for compared to The onset voltage of this reaction is always higher than the end of deintercalation voltage. materials remain remarkably stable against oxidation when they are subjected to high end-of-charge voltages. © 2001 The Electrochemical Society. All rights reserved.

A voltammetric study of pyridine-4-aldoxime (PA) at a glassy carbon electrode Error! Reference source not found.in dimethylformamide

Abstract The electroreduction of pyridine-4-aldoxime (PA) in DMF has been studied by cyclic voltammetry on a glassy carbon electrode. The behavior observed differs from that found in aqueous buffered solutions, although the same final reduction product, 4-amino-methyl pyridine (AP), is obtained. The overall four-electron reduction process is seen in this aprotic medium as two distinct voltammetric peaks. The first peak is thought to correspond to a monoelectronic transfer that yields a radical anion followed by a fast reaction involving the cleavage of the oxygennitrogen bond. The reaction of the hydroxide ion, generated at this step, with the neutral species of PA is taken as responsible for the change in the reduction mechanism. Thus, the reduction of the anion oxime species, at the potential of the second peak, is proposed. Experiments carried out with different potential programs allow that conclusion. The assignation is also based on results obtained in alkaline media. The addition of a proton donor produces changes, not only to the electroactive species, but also to the overall mechanism, making it similar to that reported in aqueous buffered solutions.

Spectroelectrochemical behaviour in dimethylformamide of pseudo-oxocarbons dianions derived from the croconate dianion

The electrochemical behaviour of croconate dianion and dicyanomethylene-substituted croconate dianions was investigated in dimethylformamide containing tetrabutylammonium hexafluorophosphate at a Pt electrode. By cyclic voltammetry, the oxidation of these dianions involves two successive reversible monoelectronic transfers which yield the corresponding radical-anions and neutral species. By reduction of these dianions, the radical-trianions are characterized by uv-vis and esr spectroscopies but are unstable. The redox potentials are strongly dependent on the number of dicyanomethylene groups. Electrochemical kinetics parameters have been determinated. Among the different oxidation states, only the dianions and radical-anions are stable. Due to their high absorption in the uv-visible domain, spectroelectrochemical studies have been carried out to characterize the redox states. The radical-anion/dianion redox couple is sufficiently cyclable for electromodulated colour changes and may be used in electrochromic applications.

Application of ultrasound technology to electroorganic synthesis: Reduction of acetophenone

Electroreduction of acetophenone in an undivided cell was chosen as a model reaction to investigate the use of ultrasonication in organic electrosynthesis. The reaction was carried out in aqueous medium (water–methanol), at neutral pH and at a cadmium or zinc cathode. Electrochemical reduction of acetophenone yields alcohol through a bielectronic transfer and pinacol through a monoelectronic transfer. Operating conditions permit to modify the reduction state of the reactant. On a cadmium cathode, the major product is the alcohol whereas on a zinc cathode, the pinacol is rather obtained. The ultrasonic activation has been studied as regards the faradaı̈c yield and the chemical selectivity. This work puts into evidence the interest of ultrasonication for electroorganic synthesis processes often submitted to passivation phenomena.

Photochemical behaviour of oxyfluorfen: a diphenyl-ether herbicide

The photochemical behaviour in different solvents of the herbicide oxyfluorfen [2-chloro-1-(3-ethoxy-4-nitrophenoxy)-4-(trifluoromethyl) benzene (CAS RN 42874–03–3)] was studied. Photochemical reactions were carried out by using a high pressure mercury arc and a solar simulator. Kinetic parameters and quantum yields were determined. Identification of the photoproducts was performed by GC-MS and the main compounds were confirmed by [ 1H] NMR. The photochemical reactions were also carried out in the presence of either a singlet or a triplet quencher, and in the presence of either a radical initiator or a radical inhibitor. Results indicate that the first excited singlet state can undergo both homolytic and heterolytic cleavage of the ethyl-oxygen bond in the side chain of oxyfluorfen. Moreover, the presence of reduction products in the reaction mixture is supposed to occur via a monoelectron transfer process with the formation of a transient exciplex during the reaction.

Photooxidations of 1,1-dialkyl-2-arylhydrazines by single electron transfer

The oxidation of substituted hydrazines through monoelectronic transfer leads regio- and stereoselectively with good yields to α-hydrazinonitriles under mild conditions.

Singlet oxygen mediated alkaloid tertiary amines oxidation by single electron transfer

A chemical study of the oxidation of tertiary amines and alkaloids through monoelectronic transfer is presented and allows us to assign to singlet oxygen a new behavior as electron acceptor during the oxidation process.