Search

The synthesis, characterization and modeling of two oligothiophenes bearing stable radicals are reported. The radical precursors 2,4-dimethyl-6-(6-(thiophen-2-yl)pyridin-2-yl)-1,2,4,5-tetrazinan-3-...

The synthesis and characterization of a new terthiophene bearing stable radical II is described. Through a cross coupling reaction between 2-tributylstannylthiophene and 6-(2,5-dibromo-thiophene-3-yl)pyridine-2-carboxaldehyde (2), 6-[2,2′:5′,2″]terthiophen-3′-ylpyridine-2-carboxaldehyde (3) was prepared. The condensation of 3 with 2, 4-diisopropylcarbonohydrazide bis-hydrochloride affords the heterocyclic tetrazane (4), which was oxidized with 1,4-benzoquinone to form the stable radical II. II characterized by IR, ESR, and cyclic voltammetry. Oxidative electropolymerization of II and its precursor 4 at oxidation peak potential of the terthiophene using cyclic voltammetric scans produces radical functionalized polyterthiophene on a platinum electrode (poly(II)-Pt).

Conducting polymers (CPs), thanks to their unique properties, structures made on-demand, new composite mixtures, and possibility of deposit on a surface by chemical, physical, or electrochemical methodologies, have shown in the last years a renaissance and have been widely used in important fields of chemistry and materials science. Due to the extent of the literature on CPs, this review, after a concise introduction about the interrelationship between electrochemistry and conducting polymers, is focused exclusively on the following applications: energy (energy storage devices and solar cells), use in environmental remediation (anion and cation trapping, electrocatalytic reduction/oxidation of pollutants on CP based electrodes, and adsorption of pollutants) and finally electroanalysis as chemical sensors in solution, gas phase, and chiral molecules. This review is expected to be comprehensive, authoritative, and useful to the chemical community interested in CPs and their applications.

A poly(terthiophene) pendant verdazyl radical was prepared via the electrochemical oxidation of either the parent radical or its precursor. Cyclic voltammetry showed a positive shift of the verdazyl radical oxidation potential in the corresponding electroactive poly(verdazyl radical-terthiophene).

An electron transfer initiated organic modification of silicon surfaces, using a donor/acceptor pair of ferrocene (Fc) and N-bromosuccinimide (NBS) (or N-bromophthalimide (NBP)), is reported for the first time. This modification method is efficient and does not require the use of heat or irradiation. Multilayer structures are formed on the surfaces through radical reactions, similar to the reduction of aryl diazonium salts. The modified surfaces were characterized by infrared reflection–absorption spectroscopy (IRRAS), X-ray photoelectron spectroscopy (XPS), and atomic force microscopy (AFM). IRRAS spectra clearly indicate a strong carbonyl stretch and the presence of a ferrocene moiety for each of the modified surfaces. XPS data show the presence of all elements from the donor/acceptor pair and provide strong evidence that the samples can be further modified by nucleophilic substitution. AFM imaging indicates the formation of dense layers that can be scratched away to reveal depth information on approxim...

The ability of the chiral electrode based on L-leucine functionalized terthiophene (poly(1)-Pt) to recognize and detect biomolecules has been studied as a function of hydrogen bonding between the chiral surface and a free L-leucine methyl ester. We characterized electrochemically the formation of hydrogen bonds by cyclic voltammetry (CV). The results show that the capacitive current of the chiral electrode poly(1)-Pt decreased by 30% due to hydrogen bonding between the chiral electrode and the free added L-leucine methyl ester. The origin of the hydrogen bonds on poly(1)-Pt has been confirmed by attenuated total reflection Fourier transform infrared (ATR-FTIR) using trifluoroacetic acid (CF3COOH) as free H-bonding species. The ATR-FTIR spectrum exhibits functionalities of free CF3COOH that form hydrogen bonds with the chiral conducting surface of poly(1)-Pt. Due to the insolubility of poly(1), NMR studies were performed on the parent monomers. The chemical shift of the amide proton in the 1H-NMR of the L-leucine functionalized terthiophene (1) shifted after addition of L-leucine methyl ester. Similar trends were observed for the carboxylic carbonyl of L-leucine methyl ester-terthiophene 2 in the 13C-NMR. In addition to the change in the 13C chemical shift, there is a considerable change in the spin–lattice relaxation time of the carbonyl carbon in 2 due to the formation of hydrogen bonds between the –COOH of 2 and the imidazole.

The synthesis and electrochemical characterization of d - and l -proline functionalized monothiophenes are reported. Both monomers 2L and 2D showed anodic peak potentials of 1.86 V vs. Fc + /Fc and their electropolymerization affords polymers that exhibit poor stability on platinum electrodes. However, the electrochemical copolymerization using cyclic voltammetry of 2L or 2D in the presence of EDOT gives polymeric films at the surface of the electrode with specific chirality. The E 1/2 of the copolymers was found to be 0.38 V vs. Fc + /Fc. The copolymers display excellent electrochemical stability and adhesion properties on the surface of platinum and ITO electrodes. Moreover, the films also undergo a reversible color change between their doped (blue-green) and undoped (blue-brown) states. Incorporation of the chiral pendant group was confirmed through the appearance of characteristic C O stretching absorptions in the IR spectra of the copolymers.

Polythiophenes bearing a specific chiral center such as L-leucine have been prepared via the electrochemical oxidation of a series of L-leucine functionalized oligothiophenes (monothiophenes and terthiophenes). These oligothiophenes have been prepared through the condensation of L-leucine methyl ester and the corresponding thiophene monomers in the presence of hydroxybenzotriazole (HOBt) and N,N'-dicyclohexylcarbodiimide (DCC) followed by hydrolysis of the esters. The electroactive polymers are electrochemically stable and exhibit excellent adhesive properties on electrode surfaces (platinum, gold, and glassy carbon) as well as interesting optical properties in both doped and undoped states. Hydrogen bonds between a free amino acid (L-leucine, D-leucine, L-alanine, D-alanine, and D/L-alanine) and the L-leucine based polythiophenes (chiral conducting surface) were probed using cyclic voltammetry. Preliminary results show that the capacitive current of a modified L-leucine-polythiophene electrode decreases as a result of the formation of a hydrogen bond barrier on the surface of the chiral conducting surface accompanied with a shift of the oxidation potential. Cyclic voltammetry responses resulting from the interaction of the chiral conducting surface with L and Dfree amino acid isomers are similar. The formation of hydrogen bonds between the chiral conducting surfaces and the free amino acids was characterized by (1)H NMR. A chemical shift was observed for the N-H group in monomer 6 as a result of the hydrogen bond formation between the L-leucine methyl ester (D-leucine methyl ester, D/L-leucine methyl ester) and monomer 6.

The synthesis, and the optical and electrochemical properties, of a series of mesitylthio (MesS-) end-capped bis(oligothienyl) sulfides are presented. The target compounds were synthesized principally by convergent protocols, whereby a series of short thiophene oligomers bearing one terminal mesitylthio (MesS-) substituent were first assembled by metal-catalyzed cross-coupling reactions and then coupled via divalent sulfur through reactions with bis(phenylsulfonyl) sulfide. The spectroscopic and electrochemical features of the bis(oligothienyl) sulfides are qualitatively similar to those of the related mesitylthio-capped fully conjugated oligothiophenes, suggesting that the degree of electronic communication between the two oligothiophene chromophores in the bis(oligothienyl) sulfides is low. Cyclic voltammetry studies on the bis(oligothienyl) sulfides reveal that these species can be reversibly oxidized to radical cations, but the reversibility of subsequent oxidations depends on oligothienyl chain length and the presence and position of more electron-rich ethylenedioxythiophene (EDOT) groups. In general, the bis(oligothienyl) sulfides possess fewer than the expected number of reversible oxidations based on comparisons with their corresponding mesitylthio-capped fully conjugated oligothiophenes; excessive charge accumulation at or near the central linking sulfur atom is believed to be responsible for the irreversible behavior. Analysis of the irreversible voltammetric response of one of the bis(oligothienyl) sulfides leads to the suggestion of a decomposition mechanism for the cationic species involving carbon-sulfur bond cleavage and subsequent coupling of thiophene fragments — a finding with potential implications for the poor environmental stability of doped poly(p-phenylene sulfide), one of the prototypical conducting polymers.Key words: conjugated materials, conducting polymers, oligothiophenes, electronic communication.

Results pertaining to the electrochemical reduction of 1,2-diacetylcyclopropane (5), 1-acetyl-2-phenylcyclopropane (6), 1-acetyl-2-benzoylcyclopropane (7), and 1,2-dibenzoylcyclopropane (8) are reported. While 6*- exists as a discrete species, the barrier to ring opening is very small (1 kcal/mol) and the rate constant for ring opening is10(7) s(-1). For 7 and 8, the additional resonance stabilization afforded by the benzoyl moieties results in significantly lower rate constants for ring opening, on the order of 10(5)-10(6) s(-1). Electron transfer to 8 serves to initiate an unexpected vinylcyclopropane --cyclopentene type rearrangement, which occurs via a radical ion chain mechanism. The results for reduction of 5 are less clear-cut: The experimental results suggest that the reduction is unexceptional, with a symmetry coefficient alpha/= 0.5, and reorganization energy consistent with a simple electron-transfer process (one electron reduction, followed by ring opening). In contrast, molecular orbital calculations suggest that 5*- has no apparent lifetime and that reduction of 5 may occur by a concerted dissociative electron transfer (DET) mechanism (i.e., electron transfer and ring opening occur simultaneously). These seemingly contradictory results can be reconciled if the increase in the internal reorganization energy associated with the onset of concerted DET is offset by a lowering of the solvent reorganization energy associated with electron transfer to a more highly delocalized LUMO.

Several cinnamyloxy carbamates and carbonates were subjected to electrochemical reduction, and the reductive fate of the cinnamyl group was investigated. Complete selectivity was observed in the removal of the cinnamyl group from oxygen versus nitrogen.

The synthesis and electrochemical properties of a series of bis(thiophene) sulfides is presented. The molecules were synthesized via either thiophenethiol substitution reactions with thienyl bromides or treatment of lithiated thiophenes with bis(phenylsulfonyl) sulfide. Bis(oligothienyl) sulfides based on thiophene, 3-hexylthiophene, and 3,4-ethylenedioxythiophene were similarly prepared. Investigation of the electrochemical properties reveal that, despite the presence of α,ω-CH positions on the two thiophene termini, not all derivatives formed polymers upon electro-oxidation. In some cases the inherent stability of the radical cation precluded coupling reactions; in others, radical cation solubility prevented electrodeposition of the putative polymer. Five of the monomers could be electropolymerized to afford poly(oligothienyl sulfides) which were characterized by electronic spectroscopy and electrochemical studies. Good correlations were found between the polymer redox properties and corresponding bis(a...

Silicon-bridged thiophene oligomers have been prepared via the reactions of lithiated (3,4-ethylenedioxy)thiophene (EDOT) (1) or 2,2′-bis-(3,4-ethylenedioxy)thiophene (biEDOT) (2) with dichlorodimethylsilane to afford bis-(2,3-dihydro-thieno[3,4-b][1,4]dioxin-5-yl)-dimethylsilane (3) and dimethyl-bis-(2,3,2′,3′-tetrahydro-[5,5′]bi[thieno[3,4-b] [1,4]dioxinyl]-7-yl)silane (4). Products 3 and 4 were characterized and show good stability in organic solvent and in air. The electropolymerization of these monomers affords stable and highly conducting polymers. The conductivity was found to be 25 and 60 S/cm for Poly3 and Poly4, respectively. Characterization data for the polymers suggested that the resulting materials have a backbone identical to p(EDOT), which formed through cleavage of the silicon–carbon (Si—C) bonds during electropolymerization.Key words: polythiophenes, EDOT, silicon, electropolymerization, Si—C bond cleavage, conductivity.

By using an electroactive species such as ferrocene (Fc), the electrochemical properties of bioorganic molecules were indirectly made accessible. 5 0 -Fc-NH-ssDNAs have a redox potential of 430–440 mV (vs. AgjAgCl) in a borate buffer (pH 9), which is characteristic of ferrocene/ferrocenium (Fc/Fc þ ) substituted by an amide group. The diffusion coefficient of Fc–ssDNA conjugates in a buffer solution was found to be 10 � 7 cm 2 s � 1 .5 0 -Fc-NH-ssDNA-S-S-R (3) was adsorbed onto a gold microelectrode surface to form a self-assembled monolayer (SAM) via a disulfide linker with a high packing density. The Fc-electrophore allows the characterization of the SAM by cyclic voltammetry (CV). The rate constant of electron transfer through DNA was estimated to be 12 s � 1 .

The syntheses of new ferrocene-monosaccharide compounds, 5-ferrocene-glucosamide (4), 5-ferrocene-glucosamido-2′-phosphate (5), and 5′-ferrocene-amido-5′-deoxyadenosine (6), are reported starting from ferrocenoyl hydroxybenzotriazole ester and the corresponding amino sugars. All compounds are investigated spectroscopically. In addition, their redox properties are investigated by cyclic voltammetry in aqueous solution. These compounds show a reversible one-electron oxidation. This redox potential in the case of 4 exhibits a significant pH dependence.

It is becoming increasingly apparent that the nucleus harbors metabolic enzymes that affect genetic transforming events. Here, we describe a nuclear isoform of lactate dehydrogenase (nLDH) and its ability to orchestrate histone deacetylation by controlling the availability of nicotinamide adenine dinucleotide (NAD(+)), a key ingredient of the sirtuin-1 (SIRT1) deacetylase system. There was an increase in the expression of nLDH concomitant with the presence of hydrogen peroxide (H2O2) in the culture medium. Under oxidative stress, the NAD(+) generated by nLDH resulted in the enhanced deacetylation of histones compared to the control hepatocytes despite no discernable change in the levels of SIRT1. There appeared to be an intimate association between nLDH and SIRT1 as these two enzymes co-immunoprecipitated. The ability of nLDH to regulate epigenetic modifications by manipulating NAD(+) reveals an intricate link between metabolism and the processing of genetic information.

The synthesis of a series of nucleobase functionalized thiophene monomers has been accomplished through the reaction of 2-bromo-1-thiophen-3-yl-ethanone with the corresponding DNA base anion. The distinctive pKa values for the various amine groups in the nucleobases provided a pathway for the creation of specific anions through selective deprotonation of these groups. Using the appropriate anion it is possible to create an amine linkage between the thiophene and nucleobase that is, analogous to that found between the deoxyribose sugar and nucleobase, in the biologically occurring nucleoside.

The electrochemical oxidation of several α,α′-di- tert -butyl pyrroles and thiophenes has been investigated in acetonitrile. Reversible cyclic voltammograms for the oxidation of one-ring α,α′-di- tert -butyl thiophenes or pyrroles were obtained at low scan rates (0.05–5 V s −1 ), indicating a large stability of their cation-radicals. Chemical evolutions without polymerization of the cation-radical were observed at longer time scales. The formal potentials E o and electron exchange standard rate constants k s were determined and compared with preceding reports for the unsubstituted analogues. From the substituent variations, the E o values for the oxidation of the unsubstituted thiophene and bithiophene were estimated as + 1.97 and + 1.49 V(SCE) respectively.

Arylpyrroles and -indoles are electrosynthesized via a S RN 1 type reaction. With pyrrolyl anion, the reaction leads mainly to α-substitution, but β-substitution and disubstitution are also observed. With indolyl anion, the main product corresponds to β-substitution. In both cases, the yield of the main product is higher than 50%

The reactivity of different aryl radicals towards anions of pyrroles is examined under S RN 1 conditions. The coupling rate constants are determined by cyclic voltammetry. The corresponding electrolyses are performed using a redox mediator.

The first imine-bridged pyridyltetrathiafulvalene building block (TTF-CH=N-Py, 1) has been synthesized via the Schiff base condensation of formyltetrathiafulvalene and 2-aminopyridine. The preparation, X-ray crystal structure, electrochemical and magnetic characterization of a 1:1 copper complex [CuII(hfac)2(TTF-CH=N-Py)] (2) are reported. The crystal structure reveals that the imine N atom participates in chelation to the paramagnetic center, thus making this ligand an attractive precursor for the assembly of pi-d systems.

Important aspects of the electrochemical reduction of a series of substituted arene sulfenyl chlorides are investigated. A striking change is observed in the reductive cleavage mechanism as a function of the substituent on the aryl ring of the arene sulfenyl chloride. With p-substituted phenyl chlorides a "sticky" dissociative ET mechanism takes place where a concerted ET mechanism leads to the formation of a radical/anion cluster before decomposition. With o-nitropheyl sulfenyl substituted chlorides a stepwise mechanism is observed where through space S...O interactions play an important role stabilizing both the neutral molecules and their reduced forms. Disulfides are generated through a nucleophilic reaction of the two-electron reduction produced anion (arenethiolate) on the parent molecule. The dissociative electron transfer theory, as well as its extension to the case of strong in-cage interactions between the produced fragments, along with the gas phase chemical quantum calculations results helped rationalize both the observed change in the ET mechanism and the occurrence of the "sticky dissociative" ET mechanism. The radical/anion pair interactions have been determined both in solution as well as in gas phase. This study shows that despite the low magnitude of in-cage interactions in acetonitrile as compared to in the gas phase, their existence strongly affects the kinetics of the involved reactions. It also shows that, as expected, these interactions are reinforced by the existence of strong electron-withdrawing substituents.

By using direct and indirect electrochemical methods, rate constants (ko) for cyclopropane ring opening of radical anions derived from the one-electron reduction of trans-1-benzoyl-2-phenylcyclopropane, trans-1-benzoyl-2-vinylcyclopropane, 2-methylenecyclopropyl phenyl ketone, spiro[anthracene-9,1'-cyclopropan-10-one], 3-cyclopropylcyclohex-2-en-1-one, and 3-(1-methylcyclopropyl)cyclohex-2-en-1-one were determined. Qualitatively, rate constants for ring opening of these (and other cyclopropyl- and cyclobutyl-containing radical anions) can be rationalized on the basis of the thermodynamic stability of the radical anion, the ability of substituents on the cyclopropyl group to stabilize the radical portion of the distonic radical anion, and the stability of the enolate portion of the distonic radical anion. On the basis of this notion, a thermochemical cycle for estimating deltaG(o) for ring opening was presented. For simple cyclopropyl-containing ketyl anions, a reasonable correlation between log(ko) and deltaG(o) was found, and stepwise dissociative electron transfer theory was applied to rationalize the results. Activation energies calculated with density functional theory (UB3LYP/6-31+G*) correlate reasonably well with measured log(ko). The derived log(ko) and deltaG(o) and log(ko) vs E(a) plots provide the basis for a "calibration curve" to predict rate constants for ring opening of radical anions derived from carbonyl compounds, in general.

[reaction: see text] Following a protocol developed by Mathivanan, Johnston, and Wayner (J. Phys. Chem. 1995, 99, 8190-8195), the radical anions of several cyclopropyl- and oxiranyl-containing carbonyl compounds were generated in an effort to measure the rate constants for their ring opening (k(o)) by laser flash photolysis. The results of these experiments are compared to those obtained from earlier electrochemical studies, and the combined data set is used to rationalize the kinetics of radical anion ring opening in a general context by using Saveant's theory pertaining to stepwise dissociative electron transfer (Acc. Chem. Res. 1993, 26, 455-461). Compared to cyclopropylcarbinyl --homoallyl rearrangements of neutral free radicals, at comparable driving force, the radical anion ring openings are slightly slower. The small difference in rate is attributed to the contribution of an additional, approximately 2 kcal/mol, solvent reorganization component for the radical anion rearrangements. The solvent reorganization energy for ring opening of these radical anions is believed to be small because the negative charge does not move appreciably in the progression reactant --transition state --product.

New (pyrrolyl)-pyridinium and quinolinium salts have been prepared selectively in high yields by reacting (pyrrolyl)-pyridine or -quinoline and their derivatives with CF 3 SO 3 CH 3 in CH 2 Cl 2 . No methylation of the nitrogen of pyrrole was observed. Preliminary investigations revealed that these salts show a good response as nonlinear optics.

Arylpyrroles and -indoles are electrosynthesized via a S RN 1 type reaction. With pyrrolyl anion, the reaction leads mainly to α-substitution, but β-substitution and disubstitution are also observed. With indolyl anion, the main product corresponds to β-substitution. In both cases, the yield of the main product is higher than 50%

Electron transfer (ET) through two configurations of double-stranded (ds)-DNA was investigated by the attachment of a ferrocenoyl (Fc)-labeled and thiol-labeled DNA to Au electrodes. The first configuration positions the Fc moiety on the same strand as the thiolate, whereas the second configuration positions the Fc group on the complementary strand. The subtle difference in structure leads to a difference in E0' values (29 mV) and in ET rate constants (25 vs 115 s-1). The results have led to a further understanding of electron transfer in ds-DNA, and several models of ET are proposed.

Efficient immobilization methods of amino acids and organic molecules on conducting surfaces were achieved using stable conducting materials such as OBT-functionalized polyterthiophene that allows readily the incorporation of specific motifs on conducting and semi-conducting surfaces. The synthesis of the electropolymerizable monomer has been performed through the protection of the carboxylic acid, followed by a Stille cross coupling reaction, deprotection of the acid and esterification using HOBT (hydroxybenzotriazole) and EDC. The corresponding polymer of 5 (poly(5)–Pt) exhibits excellent stability on a platinum electrode as shown by cyclic voltammetry, which allows the introduction of several amino acids and organic molecules on the surface of the functionalized polymer. The modified surface (poly(6)–Pt) has been characterized by ATR-Infrared showing a carbonyl stretch corresponding to an amide of the amino acids.

not Available.

not Available.

not Available.

4-Nitrophenyl sulfenyl chloride was used as a new precursor for the formation of densely packed aromatic SAMs on gold. The adsorption involves the reductive dissociation of the S-Cl bond. A well-ordered row structure corresponding to a √3 × 4 phase with a molecular area of 27.8 Å(2) is obtained.

not Available.

The synthetic strategy for the preparation of a TTF donor, π-appended with a spin bearing verdazyl radical has been developed. UV-Vis, electrochemical and EPR studies reveal that this is an attractive magnetic building block for subsequent oxidation that could afford new conducting and/or magnetic systems.

Triphenylamines with one, two, or three 3,4-ethylenedioxythiophene (EDOT) substituents attached to the para-phenyl carbons have been prepared via metal-catalyzed cross-coupling reactions. The amines with two or three EDOTs (compounds 4 and 3, respectively) can be oxidatively electropolymerized (via intermolecular coupling between two EDOT groups at their respective α-carbon atoms) to afford stable, linear and cross-linked polymers, respectively. The linear polymer (poly-4) exhibits two resolved, reversible oxidation waves corresponding to the oxidation of the amine and EDOT centers. These two oxidation processes occur at the same potential in cross-linked poly-3 giving rise to one broad, reversible oxidation wave. The observation of redox processes associated with the EDOT-based chromophores contrasts the properties of related (non-EDOT-containing) polymers for which the thiophene backbone serves only as a conjugated ‘linker’. These polymers are highly stable to electrochemical oxidation and can be electrochemically cycled hundreds of times with no detectable decomposition; color changes accompany the redox processes, interconverting between reduced (yellow) and oxidized (green–blue) forms.

not Available.