Voltammetric determination of water with inner potential reference and variable linear range based on structure- and redox-controllable hydrogen-bonding interaction between water and quinones

This communication describes a new voltammetric method for the determination of water in nonaqueous solvent by taking advantage of the structure- and redox-controllable hydrogen-bonding interaction between quinone species and water. Three kinds of quinones, i.e., tetrachloro-p-benzoquinone (TCBQ), benzoquinone (BQ), and tetramethyl-p-benzoquinone (TMBQ), are employed in this study in terms of their different structures and thereby different basicities and hydrogen-bonding interaction activities with water. The hydrogen-bonding interaction activities of the quinone species with water actually depend on the structures and the species of quinones, where the interaction activity between quinone dianion and water remains remarkably greater than that between quinone monoanion and water. The former interaction activity eventually leads to the positive shift of the half-wave potential of quinone monoanion/dianion couple, which can be essentially used for the voltammetric determination of water. The structure- and redox-controllable hydrogen-bonding interaction activities of quinones and water substantially make it possible to determine trace amount of water in the nonaqueous solution with inner reference potential and variable dynamic linear range.     

Site-specific binding of quinones to proteins through thiol addition and addition-elimination reactions

Ubiquinone-0, menaquinone-0, and 2,3,5-trimethyl-1,4-benzoquinone were site-specifically bound to free cysteine of proteins (yeast iso-1 cytochrome c as a model protein) through thioether bond formation. Model thioether quinone conjugates showed unexpected reactivity to cysteine of proteins as their parent quinones by thiol addition-elimination reaction. Cyclic voltammetry studies of the model compounds showed only minor differences in their redox potentials as compared to their parent quinones. Thioether ligation provides a general, simple, and fast method to construct model quinone protein systems. In addition, these studies also contribute to the understanding of biological activities, toxicity, and anti-cancer mechanism of quinones and thioether quinone adducts.     

Anomalous behavior in the two-step reduction of quinones in acetonitrile

The electrochemical reduction of eight quinones, 9,10-anthraquinone (1), duroquinone (2), 2,6-di-tert-butyl-1,4-benzoquinone (3), 2,6-dimethoxy-1,4-benzoquinone (4), 9,10-phenanthrenequinone (5), tetrachloro-1,2-benzoquinone (6), tetrabromo-1,2-benzoquinone (7) and 3,5-di-tert-butyl-1,2-benzoquinone (8), have been studied in acetonitrile. In every case it was found that cyclic voltammograms differed in significant ways from those expected for simple stepwise reduction of the quinone to its radical anion and dianion. The various types of deviations for the eight quinones have been cataloged and some speculation is offered concerning their origins.     

Chemiluminescence assay for quinones based on generation of reactive oxygen species through the redox cycle of quinone

A sensitive and selective chemiluminescence assay for the determination of quinones was developed. The method was based on generation of reactive oxygen species through the redox reaction between quinone and dithiothreitol as reductant, and then the generated reactive oxygen was detected by luminol chemiluminescence. The chemiluminescence was intense, long-lived, and proportional to quinone concentration. It is concluded that superoxide anion was involved in the proposed chemiluminescence reaction because the chemiluminescence intensity was decreased only in the presence of superoxide dismutase. Among the tested quinones, the chemiluminescence was observed from 9,10-phenanthrenequinone, 1,2-naphthoquinone, and 1,4-naphthoquinone, whereas it was not observed from 9,10-anthraquinone and 1,4-benzoquinone. The chemiluminescence property was greatly different according to the structure of quinones. The chemiluminescence was also observed for biologically important quinones such as ubiquinone. Therefore, a simple and rapid assay for ubiquinone in pharmaceutical preparation was developed based on the proposed chemiluminescence reaction. The detection limit (blank + 3SD) of ubiquinone was 0.05 μM (9 ng/assay) with an analysis time of 30 s per sample. The developed assay allowed the direct determination of ubiquinone in pharmaceutical preparation without any purification procedure. Figure Chemiluminescence generated through the redox cycle of quinone     

Preparation and electrochemical properties of palladium(0) complexes coordinated by quinones and 1,5-cyclooctadiene

The complexes Pd(quinone)(COD) (COD = 1,5-cyclooctadiene) are prepared by a ligand substitution reaction of Pd₂(DBA)₃ (DBA = dibenzylideneacetone) in the presence of both quinone and COD. Palladium(0) complexes coordinated by quinones only are formed in the reaction in the absence of COD. The cyclic voltammetric behavior of Pd(quinone)(COD) has been studied. The reduction potentials for quinones shifted toward negative values on coordination to palladium(0). The oxidation potentials for the central palladium(0) in Pd(quinone)(COD) depend on the electron-withdrawing ability of the free quinones, and are in the following series: quinone = p-benzoquinone < 5,8-dihydro-1,4-naphthoquinone ～ 1,4-naphthoquinone < duroquinone. The shift of oxidation potentials for Pd(quinone)(COD) on changing the quinones as ligands is in contrast to that of Pd(quinone)(triphenylphosphine)₂.     

Iptycene quinones: synthesis and structure

A practical and efficient method to synthesize iptycene quinones has been developed. As a result, a series of pentiptycene quinones 8-16 were conveniently synthesized by one-pot reaction of triptycene quinone 4 or 5 with anthracene 1 or its derivatives 2-3 in refluxing acetic acid in the presence of p-chloranil, followed by CAN oxidative demethylation. Similarly, a series of heptiptycene quinones 17-23 with U-shaped cavities were achieved with pentiptycene quinone 10 and triptycene diquinone 6 as precursors. Non-iptycene triquinones 24 with one tweezer-shaped cavity and 25 with two U-shaped cavities were synthesized by one-pot reactions of anthracene with pentiptycene triquinones 16a and 16b, respectively. Non-iptycene triquinone 26 with a dendritic structure was conveniently obtained by the reaction of anthracene with either pentiptycene diquinone 12 or triptycene triquinone 7. The structures of regioisomers 16a and 16b were determined by the single-crystal structure analysis of 16b. The structures of other regioisomers, including heptiptycene tetraquinones 19a/19b/19c and heptiptycene triquinones 23a/23b, were identified by comparative reactions.     

Synthesis of new type benzo[b]thiophene fused quinones and their tetracyanoquinodimethane derivatives

A series of new type of benzo[b]thiophene-fused 1,4-benzoquinones and their tetracyanoquinodimethane derivatives were synthesized. The cyclic voltammetric data of new type quinones and tetracyanoquinodimethane derivatives displayed different behavior. All new quinones exhibit two reduction waves corresponding to the radical anion and dianion. On the other hand, most tetracyanoquinodimethane derivatives display a singlewave reduction to the dianion. The benzo[b]thiophene moiety fused tetracyanoquinodimethane derivatives reveal more negative reduction potentials than that of tetracyanoquinodimethane.     

Design of synthetic molecular units including quinones towards the construction of artificial photosynthesis

Quinones are essential components in many biological systems, notably in photosynthesis. This is largely due to the characteristic proton-coupled redox chemistry of quinones. This review article overviews the use of quinones in studies on artificial photosynthesis, as one-electron electron acceptors, reversible proton/electron carriers, and replacements for sacrificial oxidant and reductants in photosynthetic chemical conversion. Topics included are the early attempts on intramolecular photoinduced electron transfer involving quinones, subsequent reactions after photoinduced electron transfer between pigments and quinones, photochemistry in molecular assemblies containing quinones, and photochemical quinone/hydroquinone interconversion.     

Spectral detection of terminal ring quinones

Terminal ring quinones can be detected specifically by a simple spectroscopie method involving reaction of the quinone with quinaldinium or lepidinium salts in alkaline solution. Other types of quinones and carbonyl derivatives have given negative results. 3-Ethylrhodanine can also be used as a reagent, especially for terminal ring p-quinones. All of these colorimetric procedures are amenable to quantitation.     

Spectrophotometric kinetic and determination of quinones and barbiturates.

The kinetics of 1,3-dimethylbarbituric acid with some quinones, namely 1,4-benzoquinone, 1,4-naphthoquinone and p-chloranil in 50% methyl alcohol-water mixture have been investigated spectrophotometrically at 30-50 degrees C. The reaction follows overall second-order kinetics, first order each in reactant. From the dependence of the rate constants on temperature, activation parameters have been calculated. A plot of deltaH# versus deltaS# for the reaction gave a good straight line with an isokinetic temperature of 387.66 K. The rate of reaction increases with increasing dielectric constant of the medium. Based on this reaction, a spectrophotometric determination method of quinones is described. Beer's law was obeyed within the concentration range 2.7-61.5 microg ml(-1) quinone. The method was applied for determination of barbituric, thiobarbituric and 1,3-dimethylbarbituric acids with 1,4-naphthoquinone within a concentration range of 3.2-39.5 microg ml(-1) barbiturate. The reaction mechanism and reactivity have been discussed.     

Overview of the Synthesis and Structure of Calix[n]quinones (n=4, 6, 8)

Calix[n]quinones, a class of cyclic oligomers composed of p‐benzoquinone structures connected by methylene, have multi‐conjugated carbonyl structures and adjustable cavities, which make their synthesis extremely attractive. In this minireview, synthetic methods of calix[n]quinones and recent synthetic experience of our group are summarized. The merits and demerits of various synthetic methods are briefly reviewed as well. When synthesizing calix[n]quinone (n≥6) with a larger ring, the reduction‐oxidation method is considered to be the most recommended.     

Practical C-H functionalization of quinones with boronic acids

A direct functionalization of a variety of quinones with several boronic acids has been developed. This scalable reaction proceeds readily at room temperature in an open flask using inexpensive reagents: catalytic silver(I) nitrate in the presence of a persulfate co-oxidant. The scope with respect to quinones is broad, with a variety of alkyl- and arylboronic acids undergoing efficient cross-coupling. The mechanism is presumed to proceed through a nucleophilic radical addition to the quinone with in situ reoxidation of the resulting dihydroquinone. This method has been applied to complex substrates, including a steroid derivative and a farnesyl natural product.     

Voltammetric Behavior of 1,4‐Dimethoxypillar[m]arene[n]quinones

The electrochemical properties of a series of 1,4‐dimethoxypillar[m]arene[n]quinones (DMP[m]A[n]Qs) and the interactions between individual quinone units have been investigated on glassy carbon electrode in acetonitrile. All the quinone units showed relative electron uptake behavior except 1,4‐dimethoxypillar[5]quinones (DMP[5]Q). The results have shown that the electrochemical behavior of the DMP[m]A[n]Qs is comparatively different from that of their related linear quinone analogues. The resultant properties were attributed to the close proximity of redox‐active sites as well as the delocalization of electrons on the aromatic rings. Another aspect to be considered responsible for their electronic properties was suggested to be the electrostatic repulsions between adjacent quinone units in these complex structures. Current studies provide a better understanding on the voltammetric behavior of pillararene derivatives with different numbers of quinone units as well as their future scope in certain future electrochemical applications.     

Photoreactions of p-quinones with dimethyl sulfide and dimethyl sulfoxide in aqueous acetonitrile. goerner@mpi-muelheim.mpg.de

The effects of dimethyl sulfide (DMS) and dimethyl sulfoxide (DMSO) on the photoreactions of 1,4-benzoquinone (BQ), 1,4-naphthoquinone (NQ), 9,10-anthraquinone (AQ) and several derivatives in acetonitrile/water were studied. The observed triplet state of the quinones is quenched and the rate constant is close to the diffusion-controlled limit for reactions of most quinones with DMS and lower with DMSO. Semiquinone radical anions (Q*-) produced by electron transfer from sulfur to the triplet quinone were detected. For both DMS and DMSO the yield of Q*- is similar, being generally low for BQ and NQ, substantial for AQ and largest for chloranil. The specific quencher concentrations and the effects of quinone structure and redox potentials on the time-resolved photochemical properties are discussed.     

Investigation of quinones

Naphtho[2,3-f]quinoxaline-7,12-diones add a molecule of benzenesulfinic acid to give 5-phenylsulfonyl-7, 12-dihydroxynaphtho[2,3-f]quinoxalines. The latter are oxidized to 5-phenylsulfonyl-substituted quinones, which add a molecule of benzenesulfinic acid to the oxygen atoms of the quinone grouping to give the O⁷-benzenesulfonate of 5-phenylsulfonyl-7, 12-dihydroxynaphtho[2,3-f]quinoxaline. The protonated form of naphtho[2,3-f]quinoxa-line-7, 12-dione, which is stabilized by an intramolecular hydrogen bond, as confirmed by the anomalously high basicity of angular naphtho[2,3-f]quinoxaline-7,12-dione as compared with its linear isomer, which is inert in reactions with benzenesulfinic acid, undergoes reaction.     

THE CHLOROPHYLL-SENSITIZED REACTION BETWEEN BENZOQUINONE AND ETHANOL*

The electron-transfer reaction between triplet excited chlorophyll and quinones has been extensively studied as a model of the primary reaction in photosystem II. There has also been reported a minor reaction in which the chlorophyll cation radical ostensibly oxidizes the alcohol solvent or even water, leading to a gradual net reduction of quinone, but the exact mechanism and even the existence of this reaction has been uncertain. We have examined the consequences of prolonged irradation of ethyl chlorophyllide and benzoquinone in acidulated ethanol, and find a chlorophyllide-sensitized reaction which is not analogous to the better-known autosensitized reduction of quinones in blue or UV light. In the chlorophyllide-sensitized reaction, benzoquinone is apparently converted to ethoxy-substituted quinones and quinols, and polymeric material. Ethyl chlorophyllide (or chlorophyll) is simultaneously oxidized to more polar products which themselves continue to photosensitize the reaction of quinones. The production of acetaldehyde could not be demonstrated in the sensitized reaction. Chlorophyllide-sensitized reaction of (l-hydroxyethyl)benzoquinone, ethoxybenzoquinone and 2.5-diethoxybenzo-quinone were examined for additional information. A reaction sequence, tentatively proposed to accommodate the known facts, starts with oxidative attack by quinone on an oxidized chlorophyllide radical formed by loss of a hydroxyl proton from alcohol bound as a ligand to Mg²⁺. It is not likely that this reaction is closely related to events at the oxidizing side of photosystem II.     

New method for detection and spectrophotometric determination of quinones

The reaction between 3-phenylthiazolidine-2,4-dione (I) and p-benzoquinone (II), tetrachloro-p-benzoquinone (III), and 1,4-naphthoquinone (IV) in ammoniacal medium is applied for detection and spectrophotometric determination of quinones. The absorbance-concentration relationship is linear up to 18 μg/ml of quinone concentration. The lower limits of identification in the detection reaction are 2.5, 3.0, and 1 μg for (II), (III), and (IV), respectively, which reflect high sensitivity. The reaction between (I) and quinones is proved to be a condensation reaction and highly selective.     

Research on heterocyclic quinones

7-Hydroxy-1-isoquinolones, 3-methyl-7-hydroxyisoquinoline, and 6-hydroxyisoquinoline were synthesized, and their reactions, as well as the reaction of 7-methoxyisoquinoline-5,8-quinone, with amines were studied. The problem of the transmission of the mesomeric and inductive effects of the quinone carbonyl groups through the heteroring and the increase in the electrophilicities of the quinones upon chelate formation are discussed.Translated from Khimiya Geterotsiklicheskikh Soedinenii, No. 4, pp. 500–505, April, 1977.     

Progress towards metal-free radical alkylations of quinones under mild conditions

A new method for the radical alkylation of quinones is reported. Lewis basic nitrogen additives increase the efficacy of quinone alkylations from carboxylic acids using catalytic AgNO₃ and Selectfluor as a mild oxidant. Electrochemical data suggests that certain Lewis basic additives are capable of directly reducing Selectfluor through a single-electron transfer, presumably via a charge-transfer complex. This process yields intermediates capable of promoting oxidative decarboxylation of alkyl carboxylic acids without an added metal initiator. Using this strategy, we have demonstrated progress towards a metal-free C–H quinone alkylation reaction that proceeds at room temperature under mild conditions.