Reaction Of Quinones Research Articles

Design and Characterization of an Enzymatically Active Amphiphilic Maquette Protein

Many questions still exist about how quinone molecules act as substrates for membrane oxidoreductase enzymes, as well as how quinones can act as a catalyst in energy conversion mechanisms. We apply our knowledge of electron tunneling and protein design towards defining the basic engineering requirements for quinone reactivity in natural membranes and heme proteins. We have synthesized and characterized a transmembrane, amphiphilic maquette protein, AP6, which extracts the basic structural components from Complex III necessary to perform transmembrane proton-coupled electron transfer. We have shown that our AP6 peptide assembles as a four-helix bundle protein and can potentially bind up to six bis-histidine ligated hemes tightly across a membrane interface. Given its sequence and heme binding capabilities, our AP6 design could accomplish a variety of potential functions, including: transmembrane electron transfer, electron transfer with aqueous proteins, proton-coupled electron transfer, or combining these, quinol-cytochrome c oxidoreductase activity. Through standard Complex III activity assays, we have demonstrated that AP6 has quinol-cytochrome c oxidoreductase activity in detergent micelles that is within two orders of magnitude of the activity of natural Complex III purified from R. capsulatus. This activity can be generated with a variety of reduced quinone substrates, and is dependent on the concentration of cytochrome c present. With no obvious quinone-binding site included in our protein design, AP6 provides clear evidence that a specific quinone-binding site within a membrane protein is not essential for generating significant quinol-cytochrome c oxidoreductase enzymatic activity from a heme protein.

A Study of the Reaction Between Quinone and 2R4F Cigarette Smoke Condensate

Abstract A study using atomic emission detection (AED) as an approach to explore the fate of quinone added into 2R4F cigarette smoke condensate (CSC) have been performed. Both natural isotope quinone and 13C labeled quinone were used in the study. When coupled with a gas chromatographic separation (GC/AED), the AED provided informative new data on 13C isotope enriched products generated following reactions between 2R4F CSC and the quinone. Two 13C containing species were detected by GC/AED. Matching chromatographic separation using gas chromatography/mass selective detection (GC/MSD) allowed for a structural assignment of a relatively minor CSC 13C 6quinone reaction product as nitrohydroquinone (13C6NO2HQ). The chemical mechanism accounting for the formation of 13C6NO2HQ in the CSC was envisioned to be a reaction product between HONO and 13C 6Quinone (13C6Q) to form 13C6NO2Q, followed by reduction of 13C6NO2Q to 13C6NO2HQ. The amount of 13C6NO2HQ accounted for ~6% of the added 13C6Q. Identical trends in reaction chemistries were found for experiments with 12C6Q. The major reaction product detected upon addition of 13C6Q to the 2R4F CSC sample was 13C6HQ. 13C6HQ accounted for, on average, ~47% of the initial 13C6Q concentration. Identical trends in reaction chemistries were found for experiments with 12C6Q. No additional 13C containing species were detected. A 13C AED compound independent calibration (CIC) approach under the operating conditions was not possible. This work further expands the knowledge regarding possible reactions of quinone and hydroquinone in CSC.

Benzene and dopamine catechol quinones could initiate cancer or neurogenic disease

Catechol quinones of estrogens react with DNA by 1,4-Michael addition to form depurinating N3Ade and N7Gua adducts. Loss of these adducts from DNA creates apurinic sites that can generate mutations leading to cancer initiation. We compared the reactions of the catechol quinones of the leukemogenic benzene (CAT-Q) and N-acetyldopamine (NADA-Q) with 2′-deoxyguanosine (dG) or DNA. NADA was used to prevent intramolecular cyclization of dopamine quinone. Reaction of CAT-Q or NADA-Q with dG at pH 4 afforded CAT-4-N7dG or NADA-6-N7dG, which lost deoxyribose with a half-life of 3 h to form CAT-4-N7Gua or 4 h to form NADA-6-N7Gua. When CAT-Q or NADA-Q was reacted with DNA, N3Ade adducts were formed and lost from DNA instantaneously, whereas N7Gua adducts were lost over several hours. The maximum yield of adducts in the reaction of CAT-Q or NADA-Q with DNA at pH 4 to 7 was at pH 4. When tyrosinase-activated CAT or NADA was reacted with DNA at pH 5 to 8, adduct levels were much higher (10- to 15-fold), and the highest yield was at pH 5. Reaction of catechol quinones of natural and synthetic estrogens, benzene, naphthalene, and dopamine with DNA to form depurinating adducts is a common feature that may lead to initiation of cancer or neurodegenerative disease.

Complexities of cuticular pigmentation in insects

Complexities of cuticular pigmentation in insects

The “Corey's Reagent,” 3,5-di-tert-butyl-1,2-Benzoquinone, as a Modifying Agent in the Synthesis of Fluorescent and Double-Headed Nucleosides

A new method for the synthesis of fluorescent nucleosides has been developed. It has been shown that a reaction of benzoquinone with aminopropenyl group at C-5-position of 2′-deoxyuridine or 2′-deoxycytidine and aminopropynyl group at the C-7-position of 8-aza-7-deazaadenosine under extremely mild conditions affords conjugated benzoxazole derivatives of nucleosides, which possess strong fluorescent properties. In a similar reaction 5′-amino-5′-deoxy-nucleosides form double-headed nucleoside derivatives with benzoxazole attached at C-4′-position.

A Diels-Alder Reaction Between A Cigarette Mainstream Smoke Component and Benzoquinone

Abstract A notable amount of research has been placed toward understanding the roles of benzoquinone (Q) and hydroquinone (HQ) in the chemistry and toxicity of cigarette smoke. To further understanding of the roles of these compounds in cigarette smoke, a series of reactions were performed wherein the levels and chemistries of Q and HQ were monitored after having been added to selected phases of the mainstream smoke from 2R4F cigarettes. Through the application of both fundamental organic chemistry reaction mechanistic principles and qualitative analysis of smoke chemistry, a new reaction pathway for mainstream smoke components was elucidated. During the course of these investigations, the presence of a product from a Diels-Alder reaction between a 2R4F cigarette mainstream smoke component and Q was discovered. Data from carbon-13 nuclear magnetic resonance (13C NMR), gas chromatography-atomic emission detection (GC-AED), and gas chromatography-mass selective detection (GC-MSD) revealed a Diels-Alder reaction product resulting from the reaction of benzoquinone (Q), a dienophile, and 1,3-cyclopentadiene, a diene, to yield tricyclo[6.2.1.02,7] undeca-4,9-diene-3,6-dione, more commonly referred to as cyclopentadienebenzoquinone. The reaction between Q and 1,3-cyclopentadiene was observed to have occurred when fresh mainstream vapor phase smoke (MSVP) from a 2R4F cigarette, captured in acetone, was subsequently treated with Q. Other 13C containing species were detected but inadequate signal to noise values prevented structural assignments. Accompanying the Diels-Alder reaction was an additional reaction of Q to form hydroquinone (HQ). These reactions provide additional information on the complexity of cigarette smoke, particularly as it relates to possible reactions involving Q and HQ and other cigarette smoke components.

Modification of quinone electrochemistry by the proteins in the biological electron transfer chains: examples from photosynthetic reaction centers.

Quinones such as ubiquinone are the lipid soluble electron and proton carriers in the membranes of mitochondria, chloroplasts and oxygenic bacteria. Quinones undergo controlled redox reactions bound to specific sites in integral membrane proteins such as the cytochrome bc(1) oxidoreductase. The quinone reactions in bacterial photosynthesis are amongst the best characterized, presenting a model to understand how proteins modulate cofactor chemistry. The free energy of ubiquinone redox reactions in aqueous solution and in the Q(A) and Q(B) sites of the bacterial photosynthetic reaction centers (RCs) are compared. In the primary Q(A) site ubiquinone is reduced only to the anionic semiquinone (Q(*-)) while in the secondary Q(B) site the product is the doubly reduced, doubly protonated quinol (QH(2)). The ways in which the protein modifies the relative energy of each reduced and protonated intermediate are described. For example, the protein stabilizes Q(*-) while destabilizing Q(=) relative to aqueous solution through electrostatic interactions. In addition, kinetic and thermodynamic mechanisms for stabilizing the intermediate semiquinones are compared. Evidence for the protein sequestering anionic compounds by slowing both on and off rates as well as by binding the anion more tightly is reviewed.

A facile synthesis of asterriquinone D

Abstractmagnified imageAsterriquinone D was easily synthesized in three steps from 2,5‐dichloro‐1,4‐benzoquinone. The reaction of benzoquinone with indole in the presence of Pd(OAc)2, followed by oxidation with cerium (IV) ammonium nitrate (CAN) produced 3,6‐dichloro‐2,5‐bis (3‐indolyl)‐1,4‐benzoquinone. The methoxylation of the dichloride with NaOH in CH3OH afforded asterriquinone D.

Cotton benzoquinone reductase: Up-regulation during early fiber development and heterologous expression and characterization in Pichia pastoris

Benzoquinone reductase (BR; EC 1.6.5.7) is an enzyme which catalyzes the bivalent redox reactions of quinones without the production of free radical intermediates. Using 2D-PAGE comparisons, two proteins were found to be up-regulated in wild-type cotton ovules during the fiber initiation stage but not in the fiberless line SL 1-7-1. These proteins were excised from the gel, partially sequenced and identified to be BR isoforms. PCR was used to amplify both full length coding regions of 609bp and once cloned, the restriction enzyme HindIII was used to distinguish the clones encoding the BR1 (one site) and BR2 (two sites) isoforms. Both deduced protein sequences had 203 residues which differed at 14 residues. The molecular mass and pIs were similar between the measured protein (2D-PAGE) and the theoretical protein (deduced). Heterologous proteins BR1 and BR2 were produced for further study by ligating the BR1 and BR2 clones in frame into the alpha-factor secretion sequence in pPICZalphaA vector and expressed with Pichia pastoris. Both BR1 and BR2 were approximately 26.5kDa and did enzymatically reduce 2,6-dimethoxybenzoquinone similar to the fungal BR.

Flash-Induced FTIR Difference Spectroscopy Shows No Evidence for the Structural Coupling of Bicarbonate to the Oxygen-Evolving Mn Cluster in Photosystem II

Bicarbonate is known to be required for the maximum activity of photosystem II. Although it is well established that bicarbonate is bound to the nonheme iron to regulate the quinone reactions, the effect of bicarbonate on oxygen evolution is still controversial, and its binding site and exact physiological roles remain to be clarified. In this study, the structural coupling of bicarbonate to the oxygen-evolving center (OEC) was studied using Fourier transform infrared (FTIR) difference spectroscopy. Flash-induced FTIR difference spectra during the S-state cycle of OEC were recorded using the PSII core complexes from Thermosynechococcus elongatus in the presence of either unlabeled bicarbonate or (13)C-bicarbonate. The H (12)CO 3 (-)-minus-H (13)CO 3 (-) double difference spectra showed prominent bicarbonate bands at the first flash, whereas no appreciable bands were detected at the second to fourth flashes. The bicarbonate bands at the first flash were virtually identical to those from the nonheme iron, which was preoxidized by ferricyanide and photoreduced by a single flash, recorded using Mn-depleted PSII complexes. Using the bicarbonate bands of the nonheme iron as an internal standard, it was concluded that no bicarbonate band arising from OEC exists in the S-state FTIR spectra. This conclusion indicates that bicarbonate is not affected by the structural changes in OEC upon the four S-state transitions. It is thus strongly suggested that bicarbonate is neither a ligand to the Mn cluster nor a cofactor closely coupled to OEC, although the possibility cannot be fully excluded that nonexchangeable bicarbonate exists in OEC as a constituent of the Mn-cluster core. The data also provide strong evidence that bicarbonate does not function as a substrate or a catalytic intermediate. Bicarbonate may play major roles in the photoassembly process of the Mn cluster and in the stabilization of OEC by a rather indirect interaction.

Synergism between Hydrogen Bond-type Ultraviolet Absorbers and Hindered Amine Light Stabilizers

The synergism of hydrogen bond-type ultraviolet absorbers (UVA), such as phenyl salicylate and benzotriazole type UVA, and hindered amine light stabilizers (HALS) was investigated and compared with that of benzophenone type UVA. Phenyl salicylate and benzotriazole type UVA showed a similar synergistic and antagonistic interactions with HALS to those for benzophenone type UVA, but the synergism exceeded the antagonism. The order of their synergism of preventing photooxidation was benzotriazole > phenyl salicylate > benzophenone for UVA. The order and the degree of the synergism agreed completely with those of the regeneration of new UVA by the reaction of UVA quinones, accidentally formed by scavenging peroxy radicals, with HALS. Therefore, such generation is concluded as the essence of synergism of UVA with HALS.

Voltammetry of Quinones in Unbuffered Aqueous Solution: Reassessing the Roles of Proton Transfer and Hydrogen Bonding in the Aqueous Electrochemistry of Quinones

Cyclic voltammetry studies are reported for two representative quinones, benzoquinone and 2-anthraquinonesulfonate, in buffered and unbuffered aqueous solution at different pH's. While the redox reaction of quinones in buffered water is well described as an overall 2 e-, 2 H+ reduction to make the hydroquinone, a much better description of the overall reaction in unbuffered water is as a 2 e- reduction to make the strongly hydrogen-bonded quinone dianion, which will exist in water as an equilibrium mixture of protonation states. This description helps to unify quinone electrochemistry by bridging the apparent gap between the redox chemistry of quinones in water and that in aprotic organic solvents, where quinones undergo two sequential 1 e- reductions to form the quinone dianion.

Influence of the Protein Environment on the Redox Potentials of Flavodoxins from Clostridium beijerinckii

The flavin mononucleotide (FMN) quinones in flavodoxin have two characteristic redox potentials, namely, Em(FMNH./FMNH-) for the one-electron reduction of the protonated FMN (E1) and Em(FMN/FMNH.) for the proton-coupled one-electron reduction (E2). These redox potentials in native and mutant flavodoxins obtained from Clostridium beijerinckii were calculated by considering the protonation states of all titratable sites as well as the energy contributed at the pKa value of FMN during protonation at the N5 nitrogen (pKa(N5)). E1 is sensitive to the subtle differences in the protein environments in the proximity of FMN. The protein dielectric volume that prevents the solvation of charged FMN quinones is responsible for the downshift of 130-160 mV of the E1 values with respect to that in an aqueous solution. The influence of the negatively charged 5'-phosphate group of FMN quinone on E1 could result in a maximum shift of 90 mV. A dramatic difference of 130 mV in the calculated E2 values of FMN quinone of the native and G57T mutant flavodoxins is due to the difference in the pKa(N5) values. This is due to the difference in the influence exerted by the carbonyl group of the protein backbone at residue 57.

Two-electron reduction of quinones by Enterobacter cloacae PB2 pentaerythritol tetranitrate reductase: quantitative structure-activity relationships.

In order to clarify the poorly understood mechanisms of two-electron reduction of quinones by flavoenzymes, we examined the quinone reductase reactions of a member of a structurally distinct old yellow enzyme family, Enterobacter cloacae PB2 pentaerythritol tetranitrate reductase (PETNR). PETNR catalyzes two-electron reduction of quinones according to a 'ping-pong' scheme. A multiparameter analysis shows that the reactivity of quinones increases with an increase in their single-electron reduction potential and pK(a) of their semiquinones (a three-step (e(-),H(+),e(-)) hydride transfer scheme), or with an increase in their hydride-transfer potential (E(7)(H(-))) (a single-step (H(-)) hydride transfer scheme), and decreases with a decrease in their van der Waals volume. However, the pH-dependence of PETNR reactivity is more consistent with a single-step hydride transfer. A comparison of X-ray data of PETNR, mammalian NAD(P)H : quinone oxidoreductase (NQO1), and Enterobacter cloacae nitroreductase, which reduce quinones in a two-electron way, and their reactivity revealed that PETNR is much less reactive, and much less sensitive to the quinone substrate steric effects than NQO1. This may be attributed to the lack of pi-pi stacking between quinone and the displaced aromatic amino acid in the active center, e.g., with Phe-178' in NQO1.

Kinetic and Structural Analysis of the Early Oxidation Products of Dopamine

Oxidative stress appears to be directly involved in the pathogenesis of several neurodegenerative disorders, including Alzheimer and Parkinson diseases. Nigral dopaminergic neurons are particularly exposed to oxidative stress because a pathological accumulation of cytosolic dopamine gives rise to various toxic molecules, including free radicals and reactive quinones. These latter species can react with proteins preventing them from exerting their physiological functions. Among the possible targets of quinones, alpha-synuclein is of primary interest because of its direct involvement in dopamine metabolism. Contrary to the neurotoxic processes, neuromelanin synthesis seems to play a protective role by its ability to sequester a variety of potentially damaging substances. In this study, we carried out a kinetic and structural analysis of the early oxidation products of dopamine. Specifically, considering the potential high toxicity of aminochrome for both cells and mitochondria, we focused our attention on its rearrangement to 5,6-dihydroxyindole. After the spectroscopic characterization of the products derived from the oxidation of dopamine, the structural information obtained was used to analyze the reactivity of quinones toward alpha-synuclein. Our results suggest that indole-5,6-quinone, rather than dopamine-o-quinone or aminochrome, is the reactive species. We propose that the observed reactivity could represent a general reaction pathway whenever cysteinyl residues are absent in proteins or if they are sterically protected.

Laccase-generated quinones in naphthoquinone synthesis via Diels–Alder reaction

The tandem synthesis of naphthoquinones was conducted from the reaction of laccase-generated quinones and acyclic dienes via Diels–Alder reaction. This reaction was carried out under mild condition in aqueous medium and yielded naphthoquinones up to 80%. In addition, the effect of solvent was also investigated and water was shown to be optimal for this reaction.

Reactivity of quinones for the dehydrogenation of poly(1,3‐cyclohexadiene)

AbstractThe reactivity of three types of quinones (3,4,5,6‐tetrachloro‐1,2‐(o‐)‐benzoquinone (TOQ), 2,3‐dichloro‐5,6‐dicyano‐1,4‐benzoquinone (DDQ), and 2,3,5,6,‐tetrachloro‐1,4‐(p‐)‐benzoquinone (TCQ)) was examined for the dehydrogenation of poly(1,3‐cycohexadiene) (PCHD) composed of 1,2‐cyclohexadiene and 1,4‐cyclohexadiene units. The order of reactivity was TOQ > DDQ > TCQ. The steric hindrance of CO groups in the quinones appeared to be an important factor in determining their reactivity. DDQ was found to be an appropriate dehydrogenation reagent for PCHD. The reactivity of TCQ was considerably low for PCHD containing 1,2‐cyclohexadiene units. The reactivity of TOQ was too high and side reactions occurred, causing the formation of structural defects. Copyright © 2007 Society of Chemical Industry

Reactivity of quinones as alkyl radical acceptors

The enthalpies of the addition of 11 alkyl radicals to ortho-and para-benzoquinones and substituted para-benzoquinones and the enthalpies of formation of various alkoxyphenoxyl radicals have been calculated. Experimental data for the addition of alkyl radicals to quinones are analyzed in terms of the intersection of two parabolic potential curves, and parameters characterizing this class of reactions are calculated. The classical potential barrier of the thermally neutral reaction of alkyl radical addition to benzoquinone is E e,0 = 82.1 kJ/mol. This class of reactions is compared to other classes of free-radical addition reactions. The interaction between the electrons of the reaction center and the π electrons of the aromatic ring is a significant factor in the activation energy. Activation energies, rate constants, and the geometric parameters of the transition state have been calculated for 40 reactions of alkyl radical addition to quinones. Strong polar interaction has been revealed in the addition of polar macroradicals to quinones, and its contribution to the activation energy has been estimated. Kinetic parameters, activation energies, and rate constants have been calculated for the reverse reactions of alkoxyphenoxyl radical decomposition to quinone and alkyl. The competition between chain termination and propagation reactions in alkoxyphenol-inhibited hydrocarbon oxidation is discussed.

From enolates to anthraquinones

A series of highly reactive cyclopentadienones were prepared in situ from the corresponding hydroxycyclopent-2-enones and trapped with a variety of quinones. Reaction of 1,4-naphthoquinone with 4-hydroxy-3,4-diphenyl-cyclopent-2-enone afforded 2,3-diphenylanthraquinone, whereas reaction of benzoquinone with this same cyclopentadienone precursor yielded a mixture of 6,7-diphenyl-1,4-naphthoquinone and 2,3,6,7-tetraphenyl anthraquinone. A number of other 2,3-diarylanthraquinones were likewise prepared in moderate yields from the reaction of 1,4-naphthoquinone with the appropriate 4-hydroxy-3,4-diarylcyclopent-2-enones. This method appears to be generally applicable to the synthesis of anthraquinone derivatives substituted at the 2- and 3-positions from inexpensive starting materials.Key words: anthraquinone, Diels–Alder, cyclopentadienone, in situ.

Redox Behaviour of Pyrazolyl-Substituted 1,4-Dihydroxyarenes: Formation of the Corresponding Semiquinones, Quinhydrones and Quinones

Abstract Pyrazolyl-substituted 1,4-dihydroxybenzene and 1,4-dihydroxynaphthene derivatives have been synthesized by reaction of 1,4-benzoquinone and 1,4-naphthoquinone, respectively, with pyrazole. Cyclovoltammetric measurements have shown that 1,4-benzoquinone possesses the potential to oxidize 2-(pyrazol-1-yl)- and 2,5-bis(pyrazol-1-yl)-1,4-dihydroxybenzene. The 2,5-bis(pyrazol-1-yl)- 1,4-dihydroxybenzene reacts with air to give quantitatively black insoluble 2,5-bis(pyrazol-1-yl)-1,4- quinhydrone. Black crystals of 2,5-bis(pyrazol-1-yl)-1,4-quinhydrone suitable for X-ray diffraction were grown from methanol at ambient temperature (monoclinic C2/c). The poor yields of pyrazolylsubstituted 1,4-dihydroxybenzene and 1,4-dihydroxynaphthene derivatives can be explained by the formation of insoluble black quinhydrons in the reaction of benzoquinone and naphthoquinone with pyrazole. The dianions of 2-(pyrazol-1-yl)- and 2,5-bis(pyrazol-1-yl)-1,4-dihydroxybenzene react with oxygen to give the corresponding semiquinone anions. 2,5-Bis(pyrazol-1-yl)-1,4-benzoquinone shows two reversible one-electron reduction processes in cyclovoltammetric measurements, whereas pyrazolyl-substituted 1,4-dihdroxybenzene and -naphthene derivatives undergo irreversibile electrontransfer processes.