Showing papers on "Quinone published in 1982"

Covalent Addition of H2O, Enzyme Substrates and Activators to Pyrrolo‐quinoline Quinone, the Coenzyme of Quinoproteins

Abstract: The fluorescence excitation and the adsorption spectrum of 2,7,9-tricarboxy-1H-pyrrolo [2,3-f]quinoline-4,5-dione (pyrrolo-quinoline quinone, PQQ), measured in the pH range 7.0-10.0, are quite different. However, when the temperature of the solution is lowered, the shape and maxima of these spectra become more similar. 1H-NMR in 2H2O revealed a temperature-dependent equilibrium between PQQ and a hydrated form. Evidence is presented that low temperature favours the formation of the fluorescing species which is PQQ, hydrated at the C-5 position. Even further hydration is possible since absorption, fluorescence and NMR spectroscopy of PQQ in borate buffer pH 10.0 reveal additional hydration at the C-4 position, pointing to a dihydrate. PQQ also reacts with quinoprotein enzyme substrates and activators. Spectroscopic measurements showed the existence of 5-alkoxy-5-hydroxy-PQQ and 5-amino-5-hydroxy-PQQ in the presence of alcohols and 2 M NH4Cl, pH 9.0, respectively. In the latter case, the existence of 5-imino-PQQ could also be demonstrated. Addition compounds with amines appear to be unstable. The amines become probably oxidized because pyrrolo-quinoline quinol (PQQH2) was found as the reaction product. On the other hand, an addition compound containing an imino bond could be isolated after addition of urea to a PQQ solution. Spectral characteristics of PQQ and its addition compounds are presented since these data are necessary for the spectral analysis of quinoproteins and the quantitative estimation of coenzyme.

Characterization of polycyclic ketones and quinones in diesel emission particulates by gas chromatography mass-spectrometry

Abstract: The chemical composition of two neutral, mutagenic subfractions of a diesel particulate extract sample was examined by capillary gas chromatography/mass spectrometry. Most compounds identified were polar derivatives of three- to five-ring polynuclear aromatic hydrocarbons. Ketone, quinone, carboxaldehyde, and hydroxy derivatives and their alkyl homologues were characterized. 9-Fluorenone and its C/sub 1/-C/sub 4/ alkyl homologues were the single largest family of compounds detected. Some of the compounds characterized are bacterial mutagens; the mutagenicity of others is not known at this time.

Electron and proton transfers in chemical and biological quinone systems

Abstract: Some redox chemistry and biochemistry of p-benzoquinones are summarised. In particular, the behaviour of quinols and quinones at electrode surfaces and in solution, together with the mechanism of reduction of soluble cytochrome c by quinols, produces a model of electron transfer relevant to biological systems. In such a model the biological transfers occur by collisional reactions of the quinone and quinol with the protein donors and acceptors. After collision, the detailed reactions occur via bound enzyme intermediates but electronic mobility between the donors and acceptors is provided by diffusional mobility of the quinone molecules. Such considerations have allowed a detailed investigation of the redox reactions of quinols with a complex biological multiprotein system, the bc complex. A probable mechanism of electron transfer into and through this complex is presented, together with some discussion of the mechanism of energy transduction which would operate in the intact biological system.

Some electrochemical and chemical properties of methoxatin and analogous quinoquinones.

Abstract: The present study establishes relationships between structure and reactivity for the pyrroloquinoline and phenanthroline quinones. The electrochemical reductions of 1,7- and 1,10-phenanthroline-5,6-quinones, like other quinones, are reversible and occur by 2e- transfer in a single step in aqueous solution and by two 1e(-)-transfer steps in aprotic media. The electron-withdrawing pyridine moieties both increase their potentials and stabilize their aprotic semiquinones. The electrochemistry of the cofactor methoxatin and its trimethylester derivative is similar to the phenanthroline quinones in aqueous solution. However, the electrochemical reductions of methoxatin and its triester in aprotic solutions are characterized by at least three potentials, each accounting for less than 1e-. This has been explained by the proposal of semiquinone complexing with itself and with quinone. Despite an electron-donating pyrrole moiety, methoxatin and its trimethylester have relatively high potentials in aprotic solution. This is presumably due to stabilization of radical anions by the aforementioned complexing or by delocalization with carboxylic acid and ester groups. The reduction potential of methoxatin, in both aqueous and aprotic solvent, suggests that oxidation of methanol should be a thermodynamically favorable process. No evidence for an electrochemically reduced state lower than the quinol was found for any of the compounds. Chemical reactivity is influenced by the orientation of the pyridine nitrogen. The two quinones with a pyridine nitrogen peri to a quinone carbonyl add and oxidize nucleophiles most readily.

Some physical and chemical aspects of spin trapping of organometallic radicals by quinones: optically active radical complexes

Abstract: A brief account is presented on the use of substituted quinones as spin traps for organometallic radicals and on the applications of CIDEP and esr–HPLC techniques to the study of quinone – organome...

Photochemical characterization of covalently‐linked porphyrin‐quinone complexes*

Abstract: — The fluorescence properties of a covalently-linked porphyrin-quinone complex and its zinc derivative were studied in a variety of organic solvents The kinetics of fluorescence decay for both the quinone and hydroquinone oxidation states were measured in acetonitrile, dichloromethane, dimethyl-formamide, and pentane The fluorescence yield and kinetics of decay at room temperature were little affected in the porphyrin or zinc porphyrin complexes when the attached quinone was reduced However, for these complexes the fluorescence yield and lifetimes were both substantially decreased in acetonitrile and dichloromethane when the quinone was in its oxidized state These latter decay kinetics were not explainable by a process having a single exponential decay On the other hand, little fluorescence quenching or lifetime shortening was observed in dimethylformamide or pentane, indicating unique solvent dependencies for the quenching process Evidence was obtained for photoproduced charge separation from EPR measurements on the covalently-linked zinc porphyrin-quinone complex The EPR data showed equivalent concentrations of a Zn porphyrin cation radical and a benzoquinone anion radical in acetonitrile or dichloromethane at both room temperature and 77 K The charge separated state rapidly decayed at room temperature (in sub-millisecond times) but was quite stable at 77 K It is concluded that light-induced charge separation in acetonitrile and dichloromethane at room temperature may occur from the excited singlet state with a high quantum efficiency A photoproduced charge separated state also occurred when the covalently-linked complexes were incorporated into egg yolk phosphatidylcholine liposomes The quantum yield for radical formation in this latter system was 01 and the lifetimes of the radical species formed were many minutes

A New Efficient and Stereoselective Synthesis of Ubiquinone-10

Abstract: Coupling reaction of 6-cupro-2,3-dimethoxy-5-methylhydroquinone bis(2-methoxyethoxymethyl) ether with (2E)-1-(phenylsulfonyl)-2-methyl-4-chloro-2-butene afforded the sulfone-functionalized prenylhydro quinone (6) in 82% yield. Stereoselective synthesis of ubiquinone-10 was achieved by the condensation of 6 and solanesyl bromide (yield 92%), reductive elimination of the sulfone group by sodium–ethyl alcohol in THF (yield 80%), and followed by air oxidation of the hydroquinone.

1- und 2-Elektronenschritte bei der Oxidation substituierter Paraphenylendiamine mit verschiedenen Oxidationsmitteln. II. Reaktionen mit Hexacyanoferrat

Abstract: The oxidation kinetics of several N- and ring-alkylated p-phenylenediamines with hexacyanoferrate(III) (F3) was studied in the pH-range 2,5 – 9 by means of a multimixing stopped flow technique which is described in detail. The p-phenylene diamine-derivatives (R) are oxidized via reversible one-electron steps to the semiquinone diimine radical S (rate constants k1, k−1) and the quinone diimine T (rate constants k2, k−2). – k1 and k−1 could be measured directly for all compounds, k2 and k−2 for two derivatives. – Only the unprotonated species of R, S, T, F3 are reactive. The reduction is possible by the unprotonated Fe(CN)4-6 (F2) and by its protonated form F2H. The complexes of F2 with alkali ions are inactive. In this way the respective association constants could be calculated. The kinetics of the reaction was compared with the thermodynamics, represented by potential-pH-diagrams. – The activation parameters of the reaction of p-phenylene diamine-derivatives with F3, F2 and also with iodine were measured. The activation energies of the second step (k2, k−2) are negligible. – Both oxidants attack the alkylated aminogroup of the p-phenylene diamine derivatives. The radical cation is deprotonated before it is oxidized.

Synthesis of Dihydrobenzofuran Derivatives from Substituted p-Benzoquinones

Abstract: A series of p-benzoquinones having an ester functional group in the α position of alkyl side chains was prepared. Irradiation of these quinones, except for methyl 3-methyl-2-(4-methyl-3,6-dioxo-1,4-cyclohexadienyl)-butyrate (3e), rapidly gave methyl 3-substituted 2,3-dihydro-5-hydroxybenzofuran-2-carboxylate in fairly good yields, and it was found that rearrangement of the side chain occurred concomitantly. Photolysis of quinone 3e afforded methyl 2-(2,5-dihydroxy-4-methylphenyl)-3-methyl-3-butenoate as the major product. An intermediate was postulated to account for the isolated photoproduct.

Quinone-capped porphyrins: synthesis and some chemical properties

Abstract: The 2,5-bis(hydroxyethyl) and 2,5-bis(hydroxypropyl) derivatives of hydroquinone bis(methoxymethyl) ether have been synthesised and used to ‘cap’ mesoporphyrin-II. Deprotection, oxidation, and metallation gave the title compounds. Several anomalous reactivities were observed in the capped series which may be attributed to the proximity of quinone and porphyrin moieties.

Tetrapyrroles. Part 2. Synthesis and electronic spectra of some quinone-porphyrins

Abstract: Four quinone-porphyrins have been synthesised. Their electronic spectra show several unusual features consistent with light-induced intramolecular charge-transfer.

Quinone-capped porphyrins: n.m.r. studies of static and dynamic stereochemistry and co-ordination properties

Abstract: 1 H N.m.r, spectroscopy has been used to investigate the shape, motion, and flexibility of two of the title compounds, and their magnesium derivatives, and to probe the co-ordinative properties of the latter. Coupling constant and n.O.e. results for the porphyrin moiety are analysed in terms of two possible conformations. The cap moiety for simple alkyl-capped porphyries appears to have a well defined shape. In the title compounds, however, the quinone ring is flipping rapidly and a temperature dependent ‘breathing’ is observed; the quinone is closer on average to the porphyrin in the compound with additional methylene groups in the cap. At ambient temperature molecular tumbling is severely hindered in these propellor-shaped molecules leading to rapid relaxation and broad lines, but resolution improves substantially on warming. Pyridine titration data for the magnesium derivatives indicate that the metal ion is out-of-plane 5-co-ordinate, bound intramolecularly to a quinone carbonyl, and that it can accept a 6th ligand from the unhindered side of the porphyrin, moving into the plane and pulling the quinone towards the porphyrin. The average orientation of the quinone ring appears to be perpendicular to the porphyrin.

Quinone reductases of higher plants

Abstract: NAD(P)H: quinone oxidoreductase (DT-diaphorase) was detected in 100000 x g supernatant fractions of extracts of a wide variety of higher plants. Smaller amounts were also found in microsomes and chloroplast fractions. The enzyme was partially purified from soluble extracts of several plants and the quinone reductase from Catharanthus roseus was enriched 25-fold. Plant quinone reductases have molecular weights in the range of 38000-53000 as determined by gel filtration. The plant enzyme is far less sensitive to dicoumarol than its mammalian counterpart and it is inhibited by superoxide dismutase. Quinone reductase is capable of reducing simple p-benzoquinone and naphthoquinone including vitamins K3 and K1. These results indicate that, although the plant enzyme exhibits a similar substrate specificity, it is distinguishable from mammalian DT-diaphorase particularly with respect to its mechanism of reduction.

Quinones. Part 2. General synthetic routes to quinone derivatives with modified polyprenyl side chains and the inhibitory effects of these quinones on the generation of the slow reacting substance of anaphylaxis (SRS-A)

Abstract: General synthetic routes to quinone acids (8), quinone amides (9), quinone alcohols (10), and quinone methylketones (11) with polyprenyl side chains, in which allylic alcohols (3) are employed as the key intermediates, are described. The Claisen rearrangements and the Carrot reactions of the allylic alcohols (3) with ethyl orthoacetate and diketen produced the ethyl esters (4) and the methylketones (5), respectively. Quinone products (8), (10), and (11) were recovered by oxidative demethylation of hydroquinone dimethyl ethers (4), (5), and (7) or by acid hydrolysis of hydroquinone bis(methoxymethyl) ethers (4) and (5) followed by ferric chloride oxidation. Amidation of quinone acids (8) led to the formation of quinone amides (9). Inhibitory effects of these quinone derivatives on the generation of the slow reacting substance of anaphylaxis (SRS-A) in the lungs of sensitised guinea pigs are evaluated.