Big Chemical Encyclopedia

Chemical substances, components, reactions, process design ...

Articles Figures Tables About

Quinones compounds

The decline in immune function may pardy depend on a deficiency of coenzyme Q, a group of closely related quinone compounds (ubiquinones) that participate in the mitochondrial electron transport chain (49). Concentrations of coenzyme Q (specifically coenzyme Q q) appear to decline with age in several organs, most notably the thymus. [Pg.431]

Doong R-A, H-C Chiang (2005) Transformation of carbon tetrachloride by thiol reductants in the presence of quinone compounds. Environ Sci Technol 39 7460-7468. [Pg.40]

Dinkevich F.E., Juravel T.A., Ksenzhek O.S. and Lobach G.A. The Solubility of Some Quinon Compounds in the Sulphuric Acid Solvents. (Rus.), Problems of Chemistry and Chemical Technology IVoprosy Khimii i Khimicheskoy Tekhnologiil (Ukrainian Journal). 1979 55 10-12. [Pg.479]

Since long retention times are often applied in the anaerobic phase of the SBR, it can be concluded that reduction of many azo dyes is a relatively a slow process. Reactor studies indicate that, however, by using redox mediators, which are compounds that accelerate electron transfer from a primary electron donor (co-substrate) to a terminal electron acceptor (azo dye), azo dye reduction can be increased [39,40]. By this way, higher decolorization rates can be achieved in SBRs operated with a low hydraulic retention time [41,42]. Flavin enzyme cofactors, such as flavin adenide dinucleotide, flavin adenide mononucleotide, and riboflavin, as well as several quinone compounds, such as anthraquinone-2,6-disulfonate, anthraquinone-2,6-disulfonate, and lawsone, have been found as redox mediators [43—46]. [Pg.66]

Alkali-immobile dye-releasing quinone compounds, 19 293-294 Alkali lignins, 15 19-20 Alkali manganate(VI) salts, 15 596 Alkali manganates(V), 15 592 Alkali-metal alkoxide catalysts, 10 491 Alkali-metal alkoxides, effects of, 14 252 Alkali-metal alkylstannonates, 24 824 Alkali-metal fluoroxenates, 17 329-330 Alkali-metal hydrides, 13 608 Alkali-metal hydroxides, carbonyl sulfide reaction with, 23 622 Alkali-metal metatungstates, 25 383 Alkali-metal perchlorates, 18 211 Alkali-metal peroxides, 16 393... [Pg.29]

It is well to note at this point that the dihydroxy compound is the first identifiable compound from the photolysis and photo-oxidation reactions that actually has any color. The lack of other identifiable color compounds and also some preliminary experiments lead to a proposal [9] that the oxidation of the dihydroxy compound could actually continue on to give a quinone (Scheme 18.5, top). Given the ease of oxidation of hydroquinone compounds, this would seem to be a reasonable proposal. In this preliminary report where an orange-red solid was initially observed it was speculated that the color owed itself to a quinone compound as shown. This would add significantly to compounds that actually could be the color bodies formed upon weathering exposure. [Pg.636]

Several indoline-4,7-quinones, compounds which might be considered to be p-quinonoid aminochromes, have recently been described.279-280 6-Hydroxyindoline-4,7-quinone (100) was obtained... [Pg.283]

In summary, the studies reviewed here use diverse strategies to take advantage of the redox properties of two classes of catechol-quinone compounds present in nature to design new compounds of pharmaceutical interest. In a third class of naturally occurring compounds of complex structure, simplification and removal of the redox-sensitive elements may be key to providing target structures with a novel antiviral character. [Pg.126]

Processes of charge separation in porphyrin-quinone compounds with flexible bonding... [Pg.328]

Kong and Loach [30, 31] were the first to synthesize porphyrin-quinone compounds of the P-L-Q type. The structure of the compounds they obtained (n — 2, 3) is shown in Fig. 8(a). A strong quenching of the fluorescence of the... [Pg.328]

Charge separation processes in porphyrin-quinone compounds with several flexible bridges... [Pg.331]

The high conformational mobility of porphyrin-quinone compounds with flexible bonding makes it difficult to elucidate in sufficient detail the mechanism of electron transfer between porphyrin and quinone fragments. Far greater possibilities for determining the role of mutual orientation of P and Q and the distance between them are offered by P-Q compounds in which the P and Q fragments are linked by several bridges. A P-Q compound of this... [Pg.331]

Another example of compounds with the fixed mutual location of porphyrin and quinone are the porphyrin-quinone compounds with a rigid bridge. Charge photoseparation in P-L-Q molecules in which L is the trip-ticene bridge, P is tetraphenylporphin, TPP, or its zinc complex, and Q is benzoquinone, BQ, naphthoquinone, NQ, or anthraquinone, AQ, has been studied [55]. The distance between the centres of P and Q fragments in these... [Pg.332]

The charge photoseparation in porphyrin-quinone compounds with a rigid bicyclo[2.2.2]octyl bridge, ensuring a distance between the centres of P and Q of about 16 A, has been studied [57]. The rate constant of intramolecular electron transfer from P to Q was found to depend on the dielectric properties of the medium and reached 3.3 x 107s 1 for a solution of P-L-Q in propionitrile. [Pg.333]

Fig. 10. Structure of porphyrin-quinone compounds with a rigid bicyclo[2.2.2]octyl bridge. Fig. 10. Structure of porphyrin-quinone compounds with a rigid bicyclo[2.2.2]octyl bridge.
Fig. 13. The kinetics [67] of the dark intramolecular electron transfer in a porphyrin-quinone compound (P Lr Q -> P-L-Q ) at T - 77 K. The structure of the compound is given in the upper part of the figure. Fig. 13. The kinetics [67] of the dark intramolecular electron transfer in a porphyrin-quinone compound (P Lr Q -> P-L-Q ) at T - 77 K. The structure of the compound is given in the upper part of the figure.
The results of ref. 67 show that it is indeed possible to use solutions of porphyrin-quinone compounds in electron donor solvents for modelling the stage of electron transfer from pheophytin to quinone during photosynthesis (cf. Chap. 8, Sect. 1.2). Further research on these relatively simple model systems may provide still deeper insight into the mechanisms of this stage of photosynthesis. [Pg.338]

The key to the construction of the system is the choice of the quinone redox couple in the oil phase and the oil itself. The quinone compound must be reduced by Fe(II) ions, and the reduced form must be oxidized by bromine. These requirements indicate that the redox potential must be in the range between 0.77 and 1.07 V vs. NHE. After investigating of many redox compounds, we found that 2,3-dichloro-5,6-dicyano-l,4-benzoquinone (DDQ) dissolved in n-butyronitrile may be a good candidate for the system. DDQ has a largely positive redox potential because of its strong electron withdrawing substituents. [Pg.151]

Fig. 17.10 Combination of two photocatalytic reactions via a quinone compound. Compartment I (for hydrogen evolution) and compartment II (for oxygen production) are connected through a redox couple of DDQ and DDHQ dissolved in an oil phase. Fig. 17.10 Combination of two photocatalytic reactions via a quinone compound. Compartment I (for hydrogen evolution) and compartment II (for oxygen production) are connected through a redox couple of DDQ and DDHQ dissolved in an oil phase.
Figure 17.2 illustrates our model for splitting water by solar energy. I" is important that all the redox reactions involved in thf system be reversible. The quinone compound in the organic solvent combines the two photocatalytic reactions, and its function can be compared to the electron relaying molecules in thylakoid membranes of chloroplasts. Electron transfer reactions via quinone compouncs in artificia systems have been studied as a model of photosynthesis22-23 and in an electrochemical system for acid concentration.24 ... [Pg.323]

Electron Tunneling in Bridge Porphyrin-Quinone Compounds... [Pg.39]

Processes of Charge Separation in Porphyrin-Quinone Compounds with Flexible Bonding... [Pg.39]

Charge Separation Processes in Porphyrin-Quinone Compounds with Several Flexible Bridges... [Pg.42]


See other pages where Quinones compounds is mentioned: [Pg.420]    [Pg.493]    [Pg.207]    [Pg.85]    [Pg.295]    [Pg.782]    [Pg.138]    [Pg.16]    [Pg.153]    [Pg.328]    [Pg.264]    [Pg.423]    [Pg.164]    [Pg.39]    [Pg.42]   


SEARCH



© 2024 chempedia.info