Quinol phosphates

Free-radical intermediates in the oxidation of a series of quinol phosphates by permanganate at pH 11.7 have been characterised by an esr rapid-mixing technique . Clearly a one-equivalent oxidation step to give a semiquinone phosphate radical operates in this case. 

The oxidative hydrolysis of quinol phosphate (22) and its mono- and dimethyl esters with aqueous periodate has been studied. At pH 7—8 the... 

Quinones are firmly established in photosynthesis models. But how about vitamins E and K How do quinones work in animals First of all they transport electrons in a similar way as in photosynthesis (Metzler, 1977 Voet, 1990). Second, tocopherol is known to act as an antioxidant or radical quencher. The radical chain starting with the decomposition of unsaturated lipid peroxides, for example, is inhibited by tocopherol, which produces long-lived semiquinone radicals (Scheme 7.2.10). Vitamin E prevents, for example, sterility in rats fed rancid lipids. Vitamin E in connection with carotenes is also used as a stabilizer for diet margarines containing large amounts of essential fatty acids. Another possible activity of tocopherol is participation in oxidative phosphorylation a hydroquinone is mono-esterified with phosphoric acid to form a quinol phosphate and then oxidized to the quinone. The cationic quinone-phosphate adduct then reacts with anionic phosphate to form pyrophosphate (Scheme 7.2.10), (Wang, 1969 Breslow, 1980 Isler and Brubacher, 1982). 

About 20% of an oral dose of [ H] phylloquinone is excreted in the feces unchanged, suggesting that 80% is absorbed. A further 35% to 40% of the radioactivity is recovered in the feces as a variety of conjugates of polar metabolites formed by methyl oxidation of the side chain, followed by successive -oxidation, as well as reduction of the quinone ring to the quinol, to provide the site for conjugation with glucuronic acid, phosphate, or sulfate. About 75% of the conjugates are excreted in the bile and the remainder in the urine. In... 

The free energy gained from the quinol oxidation inthe cytochrome-6c, complex allows further proton transfer from the cytoplasm to the periplasm. The 6c,-complex also mediates ET to the periplasmic side. There, soluble cytochromes accept the electrons and transport them back to the RC to reduce D+. The electron transfer is cycUc and therefore does not cause transmembrane potential. This potential is generated by the electrogenic proton translocation in the cytochrome-6c, complex. The electrochemical proton gradient is utilized by the ATP-synthase to form adenosine triphosphate from adenosine diphosphate and phosphate. 

A previous paper [1] reported on the usefulness of the spectral subtraction technique in analysing the infrared spectra of clathrates formed by quinol and by Dianin s compound. Here we report on the use of the technique in analysing the infrared spectra of some intercalates of zirconium phosphate, and the Raman spectra of some clathrates of quinol. 

The clathrates of quinol were prepared by recrystallisation from the liquid guest or by bubbling the gas through a saturated ethanol solution [3]. Samples of the a-zirconium phosphate intercalates were kindly donated by Prof. U. Costantino, University of Perugia, Italy. 

Figure 11.16 Chromatographic retention of quinol (6) and catechol (7) on the boronate-functionalized monolithic column. Mobile phase (a) 100 mM HAc (pH 2.7) (b)-(e) 10 mM sodium phosphate buffer at pH 6.0, 6.5, 7.0, and 7.5, respectively the mobile phase was changed to 100 mM HAc (pH 2.7) at 30 min. Sample quinol and catechol were dissolved in the mobile phase at a concentration of 1 mg mL" each. (Reproduced from ref. 13 with permission. Copyright 2009, John Wiley Sons, Ltd.)...

Fig. 15.2 (continued) (26) 2-polyprenyl-6-methoxyphenol (27) 2-polyprenyl-6-metho3iy-l,4-benzo-quinol (28) 2-polypienyl-3-methyl-6-methoxy-l,4-benzoquinol (29) 2-polyprenyl-3-methyl-5-hydroxy-6-methoxy-l,4-benzoquinol (30) ubiquinol (31) ubiquinone (CoQn). Abbreviations ATP adenosine triphosphate, AMP adenosine monophosphate, NADPH/NADP nicotinamide adenine dinucleotide phosphate, CTP cytidine triphosphate, CMP cytidine monophosphate, reduced/oxidized ferredoxin, SAM S -adenosyhnethionine, SAH 5-adenosylhomocysteine... 

Quinol monoethers from quinol ether phosphates... 

---