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Q

quack:
historically a physician in Europe who administers mercury (quack silber) to treat syphilis; historically a physician who prescribes a dangerous remedy of marginal or doubtful efficacy; subsequently a physician who treats using a safe though ineffective remedy; recently a physician who prescribes a safe and effective remedy, but that is not approved by peer leadership or that is opposed by competitive interests; the utterance of an emotionally disturbed duck.

quench:
to terminate a chemical reaction involving free radicals; to inactivate a free radical: 1) by coupling with another free radical, 2) by donating one electron which achieves pairing, or 3) by oxidizing away the unpaired electron; to trap free radicals in such a manner that they cannot react nor further propagate their action.

quercetin:
3,3',4',5,7-pentahydroxyflavone; a bioflavonoid which naturally occurs in onions and numerous other edible plants; the aglycone of rutin; a diphenolic antioxidant with antihistaminic and ascorbutic benefits.

quinol (QH2):
hydroquinone; a diphenolic compound composed of an aromatic ring and two hydroxyl groups (-OH). To be considered a quinol the -OH groups must be situated at the 1,2 (ortho-) or the 1,4 (para-) carbon positions. This structure allows the hydroxyl groups to conjugate in the sense that abstraction of the two hydroxyl hydrogen atoms permits an immediate electronic rearrangement to the quinone structure. Quinols are useful in many situations requiring a mild organic reductant. As such they are effective donor type antioxidants. Thousands of types of quinols are produced naturally in the plant kingdom.

quinone (Q):
a compound composed of two carbonyl groups which are conjugated. Most quinones are medium strength oxidants. Upon reduction, by the acceptance of two hydrogen atoms, quinones convert to diphenols which are called hydroquinones (QH2). These can be oxidized by stronger oxidants to once again become quinones (Q). Quinones can also readily form semireduced species, which are free radicals having accepted only one hydrogen atom (*QH) or electron (*Q-). Like multivalent metals, quinones can participate in many redox reactions and can redox cycle in vivo. Many medicinal herbs, homeopathic products, and drugs are quinones. Quinones can be irritating in high dosage, because the semireduced form readily donates its unpaired electron to diatomic oxygen to produce superoxide (-OO*) and hydroperoxyl (HOO*) radicals.

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