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.
