434 5. QUINONES 



The spontaneous oxidation of quinones in experimental media leads to 

 an uptake of oxygen. Herz (1954 b), while studying the actions of various 

 quinones on enzymes, found that correction had to be made for the non- 

 enzymic oxygen uptake (see accompanying tabulation). These results are 

 for pH 7.3 and 37o; we have seen that the oxidation rate is strongly de- 

 pendent on the pH. The theoretical uptake for complete oxidation is 

 134 //I. Wosilait and Nason (1954) isolated a NADH: quinone oxidoreduc- 

 tase but found that the nonenzymic oxidation of some quinones represented 

 a major fraction of the NADH oxidation (see accompanying tabulation). 



Inasmuch as the rate of NADH oxidation varies hyperbolically with the 

 quinone concentration for the enzymic reaction and linearly for the non- 

 enzymic reaction (as in Fig. 1-2-1), the relative importance of the two 

 reactions will depend on the quinone concentration. These results indicate 

 the need for strict controls in most studies on the quinones, but unfortu- 

 nately these controls are not included in many reports. 



Purification 



Commercial samples of the quinones are often not sufficiently pure for 

 accurate work, and some generally useful procedures will be mentioned. 

 Methods for preparation and purification of several benzo- and naphtho- 

 quinone can be found in Organic Syntheses. A simple and satisfactory 

 method for purifying 2)-benzoquinone is sublimation, large crystals forming 

 on a watchglass placed over a beaker of the warmed material; this is pref- 

 erably done in vacuo. p-Benzoquinone may also be crystallized from warm 

 water, alcohol, benzene, or ligroin; other quinones can often be purified 

 similarly. Naphthoquinones and their substituted derivatives are some- 

 times better recrystallized from ether. The water-soluble sulfonate and 

 diphosphates can usually be crystallized as the K+ or Na+ salts from con- 

 centrated warm solutions of KCl or NaCl. 



