NAPHTHAQUINONES 



67 



bacteriostatic effects and consideration to these is given in the chapter on Chemo- 

 therapy and Antibiotics. The polarographic method of study has been applied to a 

 number of these compounds and these are dealt with in the chapter on Polarography. 



Citrinin is a yellow quinone isolated from Penicillium citrinium and has anti- 

 bacterial properties (Raistrick and Smith, 1941). Fumigatin, obtained from 

 Aspergillus fumigatin is purple in colour, being 3-hydroxy-4-methoxy-2 : 5-toluquinone 

 (Anslow and Raistrick, 1938) and spinulosin, also purple, is 3 : 6-dihydroxy-4- 

 methoxy-2 : 5-ditoluquinone and is obtained from Penicillium spinulosum. The half- 

 wave potentials of these are given in the polarographic section. 



The structure and interrelations of a number of mould pigments have been studied 

 largely by Raistrick and his colleagues. These are substituted methyl anthraquinones 

 and the most recently described is 1:4: 5-trihydroxy-2-methyl anthraquinone, a 

 dark red pigment from Penicillium islandicum, which on oxidation yields cynodon- 

 tin, the 8-hydroxy derivative previously obtained from three helminthosporia. On 

 reduction and oxidation of the anthranol, chrysophanic acid is formed. Related 

 mould pigments are Helminthosporin, Catenarin, Erythroglaucin, Frangula emodin 

 and Ravenelin (Howard and Raistrick, 1949). 



Lugg, Macbeth and Winzor (1936) determined the normal electrode potentials of 

 a number of naphthaquinones by adding graded amounts of an oxidant to the reduced 

 quinones in the presence of a platinum catalyst and measuring the e.m.f. The 

 results are given in Table 12. The primary interest of these workers was the colouring 

 matters present in a sundew, Drosera Whittakeri. 



TABLE 12 

 Normal Electrode Potentl4.ls of Naphthaquinones, etc. 



Phthiocol, a pigment obtained from the tubercle bacillus is 2-methyl-3-hydroxy- 

 1 : 4-naphthaquinone and is accordingly amenable to potentiometric study. The 

 undissociated form is pale yellow, the ionised form is deep red and the reduced forms 

 are colourless. At pH 7 -0 the electrode potential when half reduced (Eq^) is — 0-18 v. 



