OXIDATION AND REDUCTION OF CAROTENOIDS 473 



Zechmeister (1934) remarked that the absence of the more highly 

 oxidized of the two chlorophylls (chlorophyll h) in brown algae, and the 

 presence in them of a strongly oxidized carotenoid (fucoxanthol) may be 

 more than a coincidence. 



Carotenoids are also present in purple bacteria, as was first shown by 

 Molisch (1907). Spirilloxanthin, C48HG6O3, with 15 double bonds, was 

 found in Spirillum rubrum by van Niel and Smith (1935). Karrer and 

 Solmssen (1935, 1936) found five new carotenoids in Rhodovihrio : rhodo- 

 violascin, rhodopin, rhodopurpurin, flavorhodin, and rhodovibrin. Rho- 

 doviolascin is the easiest to obtain in the pure state; according to Karrer 

 and Solmssen (1936), it contains 13 double bonds and has the formula 

 C4oH64(OCH3)2, thus being an ester rather than a hydrocarbon or alcohol, 

 as are most other carotenoids. Rhodoviolascin is an open-chain com- 

 pound. Its first absorption band hes comparatively far toward the red, 

 at 573 mjLi in carbon disulfide and at 526 mju in ethanol. Since it is known 

 (Vol. II, Chapter 21) that the lengthening of the conjugated double- 

 bond chain causes a shift of the absorption band towards the red, rhodo- 

 violascin probably has a chain of 13 conjugated double bonds (as against 

 11 in /S-carotene and luteol). Rhodopin, which should more correctly be 

 called rhodopol, (C40H57OH, cf. Karrer and Solmssen 1936, Karrer, 

 Solmssen, and Koenig 1938) is a tertiary alcohol with one hydroxyl group 

 and 12 double bonds. Rhodovibrin contains two oxygen atoms; its 

 formula is probably C40H68O2. Flavorhodin and rhodopurpurin are hy- 

 drocarbons, their names should thus be written as flavorhodene and 

 rhodopurpurene. 



It is worth noting that the absorption bands of bacterial carotenoids 

 are situated further towards the red than those of the carotenoids of the 

 green plants, thus paralleling the relationship between chlorophyll and 

 bacteriochlorophyll . 



Apparently, carotenoid pigments are present also in green bacteria 

 (see, for example, Katz and Wassink 1939). 



2. Oxidation and Reduction 



Molecular solutions as well as colloidal solutions of carotene are 

 quickly bleached by light. This bleaching is due to oxidation, and 

 oxidizability is a general characteristic of the carotenoids. Strain (1938) 

 has found, for instance, that, unless special precautions are taken, up to 

 50% of the leaf carotenoids may be lost by oxidation during the grinding 

 of leaves in air. Once the pigments have been extracted, the danger of 

 oxidation becomes less acute. Oxidation during extraction can be 

 prevented by heating the leaves before grinding; Strain therefore attrib- 

 utes it to a heat-sensitive enzyme. 



The carotenoids are also capable of reduction. Eleven molecules of 



