BIBLIOGRAPHY TO CHAPTER 10 273 



merely increase the quantity of sugar available for transformation into 

 ascorbic acid. 



Quite early, it was suggested that ascorbic acid, with its capacity for 

 reversible oxidation, may play the part of an oxidation-reduction catalyst. 

 A difficulty of this concept arises from the instability of the reduced 

 form in the biological pH range. Conditions are somewhat more favor- 

 able in plant cells than in animal tissues because of the lower temperature 

 and lower pH values prevailing in them. 



As an oxidation-reduction catalyst, ascorbic acid may take part 

 either in the photosynthetic process or in respiration, or both. For 

 example, if chlorophjdl is reversibl}^ oxidized in photosynthesis (c/. 

 Chapter 19, page 551), it could be reduced again by ascorbic acid, as 

 was suggested by Bukatsch (1939). 



Using Baur's language of "molecular electrochemistry," (cf. page 90), Bukatsch 

 developed a scheme, which, translated into the language of ordinary photochemistry, 

 has roughly the following meaning: Excited chlorophyll molecules either oxidize water 

 to a peroxide, or reduce carbon dioxide to formaldehyde; in the presence of the "auxili- 

 ary redox system," ascorbid acid-dehydroascorbic acid, oxidized chlorophyll is reduced 

 by ascorbic acid and reduced chlorophyll is reoxidized by dehydroascorbic acid, and 

 in this way everything is "depolarized," and ready for the next cycle. We men- 

 tioned in chapter 4 (page 93) the experiments on artificial photosynthesis which 

 Bukatsch (1939) made on the basis of this concept; he also claimed (1940) to have 

 achieved a stimulation of natural photosynthesis by the addition of ascorbic acid {cf. 

 Chapter 13). An independent experimental control of these results appears desirable. 



That ascorbic acid may serve as a catalyst in the respiration of 

 plants, was first suggested by Szent-Gyorgyi (1928, 1931). Catalytic 

 effects of ascorbic acid on the oxidation of fatty acids and sugars in vitro 

 were reported, among others, by Holtz (1936). Another catalytic activ- 

 ity of ascorbic acid, possibly related to photosynthesis, is indicated by 

 experiments of West and Ney (1936) and Kuzin (1937), who found that 

 ascorbic acid in alkaline solution accelerates the polymerization of 

 formaldehyde. 



Bibliography to Chapter 10 



Intermediates of Photosynthesis 



A. The Hypotheses of Liebig and Baeyer 



1843 Liebig, J., Ann. Chemie, 46, 58. 



1870 v. Baeyer, A., Ber. deut. chem. Ges., 3, 63. 



1913 Baur, E., Naturwissenschaften, I, 474. 



B. Low Molecular Weight Compounds in Green Plants 



(except formaldehyde, oxalic, malic, citric, and ascorbic acid) 

 1872 Gorup-Besanez, E. V., Ann. Chem. (Liebig), 161, 229. 

 1881 Reinke, J., Ber. deut. chem. Ges., 14, 2145. 



