92 PROCESSES OUTSIDE THE LIVING CELL CHAP. 4 



i. e., systems of widely different oxidation-reduction potentials. How- 

 ever, formaldehyde was obtained with all of them, and none was obtained 

 from chlorophyll or eosin sols in the absence of an auxiliary system. 

 The yield was from 16 to 70% of the material available in the two 

 carboxyl groups of chlorophyll. Baur attached a particular importance 

 to experiments with ferric salts and quercetin because both are common 

 components of plants. 



In this work, no attempt was made to prove the evolution of oxygen. 

 Assuming that oxygen might cause a partial photoxidation of chlorophyll, 

 Baur attempted to improve the yield by adding substances capable of 

 "catching" oxygen, — rubrene and carotene. Rubrene (in benzene) was 

 without effect; carotene (in palm oil suspension) increased the yield by 

 about 30%, which was considered as significant. No formaldehyde was 

 obtained from chlorophyll adsorbed on alumina (suspended in methylene 

 blue solution); from nonfiuorescent chlorophyll, preparations (copper 

 phaeophytin) and from water-soluble dyes (e. g. gallocyanin), which 

 gave no two-phase systems. Baur and Gloor (1937) tested several other 

 dyes as sensitizers and oxidants, and found that only esterified com- 

 pounds can be used, whereas compounds containing free carboxyl groups 

 gave no formaldehyde. Rhodamine derivatives were found to be even 

 better oxidants than eosin. Baur, Gloor and Kiinzler (1938) obtained 

 positive results with rhodamine both in colophony sols and collodion 

 films, and found an increase of the yield with increasing length of the 

 alcohol molecule in the ester; the free acid, rhodamine B, was ineffective. 

 They endeavored further to bring about suitable conditions for the 

 recarboxylation of the (supposedly) decarboxylated dyestuff ; and thought 

 that the use of "ol" phases (higher alcohols), which take carboxylic 

 acids out of the aqueous phase, might help to shift the equilibrium 

 RH 4- CO2 ^ RCOOH towards a more complete carboxylation (c/., 



however. Chapter 8, page 179). Different "ol" compounds were found 

 useful, particularly geraniol. The authors then used a carbon dioxide 

 atmosphere, to favor still more the recarboxylation of the oxidant. 

 Positive results were obtained, however, only with two very special 

 systems: mashed leaves in geraniol, and acetate silk-chlorophyll-cetyl 

 alcohol. The latter system formed twenty times more formaldehyde 

 than could be accounted for by the carboxyl groups of chlorophyll. 

 This experiment was announced as the first successful photochemical 

 reduction of carbon dioxide in vitro. Baur also tried to give the proof of 

 complete photosynthesis in this system by demonstrating the liberation 

 of oxygen; but the analytical results were not very consistent and the 

 authors themselves termed them "preliminary." 



Baur, Gloor and Kiinzler (1938) found that positive results can also 

 be obtained with sensitizers not containing esterified carboxyl groups, if 



