Chemical structure and biological activity 



and 2:3: 5-triiodobenzoic acid, one curve of the series a-naphthylacetic acid 

 (10~^) and 2 : 3 : 5-triiodobenzoic acid and one curve of the series a-naphthyl- 

 acetic acid (10~^) and 2:4:6-trichlorophenoxyacetic acid. In spite of the 

 good agreement between the theoretical function and the experimental 

 data, there are few deviations, especially when higher concentrations are 

 applied. Figure 7 shows such a case (2:4:5-trichlorophenoxyacetic acid (10") 

 and 2:4:6-trichlorophenoxyacetic acid). This deviation seems to be based 

 on the fact that either in the mixture itself, or in the interior of the coleoptile, 

 chemical reactions or intermolecular associations take place. The latter may 



1 



^20 



log Doncn. 

 ro~^ 70'^ 7^-2 /■^-l 



_l I L 



2:^^:6- fp/c/)/orophenoxj'aceh'c acid 



2--1-5-fnichlorophenoxyocefic acid 10° 



Figure 7. The course of the theoretical concentration-action curve of the mixture of 'I'A'.b-trichloro- 

 phenoxyacetic acid (10" per cent concn.) and 2:4: 6-trichlorophenoxj>acetic acid compared with the experi- 

 mental data (T)- Abscissa and ordinate as in Figure 1. 

 ± 



be more probable, and means formally that both acting molecules enter into 

 a gap simultaneously. Even in the case shown in Figure 7 molecidar associa- 

 tion seems to be present because the two molecules are chemically similar. 



The effect brought about by the simultaneous entry is not to be calculated 

 from the fundamental functions of the single partners of the mixture, but 

 one can obtain four correction terms. I will not occupy space here to show 

 this in detail. Further investigations will reveal whether the conclusion is 

 reversible; a deviation from the calculated values would mean that inter- 

 molecular powers influence the result. In terms of the probability calculus, 

 the two collectives are not independent of each other when experimental 

 results deviate from theoretical results. 



What I want to emphasize, however, is that the instances in which such 

 discrepancies between theory and experiment appear are very few in the 

 cases where I have had the opportunity of calculating mixture series. 

 Further calculations will have to support the considerations of probability 

 applied here, but the results obtained so far indicate the usefulness of the 

 theory based on the fundamental ideas of H, Linser (1954). 



REFERENCES 



Kaindl, K. (1954). Biophysikalische Analyse der Konzentrations-Wirkungskurven 

 von Wirkstoffen (Insbesondere Zellstreckungswuchsstoffen). Alh. Chem. 85, 985. 



Linser, H. (1954). Chemische Konstitution und zellstreckungswirkung. Versuch 

 einer allgemeinen Wirkstoffhypothese. Mh. Chem. 85, 196. 



164 



