. Bioenergetics. Bioenergetics. 53 The table shows most substances to be inactive, but also shows some of them to be highly active and to cause a maximal shift in AI concentration and still be active in M. Among the most active ones we find dinitrophenol and dinitronaphthol, both of which uncouple oxidative phosphorylation. That the two actions might actually have some relation to one another is sug- gested by the activity of dicumaroi (33) and pentachlorophenol (27), both of which are also known to uncouple. Owing to its O-CH2-COOH ,C1. a (a) 0>) Fig. 10, a: 2,4-Dichlorophenol
. Bioenergetics. Bioenergetics. 53 The table shows most substances to be inactive, but also shows some of them to be highly active and to cause a maximal shift in AI concentration and still be active in M. Among the most active ones we find dinitrophenol and dinitronaphthol, both of which uncouple oxidative phosphorylation. That the two actions might actually have some relation to one another is sug- gested by the activity of dicumaroi (33) and pentachlorophenol (27), both of which are also known to uncouple. Owing to its O-CH2-COOH ,C1. a (a) 0>) Fig. 10, a: 2,4-Dichlorophenol. b: 2,4-DichIorophenoxyacetic acid. insolubility, dicumaroi could not be tested in a higher concentra- tion than Ai. The abolition or substitution of the phenolic hydroxy group, which is essential for the uncoupling activity, also deprived the molecule of its action on rhodamin. A point worth mentioning is the great difference in the activity of two chemically closely related substances, 2,4-dichlorophenol and 2,4-dichlorophenoxyacetic acid (Fig. 10). Both substances are highly active biologically, but their activity is very different, so it is intriguing to find them different also in this simple /"« vitro experiment (see Chapters 12 and 16). In the present experiment with rhodamin, a tentative explanation for the differences in the activity of the dichlorophenol and 2-4 dichlorophenoxyacetic acid (2,4D) can be found in steric relations. If the rhodamin molecule, as well as the two chlorophenols and the nitrophenols are built of an atomic model, it is found that the active nitrophenol and nitro- naphthol can easily be brought into a position in which the phen- olic hydroxide and one NO2 group touch the two resonating N's of the dye. The same holds for the carboxylic O" and one CI (4). Please note that these images are extracted from scanned page images that may have been digitally enhanced for readability - coloration and appearance of these illustrations ma
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