Quantitative Structure Activity Relationship of Diphenylamines as Inhibitors of Photosynthetic Electron Transport and Photophosphorylation

Abstract A number of 16 substituted diphenylamines have been tested for their inhibitory activity on photosynthetic NADP reduction and photophosphorylation. The most active compounds exhibited pI50 values of 6.0 in photosynthetic electron transport and 6.8 in cyclic photophosphorylation, respectively. The inhibition site in electron flow of the diphenylamines is located between the two photosystems. Necessary for high activity is the substitution of the phenyl moieties by several strongly electron withdrawing substituents. A quantitative structure activity relationship according to a parabolic Hansch approach could be accomplished by using the Hammett electronic parameter as the only variable.