Quantitative structure-activity relationships of the inhibition of photosynthetic electron flow by substituted diphenyl ethers

The effect of 41 substituted diphenyl ethers (derivatives of nitrofen and chloroxuron) on photosynthesis in isolated spinach chloroplasts has been studied. All the chemicals were found to be inhibitors of non-cyclic electron transport; the pI₅₀ values varied from 3.17 to 7.16 (I₅₀ is the molar concentration causing 50% inhibition; pI₅₀= -log I₅₀). Based on their structures, the compounds were divided into four groups; for most groups, a correlation between the inhibition of photosynthesis and physicochemical parameters was found. Lipophilicity proved to be the most important parameter; electronic effects did not play a role. Introduction of substituents into the nitrophenyl ring of nitrofen lowered activity considerably. Nitrofen and and chloroxuron analogues seemed to inhibit at different sites in the electron transport chain. A relationship between inhibition of photosynthesis and herbicidal activity was not clear.