Structure-activity relationship studies of dibromo phenolic derivatives as photosynthetic electron chain inhibitors

A number of 2,6‐dibromophenols with different substituents in the 4‐position have been synthesised and their effect on the whole electron transport chain and on photosystem II have been determined. A study was made to relate the chemical characteristics of the 4‐substituent group and the inhibition of the uncoupled electron transport of isolated chloroplasts from spinach plants. The chemical nature of the 4‐substituent group varies greatly in the active compounds and it is therefore suggested that this group does not participate in the inhibitor‐receptor interaction. The results indicated that the inhibiting power of these compounds increased with the electron‐attracting capacity of the 4‐substituent group, decreased with increase in its size and that there was no correlation with its hydrophobic nature.