Ring-substituted 8-hydroxyquinoline-2-carboxanilides inhibited photosynthetic electron transport (PET) through photosystem (PS) II. Their inhibitory efficiency depended on the compound lipophilicity, the electronic properties of the substituent R and the position of the substituent R on the benzene ring. The most effective inhibitors showing IC50 values in the range 2.3-3.6μM were substituted in C'(3) by F, CH3, Cl and Br. The dependence of the PET-inhibiting activity on the lipophilicity of the compounds was quasi-parabolic for 3-substituted derivatives, while for C'(2) ones a slight increase and for C'(4) derivatives a sharp decrease of the activity were observed with increasing lipophilicity. In addition, the dependence of PET-inhibiting activity on electronic Hammett's σ parameter of the substituent R was observed with optimum σ value 0.06 for C'(4) and 0.34 for C'(3) substituted derivatives, while the value of σ parameter did not significantly influence the PET-inhibiting activity of C'(2) substituted compounds. Interactions of the studied compounds with chlorophyll a and aromatic amino acids present in the pigment-protein complexes mainly in PS II were documented by fluorescence spectroscopy. The section between P680 and plastoquinone QB occurring on the acceptor side of PS II can be suggested as the site of action of the compounds.

Department of Chemical Drugs Faculty of Pharmacy University of Veterinary and Pharmaceutical Sciences Palackeho 1 3 612 42 Brno Czech Republic

Department of Environmental Ecology Faculty of Natural Sciences Comenius University Mlynska dolina Ch 2 842 15 Bratislava Slovakia

Department of Pharmaceutical Chemistry Faculty of Pharmacy Comenius University Odbojarov 10 832 32 Bratislava Slovakia

Institute of Chemistry Faculty of Natural Sciences Comenius University Mlynska dolina Ch 2 842 15 Bratislava Slovakia

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