Redox-active metal(II) complexes of sterically hindered phenolic ligands: Antibacterial activity and reduction of cytochrome c. Part III. Copper(II) complexes of cycloaminomethyl derivatives of o-diphenols

Abstract

Redox-active copper(II) complexes of sterically hindered phenolic ligands have been synthesized using 5-tert-butyl-3-(pyrrolidinomethyl)-1,2-dihydroxybenzene (HLI), 5-tert-butyl-3-(piperidinomethyl)-1,2-dihydroxybenzene (HLII), 5-tert-butyl-3-(azepanylmethyl)-1,2-dihydroxybenzene (HLIII), 5-tert-butyl-3-(morpholinomethyl)-1,2-dihydroxybenzene (HLIV), and 5-tert-butyl-3-(methylpiperazinomethyl)-1,2-dihydroxybenzene (HLV). The novel compounds have been characterized by means of chemical and physico-chemical methods. The coordination core of these complexes is a square planar chromophore, [CuO2N2], and the phenolic ligands coordinate in their monoanionic forms. The ligands and Cu(II) complexes have been screened for their antibacterial activity. The lowest MIC value (0.020μmolml−1) has been found for Cu(LIII)2 and Cu(LV)2 against Mycobacterium smegmatis, Sarcina lutea and Staphylococcus aureus, and this is comparable to the value for chloramphenicol. Their antibacterial activities were found to follow the order: (1) HLI>HLV⩾HLIII∼HLII>HLIV; (2) Cu(LIII)2>Сu(LII)2∼Cu(LI)2∼Cu(LV)2>Cu(LIV)2; their reducing ability (determined electrochemically) followed the same order. The most bioactive complex, Cu(LIII)2, has the highest lipophilicity. A spectrophotometric investigation was carried out in order to estimate the rate of the reduction of bovine heart сytochrome c with the ligands and their Cu(II) complexes. HLI and the complex Cu(LIII)2 have the highest reducing abilities (determined electrochemically), which are characterized by the highest Cyt с reduction rates respectively amongst the ligands and Cu(II) complexes.