Novel 30-membered octaazamacrocyclic ligand: synthesis, characterization, thermodynamic stabilities and DNA cleavage activity of homodinuclear copper and nickel complexes

Abstract

A new 30-membered octazamacrocyclic ligand: 4,6,9,12,20,23,26,29-octaaza-35,36-dihydroxy-16,33-dimethyl-tricyclo[29.3.1.1 14,18]hexatriaconta-1(35),18(36),15,17,31,33-hexaene (L or BTBD) has been synthesized and characterized. Its coordination chemistry toward Cu(II) and Ni(II) ions has been investigated extensively by potentiometric titration in 1:1 or 1:2 (L–M) aqueous systems. L shows high complexation ability with Cu(II) and Ni(II) ions in 1:1 systems with formation constants: log K[ML]=24.01 (M=Cu), 21.04 (M=Ni), respectively. In 1:2 (L–M) systems, two metal ions were suggested to enter into the cavity separately and locate in half of the compartment without formation of μ-oxo bridged core. BTBD served as N 8O 2 −2 ligand to divalent binuclear copper and nickel complexes with similar stability constants (log K[M 2L]=15.38, 15.36, respectively). [C 30H 50Cu 2N 8O 2](ClO 4) 2·CH 3OH·2(H 2O) ( 1) crystallizes in the monoclinic space group P2 1/ n, a=7.9662(7), b=14.5925(4), c=11.614(10) Å, β=105.187(4)°, V=3905.5(6) Å 3 and Z=4. Each copper is complexed by half of the coordination sites of the dinucleating macrocycle, and completes square pyramidal polyhedron. [C 30H 50N 8Ni 2O 2(H 2O) 2](ClO 4) 2·CH 3OH·3(H 2O) ( 2) crystallizes in the triclinic space group P 1 ̄ , a=10.5559(5), b=14.6947(7), c=15.3025(10) Å, α=65.5470(10), β=80.4650(10), γ=72.7392(10)°, V=2060.92(17) Å 3 and Z=2. The X-ray crystallographic results demonstrate that each nickel ion resides in the N 4O − site and forms six-coordinated octahedron with exogenous solvents at the apex. Dinuclear copper complexes have been found have cleavage ability toward supercoiled pBR 322 DNA in the presence of H 2O 2. EPR and UV results showed that the possible cleavage mechanism was via Cu(II)OOCu(II) peroxide and leads to DNA oxidative cleavage.