DNA/protein binding and magnetic properties of a 1D Cu(II) complex containing fumarate and tridentate Schiff base ligands

The 1D copper(II) complex {[Cu₂(L)₂(fum)]·(H₂O)·(MeOH)}_n(1) has been synthesized using fumarate (fum²⁻) and a Schiff base (HL), derived from the condensation reaction of 2-amino-1-butanol and salicylaldehyde. Complex 1 has been characterized by its X-ray crystal structure, together with FT-IR, electronic absorption and fluorescence spectroscopic methods. The structural determination reveals that complex 1 crystallizes in the monoclinic system with the space group P2₁/n and forms a 1D polymeric chain, built by bridging fum ligands. Weak π⋯π and C–H⋯π interactions lead to the formation of a 3D supramolecular architecture. Complex 1 exhibits fluorescence (λ_ex, 366 nm; λ_em, 410, 433 and 462 nm) at room temperature, with a quantum yield (Φ_s) of 0.257. The interactions of complex 1 with bovine serum albumin (BSA) and human serum albumin (HSA) were studied using electronic absorption and fluorescence spectroscopic techniques, and the results show that the interaction of complex 1 with BSA/HSA occurs mainly with a ground state association process. The calculated values of the apparent association constants (at 300 K) are 1.34 × 10⁴and 1.81 × 10⁴L mol⁻¹for interactions with BSA and HSA, respectively. The number of binding sites and binding constants were calculated using a double logarithm regression equation. The interaction of complex 1 with calf thymus DNA (CT-DNA) was also investigated using electronic absorption and fluorescence spectroscopic methods. The results show that complex 1 has a binding affinity to CT-DNA of the order of 2.96 × 10⁵L mol⁻¹. Low temperature magnetic measurements reveal the existence of an antiferromagnetic interaction in complex 1. The magnetic data have been fitted considering complex 1 as a pseudo-dinuclear system, with the two copper(II) ions bridged by two carboxylate oxygen atoms, since the coupling through long fum bridge is almost nil. The best-fit parameters obtained with this model are J = −60 cm⁻¹and g_Cu= 2.20.