Copper(II) salicylideneimine complexes revisited: From a novel derivative and extended characterization of two homologues to interaction with BSA and antiproliferative activity

Abstract A novel compound bis[N-n-propyl-5-chloro-2-oxy-κO-benzylideneimine-κN-(1–)]copper(II) was prepared, along with two previously reported homologues having N-n-propylsalicylideneimine and N-n-buthyl-5-chlorosalicylideneimine ligands. Single crystal X-ray determination of three complexes reveals almost ideal CuO2N2 trans-square planar geometry. All three compounds crystalize in P-1 space group. Infrared spectra confirm coordination of iminophenolate via azomethine nitrogen and deprotonated phenolic oxygen. Electronic spectra showed strong iminophenolate-to-Cu(II) charge transfer transitions in the region 359-371 nm and d-d transition centered around 600 nm. The location of an unpaired electron of d9 configuration Cu(II), in dx2−y2 orbital is confirmed based on g-tensor values obtained by X-band ESR spectroscopy that also corresponds to square planar geometry. Cyclic voltammograms in acetonitrile solution showed one-electron reduction with cathodic peaks in the range –0.598 to –0.618 V as a result of the fast decomplexation and disproportionation of the Cu(I) complex. The interaction with BSA (Bovine serum albumin) showed 1:1 complex-protein binding with Kb constants values in 103 –105 M-1 range. Docking calculations point out only hydrophobic and π-π interactions between copper(II) complexes and BSA with average distances between two tryptophan residues and copper complexes in 20 – 24 A range. Antiproliferative testing on two tumor cell lines H460 and HCT116 and non-tumor HEK293T showed non-selectivity and close IC50 values for tumor and control lines.