Synthesis, characterization, TDDFT calculation and biological activity of tetradentate ligand based square pyramidal Cu(II) complexes

Distorted square pyramidal complexes [Cu(L-1)(H2O)].ClO4 (1), [Cu(L-2)(H2O)].ClO4(2) and [Cu(L-3)(H2O)]. ClO4 (3) (HL1 = o-{[2-(2-aminoethylamino)ethylimino]methyl}phenol; HL2 = 2-{[2-(2-aminoethylamino) ethylimino]methyl}-6-methoxyphenol; HL3 = o-{1-[ 2-(2-aminoethylamino)ethylimino]ethyl}phenol) have been synthesized, and characterized by X-ray crystallography and spectroscopic analysis. All the complexes exhibit fluorescence at room temperature [lambda(ex) = 267 nm, lambda(em) = 312, 329 and 357 nm, phi = 0.52 for 1; lambda ex = 272 nm, lem = 312, 329 and 355 nm, phi = 0.46 for 2; lambda ex = 265 nm, lambda em = 312, 356 and 377 nm, 4 = 0.33 for 3]. The electronic structure and photophysical properties of the ligands and complexes were calculated by density functional theory (DFT) and time-dependent density functional theory (TD-DFT)methods using the B3LYP, B3PW91 and MPW1PW91 functionals, with 6-31G (d-p) and LanL2DZ basis sets. The results of TD-DFT calculations are functional-dependent and among the functionals, B3LYP was able to best reproduce the experimental results. Catecholase activity of 1- 3 has been investigated using 3,5-di-tert butyl catechol (3,5-DTBC) as the model substrate and found that complexes are active for catalyzing the aerobic oxidation of 3,5-DTBC to 3,5-di-tert butyl benzoquinone (3,5-DTBQ). The compound with more distorted square pyramidal geometry shows a higher rate of catalytic activity. All the complexes have been tested for their anticancer activities in human breast (MCF7) cancer cell lines. Complexes show dose dependent suppression of cell viability with IC50 values 30, 68 and >100 mu M for 1, 2 and 3, respectively. Anticancer activities of 1- 3 and cisplatin were compared, and found that 1- 3 were relatively less active than cisplatin.