Bio-relevant cobalt(II) complexes with compartmental polyquinoline ligand: Synthesis, crystal structures and biological activities

•With same ligand, three structural difference complexes have been synthesized.•1, with two rare μ3 -η1, η1, η1-CrO42−  moieties, is a tetranuclear complex.•Complexes show effective DNA binding and cleavage activity.•Complexes could quench fluorescence of BSA in a static quenching process.•1 shows about 6-fold higher anticancer activity against HeLa cell than cisplatin.

Three new Co(II) complexes, [Co4(L)2(μ3-CrO4)2](ClO4)2 · 2CH3CN (1), [Co2(L)(μ2-na)(H2O)](ClO4)2 (2) and [Co2(L)(μ2-ba)](ClO4)2 · 0.5CH3CN (3) (Hna = nicotinic acid, Hba = benzoic acid, HL = N,N,N′,N′-tetrakis (2-quinolylmethyl)-1,3-diaminopropan-2-ol), have been synthesized and characterized by various physicochemical techniques. The Co(II) centers are connected by endogenous alkoxy bridge from L− and various extrinsic auxiliary linkers, some of which display coordination number asymmetry (5, 6-coordinated for 1 and 2; 5, 5-coordinated for 3). It is worth mentioning that complex 1 contains two rare reported μ3-η1, η1, η1-CrO42−  moieties. Susceptibility data of three complexes indicated intramolecular antiferromagnetic coupling of high-spin Co(II) atoms with exchange integral values (J) − 14.94 cm− 1, − 11.26 cm− 1 and − 13.66 cm− 1 for 1, 2 and 3, respectively. Interaction of compounds with calf thymus DNA (CT-DNA) have been investigated by absorption spectral titration, ethidium bromide (EB) displacement assay and viscosity measurement, which revealed that compounds bound to CT-DNA with a moderate intercalative mode, accompanied the affinities order: 1 > 2 ≈ 3. Three complexes exhibit oxidative cleavage of pBR322 plasmid DNA including a reliance on H2O2 as the activator. Compound 1 demonstrates an increased DNA cleavage activity as compared with 2 and 3, which could degrade super coiled DNA (SC DNA) into nicked coiled DNA (NC DNA) in lower concentration (5 μM). Moreover, all compounds could quench the intrinsic fluorescence of bovine serum albumin (BSA) in a static quenching process. Complex 1 also shows higher anticancer activity than cisplatin with lower IC50 value of incubation for both 24 h and 48 h.

Graphical abstractThe tetranuclear CoII complex, containing two rare μ3 -η1, η1, η1-CrO42−  moieties and bearing coordination number asymmetry, displays good DNA cleavage activity in a low concentration (5 μM) in the presence of H2O2.Figure optionsDownload full-size imageDownload as PowerPoint slide