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Two new copper clusters, {Cu4} and {Cu4Cd6}, with polydentate aminoalcohol ligands, diethanol propanolamine (H3L1) and bis–tris{2-[bis(2-hydroxyethyl)amino]-2-(hydroxymethyl)propane-1,3-diol} (H6L2), have been synthesized under mild conditions and characterized thoroughly by single-crystal X-ray diffraction (XRD), infrared spectroscopy, elemental analysis, powder XRD, magnetic and DFT studies, and absorption and fluorescence spectroscopy. The cluster {Cu4} exhibits a rare tetranuclear copper cubane core whereas {Cu4Cd6} forms an unusual heterometallic cage owing to the introduction of the second metal Cd into the ligand. A hexapodal ligand (H6L2) with N and O donor atoms was chosen deliberately for the construction of a high-nuclearity cluster, i.e., {Cu4Cd6}. Interestingly, both the clusters displayed significant cytotoxicity towards human cervical (HeLa) and lung (A549) cancer cells as evident from the shallow IC50 values [15.6 ± 0.8 μM (HeLa), 18.5 ± 1.9 μM (A549) for {Cu4}, and 11.1 ± 1.5 μM (HeLa), 10.2 ± 1.3 μM (A549) for {Cu4Cd6}] obtained after a 24 h incubation. However, moderate toxicity was observed toward immortalized lung epithelial normal cells (HPL1D) with IC50 values of 32.4 ± 1.2 μM for {Cu4} and 27.6 ± 1.7 μM for {Cu4Cd6}. A cellular apoptotic study using HeLa cells revealed that the {Cu4} cluster triggered apoptosis at both the early and late phases while the {Cu4Cd6} cluster facilitate apoptosis mainly at the late apoptotic stage. A standard 2′,7′-dichlorodihydrofluorescein-diacetate (DCFH-DA) test affirms that both the clusters enhanced ROS production inside the cancer cells, responsible for promoting cell apoptosis. The decanuclear {Cu4Cd6} clusters demonstrated better anticancer activity compared to the tetranuclear {Cu4} clusters, indicating the role of high nuclearity and additional Cd metal in the enhanced intracellular production of ROS. [ABSTRACT FROM AUTHOR]

Two mononuclear complexes of Co(II) and Zn(II) with a [MO6] coordination sphere, [Co(L)2(H2O)2] (1) and [Zn(L)2(H2O)2] (2), are prepared and characterized through spectral, single crystal X-ray and DFT/TD-DFT studies. The X-ray structure reveals an octahedral geometry with all the oxygen donor sets around the metal ion. DFT studies confirm the cobalt complex is high spin with a +2 oxidation state. Time dependent density functional theory (TD-DFT) shows the electronic transitions to be metal to ligand (MLCT) and intra-ligand charge transfer (ILCT) type. The complexes consolidate the crystal lattice via extensive non-covalent interactions, which are verified by Hirshfeld surface analysis. These non-covalent interactions are also responsible for the enhanced DNA binding affinity of the complexes as confirmed theoretically by molecular docking studies. The Zn(II) complex binds to DNA with more affinity due to the lesser HOMO–LUMO energy gap calculated by DFT analysis. The complexes are assessed for catecholase like activity for oxidation of 3,5-DTBC to 3,5-DTBQ in ethanol. 1 shows catecholase activity with the parameters Kcat = 168.5 h−1, KM = 0.00043 M and Vmax = 4.68 × 10−2 M min−1. ESI-MS identifies possible intermediates formed during the catalytic cycle while EPR and cyclic voltammetry confirm the mechanism of the catalytic oxidation to be metal centered rather than radical formation. The catecholase activity of 1 and inactivity of 2 are also corroborated by density functional theory (DFT) analysis. The theoretical analysis results are in good agreement with the experimental findings concerning the structure, electronic spectra, DNA binding affinity and catecholase like activity. Most interestingly, the present Co(II) complex is discovered to be a better catecholase mimic and the activity could be tuned by modifications in the metal or structural features of the ligand(s) and complexes. [ABSTRACT FROM AUTHOR]

A new mixed valence antiferromagnetic Co7 disc characterized by spectral, crystallographic and magnetic studies exhibited a solvent dependent catecholase activity with Kcat(MeOH) = 2026 h−1. This report demonstrates the first example of a discrete heptanuclear disc showing solvent dependent catecholase activity. [ABSTRACT FROM AUTHOR]