Novel {Cu} and {CuCd} clusters derived from flexible aminoalcohols: synthesis, characterization, crystal structures, and evaluation of anticancer properties.

Two new copper clusters, {Cu} and {CuCd}, with polydentate aminoalcohol ligands, diethanol propanolamine (HL) and bis-tris{2-[bis(2-hydroxyethyl)amino]-2-(hydroxymethyl)propane-1,3-diol} (HL), 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 {Cu} exhibits a rare tetranuclear copper cubane core whereas {CuCd} forms an unusual heterometallic cage owing to the introduction of the second metal Cd into the ligand. A hexapodal ligand (HL) with N and O donor atoms was chosen deliberately for the construction of a high-nuclearity cluster, i.e., {CuCd}. Interestingly, both the clusters displayed significant cytotoxicity towards human cervical (HeLa) and lung (A549) cancer cells as evident from the shallow IC values [15.6 ± 0.8 μM (HeLa), 18.5 ± 1.9 μM (A549) for {Cu}, and 11.1 ± 1.5 μM (HeLa), 10.2 ± 1.3 μM (A549) for {CuCd}] obtained after a 24 h incubation. However, moderate toxicity was observed toward immortalized lung epithelial normal cells (HPL1D) with IC values of 32.4 ± 1.2 μM for {Cu} and 27.6 ± 1.7 μM for {CuCd}. A cellular apoptotic study using HeLa cells revealed that the {Cu} cluster triggered apoptosis at both the early and late phases while the {CuCd} 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 {CuCd} clusters demonstrated better anticancer activity compared to the tetranuclear {Cu} clusters, indicating the role of high nuclearity and additional Cd metal in the enhanced intracellular production of ROS.