Two new metal complexes, namely, [Zn₂(LH)₂(N₃)₄] (1) and [Cu(L)(N₃)] (2), have been derived from a Schiff base ligand, (E)-2-(((2-(piperidine-2-yl)ethyl)imino)methyl)phenol (HL), employing azide as the secondary anionic residue. Single crystal structural analyses suggest the protonation of piperidine N during the crystallization of the dinuclear motif of complex 1, which is non-operative in the case of complex 2, governing the diverse denticity of the ligand backbone. After a thorough characterization, the complexes are investigated to check their bio-medical applications. Both complexes exhibit impressive binding efficacy with CT DNA as well as Human Serum Albumin (HSA) protein, as revealed from their electronic spectroscopic measurements. A sharp fluorescent quenching of the DNA-EtBr conjugate and HSA protein was encountered separately via the addition of complexes 1 and 2 with the quenching constant in the order of ∼10⁵ M⁻¹. A theoretical inspection through the molecular docking study has also been introduced to justify the experimental outcomes along with the determination of the interaction site and energy. Finally, both complexes are tested for anticancer activity using HeLa (cervical cancer cell) and PA1 (ovarian cancer cell) cell lines through the in vitro MTT assay, which suggests a better cancer cell killing efficacy of complex 2. The applicability of complexes 1 and 2 within the normal cell (hEG) has been concurred through the determination of much higher LD₅₀ values, indicating significantly lower cytotoxic effect on the normal cell line. Furthermore, the haemolysis assay indicates no consequential impact of complexes (1 and 2) on the RBC. Finally, the anti proliferative activities of both the complexes towards carcinoma cell lines were analysed through various nuclear and cellular staining techniques, unveiling the cell death mechanism.

A new versatile azide-bridged polymeric Cu­(II) complex, namely, [Cu­(L)­(μ1,3-N3)]∞ (1), was synthesized utilizing an N,N,O-donor piperidine-based Schiff base ligand (E)-4-bromo-2-((2-(-1-yl)­imino)­methyl)­phenol (HL), obtained via the condensation reaction of 1-(2-aminoethyl) piperidine and 5-bromo salicylaldehyde. The single-crystal X-ray diffraction analysis reveals that complex 1 consists of an end-to-end azido-bridged polymeric network, which is further rationalized with the help of a density functional theory (DFT) study. After routine characterization with a range of physicochemical studies, complex 1 is exploited to evaluate its biomedical potential. Initially, theoretical inspection with the help of a molecular docking study indicated the ability of complex 1 to effectively bind with macromolecules such as DNA and the human serum albumin (HSA) protein. The theoretical aspect was further verified by adopting several spectroscopic techniques. The electronic absorption spectroscopic analysis indicates a remarkable binding efficiency of Complex 1 with both DNA and HSA. The notable fluorescence intensity reduction of the ethidium bromide (EtBr)–DNA adduct, 4′,6-diamidino-2-phenylindole (DAPI)–DNA adduct, and HSA after the gradual addition of complex 1 authenticates its promising binding potential with the macromolecules. The retention of the canonical B form of DNA and α form of HSA during the association of complex 1 was confirmed by implementing a circular dichroism spectral study. The association ability of complex 1 with macromolecules further inspired us to inspect its impact on different cell lines such as HeLa (cervical cancer cell), PA1 (ovarian cancer cell), and HEK (normal cell). The dose-dependent and time-dependent in vitro 3-(4,5-dimethylthiazol-2-yl)-2,5-diphenyltetrazolium bromide (MTT) assay suggests an effective antiproliferative property of complex 1 with low toxicity toward the normal cell line. Finally, the anticancer activity of complex 1 toward carcinoma cell lines was analyzed by nuclear and cellular staining techniques, unveiling the cell death mechanism.

A new quercetin-based iron(III) cationic complex [Fe(Qr)Cl(H₂O)(MeO)] (complex 1) is created in the current study by condensation of quercetin with ferric chloride in the presence of Et₃N. Comprehensive spectroscopic analysis and conductometric measurement are used to pinpoint complex 1. The generated complex's +3-oxidation state has been verified by electron paramagnetic resonance (EPR) research. Density functional theory analysis was used to structurally optimize the structure of complex 1. Before biomedical use, a variety of biophysical studies are implemented to evaluate the binding capacity of complex 1 with DNA and human serum albumin (HSA) protein. The findings of the electronic titration between complex 1 and DNA, as well as the stunning fall in the fluorescence intensities of the HSA and EtBr-DNA/DAPI-DNA domain after complex 1 is gradually added, give us confidence that complex 1 has a strong affinity for both macromolecules. It is interesting to note that the displacement experiment confirms partial intercalation as well as the groove binding mechanism of the title complex with DNA. The time-dependent fluorescence analysis indicates that after interaction with complex 1, HSA will exhibit static quenching. The thermodynamic parameter values in the HSA-complex 1 interaction provide evidence for the hydrophobicity-induced pathway leading to spontaneous protein-complex 1 interaction. The two macromolecules' configurations are verified to be preserved when they are associated with complex 1, and this is done via circular dichroism spectral titration. The molecular docking investigation, which is a theoretical experiment, provides complete support for the experimental findings. The potential of the investigated complex to be an anticancer drug has been examined by employing the MTT assay technique, which is carried out on HeLa cancer cell lines and HEK-293 normal cell lines. The MTT assay results validate the ability of complex 1 to display significant anticancer properties. Finally, by using the AO/PI staining approach, the apoptotic-induced cell-killing mechanism as well as the detection of cell morphological changes has been confirmed.