Ni(II) Complexes with Schiff Base Ligands: Preparation, Characterization, DNA/Protein Interaction and Cytotoxicity Studies

Exploration of Antiproliferative Activity and Apoptosis Induction of New Nickel(II) Complexes Encompassing Carbazole Ligands

To attest the effectiveness of nickel complexes as anticancer drug candidates with minimum side effects, the present investigation describes the facile synthesis and anticancer activities of nickel(II) complexes enriched with three derivatives of carbazolone-based benzhydrazone ligands(L) having a [Ni(L)₂] composition. Analytical and spectral techniques were used to characterize the synthesized Ni(II) complexes. The single-crystal X-ray diffraction performed for complex 4 confirmed the square planar geometry with a [Ni(κ²-N,O-L)₂] arrangement. The MTT assay was carried out for the complexes to determine in vitro cytotoxicity against cancerous human-cervical carcinoma, human-colon carcinoma, and non-cancerous L929 (fibroblast) cells. All three complexes exhibited good toxicity against the cancer cells with a low IC₅₀ concentration. Complex 4, containing -OCH₃ fragment, exhibits high lipophilicity and revealed exceptional cytotoxicity against cancer cells. AO-EB fluorescent staining indicated apoptosis-associated cell morphological changes after exposure to complex 4. The apoptosis induction was further confirmed by a HOECHST-33342 fluorescent staining technique via chromosomal condensation and nuclear fragmentation. Further, reactive oxygen species (ROS) and mitochondrial membrane potential (MMP) mechanistic studies revealed that complex 4 can raise ROS levels and reduce MMP and promote mitochondrial dysfunction-mediated apoptotic cell death. Further, stimulation of late apoptosis by complex 4 in cervical cancer cells was quantitatively differentiated through the staining of phosphatidylserine externalization by flow cytometry. Furthermore, the ELISA analysis confirmed that complex 4 induced apoptosis through caspase activation.

Synthesis of an amantadine-based novel Schiff base and its transition metal complexes as potential ALP, α-amylase, and α-glucosidase inhibitors

A Schiff base ligand HL, (E)-2-((adamantan-1-ylimino)methyl)-6-allylphenol, was synthesized by condensation of amantadine with 3-allyl-2-hydroxybenzaldehyde, followed by the synthesis of its Zn(ii), Co(ii), Cr(iii), and VO(iv) complexes under reflux conditions. The synthesized compounds were comprehensively elucidated by using different spectroscopic and analytical techniques: UV-Vis, ¹H and ¹³C-NMR, FT-IR, ESI-MS, thermal, and single-crystal XRD analysis. The chemical composition of the synthesized compounds was also verified by molar conductance and elemental analysis. An octahedral geometry for Cr(iii) and Co(ii) complexes, tetrahedral for Zn(ii) complex, and square pyramidal geometry have been proposed for VO(iv) complexes. The antidiabetic activities of the synthesized compounds were also evaluated by performing in vitro α-amylase and α-glucosidase inhibition studies. The Co(ii) complex exhibited the highest α-glucosidase inhibitory activity, whereas oxovanadium(iv) and zinc(ii) complexes were also found to be effective against α-amylase. In alkaline phosphatase (ALP) inhibition studies, the HL was found to be inactive, while the complexes showed remarkable enzyme inhibition in the following order: VO > Zn > Co, in a concentration-dependent manner.

Synthesis, Structural Characterization, Hirshfeld Surface Analysis, and Antibacterial Study of Pd(II) and Ni(II) Schiff Base Complexes Derived from Aliphatic Diamine

A Schiff base bearing two methyl substituents, namely, 6,6'-((1E,1'E)-((2,2-dimethylpropane-1,3-diyl) bis(azanylylidene)) bis(methanylylidene)) bis(2-methylphenol) [H₂AD1Me] was synthesized and characterized through physicochemical and spectroscopic analyses. Then, the Schiff base was complexed with Pd(II) and Ni(II) to form [Pd(AD1Me)] and [Ni(AD1Me)], respectively. Both metal complexes were successfully obtained and characterized through several analyses, viz., melting point, elemental analysis, molar conductivity, magnetic susceptibility, FTIR, ¹H NMR, UV-vis, and single crystal X-ray diffraction. A quantitative analysis of the intermolecular interactions in the crystal structures has been performed using Hirshfeld surface analysis. Both metal complexes were crystallized in a monoclinic crystal system with the space group of P2₁/c. Additionally, the deprotonated phenolic oxygen atom (O1/O2) and azomethine nitrogen atom (N1/N2) of the ligand chelate the Pd(II) and Ni(II) ions, forming a slightly distorted square-planar complex containing three six-membered rings encircling the metal core with dsp² hybridization. The shift of ν(C=N) to a higher frequency in FTIR by 26-28 cm^-1 indicated that the complexation to Pd(II) and Ni(II) through the azomethine N was established. It was further supported through the shifting of the azomethine proton signal to higher or lower chemical shifts with Δδ = 0.43-1.15 ppm in ¹H NMR. In addition, the shifting of the n-π*(C=N) band in UV-vis spectra with Δλ = 24-40 nm indicated the involvement of azomethine nitrogen in the complexation. All the compounds showed no significant antibacterial activity against three bacterial strains, namely, Staphylococcus aureus subsp. aureus Rosenbach (ATCC 6538), Streptococcus mutans Clarke (ATCC 700,610), and Proteus vulgaris (ATCC 6380), as the percent growth inhibition calculated was less than 90%.

Interaction between laccase and diethylstilbestrol based on multispectral and chromatography analyses

Diethylstilbestrol (DES) is a synthetic form of oestrogen that does not easily degrade in the environment and can be harmful to human health. Herein, the mechanism of the interaction between laccase and DES was investigated by various spectroscopic means and high-performance liquid chromatography (HPLC). The results of fluorescence experiments showed that the quenching of intrinsic fluorescence of laccase by DES was due to a static quenching, forming a binding site. According to the Förster non-radiative energy transfer theory (FRET), the action distance R₀ between DES and laccase was 4.708 nm, r was 5.81 nm, and the energy transfer efficiency E was 22.08%, respectively. Both UV-Vis absorption spectra and FT-IR spectra indicated changes in the conformation and surroundings of the enzyme and changed in the secondary structure of laccase. Multispectral synthesis showed that the interaction of laccase with DES caused a change in the secondary structure of laccase. The degradation experiments showed that laccase could degrade DES, and the DES content decreased with time. This study provides a new theoretical basis and experimental method for further research on the reaction mechanism of the laccase degradation of DES. It may also provide a reference basis for human biological and environmental safety evaluations.

Multi-stage screening to predict the specific anticancer activity of Ni(II) mixed-ligand complex on gastric cancer cells; biological activity, FTIR spectrum, DNA binding behavior and simulation studies

The anticancer activity of a transition metal complex with [Ni(L¹)₂L²]H₂O (where L¹ and L² were acetylacetonato (acac) and 2-aminopyridine (2-ampy), respectively) was evaluated in MKN45 cell line. Methyl thiazolyl tetrazolium (MTT) assay was performed to assess the antitumor capacity of the Ni(II) complex against gastric cancer cell line MKN45. The complexexhibited high in vitro antitumor activity against MKN45 cells with IC₅₀values of 1.99 μM in 48 hrs. The alterations in the structure of cellular biomolecules (proteins, lipids, carbohydrates, and especially DNA) by the Ni(II) complex were confirmed by bio spectroscopic studies. Fourier Transformed Infrared (FTIR) spectroscopy analysis revealed significant differences between untreated and treated MKN45 cell line in the region of glycogen, nucleic acid, amide I and amide II bands (1000, 1100, ~1650, and ~1577 cm^-1). The absorption bands 1150 cm^-1 and 1020-1025 cm^-1 can be assigned to the CO bond of glycogen and other carbohydrates and are significantly overlapped by DNA. The interaction of calf thymus (CT) DNA with Ni(II) complex was explored using absorption spectral method. The UV-visible studies demonstrated that this complex was able to bind with DNA via groove, non-covalent, and electrostatic interactions, and binding constant (K_b) was found to be 3 * 10⁴. Docking simulation and Non Covalent Interaction (NCI) topological analysis were conducted to provide insights into the nature of DNA/complex interactions. The binding affinity and binding stability of complex was validated by 400-ns MD simulations.

The damage of the Watson-Crick base pairs by nickel nanoparticles: A first-principles molecular dynamics study

The nickel nanoparticles are harmful atmospheric pollutants, and the damage caused by them in humans has become a topic of great relevance. In this study we investigate the interaction of the Ni2 and Ni3 clusters with the AT and GC Watson-Crick base pairs in an aqueous medium. Molecular dynamics in combination with density functional theory are employed. A novel method is implemented to create realistic thermodynamic conditions (NVT) in the simulations. The energies, the charges of the interacting compounds, the temperature changes, and the geometric rearrangements are reported. The results show the formation of stable organometallic compounds of the nickel nanoparticles with the DNA nucleic acid bases. In this respect, the biological processes where the DNA is implicated may be altered by the formation of such super-structures.

Developing novel zinc(ii) and copper(ii) Schiff base complexes: combined experimental and theoretical investigation on their DNA/protein binding efficacy and anticancer activity

Zn(ii) and Cu(ii) Schiff base complexes having DNA and HSA binding efficacy have been exploited as cancer therapeutic agents.

Ultrasonic assisted fabrication of first MoO3/copper complex bio-nanocomposite based on Sesbania sesban plant for green oxidation of alcohols

MoO₃ nanoparticles were obtained using Sesbania sesban. Novel Schiff base ligand and its nanocomplex of copper were synthesized under ultrasonic irradiation. First MoO₃/Copper Schiff base complex nanocomposite (NMCS) based on this natural plant was prepared and characterized by TEM, SEM, AFM, FT-IR, TGA, EDAX and elemental analysis. Then atom-efficient and selective oxidation of alcohols using hydrogen peroxide catalyzed by NMCS bio-nanocomposite under ultrasonic irradiation was reported. Structurally diverse set of alcohols was transformed into desired aldehyde and ketone products with high conversion and excellent selectivity under solvent free conditions. Products were isolated easily from green media, and the catalyst could be reused six times without any appreciable decrease in catalytic activity and selectivity.

Functional Analysis of Novicidin Peptide: Coordinated Delivery System for Zinc via Schiff Base Ligand

Novicidin (NVC), is a membrane-penetrating peptide, which forms a stable complex with Zn-Schiff base with interesting antitumor selectivity. We studied NVC derivatives to determine functional roles of key amino acids in toxicity, helicity, and binding of the Zn-Schiff base complex. Trimmed derivatives highlighted the role of peptide length and helicity in toxicity and membrane penetration. The removal of Lys from position 1 and 2 strongly increases the ability to disrupt the membranes. The trimming of the N-terminal residues significantly increases the stability of peptide helicity enhancing penetrating properties. Gly residue derivatives undermined a role of peptide bending in membrane penetration and toxicity. After the substitution of the central Gly derivatives with Ile or Lys, the peptides retained toxicity. These results illustrate the minor role of central helix bending in NVC toxicity. Binding-site-peptide derivatives identified His residue as the sole Zn-Schiff base binding site and eliminated the role of other aromatic residues.

EPR and electrochemical interpretation of bispyrazolylacetate anchored Ni(ii) and Mn(ii) complexes: cytotoxicity and anti-proliferative activity towards human cancer cell lines

The cytotoxicity and antiproliferative activity are carried out along with EPR and redox interpretation.