Synthesis, characterization and biological application of four novel metal-Schiff base complexes derived from allylamine and their interactions with human serum albumin: Experimental, molecular docking and ONIOM computational study

Structural features and antiproliferative activity of Pd(II) complexes with halogenated ligands: a comparative study between Schiff base and reduced Schiff base complexes

In order to investigate the structural features and antiproliferative activity of Pd(II) complexes containing halogenated ligands with different flexibility, several Schiff base and reduced Schiff base Pd(II) complexes, namely X1X2PicPd, X1X2PyPd, X1X2Pic(R)Pd, and X1X2Py(R)Pd (where X1 = X2 = Cl, Br and I; Pic: 2-picolylamine; Py = 2-(2-pyridyl)ethylamine), were synthesized and characterized by spectroscopic methods and, in the case of Br2PyPd, Cl2Py(R)Pd and ClBrPy(R)Pd, also by X-ray crystallography. The results of the X-ray crystallography showed that in both series of complexes the Pd(II) ion has a distorted square-planar geometry, although the coordination modes of the two ligands are different. In the Schiff base-type complexes the ligand acts as a tridentate chelate with NN'O donor atoms, whereas in the reduced Schiff base-type complexes the ligand acts as a bidentate chelate with NN' donor atoms. In both series of complexes, the chloride ions occupy the residual coordination sites of the Pd(II) ion. TD-DFT calculations were performed for a better understanding of the UV-Vis spectra. From these calculations it was found that the signal appearing at ∼400 nm in the complexes with reduced Schiff base ligands (X1X2Pic(R)Pd and X1X2Py(R)Pd) is mainly due to a HOMO → LUMO transition, while for the Schiff base complex ClBrPyPd the signal is due to a HOMO → LUMO+1 transition. For the complex I2PicPd, combinations of HOMO-4 → LUMO and HOMO-2 → LUMO transitions were found to be responsible for that signal. In regard to the biological activity profile, all complexes were first investigated as proteasome inhibitors by fluorometric methods. From these enzymatic assays, it emerged that they are good inhibitors with IC50 values in the low-micromolar range and that their inhibitory activity is strictly related to the presence of the metal ion. Subsequently they were also subjected to cell-based assays (the resazurin method) to assess their antiproliferative properties by using two leukemic cell lines, namely the drug-sensitive CCRF-CEM cell line and its multidrug-resistant sub-cell line CEM/ADR5000. In this test they displayed IC50 values in the sub-micromolar and low-micromolar range determined for a selected metal complex (Br2Pic(R)Pd) and ligand (Cl2Pic(R)), respectively. Moreover, docking studies were performed on the two expected molecular targets, i.e. proteasome and DNA, to shed light on the mechanisms of action of these types of Pd(II) complexes.

Antitumor Properties of a New Macrocyclic Tetranuclear Oxidovanadium(V) Complex with 3-Methoxysalicylidenvaline Ligand

A wide variety of metal-based compounds have been obtained and studied for their antitumor activity since the intensely used cytostatic drugs (e.g., cisplatin) failed to accomplish their expected pharmacological properties. Thus, we aimed to develop a new vanadium-based drug and assess its antitumor properties using the human hepatocarcinoma (HepG2) cell line. The compound was synthesized from vanadyl sulfate, DL-valine, and o-vanillin and was spectrally and structurally characterized (UV-Vis, IR, CD, and single-crystal/powder-XRD). Compound stability in biological media, cell uptake, and the interaction with albumin were assessed. The mechanisms of its antitumor activity were determined compared to cisplatin by performing cytotoxicity, oxidative and mitochondrial status, DNA fragmentation, β-Tubulin synthesis investigation, and cell cycle studies. Herein, we developed a macrocyclic tetranuclear oxidovanadium(V) compound, [(V^VO)(L)(CH₃O)]₄, having coordinated four Schiff base (H₂L) ligands, 3-methoxysalicylidenvaline. We showed that [(V^VO)(L)(CH₃O)]₄: (i) has pH-dependent stability in biological media, (ii) binds to albumin in a dose-dependent manner, (iii) is taken up by cells in a time-dependent way, (iv) has a higher capacity to induce cell death compared to cisplatin (IC₅₀ = 6 μM vs. 10 μM), by altering the oxidative and mitochondrial status in HepG2 cells. Unlike cisplatin, which blocks the cell cycle in the S-phase, the new vanadium-based compound arrests it in S and G2/M-phase, whereas no differences in the induction of DNA fragmentation and reduction of β-Tubulin synthesis between the two were determined. Thus, the [(V^VO)(L)(CH₃O)]₄ antitumor mechanism involved corroboration between the generation of oxidative species, mitochondrial dysfunction, degradation of DNA, cell cycle arrest in the S and G2/M-phase, and β-Tubulin synthesis reduction. Our studies demonstrate the potent antitumor activity of [(V^VO)(L)(CH₃O)]₄ and propose it as an attractive candidate for anticancer therapy.

Cytotoxic oxidovanadium(IV) complexes of tridentate halogen-substituted Schiff bases: First dinuclear V(IV) complexes with O → VIV = O → VIV = O core

The reaction of potentially N,N,O-tridentate Schiff base ligands, Cl-LH, Br-LH, BrCl-LH and H-LH, with [V^IVO(acac)₂] in 2:1 ratio in methanol gave the corresponding mononuclear and dinuclear oxidovanadium(IV) complexes, VO(Cl-L)₂ (1), VO(Br-L)₂ (2), [(BrCl-L)₂(H₂O)V(μ-O)VO(BrCl-L)₂] (3) and [(H-L)₂(H₂O)V(μ -O)VO(H-L)₂] (4), in good yields. The ligands and complexes were fully characterized by elemental analysis and FT-IR spectroscopy. The ligands were also characterized by ¹H NMR spectroscopy. The oxidation state of V(IV)O with d¹ configuration in all synthesized complexes was confirmed by EPR. Moreover, the structures of 2 and 3 were determined by X-ray diffraction (XRD) analysis which revealed them as mono- and dinuclear vanadium(IV) complexes, respectively, with the ligands coordinated as bidentate chelates. The structure of 3 represents the first example of dinuclear V(IV) complex with O → V^IV = O → V^IV = O core (Cambridge Structural Database (CSD)​, version 5.42, update of May 2021). The cytotoxicity of ligands and complexes was evaluated towards ovarian (A2780), breast (MCF7) and prostate (PC3) cancer cells at 48 h. While ligands showed modest IC₅₀ values (>42 μM), all complexes turned out to be effective in the range 3.9-17.2 μM. In particular, A2780 and MCF7 cell lines were the most sensitive to the newly synthesized V(IV)O complexes.

Synthesis, Characterization, and In Vitro Insulin-Mimetic Activity Evaluation of Valine Schiff Base Coordination Compounds of Oxidovanadium(V)

Type 2 diabetes became an alarming global health issue since the existing drugs do not prevent its progression. Herein, we aimed to synthesize and characterize a family of oxidovanadium(V) complexes with Schiff base ligands derived from L-/D-valine (val) and salicylaldehyde (sal) or o-vanillin (van) as insulin-mimetic agents and to assess their potential anti-diabetic properties. Two new oxidovanadium(V) complexes, [{VVO(R-salval)(H2O)}(μ2-O){VVO(R-salval)}] and [{VVO(R-vanval)(CH3OH)}2(μ2-O)], and their S-enantiomers were synthesized and characterized. The compounds exhibit optical activity as shown by crystallographic and spectroscopic data. The stability, the capacity to bind bovine serum albumin (BSA), the cytotoxicity against human hepatoma cell line, as well as the potential anti-diabetic activity of the four compounds are investigated. The synthesized compounds are stable for up to three hours in physiological conditions and exhibit a high capacity of binding to BSA. Furthermore, the synthesized compounds display cytocompatibility at biologically relevant concentrations, exert anti-diabetic potential and insulin-mimetic activities by inhibiting the α-amylase and protein tyrosine phosphatase activity, and a long-term increase of insulin receptor phosphorylation compared to the insulin hormone. Thus, the in vitro anti-diabetic potential and insulin-mimetic properties of the newly synthesized oxidovanadium(V) compounds, correlated with their cytocompatibility, make them promising candidates for further investigation as anti-diabetic drugs.

Synthesis and Biological Screening of New 4-Hydroxycoumarin Derivatives and Their Palladium(II) Complexes

Two newly synthesized 4-hydroxycoumarin bidentate ligands (L1 and L2) and their palladium(II) complexes (C1 and C2) were screened for their biological activities, in vitro and in vivo. Structures of new compounds were established based on elemental analysis, ¹H NMR, ¹³C NMR, and IR spectroscopic techniques. The obtained compounds were tested for their antioxidative and cytotoxic activities and results pointed to selective antiradical activity of palladium(II) complexes towards ^•OH and ^-•OOH radicals and anti-ABTS (2,2′-Azino-bis(3-ethylbenzothiazoline-6-sulfonic acid) cation radical) activity comparable to that of ascorbate. Results indicated the effect of C1 and C2 on the enzymatic activity of the antioxidative defense system. In vitro cytotoxicity assay performed on different carcinoma cell lines (HCT166, A375, and MIA PaCa-2), and one healthy fibroblast cell line (MRC-5) showed a cytotoxic effect of both C1 and C2, expressed as a decrease in carcinoma cells' viability, mostly by induction of apoptosis. In vivo toxicity tests performed on zebrafish embryos indicated different effects of C1 and C2, ranging from adverse developmental effect to no toxicity, depending on tested concentration. According to docking studies, both complexes (C1 and C2) showed better inhibitory activity in comparison to other palladium(II) complexes.

Enhancement of Schiff base biological efficacy by metal coordination and introduction of metallic compounds as anticovid candidates: a simple overview

In the prevailing apocalyptic times of coronavirus disease (COVID-19), the whole scientific community is busy in designing anticovid drug or vaccine. Under such a fascination, Schiff bases or azomethine compounds are continuously interrogated for antimicrobial properties. These compounds represent interesting molecular scaffolds of huge medicinal and industrial relevance. In order to update the current literature support of such facts this article introduces the synthetic chemistry, mechanism of formation of a Schiff base, followed by biological efficacy and finally a suitable discussion on the mechanism of respective bioactivity. In most of the studies revealing the biological evaluation of azomethine functionalized frameworks, fascinated results have been recorded in case of azomethine-metal complexes as compared with the free ligands. Also, the CH=N or C=N form of organic ligands have indicated marvellous results. Therefore, in connection with the biological relevance and microbicidal implications of such metallic compounds, this works reviews the current update of microorganism fighting efficacy of azomethine metal complexes along with the introduction of some metallodrugs as excellent candidates having COVID-19 defending potentiality.

Computational investigation of molecular structures, spectroscopic properties and antitumor-antibacterial activities of some Schiff bases

Molecular structures, spectroscopic properties (IR, ¹H NMR and ¹³C NMR, UV-VIS), molecular electrostatic potential maps and some molecular properties (ionization energy, electron affinity, energy gap, hardness, electronegativity, electrophilicity index, static dipole moment and average linear polarizability) of three Schiff bases which are 2-((ethylamino)methyl)-6-methoxyphenol (HL1), 2-((ethylamino) methyl)-6-methylphenol (HL2) and 2-((ethylamino)methyl)-6-chlorophenol (HL3) were computed at B3LYP/6-31G(d) level in aqueous phase. The effects of methoxy, methyl and chloro substituents on Schiff bases were examined and it was found that the electron donating property of methyl and chlorine substituents was higher than the methoxy substituent. In order to investigate the antitumor activities of Schiff bases were docked against the breast cancer (MCF7) cell line. Molecular docking results were compared with antitumor standard 5-fluorouracil. Antitumor activity of HL2 and HL3 molecule was found to be higher than HL1 against MCF-7 cell line. In addition, in order to predict the antibacterial activities of Schiff bases were docked against the Mycobacterium tuberculosis (H37Rv) cell line. Docking results were compared with the antibacterial reference N-(salicylidene)-2-hydroxyaniline. Antibacterial activity of HL2 and HL3 molecules was found to be higher than HL1. It is estimated that the binding of the electron donating group to the ortho position of the hydroxyl group in studied Schiff bases increases both antitumor and antibacterial activity.

Biological and catalytic potential of sustainable low and high valent metal-Schiff base sulfonate salicylidene pincer complexes

ONO-Pincer Schiff base salicylidene (HSaln ligand) complexes with VO2+, UO2 2+, MoO2 2+ and Mn2+ ions (MSaln complexes = VOSaln, UO2Saln, MoO2Saln and MnSaln, respectively) were synthesized and fully characterized by different physico-chemical tools. The VOSaln complex was further treated with 1,10-phenanthroline which afforded a new VO-complex (VOSaln-Ph). All complexes and their ligands, as eco-friendly reagents, were explored for their biological potential as antibacterial and antifungal agents. Reactivity of MSaln complexes against the tested pathogen strains exhibited a remarkable inhibitory effect compared to the coordinated ligand (HSaln) and applicable standard drugs. Moreover, the MSaln complex-DNA interaction was investigated by ultraviolet-visible spectroscopy, viscosity and gel electrophoresis techniques affording binding strengths in the order: UO2Saln > MnSaln > MoO2Saln > VOSaln-Ph > VOSaln. Additionally, the biological potential of the investigated compounds was further explored by molecular docking to illustrate the nature of the drug-DNA interactions. All MSaln complexes show respectable anti-proliferative potential as anticancer agents against selected human carcinoma cell lines. Aside from the biological activities these complexes (MSaln complexes) were also investigated for catalytic efficiency in the Suzuki-Miyaura cross-coupling system of phenylboronic acid with 2-bromopyridine in water, sustainably. The results indicated that the MnSaln catalyst performed well with high yield. The catalytic potential of MnSaln was compared in water, water-ionic liquid mixtures and ionic liquids.

Synthesis of spherical Fe3O4 nanoparticles from the thermal decomposition of iron (III) nano-structure complex: DFT studies and evaluation of the biological activity

A novel Fe(III) Schiff base complex of the [FeL₂(NO₃)₂]NO₃ type where L = 2-((pyridin-4-yl)methyleneamino)-3-aminomaleonitrile was synthesized using the reflux and sonochemical methods and their antibacterial and antifungal activity were evaluated. The nanoparticles of iron oxide (Fe₂O₃) were obtained from the iron nano-structure complex as a precursor after calcination at 600 ˚C for 3 h. All the synthesized compounds were characterized by various spectroscopic techniques. The results of SEM showed that the morphology of iron nano-structure complex was rod-like while the morphology of the Fe₂O₃ nano powder was spherical. The results of the biological studies indicated that the iron nano-structure complex showed a stronger antibacterial and antifungal efficiency than its bulk complex. Finally, the empirical geometrical parameters of complexes revealed a good agreement with calculated ones at DFT-B3LYP level.

Novel insights into the effect of folate–albumin binding on the transport of ascorbic acid as an anticancer agent: chemometric analysis based on combined spectroscopic and electrochemical studies

The electrochemical behavior of ascorbic acid and folic acid upon their interaction with albumin is investigated using electrochemical, chemometric and docking studies.

DNA and HSA interaction of Vanadium (IV), Copper (II), and Zinc (II) complexes derived from an asymmetric bidentate Schiff-base ligand: multi spectroscopic, viscosity measurements, molecular docking, and ONIOM studies

The interaction of three complexes [Zn(II), Cu(II), and V(IV)] derived from an asymmetric bidentate Schiff-base ligand with DNA and HSA was studied using fluorescence quenching, UV-Vis spectroscopy, viscosity measurements, and computational methods [molecular docking and our Own N-layered Integrated molecular Orbital and molecular Mechanics (ONIOM)]. The obtained results revealed that the DNA and HSA affinities for binding of the synthesized compounds follow as V(IV) > Zn(II) > Cu(II) and Zn(II) > V(IV) > Cu(II), respectively. The distance between these compounds and HSA was obtained based on the Förster's theory of non-radiative energy transfer. Furthermore, computational molecular docking was carried out to investigate the DNA- and HSA-binding pose of the compounds. Molecular docking calculations showed that H-bond, hydrophobic, and π-cation interactions have dominant role in stability of the compound-HSA complexes. ONIOM method was utilized to investigate the HSA binding of the compounds more precisely in which molecular-mechanics method (UFF) and semi-empirical method (PM6) were selected for the low layer and the high layer, respectively. The results show that the structural parameters of the compounds changed along with binding, indicating the strong interaction between the compounds with HSA and DNA. Viscosity measurements as well as computational docking data suggest that all metal complexes interact with DNA, presumably by groove-binding mechanism.