Synthesis, characterization and DFT study of new water-soluble aluminum(III), gallium(III) and indium(III) Schiff base complexes: effect of metal on the binding propensity with bovine serum albumin in water

Water-soluble Schiff base ligands and metal complexes: an overview considering green solvent

The water-soluble metal complexes with Schiff base (SB) ligands are of great interest to green chemistry researchers due to their stability, cost-effectiveness, eco-friendly, electron-donating ability, and various applications. They have high potential to express their biological activity including anti-inflammatory, anticancer, antibacterial, antifungal, antioxidant, and DNA binding and cleavage. In the recent era, transition metal complexes have played a significant role in different processes such as hydrogenation, carbonylation, oxidation, reduction, epoxidation, hydrolysis, decomposition, and polymerization reactions in industry. However, their limited aqueous solubility may be the major limitation to their potential catalytic, industrial, and clinical applications. In industrial catalytic processes, it has been proven that water can be used as a solvent to minimize the environmental effect of different reactions as well as simple and complete separation. Water is a green solvent, flexible, non-toxic, safe, readily available, environmentally harmless, and inexpensive. Attaching different substituents on Schiff bases enhances the water solubility and catalytic activity. Studies on water-soluble SB complexes will explore these aspects and their prospects for the future evolution of their diverse applications.

Synthesis, Spectral Characterization, Thermal Investigation, Computational Studies, Molecular Docking, and In Vitro Biological Activities of a New Schiff Base Derived from 2-Chloro Benzaldehyde and 3,3'-Dimethyl-[1,1'-biphenyl]-4,4'-diamine

The current research involves the synthesis of a new Schiff base through the reaction between 2-chlorobenzaldehyde and 3,3'-dimethyl-[1,1'-biphenyl]-4,4'-diamine by using a natural acid catalyst and a synthesized compound physicochemically characterized by X-ray diffraction, Fourier transform infrared spectroscopy, 1H- and 13C-nuclear magnetic resonance, and liquid chromatography-mass spectrometry. Thermal studies were conducted using thermogravimetric, differential thermal analysis, and differential thermogravimetric curves. These curves were obtained in an inert nitrogen environment from ambient temperature to 1263 K using heating rates of 10, 15, and 20 K·min-1. Using thermocurve data, model-free isoconversional techniques such as Kissinger-Akahira-Sunose, Flynn-Wall-Ozawa, and Friedman are used to determine kinetic parameters. These parameters include activation energy, phonon frequency factor, activation enthalpy, activation entropy, and Gibb's free energy change. All of the results have been thoroughly investigated. The molecule's anti-inflammatory and antidiabetic properties were also examined. To learn more about the potential of the Schiff base and how successfully it can suppress the amylase enzyme, a molecular docking experiment was also conducted. For in silico research, the Swiss Absorption, Distribution, Metabolism, Excretion, and Toxicity algorithms were used to calculate the theoretical pharmacokinetic properties, oral bioavailability, toxic effects, and biological activities of the synthesized molecule. Moreover, the cytotoxicity tests against a human lung cancer cell line (A549) using the 3-(4,5-dimethylthiazol-2-yl)-2,5-diphenyltetrazolium bromide assay demonstrated that the synthesized Schiff base exhibited significant anticancer properties.

Recent advances in synthesis of organometallic complexes of indium

The indium complexes are being used in many applications like catalysis, optoelectronics, sensors, solar cells, biochemistry, medicine, infrared (IR) mirrors and thin-film transistors (TFTs). In organometallic complexes of indium, it forms different types of complexes with single, double, triple and tetra linkages by coordinating with numerous elements like C, N, O and S and also with some other elements like Se and Ru. So, the present study comprises all the possible ways to synthesize the indium complexes by reacting with different organic ligands; most of them are N-heterocyclic carbenes, amines, amides and phenols. The commonly used solvents for these syntheses are tetrahydrofuran, dichloromethane, toluene, benzene, dimethyl sulfoxide (DMSO) and water. According to the nature of the ligands, indium complexes were reported at different temperatures and stirring time. Because of their unique characteristics, the organometallic chemistry of group 13 metal indium complexes remains a subject of continuing interest in synthetic chemistry as well as material science.

Synthesis and Characterization of Cobalt(II) and Manganese(II) Schiff Base Complexes: Metal Effect on the Binding Affinity with β-Casein

In this study, two metal Schiff base complexes (cobalt(II) and manganese(II), were synthesized and characterized by ¹H-NMR and FT-IR analyses. The in vitro binding behavior of this complexes with β-Casein (β-CN) was investigated by using biophysical techniques. For evaluation the thermodynamics parameters of interaction between Schiff base complexes and β-CN,the fluorescence data at different temperatures were done. The results showed that the intrinsic fluorescence of the β-CN was quenched by increasing the complexes through the dynamic quenching mechanism. Also, these complexes demonstrated a considrable binding affinity to β-CN and the process is mainly entropy driven. Fluorescence resonance energy transfer was used in order to estimating the distance between donor (β-CN) and acceptor (complex). Results demonstrated that the sequence of tendency of the complexes to β-CN was as follows: Mn-Schiff base complex > Co-Schiff base complex. All these experimental results propose that β-CN might act as carrier protein for Co(II) and Mn (II) complexes to deliver it to the target molecules.

Preparation, characterization and comparison of biological potency in two new Zn(II) and Pd(II) complexes of butanedione monoxime derivatives

A novel Schiff base ligand (2-iminothiophenol-2,3-butanedione monoxime, ITBM) and its complexes with Pd(II) and Zn(II) metal ions ([M(ITBM)₂]Cl₂) were synthesized and characterized in the present study. The formulated complexes were evaluated for in vitro antioxidant activity as radical scavengers against 1,1-diphenyl-2-picrylhydrazyl radicals (DPPH^•). According to the results, antioxidant activity of Pd complex (IC₅₀=36 mg L^-1) was more effective than that of Zn(II) complex (IC₅₀=72 mg L^-1). Biophysical techniques along with computational modeling were employed to examine the binding of these complexes with human serum albumin (HSA) as the model protein. The trial findings revealed an interaction between Schiff base complexes and HSA with a modest binding affinity [K_b=6.31(±0.11)×10⁴ M^-1 for Zn(II) complex and 0.71(±0.05)×10⁴ M^-1 for Pd(II) complex at 310 K]. An intense fluorescence quenching of protein through a static quenching mechanism was occurred due to the binding of both complexes to HSA. Hydrogen bonds and van der Waals forces in both examined systems were the main stabilizing forces in the development of drug-protein complex. Based on far-UV-CD observations, the content of α-helical structure in the protein was reduced through induction by both complexes. Analysis of protein-ligand docking demonstrated binding of the two Schiff base complexes to residues placed in the IIA subdomain of HSA. In addition, Zn complex with HSA showed a stronger binding ability than that of Pd complex.Communicated by Ramaswamy H. Sarma.

Binding forces between a novel Schiff base palladium(II) complex and two carrier proteins: human serum albumi and β-lactoglobulin

Ligand binding studies on carrier proteins are crucial in determining the pharmacological properties of drug candidates. Here, a new palladium(II) complex was synthesized and characterized. The in vitro binding studies of this complex with two carrier proteins, human serum albumin (HSA), and β-lactoglobulin (βLG) were investigated by employing biophysical techniques as well as computational modeling. The experimental results showed that the Pd(II) complex interacted with two carrier proteins with moderate binding affinity (K_b ≈ .5 × 10⁴ M^-1 for HSA and .2 × 10³ M^-1 for βLG). Binding of Pd(II) complex to HSA and βLG caused strong fluorescence quenching of both proteins through static quenching mechanism. In two studied systems hydrogen bonds and van der Waals forces were the major stabilizing forces in the drug-protein complex formation. UV-Visible and FT-IR measurements indicated that the binding of above complex to HSA and βLG may induce conformational and micro-environmental changes of two proteins. Protein-ligand docking analysis confirmed that the Pd(II) complex binds to residues located in the subdomain IIA of HSA and site A of βLG. All these experimental and computational results suggest that βLG and HSA might act as carrier protein for Pd(II) complex to deliver it to the target molecules.

Metal Complexes of a Novel Schiff Base Based on Penicillin: Characterization, Molecular Modeling, and Antibacterial Activity Study

A novel Schiff base ligand of type HL was prepared by the condensation of amoxicillin trihydrate and nicotinaldehyde. The metal complexes of Co⁺², Ni⁺², Cu⁺², and Zn⁺² were characterized and investigated by physical and spectral techniques, namely, elemental analysis, melting point, conductivity, ¹H NMR, IR, UV-Vis spectra, ESR, SEM, and mass spectrometry measurements. They were further analyzed by thermal technique (TGA/DTA) to gain better insight about the thermal stability and kinetic properties of the complexes. Thermal data revealed high thermal stability and nonspontaneous nature of the decomposition steps. The Coats-Redfern method was applied to extract thermodynamic parameters to explain the kinetic behavior. The molar conductance values were relatively low, showing their nonelectrolytic nature. The powder XRD pattern revealed amorphous nature except copper complex (1c) that crystallized in the triclinic crystal system. The EPR study strongly recommends the tetrahedral geometry of 1c. The structure optimization by MM force field calculation through ArgusLab 4.0.1 software program supports the concerned geometry of the complexes. The in vitro antibacterial activity of all the compounds, at their two different concentrations, was screened against four bacterial pathogens, namely, E. coli, P. vulgaris, K. pneumoniae, and S. aureus, and showed better activity compared to parent drug and control drug.

Interaction studies of copper complex containing food additive carmoisine dye with human serum albumin (HSA): Spectroscopic investigations

In this study, the interaction between human serum albumin (HSA) and a copper complex of carmoisine dye; [Cu(carmoisine)₂ (H₂ O)₂ ], was studied in vitro using multi-spectroscopic methods. It was found that the intrinsic fluorescence of HSA was quenched by the addition of the [Cu(carmoisine)₂ (H₂ O)₂ ] complex and the quenching mechanism was considered as static quenching by formation of a [Cu(carmoisine)₂ (H₂ O)₂ ]-HSA complex. The binding constant was about 10⁴  M^-1 at room temperature. The values of the calculated thermodynamic parameters (ΔH < 0 and ΔS > 0) suggested that both hydrogen bonds and the hydrophobic interactions were involved in the binding process. The site marker competitive experiments revealed that the binding of [Cu(carmoisine)₂ (H₂ O)₂ ] to HSA primarily occurred in subdomain IIIA (site II) of HSA. The results of circular dichroism (CD) and UV-vis spectroscopy showed that the micro-environment of amino acid residues and the conformation of HSA were changed after addition of the [Cu(carmoisine)₂ (H₂ O)₂ ] complex. Finally, the binding of the [Cu(carmoisine)₂ (H₂ O)₂ ] complex to HSA was modelled by a molecular docking method. Excellent agreement was obtained between the experimental and theoretical results with respect to the binding forces and binding constant.

Design, synthesis, characterization, cytotoxicity, molecular docking and analysis of binding interactions of novel acetylacetonatopalladium(ii) alanine and valine complexes with CT-DNA and BSA

The neutral, water soluble palladium(ii) amino acid complexes, interact with CT-DNA (groove binding) and BSA (H-binding in main pocket). Molecular docking supports the interactions.