Synthesis, biological evaluation and corrosion inhibition studies of transition metal complexes of Schiff base

Quantum Chemical and Experimental Evaluation of a 4-Amino-Antipyrine Based Schiff Base as Corrosion Inhibitor for Steel Material

Electrochemical experiments such as potentiodynamic polarization, electrochemical impedance spectroscopy, and gravimetric studies have been used to examine the corrosion inhibitory efficacy of 4-[(4-nitrobenzylidene)-amino]-antipyrine (4-NBAAP) on mild steel (MS) in 1 M HCl. 4-NBAAP inhibits the corrosion of MS through a mixed inhibition mechanism, according to the electrochemical investigation. The efficiency of 4-NBAAP increases with an increase in the inhibitor concentration and decreases with an increase in temperature. The adsorption of 4-NBAAP molecules on the MS surface follows the Langmuir adsorption isotherm. To find the relationship between the 4-NBAAP molecular structure and inhibitive effect, a few thermodynamic parameters were computed. The experimental results obtained from gravimetric and different electrochemical investigations prove the superiority of the inhibitor at higher concentrations in controlling the corrosion process of the steel in aggressive environments. Also, quantum chemical studies were performed to provide further insights into the inhibition mechanism.

Novel complex compounds of nickel with 3-(1-phenyl-2,3-dimethyl-pyrazolone-5)azopentadione-2,4: synthesis, NBO analysis, reactivity descriptors and in silico and in vitro anti-cancer and bioactivity studies

A synthesized azo compound based on 4-amino antipyrine and its complexes with Ni(II) in solution and solid phase is reported. The structures of these compounds have been testified by IR and NMR spectroscopy. The combined experimental and theoretical approach was used. To study the structure and properties of the synthesized compound, as well as its possible complex formation with the Ni(II), ab initio quantum-chemical calculations were carried out using the Hartree-Fock (HF) method with the 6-31 G basis set and the electron density functional theory (DFT) method with hybrid three-parameter potential B3LYP and extended basis set 6-311++G(d,p) taking into account polarization and diffuse functions for all atoms. The geometric, energy, and electronic parameters were calculated and analyzed. The HOMO-LUMO energy gap has been calculated to determine chemical activity. Both complexes had effective inhibition against butyrylcholinesterase and acetylcholinesterase. IC50 values were found as 19.43 and 27.08 µM for AChE, 2.37 and 7.40 µM for BChE, respectively. For the anticancer outcome, high doses of compound E1 inhibited viability by about 40-45%, while this rate was around 65-70% for compound E2 at the same doses. Anticholinesterase and anticancer potential of compounds E1 and E2 also evaluated by in silico techniques. Both compounds show strong binding to VEGFR1, with E2 exhibiting superior inhibitory activity in hAChE and hBChE through shorter and stronger interactions. MD simulations suggest that E2 forms more stable complexes with hAChE and hBChE compared to E1, making it a promising candidate for further exploration in anticancer and anticholinesterase therapies.Communicated by Ramaswamy H. Sarma.

Synthesis, crystal structure, thermal stability and biological study of bis{(2-methoxy-6-[(E)-(propylimino)methyl]phenolato}nickel(II) complex

A Schiff base complex of nickel, bis{(2-methoxy-6-[(E)-(propylimino)methyl]phenolato}nickel(II) was synthesised by condensing bis(2-hydroxy-3-methoxybenzaldehyde) nickel (II) and n-propylamine in methanolic medium. Single crystal X-ray diffraction analysis of the complex revealed it to possess planar geometry with a monoclinic crystal system. The non-isothermal TG/DTA runs on this complex in a high purity (99.99 %) nitrogen environment at atmospheric pressure confirmed the absence of any coordinated water. A sharp endotherm in its DTA shows a melting temperature range of 168-171 °C. It is thermally stable up to 243 °C and decomposes in two steps, yielding NiO and carbon as residue. In addition to the methoxy group (-OCH3), infrared analysis (IR) confirmed the presence of the characteristic azomethine group (-C[bond, double bond]N-) which is also responsible for the biological action. It was further analysed by elemental analyser (C, H, N), 1H and 13C NMR as well as mass spectrometry. It showed considerable antibacterial activity towards Escherichia coli and Staphylococcus aureus when the concentration exceeds 200 μg/ml. The antifungal study shows significant inhibition with the antifungal drug imidazole as a positive control (PC). Small values of MIC, MBC/MIC indicate a lesser quantity of complex is required to inhibit the growth of micro-organisms.

Antiultraviolet, Antioxidant, and Antimicrobial Properties and Anticancer Potential of Novel Environmentally Friendly Amide-Modified Gallic Acid Derivatives

Polyphenols and amides isolated from natural products have various biological functions, such as antioxidant, antimicrobial, anticancer, and antiviral activities, and they are widely used in the fields of food and medicine. In this work, four novel and environmentally friendly amide-modified gallic acid derivatives (AMGADs), which were prepared by using different amides to modify gallic acid (GA) from Polygonaceae plants, displayed good antiultraviolet (anti-UV), antioxidant, antimicrobial, and anticancer effects. Significantly, the anti-UV capability of compounds n1 and n2 was notably superior to that of the UV absorber GA. Moreover, compound n2 possessed better 2,2-diphenyl-1-picrylhydrazyl radical (DPPH•) scavenging ability and ferric reducing antioxidant power than vitamin C. The antibacterial activities of all AMGADs, with inhibition rates of more than 96.00 and 79.00% for Escherichia coli and Staphylococcus aureus, respectively, were better than those of GA. Compound n1 had broad-spectrum anticancer activity, and its inhibitory effect on HepG2 cells exceeded that of 5-fluorouracil. The good and rich bioactivities of these AMGADs revealed that combining GA with amides is conducive to improving the activity of GA, and this study laid a good foundation for their scientific application in the fields of food and medicine.

Three metal complexes with a pyridyl Schiff base: cytotoxicity, migration and mechanism of apoptosis

Three metal complexes [CuL(NO₃)]_n (1), [Cd(HL)(NO₃)₂]_n (2) and [EuL(HCOOH)(H₂O)(NO₃)₂] (3) were synthesized with a pyridyl Schiff ligand L (N'-[(1E)-pyridin-2-ylmethylidene]pyridine-4-carbohydrazide). A crystallographic study revealed that complexes 1 and 2 have a chain structure, and complex 3 is a zero-dimensional monomer. In vitro cytotoxicity studies showed that complex 2 had the best antiproliferative activity against SMMC-7721 cells and complex 3 had the best antiproliferative activity against MDA-MB-231 cells with single-digit IC₅₀ values, both exceeding those of the control drug cisplatin by far. The cell invasion and migration ability through the transwell assay and wound-healing assay showed that the selected complexes could inhibit the invasion and migration of cancer cells. The Hoechst staining assay and ROS generation assay with SMMC-7721 cells indicated that the cytotoxic effects of complex 2 involved apoptosis induction through ROS accumulation. The apoptosis-inducing and cell cycle arrest effects of complex 2 on SMMC-7721 cells indicated that the antitumor effect was achieved through apoptosis induction and inhibition of DNA synthesis by blocking the G₀/G₁ phase of the cell cycle. In addition, complex 2 showed significant inhibition against B. dysentery with an inhibition circle diameter of 24 mm.

Innovation of Imine Metal Chelates as Corrosion Inhibitors at Different Media: A Collective Study

The corrosion inhibition of transition metal chelates derived from Schiff base ligands was tested for (mild, copper, stainless, aluminum and carbon) steel in various concentrations of (HCl, HNO₃ and H₂SO₄) acidic medium at 25 °C through (weight loss, potentiodynamic polarization, polarization curves, electrochemical impedance spectroscopy (EIS) and open circuit potential measurements (OCP)) techniques. The studied compounds were identified with various spectral, analytical and physico-chemical techniques. It was observed that the investigated compounds had a significant inhibitory impact on the corrosion of diverse steels in the medium investigated. The analysis shows that increasing the dose of the studied complexes improves the corresponding inhibitory efficiency values. Negative results of Gibb’s free adsorption energy (ΔGads0) prove the suppression process’s spontaneous and physical adsorption, which contradicts the Langmuir adsorption isotherm. As a result of this insight, a novel bridge between nuclearity driven coordinated inorganic chemistry and materials, as well as corrosion control, has been built. This review provides an overview of the use of Schiff bases and associated transition metals as potential corrosion inhibitors, including the factors that influence their application.

N-((1H-Pyrrol-2-yl)methylene)-6-methoxypyridin-3-amine and Its Co(II) and Cu(II) Complexes as Antimicrobial Agents: Chemical Preparation, In Vitro Antimicrobial Evaluation, In Silico Analysis and Computational and Theoretical Chemistry Investigations

Researchers are interested in Schiff bases and their metal complexes because they offer a wide range of applications. The chemistry of Schiff bases of heterocompounds has got a lot of attention because of the metal's ability to coordinate with Schiff base ligands. In the current study, a new bidentate Schiff base ligand, N-((1H-pyrrol-2-yl)methylene)-6-methoxypyridin-3-amine (MPM) has been synthesized by condensing 6-methoxypyridine-3-amine with pyrrole-2-carbaldehyde. Further, MPM is used to prepare Cu(II) and Co(II) metal complexes. Analytical and spectroscopic techniques are used for the structural elucidation of the synthesized compounds. Both MPM and its metal complexes were screened against Escherichia coli, Bacillus subtilis, Staphylococcus aureus and Klebsiella pneumoniae species for antimicrobial studies. Furthermore, these compounds were subjected to in silico studies against bacterial proteins to comprehend their best non-bonded interactions. The results confirmed that the Schiff base ligand show considerably higher binding affinity with good hydrogen bonding and hydrophobic interactions against various tested microbial species. These results were complemented with a report of the Conceptual DFT global reactivity descriptors of the studied compounds together with their biological scores and their ADMET computed parameters.

Transition Metal Complexes of 4-Aminoantipyrine Derivatives and Their Antimicrobial Applications

Transition metal complexes of 4-aminoantipyrine derivatives have been gaining great interest due to their rich coordination chemistry and potential applications in the field of pharmaceutical science. The presence of a free amine and a cyclic ketone functionality makes 4-aminoantipyrine an attractive amphoteric substrate for Schiff base formation. Varieties of aldehydes/ketones or amines of versatile steric, electronic and functional nature could be condensed with the 4-aminoantipyrine motif to obtain the ligand systems of multi-denticity and diverse coordination behaviour. The transition metal complexes obtained from these ligand systems exhibit unique structural and functional properties. This review compiles the important transition metal complexes developed from the Schiff base derivatives of 4-aminoantipyrine, and their utility as antibacterial and antifungal agents. Rationale of the strategies involved in the development of highly potential antimicrobial agents is discussed.

Synthesis and structures of divalent Co, Ni, Zn and Cd complexes of mixed dichalcogen and dipnictogen ligands with corrosion inhibition properties: experimental and computational studies

The structural and corrosion inhibition properties of four different transition-metal complexes of heteroleptic S-donor atom dithiophosphonate and N-donor atom phenanthroline ligands are reported. Full structural characterization of the Co, Ni, Zn and Cd complexes was achieved with the aid of single-crystal X-ray crystallography. Structural elucidation revealed the formation of a 4-coordinate Zn(ii) complex, and 6-coordinate Ni(ii) and Cd(ii), as well as a novel dithiophosphonato Co(ii) complex. The ability of the complexes with this ligand type to act as inhibitors of mild steel corrosion in 1 M HCl solution is reported for the first time. Corrosion inhibition potentials of the complexes were assessed using potentiodynamic polarization, electrochemical impedance spectroscopy (EIS), and density functional theory (DFT). The open circuit potential (OCP) time profile showed the system achieved a steady-state potential before the first 600 s after submerging the working electrode in the corrosive medium. The studied metal complexes are good inhibitors of mild steel corrosion in 1 M HCl and were found to retard the corrosion rate by forming an adsorbed pseudocapacitive film on the steel surface. The order of inhibition efficiencies was in the order Ni (94.14%) > Cd (92.28%) > Zn (91.14%) > Co (72.53%).