Self-assembled two-dimensional salicylaldimine lanthanum(III) nitrate coordination polymer

Promising Schiff bases in antiviral drug design and discovery

Emerging and re-emerging illnesses will probably present a new hazard of infectious diseases and have fostered the urge to research new antiviral agents. Most of the antiviral agents are analogs of nucleosides and only a few are non-nucleoside antiviral agents. There is quite a less percentage of marketed/clinically approved non-nucleoside antiviral medications. Schiff bases are organic compounds that possess a well-demonstrated profile against cancer, viruses, fungus, and bacteria, as well as in the management of diabetes, chemotherapy-resistant cases, and malarial infections. Schiff bases resemble aldehydes or ketones with an imine/azomethine group instead of a carbonyl ring. Schiff bases have a broad application profile not only in therapeutics/medicine but also in industrial applications. Researchers have synthesized and screened various Schiff base analogs for their antiviral potential. Some of the important heterocyclic compounds like istatin, thiosemicarbazide, quinazoline, quinoyl acetohydrazide, etc. have been used to derive novel Schiff base analogs. Keeping in view the outbreak of viral pandemics and epidemics, this manuscript compiles a review of Schiff base analogs concerning their antiviral properties and structural-activity relationship analysis.

Abd Razik. Synthesizing, Studying Molecular Docking, Characterizing, and Preliminary Evaluating Anti-Bacterial Effects of Derivatives of Serotonin Contain Imidazolidine Ring

This study included synthesis of new serotonin derivatives in which imidazolidine rings are present in their structures. The final imidazolidine derivatives compounds were synthesized by reaction of synthesized   Schiff bases derivatives of serotonin with the glycine (NH2-CH2COOH) in presence of tetrahydrofuran (THF) as a solvent. The imidazolidine derivatives were identified by physical characteristics, FT-IR spectroscopy and 1H- NMR spectroscopy. Biological activities against two Gram negative (Klebsiella and E. coli) and two Gram positive (Streptococcus pyogenes and Staphylococcus aureus) bacteria were also distinguished. All the synthesized compounds III(a-d) exhibit moderate activities on four types of bacteria comparing with the activity of standard drug (Trimethoprim) but the highest activities of these compounds occur on Streptococcus pyogenes and their least activities occur on E. coli. The synthesized compounds were studied for the molecular docking to know the interaction and affinity of binding between them and bacteria  

Tridentate imidazole-based Schiff base metal complexes: molecular docking, structural and biological studies

A novel Schiff base was synthesized by the condensation of imidazole-2-carboxaldehyde with l-histidine in an equimolar ratio. The prepared Schiff base was characterized by elemental analysis and spectral characterization techniques. It was then complexed with a series of 3-d metal(II) ions like manganese, iron, cobalt, nickel, copper and zinc. The coordination properties, nature of bonding and stability of the complexes were deduced from elemental analysis, IR, UV-vis, ¹H NMR, mass, electronic spectra, magnetic, conductivity and thermogravimetric analysis. IR studies support the tridentate behaviour of Schiff base as well as its coordination to the central metal ion through an azomethine nitrogen, deprotonated carboxylic oxygen and imidazole ring nitrogen atoms of histidine. The electronic spectra and magnetic moment data demonstrate that the complexes have an octahedral geometry, except zinc complex, which has a tetrahedral geometry. In vitro antimicrobial activity of the synthesized compounds has been shown to exhibit excellent antibacterial and antifungal activities. The antibacterial property of the prepared Schiff base was further confirmed by conducting a docking study of target proteins involved in the antibacterial mechanism.Communicated by Ramaswamy H. Sarma.

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.

Novel Schiff-base molecules as efficient corrosion inhibitors for mild steel surface in 1 M HCl medium: experimental and theoretical approach

In order to evaluate the effect of the functional group present in the ligand backbone towards corrosion inhibition performances, three Schiff-base molecules namely, (E)-4-((2-(2,4-dinitrophenyl)hydrazono)methyl)pyridine (L(1)), (E)-4-(2-(pyridin-4-ylmethylene)hydrazinyl)benzonitrile (L(2)) and (E)-4-((2-(2,4-dinitrophenyl)hydrazono)methyl)phenol (L(3)) were synthesized and used as corrosion inhibitors on mild steel in 1 M HCl medium. The corrosion inhibition effectiveness of the studied inhibitors was investigated by weight loss and several sophisticated analytical tools such as potentiodynamic polarization and electrochemical impedance spectroscopy measurements. Experimentally obtained results revealed that corrosion inhibition efficiencies followed the sequence: L(3) > L(1) > L(2). Electrochemical findings showed that inhibitors impart high resistance towards charge transfer across the metal-electrolyte interface and behaved as mixed type inhibitors. Scanning electron microscopy (SEM) was also employed to examine the protective film formed on the mild steel surface. The adsorption as well as inhibition ability of the inhibitor molecules on the mild steel surface was investigated by quantum chemical calculation and molecular dynamic (MD) simulation. In quantum chemical calculations, geometry optimized structures of the Schiff-base inhibitors, electron density distribution in HOMO and LUMO and Fukui indices of each atom were employed for their possible mode of interaction with the mild steel surfaces. MD simulations revealed that all the inhibitors molecules adsorbed in parallel orientation with respect to the Fe(110) surface.

Synthesis and characterization of metallo-supramolecular polymers

The incorporation of metal centers into the backbone of polymers has led to the development of a broad range of organometallic and coordination compounds featuring properties that are relevant for potential applications in diverse areas of research, ranging from energy storage/conversion to bioactive or self-healing materials. In this review, the basic concepts and synthetic strategies leading to these types of materials as well as the scope of available characterization techniques will be summarized and discussed.

Experimental and theoretical study of antioxidative properties of some salicylaldehyde and vanillic Schiff bases

A set of ten phenolic Schiff bases was evaluated for their antioxidative properties. Two of them, one salicylaldehyde and one vanillic, showed high activity. Parameters obtained by DFT supported the experimental findings.

The trimorphic structure of N,N'-bis(5-methylsalicylidene)-4-methyl-1,3-phenylenediamine

The new Schiff base ligand, N,N'-bis(5-methylsalicylidene)-4-methyl-1,3-phenylenediamine (H2L), has been prepared by condensation of 5-methylsalicylaldehyde with 4-methyl-1,3-phenylenediamine. It was found that this ligand crystallizes in the monoclinic space group P21/c, with Z' = 1. Further studies showed that - as a result of the one-pot metal-promoted reactions - three different polymorphic forms of H2L were obtained, with different numbers (1, 3 or 4) of symmetry-independent molecules depending on the lanthanide metal ion present in the reaction media: La (Z' = 3), Nd (Z' = 4), Sm, Tb, Ho and Yb (all Z' = 1); the last form is identical with that obtained by crystallization of the ligand itself. The geometrical features of all eight independent molecules of H2L are very similar. The relatively strong intramolecular O-H...N hydrogen bonds stabilize almost co-planar conformations of terminal rings and C-C=N-C linkers, at the same time strong hydrogen-bond donors and acceptors involved in these interactions cannot take part in the determination of supramolecular architecture. Therefore, weak intermolecular interactions are important and this can be regarded as one of the reasons for packing conflicts that lead to the presence of polymorphic forms and multiple molecules. The pseudosymmetries are observed in both forms with Z' > 1 and the degree of pseudosymmetry is described by the values of appropriate combinations of the coordinates. In order to elucidate the differences in crystal structures the Hirshfeld surface method was applied. It shows that there are only small differences in the surface shape and in the fingerprint plots; however, the volumes of voids in three structures are significantly different.

CALCULATOR FOR FINDING COMPOSITION OF (Me1)x1(Me2)x2(CcHhNnOo)x3(NO3)x4(H2O)x5(Cl)x6 TYPE COMPLEX FROM ELEMENTAL ANALYSIS DATA

The paper presents the method and numerical program along with graphical user interface for finding the probable composition of Schiff base complexes based on elemental analysis data. The applied algorithm uses sorting procedure of possible variations of number of groups under condition of electrical neutrality. The program was tested for a few examples and its usefulness was discussed.

Syntheses, characterization, biological activities and photophysical properties of lanthanides complexes with a tetradentate Schiff base ligand

A tetradentate Schiff base ligand L (N,N'-bis(1-naphthaldimine)-o-phenylenediamine) was prepared from the condensation of 2-hydroxy-1-naphthaldehyde with o-phenylenediamine in a molar ratio of 2:1. New eight lanthanide metal complexes [LnL(NO(3))(2)(H(2)O)(x)](NO(3)) {Ln(III) = Nd, Dy, Sm, Pr, Gd, Tb, La and Er, x = 0 for Nd, Sm, 1 for La, Gd, Pr, Nd, Dy, and 2 for Tb} were prepared. The characterization and nature of bonding of these complexes were elucidated by elemental analysis, spectral analysis ((1)H NMR, FT-IR, UV-vis), molar conductivity measurements, luminescence spectra and thermogravimetric studies. Analytical and spectral data revealed that the ligand L coordinates to the central Ln(III) ions by its two imine nitrogen atoms and two phenolic oxygen atoms with 1:1 stoichiometry. Under the excitation with 329 nm at room temperature, Tb and Dy complexes exhibited characteristic luminescence of the central metal ions attributed to efficient energy transfer from the ligand to the metal center. Most of Ln(III) complexes found to exhibit antibacterial activities against a number of pathogenic bacteria. We found that the antioxident activity of Ln(III) complexes on DPPH(•) is concentration dependent and higher than that of the free ligand L.

Syntheses, characterization, biological activity and fluorescence properties of bis-(salicylaldehyde)-1,3-propylenediimine Schiff base ligand and its lanthanide complexes

Eight new lanthanide metal complexes [LnL(NO(3))(2)]NO(3) {Ln(III) = Nd, Dy, Sm, Pr, Gd, Tb, La and Er, L = bis-(salicyladehyde)-1,3-propylenediimine Schiff base ligand} were prepared. These complexes were characterized by elemental analysis, thermogravimetric analysis (TGA), molar conductivity measurements and spectral studies ((1)H NMR, FT-IR, UV-vis, and luminescence). The Schiff base ligand coordinates to Ln(III) ion in a tetra-dentate manner through the phenolic oxygen and azomethine nitrogen atoms. The coordination number of eight is achieved by involving two bi-dentate nitrate groups in the coordination sphere. Sm, Tb and Dy complexes exhibit the characteristic luminescence emissions of the central metal ions attributed to efficient energy transfer from the ligand to the metal center. Most of the complexes exhibit antibacterial activity against a number of pathogenic bacteria.

Self-assembly in Schiff base lanthanide complexes — From supramolecular dimers to coordination polymers

A review is given of the latest contribution of the author’s research group to the coordination chemistry of Schiff base polyaza macrocycles and acyclic salicylaldimines. Focus is placed on the effectiveness of lanthanides in supramolecular self-assembly of the components leading to the formation of compounds with unusual properties and structures.Key words: Schiff base macrocycles, salicylaldimines, lanthanides, self-assembly, template synthesis.