ONNO Donor Research Articles

A square planar cobalt(II)-thiosemicarbazone complex. Synthesis, characterization, antiviral and anti-inflammatory potential

Considering the possible antiviral effect of cobalt compounds and known pharmacological potential of thiosemicarbazones, a new combination containing cobalt(II) ions and tetradentate thiosemicarbazone was synthesized and structurally analyzed. In the complex structure (Co1), the cobalt ion is in 2+ oxidation state and is coordinated with ONNO donor set on the thiosemicarbazone backbone. The complex molecule crystallizes in the space group P21/m and the environment of the cobalt center tends to square planar geometry. The inhibitory performance of SARS-CoV-2 and the anti-inflammatory impact of the complex molecule were investigated. It was found that Co1 has high inhibitory effects on the SARS-CoV-2 virus's 3CL main protease enzyme, ACE2:SARS-CoV2 Spike RBD interaction, and IL8. Also, it showed significant anti-inflammatory effects on the release of IL6, IL8, IL10, and TGFβ1 cytokines and wound healing during in vitro TNF-α-induced inflammation. Experimental evidence demonstrates that Co1 diminishes both IL8 gene expression and protein levels. According to in silico and experimental results, it has a drug potential. Assessing the in vivo impacts of Co1 might contribute to understanding its potential as an antiviral and anti-inflammatory agent.

Synthesis, structural characterization and biological applications of mono- and binuclear Cu(II) and Ni(II) complexes with N2O2 Schiff bases

The present work aims to synthesize and characterize new Schiff base metal complexes (Cu(II) and Ni(II)) derived from 4,5-Dichloro-o-phenylenediamine and 3,5-Dichloro-2-hydroxyacetophenone. The synthesized Schiff base and their complexes have been characterized with the support of more than a few standard physicochemical techniques such as elemental analysis, spectroscopic, thermal, and cyclic voltammetry studies. Further the molecular structures are ascertained by computational methods like density functional theory (DFT) methods. The newly synthesized Schiff base ligand acts as ONNO donor tetradentate chelate and coordinated through an azomethine nitrogen and phenoxo oxygen atom to the Cu(II) and Ni(II). Moreover, all the newly prepared compounds exhibit moderate biological activity such as antibacterial. The synthesized compounds were screened for their antibacterial by the disc agar diffusion method. Spectral analysis exhibits square planar geometry for Cu(II) & Ni(II) mono and binuclear complexes. The antimicrobial results indicate that the homo binuclear copper (II) complex was more active than the other mono and binuclear complexes. The theoretical DFT calculations were applied to verify the molecular geometry of chelators and their complexes. The DFT optimized geometries of the complexes are in agreement with experimental observations.

Synthesis, characterization and biological activity of a novel N1, N5-bis[2-hydroxyphenyl]-2-methyl-1,5-diaminopentane Schiff base: Effect of methylene spacers on biological activities

A novel ONNO donor tetradentate Schiff base ligand N,N'-bis[2- hydroxyphenyl]-2-methyl-1,5-diaminopentane (1) is synthesized and characterized by using 1H, 13C NMR spectroscopy and mass spectrometry. Biological studies on newly synthesized ligand are carried out and results are compared with the biological activities of known Schiff base ligands: N,N'-bis[{2- hydroxyphenyl }]-1,4-diaminobutane (2) and N,N'-bis[{2- hydroxyphenyl }]-1,3-diaminopropane (3). This comparative study highlights the effect of increasing methylene linkage on the biological activity of these ligands. The anti-microbial activities of all three ligands have been screened against two distinct gram-positive and gram-negative bacteria. In-vitro results of this comparative analysis are also supported by comprehensive molecular docking studies with DNA gyrase subunit B protein of gram-positive bacterium S. aureus and FabH–CoA complex of gram-negative bacterium E. coli. Experimental studies reveal that the spacer group plays a vital role in controlling the biological activities of the ligand. These findings are in good agreement with the theoretical findings. The study demonstrates that the biological activity of ligands is enhanced with increments in the number of spacers. Thus, the newly synthesized ligand (1) with the most extended spacer among the three showed the highest biological activity compared to other two ligands, similar to the popular drug Ciprofloxacin.

Exploring diaminomaleonitrile-derived Schiff base ligand and its complexes: Synthesis, characterization, computational insights, biological assessment, and molecular docking

A tetra dentate ONNO donor diaminomaleonitrile-based Schiff base ligand along with its four new complexes of Co(II), Ni(II), Cu(II), and Zn(II) have been synthesized. The computational approach has been utilized to provide a theoretical framework for understanding the electronic structure and properties of these complexes. The distorted octahedral geometry of the Schiff base metal complexes indicates that the metal ions are coordinated with the ligand through ONNO donor sites, which is further confirmed by characterization using physiochemical and spectroscopic techniques like elemental analysis, mass, electronic, infrared, 1H, and 13C spectra. In addition, magnetic behavior is analyzed using the Vibrating Sample Magnetometer(VSM). To evaluate the potential modes of biomolecular interactions with the synthesized complexes utilizing Deoxyribo Nucleic Acid(DNA) and to assess the corresponding binding constants, an absorption spectroscopic technique has been utilized. Metal complexes are reported to have a range of binding constant values from 5.45 × 104 M−1 to 4.35 × 105 M−1 with different binding modes, such as intercalation, mixed mode, and electrostatic contact. In addition, in-vitro tests for antibacterial and anti-inflammatory activity have been employed to assess the bioactivities. With an IC50 value of 209.24 µg/mL, the Zn(II) complex is found to show considerable anti-inflammatory action as well as has superior antibacterial activity among all other complexes. The existence of electron-withdrawing CN groups together with other factors can be accounted for biological activity in our reported complexes. Further, molecular docking simulations are conducted to gain insights into the molecular-level interactions and to determine the potential binding energies of inhibitors whose results are in consistent with the in-vitro investigations.

Synthesis, structural elucidation, Hirshfeld surface analysis and cytotoxicity studies of homometallic dinuclear Cu(II), Ni(II) and Zn(II) Schiff base complexes derived from m-phenylenediamine

A polydentate Schiff base ligand, L was synthesized via condensation reaction between o-vanillin (OVan) and trimethyl-m-phenylenediamine [(Me)MPD]. Its Cu(II), Ni(II), and Zn(II) dinuclear complexes were prepared through complexation with corresponding acetate salts. The compounds were characterized via CHN elemental analyzer, molar conductivity, magnetic susceptibility, TGA, IR, 1H and 13C NMR. The crystal structure of the ligand, L and zinc(II) complex, Zn2L2 were elucidated by using single crystal x-ray diffraction. The crystal structure of Zn2L2 showed that the two Zn(II) metal atoms serve as bridges between the two units of the ligand through ONNO donor atoms leading to the formation of a centrosymmetric cyclic dinuclear complex. Based on the single x-ray crystallography, the zinc atoms exhibit a distorted tetrahedral geometry. Hirshfeld surface analysis was performed to determine the intermolecular interactions in the crystal structures. From this analysis, it revealed that H···H interaction for L (55%) and Zn2L2 (62.7%) was the dominant intermolecular interaction in the total area of Hirshfeld surface. The ν(CN) and ν(CO) peaks in IR spectra of the ligand L appeared at 1615 cm−1 and 1255 cm−1, respectively. The peaks shifted to lower and higher frequency by Δν of 4–12 cm−1 in the complexes. The new peaks assignable to ν(MN) and ν(MO) were observed at 514–562 cm−1 and 422–436 cm−1, respectively, indicating the coordination of the metal centers to the azomethine N and phenolic O. The Cu(II) and Ni(II) complexes are paramagnetic with μeff of 1.90 and 2.89 B.M., respectively. The thermal gravimetric analysis revealed the presence of three lattice water molecules in Cu(II) complex. The cytotoxicity studies of all compounds were carried out against colon cancer cell lines (HCT116). The parent ligand was found to be less cytotoxic than its metal complexes. Cu(II) showed the highest activity with IC50 of 0.73 ± 0.21 μM, better than the standard 5-FU.

Spectroscopic characterization of a mononuclear oxovanadium (IV) Schiff base complex. Oxidation catalysis applications and antibacterial activities

Herein we describe the chemical synthesis of a new oxovanadium (IV) complex of an N,N-bis(1-naphthalidimine)-o phenylenediamine (VOL). The structure has been characterized by various physiochemical and spectroscopic techniques. The single crystal X-ray diffraction confirms a tetra-coordinate chelated and a planar geometry of the complex by ONNO donor sets of the ligand. Hirshfeld's surface analysis indicates that the most important inter-molecular contact within crystal packing is C-H⋯O interaction. Density Functional Theory (DFT) calculations have been used to optimize the structure and discuss the chemical reactivity through the Frontier Molecular Orbitals (FMOs). The electrochemical properties of the complex were studied by cyclic voltammetry which shows a reversible VIV/VV redox process which is consistent with the hydrodynamic voltammograms. The complex was used as catalyst for the selective oxidation of cyclohexene to the corresponding 2-cyclohexene-1-one in DMF. Finally, antibacterial activity was determined using 3 Gram negative and 2 Gram positive bacteria using disk diffusion method, it was found to be more effective against Gram positive than the Gram negative bacteria.

Synthesis, spectral, in vitro microbial and DNA cleavage studies of isatin bishydrozone metal complexes

ONNO donor Schiff bases with recent group of Co(II), Ni(II), and Cu(II) complexes have been created and analyzed using spectroscopic research, thermal analysis, magnetic susceptibility, conductance tests, and elemental analysis. Via lactonyl oxygen and azomethine nitrogen, the Schiff bases are coordinated to the metal ion. In most common organic solvents, the complexes are insoluble but soluble in DMSO. The Co(II), Ni(II), and Cu(II) complexes' antibacterial properties, tested on quartet bacteria and two fungi strains showed an increased activity with respect to the Schiff bases. The Co(II), Ni(II) and Cu(II) complexes show more pronounced DNA cleaving activity. On cyclic voltammograms, the Cu(II) or Co(II) complexes tested in the DMSO solution showed metal-centered electro activity between 1.5 and +1.5 V.

Tetracoordinated ONNO donor purine‐based Schiff base and its metal complexes: Synthesis, characterization, DNA binding, theoretical studies, and bioactivities

AbstractTetracoordinated ONNO purine‐based novel Schiff base (1) and its metal complexes Co(II), Ni(II), Cu(II), and Zn(II) (2–5) were procured from 2,6‐diaminopurine and 5‐chlorosalicylaldehyde and characterized by elemental analyses, IR, UV–Vis, magnetic measurements, ESI‐MS, 1H NMR, and 13C NMR analysis. The new complexes showed an interesting structural variation: Distorted tetrahedral (CoL, CuL, and ZnL) and tetrahedral (NiL) geometries indicate that the metal ions bind with ligands through ONNO coordination sites. Density functional theory (DFT) and neutral bond orbital (NBO) calculations were performed to obtain an understanding of the structural characteristics, orbital interactions, and electronic chemical descriptors evaluation. Absorption and fluorescence spectra have been employed to examine the calf thymus deoxyribonucleic acid (CT‐DNA)‐binding behavior of the ligand and its complexes. Pharmacological activities, including in vitro antioxidant, in vitro anti‐inflammatory, and in vitro antidiabetic assays, were performed. All compounds showed better activities compared with the free ligand. For anti‐inflammatory and antidiabetic assays, ZnL complex showed high activity, whereas CuL complex exhibited the highest antioxidant activity among other metal complexes. Moreover, the zone of inhibition (ZOI) and minimum inhibitory concentration (MIC) of the synthesized compounds were screened for in vitro antibacterial activity against Staphylococcus aureus, Escherichia coli, Klebsiella pneumoniae, and Pseudomonas aeruginosa. Here also, complexes exhibited better antibacterial activity than the free ligand, especially the ZnL complex. The docking active site interactions were gauged to predict the activity of ligand and its metal complexes by binding with distinct active sites of B‐DNA dodecamer (for DNA‐binding activity), cyclooxygenase‐2 (for anti‐inflammatory assay), and α‐amylase enzyme and α‐glucosidase enzyme of human pancreatic system (for antidiabetic assay). The results indicated that the compounds are worth further investigation as a possible therapeutic agent.

Spectroscopic investigation, molecular structure, catalytic activity with computational studies of a novel Pd(II) complex incorporating unsymmetrical tetradentate Schiff base ligand

The treatment of an unsymmetrical tetradentate Schiff base ligand with Pd(OAc)2 salt yields novel palladium(II) Schiff base complex. The generated palladium(II) complex was characterized using elemental analysis (CHN) and different spectroscopic methods such as FT-IR and 1H NMR. Single crystal X-ray diffraction (SC-XRD) investigation has also been used to examine the crystal structure of the palladium complex. It is revealed from the SC-XRD study that the palladium ion in the complex is tetra-coordinated, inhabited by ONNO donor sites of the chelated ligand in a distorted square planar manner. The non-covalent interactions were explored by Hirshfeld surface analysis. The theoretical parameters calculated by DFT using the B3LYP/Def2-TZVP level of theory revealed that the theoretical conclusions matched the actual findings. For different aryl halides, the palladium(II) complex has exhibited excellent efficiency in the Suzuki-Miyaura cross-coupling reactions (SMCR), yielding biaryls in good to high yield.

Synthesis, crystal structure, spectral characterization, theoretical and computational studies of Ni(II), Cu(II) and Zn(II) complexes incorporating Schiff base ligand derived from 4-(diethylamino)salicylaldehyde

Three new nickel(II), copper(II), and zinc(II) complexes were prepared by treating symmetrical tetradentate Schiff base ligand (H2L) with Ni(OAc)2·4H2O, Cu(OAc)2·H2O, and Zn(OAc)2·2H2O salts, respectively. The synthesized compounds were structurally characterized by elemental (CHN) and spectroscopic analysis like FT-IR and 1H NMR. Moreover, the crystal structure of the Ni(II) complex (NiL) has been determined by SC-XRD. The crystal structure investigation confirms that the metal ion is tetra coordinated by ONNO donor sites of ligand to acquire a square planar geometry, which is further compared with some related crystal structures by Cambridge structure database search. A Hirshfeld surface inspection was conducted for the sake of further investigation of the non-covalent interactions in NiL. An enrichment ratio is also calculated for the chemical species to determine the tendency of their interactions in the crystal packing. The theoretical values based on DFT using B3LYP/Def2-TZVP level of theory ensured that the expected consequences matched the experimental findings.

Synthesis, spectral characterization, crystal structures, biological activities, theoretical calculations and substitution effect of salicylidene ligand on the nature of mono and dinuclear Zn(II) Schiff base complexes

Two new zinc(II) Schiff base complexes (Z1 and Z2) are prepared by treating ONNO tetradentate Schiff base ligands (H2L1 = [6,6′-((1E,1′E)-((2,2-dimethylpropane-1,3-diyl)bis(azanylylidene))bis(methanylylidene))bis(2-methoxyphenol)] and H2L2 = [2,2′-((1E,1′E)-((2,2-dimethylpropane-1,3-diyl)bis(azanylylidene))bis(methanylylidene))bis(4-methoxyphenol)]) with acetylacetonate salt of zinc. The synthesized Schiff base ligands and their respective zinc(II) complexes were characterized by elemental analysis (CHN) and various spectroscopic techniques like FT-IR and 1H NMR. The single crystal X-ray structures of Z1 and Z2 show the effect of salicylidene ligand on the nature of mono and dinuclear Zn(II) Schiff base complexes. In Z1 complex, a square pyramidal geometry is adapted by the complex, supported by the ONNO donor atoms of the tetradentate Schiff base and a coordinated water molecule. Structural analysis of Z2 complex revealed that the compound is a centrosymmetric dimer in which the five coordinated Zn(II) atoms are linked to the opposite metal center by making μ-phenoxo bridges through one of the phenolic oxygen atoms of Schiff base ligands. The nature of various kinds of non-covalent interactions present among the sample molecules was also investigated by using QTAIM and NCI calculations. The theoretical calculations were performed by DFT using the B3LYP/Def2-TZVP level of theory, which indicated that the intended outcomes are in compliance with the actual consequences. Furthermore, the antibacterial potential of the Schiff base ligands and their corresponding zinc complexes was measured by testing them against two Gram-positive (Staphylococcus aureus and Bacillus cereus) and two Gram-negative (Escherichia coli and Pseudomonas aeruginosa) bacterial strains. The agar well diffusion method and poisoned media technique were used for screening of bacterial and fungal species, respectively. According to the results of the zone of inhibition assessments, metal complexes have comparatively more inhibition potential relative to free ligands.

Mixed ligand transition metal(II) complexes: Characterization, spectral, electrochemical studies, molecular docking and bacteriological application

Mixed ligand complexes of Cu(II), Co(II), Ni(II), Mn(II) and Cd(II) with N,N'-1,4-phenylene (2-hyboxynaphthaliden imine) (H2L) as primary ligand and 4-aminoantipyrine (4-AAp) as secondary ligand have been prepared. The newly formed complexes were characterized using elemental analysis, magnetic susceptibility, molar conductance, 1H NMR, UV–Vis., FTIR, X-ray diffraction, mass, thermal analysis and ESR techniques. The elemental analysis, data reveal the formation of [2:1:2] [M: H2L: 4-AAP] complexes. The mode of bonding between Cu(II), Ni(II), Co(Il), Mn(II) and Cd(II) and ligands has been studied by IR spectrophotometry. Electronic absorption spectra and magnetic moment measurements of the mixed-ligand complexes suggest a distorted octahedral geometry around the central metal ion and the anions X− are in the axial positions, for all compounds. The ligands are found to behave in a neutral bidentate manner, through nitrogen atom and oxygen atom of carbonyl group (secondary ligand), whereas H2L (primary ligand) coordinated through nitrogen and OH group as a neutral ligand. FT-IR spectral data shows that the ligand acted as bis-bidentate coordination through ON–NO donor system. The XRD patterns of the ligand and its mixed ligand complexes showed the polycrystalline natures. The ligand and its mixed complexes were studied for their microbial activity against some bacteria and fungi. The ligand in comparison to its mixed ligand complexes (1-5) was screened for their antibacterial activity against Klebsiella pneumoniae, Escherichia coli, Pseudomonas sp., Staphylococcus aureus and Bacillus cereus. Antifungal activities of ligand in comparison to its mixed ligand complexes (1-5) were determined against Fusarium oxysporum, Aspergillus niger and Candida albicans. It was found that the mixed ligand complex (5) is more active than other mixed ligand complexes and penicillin G against Bacillus cereus, Staphylococcus aureus, Klebsiella pneumoniae and Pseudomonas sp. The mixed ligand complex (5) is more active than the ligand and other mixed ligand complexes and miconazole against Aspergillus niger. The inhibition efficiency of the prepared ligand (H2L) against the corrosion of P355 carbon steel in HCl (2 M) solution was determined by various electrochemical methods are found to be in reasonable agreement. The morphology of protected P355 carbon steel was test by energy dispersive X-ray and scanning electron microscope (EDX–SEM).

Protein binding and cytotoxic activities of monomeric and dimeric oxido-vanadium(V) salan complexes: Exploring the solution behavior of monoalkoxido-bound oxido-vanadium(V) complex

Three ONNO donor tetradentate diamino bis(phenolato) “salan” ligands, N, N′-dimethyl-N, N′-bis-(5-chloro-2-hydroxy-3-methyl-benzyl)-1,2-diaminoethane (H2L1), N, N′-dimethyl-N, N′-bis-(5-chloro-2-hydroxy-3-isopropyl-6-methyl-benzyl)-1,2-diamino-ethane (H2L2) and N, N′-bis-(5-chloro-2-hydroxy-3-isopropyl-6-methyl-benzyl)-1,2-diaminocyclohexane (H2L3) have been synthesized by following Mannich condensation reaction. Reaction of these ligands with their corresponding vanadium metal precursors gave one oxidomethoxidovanadium(V) [VVOL1(OCH3)] (1) and two monooxido-bridged divanadium (V, V) complexes [VVOL2–3]2(μ-O) (2–3). The complexes were characterized by IR, UV–vis, NMR and ESI mass spectrometry. Also, the structure of all the complexes (1–3) was confirmed by the Single-Crystal X-ray diffraction analysis, which revealed a distorted octahedral geometry around the metal centres. The solution behavior of the [VVOL1(OCH3)] (1) reveals the formation of two different types of V(V) species in solution, the structurally characterized compound 1 and its corresponding monooxido-bridged divanadium (V, V) complex [VVOL1]2(μ-O), which was further studied by IR, and NMR spectroscopy. The electrochemical behavior of all the complexes was evaluated through cyclic voltammetry. Interaction of the salan-V(V) complexes with human serum albumin (HSA) and bovine serum albumin (BSA) were analysed through fluorescence quenching, UV–vis absorption titration, synchronous fluorescence, circular dichroism studies, and förster resonance energy transfer (FRET). Finally, the in vitro cytotoxicity of the complexes was investigated against MCF-7 and HT-29 and NIH-3T3 cell lines. Cytotoxicity value of complexes in both MCF-7 and HT-29 follows the same trend that is 3 > 1 > 2 which is in line with protein binding affinity of the complexes.

Immobilised nickel(II), dioxomolybdenum(VI) and dioxouranium(VI) complexes on polystyrene resin

New polystyrene supported mixed Schiff bases(PSCH 2 –LH 2 ) and their coordination compounds with nickel(II), dioxomolybdenum(VI), and dioxouranium(VI) have been synthesized. PSCH 2 –LH 2 have been synthesized by the reaction of chloromethylated polystyrene crosslinked with divinylbenzene(PSCH 2 –Cl) and the Schiff bases(LH 2 ) derived from 3-formylsalicylic acid, ethylenediamine or propylene diamine, and acetylacetone. The polystyrene-supported coordination compounds are of the types: PSCH 2 –LM(where M = Ni, MoO 2, UO 2 ). They have been synthesized by the reaction of PSCH 2 –LH 2 and the metal salt/metal coordination compounds in DMF. The coordination compounds have been characterized on the basis of elemental analyses, IR, reflectance, and magnetic susceptibility measurements. The shifts of the ν (C=N)(azomethine), ν (C–O)(phenolic) and ν (C–O)(enolic) stretches indicate the ONNO donor behavior of PSCH 2 –LH 2. The polystyrene-supported Ni(II) compound is square planar; MoO2 (VI) and UO2 (VI) compounds are octahedral and Zr(IV) compounds are pentagonal bipyramidal. The compounds, PSCH 2 –LM(where M = Ni, MoO 2, and UO 2 ) are diamagnetic.

Biomimetic Oxidative Bromination by cis‐Dioxidotungsten(VI) Complexes of Salan Type N,N’‐Capped Linear Tetradentate Amino Bisphenol

AbstractReaction of [WVIO2(acac)2] (Hacac=acetylacetone) with salan‐type dibasic tetradentate ONNO donor Mannich bases derived from ethylenediamine, formaldehyde and 2,4‐di‐tert‐butylphenol (H2L1), 2‐tert‐butyl‐4‐methylphenol (H2L2), 2,4‐dimethylphenol (H2L3) and 2,4‐dichlorophenol (H2L4) in a 1 : 1 ([WVIO2(acac)2] : H2L) molar ratio in refluxing MeOH gave the corresponding cis‐dioxidotungsten(VI) complexes [WVIO2L1] (1), [WVIO2L2] (2), [WVIO2L3] (3) and [WVIO2L4] (4), respectively. Characterization by elemental analysis, various spectroscopic (FT‐IR, UV‐vis, 1H and 13C NMR) studies, DFT calculations and single‐crystal X‐ray analysis of 2 and 3 suggest six‐coordinated octahedral α‐cis (symmetric) isomeric form of the complexes where ligands coordinate through the two phenolate oxygen and two amine nitrogen atoms (in a cis‐α type symmetric binding mode) with one of the N atoms of the ligand and one of the terminal O atoms of the cis‐WO2 group in the axial position. These complexes are potential catalyst precursors for the oxidative bromination of thymol and styrene. Thymol upon bromination gave three products, namely, 2‐bromothymol, 4‐bromothymol, and 2,4‐dibromothymol; later one being the major product. Oxidative bromination of styrene resulted in 2‐bromo‐1‐phenylethanol and 1‐phenylethane‐1,2‐diol; the later one is the result of nucleophilic attack of water on the α as well as β carbons both of the initially formed 1,2‐dibromo‐1‐phenylethane.

Synthesis, spectral characterization, crystal structure and antibacterial activity of nickel(II), copper(II) and zinc(II) complexes containing ONNO donor Schiff base ligands

In the present study, a series of mononuclear Ni(II), Cu(II) and Zn(II) complexes with ONNO donor salen-type Schiff base ligands, derived from different 3,5-dihalosalicylaldehyde with polymethylenediamines of varying chain length, have been prepared. All the synthesized compounds were characterized by using various spectroscopic (FT-IR and 1H NMR) and analytical (CHN etc.) techniques. Furthermore, three complexes (ZnL1, NiL3 and NiL4) were successfully characterized by single crystal X-ray diffraction. The data revealed that the geometry around Zn(II) was distorted square pyramidal for ZnL1, while NiL3 and NiL4 complexes adapted slightly distorted octahedral geometries around Ni(II). The antibacterial activities of the synthesized ligands and their respective complexes were elaborated by screening them against two strains of Gram positive (Staphylococcus aureus and Bacillus cereus) and two strains of Gram negative (Escherichia coli and Pseudomonas aeruginosa) bacteria. It was found from the measurements of zones of inhibition that metal chelates are marginally more effective than free ligands.

Synthesis, spectroscopic characterization, DFT, oxygen binding, antioxidant activity on Fe(III), Co(II) and Ni(II) complexes with a tetradentate ONNO donor Schiff base ligand

The Schiff base ligand, namely (7E)-N-benzylidene-2-styrylbenzenamine- 1,2-diamine-2,4-dihydroxy-phenol (L), was synthesized by condensation of 2,4-dihydroxybenzaldehyde with o-phenylenediamine. The reaction of the ligand with Fe(III), Co(II) and Ni(II) salts in an 1:1 ratio yielded three complexes (1?3). Different analytical tools, like elemental analysis, ESI-MS, UV?Vis, FT-IR, NMR and EPR spectroscopy, then molar conductivity and magnetic susceptibility spectra, were used to elucidate the structure of the ligand and complexes. Density functional theory calculation at the B3LYP/3- -211G++/LANL2DZ level of the theory has been carried out to optimize the geometry of the ligand and complexes. The tetradentate ligand has coordinated to metals through ONNO donors affording octahedral geometry. Complexes were studied for their oxygen-binding activity and free radical scavenging activities. Complexes 1 and 2, which contain Fe(IIl) and Co(II), displayed reversible oxygen binding activity. On the other hand, complex 3 fails to show oxygen binding. The order of antioxidant activity is: 3 > 1 > 2 > L.

Polymer complexes. LXXIV. Synthesis, characterization and antimicrobial activity studies of polymer complexes of some transition metals with bis-bidentate Schiff base

Copper(II), cobalt(II), nickel(II), manganese(II) and cadmium(II) polymer complexes of N,N`-1,4-phenylene (2-hyboxynaphthaliden imine) have been synthesized. The structure of Schiff base and polymer complexes have been characterized by elemental analysis, spectral (FT-IR, UV–Vis, 1H NMR and ESR), X-ray diffraction, magnetic moment measurements and molar conductance. The molar conductivity data indicates that the chelates are non-electrolytes for polymer complexes (1, 4 & 5). The analytical data support 1:1 (M:L) stoichiometry. FT-IR data shows the ligand function as bis-bidentate coordination through ONNO donor system. The electronic spectra along with magnetic data suggest octahedral geometry for polymer complexes. The XRD patterns of the ligand and its polymer complexes showed the polycrystalline natures. The ligand and its complexes were studied for their microbial activity against some bacteria and fungi. Our results indicated that ligand and polymer complex (3) have higher effect against S. aureus than that of penicillin by at least nine times; this effect increased by increasing the concentration. Molecular docking was used to predict the binding between ligand and two receptors of the crystal structure of Staphylococcus aureus (3q8u) and the crystal structure of E. coli (3t88). It was found that, the receptor of Staphylococcus aureu (3q8u) shows the best interaction than the receptor of E. coli (3t88) with the ligand.

Titanium (IV) complexes of some tetra-dentate symmetrical bis-Schiff bases of 1,6-hexanediamine: Synthesis, characterization, and in silico prediction of potential inhibitor against coronavirus (SARS-CoV-2).

Symmetrical bis‐Schiff bases (LH 2) have been synthesized by the condensation of 1,6‐hexanediamine (hn) and carbonyl or dicarbonyl. One of the synthesized Schiff bases has been subjected to the molecular docking for the prediction of their potentiality against coronavirus (SARS‐CoV‐2). Molecular docking revealed that tested Schiff base possessed high binding affinity with the receptor protein of SARS CoV‐2 compared with hydroxychloroquine (HCQ). The ADMET analysis showed that ligand is non‐carcinogenic and less toxic than standard HCQ. Schiff bases acting as dibasic tetra‐dentate ligands formed titanium (IV) complexes of the type [TiL(H2O)2Cl2] or [TiL(H2O)2]Cl2 being coordinated through ONNO donor atoms. Ligands and complexes were characterized by the elemental analysis and physicochemical and spectroscopic data including FTIR, 1H NMR, mass spectra, UV‐Visible spectra, molar conductance, and magnetic measurement. Optimized structures obtained from quantum chemical calculations supported the formation of complexes. Antibacterial, antifungal, and anti‐oxidant activity assessments have been studied for synthesized ligands and complexes.

10.4314/bcse.v25i2.65886

A multidentate ligand, 3,4-bis(2-iminomethylphenol)-2,2’:5,2’’-terthiophene (L), has been synthesized by the condensation of 3,4-diamino-2,2’:5,2’’-terthiophene and salicylaldehyde. The ligand and Ni(II) and Zn(II) complexes were synthesized and characterized by IR, NMR, UV-Vis, AAS, MS, molar conductivity and magnetic susceptibility measurements. The ligand behaves as neutral ONS-ONS bis-chelant towards Ni(II) in [Ni 2 LCl 4 (H 2 O) 2 ]×4H 2 O and as dibasic ONNO donor towards Zn(II) in [ZnL(NH 3 ) 2 ]. The dinuclear Ni(II) complex exhibits subnormal magnetic moment at room temperature due to metal-metal interaction through extended conjugation. The participation of the ring sulfur in bonding towards Ni(II) and the non-participation of the same towards Zn(II) are notable features. Octahedral geometries are proposed for both complexes. Cyclic voltammetric studies revealed electrochemical polymerization of the free ligand (L) but not of the Ni(II) and Zn(II) complexes. KEY WORDS : Variable denticity, 3,4-bis(2-Iminomethylphenol)-2,2’:5,2’’-terthiophene, Octahedral, Ni(II) complex, Zn(II) complex, Voltammetric studies Bull. Chem. Soc. Ethiop. 2011 , 25(2), 221-231.