Mannich Base Ligands Research Articles

Anticancer, Antioxidant and Antimicrobial Evaluation of Cr (III) and Rh(III) Complexes Derived from A New Mannich Base

The Mannich base ligand was synthesized in an ethanol medium through a condensation reaction of 2-mercaptobenzimidazole and ciprofloxacin at room temperature. Subsequently, several metal complexes of this ligand were prepared. To characterize both the base ligand and the metal complexes, various techniques were employed, including elemental analysis, FT-IR spectroscopy, UV-Vis spectroscopy, molar conductivity measurements, magnetic moment determination, and melting point analysis. The results were shown that the metal complexes formed have the formula [Cr(L)2Cl2] Cl.H2O and [Rh(L)2(H2O)2] Cl3.H2O, where L= mannich base ligand. Based on spectroscopic analytical, coordination with metal ions involves the 'N' donor atom of mannich base and 'N' atom of piprizaing ring, and two complexes are A six-coordinated octahedral structure is suggested. Molar conductivity of these complexes showed that they were electrolytic in nature. In this study, the anticancer and antioxidant potential of the Mannich base ligand and its metal complexes were investigated against MDA-MB-231 cell lines and using the DPPH free radical scavenging assay. Moreover, the in vitro efficacy of the ligand and its complexes against Gram-negative bacteria (E. coli) and Gram-positive bacteria (Staphylococcus aureus), as well as the fungal strain Candida albicans, was evaluated using the disc diffusion method. The results indicated that Cr (III) and Rh(III) complexes demonstrated the highest levels of cytotoxicity against MDA-MB-231 cell lines, enhances antioxidant and antimicrobial activity more than the free ligand. These findings suggest that these metal complexes may have promising applications in the development of novel anticancer, antioxidant and antimicrobial agents.

Design, synthesis, and evaluation of some metal ion complexes of mannich base derived from 2-Mercaptobenzimidazole as potential antimicrobial agents

This study aims to prepare new compounds and investigate them spectroscopically and biologically against selected types of positive and negative bacteria and fungi to demonstrate their biological effectiveness. The prepared ligand combining formaldehyde, indole, sulfa benzamide, and 2-mercapto benzimidazole, a Mannich base ligand (L) was synthesized. The six metal ions including Cobalt (II), Nickel (II), Copper (II), Palladium (II), Platinum (IV), and gold (III) have interacted with the ligand and formed new complexes. Different spectroscopic methods, including C.H.N.S., FTIR, UV- Range visible, 1HNMR, 13CNMR, mass spectra, magnetic moment, and molar conductivity were used to suggest the new geometry of the complexes. The result from the infrared spectrum showed that the ligand behaves as tridentate with all prepared complexes. Conductivity analysis revealed the electrolytic nature of palladium, platinum, and gold ions complexes and non-electrolytes. The antibacterial activity of the compounds that were produced was tested using an agar-well diffusion procedure towards two strains of gram-positive as well as two strains of gram-negative bacteria and fungi (Staphylococcus, Streptococcus, Escherichia coli, Pseudomonas aeruginosa, and Candida albicans) respectively at 0.02M. The standard (∆Eo) and (∆Hfo) of ligand and six complexes were calculated using the program Hyper chem 8.0.7. The research established that complexes are more stable than ligands. Calculated HOMO and LUMO and vibration frequencies using (parametric method 3 (PM3)) to find out the active sites in the ligand showed that they can coordinate and note the extent to which the results of theoretical vibrational frequencies are close to the process when calculating the vibrational frequency of the active aggregates.

Synthesis and Spectroscopic Investigation of N-(Morpholinofurfuryl) Maleimide and its Copper (II) Complex uses in Biological Applications

The Mannich base N-(morpholinofurfuryl) maleimide (MOFM) is synthesized through a Mannich reaction using Maleimide as one of the starting materials. The reaction likely involves the condensation of Maleimide with formaldehyde and a secondary amine. It is then complexed with copper (II) to form the copper complex. This complexation process might involve reacting the Mannich base with a copper (II) salt under appropriate conditions. Characterization techniques such as FT-IR, UV–visible spectroscopy, 1H, and 13C NMR spectroscopy are used to confirm the formation of the complex and determine its structural features. The antioxidant properties of both the Mannich base ligand and its copper (II) complex are evaluated using assays such as DPPH (2,2-diphenyl-1-picrylhydrazyl) and reducing power assay. These assays assess the ability of the compounds to scavenge free radicals and reduce oxidative stress. It was found that MOFM had an IC50 value of 4.1762 x 10-4 and its Cu(II) complex had 2.5772 x 10-4 which confirms the ability of the prepared compounds to scavenge free radicals and reduce oxidative stress. The antimicrobial activity of the copper (II) complex of MOFM and the ligand is tested against various microorganisms including Aspergillus niger, Candida albicans, Escherichia coli, and Staphylococcus aureus using the agar-well diffusion method. Both the compounds had good antibacterial and antifungal properties. By conducting these experiments and analyses, you can gain insights into the structural features, antioxidant properties, and antimicrobial efficacy of both the Mannich base ligand and its copper (II) complex, which could have potential applications in various fields such as pharmaceuticals, materials science, or environmental protection.

توصيف ، تحضير والتقييم الحيوي لبعض معقدات العناصر الانتقالية لقاعدة مانخ

The new mannich base ligand and its metal complexes were synthesized in ethanol medium. The mannich base is derived from the condensation reaction of morpholine and Ciprofloxacin (Cp) at room temperature. This ligand and metal complexes were characterized using elemental analysis, FT-IR, UV-Vis, and NMR spectral data, molar conductivity measurements, and melting points. Elemental analysis data show that the metal complexes formed have the general formula[Cr(L)2ClH2O] Cl.H2O, [Pt(L)2Cl2] Cl2.H2O and [Au(L)2]Cl.H2O where mannich base ligand (L) .Based on spectroscopic analytical, coordination with metal ions involves the 'O' donor atoms of carboxylate group, and the Cr(III) and Pt(IV) complexes are a six-coordinated octahedral structure while Au(III) complex is A four-coordinated square planer structure. Molar conductivity of these complexes showed that they were electrolytic in nature. The toxicity of the free ligand and their metal complexes as anticancer agents against MDA-Mb-231 cell lines was examined with different concentration. Anticancer testing revealed that all complexes were more effective than the ligand. The Au (III) complex exhibited the most significant toxicity effect than the other compounds.

Synthesis, spectroscopic analysis, computational, antibacterial, antifungal, DNA binding and antioxidant activities of cobalt(II) and zinc(II) complexes of Mannich base ligand

Biologically active small molecules of cobalt(II) and zinc(II) and complexes (MLX2⋅nH2O; M = Co(II) and Zn(II); X = Cl; n = 6 or 2) of Mannich base ligand (L) were synthesized from nicotinamide, formaldehyde and morpholine. The synthesized compounds were characterized by physicochemical, mass, proton NMR, FT-IR and UV–Visible and the results shows that the proposed structure of prepared complexes may be square planar geometry. It was further confirmed by the computational methods such as DFT calculation. Antimicrobial activities of prepared compounds were studied by well diffusion method and results shows that better antimicrobial activity at higher concentration and good activity against S. aureus and C. albicans. Antioxidant activity of prepared compounds were studied by free radical DPPH and results reveal that prepared compounds have better antioxidant activities. Moreover, DNA binding ability of prepared Co(II) and Zn(II) complexes with calf thymus DNA (CT-DNA) by UV–Visible spectroscopic method. The results have been suggested that prepared complexes can be interact with CT-DNA molecule through groove binding mode. Moreover, the binding constant of Co(II) complex (8.32 × 104 M−1) is higher than Zn(II) complex (1.20 × 104 M−1) correspondingly.

Synthesis, Structural, Morphological Characterization, and Cytotoxicity Assays of Metal Complexes Decorated SiO2 Nanoparticles Against Breast Cancer Cell Lines (MDA-MB-231)

This study examines the new synthesis of Pt (IV) and Au (III) Mannich base complexes derived from ciprofloxacin. The complexes were then used as precursors to prepare SiO2/PtO2 and SiO2/Au2O3 nanoparticles by depositing the synthesized complexes on porous silica nanoparticles. Elemental analysis, FT-IR, UV-vis, molar conductivity measurements, and melting point were used to characterize this ligand and its metal complexes. Elemental analysis data show that the general formula of the metal complexes formed is [M(L)2Cl2] nCl.H2O, where L = Mannich base ligand and M = Au(III) and Pt(IV), and n = 1,2 respectively with octahedral structure. The chemical structure and morphology of the metal oxide nanoparticles are investigated using FT-IR, XRD, AFM, TEM, and SEM. In the next step, the ligand and its complexes, SiO2/PtO2 and SiO2/Au2O3 nanoparticles were examined to investigate their toxicity (in vitro) as an anticancer agent to MDA-MB-231 cell lines by using different concentrations (50, 100, 200, and 400 µg /mL). Based on the results obtained from the cytotoxic activity, it can be concluded that the synthesized compounds are promising as new cancer candidates in the future, especially in high concentrations

From field-induced to zero-field SMMs associated with open/closed structures of bis(ZnDy) tetranuclear complexes: a combined magnetic, theoretical and optical study.

We have prepared a bis(compartmental) Mannich base ligand H4L (1,4,8,11-tetraaza-1,4,8,11-tetrakis(2-hydroxy-3-methoxy-5-methylbenzyl)cyclotetradecane) specifically designed to obtain bis(TMIILnIII) tetranuclear complexes (TM = transition metal). In this regard, we have succeeded in obtaining three new complexes of the formula [Zn2(μ-L)(μ-OAc)Dy2(NO3)2]·[Zn2(μ-L)(μ-OAc)Dy2(NO3)(OAc)]·4CHCl3·2MeOH (1) and [TM2(μ-H2L)2(μ-succinate)Ln2(NO3)2] (NO3)2·2H2O·6MeOH (TMII = Zn, LnIII = Dy (2); TMII = Co, LnIII = Dy (3)). Compound 1 contains two different bis(ZnDy) tetranuclear molecules that cocrystallize in the structure, in which acetato bridging ligands connect the ZnII and DyIII ions within each ZnDy subunit. This compound does not exhibit slow magnetic relaxation at zero field, but it is activated in the presence of an applied dc magnetic field and/or by Dy/Y magnetic dilution, showing two relaxation processes corresponding to each of the two different bis(ZnDy) units found in the structure. As revealed by the theoretical calculations, magnetic relaxation in 1 is single-ion in origin and takes place through the first excited state of each DyIII ion. When using the succinato dicarboxylate bridging ligand instead of acetate, compounds 2 and 3 were serendipitously formed, which have a closed structure with the succinate anion bridging two ZnDy subunits belonging to two different ligands. It should be noted that only compound 2 exhibits slow relaxation of magnetization in the absence of an external magnetic field. According to experimental and theoretical data, 2 relaxes through the second excited Kramers doublet (Ueff = 342 K). In contrast, 3 displays field-induced SMM behaviour (Ueff = 203 K). However, the Co/Zn diluted version of this compound 3Zn shows slow relaxation at zero field (Ueff = 347 K). Ab initio theoretical calculations clearly show that the weak ferromagnetic coupling between CoII and DyIII ions is at the origin of the lack of slow relaxation of this compound at zero field. Compound 2 and its diluted analogues 2Y and 3Zn show hysteresis loops at very low temperature, thus confirming their SMM behaviour. Finally, compounds 1 and 2 show DyIII based emission even at room temperature that, in the case of 2, allows us to extract the splitting of the ground 6H15/2 term, which matches reasonably well with theoretical calculations.

Versatile Applications of Mannich Base Ligands and their Metal ‎Complexes: A Review Article

Versatile Applications of Mannich Base Ligands and their Metal ‎Complexes: A Review Article

Reductive functionalization of CO2 under mild reaction conditions for the catalytic synthesis of N-formamides by Mannich base based Cobalt (III) complex

Reductive functionalization of carbon dioxide is an important approach which not only reduces CO2 concentration but also functionalized it for the formation of value added chemicals. In this perspective, a hexadentate mononuclear cobalt (III) complex [CoIIIL] of Mannich base ligand (H4L) was synthesized and structurally characterized by single crystal X-ray diffraction. The electronic spectra of the complex showed two bands at 448 and 561 nm corresponds to the LMCT and d-d transitions respectively. The derived inexpensive [CoIIIL] complex was very much effective as catalyst in carbon dioxide functionalization reaction. The catalytic synthesis of mono selective N-formamide product from amines was produced through diagonal transformation of carbon dioxide in presence of polymethylhydrosiloxane (PMHS) as reducing agent and [CoIIIL] complex as catalyst. The effects of various reaction parameters were examined. Broad range of substrates (aromatic as well as aliphatic amines) smoothly produced good percentage of respective N-formamides product (72–94%) under mild reaction condition utilizing 1 atmospheric CO2. The high TON (1540–2000) and TOF value (192.5–400.0 h−1) for the catalytic reactions strongly depicted the productive nature of the [CoIII(L)] catalyst. The probable mechanestics studies clearly reveals that the [CoIIIL] complex activated the Si−H bond of PMHS to react with carbon dioxide in order to form the silyl formates intermediate for activation of N–H bonds in amines, thus leading to the excellent performance of the catalytic reaction.

ZnAl2O4 Nanomaterial as a Naked-Eye Arsenate Sensor: A Combined Experimental and Computational Mechanistic Approach.

Raising public awareness over the emerging health risk due to intake of arsenic-contaminated potable water is a matter of great concern. Exploration of cost-effective, self-testing kits is a substantial way to reach out to the masses and detect the presence of arsenate in water. With this agenda, a photoluminescent Mannich base Zn(II) complex (ZnMC = [Zn2(ML)2]·(ClO4)2·(H2O); HML = Mannich base ligand) has been synthesized, and its dinuclearity was verified with single-crystal X-ray diffraction structural analysis. Among a range of anions, ZnMC was found to detect arsenate selectively by showing a turn-off emission with a color change from bright green to dark under UV light. The real-life applicability of the ZnMC probe is somewhat restricted to only sensing of arsenate, but not its removal owing to the fact of its homogeneity. Considering the efficacy of ZnMC as well as a need for its easy removal from water, slight modification has been done with chloride ions in the form of ZnMC″ (=[Zn2(ML)2(Cl)2]), and finally, an interface between homogeneous and heterogeneous solid support has been explored with a strategic fabrication of ZnMC″ grafted ZnAl2O4, named as ZAZ nanomaterial. This not only imparts successful segregation of arsenate from drinking water but also provides naked-eye detection under ambient light as well as UV light. Thermodynamic parameters associated with the binding of arsenate to ZnMC and ZAZ have been evaluated through isothermal calorimetric (ITC) measurements. Steady-state and time-resolved fluorescence titration study, absorption titration study, scanning electron microscopy (SEM), transmission electron microscopy (TEM), and computational calculations have been performed to get deep insights into the sensing properties. Proper justification of the sensing mechanism is the highlight of this work. ZAZ nanomaterial has been exploited to produce a self-test paper kit for arsenate detection with a limit of 9.86 ppb, which potentially enables applications in environmental monitoring.

Cancer-Targeted Chitosan-Biotin-Conjugated Mesoporous Silica Nanoparticles as Carriers of Zinc Complexes to Achieve Enhanced Chemotherapy In Vitro and In Vivo.

Despite being the most common component of numerous metalloenzymes in the human body, zinc complexes are still under-rated as chemotherapeutic agents. Herein, the present study opens up a key route toward enhanced chemotherapy with the help of two ZnII complexes (ZnMBC) synthesized alongside Mannich base ligands to upsurge biological potency. Further, well-established mesoporous silica nanoparticles (MSNs) have been chosen as carriers of the titled metallodrugs in order to achieve anticancer drug delivery. A pH-sensitive additive, namely, chitosan (CTS) conjugated with biotin is tagged to MSNs for the targeted release of core agents inside tumors selectively. In general, CTS blocks ZnMBC inside the mesopores of MSNs, and biotin acts as a targeting ligand to improve tumor-specific cellular uptake. CTS-biotin surface decoration significantly enhanced the cellular uptake of ZnMBC through endocytosis. A panel of four human cancer cell lines has revealed that ZnMBC (1/2)@MSNs-CTS-biotin nanoparticles (NPs) exhibits unprecedented enhanced cytotoxicity toward cancer cells with IC50 values ranging from 6.5 to 28.8 μM through induction of apoptosis. NPs also possess great selectivity between normal and cancer cells despite this potency. Two-photon-excited in vitro imaging of normal (HEK) and cancer (HeLa) cells has been performed to confirm the biased drug delivery. Also, NP-induced apoptosis was found to be dependent on targeting DNA and ROS generation. Moreover, a lower range of LD50 values (153.6-335.5 μM) were observed upon treatment zebrafish embryos with NPs in vivo. Because of the anatomical similarity to the human heart, the heart rate of NP-treated zebrafish has been analyzed in assessing the cardiac functions, which is in favor of the early clinical trials of ZnMBC (1/2)@MSNs-CTS-biotin candidates for their further evaluation as a chemotherapeutic and chemopreventive agent toward human cancers, especially adenocarcinoma.

Synthesis of Cu(II) complexes by N,O‐donor ligand transformation and their catalytic role in visible‐light‐driven alcohol oxidation

AbstractVisible‐light‐driven photoreactions using metal complexes as catalysts are currently a research hotspot in terms of the development of environmentally friendly sustainable processes. To develop potential copper‐based photocatalysts, a Mannich base ligand, namely, 2,4‐dichloro‐6‐((4‐(2‐hydroxyethyl)piperazin‐1‐yl)methyl)phenol (H2L), has been synthesized and characterized. Two copper complexes [Cu (HL1)] (1) and [Cu (HL2)] (2) have been obtained from H2L, where the ligand undergoes an unprecedented transformation plausibly via oxidation of piperazine ring to ketone, subsequent oxidation of enol and nucleophilic attack of methanol followed by hydrolysis of amide bond, resulting piperazine ring cleavage. Under the irradiation of visible light, these catalysts can oxidize primary alcohols into corresponding aldehydes with very good conversion and high selectivity in the presence of molecular oxygen. The photocatalysts could be recovered almost quantitatively after completion of the catalytic cycle and recycled at least four times without much depreciation of catalytic activity. A plausible mechanistic pathway for alcohol oxidation has been explored through electrospray ionization mass spectrometry (ESI‐MS) spectrometric, cyclic voltammetry, UV–vis, and computational study.

Synthesis, characterization, DNA/BSA binding and cytotoxicity studies of Mononuclear Cu(II) and V(IV) complexes of Mannich bases derived from Lawsone

A series of new mononuclear copper complexes (1–5) and a vanadium complex (6) were synthesized using bidentate Mannich base ligands derived from bioactive molecule Lawsone. The structure of these new molecules/complexes (1–6) were characterized by various spectroscopic techniques such as UV-Vis, FT-IR, EPR, and ESI-MS. The structure of complex 1 was also confirmed by single crystal X-ray diffraction analysis, which revealed that complexes containing copper atom has slightly distorted square planar geometry. Computational studies were carried out for the synthesized compounds (1–6) using the DFT method with B3LYP/6–311 G (d, p) and LanL2DZ basis sets to assess the bond length, bond angle, HOMO, and LUMO energy gap (∆E). The CT-DNA and BSA binding (protein binding affinity) studies revealed that complex 4 exhibited the highest DNA binding affinity and complexes 5 and 6 exhibited the highest protein binding affinity. The cytotoxic activity of complexes 3–6 was evaluated using MTT assay along with the apoptosis assessment (AO/EB staining) against HepG2 (human liver carcinoma cell line). Furthermore, the data revealed that all the complexes 3–6 displayed very good anticancer activity with IC50 values in the range of 5.46–2.71 µM which is comparable with that of standard anticancer drug.

Antimicrobial activity of transition metal (II) complexes based on a Mannich base ligand

In this study, the authors report the synthesis of a new Mannich base formed by the condensation of pyrrole (C4H5N), 4-hydroxybenzaldehyde (C7H6O2) and phthalimide (C8H5NO2) and the respective copper (II) (Cu2+), nickel (II) (Ni2+) and cobalt (II) (Co2+) transition metal complexes derived from the ligand. The synthesized ligand and the metal complexes were characterized using elemental analysis, electrical conductivity studies and spectral studies. The geometry of the Mannich base metal (II) complexes was studied by ultraviolet–visible and electron spin resonance spectroscopy, and all the complexes were found to adopt square planar geometry. Among all the complexes, the cobalt complex was observed to show better antioxidant properties. It is noteworthy to mention that the copper complex is observed to exhibit better deoxyribonucleic acid cleavage activity at all concentrations compared with other complexes.

Studies on the Spectral, Anti-Bacterial and Anti-Fungal Activities of 1-((Dicyclohexylamino) (Phenyl) Methyl) Pyrrolidine-2, 5-Dione and Few of its Metal Complexes

1-((dicyclohexylamino)(phenyl)methyl) pyrrolidine-2,5-dione (SDB) has been synthesized as a result of succinimide, benzaldehyde and dicyclohexylamine Mannich base condensation and its CoII, NiII and CuII complexes were prepared. The structure of the Mannich Base ligand (SDB) was elucidated on the basis of FT-IR, 1H NMR, 13C NMR and Mass spectral studies. The monomeric and non-electrolytic nature of the metal complexes is evidenced by their magnetic susceptibility and low conductance data studies. Spectral tests, mainly FT-IR studies as well as elemental analysis, were carried out to verify the structures of the newly synthesized compounds. All the metal complexes possess a six-coordinate geometry. The synthesized ligand and its metal complexes have been tested against Gram-positive strains (Staphylococcus aureus and Micrococcus luteus), Gram-negative strains (Escherichia coli and Pseudomonas aeruginosa) and fungal strains (Aspergillus niger and Aspergillus fumigates) for their in vitro anti-bacterial and anti-fungal activities. Preliminary antimicrobial studies of the ligand and their metal complexes have also been carried out in order to understand the toxic effect of ligands and metal complexes against the selective microbes. The results showed that the metal chelates of the ligands showed higher antimicrobial activities than the free ligand SDB and CoII complexes possess higher activity than the other metal complexes.

Novel Cu(II) and Ni(II) complexes of nicotinamide based Mannich base: Synthesis, characterization, DFT calculation, DNA binding, molecular docking, antioxidant, antimicrobial activities

Nicotinamide incorporating Mannich base ligand (L), Cu(II) and Ni (II) complexes of [CuLCl2].2H2O (1) and [NiLCl2].2H2O (2) were synthesized and characterized by elemental analysis, FT-IR, UV–Visible, ESR and mass spectrometric methods. The square planar geometry of the complexes (1 and 2) were confirmed from analytical and diverse spectroscopic methods. Cyclic votammetric behaviors of complexes (1 and 2) were studied. The optimized geometry of L, complexes (1 and 2) were obtained by Density Functional Theory (DFT) calculations. DNA binding ability of complexes (1 and 2) were studied by electronic absorption and fluorescence techniques. Both the spectroscopic results show that complex 1 (9.64 × 104 M−1) has good binding affinity than complex 2 (6.07 × 104 M−1). The interaction of complexes (1 and 2) with CT-DNA was explored by Molecular docking analysis revealed that an efficient interaction of complexes (1 and 2) with the DNA. The results indicate that prepared complexes (1 and 2) have better binding ability with DNA double helix. Antioxidant activities of complexes (1 and 2) have studied by DPPH method and results suggest that prepared complexes (1 and 2) have better radical scavenging ability. Antimicrobial activities of ligand (L) and complexes (1 and 2) were tested against selected bacterial and fungal pathogens results shows that prepared compounds have higher antimicrobial activity against E. coli and A. niger antimicrobial species than others.

Catalytic promiscuity of a copper(II)-Mannich base complex having unprecedented radical pathway in catecholase activity

A flexible single-side Mannich base ligand namely 4-(tert-butyl)-2-((ethyl(2-hydroxyethyl)amino)methyl)phenol (H2L) having O, N, O donor sites has been designed and synthesized using 4-(tert-butyl)phenol, formaldehyde and 2-(ethylamino)ethanol as precursors with the view to prepare polynuclear complex(s). In the first attempt a tetranuclear copper (II) complex, [Cu4(L)2(HL)2].(ClO4)2·H2O (1) has been synthesized employing H2L and copper(II) perchlorate with the aim to explore catalytic promiscuity of the species. Detailed experimental investigations suggest that in solution complex 1 exits as a dinuclear entity. The dinuclear species is a square-planar CuII complex as is evident from EPR and UV–Vis spectral studies. It exhibits excellent catalytic activities in catalyzing the oxidation of 3,5-di-tert-butyl catechol (3,5-DTBC) to 3,5-di-tert-butyl quinone (3,5-DTBQ); oxidation of o-aminophenol to phenoxazinone and PO bond hydrolysis of 4-nitrophenyl phosphate. Amazingly, complex 1 catalyses the aerobic oxidation of 3,5-DTBC not by well established metal centered redox participation, rather via a ligand centered radical pathway, a completely new finding in copper(II) based catechol oxidase modeling as are verified by experiments and seconded by DFT calculations.

Antibacterial activity studies of Co(II), Ni(II), Cu(II) and Zn(II) complexes with Mannich base ligand

A Mannich base ligand (L) was prepared by reacting 2-mercaptobenzimidazole, diphenylamine and benzaldehyde. This ligand (L) was further used for the preparation of four metal complexes with Co(II), Ni(II), Cu(II) and Zn(II) ions. The reactions were monitored by TLC. The synthesized compounds were structurally characterized using FTIR spectroscopy, UV-Visible spectroscopy, 1H- and 13C-NMR spectroscopy, ICP-OES/atomic absorption spectroscopy. It has been observed that the ligand (L) behaved in a monoanionic bidentate mode and the geometry of resulting complexes was tetrahedral. Conductivity analysis revealed their non-electrolytic nature. Antibacterial activity of the synthesized compounds was assessed through an agar well diffusion method against four strains of Gram-negative bacteria. L-Zn(II) complex showed best activity at all four concentrations against the four strains of Gram-negative bacteria. KEY WORDS: Metal complexes, Mannich bases, 2-Mercaptobenzimidazole, Antibacterial activity Bull. Chem. Soc. Ethiop. 2019, 33(3), 485-492.DOI: https://dx.doi.org/10.4314/bcse.v33i3.9

Inclusion of Ln(III) in the Complexes of Co(II) with a Mannich Base Ligand: Development of Atmospheric CO2 Fixation and Enhancement of Catalytic Oxidase Activities.

The reaction of the Mannich base ligand (H2L = N, N'-dimethyl- N, N'-bis(2-hydroxy-3-methoxy-5-methylbenzyl)ethylenediamine) with Co(OAc)2·4H2O and Ln(III) nitrate salts (Ln = Gd, Tb, and Dy) under basic conditions afforded three carbonato-bridged isostructural tetranuclear heterometallic Co(II)-Ln(III) complexes (Co2Gd2L2(μ4-CO3)2(NO3)2] (1), [Co2Tb2L2(μ4-CO3)2(NO3)2] (2), and [Co2Dy2L2(μ4-CO3)2(NO3)2] (3)) by atmospheric CO2 fixation. In all structures, two dinuclear [(CoIIL)LnIII(NO3)] units are linked via two μ4-carbonato groups to form the tetranuclear CoII2LnIII2 core. The geometry around two penta-coordinated Co(II) ions is distorted square pyramid, and that around two nona-coordinated Ln(III) ions is intermediate between "spherical tricapped trigonal prism" and "spherical capped square antiprism" in all complexes. The complexes (1-3) showed catecholase-like and phenoxazinone-synthase-like catalytic activities. The kcat values calculated for the catecholase-like reaction were 254.5, 272.4, and 291.3 h-1, and for the phenoxazinone-synthase-like reaction they were 2930.6, 2965.2, and 2998.5 h-1 for complexes 1-3, respectively. The probable pathways for these two oxidase reactions have been proposed by the analyses of mass spectral data. For all of the compounds, the variable temperature magnetic susceptibility and isothermal magnetization data were investigated. The complexes exhibited overall ferromagnetic behavior, which was evident from the isothermal magnetization curves. AC magnetic susceptibility measurements revealed the slow relaxation of magnetization in complexes 2 and 3 but very negligible in 1. The activation energy barriers ( Ueff) for the slow relaxation process were evaluated and found to be 1.99, 2.79, and 8.98 K for 1, 2, and 3, respectively.

The catalytic activities and magnetic behaviours of rare μ3-chlorido and μ1,1,1-azido bridged defective dicubane tetranuclear Mn(ii) complexes.

Reaction of Mn(ii) salts with a flexidentate Mannich base ligand, N,N'-dimethyl-N,N'-bis(2-hydroxy-3-methoxy-5-methylbenzyl)ethylenediamine (H2L) in the presence of chloride or azide ions yielded two new tetranuclear complexes, [Mn4L2(μ3-Cl)2Cl2] (1) and [Mn4L2(μ1,1,1-N3)2(N3)2] (2). Single crystal X-ray structural analyses reveal that these two discrete tetranuclear Mn(ii) complexes possess defective dicubane cores with two μ3-Cl (for 1) or two μ1,1,1-N3 bridges (for 2). One of the triply bridging groups is situated above and the other one below the plane of the four Mn(ii) ions. In both complexes, all Mn(ii) ions are in a hexa-coordinated distorted octahedral environment. Both complexes 1 and 2 exhibit catecholase like activity and phenoxazinone synthase-like activity under ambient conditions. The turnover numbers (kcat) for the aerobic oxidation of 3,5-di-tert-butylcatechol are 1492.4 and 1431.2 h-1 and those of o-aminophenol are 2265.5 and 2132.2 h-1 for complexes 1 and 2, respectively. Mass spectral analyses were performed to get an idea about the probable mechanistic pathway for these catalytic reactions. Variable temperature magnetic susceptibility measurements of a solid sample reveal that both the complexes are antiferromagnetically coupled. The coupling constants are calculated to be J1 = -0.19 cm-1, J2 = -6.87 cm-1 and J3 = -0.70 cm-1 for 1 and J1 = 0.11 cm-1, J2 = -0.64 cm-1 and J3 = 0.11 cm-1 for 2 and these values are rationalized by DFT calculations.