Tetradentate Chelating Agent Research Articles

Structural variety of Cu (II), Ni (II), and Co (II) complexes of a hydrazone based on 5‐acetyl‐4‐hydroxy‐2H‐1,3‐thiazine‐2,6(3H)‐dione: Synthesis, spectroscopic, density functional theory, antitumor, and docking studies

New nickel (II), cobalt (II), and several copper (II) complexes have been synthesized from the hydrazone ligand (AHTDSH; H2L); which obtained from 5‐acetyl‐4‐hydroxy‐2H‐1,3‐thiazine‐2,6(3H)‐dione with salicylaldehyde hydrazone. The structures of H2L ligand and the prepared complexes were confirmed by spectroscopic and analytical techniques. The ligand behaves as bis (monobasic bidentate) and dibasic tetradentate chelating agent via azomethine nitrogen and phenolic oxygen atoms. Octahedral geometries have been assigned for the prepared complexes. The Coats–Redfern equations were used to estimate the kinetic parameters (Ea, A, H, S, and G) of the thermal decomposition stages. The molecular structural characteristics of the ligand and its metal complexes were estimated based on density functional theory (DFT) level implemented in the Gaussian 09 software at B3LYP/6‐311G(d,p) level and the theoretical data were connected with the results of the experimental work. The anticancer activity of AHTDSH ligand and its complexes was demonstrated toward HepG2 cell lines. The interaction between the chemical and the active site of the CDK2 kinase was examined using a docking study of the hydrazone ligand and its complexes.

Preparation of immobilized lipase on Co2+-chelated carboxymethyl cellulose based MnFe2O4 magnetic nanocomposite particles

Lipase immobilization was performed via physical adsorption on a novel metal-chelating nanostructure consisted of (S)-N-(5-Amino-1-carboxypentyl) iminodiacetic acid (NTA), as a tetra-dentate chelating agent, grafted onto MnFe2O4 nanoparticles coated with carboxymethyl cellulose (CMC) for Co2+-chelated affinity lipase adsorption. The influential immobilization parameters for enzyme adsorption were investigated. The maximum amount of immobilized lipase (8.5 mg/g adsorbent) was obtained at modified conditions with initial enzyme concentration of 2 mg/mL and adsorbent dosage of 1 mg/mL after 90 min incubation at 50 mM buffer citrate at pH 5. The Fourier transform infrared spectroscopy (FTIR), energy dispersive spectroscopy (EDS), and elemental mapping provided evidence of successful immobilization of lipase. The results of kinetic study revealed that the adsorption of lipase followed pseudo second order kinetic model. Investigation on the enzymatic properties demonstrated that the immobilized lipase possesses remarkable thermal stability at 60 °C for 120 min, as the catalytic activity of immobilized lipase was 75% higher than that of free lipase at the same temperature. Beside, the immobilized lipase still retained 70% of its initial activity after 7 successive recycles, suggesting the new designed Co2+-chelated magnetic nanostructure as a great matrix for the non-covalent enzyme immobilization.

Structural and theoretical studies of iron(III) and copper(II) complexes of dianion N1,N4-bis(salicylidene)-S-alkyl-thiosemicarbazide

Iron(III) and copper(II) complexes with an allyl N'-(1-(2-hydroxyphenyl)ethylidene)carbamohydrazonothioate·hydrobromide (H2L) and ethyl N'-5‑bromo-2-hydroxybenzylidenecarbamohydrazonothioate·hydrobromide (H2L') ligands were synthesized and characterized by elemental analysis, FT-IR spectroscopy and molar conductivity. Single crystal X-ray crystallography reveals that the iron and copper complexes have square pyramidal and square planar geometries, respectively. The ligands act as a binegative tetradentate chelating agent and they are bonded to the metal center through the phenolic oxygen, isothioamide nitrogen, and azomethine nitrogen atoms. The fifth site of the Fe(III) coordination sphere in both Fe complexes is occupied by chloride ion. Density functional theory method was used to complement the structural and spectroscopic data obtained experimentally. We also performed docking calculations of the complexes with human serum albumin and the copper complex binds preferentially.

Cellulose-tethered tetradentate chelating agent for pyridoxine determination

The test method of determination of the pyridoxine (vitamin B6) containing hydroxyaryl group comprises its azo coupling with chromogenic indicator diazo test strip, a reagent with functional diazoaryl group attached to the cellulose carrier through 1,3-diphenoxypropane bridge. This test strip reaction affords cellulose-tethered tetradentate chelating agent capable of forming chromogenic blue-violet complex with CuII ion.

Determination of pyridoxine by means of an indicator diazo-test strip

Pyridoxine (vitamin B6) plays an important role in the body’s metabolism. Reaction of azocoupling with diazoaryl compound underlies in a basis a known photometric method of its chemical analysis. This method is not selective. In the present work the test method of determination of the pyridoxine containing in a molecule hydroxyarylgroup, was proposed by them azocoupling with chromogenic indicator diazo test strip, consisting of a covalently fixed on cellulose reagent with functional diazoaryl group, attached to the cellulose carrier through 1,3-diphenoxypropane bridge. This test strip interaction with resulted in formation of cellulose tetradentate chelating agent, capable to enter the subsequent chromogenic reaction with copper (II) ion. Formation of blue-violet complex of azoderivative pyridoxine with copper was used for determination of the content of pyridoxine (vitamin B6) in a number of his pharmaceutical preparations.

Extraction of metals from high grade waste printed circuit board by conventional and hybrid bioleaching using Acidithiobacillus ferrooxidans

Bioleaching of selected metals, viz. Cu, Zn, Pb, Ni from e-waste in the form of high grade waste printed circuit board (PCB) of computer is comparatively assessed using pure culture of Acidithiobacillus ferrooxidans with and without the supplementation of lemon juice containing 0.2 M citric acid as active constituent and natural tetradentate chelating agent to simulate hybrid and conventional conditions, respectively. Metal leaching from the comminuted PCB is observed to vary greatly under the conventional and hybrid bioleaching conditions showing better solubilization in the hybrid approach due to the chelating effect of citric acid. At a pulp density of 7.5 g/L and the comminution fines in the size range of 0.075–1 mm, the maximum leaching of 94% Cu, 92% Zn, 64% Pb and 81% Ni are observed at 18 days of hybrid bioleaching with an asymptotic trend from 12 days onward. Measurement of the exopolymeric substances (EPS) production during bioleaching indicates a profound role in the leaching of metals. Extraction through chemical precipitation yields more than 99% of the selected metals from bioleached liquor. Hybrid bioleaching technique followed by chemical precipitation can be deliberated as a complete solution for metal recycling for resource recovery from e-waste.

Synthesis, bioevaluation and gamma scintigraphy of 99mTc-N-2-(furylmethyl iminodiacetic acid) complex as a new renal radiopharmaceutical

A ligand of N-2-(furylmethyl iminodiacetic acid) (FMIDA) has been easily labeled by a tetradentate chelating agent of [99mTc]. Factors like a stannous chloride solution as a reducing agent (100 μg), substrate amount (100 μg), pH (7), in vitro stability (8 h) and temperature (37 °C) have been systematically studied to optimize high radiochemical yield (98.0%). The radiochemical conversion was calculated on thin-layer chromatography, paper electrophoresis, and high performance liquid chromatography. Biodistribution study showed that this complex was removed from the kidneys and bladder path way during 1 h post injection. Therefore, [99mTc]FMIDA may be used as renal function radiotracer.

Rates of nickel(II) capture from complexes with NTA, EDDA, and related tetradentate chelating agents by the hexadentate chelating agents EDTA and CDTA: Evidence of a “semijunctive” ligand exchange pathway

Many siderophores and metallophores produced by soil organisms, as well as anthropogenic chelating agent soil amendments, rely upon amine and carboxylate Lewis base groups for metal ion binding. UV–visible spectra of metal ion-chelating agent complexes are often similar and, as a consequence, whole-sample absorbance measurements are an unreliable means of monitoring the progress of exchange reactions. In the present work, we employ capillary electrophoresis to physically separate Ni(II)-tetradentate chelating agent complexes (NiL) from Ni(II)-hexadentate chelating agent complexes (NiY) prior to UV detection, such that progress of the reaction NiL+Y→NiY+L can be conveniently monitored. Rates of ligand exchange for Ni(II) are lower than for other +II transition metal ions. Ni(II) speciation in environmental media is often under kinetic rather than equilibrium control. Nitrilotriacetic acid (NTA), with three carboxylate groups all tethered to a central amine Lewis base group, ethylenediamine-N,N′-diacetic acid (EDDA), with carboxylate-amine-amine-carboxylate groups arranged linearly, plus four structurally related compounds, are used as tetradentate chelating agents. Ethylenediaminetetraacetic acid (EDTA) and the structurally more rigid analog trans-cyclohexaneethylenediaminetetraacetic acid (CDTA) are used as hexadentate chelating agents. Effects of pH and reactant concentration are explored. Ni(II) capture by EDTA was consistently more than an order of magnitude faster than capture by CDTA, and too fast to quantify using our capillary electrophoresis-based technique. Using NiNTA as a reactant, Ni(II) capture by CDTA is independent of CDTA concentration and greatly enhanced by a proton-catalyzed pathway at low pH. Using NiEDDA as reactant, Ni(II) capture by CDTA is first order with respect to CDTA concentration, and the contribution from the proton-catalyzed pathway diminished by CDTA protonation. While the convention is to assign either a disjunctive pathway or adjunctive pathway to multidentate ligand exchange reactions, our results indicate that a third “semijunctive” pathway is necessary to account for slow reactions progressing through LNiY ternary complexes. Ligand exchange pathways with NTA-type chelating agents are assigned a disjunctive pathway, while pathways with EDDA-type chelating agents are assigned a semijunctive pathway. Based upon operative mechanism(s), magnitudes of exchange rates and effects of ambient geochemical conditions can be predicted.

Iron(III), nickel(II) and zinc(II) complexes based on acetophenone-S-methyl-thiosemicarbazone: synthesis, characterization, thermogravimetry, and a structural study

New complexes, [Fe(L)Cl], [Ni(L)], and [Zn(L)C2H5OH] (1–3), were synthesized by template reaction of 2-hydroxy-acetophenone-S-methyl-thiosemicarbazone with 2-hydroxy-benzaldehyde. The compounds were characterized by elemental analysis, magnetic measurements, FT-IR, 1H NMR, UV–visible, and ESI–MS spectra. In these complexes, the ligand is coordinated to the metal ion as dinegatively charged tetradentate chelating agents via the N2O2 donor set. The iron(III) and zinc(II) complexes exhibit square pyramidal geometry whereas the nickel(II) complex has a square planar geometry. The crystal structure of 1, determined by X-ray diffraction method, indicates that 1 crystallizes in the monoclinic space group P21/c with Z = 4. Thermal decompositions of the compounds have been investigated using TGA in air.

Synthesis, spectroscopic, thermal and antimicrobial studies of neodymium(III) and samarium(III) complexes derived from tetradentate ligands containing N and S donor atoms

Trivalent lanthanide complexes of the type [Ln(L)Cl(H2O)2] (where Ln=Nd(III) or Sm(III) and LH2=Schiff bases derived by the condensation of 3-(phenyl/substitutedphenyl)-4-amino-5-mercapto-1,2,4-triazole with diacetyl/benzil) have been synthesized by the reactions of anhydrous lanthanide(III) chloride with Schiff bases in methanol. The structures of the complexes have been proposed on the basis of elemental analysis, electrical conductance, magnetic moment, spectroscopic measurements (IR, 1H, 13C NMR and UV–vis spectra) and X-ray diffraction studies. The spectral data reveal that the Schiff base ligands behave as dibasic tetradentate chelating agents having coordination sites at two thiol sulfur atoms and two azomethine nitrogen atoms. The presence of coordinated water in metal complexes was confirmed by thermal and IR data of the complexes. All the Schiff bases and their metal complexes have also been screened for their antibacterial activity against Bacillus subtilis, Staphylococcus aureus and antifungal activities against Aspergillus niger, Curvularia pallescens and Colletotrichum capsici.

Vanadium complexes with quadridentate Schiff bases

The Schiff base ligands N,N′-(±)-trans-bis(3,5-dichloro-2-hydroxyacetophenone)-1,2-cyclohexanediamine (H2L1) and N,N′-(±)-trans-bis(5-chloro-4-methyl-2-hydroxyacetophenone)-1,2-cyclohexanediamine (H2L2) were derived from the condensation of trans-1,2-diaminocyclohexane with 3,5-dichloro-2-hydroxyacetophenone or 5-chloro-4-methyl-2-hydroxyacetophenone, respectively. Both these ligands formed well-defined complexes with vanadium (IV) and (V) under suitable experimental conditions. These complexes have been characterized by elemental analysis, molar conductivity, magnetic moments, infrared, electronic spectra, ESR, X-ray diffraction, and thermogravimetric analysis. X-ray diffraction study of [VO(L2)]·H2O complex indicated its monoclinic crystal system with a = 9.8525, b = 23.6271, c = 9.0904 A, and β = 97.87°. The complexes [VO(L1)]·H2O and [VO(L2)]·H2O have been examined as catalysts for epoxidation of styrene in the presence of hydrogen peroxide as oxidant. The IR spectral data suggest that both the ligands behave as dibasic tetradentate chelating agent with ONNO donor atoms sequence toward cental metal ion.

New Insights into the Chemistry of Oxovanadium(IV) Complexes with N4 Coordinating Ligands

The syntheses of new oxovanadium(IV) complexes having general formula [VO(mac)]SO4 have been carried out by using in situ method of preparation where vanadyl ion acts as kinetic template for the ligands derived by condensation of 2,2′-pyridil with 1,2-diaminopropane and 1,3-diaminopropane. The complexes were characterized by elemental analyses, molar conductance, magnetic moments, and spectral (infrared, electronic, and electron spin resonance) data. All the oxovanadium(IV) complexes are five coordinate wherein derived ligands act as tetradentate chelating agents.

Template synthesis and X-ray structural characterization of nickel(II) and zinc(II) complexes of tetradentate SNNS ligands formed by condensation of phthalaldehyde with S-methyldithiocarbazate and 4N-methyl-3-thiosemicarbazide

The reaction of phthalaldehyde (1,2-benzenedialdehyde) with S-methyldithiocarbazate does not lead to the formation of the expected open-chain linear Schiff base, phthalaldehyde bis(S-methyldithiocarbazonate) but a cyclic diazine dithiocarbazate is obtained which has been characterized by spectroscopic and X-ray diffraction. However, if the reaction of phthalaldehyde with S-methyldithiocarbazate is carried out in the presence of nickel(II) and zinc(II) acetate salts, stable metal complexes of empirical formula, [M(phthalsme)] (M=Ni, Zn; phthalsme=doubly deprotonated form of the Schiff base, phthalaldehyde bis(S-methyldithiocarbazonate) are obtained. Likewise, the reaction of 4N-methyl-3-thiosemicarbazide with phthaladehyde in the presence of nickel(II) acetate also yields a crystalline nickel(II) complex, [Ni(phthaltsc)] (phthaltsc=doubly deprotonated form of the teradentate phthaladehyde bis(4N-methyl-3-thiosemicarbazone) ligand. The complexes, [Ni(phthalsme)], [Ni(phthaltsc)] and [Zn(phthalsme)(DMF)] have been characterized by a variety of physico-chemical techniques and their structures have been determined by X-ray diffraction. In these complexes, the ligands are coordinated to the metal ion as dinegatively charged tetradentate chelating agents via the two thiolate sulfur atoms and the azomethine nitrogen atoms. The nickel complexes, [Ni(phthalsme)] and [Ni(phthaltsc)] exhibit a distorted square–planar geometry whereas the zinc complex, [Zn(phthalsme)(DMF)] is five-coordinate and square-pyramidal with the dianionic Schiff base occupying the basal plane of the square-pyramid and the oxygen atom of dimethylformamide in the apical coordination site.

Synthesis of Oxovanadium(IV) Complexes with Tetraaza Coordinating Ligands

Oxovanadium(IV) complexes of the type [VO(mac)]SO4 (where mac = tetraaza macrocyclic ligands derived by condensation of thenil with 1,4‐diaminobenzene or 3,4‐diaminopyridine and their reaction with β‐diketones) have been prepared using vanadyl ion as kinetic template. The prepared macrocyclic complexes were characterized by elemental analyses, molar conductance, magnetic moments, and infrared, electronic, and electron spin resonance data. From the spectroscopic studies, five‐coordinate square‐pyramidal geometry for the VO2+ complexes have been proposed wherein derived ligands act as tetradentate chelating agents.

Synthesis and characterization of cis-dioxomolybdenum(VI) complexes having furil as precursor molecule

Synthesis of some new dioxomolybdenum(VI) complexes having general formula [MoO2(mac)](acac)2, (where mac = tetraazamacrocyclic ligands derived from condensation of furil with 1,2-diaminobenzene or 2,3-diaminopyridine and their reaction with ?-diketones) using dioxometal ion as kinetic template are reported. The prepared complexes have been characterized by molar conductance, elemental analyses, infrared and electronic data. The spectral data indicate that ligands act as tetradentate chelating agent. Due to their biological relevance, molybdenum catalyzed oxygen transfer reactions have great interest. All the dioxomolybdenum(VI) complexes have octahedral geometry with six coordination.

Synthesis and structural characterization of novel square pyramidal oxovanadium(IV) complexes with ligands having N and O donor atoms

Oxovanadium(IV) complexes having the general formula [VO(L)] were designed and synthesized using vanadyl ion as kinetic template with ligands derived by condensation of \beta-diketones such as acetylacetone, benzoylacetone, thenoyltrifluoroacetone, and dibenzoylmethane with 2-amino-3-hydroxypyridine or 2-aminobenzoic acid or 2-aminonicotinic acid. Tentative structures of the complexes were proposed on the basis of elemental analysis, molar conductance, magnetic moments, and spectral (infrared, electronic and electron spin resonance) data. All the oxovanadium(IV) complexes are 5-coordinated wherein derived ligands act as tetradentate chelating agents.

Synthesis, characterization and in vitro evaluation of new oxorhenium- and oxotechnetium-CCK4 derivatives as molecular imaging agents for CCK2-receptor targeting

The goal of this study is to design new 99mTc-radiolabelled shortened CCK derivatives that might be suitable for the molecular imaging of cholecystokinin-2 receptors (CCK2-R), these receptors being over-expressed in a number of neuroendocrine tumors such as medullary thyroid cancer and small-cell lung cancer. For this purpose, we designed several modified CCK4 analogs bearing an ON2S tetradentate chelating agent at the N-terminus, the CCK4 sequence representing the minimal peptide sequence that presents nanomolar affinity and activity towards the CCK2-R. Four peptide conjugates of general formula (Trt)SN2OPh–(X)n–CCK4 (X=β-alanine or 6-aminohexanoic acid spacers; n=0, 2, 4) and their oxorhenium peptide conjugates have been synthesized and characterized. In vitro evaluation of these compounds showed a close relationship between the nature and the length of the spacer and the corresponding binding affinity values. The most promising oxorhenium complex 5-Re exhibited potent CCK2-receptor agonist properties in promoting the production of inositol phosphate in COS-7 cells (EC50=5.17nM). Preliminary 99mTc-radiolabelling studies with peptide conjugates 3 or 5 led exclusively to the corresponding 99mTcO-complexes 3-Tc and 5-Tc, which exhibited high resistance towards an excess of cysteine and satisfactory stabilities in human serum. To conclude, the promising in vitro characteristics of compounds 5-Re, 5-Tc illustrate the feasibility to develop stable radiolabelled shortened CCK4 derivatives with a nanomolar CCK2-R affinity.

Microwave assisted synthesis, spectroscopic and antibacterial studies of titanocene chelates of Schiff bases derived from 3-substituted-4-amino-5-hydrazino-1,2,4-triazoles

The reactions of bis(cyclopentadienyl)titanium(IV) chloride with a new series of Schiff bases (LH2), derived by condensing 3-(phenyl/2-chlorophenyl/4-nitrophenyl)-4-amino-5-hydrazino-1,2,4-triazoles with salicylaldehyde or 2-hydroxyacetophenone, have been studied both by conventional stirring method and also by using microwave technology. The products of type [(η5-C5H5)2Ti(L)] have been isolated in both cases. Tentative structural conclusions are drawn for the reaction products based upon physico-chemical and spectroscopic methods. The ligands behave as dibasic, tetradentate chelating agents and a six-coordinated structure have been assigned to these derivatives. Studies were conducted to assess the growth inhibiting potential of the free Schiff bases and their complexes against various bacterial strains.

Template synthesis and characterization of oxovanadium(IV) complexes with tetraaza macrocyclic ligands and their activity on potato virus X

The oxovanadium(IV) complexes (I) of the type [VO(L)]SO4 have been prepared using an in-situ method of synthesis with ligands derived from di-2-thienylethanedione with 1,2-diaminobenzene or 2,3-diaminopyridine. These parent complexes have been further reacted with μ-diketones to yield macrocyclic complexes (II) of types [VO(mac)]SO4 (where mac = macrocyclic ligands derived by condensation of amino group of parent complex with μ-diketones), wherein the VO2+ cation acts as a template. Tentative structures of these complexes have been proposed on the basis of elemental analysis, electrical conductance, magnetic moments and spectral (infrared, electronic and electron spin resonance) data. The oxovanadium(IV) complexes are five coordinated wherein the tetraaza macrocyclic ligands act as tetradentate chelating agents. All the complexes are found to inhibit the infectivity of potato virus X, when checked using the test plant Chenopodium amaranticolor.

Organotin(IV) oxo -homoscorpionate: preparation, spectroscopic characterization and antimicrobial properties

An oxo-homoscorpionate ligand [potassium bis(phthalato)borate] (KL) was prepared by solid state reaction of potassium borohydride and phthalic acid (1 : 3 molar ratio). The ligand is uninegative and can be a bi, tri and tetra-dentate chelating agent. The di- and tri-organotin(IV) complexes of this ligand are formed by replacement of chloride in R2SnCl2 and (R = methyl, butyl and R′ = phenyl and butyl). The ligand and all its complexes were characterized by elemental analyses and spectral studies (IR, 1H, 13C, 119Sn NMR and ESI mass spectra). Spectroscopic data reveal that all the complexes are hexacoordinate; the diorganotin complexes have trans octahedral geometry while the triorganotin complexes are distorted octahedral geometry. The toxicity of these organotin(IV) derivatives on selected microbes was considered. The compounds exhibit antibacterial (Bacillus anthracius and Escherichia coli) and antifungal (Candida albicans and Penicillium italicum) activities in vitro. The ligand shows less toxicity towards the microorganisms and its toxicity significantly increased after complexation with organotin(IV). Triorganotin derivatives (R3SnL) of the ligand are more effective compared to diorganotin derivatives (R2SnL2).