Derived Schiff Base Ligands Research Articles

Curcumin derived Schiff base ligand and their transition metal complexes: Synthesis, spectral characterization, catalytic potential and biological activity

Curcumin derived Schiff base ligand, (CL), was prepared by condensation of 1,7-bis-(4-hydroxy-3-methoxyphenyl)-1,6-heptadiene-3,5-dione (curcumin) with amino ethylene piperazine (AEP). The transition metal complexes of CL were also successfully synthesized and characterized by various spectroscopic techniques. Non-electrolytic nature of complexes was ascertained by molar conductance values. Thermogravimetric analysis confirms that all the metal complexes are stable up to 600 °C. The metal to ligand stoichiometry of synthesized metal complexes was confirmed by micro analytical data as 1:1 (metal: ligand). Co(II), Ni(II) and Zn(II) ion forms the complexes with an octahedral geometry while the geometry of Cu(II) complex can ascribed as square planar by UV–vis and EPR spectroscopic studies. Catalytic power and antioxidant activity of these complexes have been evaluated and results shows that Co(II) complex is catalytically more active while the Cu(II) and Zn(II) complex were found with more potent antioxidant activity, comparatively. The synthesized compounds have also been tested for their in-vitro cytotoxic potential, the obtained results shows moderate to good cytotoxicity on tested human cancer cell lines. The most effective compounds on cell lines MDA-MB-231 and KCL22 was [(CL)Cu] while on HeLa cell line the [(CL)Zn(H2O)2] was found with prominent cytotoxicity. Anthelmintic activities of these compounds have been performed using Pheretima posthuma. The recorded order of anthelmintic activity of ligand (CL) and their metal complexes was found to have the trend as: [(CL)Cu]>[(CL)Zn(H2O)2]>[(CL)Co(H2O)2]>[(CL)Ni(H2O)2]>CL.

Crystal structure, optical properties, DFT analysis of new morpholine based Schiff base ligands and their copper(II) complexes: DNA, protein docking analyses, antibacterial study and anticancer evaluation

New morpholine derived Schiff base ligands (HL1 and HL2) and their Cu(II) complexes [Cu(L1)2] (1) and [Cu(L2)2] (2) have been synthesized and characterized by 1H NMR, IR, UV–Vis, EPR studies and cyclic voltammetric analyses. Single crystal X-ray crystallography studies confirm the structure of newly synthesized Schiff base ligands HL1and HL2. The ground state electronic structures of Cu(II) complexes 1 and 2 have been investigated by DFT/B3LYP theoretical analysis with 6-31G (d,p) and LANL2DZ basis set. The affinity towards DNA and protein molecules have been evaluated using computational docking analysis and complex 2 expose significant binding ability with DNA as well as protein due to its towering hydrophobicity. Consequently, complex 2 reveals superior antibacterial activity against some bacterial species besides anticancer activity on human breast cancer (MCF-7) cells than complex 1 and Schiff base ligands (HL1 and HL2). These preliminary investigations strongly recommended that complex 2 can be used as a better antibacterial plus anticancer agent.

In-vitro Anticancer Activity of Copper (II) and Zinc (II) Complexes with Derived Schiff Base Ligands

In-vitro Anticancer Activity of Copper (II) and Zinc (II) Complexes with Derived Schiff Base Ligands

Template synthesis, structural variation, thermal behavior and antimicrobial screening of Mn(II), Co(II) and Ni(II) complexes of Schiff base ligands derived from benzyl carbazate and three isomers of acetylpyridine

Complexes of Mn(II), Co(II) and Ni(II) with ligands derived from the condensation of benzyl carbazate with three stereoisomers of acetylpyridine have been synthesized using a template method. The complexes have the compositions [Ni(bc-2ap)2] (1), [M(NCS)2(bc-3ap)2(bc)]·H2O; M=Co (2) or Ni (3), [Mn(NCS)2(bc-3ap)4]·2CH3OH (4), [M(NCS)2(bc-3ap)4]·2H2O; M=Co (5) or Ni (6) and [M(NCS)2(bc-4ap)2(CH3OH)2]; M=Mn (7) or Co (8) [where bc=benzyl carbazate, 2ap, 3ap and 4ap=2-, 3- and 4-acetylpyridine]. Characterization of the products involved elemental analysis, IR, UV–vis and 1H NMR, and in the case of 1, 2, 4, 5 and 8 single crystal X-ray structures have been determined. These are all six coordinate with octahedral coordination geometries. Compound 1 is unique with the 2-acetylpyridine ligand undergoing enolisation and deprotonation with two of the uninegative ligands coordinating to the Ni(II) cation in a tridentate chelate fashion. For 2 to 8 the charges of the M(II) cations are balanced in each case by two thiocyanato ligands, mutually cis for 2 and 3 but trans for 4–8. In these latter six-coordinate complexes, 2–8, the benzyl carbazate derived Schiff base ligands bind to the metal atoms in a trans monodentate fashion via the pyridine N atoms, two for 2, 3, 7 and 8 and four such ligands for 4, 5 and 6. In addition to the thiocyanato anions, the remaining coordination positions are filled by bidentate chelate carbazate molecules for 2 and 3, and two trans oriented methanol molecules for 7 and 8. Thermal reactivity of the complexes was studied by TG-DTA. In addition, antimicrobial screening confirmed that all of the complexes, except 1, have a moderate to good range of activity against both Gram-positive and Gram-negative bacterial strains and also against fungi.

New Cu(II) complexes with pyrazolyl derived Schiff base ligands: Synthesis and biological evaluation

Since the discovery of cisplatin there has been a continuous pursuit for new metallodrugs showing higher efficacies and lower side effects. In this work, new copper(II) complexes (C1–C6) of Schiff bases derived from pyrazolyl were developed. Through condensation of 5-methyl-1H-pyrazole-3-carbohydrazide with different aromatic aldehydes – pyridoxal, salicylaldehyde, 3-methoxy-2-hydroxybenzaldehyde, 3-ethoxy-2-hydroxybenzaldehyde and 2-hydroxynaphthene-1-carbaldehyde – a set of new pyrazole based “ONO” tridentate Schiff bases were obtained in moderate to good yields – L1–L6, as well as their Cu(II)-complexes. All compounds were characterized by analytical techniques and their molecular formulae established. The antioxidant potential of all compounds was tested, yielding low activity in most cases, with the exception of L1 and C5. The Cu(II) complexes were tested for their aqueous stability, and for their interaction with biological molecules, namely DNA and HSA (human serum albumin), through fluorescence quenching experiments (and electrophoresis for DNA). With the exception of C3, all the synthesized complexes were able to interact with DNA and HSA. Their cytotoxic activity against two cancer cell lines (MCF7 — breast and PC3 — prostate) was also evaluated. Complexes C5 and C6, with larger aromatic systems, showed much higher cytotoxicity (in the low μM range), than C1–C4, as well as IC50 values much lower than cisplatin. For C6 the results suggest that the mechanisms of cell death do not seem to be mediated by apoptosis, through caspases 3/7 activation, but by involving membrane potential and imbalance in physiological elements such as P, K and Ca.

Synthesis and characterization of lanthanide complexes prepared with 2-((E)-(1-hydroxy-2-methylpropan-2-ylimino)methyl)-6-methoxyphenol

Rare-earth complexes of the general formula [Ln(H2L1)2(NO3)3] [Ln = Gd (1), Ho (2) or Nd (3)] were prepared from an o-vanillin derived Schiff base ligand, 2-((E)-(1-hydroxy-2-methylpropan-2-ylimino)methyl)-6-methoxyphenol (H2L1). The single-crystal X-ray diffraction studies and SHAPE analyses of the Gd(III) and Ho(III) complexes show that the complexes are ten-coordinate and exhibit distorted tetradecahedron geometries. The phenolate oxygen-bridged dinuclear complex, [Ce2(H2L1)(ovan)3(NO3)3] (4, ovan = monodeprotonated o-vanillin), was obtained from the reaction of Ce(NO3)3∙6H2O with H2L1. X-ray analysis revealed that hydrolysis of H2L1 occurred to yield o-vanillin, which bridged two cerium atoms with the Ce⋯Ce distance equal to 3.8232(6) Å. The Ce(III) ions are both ten-coordinate, but have different coordination environments, showing tetradecahedron and staggered dodecahedron geometries, respectively. With proton migration occurring from the phenol group to the imine function, complexation of the lanthanides to the ligand gives the Schiff base a zwitterionic phenoxo-iminium form.

Experimental and theoretical study on a new copper(II) complex derived from pyridoxal hydrochloride and 1,2-diaminocyclohexane

In this work, guided by a pyridoxal derived Schiff base ligand, H2PydChda [5-Hydroxymethyl-4-({2-[5-hydroxymethyl-2-methylpyridin-3-hydroxy-4-ylethylene)-amino]-cyclohexylimino}-methyl)-2-methylpyridin-3-ol], a new copper(II) complex, [Cu(PydChda-2H+)]2·4ClO4·2H2O was constructed and structurally characterized by single crystal X-ray diffraction study. DFT calculations further substantiate the experimental features. Additionally, experiments were performed to demonstrate the accessibility to any enzymatic activity and the complex provides positive response for phosphatase activity towards 4-NPP substrate.

Recyclable chiral dinuclear copper(II) complexes catalyzed asymmetric Friedel–Crafts alkylation of 1-naphthol using N-tosyl aldimine

A highly efficient dinuclear copper complex catalyzed Friedel–Crafts reaction has been demonstrated for the alkylation of 1-naphthol using N-tosyl aldimine. In this context, various chiral amino alcohol derived Schiff base ligands with different achiral and chiral linkers were synthesized and their copper (II) complexes were generated in situ. One of the dinuclear copper complexes with chiral linker has emerged as an efficient catalyst and affords the desired arene products in excellent enantioselectivities (ee up to 99%) with very good yields (up to 98%). The dinuclear catalyst used in this study was recoverable and recyclable with retention of its catalytic activity.

Dicynamide bridged two new zig-zag 1-D Zn(II) coordination polymers of pyrimidine derived Schiff base ligands: Synthesis, crystal structures and fluorescence studies

Two new zigzag 1-D polymeric Zn(II) coordination polymers {[Zn(L1)(μ1,5-dca)](H2O)}n (1), {[Zn(L2)(μ1,5-dca)](ClO4)}n (2) of two potentially tridentate NNO-, NNN-, donor Schiff base ligands [2-(2-(4,6-dimethylpyrimidin-2-yl)hydrazono)methyl)phenol] (L1), [1-(4,6-dimethylpyrimidin-2-yl)-2-(dipyridin-2ylmethylene)hydrazine] (L2) have been synthesized and characterized by elemental analyses, IR and 1H NMR, fluorescence spectroscopy and single crystal X-ray crystallography. The dicyanamide ions act as linkers (μ1,5 mode) in the formation of these coordination polymers. Both the complexes 1 and 2 have same distorted square pyramidal geometry around the Zn(II) centres. The weak forces like π⋯π, CH⋯π, anion⋯π interactions lead to various supramolecular architectures. Complex 1 shows high chelation enhanced fluorescence compared to that of 2. The fluorescence spectral changes observed high selectivity towards Zn(II) over other metal ions such as Mn(II), Co(II), Ni(II), Cu(II).

Synthesis and Characterization of Glucose Derived Dioxo-molybdenum (VI) Complexes and Their Application in Sulphide Oxidation

Three new molybdenum (VI) complexes of 4,6-O-ethylidene-β-d-glucopyranosylamine derived ligands has been synthesized and the same has been used in the oxidation of thioanisole along with an earlier reported analogous complex. A selective oxidation of thioanisole to methyl phenyl sulphoxide in high yield is achieved using 1:1 mixture of thioanisole and urea hydrogen peroxide (UHP) in ethanol. A longer reaction time or excess of UHP, leads to the formation of corresponding sulphone, which was confirmed using HPLC and NMR measurements. The oxidation of thioanisole into corresponding sulphoxide and sulphone has been explored using dioxo-molybdenum (VI) complexes of 4,6-O-ethylidene-β-d-glucopyranosylamine derived Schiff base ligands.

Imino-4-Methoxyphenol Thiazole Derived Schiff Base Ligands: Synthesis, Spectral Characterization and Antimicrobial Activity

Two imino-4-methoxyphenol thiazole derived Schiff bases, 3-(5-nitrothiazol-2-ylimino)methyl)-4-methoxyphenol (4) and 3-(5-ethyl-1,3,4-thiadiazol-2-ylimino)methyl)-4-methoxyphenol (5) were synthesized by condensing 2-amino-5-nitrothiazole (1) and 2-amino-5-ethyl-1,3,4-thiadiazole (2) with 5-hydroxy-2-methoxybenzaldehyde (3). The obtained ligands were characterized by using UV-visible, 1H, 13C-NMR and MS techniques. Data obtained from the above techniques confirmed the molecular structures of the obtained compounds. The optimized structures of the compounds were done using ACD simulation software. The synthesized compounds were tested for their antibacterial (E. coli and R. solanacearum) and antifungal (F. oxysporum and A. niger) activities. The results from these studies showed that the compounds are moderately active against the tested species of bacteria and fungi. The microbial growth inhibition by compound 4 was significantly higher than compound 5. Microbial growth inhibition activity of both the compounds was less compared with their standard drugs.

DNA/protein interaction, cytotoxic activity and magnetic properties of amino-alcohol Schiff base derived Cu(ii)/Ni(ii) metal complexes: influence of the nuclearity and metal ions

The reactions of amino-alcohol derived Schiff-base ligands with Cu(ii) and Ni(ii) salts have afforded four novel polynuclear complexes, which exhibited interesting magnetic and cytotoxic properties.

X-ray structure analysis, electronic and vibrational circular dichroism of chiral-at-metal dioxidovanadium(V) complexes with amino acids derived Schiff base ligands

Five new chiral dioxidovanadium Schiff base complexes derived from l-valine, l-leucine, l-histidine, l-threonine and d-threonine were synthesized and characterized by elemental analysis, 1H and 51V NMR and IR spectra. The absolute configurations of the complexes were determined by X-ray single crystal analysis in solid state and by electronic and vibrational circular dichroism in CH3CN solution. The l-threoninato complex, which contains two stereogenic centers in the amino acid site, does not show epimerization of the amino acid, in contrast with the analogical isoleucine-derived complexes reported recently. Conglomerate crystallization was observed in racemic dl-valine- and dl-threonine-derived complexes.

Five new pseudohalide bridged Mn(II) complexes of pyrimidine derived Schiff base ligands: Synthesis, crystal structures and magnetic properties

Four new azide bridged dinuclear Mn(II) complexes [Mn(L1)(μ1,1-N3)(N3)]2 (1), [Mn(L2)(μ1,1-N3)(N3)]2 (3), [Mn(L3)(μ1,1-N3)(N3)]2[(N3)Mn(L3)(μ1,1-N3)(N3)]2 (4) and [Mn(L4)(μ1,1-N3)(N3)]2[Mn(L4)(μ1,1-N3)(N3)]2 (5) and one new dicynamide bridged binuclear Mn(II) complex {[Mn2(L1)2(dca)2(H2O)2(μ1,5-dca)](ClO4)} (2) have been synthesized using the pyrimidine derived primary Schiff base ligands Ln (n=1–4), with azide and dicynamide as bridging ligands. All the five complexes were characterized by elemental analyses, IR spectroscopy and single crystal X-ray crystallography, together with magnetic measurements of 1–4. The tridentate Schiff base ligands are the [1+1] condensation products of 2-hydrazino-4,6-dimethyl pyrimidine with 2-acetyl pyridine, pyridine-2-carbaldehyde, 2-benzoyl pyridine and di(2-pyridyl) ketone for Ln (n=1–4), respectively. All the complexes except 2 contain Mn(II)-azido links in which the Mn(II) centres are bridged by a di-μ1,1-azido (double EO) group. The double EO bridging fragments in the complexes are similar with bridging angles (Mn–N–Mn) ranging from 102.59° to 104.81°. Magnetic property studies reveal that in 1, 3 and 4 intramolecular ferromagnetic interactions are mediated through the EO azido bridges with J parameters in the range 4.3–5.12cm−1, while a weak antiferromagnetic interaction prevails in 2 (J=−0.12cm−1) via μ1,5-dicynamide bridges. In addition, complexes 1, 3 and 4 show weak intermolecular antiferromagnetic interactions (J=−0.025 to −0.027cm−1).

Design, spectral characterization and biological studies of transition metal(II) complexes with triazole Schiff bases

A new series of three biologically active triazole derived Schiff base ligands L1–L3 have been synthesized in equimolar reaction of 3-amino-1H-1,2,4-triazole with pyrrol-2-carboxaldehyde, 4-bromo-thiophene-2-carboxaldehyde, and 5-iodo-2-hydroxy benzaldehyde. The prepared Schiff bases were used for further complex formation reaction with different metal elements like Co(II), Ni(II), Cu(II) and Zn(II) as chlorides by using a molar ratio of ligand:metal as 2:1. The structure and bonding nature of all the compounds were identified by their physical, spectral and analytical data. All the metal(II) complexes possessed an octahedral geometry except the Cu(II) complexes which showed a distorted octahedral geometry. All the synthesized compounds, were studied for their in vitro antibacterial, and antifungal activities, against four Gram-negative (Escherichia coli, Shigella sonnei, Pseudomonas aeruginosa and Salmonella typhi) and two Gram-positive (Bacillus subtilis and Staphylococcus aureus) bacterial strains and against six fungal strains (Trichophyton longifusus, Candida albicans, Aspergillus flavus, Microsporum canis, Fusarium solani and Candida glabrata) by using agar-well diffusion method. It has been shown that all the synthesized compounds showed moderate to significant antibacterial activity against one or more bacterial strains. In vitro Brine Shrimp bioassay was also carried out to investigate the cytotoxic properties of these compounds. The data also revealed that the metal complexes showed better activity than the ligands due to chelation/coordination.

Three new 1D Cu(II) coordination polymers and a binuclear Cu(II) complex of two pyrazole derived Schiff base ligands: Heterocyclic ring substitution and anion dependent structural variations – Spectral studies

Three new zig-zag 1D coordination polymers and a binuclear complex of Cu(II) involving pyrazole based tri- and pentadentate schiff base ligands (Z)-2-(2-(5-methyl-1H-pyrazole-3-carbonyl)hydrazono)-2-phenylacetic acid (L′1) and (Z)-2-(2-(5-methyl-1-(pyridin-2-yl)-1H-pyrazole-3-carbonyl)hydrazono)-2-phenylacetic acid (L′2) are reported in this work. The ligand precursors L1 and L2 have been transformed into L1′ and L2′ during the course of reaction with metal ions in which the ester groups have been changed to carboxylate group. The 1D coordination polymers, namely, [Cu(L′1)(ClO4)2(H2O)]n (1), [Cu(L′2)(ClO4)]n (3), [Cu(L′2)(NO3)]n (4) and a binuclear complex [Cu2(L′1)2Cl2] (2) have been synthesized. The complexes 1–3 are of distorted octahedral geometry and the complex 2 is distorted square pyramidal. Interestingly, these structural variations are dependent on counterions and substituent on the pyrazole ring. These have been characterized by elemental analyses, UV, IR, single crystal X-ray diffraction, electrochemical and photoluminescence studies. L′1 serves as tridentate NNO donor where pyrazole nitrogen, azomethine nitrogen and ligand carboxylate group are coordinatively active, leaving the carbonyl oxygen of carbohydrazide part inactive. The same situation (coordination modes) arises in another pentadentate NNNOO donor L′2 where extra pyridine nitrogen is coordinated. The complexes 3 and 4 have considerable fluorescence emission while the rest of the complexes and the ligand molecules are fluorescent silent.

Dicopper(II) complexes of a tridentate pyrimidine derived Schiff base ligand: Syntheses, crystal structures and catalytic reactions

Three new dinuclear Cu(II) complexes, [Cu2(L)2(L1)]PF6 (1), [Cu2(L)2(L2)]PF6 (2) and [Cu2(L)2(L3)]PF6 (3), of a potentially tridentate NNO-donor Schiff base ligand [HL=2-(2-(4,6-dimethylpyrimidin-2-yl)hydrazono)methyl)phenol] and the ancillary ligands [HL1=benzoic acid, HL2=salicylic acid, HL3=4-amino benzoic acid] have been synthesized and characterized by elemental analyses, IR, single crystal X-ray crystallography, spectroscopic, electrochemical and catalytic studies. The ligand HL is the [1+1] condensation product of salicylaldehyde with 2-hydrazino-4,6-dimethyl pyrimidine. In the complexes 1, 2 and 3, two Cu(II) centers are bridged by the carboxylic oxygen atoms of the respective acid moiety. All the metal centres have square-based pyramidal (SP) geometries (Γ=0.120, 0.124, 0.109 for 1, 2 and 3, respectively). The dinuclear Cu(II) complexes show high catalytic activity and selectivity for the epoxidation of styrene, cyclohexene and cyclooctene using tert-butyl hydroperoxide (TBHP) as the oxidant.

Synthesis and studies of rare acylhydrazine bridged strong antiferromagnetically coupled dicopper(II) and dioxovanadium(V) complexes of a pyridyl-pyrazole derived Schiff base ligand

A binuclear acylhydrazine bridged Cu(II) complex, [Cu2(L)(NO3)3(H2O)] (1), and an anti-orthogonal binuclear oxovanadium(V) complex, [V2O4(L)2] (2), have been synthesized and characterized spectroscopically and crystallographically. The ligand HL has two potentially bridging functional groups (μ-O, μ-N–N) and consequently can exist in the following coordination conformers: (a) metal centers bridged by μ-O, (b) metal centers bridged by μ-N–N. A rare acylhydrazine bridged (a) type configuration exists in the dinuclear Cu(II) complex 1. The bridging ligand mediates a strong antiferromagnetic coupling (J=−99cm−1). The exchange pathway parameters have also been evaluated from density functional theoretical calculations to corroborate the bridging signatures with experimental findings (J=−93.96cm−1). Molecule 2 has a centrosymmetric structure with each vanadium center having a distorted octahedral geometry. It shows a one step irreversible reduction at +0.43V. The bond angles, bond lengths and torsion angles in 2 are correlated with DFT.

Antibacterial and antifungal metal based triazole Schiff bases

A new series of four biologically active triazole derived Schiff base ligands (L1–L4) and their cobalt(II), nickel(II), copper(II) and zinc(II) complexes (1–16) have been synthesized and characterized. The ligands were prepared by the condensation reaction of 3-amino-5-methylthio-1H-1,2,4-triazole with chloro-, bromo- and nitro-substituted 2-hydroxybenzaldehyde in an equimolar ratio. The antibacterial and antifungal bioactivity data showed the metal(II) complexes to be more potent antibacterial and antifungal than the parent Schiff bases against one or more bacterial and fungal species.

ChemInform Abstract: Enantioselective Vanadium‐Catalyzed Oxidation of 1,3‐Dithianes from Aldehydes and Ketones Using β‐Amino Alcohol Derived Schiff Base Ligands.

Abstract1,3‐Dithiane substrates, derived from aromatic aldehydes, are oxidized to the corresponding sulfoxides with excellent enantioselectivities.