Antibacterial activity of transition metal complexes containing a tridentate NNO phenoxymethylpenicillin‐based Schiff base. An anti‐MRSA iron (II) complex

Transition metal complexes containing a phenoxymethylpenicillin‐derived Schiff base (HL) 3 obtained from the condensation of phenoxymethylpenicillin (PMP) 1 , with 1,2‐diaminobenzene 2 , were prepared. Spectroscopic and physicochemical techniques, namely, UV–Vis, FT‐IR, ¹H‐NMR, EPR, mass spectrometry, magnetic susceptibility, molar conductance, DFT studies, together with elemental and thermal analyses were used to characterize the synthesized complexes. Based on the characterization studies, the general formulae [ML (OAc)(H₂O)₂] where M = Fe 4 , Co 5 , Ni 6 , Cu 7 , and Zn 8 , were proposed for the complexes. The Schiff base ligand 3 behaved as a monoanionic tridentate NNO chelating agent. On the basis of magnetic and spectral data an octahedral geometry for all the complexes was suggested. Schiff base ligand 3 , and the metal complexes 4 – 8 were tested against G(+) or bactericidal activity by agar disc diffusion method and minimal inhibitory concentration (MIC). The results were compared with the activity of the standard drug PMP 1 . In vitro bacterial viability revealed that 3  had similar activity than 1 and exhibited modification in its bactericidal activity when formed metal complexes. It was found that the complexes 4 , 6 and 7 exhibited much better bactericidal activity than 1 against methicillin‐resistant Staphilococcus Aureus (MRSA) being complex 4 the most promising compound showing a MIC value of 0.042 μmol/ml.     

Four‐, five‐ and six‐coordinated transition metal complexes based on naphthalimide Schiff base ligands: Synthesis,crystal structure and properties

Two bidentate Schiff base ligands (HL¹ = N‐n‐butyl‐4‐[(E)‐2‐(((2‐aminoethyl)imino)methyl)phenol]‐1,8‐naphthalimide; and HL² = N‐n‐butyl‐4‐[(E)‐2‐(((2‐aminoethyl)imino)methyl)‐6‐methoxyphenol]‐1,8‐naphthalimide) with their metal complexes [Cu(L¹)₂] ( 1 ), [Zn(L¹)₂(Py)]₂?H₂O ( 2 ) and [Ni(L²)₂(DMF)₂] ( 3 ) have been synthesized and characterized. Single‐crystal X‐ray structure analysis reveals that complex 1 has a four‐coordinated square geometry, while complex 2 is a five‐coordinated square pyramidal structure and complex 3 is a distorted six‐coordinated octahedral structure. Cyclic voltammograms of 1 indicate an irreversible Cu²⁺/Cu⁺ couple. In vitro antioxidant activity assay demonstrates that the ligands and the two complexes 1 and 3 display high scavenging activity against hydroxyl (HO^?) and superoxide (O₂^??) radicals. Moreover, the fluorescence properties of the ligands and complexes 1 – 3 were studied in the solid state. Metal‐mediated enhancement is observed in 2 , whereas metal‐mediated fluorescence quenching occurs with 1 and 3 .     

Synthesis,characterization, optical and anti-bacterial properties of benzothiazole Schiff bases and their lanthanide (III) complexes

Two new Schiff base ligands comprising benzothiazole derivatives, namely (N,N′,E,N,N′E)-N,N′-(1,3-phenylenebis(methanylylidene))bis(5-nitrobenzo[d]thiazoL2-amine (L1) and (N,N′,E,N,N′E)-N,N′-(1,3-phenylene-bis(methanylylidene))bis(5-methylthiazo-L2-amine (L2), have been synthesized and thoroughly characterized using FTIR, ¹H NMR, mass UV/vis and fluorescence spectral techniques. Further, L1 and L2 lead to the formation of lanthanide complexes 1–6 with Ce(III), Nd(III), and Pr(III) ions in 1:2 (metal:ligand) stoichiometry. UV/vis spectra of L1, L2 and 1–6 exhibit characteristic ligand centered absorptions in the range of 230–350 nm. Besides, both ligands and complexes show significant emissions and good anti-bacterial activity against pathogenic bacteria. Ligands and complexes display anti-bacterial activity against bacteria Staphylococcus aureus (S. aureus) (MTCC 1144) causing skin infection and food poisoning and pimple-causing bacteria propionic bacteria acnes (P. acnes) (MTCC 1951).     

Synthesis,characterization, and antioxidant activity of heterocyclic Schiff bases

Schiff base derivatives have gained great importance due to revealing a great number of biological properties. Schiff bases were synthesized by treatment of 4-amino-1,5-dimethyl-2-phenyl-1H-pyrazol-3(2H)-one ( 1 ) with various aldehydes in methanol at reflux. In addition, diamine was reacted with an aldehyde to yield the corresponding Schiff bases. The structures of synthesized Schiff bases were elucidated by spectroscopic methods such as microanalysis, ¹H-NMR, ¹³C-NMR, and FTIR. Antioxidant activities of synthesized Schiff bases were carried out using different antioxidant assays such as 1,1-diphenyl-2-picryl-hydrazyl free radical (DPPH^•) scavenging, 2,2′-azino-bis(3-ethylbenzthiazoline-6-sulfonic acid) (ABTS) radical scavenging, and reducing power activity. (E)-4-((1H-indol-3-yl)methyleneamino)-1,5-dimethyl-2-phenyl-1H-pyrazol-3(2H)-one ( 3 ), (E)-1,5-dimethyl-4-((2-methyl-1H-indol-3-yl)methyleneamino)-2-phenyl-1H-pyrazol-3(2H)-one ( 5 ), (E)-1,5-dimethyl-2-phenyl-4-(thiophen-2-ylmethyleneamino)-1H-pyrazol-3(2H)-one ( 7 ), (E)-1,5-dimethyl-2-phenyl-4-(quinolin-2-ylmethyleneamino)-1H-pyrazol-3(2H)-one ( 9 ), (1S,2S,N1,N2)-N1,N2-bis((1H-indol-3-yl)methylene)cyclohexane-1,2-diamine ( 11 ), and (1S,2S,N1,N2)-N1,N2-bis((2-methyl-1H-indol-3-yl)methylene)cyclohexane-1,2-diamine ( 12 ) were synthesized in high yields. Compound 5 displayed a good ABTS^•+ activity. Compound 3 revealed the outstanding activity in all assays. Compound 7 has the best-reducing power ability in comparison to other synthesized compounds. Although compounds 5, 11, 12 are new, compounds 3, 7, 9 are known. Due to revealing a good antioxidant activity, the synthesized compounds ( 3, 5, 7 ) have the potential to be used as synthetic antioxidant agents.     

Synthesis,structural characterization,antimicrobial, antioxidant and DNA binding studies of some novel homo‐binuclear Schiff base metal (II) complexes

A novel bi‐nucleating Schiff base ligand, 6,6′‐(((1E,1′E)‐thiophene‐2,5‐diylbis (methaneylylidene))bis (azaneylylidene))bis (3,4‐dimethylaniline), and five binuclear M (II) complexes were synthesized. The bi‐nucleating Schiff base ligand and its metal complexes were characterized using various physicochemical techniques, e.g. elemental analyses, spectroscopic methods, conductivity and magnetic moment measurements. The low molar conductance of the complexes in dimethylsulfoxide shows their non‐electrolytic nature. The antibacterial activities were screened against pathogenic bacteria (Staphylococcus aureus, Escherichia coli, Pseudomonas putida and Bacillus subtilis). The antifungal activity was screened against Aspergillus niger, Aspergillus flavus and Rhizoctonia bataicola. The antimicrobial activity data showed that the metal complexes are more potent than the parent Schiff base ligand against microorganisms. The antioxidant activities of the synthesized compounds were investigated through scavenging activity against 2,2‐diphenyl‐2‐picrylhydrazyl, superoxide anion, hydroxyl and 2,2′‐ azinobis (3‐ethylbenzothiazoline‐6‐sulfonic acid) radicals. The complexes have superior radical scavenging activity than the free ligand and the scavenging effects of the Cu (II) complex are stronger than those of the other complexes. DNA binding studies were performed using electronic spectroscopy, fluorometric competition studies and viscosity measurements. The data indicated that there is a marked enhancement in biocidal activity of the ligand under similar experimental conditions because of coordination with metal ions.     

Organotin(IV) complexes of dibasic tridentate Schiff bases containing ONO donor atoms

Organotin(IV) Schiff base complexes of the type (L)SnR₂ [where R?CH₃, C₆H₅ or CH₂CH₂CO₂ CH₃], (LH)Sn(C₆H₅)₃ and (L)SnCl(CH₂CH₂CO₂ CH₃) [where LH₂?2-N-salicylideneimino-2-methyl-1-propanol, derived from the condensation of salicylaldehyde and 2-amino-2-methyl-1-propanol] have been prepared and characterized on the basis of their elemental analyses, IR, ¹H, ¹³C and ¹¹⁹Sn NMR studies. In these mononuclear complexes the Schiff base acts either as a dianionic tridentate or as a monobasic bidentate moiety by coordinating through an alkoxy group, an azomethine nitrogen and a phenoxide ion to tin. Sulphur dioxide inserts in the tin–methyl/–phenyl bond in the above Schiff base complexes to give tin–O–sulphinates of formulae (L)RSn(SO₂R) and (LH)(C₆H₅)₂Sn(SO₂C₆H₅).     

Synthesis and antioxidant activities of Schiff bases and their complexes: a review

Schiff bases, named after Hugo Schiff , are aldehyde‐ or ketone‐like compounds in which the carbonyl group is replaced by imine or azomethine group. They are widely used for industrial purposes and also have a broad range of applications as antioxidants. An overview of antioxidant applications of Schiff bases and their complexes is discussed in this review. A brief history of the synthesis and reactivity of Schiff bases and their complexes is presented. Factors of antioxidants are illustrated and discussed. Copyright © 2016 John Wiley & Sons, Ltd.     

两种含硫Schiff碱及其配合物的合成与光谱性质

合成了2-氨基噻唑缩5-溴水杨醛(HBrsatz)和2-乙酰噻吩缩4-羟基苯甲酰腙(Hetphz)两种含硫Schiff碱及其配合物[Cu(Brsatz)2](Ⅰ)和[Cd(H2O)(Hetphz)(phen)](NO3)2(Ⅱ),通过元素分析、红外光谱和紫外光谱对它们的结构进行了表征,并研究了它们在DMF溶液中的发光性质,结果表明HBrsatz和Hetphz及配合物Ⅱ具有较强的荧光发射.     

Some divalent metal(II) complexes of novel potentially tetradentate Schiff base N,N′‐bis(2‐carboxyphenylimine)‐2,5‐thiophenedicarboxaldhyde: Synthesis,spectroscopic characterization and bioactivities

A novel tetradentate dianionic Schiff base ligand, N ,N ′‐bis(2‐carboxyphenylimine)‐2,5‐thiophenedicarboxaldhyde (H₂L) and some first row d‐transition metal chelates (Co(II), Cu(II), Ni(II) and Zn(II)) were synthesized and characterized using various physicochemical and spectroscopic methods. The spectroscopic data suggested that the parent Schiff base ligand coordinates through both deprotonated carboxylic oxygen and imine nitrogen atoms. The free Schiff base and its metal chelates were screened for their antimicrobial activities for various pathogenic bacteria and fungi using the agar well diffusion method. The antibacterial and antifungal activities of all the newly synthesized compounds are significant compared to the standard drugs ciprofloxacin and nystatin. The antioxidant activities of the compounds were determined by reduction of 1,1‐diphenyl‐2‐picrylhydrazyl and compared with that of vitamin C as a standard. DNA binding ability of the novel Schiff base and its complexes was investigated using absorption spectroscopy, fluorescence spectroscopy, viscosity measurements and thermal denaturation. The obtained results clearly demonstrate that the binding affinity with calf thymus DNA follows the order: Cu(II) complex > Ni(II) complex > Zn(II) complex > Co(II) complex >H₂L. Furthermore, the DNA cleavage activity of the newly synthesized ligand and its metal complexes was investigated using supercoiled plasmid DNA (pUC18) gel electrophoresis.     

Design and synthesis of triazole Schiff bases and their oxovanadium(IV) complexes as antimicrobial agents

A new class of triazole Schiff bases have been prepared by the reaction of 3,5-diamino-1,2,4-triazole with methyl-, chloro-, and nitro-substituted furan-2-carboxaldehydes in an equimolar ratio (1?:?1). The bidentate ligands were characterized by IR, ¹H-, and ¹³C-NMR, microanalysis, and mass spectrometry. The Schiff bases were complexed with vanadyl(IV) sulfate in a molar ratio (M?:?L) 1?:?2, [M(L)₂]SO₄ (where L?=?L¹–L⁵ and M?=?V^IVO) in a square-pyramidal geometry. In vitro antibacterial activity was determined by screening the compounds against four Gram-negative (Escherichia coli, Shigella flexenari, Pseudomonas aeruginosa, and Salmonella typhi) and two Gram-positive (Staphylococcus aureus and Bacillus subtilis) bacterial strains and in-vitro antifungal activity was carried out on Trichophyton longifucus, Candida albican, Aspergillus flavus, Microscopum canis, Fusarium solani, and Candida glaberata strains.     

Synthesis of asymmetrical tridendate Schiff bases and metal complexes and investigation of anticarcinogen effects on human colon and cervical cancers

The metal complexes of Zn(II), Ni(II), Cu(II) and Pb(II) with asymmetrical Schiff bases were synthesized. The asymmetrical Schiff base was obtained through the condensation of 1,2-phenylenediamine, 4-methyl-1,2-phenylenediamine, 2-hydroxy-1-napthaldehyde and biphenyl-4-carbaldehyde. The new Schiff base ligands (L₁' and L₂') and their metal complexes were characterized by TG/DTG, FT-IR, ¹H-NMR, UV–Vis, ESR, powder XRD, elemental analysis, magnetic moment and fluorescence studies. The powder XRD studies indicate that Co(II) and Cu(II) complexes are amorphous, while Ni(II) and Zn(II) complexes are crystalline. The anticarcinogenic effects of L₁' and L₂' were also investigated against colon (SW-620) and cervical cancer (HeLa) cell lines and compound L₂' was found to possess the highest anticarcinogenic potential, with 16.7 µM and 27.5 µM of IC₅₀ values for HeLa and SW620 cells, respectively.     

Spectroscopic and biological properties of platinum complexes derived from 2-pyridyl Schiff bases

The reactions of a range of aromatic primary amines with pyridine-2-carboxaldehyde were reported, highlighting the effect of the substituents of the amine on the outcomes of the Schiff base reactions. The variant products of the Schiff base reactions were reacted with cis-[PtCl₂(DMSO)₂], generating platinum(II) complexes with PtCl₂(N^N) general formula. The ligands and platinum(II) complexes were identified and characterized by IR and NMR spectroscopic methods. Single crystal XRD offered structural confirmation for three of the organic compounds and two platinum complexes. The spectral, antimicrobial, DNA-binding and molecular docking of the platinum complexes were studied, highlighting the effect of the different functional group in the Schiff base ligands on their properties. In general, introducing the electron-withdrawing group nitro or acetyl in the 2-pyridyl Schiff base ligands, results in a red-shift in the absorption maxima of the platinum complex. In addition, the enhancement in the antimicrobial activities and the increase in the ct-DNA-binding affinity were also observed when the nitro or acetyl functional group is introduced to the Schiff base ligand in the platinum(II) complex.     

Metal‐based antitumor,cytotoxic and antimicrobial activity: pharmacological evaluation of Knoevenagel condensate β‐diketone Schiff base thiosemicarbazone Cu(II) and Zn(II) complexes

Knoevenagel condensate Schiff base ligands [L = 3‐cinnamalideneacetylacetone‐thiosemicarbazone (CAT)/3‐cinnama‐ lideneacetylacetoneethylthiosemicarbazone (CAET)/3‐cinnamalideneacetylacetonephenylthiosemicarbazone (CAPT)] and their copper/zinc complexes were synthesized. They were characterized by analytical and spectral techniques. From these data it was found that the ligands adopt square‐planar geometry on metalation with Cu²⁺ and Zn²⁺. To evaluate the antitumor and cytotoxic activity of the synthesized complexes in mice and human cancer cell lines, the antitumor activity of the complexes was evaluated against an Ehrlich ascites carcinoma (EAC) tumor model. The activity was assessed using survival time and short‐term in vitro cytotoxic activity. Oral administration of complexes (100 mg/kg) increased the survival time. The cytotoxic activity of complexes was evaluated using human breast cancer (MDA‐MB‐231), colon cancer (HCT‐116) and nonsmall lung cancer (NCI‐H‐23) cell lines. Both the complexes possessed significant antitumor and cytotoxic activity on EAC and human cancer cell lines. The in vitro antimicrobial screening effect of the investigated compounds was also tested against the various organisms by well diffusion method. Copyright © 2009 John Wiley & Sons, Ltd.     

Pd(II) complexes of Schiff bases and their application as catalysts in Mizoroki–Heck and Suzuki–Miyaura cross‐coupling reactions

Schiff bases of 2‐(phenylthio)aniline, (C₆H₅)SC₆H₄N?CR (R = (o‐CH₃)(C₆H₅), (o‐OCH₃)(C₆H₅) or (o‐CF₃)(C₆H₅)), and their palladium complexes (PdLCl₂) were synthesized. The compounds were characterized using ¹H NMR and ¹³C NMR spectroscopy and micro analysis. Also, electrochemical properties of the ligands and Pd(II) complexes were investigated in dimethylformamide–LiClO₄ solution with cyclic and square wave voltammetry techniques. The Pd(II) complexes showed both reversible and quasi‐reversible processes in the ?1.5 to 0.3 V potential range. The synthesized Pd(II) complexes were evaluated as catalysts in Mizoroki–Heck and Suzuki–Miyaura cross‐coupling reactions. Copyright © 2015 John Wiley & Sons, Ltd.     

Metal‐based antibacterial and antifungal amino acid derived Schiff bases: their synthesis,characterization and in vitro biological activity

A new series of antibacterial and antifungal amino acid derived Schiff bases and their cobalt(II), copper(II), nickel(II) and zinc(II) metal complexes have been synthesized and characterized by their elemental analyses, molar conductances, magnetic moments, IR and electronic spectral measurements. The spectral data indicated the Schiff base ligands ( L ₁– L ₅) derived by condensation of salicylaldehyde with glycine, alanine, phenylalanine, methionine and cysteine, to act as tridentate towards divalent metal ions (cobalt, copper, nickel and zinc) via the azomethine‐N, deprotonated carboxyl group of the respective amino acid and deprotonated oxygen atom of salicylaldehyde by a stoichiometric reaction of M: L (1:2) to form complexes of the type K₂[M( L )₂] [where M = Co(II), Cu(II), Ni(II) and Zn(II)]. The magnetic moments and electronic spectral data suggested that all complexes have an octahedral geometry. Elemental analyses and NMR spectral data of the ligands and their Zn (II) complexes agree with their proposed structures. The synthesized ligands, along with their metal complexes, were screened for their in‐vitro antibacterial activity against four Gram‐negative (Escherichia coli, Shigella flexeneri, Pseudomonas aeruginosa and Salmonella typhi) and two Gram ‐ positive (Bacillus subtilis and Staphylococcus aureus) bacterial strains and for in‐vitro antifungal activity against Trichophyton longifusus, Candida albicans, Aspergillus flavus, Microsporum canis, Fusarium solani and Candida glaberata. The results of these studies show the metal complexes to be more antibacterial/antifungal against one or more species as compared with the uncomplexed Schiff base ligands. The brine shrimp bioassay was also carried out to study their in‐vitro cytotoxic properties. Only three compounds ( 2, 11 and 17 ) displayed potent cytotoxic activity as LD₅₀ = 8.196 × 10^?4, 7.315 × 10^?4 and 5.599 × 10^?4 M /ml respectively, against Artemia salina. Copyright © 2007 John Wiley & Sons, Ltd.     

Ruthenium complexes of Schiff base ligands as efficient catalysts for catechol–hydrogen peroxide reaction

Zeolite Y-encapsulated ruthenium(III) complexes of Schiff bases derived from 3-hydroxyquinoxaline-2-carboxaldehyde and 1,2-phenylenediamine, 2-aminophenol, or 2-aminobenzimidazole (RuYqpd, RuYqap and RuYqab, respectively) and the Schiff bases derived from salicylaldehyde and 1,2-phenylenediamine, 2-aminophenol, or 2-aminobenzimidazole (RuYsalpd, RuYsalap and RuYsalab, respectively) have been prepared and characterized. These complexes, except RuYqpd, catalyze catechol oxidation by H₂O₂ selectively to 1,2,4-trihydroxybenzene. RuYqpd is inactive. A comparative study of the initial rates and percentage conversion of the reaction was done in all cases. Turn over frequency of the catalysts was also calculated. The catalytic activity of the complexes is in the order RuYqap > RuYqab for quinoxaline-based complexes and RuYsalap > RuYsalpd > RuYsalab for salicylidene-based complexes. The reaction is believed to proceed through the formation of a Ru(V) species.     

双水杨醛缩环己二胺类西佛碱及其配合物的合成、性质研究

合成了两种双水杨醛缩环已二胺类西佛碱N，N’-(二羟苯次甲基)环已二胺(1)和N，N’-二(3，5-二叔丁基-2-羟苯次甲基)环已二胺(2)，以及它们的金属锌配合物(3)和(4)，通过核磁共振、元素分析和红外光谱确定了四种物质的结构，研究了它们的紫外吸收光谱、荧光光谱，测定了(3)和(4)的荧光量子效率．(4)中四个叔丁基的存在使其荧光量子效率提高．此类双西佛碱金属配合物可以应用于有机电致发光材料中．     

The structures and cyclic voltammetry of three copper(II) complexes derived from bulky ortho-hydroxy Schiff bases

Three copper(II) complexes derived from bulky ortho-hydroxy Schiff base ligands, (1)-(3), were synthesized and characterized by chemical analysis, UV-Vis, IR, μ_eff and mass spectrometry. The solid state structures of compounds (1)-(3) were determined. The solid state X-ray diffraction studies of these compounds show that the geometry is intermediate between square planar and tetrahedral. Moreover, EPR studies in DMF solution at 77 K suggest that the geometry of these complexes in solution is different from that observed in the solid state by X-ray crystallography. Furthermore, cyclic voltammetry studies performed for (1)-(3), indicate a dependence of the cathodic potentials upon conformational and electronic effects.     

Synthesis,characterization and antimicrobial activity of a bidentate NS Schiff base of S-benzyl dithiocarbazate and its divalent complexes

The reaction of S-benzyl dithiocarbazate (SBDTC) with 2,4,5-trimethoxybenzaldehyde afforded a bidentate NS Schiff base 1 (benzyl-3-N-(2,4,5-trimethoxyphenylmethylenehydrazine carbodithioate), which on further reaction with M(II) (where M(II) = nickel(II), zinc(II), palladium(II) and copper(II)) in ethanol under reflux yielded bis-chelated inner complexes [ML₂] 2–5 with deprotonated L. The ligand and its complexes were characterized by physicochemical techniques, viz., molar conductance, magnetic susceptibility measurement, IR, NMR, UV–Vis and mass spectroscopic techniques. The crystal structures of 1 and 5 were also determined by single-crystal X-ray crystallography. The crystal structure analysis showed that the ligand exists in its thione tautomeric form. In the complexes, each of the two deprotonated ligands chelated the metal ions through the β-nitrogen and the thione sulfur forming five-membered rings. The copper(II) complex (5) exhibited a square-planar geometry, where the two N₂S₂ chromophores are arranged trans. All the compounds showed strong antibacterial activity against S.-β-hemolyticus, Klebsiella pneumoni, and Escherichia coli. The compounds also showed strong antifungal activity against Aspergillus fumigatus, Aspergillus niger, Aspergillus flavus, and Candida albicans with the exception of the palladium(II) complex (4) which showed no activity, while all the compounds showed no activity against Fusarium vasinfectum.     

EPR character of gadolinium complexes with noncyclic polyether Schiff bases and its solvent effects

EPR characters of three new gadolinium complexes with noncydic polyether Schiff bases in powder or organic solvents, including various oxyethylene chain lengths and different substituting groups in ligands, are investigated respectively. Some regularities are summed up. The difference of EPR character in various solvents, particularly at different temperatures, has been examined. The 'single peak effect' due to THF solvent at low temperature is observed for the first time. This phenomenon is explicated.