Synthesis,structural characterization and biological activities of metal(II) complexes with Schiff bases derived from 5-bromosalicylaldehyde: Ru(II) complexes transfer hydrogenation

In this study, two novel Schiff base ligands (L¹ and L²) derived from condensation of methyl 2-amino-6-methyl-4,5,6,7-tetrahydrothieno[2,3-c]pyridine-3-carboxylate and methyl 2-amino-6-phenyl-4,5,6,7-tetrahydrobenzo[b]thiophene-3-carboxylate, both starting matter with 5-bromo-salicylaldehyde, and their Zn(II) and Ni(II) metal complexes have been prepared using a molar ratio of ligand:metal as 1:1 except the Ru(II) complexes 1:0.5. The structures of the obtained ligands and their metal complexes were characterized by elemental analysis, FT-IR, ¹H NMR, ¹³C NMR, UV–vis, thermal analysis methods, mass spectrometry, and magnetic susceptibility measurements. Antioxidant and antiradical activity of Schiff base ligands and their metal complexes were been evaluated in vitro tests. Antioxidant activities of metal complexes generally were more effectives than free Schiff bases. 1c and 2c were used as catalysts for the transfer hydrogenation (TH) of ketones. 1c, 2c complexes were found to be efficient catalyst for transfer hydrogenation reactions.     

Phosphorus‐based Schiff bases and their complexes as nontoxic antioxidants: Structure–activity relationship and mechanism of action

Phosphorus‐based Schiff base were synthesized by treating bis{3‐[2‐(4‐amino‐1.5‐dimethyl‐2‐phenyl‐pyrazol‐3‐ylideneamino)ethyl]‐indol‐1‐ylmethyl}‐phosphinic acid with paraformaldehyde and characterized as a novel antioxidant. Its corresponding complexes [(VO)₂L(SO₄)₂], [Ni₂LCl₄], [Co₂LCl₄], [Cu₂LCl₄], [Zn₂LCl₄], [Cd₂LCl₄], [Hg₂LCl₄], [Pd₂LCl₄], and [PtLCl]Cl₂ were analyzed by Fourier transform‐infrared, (¹H and ¹³C) nuclear magnetic resonance, and mass and UV–Vis spectroscopy. Experimental data showed that the ligand coordinated with the metal ions via donor atoms such as nitrogen to form an octahedral arrangement of the Schiff base around the central transition‐metal atom. The nature of these complexes was identified using the molar ratio and Job's methods, with the results agreeing with a metal‐to‐ligand (M:L) molar ratio of 2:1, expect for Pt, whose M:L was 1:1. Thermodynamic activation parameters such as ?E*, ?H*, ?S*, ?G*, and K were determined from the thermogravimetric analysis curve using the Coats–Redfern method. The antioxidant activities of the prepared compounds were assessed by using 1.1‐diphenyl‐2‐picrylhydrazyl as the free radical, and the results show that the complex Schiff bases were found to possess potent antioxidant activity. The structure–activity relationship of the ligand and its complexes indicates that the presence of electron‐donating moieties, such as Co(II) and Ni(II), in the chemical structure increases the antioxidant activity, whereas the Pt(IV) and Pd(II) complexes diminished the antioxidant activity, indicating the superior activity of the hydroxyl radical (OH^·) over the superoxide radical.     

Diorganotin(IV) complexes with 2-benzoylpyridine and 2-acetylpyrazine N(4)-phenylthiosemicarbazones: Synthesis, crystal structures and biological activities

Four diorganotin(IV) complexes [(Me)₂Sn(L¹)(CH₃COO)]·CH₃CH₂OH (1), [(Ph)₂Sn(L¹)(CH₃COO)]·CH₃CH₂OH (2), [(Me)₂Sn(L²)Cl] (3) and [(Ph)₂Sn(L²)(CH₃COO)] (4) where HL¹ = 2-benzoylpyridine N(4)-phenylthiosemicarbazone and HL² = 2-acetylpyrazine N(4)-phenylthiosemicarbazone have been synthesized and characterized by elemental analysis, IR MS, ¹H NMR and single-crystal X-ray diffraction studies. Schiff bases in their deprotonated forms coordinate to tin(IV) via pyridine/pyrazine nitrogen atom and the nitrogen atom and sulfur atoms of the thiosemicarbazone moiety. The tin atom is seven-coordinated in 1, 2 and 4 containing one acetato group, respectively, and six-coordinated in 3 containing one chloride ion. Biological studies, carried out in vitro against selected bacteria and K562 leukaemia cells, respectively, have shown that different substituted groups attached at the thiosemicarbazone moieties and different diorganotin(IV) groups showed distinctive differences in the biological property.     

Synthesis,spectroscopic characterization,biological screening and in vitro cytotoxic studies of 4‐methyl‐3‐thiosemicarbazone derived Schiff bases and their Co (II), Ni (II), Cu (II) and Zn (II) complexes

A series of twenty compounds inclusive of bidentate Schiff bases derived from condensation of 4‐methyl‐3‐thiosemicarbazide with substituted derivatives of napthaldehyde/benzaldehyde/salicylaldehyde and their mononuclear Co (II), Ni (II), Cu (II) and Zn (II) complexes in molar ratio (1:1) were synthesized and characterized. The coordination behavior, modes of bonding and overall geometry of the compounds was known from the elemental analysis, spectral techniques (IR, UV–Vis, ¹H NMR, ¹³C NMR, ESR and ESI‐mass), magnetic moment measurements, molar conductance, thermal and powder XRD studies. The studies revealed octahedral geometry for all the complexes where ligands coordinated in a neutral bidentate manner (NS) via nitrogen atom of azomethine group and sulphur atom of thione group with the metal centre. In vitro biological effects of the compounds were tested against four bacterial species and two fungal strains. The results indicated that the metal complexes showed a marked enhancement in biocidal activity in comparable with the parent Schiff bases. In vitro anticancer activity against the malignant tumor cell lines; human alveolar adenocarcinoma epithelial cell line (A549), human breast adenocarcinoma cell line (MCF7), human prostate cancer cell line (DU145) and human normal lung cell line (MRC‐5) using MTT assay, exposed compound 16 as a leading member with lowest IC₅₀ value of 10.6 ± 0.14 μM against (A549) cell line.     

Synthesis,characterization, and antibacterial activity of two zinc(II) complexes with Schiff bases derived from rimantadine

The reactions of zinc(II) chloride and two Schiff base ligands derived from rimantadine and 5-chlorosalicylaldehyde/4-methoxysalicylaldehydes, generated two novel complexes [Zn(L¹)₂Cl₂] (I) and [Zn(L²)₂Cl₂] (II), where L¹ = 2-((1-(1-adamantan-1-yl)ethyl)-iminomethyl)-4-chlorophenol, L² = 2-((1-(1-adamantan-1-yl)ethyl)iminomethyl)-5-methoxyphenol. The complexes were characterized by the means of IR, ¹H NMR, elemental analysis, molar conductance and thermal analysis. A single-crystal X-ray diffraction analysis reveals that both complexes crystallize in orthorhombic system, space group Fdd2 for I and Pbcn for II. In two complexes crystals, each asymmetric unit consists of one zinc(II) ion, two corresponding Schiff base ligands and two chlorine atoms; the central zinc atom lies on a twofold rotation axis and is four-coordinate via two chlorine atoms and two oxygen atoms from the Schiff base ligands, forming a distorted tetrahedral geometry.     

Antimicrobial,antioxidant and SOD activities of copper(II) complexes derived from 2-aminobenzothiazole derivatives

A series of Cu(II) complexes have been synthesized from bidentate Schiff base ligands (by condensation of Knoevenagel condensate of acetoacetanilide (obtained from substituted benzaldehydes and acetoacetanilide) and 2-aminobenzothiazole). They were characterized by elemental analysis, IR, ¹H NMR, ¹³C NMR, UV–vis., molar conductance, magnetic moment, ESR spectra and electrochemical studies. Based on the magnetic moment, ESR, and electronic spectral data, a distorted square planar geometry has been suggested for the complexes. Antibacterial and antifungal screening of the ligands and their complexes reveal that all the complexes show higher activities than the ligands. The antioxidant activities of the ligands and complexes were determined by superoxide and hydroxyl radical scavenging methods in vitro, indicating that the complexes exhibit more effective antioxidant activity than the ligands alone. The results show that the Cu(II) complexes also have similar superoxide dismutase activity to that of native Cu, Zn-SOD. All complexes exhibit suitable Cu(II)/Cu(I) redox potential (E_1/2) to act as synthetic antioxidant enzyme mimics.     

Cytotoxic urea Schiff base complexes for multidrug discovery as anticancer activity and low in vivo oral assessing toxicity

Novel mononuclear complexes 2–8 derived from hybrid Urea Schiff base HL were synthesized using various metal Ni²⁺, Fe³⁺, Cu²⁺, Co²⁺, Mn²⁺, Zn²⁺, and Cr³⁺. The results revealed the ligand HL reacts with metal ions as monobasic or neutral monodentate chelator it via the nitrogen of azomethine and deprotonated/protonated phenolic oxygen atom adopting octahedral geometry. The elemental analysis of the complexes showed the bonding of the ligand with the metal ions in a ratio of 1: 1 in all-metal complexes. XRD analysis of the ligand and its complexes indicate a monoclinic, tetragonal, orthorhombic corresponding to urea Shiff base (1) and zinc complex (7), nickel complex (2), and cobalt complexes (5), respectively. The bioactivity of synthesized compounds was tested and screened against three cancer cell lines PC3 (prostate), SK-OV-3 (ovarian), and HeLa (cervical). The results revealed a weak activity for the ligand, whereas nickel and iron complexes present moderate activities against three cancer cells. The best results were mentioned with copper and proved the best results against three cancer cells PC3, SKOV3, and HeLa displaying an excellent activity with IC₅₀ values of 0.71 ± 0.06, 0.12 ± 0.06, and 0.79 ± 0.23 μg/mL respectively. Moreover, the urea Schiff base complexes showed good safety in vivo toxicity test. The present study demonstrates that all urea Schiff base complexes is inactive against saint tissue and five metal complexes investigated herein can be effective and promising chemotherapeutic drugs for ovarian cancer cell SKOV3, emphasizing the copper-urea Schiff base complex.     

Synthesis and characterization of biologically active new Schiff bases containing 3‐functionalized 1,2,4‐triazoles and their zinc(II) complexes: crystal structure of 4‐bromo‐2‐[(E)‐(1H‐1,2,4‐triazol‐3‐ylimino)‐ methyl]phenol

Biologically active triazole Schiff bases ( L ¹  L ³ ) derived from the reaction of 3‐amino‐1,2,4‐triazole with chloro‐, bromo‐ and nitro‐ substituted salicylaldehydes and their Zn(II) complexes (1–3) have been synthesized and characterized by their physical, spectral and analytical data. Triazole Schiff bases potentially act as tridentate ligands and coordinate with the Zn(II) metal atom through salicylidene‐O, azomethine‐N and triazole‐N. The complexes have the general formula [M(L‐H)₂], where M = zinc(II) and L = ( L ¹ – L ³ ), and observe an octahedral geometry. The Schiff bases and their Zn(II) complexes have been screened for in‐vitro antibacterial, antifungal and brine shrimp bioassay. The biological activity data show the Zn(II) complexes to be more potent antibacterial and antifungal than the parent simple Schiff bases. Copyright © 2011 John Wiley & Sons, Ltd.     

Synthesis,crystal structure,spectroscopic, and biological studies on Cu(II) complexes of N,O donor dimethyl isoxazole Schiff bases

Cu(II) complexes with Schiff bases DMIIMP, DMIIMBD, DMIIMBP, DMIIMCP, DMIIMMP, and DMIIMNP (see Introduction for definitions) are derived from condensation of 3,4-dimethyl 5-amino-isoxazole with salicylaldehyde and substituted salicylaldehydes. The newly synthesized ligands were characterized by IR, UV-Vis, ¹H NMR, ¹³C NMR, mass spectra, and elemental analysis. The Cu(II) complexes were characterized by IR, UV-Vis, ESR, elemental analysis, magnetic moments, thermogram, DTA, and single crystal analysis. The complexes have general formula [M(L)₂]. The Schiff bases are bidentate coordinating through the azomethine nitrogen and phenolic oxygen of salicylaldehydes. Based on the analytical and spectral data, four-coordinate geometry is assigned for all the complexes. ESR and single crystal analysis suggests square planar geometry for all complexes. [Cu(DMIIMP)₂] crystallizes in the orthorhombic system. Antimicrobial studies of Schiff bases and their metal complexes show significant activity with the metal complexes showing more activity than corresponding Schiff bases. Cytotoxicity of the copper complexes on human cervical carcinoma cells (HeLa) was measured using the Methyl Thiazole Tetrazolium assay.     

Synthesis and biological activity of trinuclear seven-coordinated tin(IV) complexes derived from tridentate ligands and trimesic acid

The synthesis of trinuclear Sn(IV) complexes 5a–h – prepared in a one-pot reaction of 2-amino-4-R-phenol (R=H, Me, Cl, NO₂), 2-pyridine-carboxaldehyde, 1,3,5-benzenetricarboxylic acid (trimesic acid, H₃BTC), and dibutyl and dioctyltin oxides – is described. These compounds were characterized by elemental analysis, mass spectrometry, IR, and multinuclear NMR spectroscopy. The structures of 5a and 5b were also determined by single-crystal X-ray analysis. The trinuclear tin system is formed by bridges through the carboxylate moieties. The metal centers are seven-coordinate and the coordination polyhedron of tin can be depicted as distorted pentagonal-bipyramidal (PBP), where the equatorial plane consists of three oxygens and two nitrogens and the organic groups occupy the axial positions. The work presented here combines the useful properties of Schiff bases and H₃BTC ligands in the formation of organotin(IV) complexes, and investigates the likely antioxidant (DPPH and TBARS) and anti-inflammatory activity (TPA) of the new substances.     

混合二烃基二氯化锡与2-羟基-1-萘醛缩苯胺类席夫碱配合物的合成与表征

由混合二烃基二氯化锡(RR′SnCl₂)与2-羟基-1-萘醛缩苯胺类席夫碱反应,合成了18种新的有机锡配合物。经元素分析,IR、¹H NMR、¹³CNMR和TG-DSC测定,确认配合物为有机锡与席夫碱的121加成物,配体以酚羟基氧原子和锡原子配位。     

Preparation and characterization of some transition metal complexes of benzoic acid hydrazones of 2-aminonicotinaldehyde

Summary Cu^II, Ni^II, Co^II, Zn^II and Pd^II complexes of tridentate Schiff base ligands derived from the condensation of benzoic acid hydrazides with 2-aminonicotinaldehyde have been prepared and characterized. For M=Cu, Ni, Co and Zn the complexes were formulated as [M(ligand)(H₂O)X] (X=Cl, Br), with a distorted octahedral geometry and tridentate Schiff base ligands. The Pd complexes were formulated as Pd(ligand)Cl₂, with square planar geometries and bidentate Schiff base ligands. The e.s.r. spectra of the Cu^II complexes are discussed.     

Structural and conformational analysis of neutral dinuclear diorganotin(IV) complexes derived from hexadentate Schiff base ligands

The synthesis of three hexadentate Schiff base ligands has been carried out, which contain two sets of ONO donor atoms. These were reacted with diorganotin(IV) dichloride derivatives (R = Me, nBu, Ph) to prepare seven dinuclear diorganotin(IV) complexes in moderate yields. Aside from IR and NMR (¹H, ¹³C, ¹¹⁹Sn) spectroscopic studies, mass spectrometry and elemental analysis, four tin complexes were characterized by X-ray diffraction analysis. The spectroscopic analyses showed that in solution the tin atoms have five-coordinate environments with a distorted trigonal bipyramidal geometry. Each tin atom is coordinated to the nitrogen atom and forms covalent bonds with two oxygen atoms and two carbon atoms. Due to the presence of a methylene group as bridge between the two ONO chelates, the overall molecular structures can have cis or trans conformation, having either mirror or C₂-symmetry. While in solution a fast equilibrium can be supposed, in the solid state different intermediate conformations have been detected. Furthermore, for the dialkyltin derivatives Sn?O intermolecular interactions were found allowing for a dimeric or crinkled polymeric organization, whereas for the diphenyltin derivatives no such interactions were observed.     

Synthesis,spectral characterization,thermal, computational and antibacterial studies of lanthanide complexes with 2-fluorobenzoic acid-(5-R-2-hydroxy-benzylidene)hydrazide {R = chloro or bromo)

Tridentate Schiff base ligands, 2-Fluorobenzoic acid-(5-chloro-2-hydroxy benzylidene)hydrazide {H₂L_Cl} and 2-Fluorobenzoic acid-(5-bromo-2-hydroxybenzylidene)hydrazide {H₂L_Br} have been used to prepare a variety of lanthanide complexes [HNEt₃][LnL_x(NO₃)₂(H₂O)]H₂O, Ln = La, Pr, Nd, Sm, Eu, Gd, Tb, Dy and Er. The ¹H and ¹³C NMR of lanthanum in conjunction with the infrared, elemental, thermal, molecular mass and conductance measurements enable the assignment of the formula to these complexes. The anionic unit [LnL_x(NO₃)₂(H₂O)]^? contains one tridentate ONO-donor, L^2?, which coordinates the metal ions via the phenolate-O, the imine-N and the deprotonated amide-O atoms in enol tautomeric form. The coordination environment around central metal ion is completed by two bidentate nitrate ligands and one coordinated water molecule to give a coordination number of eight for Ln(III). In order to get a better insight into the structural features of the complexes, their molecular geometries were fully optimized using density functional theory calculations at the M06-2X/6-31G¹ level of theory. The antibacterial activity results, on a panel of six different bacterial strains, show that the activity of the complexes is higher than that of the free ligands and in some cases higher than that of amoxicillin which is taken as standard reference drug. Compared to the free ligands, the emission spectra of the complexes exhibit a blue-shift with a clear enhancement in the emission intensity.     

In-vitro antibacterial activity of Ni(II), Cu(II), and Zn(II) complexes incorporating new azo-azomethine ligand possessing excellent antioxidant,anti-inflammatory activity and protective effect of free radicals against plasmid DNA

Azo Schiff base ligand 2-hydroxy-3-methoxy-5-(tolyldiazenyl)benzaldehyde oxime (HL¹) and 2-hydroxy-3-methoxy-5-(methoxyphenyl)benzaldehyde oxime (HL²) were prepared along with their transition metal complexes of Ni(II), Cu(II), and Zn(II). Ligands and their metal complexes were characterized by several analysis techniques. In- vitro antibacterial, antioxidant and anti-inflammatory activities of synthesized ligands and their metal complexes have been studied. Biological study showed that amongst all the synthesized compounds, Cu(II) complexes possessed excellent antibacterial activity than standard antibiotic Chloramphenicol. Ligands (HL¹) and (HL²) showed excellent antioxidant as well as anti-inflammatory activity. Both the ligands were tested for their protective effect of free radicals against plasmid DNA and it was found that both the ligands showed good DNA nicking activity.     

Green synthesis of new Ge(IV) complexes with bio-potent ligands and their antimicrobial,DNA cleavage,and antioxidant activities

Green microwave supported synthesis, spectral, antimicrobial, DNA cleavage, and antioxidant studies of Ge(IV) complexes with bio-potent ligands, 1-acetylferrocenehydrazinecarboxamide (L¹H) and 1-acetylferrocenehydrazinecarbothioamide (L²H) have been carried out. The ligands and their respective complexes have been characterized on the basis of elemental analysis, IR, ¹H and ¹³C NMR spectra, and X-ray powder diffraction studies. The ligands are coordinated to the Ge(IV) via azomethine nitrogen and thiolic sulfur atom/ enolic oxygen atom. Both ligands and their complexes demonstrated appreciable fungicidal and bactericidal properties. The metal complexes demonstrated stronger antimicrobial than the respective free ligands. DNA cleavage activity of the complexes study revealed higher activity of the complexes than the ligands. Antioxidant activity of the complexes was tested for their hydrogen peroxide scavenging.     

Crystal structures,electrochemical properties,antioxidant screening and in vitro cytotoxic studies on four novel Cu(II) complexes of bidentate Schiff base ligands derived from 2-methoxyethylamine

Four novel Schiff base ligands and their copper(II) complexes, [Cu(L¹)₂] (1), [Cu(L²)₂] (2), [Cu(L³)₂] (3), and [Cu(L⁴)₂] (4), were synthesized and characterized by elemental analyses, FT-IR, and UV–Vis spectroscopy. The ligands were synthesized from the condensation of 2-methoxyethylamine with various salicylaldehyde derivatives (x-salicylaldehyde for HLⁿ, x = H (n = 1), 5-Br (n = 2), 3-OMe (n = 3), and 4-OMe (n = 4)). The molecular structures of 1, 2, and 3 were determined by the single crystal X-ray diffraction technique. The redox behavior studies of the complexes in acetonitrile display the electronic effects of the groups on the redox potential. The antioxidant activity of the Schiff base ligands and their Cu(II) complexes was evaluated using the 1,1-diphenyl-2-picrylhydrazyl (DPPH) radical scavenging method and FRAP assay. Furthermore, the in vitro anticancer activity of compounds was screened, including MTT and migration assays against gastric cancer cell line (MKN-45). The results show that all ligands and complexes have antioxidant and anticancer activity in a concentration-dependent way.     

Synthesis,Spectral, and 3D Molecular Modeling of Tin(II) and Organotin(IV) Complexes of Biologically Active Schiff Bases Having Nitrogen and Sulfur Donor Ligands

Reaction of tin(II) chloride and dimethyltin dichloride with Schiff bases derived from S-benzyldithiocarbazate leads to the formation of a new series of tin(II) and organotin(IV) complexes of general formula SnCl ₂ .L and Me ₂ SnCl ₂ .L (where L = Schiff bases are derived from the condensation of S-benzyldithiocarbazate with heterocyclic aldehydes). An attempt has been made to prove the structures of the resulting complexes on the basis of elemental analysis, conductance measurements, molecular weight determinations, infrared, and multinuclear magnetic resonance ( ¹ H, ¹³ C, and ¹¹⁹ Sn NMR) spectral studies. A few representative ligands and their tin complexes have also been screened for their antibacterial and antifungal activities and found to be quite active in this respect.     

New Schiff Bases Containing Silicon and Their Co(II) and Cu(II) Complexes: Synthesis,Complexation, Characterization,and Antimicrobial and Electrochemical Properties

Two novel Schiff base ligands, 4-((3-(trimethoxysilyl)propylimino)methyl)benzene– 1,2,3-triol (L¹H) and 4-((3-(triethoxysilyl)propylimino)methyl)benzene–1,2,3-triol (L²H), have been synthesized by the reaction of 2,3,4-trihydroxybenzaldehyde with 3-aminopropyltrimethoxysilane and 3-aminopropyltriethoxysilane, respectively. The mononuclear Co^II and Cu^II complexes of these Schiff bases were prepared. The complexes of the Schiff bases are formed by coordination of N, O atoms of the ligands. The proposed structures were confirmed by elemental analyses, FT-IR, and UV-visible spectroscopy, magnetic susceptibility, and conductance measurements; the ¹H NMR spectra of the ligands were also recorded. The analytical data show that the metal to ligand ratio in the complexes containing silicon is 1:2. The electrochemical properties of the complexes have been investigated at 100 mVs^?1 scan rate in DMSO. In addition, the antimicrobial activity of L¹H and L²H Schiff ligands, and their [M(L¹)2] and [M(L²)2] type coordination compounds, were investigated.