Stability Of Metal Complexes Research Articles

Kinetic and Thermodynamic Stabilization of Metal Complexes by Introverted Coordination in a Calix[6]azacryptand.

The Huisgen thermal reaction between an organic azide and an acetylene was employed for the selective monofunctionalization of a X6 -azacryptand ligand bearing a tren coordinating unit [X6 stands for calix[6]arene and tren for tris(2-aminoethyl)amine]. Supramolecular assistance, originating from the formation of a host-guest inclusion complex between the reactants, greatly accelerates the reaction while self-inhibition affords a remarkable selectivity. The new ligand possesses a single amino-leg appended at the large rim of the calixarene core and the corresponding Zn(2+) complex was characterized both in solution and in the solid state. The coordination of Zn(2+) not only involves the tren cap but also the introverted amino-leg, which locks the metal ion in the cavity. Compared with the parent ligand deprived of the amino-leg, the affinity of the new monofunctionalized X6 tren ligand 6 for Zn(2+) is found to have a 10-fold increase in DMSO, which is a very competitive solvent, and with an enhancement of at least three orders of magnitude in CDCl3 /CD3 OD (1:1, v/v). In strong contrast with the fast binding kinetics, decoordination of Zn(2+) as well as transmetallation appeared to be very slow processes. The monofunctionalized X6 tren ligand 6 fully protects the metal ion from the external medium thanks to the combination of a cavity and a closed coordination sphere, leading to greater thermodynamic and kinetic stabilities.

Pharmacophore hybrid approach of new modulated bis-diimine CuII/ZnII complexes based on 5-chloro Isatin Schiff base derivatives: Synthesis, spectral studies and comparative biological assessment

Novel bioactive 5-chloro isatin based Schiff base ligands, (N,N'E,N,N'Z)-N,N’-(5-chloroindoline-2,3-diylidene)bis(5-nitrobenzo [d]thiazol-2-amine), L1 and (N,N'E,N,N'Z)-N,N’-(5-chloroindoline-2,3-diylidene)bis(5-nitrothiazol-2-amine), L2 derived from 2-amino 5-nitrobenzothiazole and 2-amino 5-nitrothiazole and their metal complexes, [Cu(L1)2]Cl2;1, [Zn(L1)2(H2O)2]Cl2;2, [Cu(L2)2]Cl2;3 and [Zn(L2)2(H2O)2]Cl2;4 have been synthesized. The composition, stoichiometry and geometry of the proposed ligands and their complexes have been envisaged by the results of elemental analyses and spectroscopic data (FT-IR, 1H NMR and 13C NMR, Mass and EPR). The molar conductivity values of the metal complexes revealed their ionic nature. The thermal stability of metal complexes was demonstrated by TGA/DTA studies while the crystalline nature of the complexes has been ascertained by XRD. Furthermore, a comparative account of in vitro antibacterial study against different bacterial strains with respect to standard antibiotic and scavenging activity against standard control at different concenterations unfolded pronounced antibacterial and radical scavenging potencies of the metal complexes as compared to free ligands. In addition, in vitro cytotoxicity of ligands and its metal complexes was also screened on MCF7 (Human breast adenocarcinoma), HeLa (Human cervical carcinoma) and HepG2 (Human Hepatocellular carcinoma), cell lines and normal cells (PBMC). The antiproliferative outcomes revealed that metal complexes exhibit superior activity in general as compared to free ligands (L1 and L2) where metal complexes (1 and 2) of 5-chloro isatin linked benzothiazole motif (L1) are found to have better prospect of acting as chemotherapeutic agents which can be explained in terms of greater biopotency, planarity and conjugation against all the tested cancer cell lines with IC50<2.80μM.

Controlled Flexible Coordination in Tripodal Iron(II) Phosphane Complexes: Effects on Reactivity

The possibility to alter properties of metal complexes without significant steric changes is a useful tool to tailor the reactivity of the complexes. Herein we present the synthesis of iron complexes with the tripodal phosphane ligands Triphos and Triphos(Si) and report on their different coordination properties. Whereas reaction of Triphos(Si) and FeX2 (X = Cl, Br) exclusively afforded (Triphos(Si))FeX2 with a κ(2)-coordinated ligand, the homologous C-derived Fe complexes show rapid conversion in solution to afford [(Triphos)Fe(CH3CN)3][Fe2Cl6] or [(Triphos)Fe(CH3CN)3][FeBr4], respectively. The structural conversion was found to be temperature- and solvent-dependent and was accompanied by a linear change of the overall magnetization. The different ligand influence was shown to have a significant effect on the ability of (Triphos(Si))FeCl2 and (Triphos)FeCl2 to perform the Sonogashira cross-coupling reaction of 4-iodotoluene and phenyl acetylene as well as the hydrosilylation of acetophenone. The results presented herein show the different coordination properties of two structurally homologous tripodal ligands and demonstrate the importance of geometrically controlled ligand field splitting on the stability and reactivity of metal complexes. The C/Si exchange therefore provides a simple and straightforward tool to manipulate properties and reactivity of metal complexes.

Indolylindolinone: Easily Accessible, Tunable, and Wide-range Absorbing Dyes

Abstract Dehydrative coupling between indoles and isatins provided indolylindolinones in good yields as novel dyes with wide-range absorption due to intramolecular charge-transfer interactions. The HOMO and LUMO levels of indolylindolinones could be manipulated individually by the introduction of substituents on the indole and isatin units, respectively. Indolylindolinones served as a bidentate ligand to Ni(II) and Cu(II) ions to provide stable metal complexes. Metal coordination induced large bathochromic shift of the lowest-energy absorption band to the near-infrared region.

Calorimetric studies of ternary complexes of Ni(II) and Cu(II) nitrilotriacetic acid and N-acetyloligohistidines

The thermodynamics of Cu2+- and Ni2+-NTA binding to polypeptides containing 2–6 histidine residues in neutral buffered aqueous solutions were characterized by isothermal titration calorimetry (ITC). The apparent dissociation constants of ternary complexes of N-acetylhexahistidine-Ni2+-NTA and N-acetylhexahistidine-Cu2+-NTA were 69.5μM and 27.1μM, respectively. Decreased number of histidine residues in the oligohistidine fragment caused gradual decrease in the stability of the mixed metal complexes and a change in the binding stoichiometry from ∼1:1 for N-acetylhexahistidine and N-acetylpentahistidine to ∼0.5:1 for N-acetyltetrahistidine and ∼0.3:1 for N-acetyltrihistidine, N-acetyldihistidine and N-acetylhistidine ligands. In all cases, the binding interactions are shown to be enthalpically favored. Other metal cations formed less stable mixed metal complexes with stability constants in the order of Cu2+>Ni2+>Mg2+, Co2+, Zn2+>>Mn2+, Ca2+. The significance of the data is discussed in terms of important practical applications.

Luminescent Eu3+-doped NaLa(WO4)(MoO4) and Ba2CaMoO6 prepared by the modified Pechini method

Modified Pechini synthesis routes were developed for synthesis of the novel red phosphor materials NaLa(WO4)(MoO4):Eu3+ and Ba2CaMoO6:Eu3+. Phase pure NaLa(WO4)(MoO4):Eu3+ was obtained at calcination temperatures ≥600 °C using malic acid or tartaric acid as complexing agents. Phase pure Ba2CaMoO6:Eu3+ was attained using EDTA and citric acid, at calcination temperatures ≥800 °C. Choice of complexing agents were discussed on the basis of the solubility of the precursors, metal complex stability constants and conformations of the complexes. The powder properties were characterised using X-ray diffraction, thermal analysis and electron microscopy. Photoluminescence emission intensity was studied as a function of the complexing agents used and calcination temperature of the powders. Maximum emission intensity for NaLa(WO4)(MoO4):Eu3+ was obtained at a calcination temperature of 600 °C, whereas the maximum for Ba2CaMoO6:Eu3+ was obtained after calcination at 1100 °C. Both materials displayed desirable optical properties for use as phosphors in white light-emitting diodes. Phase pure NaLa(WO4)(MoO4):Eu3+ and Ba2CaMoO6:Eu3+ red phosphor materials were synthesised by the modified Pechini route, thus permitting lower calcination temperatures which resulted in increased emission intensity for NaLa(WO4)(MoO4):Eu3+.

The thermodynamics and biodegradability of chelating agents upon metal extraction

Chelation technology, one of emerging green approaches, has shown its potential to extract metals from industrial waste; however, the stability of metal–chelate complexes and the biodegradability of chelating agents are opposing aspects which need to be balanced carefully in order to develop a sustainable metal extraction process. In present study, stability of transition metal (Ni2+, Co2+, Rh3+, Mo6+) complexes with different aminopolycarboxylic chelating ligands (EDTA, EDDS, NTA) was investigated using density functional theory (DFT) calculations and the results were compared to previous experimental studies (Chauhan et al., 2012, 2013b; Cruywagen et al., 1994; Smith and Sawyer, 1968a;Marcus, 1985). Desolvation and complexation processes were examined to rationalize the thermodynamics of ligand substitution reactions using generalized gradient approximations (GGA) and hybrid DFT methods. A combination of explicit metal–water complexation and implicit solvation treatment was used to calculate the free energies of desolvation and chelation. Standard state corrections were also included for solvation free energies to enable a direct comparison with literature values. Thermodynamic analysis was performed in order to estimate the metal–ligand binding free energies at room and elevated process temperatures. Existence of different Rh3+ species in solution and in complexes was also explored and the most stable complex was identified. Differences in the coordination chemistry associated with Mo6+ were observed which motivated to perform free energy calculations upon MoO3 as a central coordination unit for different metal-to-ligand complexes (1:1, 2:1) in order to characterize the thermodynamically most stable complex at optimum reaction pH. In general, the metal–chelate ligand complexes followed the stability trend i.e. (EDTA)>(EDDS)>(NTA). The high stability of EDTA4− ligand with a favorable minimal strain can be the reason for its inherent resistance to degradation; it is therefore reckoned to consider the environmental impact of chelate assisted metal extraction processes by assessing ligand degradation pathways also. Possible pathways for the biodegradability of the chelating agents were investigated by calculating the bond dissociation energies of the ligands.

Potentiometric and spectroscopic study of the interaction of 3d transition metal ions with inositol hexakisphosphate

Among myo-inositol phosphates, the most abundant in nature is the myo-inositol hexakisphosphate, InsP6. Although it is known to be vital to cell functioning, the biochemical research into its metabolism needs chemical and structural analysis of all the protonation, complexation and precipitation processes that it undergoes in the biological media. In view of its high negative charge at physiological level, our group has been leading a thorough research into the InsP6 chemical and structural behavior in the presence of the alkali and alkaline earth metal ions essential for life. The aim of this article is to extend these studies, dealing with the chemical and structural features of the InsP6 interaction with biologically relevant 3d transition metal ions (Fe(II), Fe(III), Mn(II), Co(II), Ni(II), Cu(II) and Zn(II)), in a non-interacting medium and under simulated physiological conditions. The metal-complex stability constants were determined by potentiometry, showing under ligand-excess conditions the formation of mononuclear species in different protonation states. Under metal ion excess, polymetallic species were detected for Fe(II), Fe(III), Zn(II) and Cu(II). Additionally, the 31P NMR and UV–vis spectroscopic studies provided interesting structural aspects of the strong metal ion-InsP6 interaction.

Mechanical stability of bivalent transition metal complexes analyzed by single-molecule force spectroscopy.

Multivalent biomolecular interactions allow for a balanced interplay of mechanical stability and malleability, and nature makes widely use of it. For instance, systems of similar thermal stability may have very different rupture forces. Thus it is of paramount interest to study and understand the mechanical properties of multivalent systems through well-characterized model systems. We analyzed the rupture behavior of three different bivalent pyridine coordination complexes with Cu2+ in aqueous environment by single-molecule force spectroscopy. Those complexes share the same supramolecular interaction leading to similar thermal off-rates in the range of 0.09 and 0.36 s−1, compared to 1.7 s−1 for the monovalent complex. On the other hand, the backbones exhibit different flexibility, and we determined a broad range of rupture lengths between 0.3 and 1.1 nm, with higher most-probable rupture forces for the stiffer backbones. Interestingly, the medium-flexible connection has the highest rupture forces, whereas the ligands with highest and lowest rigidity seem to be prone to consecutive bond rupture. The presented approach allows separating bond and backbone effects in multivalent model systems.

H2CHXdedpa and H4CHXoctapa-chiral acyclic chelating ligands for (67/68)Ga and (111)In radiopharmaceuticals.

The chiral acyclic ligands H2CHXdedpa (N4O2), H2CHXdedpa-bb (N4O2), and H4CHXoctapa (N4O4) (CHX = cyclohexyl/cyclohexane, H2dedpa = 1,2-[[6-carboxy-pyridin-2-yl]-methylamino]ethane, bb = N,N'-dibenzylated, H4octapa = N,N'-bis(6-carboxy-2-pyridylmethyl)-ethylenediamine-N,N'-diacetic acid) were synthesized, complexed with Ga(III) and/or In(III), and evaluated for their potential as chelating agents in radiopharmaceutical applications. The ligands were compared to the previously studied hexadentate H2dedpa and octadentate H4octapa ligands to determine the effect adding a chiral 1R,2R-trans-cyclohexane to replace the ethylenediamine backbone would have on metal complex stability and radiolabeling kinetics. It was found that [Ga(CHXdedpa)](+) showed very similar properties to those of [Ga(dedpa)](+), with only one isomer in solution observed by NMR spectroscopy, and minimal structural changes in the solid-state X-ray structure. Like [Ga(dedpa)](+), [Ga(CHXdedpa)](+) exhibited exceptionally high thermodynamic stability constants (log KML = 28.11(8)), and the chelate retained the ability to label (67)Ga quantitatively in 10 min at room temperature at ligand concentrations of 1 × 10(-5) M. In vitro kinetic inertness assays demonstrated the [(67)Ga(CHXdedpa)](+) complex to be more stable than [(67)Ga(dedpa)](+) in a human serum competition, with 90.5% and 77.8% of (67)Ga remaining chelate-bound after 2 h, respectively. Preliminary coordination studies of H4CHXoctapa with In(III) demonstrated [In(CHXoctapa)](-) to have an equivalently high thermodynamically stable constant as [In(octapa)](-), with log KML values of 27.16(9) and 26.76(14), respectively. The [(111)In(CHXoctapa)](-) complex showed exceptionally high in vitro kinetic inertness over 120 h in human serum, comparing well with previously reported [(111)In(octapa)](-) values, and an improved stability compared to the current industry "gold standards" 1,4,7,10-tetraazacyclododecane-1,4,7,10-tetraacetic acid (DOTA) and diethylenetriaminepentaacetic acid (DTPA). Initial investigations reveal that the chiral acyclic hexadentate H2CHXdedpa and octadentate H4CHXoctapa ligands are ideal candidates for radiopharmaceutical elaboration of gallium or indium isotopes, respectively.

Studies of Binary Complexes of Metal Ions with 2, 2-Bipyridyl by Potentiometry

In biological systems transition metal ions exists in the form of different metal ligand complexes therefore investigations on the stability of metal complexes in relation with various structural features are important. Such type of study will help for understanding the driving forces leading to the formation of such complexes in the biological systems. Here we have reported systematic potentiometric studies on the formation of metal ligand complexes of transition metal ions with 2, 2- bipyridyl ligand in aqueous solution at 27 0 C temperature in the presence of electrolyte 1N NaNO3. The protonation constant and metal ligand stability constants were determined using Irving Rossotti titration technique. Data obtained from titrations were analysed by SCOGS computer programs. The protonation constant values obtained by half integral method and point wise method are in agreement.

Synthesis, structural studies, kinetic stability, and oxidation catalysis of the late first row transition metal complexes of 4,10-dimethyl-1,4,7,10-tetraazabicyclo[6.5.2]pentadecane.

Synthetic details for 4,11-dimethyl-1,4,8,11-tetraazabicyclo[6.5.2]pentadecane, the dimethyl ethylene cross-bridged homocyclen ligand are presented for the first time. Its novel Mn(2+), Fe(2+), Mn(3+), and Fe(3+) complexes have been synthesized and characterized. X-ray crystal structures were obtained for both manganese complexes, along with five additional Co(3+), Cu(2+), and Zn(2+) structures, the first structural characterization of complexes of this ligand. Each complex has the cis-V configuration of the cross-bridged macrocycle ring, leaving cis labile binding sites for interaction of the complex with oxidants and/or substrates. The copper(II) complex kinetic stability in 5 M HCl and at elevated temperatures was determined and compared to related complexes in the literature. The electronic properties of the manganese and iron complexes were evaluated using solid state magnetic moment determination and acetonitrile solution electronic spectroscopy, revealing high spin metal complexes in all cases. Cyclic voltammetry in acetonitrile of the divalent iron and manganese complexes revealed reversible redox processes, suggesting catalytic reactivity involving electron transfer processes are possible for both complexes. Screening of the Mn(2+) and Fe(2+) complexes for oxidation catalysis using hydrogen peroxide as the terminal oxidant showed both complexes are worthy of continued development.

Versatile O- and S-functionalized 1,2,3-triazoliums: ionic liquids for the Baylis–Hillman reaction and ligand precursors for stable MIC-transition metal complexes

A series of O- and S-functionalized triazolium salts display high performance in the Baylis–Hillman addition and allow the one-pot formation of MIC-transition metal complexes.

Controls on the stratigraphic distribution and nitrogen isotopic composition of zinc, vanadyl and free base porphyrins through Oceanic Anoxic Event 2 at Demerara Rise

The Cenomanian–Turonian black shales of the Demerara Rise (DR) contain a wide range of tetrapyrroles and allow porphyrin analysis through Oceanic Anoxic Event 2 (OAE 2), making this site unique. The sediments provide an excellent opportunity to study the factors controlling the stratigraphic distribution and N isotopic composition of porphyrins. Three C33 bicycloalkanoporphryins (BiCAPs) are present as free bases (FBs) and as complexes with Zn and VO in quantities sufficient for compound-specific isotope analysis (CSIA) and were the focus of this study. The stratigraphic distribution of BiCAPs is controlled, foremost, by metal availability rather than sedimentary Eh/pH conditions or post depositional maturity. Titration of the local water column metal reservoir with sulfide and organic matter during OAE 2 resulted in a high concentration of FB BiCAPs and a very low concentration of metallo-BiCAPs. Conversely, high metal concentration occurs in sediments above and below the OAE, and Zn and VO porphyrin abundances mirror bulk metal concentration. The highest total concentration of porphyrins was where metal concentration was highest, suggesting that porphyrin preservation is enhanced by the increased stability of metal complexes. Unexpectedly, the total concentration of porphyrins was lowest during the heart of OAE 2, in an interval of higher total organic carbon (TOC) content, where enhanced preservation would be expected; we suggest this was the result of decreased preservation of extractable tetrapyrroles in the absence of available metals. The high reactivity of Zn2+ with sulfide limited the formation of Zn complexes to the non-sulfidic regions in the water column or at the sediment/water interface. The formation of VO porphyrins occurred exclusively within the sediments from available FBs or through transmetallation with other metallo-BiCAPS (Zn, Ni, Cu).The formation of the metal complexes had a N isotope effect. We observed significant differences in the δ15N values of the three most abundant BiCAPs. VO BiCAPs were systematically 15N-depleted by an average of 2.5±1.5‰ relative to FBs, and Zn BiCAPs were equivalent to FB BiCAPs within error (15N enriched by+0.1‰) but were variable (±1.5‰). The δ13C values of the Zn, VO and FB BiCAPs were equivalent, suggesting that the three compounds share a common chlorophyll source, in agreement with structural data. The significant difference in δ15N values between the VO and FB BiCAPs suggests that δ15N values of VO porphyrins are controlled by N isotopic effects during VO porphyrin formation. Under experimental conditions, the formation of Zn octaethylporphyrin had a fractionation (εproduct/reactant −3.9) consistent with the differences between FB and VO BiCAPs, supporting a diagenetic origin for the differences in δ15N. The δ15N values of the porphyrins in these ancient sediments have been used to reconstruct the δ15N value of the primary phototrophic biomass and the ecological balance of chlorophyll a producing organisms via the εpor proxy. If the δ15N values of porphyrins are indeed altered by metal–ligand reactions, the application for paleoenvironmental reconstruction may require a more complete analysis of the range of metalloporphyrins in a given structural class. The covariance of bulk, BiCAP, porphyrin class and kerogen δ15N through OAE 2 suggests that the variability in δ15N reflects primary N cycle dynamics and that the εpor proxy can be viable in ancient sediments despite these complexities.

Small bifunctional chelators that do not disaggregate amyloid β fibrils exhibit reduced cellular toxicity.

Multifunctional metal chelators that can modulate the amyloid β (Aβ) peptide aggregation and its interaction with metal ions such as copper and zinc hold considerable promise as therapeutic agents for Alzheimer’s disease (AD). However, specific rather than systemic metal chelation by these compounds is needed in order to limit any side effects. Reported herein are two novel small bifunctional chelators, 2-[2-hydroxy-4-(diethylamino)phenyl]benzothiazole (L1) and 2-(2-hydroxy-3-methoxyphenyl)benzothiazole (L2), in which the metal-binding donor atoms are integrated within a molecular framework derived from the amyloid-binding fluorescent dye thioflavin T (ThT). The metal-binding properties of L1 and L2 were probed by pH spectrophotometric titrations to determine their pKa values and the corresponding metal complex stability constants, and the isolated metal complexes were structurally characterized. The amyloid-fibril-binding properties of L1 and L2 were investigated by fluorescence titrations and ThT competition assays. Interestingly, L1 and L2 do not lead to the formation of neurotoxic Aβ42 oligomers in the presence or absence of metal ions, as observed by native gel electrophoresis, Western blotting, and transmission electron microscopy. In addition, L1 and L2 were able to reduce the cell toxicity of preformed Aβ42 oligomers and of the copper-stabilized Aβ42 oligomers. Given their ability to reduce the toxicity of soluble Aβ42 and Cu-Aβ42 species, L1 and L2 are promising lead compounds for the development of chemical agents that can control the neurotoxicity of soluble Aβ42 species in AD.

A novel thiolated human-like collage zinc complex as a promising zinc supplement: Physicochemical characteristics and biocompatibility

To improve zinc binding ability to human-like collagen (HLC) and stability of metal complex, HLC was thiolated by mercaptosuccinylation reaction with S-acetylmercaptosuccinic anhydride (S-AMSA) at pH8.0. One mole of thiolated HLC–Zn (SHLC–Zn) complex possessed 24.3mol zinc ions when pH was 8.0 and zinc concentration was 15mM. The physicochemical properties and biocompatibility of thiolated HLC–Zn (SHLC–Zn) complex were investigated by UV–vis, CD, electrophoresis analysis, differential scanning calorimetry (DSC) and cell viability assay, respectively. The results showed that SHLC–Zn complex(1) exhibited higher zinc ions than that of native HLC and still maintained the secondary structure of HLC though interaction occurred between SHLC and zinc ions, (2) increased the apparent molecular weight when compared with native HLC, (3) exhibited greater thermal stability than native HLC, and (4) presented toxicity free for BHK cells. This study suggests that the SHLC–Zn complex is a potential nutrition as well as zinc supplement in the medical application.

Structural, DFT and biological studies on Co(II) complexes of semi and thiosemicarbazide ligands derived from diketo hydrazide

Three ligands have been prepared by addition ethanolic suspension of 2-hydrazino-2-oxo-N-phenyl-acetamide to phenyl isocyanate (H2PAPS), phenyl isothiocyanate (H2PAPT) and benzoyl isothiocyanate (H2PABT). The Co(II) chloride complexes were prepared and characterized by conventional techniques. The isolated complexes were assigned the formulaes, [Co(HPAPS)Cl(H2O)2]H2O, [Co(HPAPT)Cl]H2O and [Co(H2PABT)Cl2], respectively. The IR spectra of complexes shows that H2PAPS behaves as a mononegative tridentate via CO of hydrazide moiety and enolized CO of hydrazide moiety and CN (azomethine) group due to enolization of CO isocyanate moiety. H2PAPT behaves as mononegative tridentate via one CO of hydrazide moiety and thiol CS and NH groups and finally H2PABT behaves as neutral tetradentate via one CO of hydrazide moiety, CO of benzoyl moiety, CS due to enolization of the second CO of hydrazide moiety and new CN (azomethine) groups. The vibrational frequencies of the IR spectra of ligands which were determined experimentally are compared with those obtained theoretically from DFT calculations. Also, the bond lengths, bond angles, HOMO, LUMO and dipole moments have been calculated. The calculated HOMO–LUMO energy gap reveals that charge transfer occurs within the ligand molecules. The calculated values of binding energies indicates the stability of metal complexes is higher that of ligand. Also, the kinetic and thermodynamic parameters for the different thermal degradation steps of the complexes were determined by Coats–Redfern and Horowitz–Metzger methods. The antibacterial activities were also tested against Bacillus subtilis and Escherichia coli bacteria. The free ligands showed a higher antibacterial effect than their Co(II) complexes except [Co(HPAPS)Cl(H2O)2]H2O which shows higher activity than corresponding ligand. The antitumor activities of the Ligands and their Co(II) complexes have been evaluated against liver (HePG2) and breast (MCF-7) cancer cells. All ligands were found to display cytotoxicity that are better than that of Fluorouracil (5-FU), while Co(II) complexes show low activity except [Co(HPAPS)Cl(H2O)2]H2O which showed higher activity than corresponding ligand.

Synthesis, Characterization and Antimicrobial Activities of Some Nicotinamide – metal Complexes

Some transition metal complexes of nicotinamide have been prepared and characterized using melting point, conductivity measurement, infrared, electronic, HNMR and atomic absorption spectroscopic methods. . The antibacterial and antifungal studies of the metal complexes and the ligand have been evaluated against Escherichia coli , Staphylococcus and Bacillus subtilis , Aspergillus flavus, Aspergillus niger and penicillum species. It was found that nicotinamide formed stable metal complexes with these metal ions. The analysis of the spectroscopic data shows that nicotinamide act as monodentate, coordinating through the nitrogen atom of the pyridine ring. All the complexes exhibit 4- coordinate geometry. The results of the antimicrobial studies showed that the metal complexes have higher inhibitory activity than the original nicotinamide against the tested bacteria and fungi species. Keywords : Synthesis, Metal complexes, Nicotinamide, Antibacterial, Antifungal

Synthesis, spectroscopy and X-ray crystal structures of some zinc(II) and cadmium(II) complexes of the 2-pyridinecarboxaldehyde Schiff bases of S-methyl- and S-benzyldithiocarbazates

The Schiff bases formed by condensation of S-methyl- and S-benzyldithiocarbazate with 2-pyridinecarboxaldehyde react with zinc(II) and cadmium(II) acetates to form stable metal complexes of general formulas, [Zn(NNS)(CH3COO)]2 and [M(NNS)2] (M=Zn2+, Cd2+; NNS−=anionic forms of the 2-pyridinecarboxaldenhdye Schiff bases of S-methyl- and S-benzyldithiocarbazate, respectively) which have been characterized by a variety of physico-chemical techniques and X-ray crystallographic structure analysis. The complexes, [Zn(NNS)(CH3COO)]2 are acetate anion-bridged centrosymmetric dimers in which each of the Schiff bases is coordinated to the zinc(II) ions as a uninegatively charged NNS tridentate chelating agent coordinating via the pyridine nitrogen atom, the azomethine nitrogen atom and the thiolate sulfur atom. The acetate anion acts as a bridging bidentate ligand coordinating with the two zinc atoms in a syn–syn manner. Each zinc(II) ion in the dimer adopts an approximately square-pyramidal geometry. The bis-ligand complexes, [M(NNS)2] (M=Zn2+, Cd2+) have distorted octahedral structures in which the two anionic Schiff bases are coordinated to the metal ions meridionally as NNS tridentate chelating agents via the pyridine nitrogen atom, the azomethine nitrogen atom and the thiolate sulfur atom.Both the mono- and bis-ligand zinc(II) complexes exhibit strong cytotoxic activity against the HELA (human cervical cancer) cell lines. Some of these compounds exhibit stronger cytotoxicity against HELA than the commercially important anticancer drug, Tamoxifen.

Stability and Antimicrobial Activity of Transition Metal (II) Complexes with SNO and ONO Functionalized Ligand: A Computational Study

In this work, the structural, surface potential, and antimicrobial aspects of a set of recently synthesized and published complexes offivetransition metals(II) are investigated using the semiempirical PM6 and B3LYP/6-31G* methods. The complexes ML 2[M = Ni, Cu, and Zn] are mainly composed of 2-thiophenecarbaldehyde isonicotinoylhydrazone containing a trifunctional SNO-donor system.Experimentally,the complexes were synthesized and characterized using their conductivity, IR, and partially using