Stability Of Metal Complexes Research Articles

Zn2+’s Ability to Alter the Distribution of Cu2+ among the Available Binding Sites of Aβ(1–16)-Polyethylenglycol-ylated Peptide: Implications in Alzheimer’s Disease

The formation of mixed copper(II) and zinc(II) complexes with Aβ(1-16)-PEG has been investigated. The peptide fragment forms stable mixed metal complexes at physiological pH in which the His13/His14 dyad is the zinc(II)'s preferred binding site, while copper(II) coordination occurs at the N-terminus also involving the His6 imidazole. Copper(II) is prevented by zinc(II) excess from the binding to the two His residues, His13 and His14. As the latter binding mode has been recently invoked to explain the redox activity of the copper-Aβ complex, the formation of ternary metal complexes may justify the recently proposed protective role of zinc(II) in Alzheimer's disease. Therefore, the reported results suggest that zinc(II) competes with copper for Aβ binding and inhibits copper-mediated Aβ redox chemistry.

Synthesis, characterisation, thermal stability and antimicrobial activities of transition metal complexes of plumbagin and its azo derivatives

Synthesis, characterisation, thermal stability and antimicrobial activities of transition metal complexes of plumbagin and its azo derivatives

Research on Some Aromatic Schiff Base Compounds and Metal Complexes with Different Substituted Groups

Two aromatic Schiff base derivatives and the corresponding metal complexes with different substituted groups were synthesized and characterized by many methods. The products were characterized by UV-Vis spectra, FT-IR spectra and thermal analysis, while the thermal stability was measured by TG-DTA instrument. FT-IR analysis indicated that the nitrogen atom in imino group and oxygen atom in phenolic hydroxyl group participated in coordinating with transition metal ion in different bridged mode. UV spectra also verified that different coordination modes can be performed between metal ions and ligands. In addition, the thermal stability of metal complexes had been obviously superior to that of the ligands. All results give a useful clue to obtain Schiff base derivatives with versatile property by regulating intramolecular substituted group and species of metal ion. The present results have showed potential application in fields of functional material and catalyst.

From Conventional to Unusual Enzyme Inhibitor Scaffolds: The Quest for Target Specificity

The tremendous challenge presented by the specific molecular recognition of single biomacromolecular targets within complex biological systems demands novel and creative design strategies. This Minireview discusses some conventional and unusual approaches for the design of target-selective enzyme inhibitors with a focus on the underlying chemical scaffolds. These include complicated natural-product-like organic molecules, stable octahedral metal complexes, fullerenes, carboranes, polymetallic clusters, and even polymers. Thus the whole repertoire of organic, inorganic, and macromolecular chemistry can be applied to tackle the problem of target-specific enzyme inhibition.

Stability of transition metal complexes involving three isomeric quinolyl hydrazones

The stability constants of three isomeric quinolyl hydrazones; {4,6-(para); 4,7-(meta) and 4,8-MeBHQ(ortho)} towards some bivalent metal ions have been determined in 75% solvent (dioxane, isopropanol, ethanol and methanol)–water by a pH-titrimetry. The insertion of the Me-group in the 8-position decreases the stability of the complexes to a great extent. The complexation of the ortho-derivative is endothermic, whereas that of the para-derivative is exothermic. Using the solvent parameters, the stability constants of the para-derivative towards Co(II), Ni(II) and Cu(II) ions were evaluated in aqueous medium by five different methods. Also, the electronic absorption spectra of the ortho-hydrazone have been studied in solvents of various polarities to investigate the dependence of the band shift (Δ ύ) on the solvent parameters viz. 1/ D, Z, E T, DN, AN and (α, β, π*). The interaction of the hydrazones with CoCl 2·6H 2O afforded an octahedral complex in case of the ortho-hydrazone and square planar complexes in case of the meta- and para-hydrazones.

Synthesis of a chloro protected iridium nitrido complex

Intramolecular activation processes of vulnerable ligand C-H bonds frequently limit the thermal stability and accessibility of late transition metal complexes with terminal metal nitrido units. In this study chloro substitution of the 2,6-ketimine N-aryl substituents (2,6-C(6)H(3)R(2), R = Cl) of the pyridine, diimine ligand is probed to increase the stability of square-planar iridium nitrido compounds. The thermal stability of iridium azido precursor and nitrido compounds was studied by a combination of thermoanalytical methods (DTG/MS and DSC) and were compared to the results for the related complexes with 2,6-dialkyl substituted N-aryl groups (R = Me, iPr). The investigations were complemented by DFT calculations, which allowed us to unravel details of the thermal decomposition pathways and provided mechanistic insights of further conversion steps and fluctional processes. The DTG/MS and DSC measurements revealed two different types of thermolysis pathways for the azido compounds. For the complexes with R = Cl and iPr substituents, two well-separated exothermic processes were observed. The first moderately exothermic loss of N(2) is followed by a second, strongly exothermic transformation. This contrasts the experimental results for the compound with 2,6-dimethyl substituents (R = Me), where both steps proceed concurrently in the same temperature range. The separation of the two thermal steps in the 2,6-dichloro substituted derivative allowed us to develop a protocol for the isolation of the highly insoluble nitrido complex, which was characterized by UV/vis, IR-spectroscopy and elemental analysis. Its constitution was further confirmed by reaction with silanes, which gave the corresponding silyl amido complexes.

Transition metal complexes bearing a 2,2-bis(3,5-dimethylpyrazol-1-yl)propionate ligand: one methyl more matters

The new N,N,O ligand 2,2-bis(3,5-dimethylpyrazol-1-yl)propionic acid (2,2-Hbdmpzp) (2) and its transition metal complexes [Mn(2,2-bdmpzp)(CO)(3)] (3), [Re(2,2-bdmpzp)(CO)(3)] (4), [Cu(2,2-bdmpzp)(2)] (5), and [Ru(2,2-bdmpzp)Cl(L)(PPh(3))] [L = PPh(3) (6), N(2) (7), CO (8a/b), SO(2) (9a/b)] have been synthesized, characterized and compared to analogous complexes bearing a bis(3,5-dimethylpyrazol-1-yl)acetic acid. It was found that the additional methyl group has a remarkable influence on the stability and reactivity of transition metal complexes.

The relative stability of macrotricyclic metal complexes in M(II)-thiocarbohydrazide-acetone (M = Mn, Fe, Co, Ni, Cu, Zn) ternary systems according to the data of quantum-chemical calculations

The B3LYP hybrid method of density functional theory with the 6–31G(d) basis set was used to calculate the optimum geometry and standard thermodynamic parameters of Mn(II), Fe(II), Co(II), Ni(II), Cu(II), and Zn(II) macrotricyclic complexes with MN2S2 and MN4 chelate nodes. The calculations were performed using the Gaussian 98 package. Such complexes could in principle appear because of temperature processes between gelatin-immobilized hexacyanoferrates(II) of the corresponding M(II) metal ions, thiocarbohydrazide, and acetone. For all the M(II) metals considered, complexes with MN2S2 chelate nodes were stablest. The standard Gibbs energies Δf G 298 ° values were positive for all the complexes specified.

ChemInform Abstract: Carbodiphosphoranes and Related Ligands

AbstractReview: 149 refs.

Coordination Properties of Ionic Liquid-Mediated Chromium(II) and Copper(II) Chlorides and Their Complexes with Glucose

The structural and coordination properties of complexes formed upon the interaction of copper(II) and chromium(II) chlorides with dialkylimidazolium chloride (RMIm(+)Cl(-)) ionic liquids and glucose are studied by a combination of density functional theory (DFT) calculations and X-ray absorption spectroscopy (XAS). In the absence of the carbohydrate substrate, isolated mononuclear four-coordinated MeCl(4)(2-) species (Me = Cu, Cr) dominate in the ionic liquid solution. The organic part of the ionic liquid does not directly interact with the metal centers. The interactions between the RMIm(+) cations and the anionic metal chloride complexes are limited to hydrogen bonding with the basic Cl(-) ligands and the overall electrostatic stabilization of the anionic metal complexes. Exchange of Cl(-) ligands by a hydroxyl group of glucose is only favorable for CrCl(4)(2-). For Cu(2+) complexes, the formation of hydrogen bonded complexes between CuCl(4)(2-) and glucose is preferred. No preference for the coordination of metal chloride species to specific hydroxyl group of the carbohydrate is found. The formation of binuclear metal chloride complexes is also considered. The reactivity and selectivity patterns of the Lewis acid catalyzed reactions of glucose are discussed in the framework of the obtained results.

Dramatic enhancement of the stability of rare-earth metal complexes with α-methyl substituted N, N-dimethylbenzylamine ligands

Stepwise substitution of benzylic CH 2 protons in ortho-metallated N, N- di methyl benzyl amine (dmba) ligands leads to chiral ortho-metallated N, N,α- tri methyl benzyl amine (tmba) and cumyl- N, N- dimethyl amine (cuda) ligands. These larger ligands with less or no acidic protons in benzylic position prove to stabilize some of those homoleptic tris-aryls of the larger (middle) and largest (early) rare-earth metal cations, for which such tris-aryl or tris-dmba complexes could not be synthesized so far. The syntheses, characterization and crystal structures of [Li(cuda)], [(tmba) 2Lu(μ-Cl)] 2 ( 1), [(tmba) 2Y(μ-Cl)] 2 ( 2), [Y(tmba) 3] ( 3), [Dy(tmba) 3] ( 4), [Nd(tmba) 3] ( 5), [Sm(tmba) 3] ( 6), and [Sm(cuda) 3] ( 7) are reported, trends in complex stability are discussed.

ChemInform Abstract: Phosphine Complexes of the Early Metals and the Lanthanoids

The coordination chemistry of the mixed-donor tridentate ligand -N(SiMezCH2PR2)2 with the early transition metals of groups 3 and 4 and the lanthanide elements will be presented. This ancillary ligand has allowed for the formation of phosphine complexes of these hard elements which has in turn induced new reactivity patterns for hydrocarbyl ligands. The stability and reactivity of metal complexes are a function of both the position of the metal in the periodic table and the nature of the ligands. While the former provides for diverse chemical reactivity, it is

ChemInform Abstract: Synthesis of Stable Free Radicals: A Novel Family of Oligopyridine Based Nitronyl-Nitroxide Biradicals.

Abstract Diformyl substituted pyridines (at the 2,5 and 2,6 positions), 2,2′-bipyridines (at the 4,4′, 5,5′, and 6,6′ positions), 3,6-di-(6-carboxyaldehyde-2-pyridyl)-pyridazine and 2,9-dicarboxyaldehyde-1,10-phenanthroline react with N,N′-dihydroxy-2,3-diamino-2,3-dimethylbutane to yield the bis-N,N′-dihydroxyimidazolidine. Mild oxidation afforded the corresponding nitronyl-nitroxide biradicals 1 to 7. These ligands are highly colored and form very stable transition metal complexes.

A Triazacyclononane‐Based Bifunctional Phosphinate Ligand for the Preparation of Multimeric 68Ga Tracers for Positron Emission Tomography

For application in positron emission tomography (PET), PrP9, a N,N',N''-trisubstituted triazacyclononane with methyl(2-carboxyethyl)phosphinic acid pendant arms, was developed as (68)Ga(3+) complexing agent. The synthesis is short and inexpensive. Ga(III) and Fe(III) complexes of PrP9 were characterized by single-crystal X-ray diffraction. Stepwise protonation constants and thermodynamic stabilities of metal complexes were determined by potentiometry. The Ga(III) complex possesses a high thermodynamic stability (log K([GaL])=26.24) and a high degree of kinetic inertness. (68)Ga labeling of PrP9 is possible at ambient temperature and in a wide pH range, also at pH values as low as 1. This means that for the first time, the neat eluate of a TiO(2)-based (68)Ge/(68)Ga generator (typically consisting of 0.1 M HCl) can be directly used for labeling purposes. The rate of (68)Ga activity incorporation at pH 3.3 and 20 degrees C is higher than for the established chelators DOTA and NOTA. Tris-amides of PrP9 with amino acid esters were synthesized to act as models for multimeric peptide conjugates. These conjugates exhibit radiolabeling properties similar to those of unsubstituted PrP9.

Fabrication and characterisation of Fe3O4 nanowires via an ethylenediamine-assisted route

In this article, Fe3O4 nanowires were synthesised from iron chloride, using ethylenediamine (EN)–water mixed solvent as the medium. The as-prepared powders were characterised in detail by conventional techniques, such as X-ray powder diffraction, selected area electron diffraction, transmission electron microscope and field-emission scanning electron microscopy. An EN is a bidentate ligand and it can react with metal ions to form relatively stable metal complexes which plays important roles in the formation of the products in the process. And their magnetic properties were evaluated on a vibrating magnetometer. The sample exhibits a high first discharge capacity of 902 mAh/g, which enables it to be used for a lithium-ion battery.

Adsorption mechanisms of metal cations from water on an oxidized carbon surface

Adsorption of Cr(III), Mn(II), Cu(II) and Zn(II) on an oxidized activated carbon cloth was studied. Its surface chemistry was characterized by potentiometric titration. This technique revealed the amount of surface oxygen functionalities and their acidity constant distribution. The acidity constant range involved in the metal cation adsorption was obtained from this distribution. Metal cation adsorption increased with higher adsorption temperature due to the increase in the negative surface charge of the oxidized activated carbon. Adsorption was by proton exchange and the number, amount and strength of the surface acid groups involved could be obtained. The proton exchange was by an inner-sphere or outer-sphere surface metal complex formation mechanism. In the case of divalent cation adsorption, the increase in temperature changed the adsorption mechanism from outer-sphere to inner-sphere. However, the adsorption mechanism of Cr(III) was outer-sphere and independent of temperature. Adsorption capacity augmented with the increase in the charge-to-size ratio of the hexa-aquo cations. In addition, the adsorption capacity of divalent cations increased with the rise in stability of the surface metal complex formed.

Synthesis and structural characterization of a fused bispyrone and preparation of the first metal bispyrylium complexes

Dehydroacetic acid reacts with acetic anhydride in the presence of perchloric acid to give a salt which upon careful neutralization affords a fused bis-gamma-pyrone. The bis-gamma-pyrone forms stable metal complexes with Li, Mg, Cu(II), Ni(II), Zn, Fe(II), Co(II) and Ba perchlorates whose crystal structures reveal that the ligand possesses significant bispyrylium character while the metal is coordinated at the negatively charged edge of the structure.

Synthesis, Characterization and Hydrolysis of Osmium Tetraphosphorus Complexes

AbstractThe reaction of [CpOs(PPh3)2Cl] (1) with one equivalent of white phosphorus in the presence of AgOTf (OTf = triflate, OSO2CF3) as chloride scavenger affords the stable metal complex [CpOs(PPh3)2(η1‐P4)]OTf (2), which contains the tetrahedral P4 η1‐bound to the CpOs(PPh3)2 metal fragment. Addition of [CpRu(PPh3)2(OTf)] to 2 yields the heterobimetallic species [{CpRu(PPh3)2}{CpOs(PPh3)2}(μ,η1:1‐P4)](OTf)2 (3), in which the tetrahedral P4 is bound to two different metal fragments through two phosphorus atoms. The compounds have been characterized by elemental analysis, IR and NMR spectroscopy, and their crystal structures have been determined by X‐ray diffraction. The coordinated P4, at variance with the free ligand, reacts with an excess amount of water in thf under mild conditions to yield several products, most of which have been characterized.

Metal Complexation and Biodegradation of EDTA and S,S-EDDS: A Density Functional Theory Study

The complexation reactions of ethylenediaminetetraacetate (EDTA(4-)) and S,S-ethylenediaminedisuccinate (S,S-EDDS(4-)) with Co(2+), Ni(2+), Cu(2+), Zn(2+), and Cd(2+) cations are investigated by using the DFT/B3LYP method. The hydration reaction of each metal ion with solvent water cluster is considered with a mixed cluster/continuum model. The subsequent metal complexation is treated as a substitution reaction of the coordinated water molecules by the amino polycarboxylic acid ligand. Thermodynamic cycles are schemed to evaluate the free energy changes for both hydration and complexation processes. The values of complexation free energy changes show that the stabilities of metal complexes with the isomeric ligands follow the order of [M(S,S-EDDS)](2-) in trans(O(6))-conformer < [M(S,S-EDDS)](2-) in trans(O(5))-conformer < [M(EDTA)](2-), implying that the failure to observe the trans(O(6)) conformer under experimental conditions is attributed to its inherent instability. The same trend appears in our steric strain analysis on the various chelate rings in complexes. Because the [M(S,S-EDDS)](2-) in trans(O(6)) complex is not available, we focus on the other two series of complexes with concerned metal ions. The stabilities decrease in the order Cu(2+) > Ni(2+) > Co(2+) > Zn(2+) > Cd(2+) and Cu(2+) > Ni(2+) > Co(2+) > Cd(2+) > Zn(2+) for trans(O(5))-[M(S,S-EDDS)](2-) and [M(EDTA)](2-), respectively. These two tendencies are shown to be consistent with the decrease in the metal-to-ligand charge transfer. Meanwhile, a good quantitative correlation is found between the complexation free energies and the dipole moments for all complexes (excluding the case of Cu(2+)). The far-infrared spectra are present to investigate the characteristics of metal-dependent vibrations, and the further natural bond orbital (NBO) method is taken to show the nature of metal-ligand bonding interactions. Finally, and perhaps most importantly, degrading products of both amino polycarboxylic acids are successfully predicted through calculating the dissociation energies of all C-N bonds in free EDTA, S,S-EDDS, and their successive products. Degradation mechanisms with intramolecular hydrogen transfer are proposed for the biodegradation reactions of S,S-EDDS and its product N-(2-aminoethyl) aspartic acid (AEAA).

Analyzing several chelating agents and their effect on elemental composition of Lolium perenne and two growth media by capillary zone electrophoresis and inductively coupled plasma optical emission spectrometry

Capillary zone electrophoresis (CZE) along with ICP-OES was used for the determination of several chelating agents in clay and black soil, and in plants (Lolium perenne) grown in these matrices. Elemental levels in all the samples (Al, As, Ca, Cd, Cu, Fe, K, Mg, Mn, Pb, S and Zn) were investigated by inductively coupled plasma optical emission spectrometry (ICP-OES). Compared to previous methods, much shorter total analysis times were accomplished by the validation of an internal standard method for CZE analysis. The solubility of elements increased noticeably in the soils treated by the chelating agents before cultivation, and this phenomenon was strictly metal complex stability constant dependent. The most persistent chelating agents were triethylenetetraaminehexaacetic acid (TTHA) and 1,3-diaminopropanetetraacetic acid (PDTA). Both agents were bound to the growth medium and taken up by ryegrass, while only small proportions of them were degraded during cultivation. Diethylenetriaminepentaacetic acid (DTPA), ethylenediaminetetraacetic acid (EDTA) and nitrilotriamineacetic acid (NTA), mainly bound to the clay matrix during the 19 days cultivation, but after 40 days cultivation in black soil they were degraded to smaller acids. The results clearly show uptake of chelating agents by plants and are a clear indication of the degradation of chelating agents.