Complex Formation Of Metal Ions Research Articles

Kinetics and mechanism of metal extraction with acidic organophosphorus extractants (I): Extraction rate limited by diffusion process

The extraction mechanism of metal ion by acidic organophosphorus extractant was discussed by taking into account the physicochemical properties of extractant. Since the acidity of the extractant is higher than that of chelating agent, the rate of complex formation of metal ion with the extractants is rapid compared to that with the chelating agents. It is found that the rate determining step of the extraction such as Cu(II) and Co(II) by 2-ethylhexyl phosphonic acid mono-2-ethylhexyl ester is not the complex formation at the interface, but the diffusion of the metal complex in the organic stagnant film, which is instantaneously formed at the interface. This result was also confirmed by the stirring speed dependence of the initial extraction rate. Furthermore, the time course of Co(II) extraction from the initial stage to the equilibrium state was quantitatively interpreted by considering only the diffusion rates of reactants and products in both stagnant films.

The effect of metal ion complex formation on acidic depurination of 2′-deoxyadenosine and 2′-deoxyguanosine

The substitution inert N7-(dien)Pt(II) complex of 2′-deoxyguanosine has been shown to undergo acidic depurination200 times less readily than the uncomplexed nucleoside, whereas the corresponding N1- and N7-complexes of 2′-deoxyadenosine are depurinated almost as rapidly as the nucleoside itself. Theseobservations have been compared to the influences that severalsubstitution labile metal ions exerted on the rate of depurination. Accordingly, the effects of (dien)Pd(II), Co(II),Ni(II), Cu(II), Zn(II) and Cd(II) ions on the acidic hydrolysis of2′-deoxyadenosine and 2'-deoxyguanosine have been accounted for by competitive attachment of protons and metal ions to the N1 and N7 sites. The applicability of metal ions in chemical DNA sequencing is briefly discussed.

Equilibrium Study of the Complex Formation of some Bivalent Transition Metal Ions with Sulphur Oxygen Donor Ligands

Equilibrium Study of the Complex Formation of some Bivalent Transition Metal Ions with Sulphur Oxygen Donor Ligands

Equilibrium Study of the Complex Formation of some Bivalent Transition Metal Ions with Sulphur Oxygen Donor Ligands

Equilibrium Study of the Complex Formation of some Bivalent Transition Metal Ions with Sulphur Oxygen Donor Ligands

Complex formation with some Bidentate Ligands. Part-Ill. Solution Equilibria in the Complex Formation of Bivalent Metal Ions with Thiosemicarbazones of vic-Hydroxy aldehydes

Complex formation with some Bidentate Ligands. Part-Ill. Solution Equilibria in the Complex Formation of Bivalent Metal Ions with Thiosemicarbazones of vic-Hydroxy aldehydes

Complex Formation with some Bidentate Ligands. I. Solution Equilibria in the Complex Formation of Bivalent Metal Ions with some vic-Hydroxy Aldehydes

Complex Formation with some Bidentate Ligands. I. Solution Equilibria in the Complex Formation of Bivalent Metal Ions with some vic-Hydroxy Aldehydes

Acid-base and metal ion complex formation properties of polymers containing amino acid residues

Synthese d'une nouvelle famille de polyampholytes; nouvelle methode de calcul pour determiner leurs constantes de stabilite des complexes et leurs proprietes acide-base et de complexation

Binding of metal ions by polyethylenimine and its derivatives

AbstractMeasurements have been made of the binding of divalent metal ions, Cu2+, Ni2+, Co2+, and Zn2+ ions, by polyethylenimine (PEI) and its acetyl or alkyl derivatives by the equilibriumdialysis technique. These metal ions, in particular the Cu2+ ion, exhibited tremendously remarkable binding affinity toward PEI. The extent of complexation of the polymer with the metal ions was decreased markedly by acetylation or alkylation of the polymer. PEI with no primary amine showed an appreciable decrease in its affinity for the metal ion. These results indicate the participation of the primary amine of the polymer in the formation of the complex. A cooperative binding isotherm was observed in PEI–metal ion complex formation, suggesting swelling or conformational change of the polymer induced by this coordination process. Binding of the Cu2+ ion by PEI was found to be essentially independent of temperature over the range 5–35°C.

ChemInform Abstract: Rates and Equilibria of Alkali Metal and Silver Ion Complex Formation with Monensin in Ethanol.

AbstractDie Stabilitätskonstanten der Monensin‐Komplexe (M‐Mon) nehmen in Ethanol im Sinne M = Ag+ g Na+ K Rb Li+ g Cs+ von log K = 8.94 bis zu log K = 5.35 ab.

Rates and equilibria of alkali metal and silver ion complex formation with monensin in ethanol

Constantes de stabilite et vitesses de formation et de dissociation des complexes. Les constantes de vitesse de dissociation sont sensibles a la taille des cations

Thermodynamic aspects of solvophobic forces in simple and mixed complex formation of metal ions with biofunctional ligands

Solvophobic [1] or hydrophobic [2, 3] interactions are known to occur in biomolecules and to contribute to the formation of distinct structural conformations, which provide the specificity and the reversibility required in most biological processes [4]. These forces occur between two aliphatic or alicyclic groups, between two aromatic groups and between aliphatic and aromatic groups. As regards metal complexes of low molecular weight, the presence of this interaction has been invoked to explain i) the biological activity of some coordination compounds [5, 6]; ii) the stability enhancement of some ternary complexes [7]; and iii) other distinct in their reactivity [8] and their thermodynamic properties [9]. The appearance of this so-called ‘secondary’ bond has usually been inferred from potentiometric titrations, UV-difference spectra and NMR shift measurements. Recently, we have shown that the calorimetric technique is a very powerful tool to bring to light the solvophobic interactions in some ATP metal complexes [9]. In particular, the effect of these forces resulted in a more favourable enthalpic and in a less favourable entropic contribution for [M(ATP)(trp)] 3− with respect to [M(ATP)(ala)] 3− species. As for zinc(II) complexes, the difference was more pronounced in comparison with what was found for copper(II). The formation of [Zn(ATP)(trp)] 3− was about 10 Kcal mol −1 more exothermic and 30 e.u. lower with respect to [M(ATP)(ala)] 3−. Bearing in mind that in the latter complex stacking interaction is not possible, this difference has been assumed as an index of the presence of solvophobic interaction. Such a favourable trend in ΔH° values has been found for other mixed complexes of zinc(II) with ATP and some biofunctional ligands [10]. Furthermore, on the basis of the thermodynamic properties, the study of the mixed complexes of 2,2′-bipyridyl and mono- or di-alkyl substituted malonate ligands with copper(II) and zinc(II), has shown that the occurring of solvophobic forces is dependent on the geometrical coordination requirement of metal ions. Finally, the role of these interactions in the thermodynamic stereoselectivity of some dipeptide complexation has also been assessed. For example, the formation of [Cu(L,L-leu,leuH −1)] complex is more enthalpically and less entropically favoured with respect to [Cu(L,D-leu,leuH −1)] species. This behaviour is due to favourable orientation of side chains which gives rise to a solvophobic interaction in the ‘pure’ with respect to the ‘mixed’ derivative.

Multifunctional behavior as an aid in deducing metalloenzyme and model reaction mechanisms

The ability of a substance to participate in competing reactions presents difficulties but if the problems can be resolved a clearer picture of the behavior in all reaction modes may be forthcoming. Oxalacetate is involved in a number of different biological reactions which are catalyzed by metalloenzymes. Many of these reactions are amenable to independent investigation in model systems employing metal ions. Decarboxylation is one reaction mode of oxac 2− which has attracted interest for many years owing to strong resemblances between the rate dependencies of the enzymic and model systems on metal ion concentration. The Steinberger-Westheimer mechanism had early been accepted as the means by which metal ions catalyzed oxac 2− decarboxylation: ▪ Prevailing evidence indicates that the activation barrier is lowered by the complexation of the high energy enolate of pyruvate. Enolization and hydration reactions of oxac 2− procede within the same time frame and are closely entwined. Resolved rate data show that the reactions are subject to acid and base catalysis. Proton catalysis appears to be equally effective for both, but large differences are evident in base catalysis. Hydration rates are sensitive to possessing an oxygen donor atom. OH − is a very efficient catalyst and even H 2O catalyzed rates are appreciable. Tertiary amines are found to be weak catalysts. Enolization appears to be more susceptible to softer bases. The rate constant for the OH− catalyzed path is 1 6 as large as that determined for hydration, and H 2O catalysis is negligible; however, tertiary amines are potent catalysts and the more basic ones exceed OH − in activity. different sites are involved in catalysis. Enolization involves the removal of a CH 2 proton from oxac 2−, while in hydration the base attacks the keto carbon atom through an H 2O molecule, C(O)CH 2 + HOH··B ⇌ C(O −)(OH)CH 2 + BH +. In either case, an oxyanion is formed at the 2-carbon atom. Metal ion complex formation has a relatively small effect on the rate constant for acid catalyzed enolization, suggesting that there is little interaction between the metal ion and the site for proton attack, the keto group oxygen atom. In contrast, the rates along the base catalyzed pathways are strongly influenced by a metal ion and exhibit increases that appear more dependent on the nature of the catalyst than on the reaction mode. The presence of Mg(II) induces increases of three orders of magnitude in the rates of OH − catalyzed enolization and hydration, while the H 2O catalyzed pathway for hydration and the tertiary amine catalyzed pathways for both reactions undergo rate increases of 20–30 fold. A charge is apparent in these figures, but, especially in the case of OH −, the metal ion must interact with, and stabilize the intermediate oxyanions in ways similar to that by which decarboxylation is promoted. Rates of ketonization of enolpyruvate are also being investigated. Consistent with the charge differences acid catalysis is slower, and base catalysis is faster with enolpyruvate than with oxac 2−. Complexing metal ions show very strong cooperativity with base catalysts. Here again, the metal ion seems to function as stabilizer of the intermediate oxyanion. The coordinating abilities of metal ions are paramount in their causing activation barriers to be lowered in these model reactions. However, recent evidence obtained in a detailed study of enzymic decarboxylation suggest that an enzyme may not utilize this function of a metal ion, but may achieve greater catalytic efficacy through other mechanisms, such as proton transfer.

Thermodynamic and kinetic studies on complex formation of alkaline earth metal ions with diaza-crown ethers in methanol

Stability constants K s and rate constants of formation and dissociation of alkaline earth metal complexes with the diaza-crown ethers (2,2) and (2,2-Me 2) in methanol are reported, together with corresponding thermodynamic parameters. It od shown that it is possible to determine the dissociation rate constants k d of these crown ether complexes from stopped-flow experiments. The values of K s and k d for (2,2,) complexes are displaced parallel with respect to the corresponding values for (2,2-Me 2) complexes, and variations of K s with metal ion radius are reflected in similar (inverse) variations of k d. However, enthalpies and entropies of reaction and activation point to differences in the behaviour of the two ligands.

Complex formation of picloram and related chemicals with metal lons

The complex formation of metal ions with pyridine carboxylic acids was estimated with polarography and spectrophotometry. Picloram (4-amino-3,5,6-trichloropicolinic acid), α-picolinic acid, fusaric acid, dipicolinic acid, and quinolinic acid formed complexes with Fe(III) or Cu(II) whose coordination involves, most probably, a lone pair of electrons of pyridine nitrogen and a carboxylic group. Picloram-metal complexes were, however, estimated to be relatively unstable compared to other pyridine-α-carboxylic acids tested. Effects of pyridine carboxylic acids on oxidation of indole-3-acetic acid (IAA) were tested in vitro in a horseradish protoheme peroxidase system. No significant effect of the pyridine carboxylic acids was observed at 2 × 10 −4 M. Also, no concentration effect of picloram (10 −5 to 3 × 10 −3 M) was obtained. These results suggest that the phytotoxic action of picloram may not result from the depletion of free metal ions in plants nor inhibition of activity of metal-containing enzymes through strong chelation as hypothesized. Thus, auxin activity of picloram should be explained in other wasy.

Metal ion complex formation constants of some sedimentary humic acids with Zn(II), Cu(II) and Cd(II)

Metal ion complex formation constants were determined for several sedimentary humic acids (SHA) derived from a fresh water lake and several coastal marine environments, using a method based on size exclusion chromatography. Only one type of binding site was observed in all cases, and conditional log Kf values of between 5 and 7 (at pH 8, I = 0.01 M) were found. Elemental composition of the SHA was similar to soil HA, except that nitrogen content was significantly higher in the SHA. Other chemical properties of the SHA were consistent with those reported by other workers. While spectroscopic measurements indicated that the SHA may have contained significant amounts of polysaccharide compounds which were not removed by conventional separation and purification procedures, analysis indicated only very low levels of polysaccharides were present in the SHA.

The Influence of Small Monovalent Cations on Neighbouring Hydrogen Bonds of Aquo-Protein Complexes

Abstract The influence of small monovalent metal ions on hydrogen bonds of aquo-protein complexes is studied on Li+/HCONH2-OH2 as an example. Using results obtained from ab initio calculations with minimal GLO basis sets, the remarkable changes in the hydrogen bond energy and charge distribution, due to metal ion complex formation, are discussed. The metal ion seems to enhance strongly the donor-acceptor interaction of the O ... H-N-C=0 hydrogen-bonded system.

Experimental determination of the complexity sum in investigating metal ion complex formation

Experimental determination of the complexity sum in investigating metal ion complex formation

A spin-label assay for metal ion chelation and complex formation

The electron spin resonance (ESR) lines of nitroxide spin labels are broadened by electron spin exchange reactions that take place during collisions with paramagnetic ions. The degree of line broadening is greatly reduced when the paramagnetic ion forms a coordination bond with certain functional groups on organic molecules. These observations form the basis for a spin-label assay for metal ion chelation and complex formation. This paper describes the characteristics of such an assay for divalent nickel ions and the spin label TEMPONE (2,2,6,6-tetramethylpiperidone- N-oxyl). The chelation of Ni 2+ by cysteine and the interaction of Ni 2+ with sodium dodecyl sulfate micelles and phospholipid vesicles are demonstrated. In addition to monitoring interactions of paramagnetic ions, the assay also allows the detection of interactions of nonparamagnetic ions that compete with the paramagnetic ions for binding sites. A kinetic analysis of competition between Ni 2+ and Zn 2+ ions for binding sites on phospholipid vesicles is presented. There are several advantages of the spin-label line-broadening assay compared to other conventional assays for metal chelation and complex formation. The line-broadening assay does not require that the sample be optically clear or chemically defined, it requires only very small quantities of material, it can detect as little as 0.4 to 1 μmol of complexing agent, and it may be utilized in complex biological systems including subcellular organelles and macromolecules.

ChemInform Abstract: OPEN‐CHAIN POLYETHERS. INFLUENCE OF AROMATIC DONOR END GROUPS ON THERMODYNAMICS AND KINETICS OF ALKALI METAL ION COMPLEX FORMATION

Chemischer InformationsdienstVolume 10, Issue 34 Article ChemInform Abstract: OPEN-CHAIN POLYETHERS. INFLUENCE OF AROMATIC DONOR END GROUPS ON THERMODYNAMICS AND KINETICS OF ALKALI METAL ION COMPLEX FORMATION B. TUEMMLER, B. TUEMMLERSearch for more papers by this authorG. MAASS, G. MAASSSearch for more papers by this authorF. VOEGTLE, F. VOEGTLESearch for more papers by this authorH. SIEGER, H. SIEGERSearch for more papers by this authorU. HEIMANN, U. HEIMANNSearch for more papers by this authorE. WEBER, E. WEBERSearch for more papers by this author B. TUEMMLER, B. TUEMMLERSearch for more papers by this authorG. MAASS, G. MAASSSearch for more papers by this authorF. VOEGTLE, F. VOEGTLESearch for more papers by this authorH. SIEGER, H. SIEGERSearch for more papers by this authorU. HEIMANN, U. HEIMANNSearch for more papers by this authorE. WEBER, E. WEBERSearch for more papers by this author First published: August 21, 1979 https://doi.org/10.1002/chin.197934109Read the full textAboutPDF ToolsRequest permissionExport citationAdd to favoritesTrack citation ShareShare Give accessShare full text accessShare full-text accessPlease review our Terms and Conditions of Use and check box below to share full-text version of article.I have read and accept the Wiley Online Library Terms and Conditions of UseShareable LinkUse the link below to share a full-text version of this article with your friends and colleagues. Learn more.Copy URL Share a linkShare onFacebookTwitterLinked InRedditWechat No abstract is available for this article. Volume10, Issue34August 21, 1979 RelatedInformation

Study of Metal–Polycarboxylate Complexes Employing Ion-selective Electrodes. III. Complex Formation between Maleic Acid Copolymers and Bivalent Transition Metal Ions

Abstract The complex formation of bivalent transition metal ions, Mn(II), Co(II), Ni(II), Cu(II), and Zn(II), with copoly(maleic acid–ethylene) and copoly (maleic acid-styrene) in aqueous solution was studied by potentiometric titration at 25 °C and the ionic strength of 0.1. The systems containing copper(II) ions were investigated by potentiometry employing the copper(II) ion-selective electrode. The titration curves of the bivalent metal–copoly(maleic acid–ethylene) systems were situated in a lower pH region than in the absence of the metal ions. The complex formed involves two carboxylate groups: primary and secondary. The equilibrium constant of the copper(II) complex was estimated to be 10−2.6. In copoly (maleic acid–styrene) systems, however, the titration curves in the absence and presence of bivalent metal ions overlapped partly in the first neutralization step. From the potentiometric results employing the ion-selective electrode, it was observed that the concentrations of copper(II) ions decrease slightly in the region of overlap. This anomalous behavior is due to the acid dissociation influenced by the conformational transition, including the effect of the side groups of the polymers.