Interaction Of Metal Cations Research Articles

Complexation of poly(vinylpyrrolidone) and gelatin with some transition metal chlorides in aqueous solution

Complexation of poly(vinylpyrrolidone) and gelatin with certain metal chlorides (HgCl2, CdCl2, CoCl2, and ZnCl2) have been investigated by viscosimetric and spectrophotometric techniques in aqueous solutions. While the change in intrinsic viscosity, [η], of poly(vinylpyrrolidone) has shown a discontinuity with a concentration of metal chlorides, gelatin showed a steady decrease with increasing metal chloride concentration. The decreasing order of effectiveness of cations in complex formation is Hg2+ > Cd2+ > Co2+ > Zn2+ for poly(vinylpyrrolidone) and Zn2+ > Co2+ > Cd2+ > Hg2+ for gelatin solutions. It has been suggested that the poly(vinylpyrrolidone)/metal cation interaction is a charge-controlled reaction, and gelatin/metal cation is a covalent coordination in character. A similar metal cation effect has been observed for poly(vinylpyrrolidone) by UV-VIS spectrophotometry. © 1998 John Wiley & Sons, Inc. J Appl Polym Sci 68: 891–895, 1998

Experimental studies of the interaction of aqueous metal cations with mineral substrates: Lead, cadmium, and copper with perthitic feldspar, muscovite, and biotite

The interactions between each of the metal ions copper(II), cadmium(II), and lead(II) in aqueous solution and the surfaces of the minerals muscovite, biotite, and perthitic feldspar have been studied using batch sorption experiments and X-ray photoelectron (XPS) and X-ray absorption (XAS) spectroscopies. The purpose of the work has been to establish the extent of removal from solution of these metal ions by interaction with the mineral surfaces and the mechanisms involved (whether ion exchange, precipitation, or adsorption). The experiments utilised both powdered samples and flat polished or cleaved surfaces of natural minerals which were characterised compositionally and structurally by electron probe microanalysis and X-ray diffraction. Reaction solutions contained Cu (II) , Cd (II) , or Pb (II) in a background electrolyte of NaNO 3 (0.1 or 0.01 M) at a pH of 5.4 ± 0.2 with a wide range of initial concentrations. The extent of uptake of each of the metals by a particular mineral substrate was measured by analysis of the liquid portion separated by centrifugation after a controlled period of exposure (solution analyses were performed by atomic absorption spectroscopy or by inductively coupled plasma mass spectroscopy as appropriate). The data obtained were used to plot sorption isotherms for the various metal ions and substrates showing the dependence of uptake on initial concentration of metal in solution and background electrolyte concentration. Studies of the reacted mineral surfaces using XPS were used to identify the chemical speciation and bonding environment of Cu, Cd, and Pb present at the surface and to assess surface coverage in planar surface samples and whether significant infiltration of the metal cation into the mineral surface had occurred. Parallel studies using XAS (in particular Extended X-ray Absorption Fine Structure Spectroscopy-EXAFS) were employed to determine the local environments of Cu, Cd, and Pb at the surface of powdered mineral samples. Planar surfaces of muscovite, biotite, and perthitic feldspar exposed to Cu(II) and of muscovite exposed to Cd(II) were also studied using Reflection Extended X-ray Absorption Fine Structure (REFLEXAFS) spectroscopy. The results show that muscovite, biotite, and perthitic feldspar have surfaces that can strongly interact with (and remove) particularly Cu (II) and Pb (II) in such mildly acidic aqueous solutions. Biotite also strongly interacts with Cd(II) in solution. Generally biotite provides the most reactive mineral surface followed by muscovite, with perthitic feldspar being the least reactive. Of the possible mechanisms for removal of metals under the conditions of these experiments, precipitation was not observed, but three other mechanisms (inner-sphere complexation, outer-sphere complexation, and ion exchange) were all observed. The inner-sphere complexation and ion exchange mechanisms often take place in combination: however, Pb (II) forms no outer-sphere complexes on the surfaces of these minerals, and Cd (II) forms only outer-sphere complexes with perthitic feldspar and muscovite. Cu(II) in solution promotes the release of K + from the surface region of muscovite and, particularly, biotite, and subsequent uptake of Cu (II) by ion exchange. These findings have important environmental implications and show the significant role that major rock-forming aluminosilicates may play in the geochemical cycling of Cu(II), Cd(II), and Pb(II).

Fourier transform mid- and far-infrared specular reflectance studies of the polarizability of ion-containing polymers and oxidized polyethylene and its application to adhesion

The dielectric properties of selected ion-containing polymers have been studied by specular reflectance spectroscopy through the mid- and far-infrared regions. These reflectance spectra and the resulting dielectric spectra were measured on (1) surface-oxidized and cation-exchanged polyethylene and bulk ionomers based on (2) ethylene-co-methacrylic acid copolymers, and (3) partially para-sulfonated polystyrene. The chemical nature of the near surface region and its response to applied fields was studied for these materials. The far-infrared spectra were studied to examine the interaction of metal cations with anionic sites, and the polarizability in the far-infrared was found to vary systematically with the identity of the cation. Adhesion forces resulting from dispersion interactions due to polarization mechanisms at mid- and far-infrared frequencies were calculated by Lifshitz theory for polymer–Pyrex glass substrate pairs.

Interaction of divalent metal cations and nucleotides: A computational study

In this study, the anionic phosphate group of nucleotides was found to be the best site to bind the divalent metal cations Be2+, Mg2+, Zn2+, Cd2+, Hg2+ and Pb2+ to form the most stable complexes. Molecular orbital calculations at the semiempirical level were performed on nucleotidemetal cation complexes to report energies of complexation reactions, geometrical parameters of complexes and charge distributions on the complexes. In the discussion, complexational preferences of divalent metal cations, the charge transfer involved in the binding of the metal cations to the phosphate anion of the nucleotides and their conformational effects are included.

Raman spectroscopy of DNA-metal complexes. I. Interactions and conformational effects of the divalent cations: Mg, Ca, Sr, Ba, Mn, Co, Ni, Cu, Pd, and Cd

Interactions of divalent metal cations (Mg2+, Ca2+, Ba2+, Sr2+, Mn2+, Co2+, Ni2+, Cu2+, Pd2+, and Cd2+) with DNA have been investigated by laser Raman spectroscopy. Both genomic calf-thymus DNA (> 23 kilobase pairs) and mononucleosomal fragments (160 base pairs) were employed as targets of metal interaction in solutions containing 5 weight-% DNA and metal:phosphate molar ratios of 0.6:1. Raman difference spectra reveal that transition metal cations (Mn2+, Co2+, Ni2+, Cu2+, Pd2+, and Cd2+) induce the greatest structural changes in B-DNA. The Raman (vibrational) band differences are extensive and indicate partial disordering of the B-form backbone, reduction in base stacking, reduction in base pairing, and specific metal interaction with acceptor sites on the purine (N7) and pyrimidine (N3) rings. Many of the observed spectral changes parallel those accompanying thermal denaturation of B-DNA and suggest that the metals link the bases of denatured DNA. While exocyclic carbonyls of dT, dG, and dC may stabilize metal ligation, correlation plots show that perturbations of the carbonyls are mainly a consequence of metal-induced denaturation of the double helix. Transition metal interactions with the DNA phosphates are weak in comparison to interactions with the bases, except in the case of Cu2+, which strongly perturbs both base and phosphate group vibrations. On the other hand, the Raman signature of B-DNA is largely unperturbed by Mg2+, Ca2+, Sr2+, and Ba2+, suggesting much weaker interactions of the alkaline earth metals with both base and phosphate sites. A notable exception is a moderate perturbation by alkaline earths of purine N7 sites in 160-base pair DNA, with Ca2+ causing the greatest effect. Correlation plots demonstrate a strong interrelationship between perturbations of Raman bands assigned to ring vibrations of the bases and those of bands assigned to exocyclic carbonyls and backbone phosphodiester groups. However, strong correlations do not occur between the Raman phosphodioxy band (centered near 1092 cm-1) and other Raman bands, suggesting that the former is not highly sensitive to the structural changes induced by divalent metal cations. The structural perturbations induced by divalent cations are much greater for > 23-kilobase pair DNA than for 160-base pair DNA, as evidenced by both the Raman difference spectra and the tendency toward the formation of insoluble aggregates. In the presence of transition metals, aggregation of high-molecular-weight DNA is evident at temperatures as low as 11 degrees C. A relationship between DNA melting and aggregation is proposed in which initial metal binding at major groove sites locally destabilizes the B-DNA double helix, causing displacement of the bases away from one another and exposing additional metal binding sites. Metal cation linkage of two displaced bases would allow separate DNA strands to crosslink. Aggregation is proposed to result from the formation of an extended network of these crosslinks.

Raman spectroscopic study of the interaction of metal ions with pyridine and maleimide — models for nucleic acids

Raman spectroscopy was used to study the interaction of various monovalent, divalent and trivalent metal cations with pyridine and maleimide in aqueous solution. The results show that transition-metal ions interact extensively with the nitrogen donor in pyridine. With maleimide, metal binding by the nitrogen atom with displacement of the proton occurs with ions such as Hg2+, Ni2+ and Zn2+. Other ions such as Cu2+, La3+ and Mg2+ cause the deprotonation of maleimide and interact with the resulting enolate anion. Ag+ and Cd2+ ions share both modes of interaction. Relevant conclusions from this study are extended to the special case of metal binding by double-stranded DNA.

Comparison of silica-based and polymer-based cation exchangers for the ion chromatographic separation of transition metals

Silica gel- and polymer-based exchangers differ not only in the substrate but usually also in the structure of their sulphonic acid exchange group. The performance and chromatographic behaviour of modern macroporous poly(styrene-divinylbenzene) polymers of 5-μm particle size after surface sulphonation were examined. Further, two commercially available silica gel cation exchangers were investigated as references for what is now possible and how the chromatographic performance is influenced by the substrate and the structure of the exchange site. The influence of the capacity of surface-sulphonated exchangers for acid and complexing eluents, which are necessary when transition metals are to be separated, was studied. The interaction of polarizable metal cations with the π-system of the polymer depends on the resin capacity, and a comparable dependence for H + and complexing eluents was found. The distance of the functional group from the core influences the adsorption effects dramatically. Lowering the non-specific interaction increases the chromatographic efficiency rapidly. The performance of silica gel-based exchangers is nearly one order of magnitude better than that of surface-sulphonated exchangers. The selectivity of the exchangers investigated is strongly dependent on the structure of the exchange site and on the resin capacity.

Vibrational spectroscopic study of the interaction of metal ions with diethyl phosphate, a model for biological systems

We have studied, using Raman and infrared spectroscopy, the interaction of various monovalent, divalent, and trivalent metal cations with the [Formula: see text] group of diethyl phosphate in aqueous solution, at metal: phosphate ratios ranging from 1:40 to 6:1. The results show that the metal cations interact with the phosphate groups in various ways and to different extents. Spectral characteristics for some specific types of interactions are presented, namely, for direct metal binding by one of the oxygen atoms in the [Formula: see text] group, the formation of water-separated ion pairs, and non-specific electrostatic interactions.

Fourier transform electron spin echo envelope modulation of a S=1/2, I=5/2 spin system: An exact analysis and a second order perturbation approach

Electron spin echo envelope modulation (ESEEM) induced by 27Al nuclei can be used to characterize the interactions of paramagnetic transition metal cations with the framework of various aluminosilicates. The quantitative analysis of such systems is complex due to the 27Al nuclear quadrupole interaction which is often large and unknown. In order to obtain a better understanding of the various spectral features of the 27Al modulation, the ESEEM of a S= (1)/(2) I= (5)/(2) spin system in orientationally disordered systems was investigated in the frequency domain. The relative contributions of the various electron-nuclear double resonance (ENDOR) frequencies to the Fourier transform (FT) ESEEM spectrum were studied as a function of the size of the nuclear quadrupole coupling constant and of the relative orientation of the nuclear quadrupole tensor with respect to the g-tensor. The parameters range investigated is that expected from Cu2+ interacting with framework Al in zeolites. Two approaches were employed in the calculations, exact diagonalization of the nuclear Hamiltonian and a second order perturbation treatment of the quadrupole interaction. It is found that the second order perturbation approach applies up to e2qQ/h<7 MHz. The conditions under which the FT-ESEEM spectrum is dominated by the ‖ (1)/(2) 〉−‖− (1)/(2) 〉 ENDOR transitions were explored as well. This occurs when e2qQ/h is relatively large and it strongly depends on the orientation of the quadrupole tensor. When the FT-ESEEM can be described only by the ‖ (1)/(2) 〉−‖− (1)/(2) 〉 ENDOR transitions, the simulations are significantly simplified since these can be calculated using the analytical expressions obtained by perturbation theory also for a quadrupole coupling constant as large as 10 MHz.

Structure and properties of complex transition‐metal (II) salts of ethylene‐methacrylic acid copolymer with 1,3‐bis (aminomethyl) cyclohexane

AbstractThermal properties by differential scanning calorimetry, stiffness, and melt flow rate (MFR) were measured for the complex transition‐metal (Zn(II), Cu(II), Mn(II), and Co(II)) salts of ethylene‐methacrylic acid copolymer (EMAA) with 1,3‐bis(aminomethyl)‐cyclohexane (BAC). It was found that the strength of both ionic interactions of metal cations with carboxyl groups and coordination bonds of amino groups to metals differ among metal species. In particular, the complex Mn salts are weaker than the complex salts of the other transition metals, which corresponds with Irving‐Williams series of stability constants of transition metal‐ion complexes. Stiffness depends predominantly on the degree of crystallinity of ionic crystallites in ionic clusters, which depends on the ionic species.

ChemInform Abstract: Amine Selective Coloration with Chromoacerands

Amine selective complexation of some azophenol-dyed crowns with concurrent coloration and molecular structures of two sec. amine-dyed crown complexes are reported as well as selective colorations of enantiomeric amines with chiral azophenol crowns and of diamines with bisazophenol crown. INTRODUCTION A variety of complexes and inclusion compounds between tcationic or neutral guest and neutral host, e.g. crowns, cryptands, cyclodextrins, and antibiotics has been studied to develop the phase-transfer catalysis and to elucidate the mechanism of enzyme/substrate and naturally occurring ionophore /metal cation interactions so far. On the other hand, studies on complexation involving the coulombic attractive force between oppositely charged hosts and guests have been expected to draw a new trend in molecular recognition, since this additional binding force will affect the stability and selectivity of the complex other than ion-dipole interaction and/or hydrogen bonding. Previously we reported design and syntheses of a series of ligands which c selectively bind a given metal ion and undergo concurrently color ch gel e.g. lithium ion selective color tion with azophenol-dyed crowns?7 and azophenol spherand-like cyclophanefj, sion with benzothiazolylphenol crowns,'j and their application to lithium ion analyses. BP thium ion specific fluorescent emisAMINE SELECTIVE COMPLEXATION-COLORATION5 Now we wish to report selective complexation of protonated amines by the use of azophenol crowns 1-6 and podand 7 which have a phenol group in the cavity to yield the corresponding ammonium phenolate complex 1 0 (Scheme 1 ). The colored complex 1 0 must be differentiated from simple ion-dipole type complexes by an additional binding force, that is, coulombic interaction between the host phenolate anion and the guest ammonium cation. We recently observed such a perching type complexation of protonated amines by the phenolate anion and ether oxygens of the azophenol crowns.

Amine selective coloration with chromoacerands

Abstract

Extraction of Zn(II), Cd(II), and Hg(II) by dodecyloligo(oxyethylene) carboxylic acids

The synthesis of a series of n-dodecyloligo(oxyethylene) carboxylic acids of general formula C12H25(OCH2CH2)nOCH2COOH (n = 0 to 5) and application of these compounds for the separation of Zn(II), Cd(II), and Hg(II) in extraction are reported. Negligible extractability of the metal ions investigated was found using dodecyloxyacetic acid (n = 0) which indicated that complexation resulted from metal–cation interaction with oxygen atoms of the polyoxyethylene chain incorporated into the molecule of complexon. In extractions from aqueous solutions containing ZnCl2, CdCl2, HgCl2, and NaOH (pH regulator), loading of the organic phases increased for extractants with more oxyethylene units. In particular, Hg(II) extractability and molecular structure of the extractant are related. The selectivity of extraction increased drastically if NaCl was added to the initial aqueous phase, as the extractabilities of Cd(II) and, particularly, Hg(II) declined while the extractability of Zn(II) remained high. Selectivity of extraction is produced by the complex chemical equilibria resulted from complexation of the metal cation by an alkyloligoether carboxylic acid in the organic phase and by Cl− and OH− anions in the aqueous phase. Thus, aqueous solution parameters greatly influence the efficiency and the selectivity of the extraction process and suitable experimental conditions are very important.

Electrochemisorption — a cluster approach

A simple semiempirical quantum chemical approach (Extended Hückel Theory) is shown to give a reasonable description of the electronic structural aspects of chemisorption on the mercury model surface. Chemisorptive interaction of alkali metal atoms and cations, halogen atoms and anions, and water molecules with a charge-neutralized hexagonal close-packed cluster of seven Hg atoms is studied. Adsorption of H, C, N and O atoms on the same model cluster is studied for comparison with earlier work. Chemisorption energies, charge transfer, interaction distance and hydration effects are discussed and compared with experimental results where available.

Homogeneous reaction involving components of different redox couples—II. polarographic studies of the interactions of alkali metal cations with athracene and fluoranthene dianions in N,N-dimethylformamide and acetonitrile

The polarographic behavior of mixtures of anthracene (An), fluoranthene (Fa) and alkali metal cations in N,N-dimethylformamide (DMF) or acetonitrile (ACN) indicates that the electrogenerated dianion of the hydrocarbon reacts with the metal cation in the diffusion layer to form ion complexes. This results, in the case of sodium or lithium cations with anthracene in both DMF and ACN, in the appearance of inverted polarographic waves. In the case of other alkali metal cations (K +, Rb +), the intensity of the polarographic wave due to the reduction to the hydrocarbon dianion is simply decreased. The stoichiometries and mechanisms of the interactions are discussed. In the presence of proton donors such as water, a competing reaction for the dianion results. The polarograms are simulated by digital approximation techniques.

The interaction of alkali metal cations with aromatic molecules in complexes of the type M[AlMe3X]�aromatic, M[Al2Me6X]�aromatic, and related

The crystal structures of 13 compounds of the form M[Al2Me6X]·aromatic and related have been examined in order to learn about the M+...aromatic approach. Four types of interactions have been discerned: (1) metal...aromatic, (2) metal...aromatic...metal, (3) aromatic...metal...aromatic, and (4) no metal...aromatic contact. It was found that the closest K+...C(aromatic) and Cs+...C(aromatic) separations are essentially equal after a correction for the difference in metal radii. The strength of the K+...aromatic attraction was found to be sufficient to move the K+ ion 0.3 A out of the plane of the crown ether in two complexes of dibenzo-18-crown-6.

14N NMR of lipid bilayers: effects of ions and anesthetics.

The interaction of divalent and trivalent metal cations, ferricyanide, a lipophilic ion (tetraphenylborate), and a local anesthetic (tetracaine) with the phosphocholine head group of egg lecithin was investigated by using wide-line 14N and 31P NMR. Measurements of the 14N quadrupolar splittings in the presence of a variety of perturbing agents demonstrated that the 14N NMR technique can be used to directly monitor ion or anesthetic binding. The 14N quadrupolar splitting (delta nu Q) is a measure of the order parameter of the C beta-N bond segment, and changes in delta nu Q as large as 3.5 kHz were observed. Moreover, a comparison of the changes in the quadrupolar splittings induced by the binding of ions or anesthetics provided a sensitive method of discriminating between these perturbing agents in their ability to alter the orientational order of the C beta-N bond segment of the phosphocholine moiety. Without exception, addition of metal ions or anesthetics always resulted in a decrease of the 14N delta nu Q. This reduction reflects a change in the average orientation or degree of motional averaging at the C beta-N bond segment position. In the case of metal ion binding, the strength of the interaction increased with the charge of the metal ion in the order Ca2+ less than Ln3+, in agreement with a previous 2H NMR study [Akutsu, H., & Seelig, J. (1981) Biochemistry 20, 7366-7373].(ABSTRACT TRUNCATED AT 250 WORDS)

DNA–divalent metal cation interactions measured by electrophoretic light scattering

We have used the laser Doppler technique of electrophoretic light scattering to study the electrokinetic and gross conformational manifestations of the binding of divalent cations to DNA in low-salt solutions. By electrokinetic assay, divalent ion affinities to DNA in the 5–500 μM range increase in the order Mn+2<Co+2<Mg+2<Cu+2. The ELS spectra show that Cu+2 denatures double-stranded DNA in the 50–200 μM concentration range, thereby augmenting the reduction in electrophoretic mobility. Counterion condensation theory correctly predicts the form of the electrophoretic mobility reduction for territorially bound ions such as Mg+2, but the absolute magnitudes of electrophoretic mobility predicted by an equation deduced from condensation theory overestimate our experimental values.

Synthesis, hyperfine interactions, and lattice dynamics of a crown ether intercalation compound of FeOCl

The anisotropic van der Waals layer compound FeOCl has been intercalated with the cyclic polyether 1,7,10,16-tetraoxa-4,13-diazacyclo-octadecane (Kryptofix-22 or Krypt) to give a matrix in which the ’’guest’’ to ’’host’’ ratio is 1:18. This intercalate has been studied by x-ray power diffraction, 57Fe Mössbauer, and Fourier transform infrared spectroscopy. The Mössbauer spectra above the magnetic ordering temperature (but below 150 K) show the existence of two types of iron atoms in the structure. The majority iron atoms display the sigmoid temperature dependence of the quadrupole hyperfine interaction parameter which has been associated with a transition of the lattice from a three-dimensional solid at low temperatures to a quasi-two-dimensional solid at high temperatures. The minority iron atoms are characterized from the isomer shift and quadrupole splitting parameters as ’’Fe(II)’’, and are those iron atoms which interact directly with the lone pair electrons on the nitrogen atoms of the intercalant. The observed b-axis expansion at room temperature is 4.28 Å, which is significantly smaller than the ring diameter reported for the uncomplexed polyether. These data suggest significant interpenetration of the intercalant guest molecule into the van der Waals layer defined by the chlorine atoms. The midrange infrared spectra of the intercalate do not show any evidence for the type of polyether–metal cation interaction which has been reported for lanthanide complexes of this molecule. The lattice dynamical properties of the solid as probed by the 57Fe Mössbauer active atom are discussed in detail.

Structure and bonding inN-methylacetamide complexes of alkali and alkaline earth metals

A detailed crystallographic investigation ofN-methylacetamide com­plexes of Li, Na, K, Mg and Ca has been made in view of its importance in the coordination chemistry and biochemistry of alkali and alkaline earth metals. The metal ions bind to the amide oxygen causing an increase in the carbonyl distance and a proportionate decrease in the central C—N bond distance. The decrease in the central C—N distance is accompanied by an increase in the distance of the adjacent C—C bond and a decrease in the adjacent C—N bond distance. The metal ion generally deviates from the direction of the lone pair of the carbonyl oxygen and also from the plane of the peptide, the out-of-plane deviation varying with the ionic potential of the cation. The metal-oxygen distance in alkali and alkaline earth metal complexes of a given co­ordination number also varies with the ionic potential of the cation, as does the strength of binding of the cations to the amide. The amide molecules are essentially planar in these complexes, as expected from the increased bond order of the central C—N bond. The NH bonds of the amide are generally hydrogen bonded to anions. The structures of the amide complexes are compared with those of other oxygen donor complexes of alkali and alkaline earth metals. The structural study described here also provides a basis for the interpretation of results from spectroscopic and theoretical investigations of the interaction of alkali and alkaline earth metal cations with amides.