Cation complexation with p-tert-butylcalix[5]arene pentacarboxylic acid derivative: an allosteric regulation of the first metal ion for stepwise extraction of the second ion

A calix[5]arene based solvent extraction reagent 3, appending carboxylic acid groups at the lower rim, has been developed and its complexation behavior towards some transition metal ions has been studied. The host 3 can selectively and quantitatively extract Pb(II) ions above pH 1.8 while other divalent ions such as Cu(II), Zn(II), Co(II), Ni(II) are extracted quantitatively only above pH 3.0. The outstanding Pb(II) selectivity of 3 comes from the size fit complementarity effect of the Pb(II) ion in the calix[5]arene cavity. One molecule of 3 extracts two Pb(II) ions in a stepwise manner. The first Pb(II) ion is extracted into the deep cavity of the calix[5]arene defined by phenoxy oxygen atoms. The first complexed Pb(II) ion acts as a template to bring the host into a cone conformation and induces a positive allosteric effect for the extraction of the second Pb(II) ion at an oxygen rich coordinating site composed of carboxyl groups. Both the Pb(II) ions are extracted through an ion exchange mechanism and the electroneutral complex in the organic phase is formed by the release of an equivalent number of hydrogen ions into aqueous solution. The loaded Pb(II) is easily back-extracted from Pb(II)-complexed 3 using dilute acid solution.     

Functional monomers and polymers. CVIII. Photodimerization of pendant thymine bases in thymine containing poly-lysine derivatives

The photodimerization reaction of pendant thymine bases in thymine-containing poly-lysine derivatives was studied over a wide range in aqueous solution. It was found that the quantum yield of the photodimerization of pendant thymine bases is affected mainly by the conformation of the polymers in solution. The differences in photoreaction behavior were discussed for poly-D -, poly-L -, and poly-DL -lysine derivatives.     

Electrochemical functions of metallosupramolecular nanomaterials

Self-assembly of metal ions and organic ligands results in the formation of extended or discrete metallosupramolecular structures. In case of neutral ditopic ligands such as bisterpyridines, extended metallosupramolecular coordination polyelectrolytes (MEPEs) are formed. Metal ion-induced self-assembly of 1,4-bis(2,2':6',2'-terpyridin-4'-yl)benzene with Fe(II) or Co(II) results in MEPEs with interesting electrochemical properties. These MEPEs reversibly change their color when oxidized or reduced. The heterometallic MEPE consisting of Fe(II) and Co(II) combines the properties of the individual MEPEs and therefore shows their different states: red-purple, blue, and transparent. On the other hand, complexation of cyclic phenylazomethines with metal ions results in discrete metallosupramolecular structures. We find that metal ion assembly to the organic module occurs in a stepwise fashion because of a difference in the basicity of the imine conformers, and the metal ion assembly can be controlled electrochemically. This example illustrates how metal ion binding can be controlled by the conformation of the receptor, an important step toward assembling organic ligands and metal ions in predictable ways.     

Potentiometric and spectrophotometric flow-injection determinations of metal ions with use of metal ion buffers

Potentiometric and spectrophotometric flow-injection determinations of metal ions, based on metal ion buffers, are described. A copper(II) ion-selective electrode and copper(II) ion buffers containing nitrilotriacetic acid (NTA) or ethylenebis(oxyethylenedinitrilo)tetraacetic acid (EGTA) are used for determination of ca. 10^?3 M transition metal ions or of calcium in the presence of magnesium. Spectrophotometric determination of transition metal ions is achieved by using a zinc ion buffer solution containing NTA and xylenol orange as indicator. Zinc concentrations up to 2 M can be determined by using large dispersion in the manifold. The factors influencing the sensitivity of the proposed methods are discussed.     

Adsorption of Cu(II) and Ni(II) on solid humic acid from the Azraq area, Jordan

Isotherms of adsorption of Cu(II) and Ni(II) onto solid Azraq humic acid (AZHA) were studied at different pH (2.0-3.7) values and 0.1 M NaClO4 ionic strength. The Langmuir monolayer adsorption capacity was found to range from 0.1 to 1.0 mmol metal ion/g AZHA, where Cu(II) has higher adsorptivity than Ni(II). The previously reported NICA-Donnan parameters for sorption of Cu(II) on HA fit the amount of Cu(bound) determined in the present study at pH 3.7 but underestimates those at pH values of 3.0, 2.4, and 2.0. The contribution of low affinity sites to binding of metal ions increases with decreasing pH and increasing metal ion loading. The aggregation of HA, which is facilitated by decreasing pH and increasing metal loading, may increase the ability of low-affinity sites to encapsulate metal ions. The binding of Ni(II) to HA exhibits less heterogeneity and less multidentism than that of Cu(II). AZHA loaded with Cu(II) and Ni(II) was found to be insoluble in water with no measurable amount of desorbed metal ions.     

Probing the copper(II) binding features of angiogenin. Similarities and differences between a N-terminus peptide fragment and the recombinant human protein

The angiogenin protein (hAng) is a potent angiogenic factor and its cellular activities may be affected by copper ions even if it is yet unknown how this metal ion is able to produce this effect. Among the different regions of hAng potentially able to bind copper ions, the N-terminal domain appears to be an ideal candidate. Copper(II) complexes of the peptide fragments encompassing the amino acid residues 4-17 of hAng protein were characterized by potentiometric, UV-vis, CD, and EPR spectroscopic methods. The results show that these fragments have an unusual copper(II) binding ability. At physiological pH, the prevailing complex species formed by the peptide encompassing the protein sequence 4-17 is [CuHL], in which the metal ion is bound to two imidazole and two deprotonated amide nitrogen atoms disposed in a planar equatorial arrangement. Preliminary spectroscopic (UV-vis, CD, and EPR) data obtained on the copper(II) complexes formed by the whole recombinant hAng protein, show a great similarity with those obtained for the N-terminal peptide fragments. These findings indicate that within the N-terminal domain there is one of the preferred copper(II) ions anchoring site of the whole recombinant hAng protein.     

Characterization of metal ions in coordinating solvent mixtures by means of Raman spectroscopy.

Titration Raman spectroscopy has been developed for studying the solvation structure of metal ions in solution. The method affords us the solvation number, and the value thus obtained in neat solvents is in good agreement with that determined by EXAFS. The method is then applied to solvent mixtures, and the individual solvation number for each solvent is extracted. In a solvent mixture of N,N-dimethylformamide (DMF) and N,N,N',N'-tetramethylurea (TMU), the metal ion prefers DMF to TMU, which is ascribed to the solvation steric effect. The same applies also for the solvent mixture of N,N-dimethylpropionamide (DMPA) and DMF. However, unlike TMU, DMPA changes its conformation from the planar cis to non-planar staggered upon solvation to the metal ion. The enthalpy for the conformational change of DMPA is positive in the bulk, while it is significantly negative in the coordination sphere of the manganese(II) ion. Here, we briefly describe the procedure of measurements and analyses for the titration Raman spectroscopy, and review the solvation structure of the alkaline earth, first transition metal(II) and lanthanide(III) ions in some solvent mixtures in view of solvation steric effect.     

Macrocyclic receptor showing extremely high Sr(II)/Ca(II) and Pb(II)/Ca(II) selectivities with potential application in chelation treatment of metal intoxication

Herein we report a detailed investigation of the complexation properties of the macrocyclic decadentate receptor N,N'-Bis[(6-carboxy-2-pyridil)methyl]-4,13-diaza-18-crown-6 (H(2)bp18c6) toward different divalent metal ions [Zn(II), Cd(II), Pb(II), Sr(II), and Ca(II)] in aqueous solution. We have found that this ligand is especially suited for the complexation of large metal ions such as Sr(II) and Pb(II), which results in very high Pb(II)/Ca(II) and Pb(II)/Zn(II) selectivities (in fact, higher than those found for ligands widely used for the treatment of lead poisoning such as ethylenediaminetetraacetic acid (edta)), as well as in the highest Sr(II)/Ca(II) selectivity reported so far. These results have been rationalized on the basis of the structure of the complexes. X-ray crystal diffraction, (1)H and (13)C NMR spectroscopy, as well as theoretical calculations at the density functional theory (B3LYP) level have been performed. Our results indicate that for large metal ions such as Pb(II) and Sr(II) the most stable conformation is Δ(δλδ)(δλδ), while for Ca(II) our calculations predict the Δ(λδλ)(λδλ) form being the most stable one. The selectivity that bp18c6(2-) shows for Sr(II) over Ca(II) can be attributed to a better fit between the large Sr(II) ions and the relatively large crown fragment of the ligand. The X-ray crystal structure of the Pb(II) complex shows that the Δ(δλδ)(δλδ) conformation observed in solution is also maintained in the solid state. The Pb(II) ion is endocyclically coordinated, being directly bound to the 10 donor atoms of the ligand. The bond distances to the donor atoms of the pendant arms (2.55-2.60 ?) are substantially shorter than those between the metal ion and the donor atoms of the crown moiety (2.92-3.04 ?). This is a typical situation observed for the so-called hemidirected compounds, in which the Pb(II) lone pair is stereochemically active. The X-ray structures of the Zn(II) and Cd(II) complexes show that these metal ions are exocyclically coordinated by the ligand, which explains the high Pb(II)/Cd(II) and Pb(II)/Zn(II) selectivities. Our receptor bp18c6(2-) shows promise for application in chelation treatment of metal intoxication by Pb(II) and (90)Sr(II).     

Heavy metal ion uptake properties of polystyrene-supported chelating polymer resins

Metal ion uptake properties of polystyrene-supported chelating polymer resins functionalized with (i) glycine, (ii) hydroxy benzoic acid, (iii) Schiff base and (iv) diethanol amine have been investigated. The effects of pH, time and initial concentration on the uptake of metal ions have been studied. The uptake of metal ion depends on pH. The resins are more selective at pH 10 for Pb(II) and Hg(II), whereas at pH 6 they are found to be Cd(II) and Cr(VI) selective. Metal ion uptake properties of resins follow Freundlich’s equation. The resins are recyclable and are therefore employed for the removal of heavy metal pollutants from industrial waste water.     

不同价态金属离子对DNA构象的影响

用紫外分光光度法研究了不同价态金属离子对DNA大分子溶液构象的影响。研究结果显示: 金属离子与DNA的作用使DNA溶液的紫外吸收值下降, 即呈现减色效应, 同时减色效应的强弱与金属离子的价态有关。随着价态升高, 减色效应增强。由此说明, 金属离子与DNA的作用使DNA的构象趋于缩拢; 且随着金属离子价态升高, 缩拢程度增强, 甚至产生缩合。还用现代多聚电解质理论对以上现象进行了讨论, 结果是令人满意的。     

On-line preconcentration system for lead(II) determination in waste water by atomic absorption spectrometry using active carbon loaded with Pyrogallol Red.

An on-line system for enrichment and determination of lead(II) is presented. It is based on the adsorption of lead(II) ions on a minicolumn packed with active carbon loaded with Pyrogallol Red. After preconcentration step, the metal ions are eluted automatically by 5.0 ml of 0.50 M nitric acid solution and the lead ion contents were determined by atomic absorption spectrometry. The influence of chemicals, pH and flow variables were studied as well as effect of potential interfering ions. Under the optimum conditions, the lead ions in aqueous samples were concentrated about 100 fold by the column. The detection limit was 0.001 microg ml(-1). The recovery percent of spliced lead(II) was in the range of 98%-103%.     

The effect of aspartic acid on the binding of transition metals to kaolinite

The effect of aspartic acid on the adsorption of Pb(II), Cu(II), Zn(II), Co(II), and Mn(II) on kaolinite at 25 degrees C in the presence of 5 mM KNO3 was investigated by means of potentiometric titrations and adsorption measurements over a range of pH and concentration. Data were modeled by extended constant capacitance models. Aspartic acid slightly enhanced the adsorption of Pb(II), Zn(II), and Co(II) at low pH, but inhibited the adsorption of all the metal ions at higher pH. Adsorption of Cu(II) and Co(II) was inhibited strongly. Because aspartic acid is adsorbed only weakly by kaolinite, inhibition of metal ion adsorption depends on the ability of aspartic acid to form complexes with the various metal ions together with the adsorption characteristics of these complexes. In particular suppression of adsorption at high pH arises from competition between surface sites and dissolved aspartate ions for the available metal ions. Cu(II) and Co(II) form complexes with aspartic acid more strongly than the other metals. As these complexes do not adsorb, Cu(II) and Co(II) suffer greater suppression from aspartic acid than the other metals. There was no evidence of adsorption of aspartic acid complexes to the permanently charged kaolinite faces.     

Neocuproine-extended porphyrin coordination complexes. 2. Spectroscopic properties of the metalloporphyrin derivatives and investigations into the HOMO ordering

The synthesis of a porphyrin compound, 1, containing a 2,9-dimethyl-1,10-phenanthroline moiety that is fused at the beta-pyrrole positions is reported. The absorption spectra of the free-base, copper(II), and zinc(II) derivatives have been studied. On the basis of absorption band intensities, the HOMO of the free base (H21) and its copper and zinc complexes (Cu1 and Zn1) was determined to be of a1u symmetry. Relative to H21, compounds Cul and Znl show enhanced spectral changes upon external metal ion binding. Although the HOMO is the same in all three compounds, the energy gap between the two highest occupied orbitals is greater for Cu1 and Zn1 than it is for the free-base compound. Several metal ions (Ni2+, Cu+, Cu2+, Zn2+, Li+) were examined in their binding to the phenanthrolinic group by measuring the resulting changes in the absorption spectra. It is shown that the observed changes in the absorption spectra are insensitive to the nature of the metal ion coordinated by the phenanthroline moiety. Significant differences in the absorption and emission spectra between Zn1 and [Zn(Zn1)2]2+ clearly demonstrate that the porphyrin pi-system is strongly affected by the binding of metal ions at the fused phenanthrolinic moiety.     

Uptake and extraction chromatographic separation of mercury(II) by triisobutylphosphine sulfide (TIBPS) sorbed on silica gel and decontamination of mercury containing effluent

Batch experiments on the uptake of (Hg(II)) from nitric acid medium by coated inert support have been conducted. The effect of different variables like equilibration time, concentration of acid, metal ion and extractant has been studied. Binary separations of Hg(II) from other metal ions have been carried out. Experiments to evaluate the recycling capacity of the columns reveal a practically insignificant change in the extraction efficiency of the extractant. The practical utility of the columns has been demonstrated by decontaminating mercury containing waste effluent.     

Enhanced metal extractive behavior using dual mechanism bifunctional polymer: an effective metal chelatogen

A new class of chelating polymers using Amberlite XAD-16 (AXAD-16) modified with (N-(3,4-dihydroxy)benzyl)-4-amino,3-hydroxynapthalene-1-sulphonic acid has been developed based on dual mechanism bifunctional polymers, for the extraction of transition and post-transition metal ions. The optimum pH conditions for the quantitative sorption of metal ions were studied. The developed method showed superior extraction qualities with high metal loading capacities of 71, 85, 182, 130 and 46 mg g⁻¹ for Ni(II), Cd(II), Pb(II), Cu(II) and Co(II), respectively. The rate of metal ion uptake i.e. kinetics studies performed under optimum levels showed a time duration of <5 min except for Co(II) which required 20 min, for complete metal ion saturation. Desorption of metal ions were effective with 15 ml of 2 M HCl/HNO₃ prior to detection using flame atomic absorption spectrophotometer. The chelating polymer was highly ion-selective in nature even in the presence of large concentrations of alkali and alkaline earth metal ions, with a high preconcentrating ability for the metal ions of interest. The developed chelating matrix was tested on its utility with synthetic and real samples like river/sea/tap/well water samples and also with multivitamin/mineral tablets, showed R.S.D. values of <2.5% reflecting on the accuracy and reproducibility of data using the newly developed resin matrix.     

Chelating Polymers. II. Amino Acetic Acid Chelating Polymers Derived from Hydroxyarylamino Acetic Acids

The prototype dimeric chelating compounds 3,3′-methylenebis-[N(4-hydroxyphenyl) iminodiacetic acid] and 3,3′-methylenebis-[N(4-methoxyphenyl) iminodiacetic acid] were synthesized and characterized by composition analysis, infrared spectroscopy, and potentiometric titration data. Their chelating characteristics with Cu(II), Ni(II), Co(II), and Zn(l1) ions were established by composition analysis and comparative infrared spectroscopy.

The results suggest chelation and structures of the usual iminodiacetatometal complex type for the Ni(II), Co(II), and Zn(I1) compounds of 3,3′methylenebis-[N-(4-hydroxyphenyl) iminodiacetic acid] and for the Cu(I1, Ni(II), and Co(I1) compounds of 3,3′-methylenebis-[N-(4-methoxyphenyl) iminodiacetic acid]. The composition analysis of each of these compounds indicates 1:2:2 mole ratios of ligand to metal ion to water. Square planar structures are proposed wherein the two iminodiacetatometal chelate moieties are essentially independent of each other.

The composition analysis of the Cu(II) compound of 3,3′-methylenebis-[N-(4-hydroxyphenyl) iminodiacetic acid] indicates a 1:2:1 mole ratio of ligand to metal ion to water. Structures are proposed in which some of the carboxylate groups are bridges between two metal coordination centers.

The composition analysis of the Zn(II) compound of 3,3′-methylenebis-[N-(4-methoxyphenyl) iminodiacetic acid] indicates a 1:1 mole ratio of ligand to metal ion. A structure is proposed in which both nitrogen atoms and two of the four carboxylate groups of the dimeric ligand are coordinated to the same metal ion.

A preliminary investigation was made of oligomeric compounds analogous to the prototype dimeric compounds.     

Binding cadmium and copper ions with chemically modified cellulosic materials

Equilibrium sorption of cadmium and copper ions by modified and unmodified maize stalk was studied using a range of metal-ion concentrations and temperatures at various metal ion-substrate contact periods. The amount of metal ion removed from solution depended on the metal ion concentration, the metal ion-substrate contact period and the metal ion type. The level of metal ion uptake reached 15 mg/g of the substrate for cadmium ions at 0 degree C and was of the order Cd(II) greater than Cu(II). Modification improved the metal ion binding capacity of the substrate and increased the rate of metal ion uptake. The influence of temperature on the level and rate of metal ion uptake by the substrate was investigated.     

Study of peptide-ligand interactions in open-tubular capillary columns covalently modified with porphyrins

The inner surface of fused silica capillaries has been covalently modified with different porphyrins (deuteroporphyrin, complexes of deuteroporphyrin with metal ions Fe(III), Cu(II), Zn(II), Ni(II), and Cu(II)-meso-tetra (carboxyphenyl) porphyrin) and it was applied for the separation of biologically active peptides by open-tubular capillary electrochromatography. Separations were performed in a mobile phase composed of 25?mM potassium phosphate, pH 4.0, 5%?v/v ACN and 10?mM hydroquinone. Changes in the effective electrophoretic mobility of peptides were studied concerning porphyrin central metal atom, attachment geometry, and the presence of coordinating or aromatic amino acid residues in the peptide sequence. The results showed that differences in metal core on the porphyrin and the spatial conformation of attached porphyrin result in changes in the analyte interaction with the stationary phase.     

On the mechanism of electroreduction of sulphur-containing ligands induced by the electroreduction of transition metal cations

The large scale electrolysis of Zn(II), Cd(II), Hg(II), Cu(II), Ni(II), Co(II), Co(III), Fe(II), Mn(II), Cr(II), Cr(III), Bi(III), In(III) and Sb(III) at mercury electrodes in presence of mercaptoacetic acid, 3-mercaptopropionic acid, cysteine and thiourea was carried out and the products were investigated. In case of transition metal ions the catalytic reduction of organic compounds resulting in the formation of sulphide ions was found. There are two possible ways of the production of these ions: (i) consisting in the formation of a complex between transition metal ion and organic ligand which is subsequently, reduced, and (ii) direct electroreduction of organic compound on the electrode modifiied by the deposition of metal and metal sulphide. For both cases the mechanism of electroreduction was discussed.     

Enantioseparation of α‐hydroxy acids by chiral ligand exchange CE with a dual central metal ion system

Using two kinds of central metal ions in a background electrolyte, ligand exchange CE was investigated for the simultaneous enantioseparation of dl ‐malic, dl ‐tartaric, and dl ‐isocitric acids. Ligand exchange CE with 100 mM d ‐quinic acid as a chiral selector ligand and 10 mM Cu(II) ion as a central metal ion could enantioseparate dl ‐tartaric acid but not dl ‐malic acid or dl ‐isocitric acid. A dual central metal ion system containing 0.5 mM Al(III) ion in addition to 10 mM Cu(II) ion in the background electrolyte enabled the simultaneous enantioseparation of the three α‐hydroxy acids. These results suggest that the use of a dual central metal ion system can be useful for enantioseparation by ligand exchange CE.