Transfer activity coefficients of crown ethers and their complexes with univalent metal ions between pairs of polar organic solvents

From a comparison of transfer activity coefficients, [(LM⁺)]_PC,2 between propylene carbonate and solvent S₂ of alkali or silver ions complexed with dibenzo-substituted crown ethers (L=DB-18-cr-6, DB-21-cr-7, DB-24-cr-8, DB-30-cr-10) it can be concluded that in the complex LM⁺ both L and M⁺ are solvated, particularly in solvents of high donicity, e.g., N,N-dimethylformamide. From the abnormally low ionic mobility of DB-30-cr-10K⁺ in acetonitrile and the high value of the association constant of the ion pair DB-30-cr-10KBr it is concluded that the outer solvent shell is stripped upon formation of the ligand separated ion pair. A linear relation is found between [log (LM⁺)]_PC,2 and [log(M⁺)]_PC,2 only when L is 18-cr-6, B-18-cr-6, or DB-18-cr-6. Deviation from the linearity of complexes of the larger dibenzo crown ethers is attributed to the flexibility of L. It is shown that solution of 18-cr-6, DB-18-cr-6 and DB-30-cr-10 is enthalpy assisted to a greater extent in acetonitrile than in methanol, while the entropy of solution is more favorable in the latter.     

Separation and evaluation of soybean protein hydrolysates prepared by immobilized metal ion affinity chromatography with different metal ions

Metal ion affinity chromatography is widely used to purify peptides on the basis of the dissimilarities of their amino acids. However, researchers are interested in the separation differences between different metal ions in this method. In our study, four kinds of commonly used metal ions are compared by the amount of immobilized metal ion on iminodiacetic acid-Sepharose and binding amount of soybean peptide to immobilized iminodiacetic acid-Mn(+) adsorbents and evaluated by high-performance liquid chromatography (HPLC) profiles. The results show that due to the different adsorption behaviors of metal ions, the binding ability order of soybean protein peptide on the column should be Fe(3+) > Cu(2+) > Zn(2+) > Ca(2+). The HPLC profiles show that peptides adsorbed by four kinds of metal ions display similar strong hydrophobic characteristics.     

Separation of metal ions by different stationary extraction zones on a glass paper

A separation method using some extraction zones consisting of different organic extractants adsorbed on a sheet of supporting material, has been devised for separation of metal involving radionuclides. Glass paper is the best support to retain liquid extractants zonally, so as not to mix, and TBP, TOPO and TOA retained on it, are employed as example. After feeding of metal ions and washing with developing solution by the descending technique, each element is retained by an appropriate extraction zone, and detection and determination are carried out radiometrically. Separations of Sn−Cd−Bi−As, Sn−Cd−Ag, Fe−Co−Zn and Sn−Sb−Bi in 2M HCl system are demonstrated.     

Cyclic beta-tetra- and pentapeptides: synthesis through on-resin cyclization and conformational studies by X-ray, NMR and CD spectroscopy and theoretical calculations

The solution-phase synthesis of the simplest cyclic beta-tetrapeptide, cyclo(beta-Ala)4 (4), as well as the solid-phase syntheses through side chain anchoring and on-resin cyclization of the cyclic beta3-tetrapeptide cyclo(-beta3hPhe-beta3hLeu-beta3hLys-beta3hGln-) (14) and the first cyclic beta3-pentapeptide cyclo(-beta3hVal-beta3hPhe-beta3hLeu-beta3hLys-beta3hLys-) (19) are reported. Extensive computational as well as spectroscopic studies, including X-ray and NMR spectroscopy, were undertaken to determine the preferred conformations of these unnatural oligomers in solution and in the solid state. cyclo(beta-Ala)4 (4) with no chiral side chains is shown to exist as a mixture of rapidly interchanging conformers in solution, whereas inclusion of chiral side chains in the cyclo-beta3-tetrapeptide causes stabilization of one dominating conformer. The cyclic beta3-pentapeptide on the other hand shows larger conformational freedom. The X-ray structure of achiral cyclo(beta-Ala)4 (4) displays a Ci-symmetrical 16-membered ring with adjacent C=O and N-H atoms pointing pair wise up and down with respect to the ring plane. CD spectroscopic examinations of all cyclic beta-peptides were undertaken and revealed results valuable as starting point for further structural investigations of these entities.     

Potentiometric selectivity coefficients of liquid ion-exchange membranes for univalent and divalent ions

Digital simulation has been used to calculate potential—activity responses and concentration-dependent selectivity coefficients for membranes bathed in mixtures of univalent and divalent ions. For an ideal, dissociated, univalent-site liquid ion-exchange membrane, more accurate computations, based on Nernst—Planck equations, were possible than have been reported previously. Simulation results were used with four suggested equations for the membrane potential (including the IUPAC recommendation) to determine which equation gives best fit and most nearly constant selectivity coefficients. When concentration profiles found by digital simulation are employed, improved response equations are given which closely describe the dependence of surface concentrations on the mobility ratio for the bi-ionic case. From these equations a closed form solution to the diffusion equation yields an explicit expression relating the bi-ionic selectivity coefficient to membrane loading, single ion partition coefficients, and ion mobilities.     

Separation of metal ions by capillary electrophoresis

A number of experimental parameters have been optimized for the separation of 26 metal ions, including alkali, alkaline earth, transition and lanthanide metal ions. Experimental parameters that were evaluated included nature of indirect-detection reagent, pH of electrolyte, concentration of complexing agent and nature of the surface of the capillary; unbonded and C₁ and C₁₈ bonded phases were studied. In addition the effect of internal diameter on linearity and signal-to-noise ratio was examined, and separation efficiency was determined for a variety of experimental conditions. Detection limits (signal-to-noise RATIO = 3) were ca. 1 μg/ml for the lanthanides, ca. 0.6 μg/ml for transition and alkaline earth ions and ca. 0.1–0.8 μg/ml for alkali metal ions. The average relative standard deviations of were 3.7, 5.1 and 2.5% on unbonded, C₁ and C₁₈ capillaries, respectively. Whereas conventional regression analysis suggested that the calibration curves were linear over the range of 1·10⁻⁵ to 4·10⁻⁴ mol/l, sensitivity plots showed that the results were actually linear to within 6% only over the range of 2.5·10⁻⁵ to 4·10⁻⁴ mol/l.     

Stability constants of diaza-crown-ether complexes of univalent metal ions and free energies of transfer of ligand and complexes from acetonitrile to several solvents

1:1 complexes of 1,7,10,16-tetraoxa-4,13-diazacyclooctadecane (2,2) with Ag⁺ and T1⁺ have been determined by potentiometric pAg measurements in several polar nonaqueous solvents at 25°C. A comparison of the results with those for the cryptand (2,2,2) including alkali metal ions shows that interactions for a given ion with the two ligands are similar but differ considerably for different ions. The free energies of transfer of ligand (2,2) and its complexes have been determined from distribution measurements and are around zero between acetonitrile and aprotic solvents.     

Richter cyclization and co-cyclization reactions of triazene-masked diazonium ions

The conventional Richter cyclization involves diazotization of 2-alkynylanilines with HX (aq) (X = Br or Cl) and NaNO₂, followed by spontaneous ring closure to give a mixture of 4-halocinnoline and 4-cinnolinone products. The different products result from competing attack of X⁻ and H₂O, respectively, upon an intermediate 2-alkynylphenyl diazonium ion during the cyclization step. In order to improve the chemoselectivity of this reaction, we have utilized triazenes as masked diazonium ions. These can be unmasked using MeSO₃H in anhydrous solvents and the resultant 2-alkynylphenyl diazonium ion cyclized chemoselectively by the incorporation of a specifically added nucleophile. This process has been extended to tethered nucleophiles, leading to a Richter induced co-cyclization process to give ring-fused cinnolines.     

The formation of medium-sized rings by the intramolecular cyclization of arylnitrenium ions

The synthesis of an aminodibenzo[a,c]octadiene and an aminodibenzo[a,c]octatriene, guided by molecular mechanics calculations, was effected by the intramolecular cyclization of the corresponding open chain nitrenium ions. Also reported is the predicted failure to synthesize another aminodibenzo[a,c]octadiene using this method.     

Binding of metal ions by polyethylenimine and its derivatives

Measurements 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.     

Electricoswitchable bonding of metal ions and complexes by calixarenes

The results of authors on designing electroswitchable supramolecular systems based on calix[4]arenes, calix[4]resorcinols, and transition metal ions and complexes are summarized. We consider systems in which the switching is performed owing to electrochemical reactions both of groups grafted to the macrocycle and bound substrates. Examples of electrochemically switchable luminescence are given.     

Adsorption of univalent and bivalent metal nitrates on hydrous lead dioxide Adsorption behaviour of potassium, cupric, zinc, cadmium and nitrate ions

The individual adsorption behaviour of potassium, cupric, zinc, cadmium and nitrate ions on hydrous lead dioxide (HLD) was investigated. HLD was found to be an amphoteric ion-exchanger with an equi-adsorption point in the vicinity of pH 4.6. For bivalent metal ions, the amount of adsorption increased with pH (at pH > 3) and there was almost 100% adsorption at pH > 6. Both the adsorption capacity and the adsorption affinity on HLD were in the order copper(II) > zinc(II) > cadmium(II).     

Investigation of ion-electrode interactions of linear polyimides and alkali metal ions for next generation alternative-ion batteries

Organic electrode materials offer unique opportunities to utilize ion-electrode interactions to develop diverse, versatile, and high-performing secondary batteries, particularly for applications requiring high power densities. However, a lack of well-defined structure–property relationships for redox-active organic materials restricts the advancement of the field. Herein, we investigate a family of diimide-based polymer materials with several charge-compensating ions (Li⁺, Na⁺, K⁺) in order to systematically probe how redox-active moiety, ion, and polymer flexibility dictate their thermodynamic and kinetic properties. When favorable ion-electrode interactions are employed (e.g., soft K⁺ anions with soft perylenediimide dianions), the resulting batteries demonstrate increased working potentials and improved cycling stabilities. Further, for all polymers examined herein, we demonstrate that K⁺ accesses the highest percentage of redox-active groups due to its small solvation shell/energy. Through crown ether experiments, cyclic voltammetry, and activation energy measurements, we provide insights into the charge compensation mechanisms of three different polymer structures and rationalize these findings in terms of the differing degrees of improvements observed when cycling with K⁺. Critically, we find that the most flexible polymer enables access to the highest fraction of active sites due to the small activation energy barrier during charge/discharge. These results suggest that improved capacities may be accessible by employing more flexible structures. Overall, our in-depth structure–activity investigation demonstrates how variables such as polymer structure and cation can be used to optimize battery performance and enable the realization of novel battery chemistries.

Organic electrode materials offer unique opportunities to utilize ion-electrode interactions to develop diverse, versatile, and high-performing secondary batteries, particularly for applications requiring high power densities.     

Quenching mechanisms of uranyl luminescence by metal ions

The quenching reaction of uranyl luminescence by metal ions in a lower valence state such as Fe²⁺, Tl⁺ and Ce³⁺ is diffusion-controlled and the dominant process of the reaction is concluded to be an electron transfer from the quenchers to uranyl ion. In case of many transition metal and lanthanide ions including Ce(IV), MnO₄⁻ and Cr₂O₇²⁻, the electron transfer is impossible energetically and the energy transfer is predominant.     

Nucleophilic transition metal based cyclization of allenes

Allenes bearing a pro-nucleophile can be cyclized on treatment with a wide variety of transition metal catalysts and reagents: palladium, cobalt, ruthenium, silver, rhodium, lanthanides, gold. The nucleophilic groups can be nitrogen, oxygen or carbon based and can form rings of various sizes, often with good control of stereochemistry. A variety of mechanisms can be proposed for these reactions and the metal complex can be used to introduce a variety of functional groups during cyclization. Several heterocyclic natural products have been prepared using a selection of these reactions.     

Chelation of transition metal ions by peptide nanoring

We have computationally studied the energetics and electronic structures of a chelate system where the guest cation is a transition metal (TM) and the host ligand is a peptide nanoring (PNR). The trapping of a TM cation by a cyclic peptide skeleton is primarily caused by the electrostatic interaction. The exchange interaction plays a secondary role in determining the relative stability in accordance with the spin multiplicity. An interesting feature of this chelate system is that a TM cation can also be trapped by the side-chain aromatic groups of the PNR via pi-d hybridization. However, the spin multiplicity of the system changes the trapped form. When the chelate system has spin singlet multiplicity, a Fe(2+) cation, for example, is not trapped by the single-phenyl group but is preferentially sandwiched by the two phenyl groups. In contrast, a Fe(2+) cation can be trapped by single as well as by double-phenyl groups when the chelate system has higher spin multiplicity, such as triplet and quintet. These two different trapping forms are caused by the difference in the number of valence electrons of TM cations. For this chelate system, the newly occupied molecular orbital (MO) has an interbenzene antibonding character. Therefore, an electron occupying this MO state favors the mutual separation of two benzene molecules. Because the electron occupation of this MO varies in accordance with the spin multiplicity, one can predict the preference for the single-phenyl-group trapping process rather than the double-phenyl-group process systematically as well as consistently.     

Membrane transport of metal ions by bisdithiophosphonyl podands

Russian Journal of General Chemistry -     

Biosorption of precious metal ions by chicken feather

Chicken feather (C-feather) is an intricate network of stable and water-insoluble protein fibers with high surface area and is an abundant bioresource. C-feather protein was found to accumulate various precious metal ions (gold and platinum metals) selectively from their dilute aqueous solutions in high yield and in short contact time, depending on pH and characteristics of the individual precious metal ions. Under certain condition, the sequestering level of precious ions, Au(III), Pt(II), and Pd(II) approaches about 17, 13, and 7% of dry wt of C-feather, respectively. Gold(III) potassium cyanade was also accumulated up to 5.5% at pH 2.0. The presence of 100-fold (mol) of coexisting cations, such as Na⁺, Fe(III), Cu(II), and Ni(II), did not show a discernible effect on the precious metal uptake rate and capacity of C-feather. Experiment suggested C-feather is promising for use in the removal/recovery of precious metals as well as water pollution control. A qualitative discussion is given about the excellent adsorption behavior of C-feather.