Synthesis, characterization and metal adsorption properties of the new ion exchanger polymer 3-n-propyl(4-methylpyridinium) silsesquioxane chloride

The preparation and anion exchange properties of 3-n-propyl(4-methylpyridinium) silsesquioxane chloride polymer are described. This new polymer was prepared by the sol-gel processing method and is designated as SiPic+Cl-. It is insoluble in water and showed an anion exchange capacity of 1.46x10(-3) mol g-1. The adsorption isotherms of ZnCl2, CdCl2 and HgCl2 were determined from aqueous solutions and the adsorption equilibria simulations fit the model of fixed bidentate centers with the absence of lateral interactions and energetic heterogeneity between them. The metal ions diffuse into the solid solution interface and are dominantly present as MCl2-(4) species for Zn(II), MCl(2-)4 and MCl-3 species for Cd(II) and MCl-3 species for Hg(II).     

Separation of vanillylmandelic (VMA) and homovanillic (HVA) acids from urine for assay by a two resin column system

A procedure is described for separating vanillylmandelic acid (VMA) and homovanillic acid (HVA) from urine so that they can be assayed by chemical means or gas chromatography. The process comprises passing a threefold diluted urine over cation exchange column (AG 50W-X12) to remove catecol amines and amino acids. The VMA and HVA is then adsorbed from the diluted urine to an anion exchange column (AG 2-X8). After washing with water, the HVA and VMA are eluted with an NaCl-K₂CO₃ solution. The VMA can be determined by oxidation to vanillin directly. By extraction with n-pentanone-2, after acidification and evaporation to dryness, the residue may be redissolved for processing or treated with a methylating reagent for gas chromatography. For the latter purpose, 4-methoxy benzophenone is recommended as the internal standard.     

量热研究铝与钠蒙脱土交换反应

Exchange enthalpies of aluminum with Na-montmorillonite suspension are determined at 3O3.15K and PH=3, and 4, using titration calorimetry and the exchange reaction mechanism are further studied by combining calorimetric results and exchange isotherm determined by static method. The adsorption of aluminum on Na-montmorillonite is endothermic, and therefore exchange reaction is a process driven by entropy. X-ray diffraction patterns of montmorillonite saturated by Na+ and Al3+ are determined at wet and dry state respectively. The results show Al3+ adsorbed on the clay can dramatically reduce the expansion of montmorillonite because Al3+prevents osmotic swelling.     

Radiohochspannungsionophoretische Untersuchungen der Isotopenaustauschreaktionen zwischen Polythionaten,Thiosulfat und Sulfit

The isotopic exchange of³⁵S between thiosulfate/sulfite and tetrathionate/thiosulfate is examined. The kinetic data are determined. In both cases the reactions are of second order. As the isotopic exchange between tetrathionate/thiosulfate is very fast, these reaction components are used in high dilution. Furthermore, the extent of exchange during the separation is determined.      

The effects of ionizing radiations on synthetic organic ion exchangers

Effects of ionizing radiations on organic ion exchangers are recognized as a vexing problem in the processing of special nuclear materials and high specific activity radioactive waste forms. An extensive literature survey, started in 1976 and updated periodically, indicates that radiation decomposition of ion exchange materials has the potential for a variety of undesirable consequences. It is also apparent from this survey that systematic efforts to identify and resolve these problems and to develop radiation resistant ion exchangers are extremely limited. There is, however, widely scattered information in the literature that is useful in designing and operating ion-exchange-based process systems with reasonable assurance of safety. The compilation of experimental data presented in this paper can contribute to better design and safer operations of synthetic organic ion exchange systems at nuclear material processing facilities.     

Milestones in electron crystallography

Electron crystallography determines the structure of membrane embedded proteins in the two-dimensionally crystallized state by cryo-transmission electron microscopy imaging and computer structure reconstruction. Milestones on the path to the structure are high-level expression, purification of functional protein, reconstitution into two-dimensional lipid membrane crystals, high-resolution imaging, and structure determination by computer image processing. Here we review the current state of these methods. We also created an Internet information exchange platform for electron crystallography, where guidelines for imaging and data processing method are maintained. The server (http://2dx.org) provides the electron crystallography community with a central information exchange platform, which is structured in blog and Wiki form, allowing visitors to add comments or discussions. It currently offers a detailed step-by-step introduction to image processing with the MRC software program. The server is also a repository for the 2dx software package, a user-friendly image processing system for 2D membrane protein crystals.     

A thermoanalytical assessment of an organoclay

High resolution thermogravimetric analysis (TG) has attracted much attention in the synthesis of organoclays and its applications. In this study, organoclays were synthesised through ion exchange of a single cationic surfactant for sodium ions, and characterised by methods including X-ray diffraction (XRD) and TG. The changes of surface properties in montmorillonite (MMT) and organoclays intercalated with surfactant were determined using XRD through the changes in the basal spacing. The TG was applied in this study to investigate more information of the configuration and structural changes in the organoclays with thermal decomposition. There are four different decompositions steps in differential thermogravimetric curves. The obtained TG steps are relevant to the arrangement of the surfactant molecules intercalated in MMT and the thermal analysis indicates the thermal stability of surfactant modified clays. This investigation provides new insights into the properties of organoclays and is important in the synthesis and processing of organoclays for environmental applications.     

The complexation of protonated peptides with saccharides in the gas phase decreases the rates of hydrogen/deuterium exchange reactions

Gas-phase noncovalently bound complexes are probed by hydrogen/deuterium exchange. The complexes, composed of a protonated amino acid and a monosaccharide, are investigated to observe the effects of complexation on the rates of exchange. Rate constants are determined and compared for complexed and uncomplexed amino acids. The overall rate constant, which corresponds to exchange of a specific number of hydrogens, is deconvoluted to yield site-specific rate constants. Complexation of amino acids with saccharides significantly decreases the rate constants of the exchange. Results of molecular orbital calculations are provided to explain the decrease in the rates.     

Geological,mineralogical and ion exchange characteristics of zeolite rocks from Bulgaria

Zeolite rocks from different locations in Bulgaria are characterized in geological-mineralogical respect and as ion exchangers for cesium and strontium radionuclides. The basic equilibrium and kinetic exchange parameters are determined. The influence of the mineralogical and chemical composition of the zeolite rocks on the ion exchange properties is shown.     

Kinetics and equilibria of proton exchange in the lowest excited singlet states of 8-methoxyquinoline and 8-methoxyquinaldine: analysis of some complex fluorimetric titration curves

The determination of the rate constants for proton exchange in the lowest excited singlet states of 8-methoxyquinoline and 8-methoxyquinaldine from the pH dependences of their fluorescence spectra is complicated by overlap of the spectra of the conjugate acids and bases of both compounds and by the enhancement of 8-methoxyquinoline fluorescence at high pH by a process apparently unrelated to proton exchange. The fluorimetric titration data are analyzed in ways which compensate for these difficulties and the kinetic parameters of excited-state proton exchange determined. Qualitative relationships between the parameters of excited-state proton exchange, electronic structure and steric factors are considered.     

Effect of the steric accessibility of the exchange site in long-chain quaternary ammonium salts on the anion-exchange extraction of divalent ions

The constants of anion-exchange extraction of divalent ions by quaternary ammonium salts of various structures were determined. The exchange constants depend significantly on steric accessibility of the exchange site. For the exchange of small-size anions, the affinity of the ion exchanger for divalent ions is higher than for monovalent ions. For large divalent anions, the exchange constant may increase or decrease, depending on the size of a monovalent anion. The obtained results are explained by the specifics of the ion-pair association of monovalent and divalent anions with quaternary ammonium cations.     

牛磺酸和甘氨酸在D290树脂上的离子交换平衡

研究了牛磺酸与甘氨酸在阴离子树脂D290上的离子交换平衡.采用静态法分别进行牛磺酸/氢氧根/D290树脂和甘氨酸/氢氧根/D290树脂体系的离子交换平衡实验并测定等温线;在不同的离子强度下进行了牛磺酸/甘氨酸/氢氧根/D290阴离子交换树脂体系的离子交换平衡实验,测定牛磺酸和甘氨酸在碱性条件下的竞争交换平衡等温线.实验结果表明,牛磺酸在D290阴离子交换树脂上的交换量大于甘氨酸的交换量,阴离子交换树脂对牛磺酸和甘氨酸的选择性系数分别为STau-,OH-=2.55,SGly-,OH-=1.65.在牛磺酸/甘氨酸/氢氧根/D290树脂体系中,D290树脂对牛磺酸/甘氨酸/氢氧根3种离子的选择性从高到底顺序是:牛磺酸＞甘氨酸＞氢氧根.树脂对牛磺酸的选择性要大于对甘氨酸的选择性.随着溶液中离子强度的增大,树脂对牛磺酸与甘氨酸之间的选择性下降.     

Features of the exchange of cesium on Co3[Co(CN)6]2·12H2O

The concentration dependence of the kinetics and equilibrium characteristics for the exchange of cesium ions on cobalt hexacyanocobaltate(III) has been studied. It is found that the rate of cesium sorption increases with decreasing cesium concentration in solution. The exchange reaction proceeds via two stages, the first stage is rather fast followed by a much slower one. The equilibrium characteristics of the distribution coefficients for cesium are interpreted in terms of the Langmuir-Hückel isotherm. The heat of sorption and activation energy are determined from the temperature dependence of the exchange reaction.     

Sorption thermodynamics of cobalt(II) cations on iron-manganese concretions

Isotherm of ion exchange of Co²⁺ and Na⁺ cations on iron-manganese concretions is thermodynamically described using a modified Langmuir equation. The thermodynamic characteristics of the ion exchange are determined.     

Radiochemical investigation of the electron exchange reaction between tin(II) and tin(IV) in hydrochloric acid solutions

This paper is concerned with the study of isotope exchange reaction between Sn(II) and Sn(IV) in hydrochloric acid solutions. The kinetics of the exchange reaction of tin in these solutions were studied by extraction of Sn(IV)-hydroxyquinolate into chloroform.¹¹³Sn tracer, initially in the Sn(IV) state, was used. The rate of exchange reaction was determined at 22°C in a wide range of hydrochloric acid concentrations (2.8–12M). The dependence of the exchange rate on the concentration of chloride and hydrogen ions in these solutions (ionic strength: I∼8 and I∼12) are given. The activation energy dependence on chloride ion concentration at I∼12 was determined. The possible mechanism of the exchange reaction between tin(II) and tin(IV) is discussed on the basis of these data.     

The differential enthalpy of ion exchange on selective ionites

The problem of the experimental determination of the differential enthalpy of ion exchange is considered. The high errors in the enthalpies of ion exchange based on experimental corrected equilibrium coefficients substantially decrease the value of the parameters obtained this way. A method is suggested for finding the differential enthalpies of ion exchange on selective ionites on the basis of an analysis of only the composition of solutions in equilibrium systems at two temperatures. This allows the enthalpies to be determined with substantially lower errors than when traditional techniques are used.     

Mechanisms of exchange modulation in trimethylenemethane-type biradicals: the roles of conformation and spin density

The molecular structures and magnetic properties of six dinitroxide biradicals are described. Five of the dinitroxides are trimethylenemethane-type (TMM-type) biradicals; that is, the intramolecular exchange parameter, J, is modulated by a carbon-carbon double bond. However, the efficacy of the carbon-carbon double bond as an exchange coupler is determined by the molecular conformation. Our results show that the exchange parameters correlate with phenyl-ring torsion angles (phi) via a simple Karplus-Conroy-type relation: J = 44 cos(2) phi - 17. Comparison of these results to those obtained for our isostructural series of bis(semiquinone) biradicals shows that both the magnitude of J and the resistance of ferromagnetic J to bond torsions is proportional to the spin density adjacent to the exchange coupler.     

Determination of Stability Constants of Metal Complexes by Capillary Electrophoresis

The stability constants of several divalent first row transition and trivalent lanthanide metal complexes were determined by capillary electrophoresis (CE) methods. Four different approaches, i.e. direct formation, ligand exchange, metal exchange and metal-ligand double exchange were developed. To verify if these CE methods are indeed applicable, the stability constant of CuHEDTA was re-determined to be 17.47 ± 0.20 (consistent with the published 17.50) using the CuEDTA and ZnHEDTA metal-ligand double exchange approach. The stability constants of lanthanide (Ce³⁺ and Eu³⁺) and transition metal (Ni²⁺ and Zn²⁺) complexes of an aminopolycarboxylate ligand, DO2A (1,7-dicarboxymethyl-1,4,7,10-tetraazacyclododecane) were measured under the direct complex formation condition. The stability constant of the NiDO2A complex was determined by the ligand exchange method using 1,4,8,11-tetraazaundecane (2,3,2-tet) as the competing ligand. The stability constant of CuDO2A complex was determined by the metal exchange method using Zn²⁺ ion as the competing metal ion, and complex formation competitions of Ni²⁺ and Cu²⁺ between DO2A and 2,3,2-tet were studied by the metal-ligand double exchange method. Effects of experimental conditions and the advantages and limitations of these CE methods are discussed.     

Application of Acoustic Spectroscopy to Investigation of Microinhomogeneous Media

Main mechanisms of absorption and dispersion of sound velocity in microinhomogeneous media are considered. Existing formulas for the velocity and absorption of sound in dispersion media is generalized to the case of continuos dispersed phase particle size distribution. The obtained relations were used for the analysis of the acoustic spectra of dodecane-based magnetic fluid measured in the 12–2000 MHz frequency range at temperatures varied from 0 to 80°C. The distribution of the volume fraction over particle sites in the examined magnetic fluid was described by a lognormal function. Parameters characterizing particle size distribution were determined. The analysis of the results of processing of the acoustic spectra of magnetic fluid indicated that the main contribution to the additional absorption (compared to absorption in the dispersion medium) originates from the friction and heat exchange between the particles and dispersion liquid. Absorption of sound due to scattering by the particles was negligibly small.     

Proton transfer in the 1,1-dinitroethane/n-dibutylamine complex

The ¹H NMR spectra of 1,1-dinitroethane/n-dibutylamine solutions in CCl₄ have been investigated. It is shown that two types of complexes, the CH … N hydrogen bond complex and the ion pair are present in the solution simultaneously, with slow exchange through proton transfer between them. The exchange rates, activation energy and enthalpy of proton transfer are determined. It can be concluded that the act of proton transfer from carbon to nitrogen and back is kinetically determined.