Swelling of NaMg-montmorillonites and hydration of interlayer cations: a Monte Carlo study

While the swelling behavior of laboratory-prepared homoionic montmorillonites has been studied extensively in numerous experimental and simulation works, far less attention has been given to much more abundant natural montmorillonites, containing a mix of monovalent and/or bivalent cations in interlayer spaces. We carried out a series of Monte Carlo simulations in order to investigate the reasons for the remarkable difference of experimental swelling patterns of a natural Na-rich/Mg-poor montmorillonite and a homoionic Na-montmorillonite. The simulations reproduced the swelling pattern of a natural montmorillonite, suggesting a mechanism of its hydration different from that of the homoionic montmorillonite. We also found that the differences in size and hydration energy of Mg2+ and Na+ ions have strong implications for the structure and the internal energy of interlayer water. This leads to a difference in the layer spacings of the simulated Mg- and Na-montmorillonites as large as approximately 2.1 A at lower water contents.     

Influence of various chromatographic parameters on the separation of natural mixtures under column overloading conditions

The furocoumarin fraction of the extract of fruits of the Apiaceae family was separated on preparative scale using a steel column (Prepco 32). The influence of volume overloading, concentration overloading and eluent composition on the separation efficiency was examined.Preliminary report on this work was presented at the 5th International Symposium on Pharmaceutical and Biomedical Analysis in Stockholm, Sweden, 21–24 September 1994Dedicated to Professor Dr. Dr. h.c. mult. J.F.K. Huber on the occasion of his 70th birthday     

Alternative Synthetic Routes to Epoxy Polymer – Clay Nanocomposites using Organic or Mixed-Ion Clays Modified by Protonated Di/Triamines (Jeffamines)

The use of homoionic organic clays and mixed-ion organic/inorganic clays modified by di- or triamines (Jeffamines), which are being used as epoxy resin curing agents, in the synthesis of polymer nanocomposites has been studied in this work. Our aim is to enhance polymer crosslinking and interfacial adhesion in the nanocomposite structure by utilizing the functionality of the di/triamines on the surface of clay nanolayers and by reducing the organic modifier via formation of homostructured mixed-ion organic/inorganic clays. The results show that the use of homoionic organic clays exchanged with relatively short chain di- or triamines and mixed-ion organic/inorganic clays partially exchanged (ca. 35%) with long chain diamines resulted in intercalated structures with enhanced thermo-mechanical properties (Young's Modulus, Storage Modulus). On the other hand, homoionic organic clays exchanged with long chain diamines and triamines resulted in exfoliated nanocomposites but with compromised mechanical properties due to the plasticizing effect of the long chain amine modifiers.     

Foundations of thermo-dielectrical analysis

The dielectric susceptibility of dehydrated homoionic zeolites was calculated by using a cation hopping model consisting of classical jumps over a barrier. The calculation method was based on determination of the response function of the homoionic dehydrated zeolite under transient excitation. The dielectric susceptibility expression obtained was compared with experimental dielectric spectra at different temperatures and the activation energy for cationic diffusion in the zeolites tested was also calculated. The results were within the range of values reported for cationic migration in the solid state. Further, there is a clear difference between the activation energies of Na and Ca diffusion and this fact forms a quantitative basis for the explanation of the thermodielectric thermograms of homoionic sodium and calcium zeolites and promote the understanding of the role of cationic polarization and cationic migration in thermodielectric analysis.

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Zusammenfassung Unter Anwendung eines Kationen-Hüpfmodelles, bestehend aus klassischen Hürdensprüngen, wurde die dielektrische Suszeptibilität von dehydratierten homoionischen Zeolithen berechnet. Die Berechnungsmethode basiert auf der Bestimmung der Antwortfunktion des dehydratierten homoionischen Zeolithen während einer vorübergehenden Anregung. Der ermittelte Ausdruck für die dielektrische Suszeptibilität wurde mit experimentellen dielektrischen Spektren bei verschiedenen Temperaturen verglichen, weiterhin wurde die Aktivierungsenergie für die Diffusion der Kationen in die untersuchten Zeolithe berechnet. Die Ergebnisse liegen in dem Wertebereich, der in der Literatur für die Kationenwanderung im festen Zustand beschrieben wurde. Es besteht ferner ein eindeutiger Unterschied zwischen der Aktivierungsenergie von Na- bzw. Ca- Diffusion. Dies bietet eine quantitative Grundlage zur Erläuterung thermodielektrischer Thermogramme von homoionischen Natrium- und Calciumzeolithen und hilft, die Rolle von Kationenpolarisation und -Wanderung in der thermodielektrischen Analyse besser zu verstehen.

     

Thermogravimetric investigation of thermal decomposition of copper(II) complexes with methylpyrido[2,3-d]imidazole derivatives

Solid-state complexes with the formulae CuL _x X₂·nH₂O, wereL=2-methyl-, 5-methyl-, or 7-methylpyrido[2,3-d]imidazole,X=NO ₃ ^– or Cl^–,x=2 or 3, andn=1 or 2, were subjected to thermogravimetric analyses. The kinetic parameters were calculated according to the Coats-Redfern method. Reactions paths are proposed and their agreement with the data obtained from TG curves is checked.The authors thank Dr. W. Surga for XRD analyses, and Dr. B. Kowalczyk and Dr. M. Czerwinski from the Pedagogical University in Czestochowa for providing access to the computer application allowing calculation of the kinetic parameters.     

HIGH RESOLUTION GAS ADSORPTION STUDY ON ILLITES PERMUTED WITH VARIOUS CATIONS ASSESSMENT OF SURFACE ENERGETIC PROPERTIES

ABSTRACT

Ar and N₂ high resolution adsorption volumetry coupled to the Derivative Isotherm Simulation method was applied on nine homoionic illite samples (Li ?, Na ? K ? Rb ? Cs ? Mg ? Ca ? Sr ? and Ba ? illites). By comparing the adsorption isotherms it appears that the nature of the surface cation strongly influences the adsorption mechanisms.

The lateral and basal surface areas can only be derived from argon adsorption on monovalent samples. The argon adsorption energies varv with the nature of the surface compensating cation. Both cation size and electronegativity are involved. These interactions can, in first approach, be expressed in terms of surface tensionsγ_sv ^LW. Specific interactions appear when nitrogen is used revealing high energy adsorption sites located on basal faces. These sites could be related to some polar properties of the surface.     

XRD-Studies of SiC/Si layers on carbon substrates

Structural investigations of thin films of SiC, SiC with free silicon and various titanium suicides (TiSi₂, TiSi and Ti₅Si₃) are described. The crystal phases have been identified using X-ray diffractometry. The growth of reaction products from surface reactions between silicon and deposited titanium can be observed.Dedicated to Professor Dr. rer.nat. Dr. h.c. Hubertus Nickel on the occasion of his 65th birthday     

Dehydration enthalpy of alkali-cations-exchanged montmorillonite from thermogravimetric analysis

Dehydration of a series of homoionic alkali-exchanged montmorillonites is studied at different treatment temperatures by means of thermogravimetric analysis. More specifically, we investigate the last stages of dehydration when the number of adsorbed water molecules corresponds, at maximum, to a monolayer. Weight losses are measured at several constant temperatures as a function of time. Application of Van't Hoff's law yields the dehydration enthalpy. Trends and data similar to those reported from other experimental conditions are found. Comparison with X-ray data and with the dissociation enthalpy of alkali cation/water complexes shows that dehydration of weakly hydrated homoionic alkali montmorillonites results from the competition between opposite energy contributions due to (i) the cation solvation, (ii) the hydration of the silicate interlayer surface, and (iii) the structural swelling. So, depending on the balance between these various energy contributions, different behaviors are observed according to the nature of the alkali cations.     

Studies on nucleic acid chemistry: VII. Synthesis of four oligoribonucleotides of dihydrouridine (D) loop of yeast alanine transfer RNA

This article described the preparation and the protection of 3′-DMP and dihydrouridine (Dr) as well as the synthesis of four oligoribonucleotides composed of them. DMP and Dr were obtained by hydrogenation of 3′-UMP and Ur under acidic conditions in the presence of platinum dioxide. They were monomethoxytritylated and benzoylated to (MeOTr)-D_bzp and (MeOTr) D_bzs, respectively. The latter was converted to D_bzs, by demonomethoxytritylation. The oligoribonucleotides containing DMP or Dr—ApGpD, DpApG, ApGpDpC and ApGpDpCpGpG were synthesized via phosphodiester approach and DCC was used as condensing reagent. DpApG was also synthesized via phosphotriester approach and TPST, MSTe, MSNI and MSNT were used as condensing reagents for a preliminary comparison of the coupling yields. These synthetic oligoribonucleotides were checked for purity and nucleotide sequences as usual. ApGpDpCpGpG and DpApG had been used for enzymatic synthesis of ApGpDpCpGpGpDpApG, which had been in turn successfully used for the total syntheses of the 5′-half molecule and the whole molecule of yeast alanine t-RNA     

Calculation of the ground states of molecules with closed shells via Feynman diagrams

A Feynman-diagram calculation is performed for the ground-state energies of molecules of the XY_p type with closed electron shells. The first two orders in perturbation theory are considered.We are indebted to Dr. V. V. Tolmachev for proposing the topic and for substantial assistance in deriving the results, and also to Dr. U. I. Safronova for constant interest.     

Solid-Phase Extraction of Polybrominated Diphenyl Ethers in Human Plasma – Comparison with an Open Column Extraction Method

A solid phase extraction (SPE) method in combination with silica gel cleanup to analyse tri-to heptabrominated diphenyl ethers in human plasma was validated. All congeners showed recoveries over 70% except for BDE #183, which showed recoveries around 45%. The method was tested on 21 individual plasma samples which were extracted with both the SPE method and an open column extraction method using Hydromatrix. Method detection limits were of the same order of magnitude for both methods, ranging from 0.0076 to 0.13 ng g^–1 (l.w.) depending on the congener. The SPE extraction method meets the demand for a faster, less solvent-and sample-demanding method with lower contamination risk due to fewer steps compared to the open column extraction.Acknowledgements The Knowledge Foundation in Sweden is acknowledged for supporting this project financially. Brock Chittim, Wellington Laboratories, Guelph, Canada is acknowledged for providing BDE standards. Dr. Cathrine Thomsen at the National Institute for Public Health, Oslo, Norway is acknowledged for helpful discussions and instruction of solid phase extraction. Anne-Marie Porat at Haluxa, Sweden is acknowledged for the blood sampling of the electronic dismantling workers. Personnel at WÅAB are acknowledged for their support in the different sampling events.     

The uptake of radioisotopes onto clays and other natural materials

Montmorillonite and illite clays were examined for their ability to take up cesium and strontium radioisotopes from solution. Uptakes onto near homoionic Na, Ca, Mg and Sr clays were assessed by distribution coefficients measured at different Na, Cs, Mg, Ca and Sr solution concentrations. Some experiments were carried out at different pH, and to check the effect of differing anions. In addition measurements of the uptake of ruthenium species were made.     

An interlaboratory comparison of energy dispersive X-ray microanalysis (EDX) of titanium and zirkonium nitrides

The results of an interlaboratory comparison of energy dispersive X-ray microanalysis of TiN_0.84 and ZrN were presented. The microprobe group of the German Physical Society (DPG) and the Federal Institute for Materials Research and Testing (BAM) had initiated the interlaboratory comparison. The primary aim was to test modern EDX systems equipped with ultrathin windows concerning the accuracy and reliability of the analysis of compounds containing light elements. The participants from 23 laboratories performed the analysis at different primary energies, in the standard-less mode as well as on the base of own standards, and considering Ti-K or Ti-L in case of TiN_0.84. The results show a slight overestimation of the nitrogen content and a large standard deviation from the mean value. Reasons for the scattering of the results are discussed.Dedicated to Professor Dr. rer. nat. Dr. h.c. Hubertus Nickel on the occasion of his 65th birthday     

In-depth analysis of glass fibers

Two types of commercial glass fibers were subjected to attack in strongly basic KOH solutions. The resulting leach solutions were analysed for Na, Ca, and Si. This showed that the corrosion process attacks the fibers incongruently. Although there are some distinct differences in the performance of these fibers, to a first approximation both types behave similarly. Further, the fibers were depth profiled using a recently developed SNMS technique for fiber in-depth analysis. This showed that both types of fibers behave in a quite dissimilar manner. The fibers were weathered already without any treatment. Although both fibers show alkali ion exchange and network splitting processes, on one of the fiber layers enriched in SiO₂, Fe₂O₃, and CaO are formed by a redeposition process from the leach solution.Dedicated to Professor Dr. rer. nat. Dr. h.c. Hubertus Nickel on the occasion of his 65th birthday     

Study of stressed hard coatings and of their abrasive particles by AES and REM

Chromium nitride and chromium oxide were deposited by arc PVD and APS on steel substrates to be worn in a testing set up simulating the abrasion process of a screw rotor compressor. The damage of Cr _x N is more severe than that of Cr₂O₃. The abrasive particles were collected on glassy carbon with a Batelle impactor and analyzed by AES and REM. Particles from the Cr _x N coating are totally oxidized, in contrast to particles from Cr₂O₃ which are not chemically influenced. No oxidation can be detected on the surface of the treated Cr _x N coating. The Cr₂O₃ coating is not affected either.Dedicated to Professor Dr. rer. nat. Dr.h.c. Hubertus Nickel on the occasion of his 65th birthday     

An electron-microscopic study of Na-attapulgite particles

A scheme for the separation, purification and preparation of sub-micron, homoionic, Na-attapulgite from a natural mineral deposit is presented together with represen-tative analysis of the particle size distribution. Transmission electron microscopic examination indicated that particles were predominantly <1μm long and “lath-like” with aspect ratios (length:width:thickness) 100:3:1 which provide for a variety of modes of particle/particle interaction. The scheme involves physical and mild chemical treatment of the natural material and appears to preserve the physico-chemical integrity of the attapulgite particles and provides material within a narrow size range. Received: 30 March 1998 Accepted: 27 April 1998     

Interaction of sodium dodecylsulfate (SDS) with homoionic montmorillonites: adsorption isotherms and metal-ion release

The interaction of dodecylsulfate anions (DS^–) with homoionic Ca-, Mg-, Ni-, Cu-, Cd-, Pb- and Fe-montmorillonites were investigated. Mg- and Cd-montmorillonite do not adsorb DS^–, and an anion exchange at the edges of the clay mineral does not take place. Three different adsorption processes are identified on the other montmorillonites: i) Fe-montmorillonite is covered with amorphous iron hydroxide, and DS^–-anions are bound at positively charged sites. ii) On Ca- and Pb-montmorillonite DS^– is precipitated as Me(DS)₂. iii) On Ni- and Cu-montmorillonite DS^– forms ion pairs with the cations on the surface. In all cases DS^– is not bound above the CMC but the metal ions are mobilized from the surface either by solubilization of the precipitates or by formation of mixed micelles.     

Mass spectrometric analysis of ceramics after decomposition with elemental fluorine

The features of a combustion with elementary fluorine for the case of compact SiC ceramics and model substances for boron containing ceramics (H₃BO₃ and Na₂B₄O₇) were investigated with the aim of their decomposition and analysis. On-line detection of the gaseous decomposition products by quadrupole mass spectrometry using electron impact ionisation was studied. Limitations by blanks and transport interferences were investigated. Standard addition as well as the isotope dilution technique were used for calibration in the case of B, C and W at the trace and major component level.Dedicated to Professor Dr. rer. nat. Dr. h.c. Hubertus Nickel on the occasion of his 65th birthdayDeceased May 1995.     

Combination of RBS analysis and infrared vibrational spectroscopy for the characterization of semiconducting β-FeSi2 films

The analytic power of RBS and FTIR measurements for the characterization of chemical and structural properties of thin films is compared for the case of semiconducting FeSi _x films. It is shown that these methods, which both are nondestructive, are complementary with respect to their sensitivity to certain film properties (composition, degree of compound formation, crystalline quality, film thickness). For FeSi _x films the FTIR technique is favourable for rapid monitoring of chemical bonding and of the structural properties without special sample preparation.Dedicated to Professor Dr. rer. nat. Dr. h.c. Hubertus Nickel on the occasion of his 65th birthday     

Kombination wirksamer Trennverfahren mit modernen analytischen Methoden in der Naturstoffchemie

Zusammenfassung Aus Crotonöl konnten durch Anwendung multiplikativer Verteilungs- und chromatographischer Verfahren die entzündlichen und cocarcinogenen Substanzen A1–A4 und B1–B7 rein dargestellt werden. Diese Substanzen sind Diester des polyfunktionellen Diterpenalkohols Phorbol, C₂₀H₂₈O₆ mit jeweils einer kurzkettigen (Essig-, (+)-S-2-Methylbutter-, Tiglinsäure) und einer langkettigen Fettsäure (Capryl-, Caprin-, Laurin-, Myristin-, Palmitinsäure). Die Teilsynthese einiger Substanzen wird angegeben. Aus den UV-, IR- und KMR-Daten und chemischen Befunden werden Teilformeln für Phorbol abgeleitet und diskutiert.

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Summary The compounds A1–A4 and B1–B 7 have been isolated from croton oil in pure state by multiplicative distribution and chromatography. These compounds are di-esters of the polyfunctional diterpene alcohol phorbol C₂₀H₂₈O₆ each with a short chain (acetic-, (+)-S-2-methyl-butanoic-, tiglic acid) and a long chain fatty acid (octanoic-, decanoic-, dodecanoic-, tetradecanoic-, hexadecanoic acid). The partial synthesis of some compounds is described. From ultraviolet-, infrared-, nmr-spectra and from chemical evidence partial structures for phorbol are being discussed.

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Für die Messung von KMR-, Massen- und CD-Spektren und anregende Diskussionen danken wir den Herren Dr. J. Sonnenbichler, München, Dr. J. Jochems, Heidelberg, Dr. A. Mannschreck, Heidelberg, Dr. H. Budzikiewicz, Braunschweig, Dipl.-Chem. C. Wünsche, Heidelberg, Doz. Dr. G. Snatzke, Bonn, und V. Scheidel, Heidelberg.

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Vorgetragen von H. Kubinyi.