The Isolation of Single MMX Chains from Solution: Unravelling the Assembly–Disassembly Process

Herein, we provide a systematic theoretical and experimental study of the structural and optical properties of MMX (M=metal, X=halide) chains. The influence of solvent, temperature, and concentration has been analyzed to find suitable parameters for initial building‐block associations in solution. By using density functional calculations, we have computed the dissociation energy of different MMX oligomers (up to the tetramer) in the gas phase. On the basis of these findings, we discuss the most likely disassembly scenario and propose a new interpretation of these compounds. We also calculated the charge redistribution that occurs upon MM+XMMX binding in vacuum. Time‐dependent density functional theory (TDDFT) is used to calculate the UV/visible spectra of different MMX chains up to the tetramer in the gas phase. The implications of these theoretical findings in the analysis of our experiments are discussed in the text. The overall body of data presented suggests a new way of looking at such linear structures. By taking into account these new data, we have been able to isolate single/few MMX chains on mica.     

Rhenium measurements on North Atlantic seaweed samples by ID-ICP-MS: An observation on the Re concentration factors

Summary The estimation of the Re concentration factor (CF) has been carried out to provide additional field information on the biochemical similarities between Re and Tc. Re concentration in brown seaweed samples from the North Atlantic Coast were measured using ID-ICP-MS. The chemical yields were quantitative, and the concentrations were distributed within a narrow range of 65-80 ng/g d.w. CF of Re was approximately 1.2 ^. 10⁴ on average, i.e., one order of magnitude less than that found for ⁹⁹Tc.     

Kinetics and mechanism of thermal decomposition of cadmium(II) complexes with substituted thioureas

From the thermal decomposition curves of cadmium(II) complexes with substituted thioureas (methyl-, dimethyl-, ethyl-, diethyl-, butyl-, dibutyl-, phenyl-, diphenyl-, acetyl- and benzoylphenylthiourea), the kinetic parameters of the thermal decompositions of these complexes were determined and a decomposition mechanism was suggested. The following thermal stability sequence is given for the Cd(II) complexes: complexes with alkylthioureas < complexes with phenylthioureas < complexes with acylthioureas.

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Zusammenfassung Die kinetischen Parameter der thermischen Zersetzung von Verbindungen der Formeln Cd(MeTM)₄(ClO₄)₂, Cd(DMeTM)₄(ClO₄)₂, Cd(EtTM)₄(ClO₄)₂, Cd(DEtTM)₄(ClO₄)₂, Cd(BuTM)₄(CtO₄)₂, Cd(DBuTM)₄(ClO₄)₂, Cd(AcTM)₃(ClO₄)₄, Cd(FTM)₄(ClO₄)₂ und Cd(DFTM)₄(ClO₄)₂ wurden mittels TG and DTG untersucht. Die Reaktionsordnung (n) und die Aktivierungsenergie (E _a) wurden nach der graphischen Methode ermittelt.

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An lonophoretic study of the interactions between metal lons and 1-phenyl-3-pyrazolidinone

Summary The ionic behaviour of 1-phenyl-3-pyrazolidinone (phenidone) at different pH values and its complexes with a selected group of metal ions such as Mg(II), Al(III), Cr(III), Mn(II), Fe(III), Co(II), Ni(II), Cu(II) and Zn(II) were investigated in the pH range of 1–13 by paper electrophoresis. pH-mobility curves were determined for phenidone, the nine metal ions and 21 metal-ligand systems with 1, 110 and 1100 metal: ligand ratios. The effect of the pH on complex formation and the influence of the phenidone concentration on the metal ion mobilities are discussed.Presented at the XXII International Conference on Coordination Chemistry, August 23–27, 1982, Budapest (Hungary).     

Statistical properties of spin-adapted reduced Hamiltonians

The first two moments of the spectral density distributions of the second- and the third-order spin-adapted reduced Hamiltonian (SRH ) matrices have been calculated and compared with the corresponding quantities describing the full configuration interaction (FCI ) Hamiltonian matrix. It has been demonstrated that the differences between the SRH and FCI spectral density distributions sharply increase with increasing difference between the number of electrons and the order of SRH . © 1994 John Wiley & Sons, Inc.     

Column switching in zone electrophoresis on a chip

This feasibility study deals with column switching in zone electrophoresis (ZE) separations on a column coupling (CC) chip. The column switching implemented into the ZE separations an on-chip sample clean up applicable for both the multicomponent and high salinity samples. In addition, complemented by different separation mechanisms in the coupled columns (channels), it provided benefits of two-dimensional separations. Properly timed column switching gave column-to-column transfers of the analytes, characterized by 99-102% recoveries, delivered to the second separation stage on the chip the analyte containing fractions contaminated only with minimum amounts of the matrix constituents. A diffusion driven transport of the matrix constituents to the second channel of the chip (due to direct contacts of the electrolyte solutions in the bifurcation region), representing 0.1-0.2% of the loaded sample constituents, was found to accompany the sample clean up performed on the CC chip. This source of potential disturbances to the separation in the second channel, however, is not detectable in a majority of practical situations. With respect to a 900 nl volume of the sample channel on the CC chip, the electric field and isotachophoresis (ITP) stackings were employed to minimize the injection dispersion in the separations and concentrate the analytes. Here, the column switching, removing a major part of the stacker from the separation system, provided a tool effective in a control of the destacking of analytes. Highly reproducible ZE separations as attained in this work also for the chip-to-chip and equipment-to-equipment frames can be ascribed, at least in part, to suppressions of electroosmotic and hydrodynamic flows of the solutions in which the separations were performed.     

Classification of protein disulphide-bridge topologies

The preferential occurrence of certain disulphide-bridge topologies in proteins has prompted us to design a method and a program, KNOT-MATCH, for their classification. The program has been applied to a database of proteins with less than 65% homology and more than two disulphide bridges. We have investigated whether there are topological preferences that can be used to group proteins and if these can be applied to gain insight into the structural or functional relationships among them. The classification has been performed by Density Search and Hierarchical Clustering Techniques, yielding thirteen main protein classes from the superimposition and clustering process. It is noteworthy that besides the disulphide bridges, regular secondary structures and loops frequently become correctly aligned. Although the lack of significant sequence similarity among some clustered proteins precludes the easy establishment of evolutionary relationships, the program permits us to find out important structural or functional residues upon the superimposition of two protein structures apparently unrelated. The derived classification can be very useful for finding relationships among proteins which would escape detection by current sequence or topology-based analytical algorithms.     

Thermal research of montmorillonite synthetized from the oxides SiO2-Al2O3-MgO-CaO

The thermal behaviour of synthetic montmorillonite of relatively simple chemical composition has been studied and interpreted. Montmorillonite was prepared by hydrothermal synthesis at 300° and 8.8 MPa during 165 hours. With the methods of DTA, DTG, TG, X-ray diffraction analysis, infrared spectroscopy and electron microscopy it was proved that the synthetic montmorillonite is a monomineral sample and no differences from natural montmorillonite were observed.

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Zusammenfassung Das thermische Verhalten synthetischer Montmorillonite verhältnismässig einfacher chemischer Zusammensetzung wurde untersucht und gedeutet. Montmorillonit wurde durch hydrothermische Synthese bei 300°C und 8.8 MPa in 165 Stunden hergestellt. Durch die Methoden der DTA, DTG, TG, Röntgendiffraktionsanalyse, Infrarotspektroskopie und Elektronenmikroskopie wurde erwiesen, daß synthetische Montmorillonit eine monominerale Probe ist und keine Abweichungen von natürlichem Montmorillonit beobachtet werden konnten.

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Studies on the thermal decompositions of As-triazine derivatives and their compounds with metal ions

The thermal decompositions of the new complex salts of Mn(II), Co(II), Ni(II), Cu(II) and Zn(II) with 5,6-diethoxyearbonylmethyl-3-seleno-1,2,4-triazine (HSeTEK) and 5,6-diethoxycarbonylmethyl-3-thio-1,2,4-triazine (HTTEK) were investigated on the basis of the respective thermal curves. The thermoanalytical investigations indicate that HSeTEK, HTTEK, and their complexes with metal ions all undergo three-stage changes as the temperature is raised. The stages of pyrolysis established from the thermal data were compared, and the rates and stages of pyrolysis were related to the structures of the compounds.

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Zusammenfassung Die thermische Zersetzung der neuen Komplexsalze von Mn(II), Co(II), Ni(II) und Cu(II) mit 5,6-Diäthoxycarbonylmethyl-3-seleno-1,2,4-triazin (HSeTEK) und 5,6-Diäthoxycarbonylmethyl-3-thio-1,2,4-triazin (HTTEK) wurden auf der Grundlage der entsprechenden thermischen Kurven untersucht. Die thermoanalytischen Untersuchungen zeigen, daß HSeTEK, HTTEK und deren mit Metallionen gebildeten Komplexe bei Temperaturerhöhung einer jeweils dreistufigen Umwandlung unterliegen. Die auf der Basis der thermischen Daten festgestellten Pyrolysestufen wurden verglichen und Geschwindigkeit und Abschnitte der Pyrolyse mittels der Struktur der Verbindungen erläutert.

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