The additivity principle in pyrolysis—gas chromatography of brown coal

Pyrolysis—gas chromatography of brown coal exhibits additive properties and it is therefore possible to construct the pyrogram of the original coal from the individual pyrograms of the bitumen, humic acids, lignin and humin fractions. The contents of phenols in the pyrograms are typical for all of the above classes except bitumen and are in agreement with the contents of the individual groups in the original coal. The results suggest that the separation does not bring about significant chemical changes in individual brown coal fractions.     

Aggregation-free and high stability core–shell polymer nanoparticles with high fullerene loading capacity,variable fullerene type,and compatibility towards biological conditions

Fullerenes have unique structural and electronic properties that make them attractive candidates for diagnostic, therapeutic, and theranostic applications. However, their poor water solubility remains a limiting factor in realizing their full biomedical potential. Here, we present an approach based on a combination of supramolecular and covalent chemistry to access well-defined fullerene-containing polymer nanoparticles with a core–shell structure. In this approach, solvophobic forces and aromatic interactions first come into play to afford a micellar structure with a poly(ethylene glycol) shell and a corannulene-based fullerene-rich core. Covalent stabilization of the supramolecular assembly then affords core-crosslinked polymer nanoparticles. The shell makes these nanoparticles biocompatible and allows them to be dried to a solid and redispersed in water without inducing interparticle aggregation. The core allows a high content of different fullerene types to be encapsulated. Finally, covalent stabilization endows nanostructures with stability against changing environmental conditions.

A polymer nanoparticle approach to biorelevant and robust fullerene nanoparticles is presented.     

Catalytic, asymmetric synthesis of α,α-disubstituted amino acids

Copper(salen) complex 1 has been found to catalyse the asymmetric alkylation of enolates derived from a variety of amino acids. There is a clear relationship between the size of the side chain in the substrate and the enantioselectivity of the process, so that the enantioselectivity decreases in the order alanine>aminobutyric acid>allylglycine>leucine>phenylalanine>valine. A transition state model which accounts for the influence of the size of the side chain on the enantioselectivity of the reactions is presented.     

1-(Organosulfonyloxy)-3(1H)-1,2-benziodoxoles: Preparation and Reactions with Alkynyltrimethylsilanes

Organosulfonyloxy derivatives of 1,2-benziodoxol-3(1H)-one (3a-c) and 3,3-bis(trifluoromethyl)-3(1H)-1,2-benziodoxole (5a-c) can be prepared in high yield by the reaction of 1-hydroxybenziodoxoles 1 or 4 and the corresponding sulfonic acids or Me(3)SiOTf in the form of stable, but moderately hygroscopic, microcrystalline solids. Reaction of the triflate derivatives 3a and 5a with alkynyltrimethylsilanes affords either alkynyliodonium triflates 6, or (E)-beta-(trifluoromethanesulfonyloxy)alkenyliodonium triflates 7, while the same reaction in the presence of pyridine selectively gives the respective 1-alkynylbenziodoxoles 8 and 9 in 82-90% yield.     

Über die Extrahierbarkeit des Wolfram(VI)-rhodanids

Zusammenfassung Die Anwendbarkeit des Wolfram(VI)-komplexes mit Rhodanid für die analytische Praxis wurde untersucht; durch seine Löslichkeit in organischen Lösungsmitteln eignet sich der Komplex gut zur Trennung von anderen Elementen.Unter Zuhilfenahme des radioaktiven Wolframisotopes¹⁸⁵W konnten die optimalen Extraktionsbedingungen, wie Säure- und Rhodanidkonzentration, rasch ermittelt werden. Bei der Untersuchung verschiedener organischer Lösungsmittel zeigte Amylalkohol sowohl in reiner Form als auch in Mischungen mit Chloroform die besten Extraktionseigenschaften.Da der Komplex zu den stärksten des Wolframs gehört, stören bei der Durchführung von Analysen nur wenige Anionen, am meisten Fluorid. Von den Kationen werden nach Reduktion des Eisens, wozu Ascorbinsäure empfohlen wird, nur wenige andere mitextrahiert; am störendsten wirkt Molybdän, das mitausgeschüttelt wird und anschließend entfernt werden muß. Zur Bestimmung des Wolframs eignet sich dann am besten die Hydrochinonmethode.

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Summary A study was made of the use of tungsten(VI) complex with thiocyanate in analytical practice. Because of its solubility in organic liquids the complex is well suited for separation from other elements.By using the radioactive isotope¹⁸⁵W, the optimal extraction conditions, such as the acid- and thiocyanate concentration, could be rapidly determined. When various organic solvents were tried, it was found that amyl alcohol, either by itself or mixed with chloroform, had the best extraction characteristics.Since the complex is one of the most stable formed by tungsten, only a few anions interfere in the analysis; fluoride causes the most trouble. Among the cations, only a few interfere after the iron has been reduced (ascorbic acid is recommended for this purpose). The greatest interference comes from molybdenum, which is co-extracted and has to be removed subsequently. The hydroquinone method is then the best procedure for determining the tungsten.

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Résumé On a cherché à appliquer le complexe tungstène-VI-thiocyanate à l'analyse. Grâce à sa solubilité dans les solvants organiques, le complexe se prête bien à la séparation d'avec les autres éléments.Au moyen de l'isotope radioactif du tungstène¹⁸⁵W, on a pu trouver rapidement les conditions optimales d'extraction, ainsi que la concentration en acide et en thiocyanate. Après essai de divers agents de dissolution organiques, l'alcool amylique a montré les meilleures propriétés extractives, aussi bien sous sa forme pure qu'en mélange avec le chloroforme.Etant donné que le complexe est l'un des plus robustes du tungstène, seuls quelques anions gênent pour effectuer les analyses, et surtout les fluorures. Parmi les cations, après réduction du fer pour laquelle l'acide ascorbique est recommandé, seuls quelques autres sont extraits avec lui; le molybdène présente l'action la plus gênante, il doit être masqué et séparé complètement. Pour le dosage du tungstène, la méthode à l'hydroquinone convient alors le mieux.

     

Tröger's base scaffold in racemic and chiral fashion as a spacer for bisdistamycin formation. Synthesis and DNA binding study

‘Head-to-head’ oligo-N-methylpyrrole peptide dimers linked by a methano[1,5]diazocin scaffold are presented in racemic as well as chiral fashion. Their DNA binding activities were assayed on calf thymus DNA, poly(dA-dT)₂, and poly(dC-dG)₂ by NMR and ECD spectroscopies, and fluorescence probe displacement assay. The presented dimers prefer AT sequences, but show higher affinity to poly(dC-dG)₂ than distamycin A. The (4R,9R) configuration of methanodiazocin bridge was found to be better suited for interaction with ct-DNA and poly(dA-dT)₂ than (4S,9S) configuration.     

Lösungsmitteleinfluß auf das Redoxverhalten von Bistriphenylphosphinquecksilber(II)-perchlorat

The influence of solvents on the redox behaviour of bistriphenylphosphinomercury perchlorate has been investigated by polarographic, voltammetric and potentiometric methods. The electrode process was found to be reversible in acetonitrile, propylene carbonate, N,N-dimethylformamide and dimethyl sulfoxide. An irreversible process was observed in nitromethane employing the dropping mercury electrode as well as in N,N-dimethylthioformamide and N-methyl-2-thiopyrrolidinone employing the rotating platinum electrode. Half wave potentials and diffusion coefficients have been measured. A linear relationship between theE _1/2 and the donor number (DN) of the solvent has been found for the reversible electrode reactions. Ligand replacement occurs in N,N-dimethylthioformamide and N-methyl-2-thiopyrrolidinone.

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Treating singularities present in the Sutcliffe-Tennyson vibrational Hamiltonian in orthogonal internal coordinates

Two methods are developed, when solving the related time-independent Schrodinger equation (TISE), to cope with the singular terms of the vibrational kinetic energy operator of a triatomic molecule given in orthogonal internal coordinates. The first method provides a mathematically correct treatment of all singular terms. The vibrational eigenfunctions are approximated by linear combinations of functions of a three-dimensional nondirect-product basis, where basis functions are formed by coupling Bessel-DVR functions, where DVR stands for discrete variable representation, depending on distance-type coordinates and Legendre polynomials depending on angle bending. In the second method one of the singular terms related to a distance-type coordinate, deemed to be unimportant for spectroscopic applications, is given no special treatment. Here the basis set is obtained by taking the direct product of a one-dimensional DVR basis with a two-dimensional nondirect-product basis, the latter formed by coupling Bessel-DVR functions and Legendre polynomials. With the basis functions defined, matrix representations of the TISE are set up and solved numerically to obtain the vibrational energy levels of H3+. The numerical calculations show that the first method treating all singularities is computationally inefficient, while the second method treating properly only the singularities having physical importance is quite efficient.     

Human topoisomerase I poisoning: docking protoberberines into a structure-based binding site model

Summary Using the X-ray crystal structure of the human topoisomerase I (top1) – DNA cleavable complex and the Sybyl software package, we have developed a general model for the ternary cleavable complex formed with four protoberberine alkaloids differing in the substitution on the terminal phenyl rings and covering a broad range of the top1-poisoning activities. This model has the drug intercalated with its planar chromophore between the −1 and +1 base pairs flanking the cleavage site, with the nonplanar portion pointing into the minor groove. The ternary complexes were geometry-optimized and relative interaction energies, computed by using the Tripos force field, were found to rank in correct order the biological potency of the compounds; in addition, the model is also consistent with the top1-poisoning inactivity of berberine, a major prototype of the protoberberine alkaloids. The model might serve as a rational basis for elaboration of the most active compound as a lead structure, in order to develop more potent top1 poisons as next generation anti-cancer drugs.     

Square-Planar Nickel(II) O,O′-Dialkyldithiophosphato Complexes with Triphenylphosphine of the Type [NiX(S2P{OR}2)(PPh3)] (X = Cl,Br, I and NCS)

A series of new [NiX(S₂P{O-c-Hex}₂)(PPh₃)](X = Cl^–, Br^–, I^– and NCS^–)(1)–(4) and [Ni(NCS)(S₂P{OR}₂)(PPh₃)][R =n-Pr (5), i-Pr (6)] complexes has been synthesized and characterized by elemental analyses, f.i.r., i.r., u.v.–vis., ¹H-, ¹³C{¹H}- and ³¹P{¹H}-n.m.r. spectra, magnetochemical and conductivity measurements. A single crystal X-ray analysis of [Ni(NCS)(S₂P{O-n-Pr}₂)(PPh₃)](5) reveals the molecular structure of the complex and confirms a square-planar geometry around the central atom of nickel with the NCS anion coordinated via the nitrogen atom.