Complexation and Self-Assembling of Sulfonatomethylated Calix[4]resorcinarene with Both Organic and Lanthanide Ions in Aqueous Media

The stoichiometry and binding constant of the paramagnetic lanthanide ion(Gd³⁺) with sulfonatomethylated calix[4]resorcinarene (H₈Xna₄) were evaluated from the NMR relaxation data. Both ¹H NMR spectroscopy and NMR relaxation data indicate that interaction of tetramethylammonium (TEMA) and N-methylpyridinium (MePy) cations with H₈Xna₄ in the presence of Ln³⁺ (Lu³⁺ or Gd³⁺) results in theformation of ternary complexes [Ln(G)H₈X] with lanthanide ions,coordinated via sulfonate groups and organic cation included intothe cavity of H₈Xna₄. The inclusion of long-chainedN-decyl-(DePy) and N-cetylpyridinium (CPy) ions into H₈Xna₄ cavity leads to self-assembling which can be revealed by NMR relaxation method with Gd³⁺ probe ions. The excess of alkylpyridinium or TEMA cations leads to disassembling of (Gd)_n(H₈X)_m(RPy)_maggregates.     

Structural and electronic properties of phosphino(oligothiophene) gold(I) complexes

A series of gold(I) complexes containing phosphino(oligothiophene) ligands of varying conjugation length has been prepared. Solid state crystal structures of (PT3)AuCl (PT3 = 5-diphenylphosphino-2,2':5',2' '-terthiophene) and AuCl(PTP)AuCl (PTP = 2,5-diphenylphosphinothiophene) have been obtained. The complex AuCl(PTP)AuCl crystallizes as a dimer with two intermolecular Au-Au contacts. Variable temperature NMR spectroscopy is used to demonstrate the presence of aurophilic interactions in solution for AuI(PTP)AuI. Dual emission is observed for AuCl(PTP)AuCl in solution and is attributed to emission from both monomer and dimer. In the solid state, dimer emission is dominant. The iodo analogue, AuI(PTP)AuI, shows only low energy dimer emission in both solution and the solid state. Compounds in which the ligands contain longer bridges (either bithienyl or terthienyl) show absorption and emission bands due to the pi-pi* transition only, both in solution and the solid state.     

Photochemische Reaktionen. 85. Mitteilung [1]. Zur Photochemie von α, β-Epoxy-eucarvon

Photochemistry of α,β-epoxy-eucarvone . On π,π^*-excitation (λ = 254 nm) 4 isomerizes to the bicyclic ketoaldehyde 5 ; on n,π^*-excitation (λ ? 280 nm) 4 gives 5 , the β,γ-unsaturated ketone 6 , the enone 7 and the cyclobutanone 8 . Scission of the (C—C)-bond of the oxirane 4 would give the dihydrofurane e , which could isomerize to the ketoaldehyde 5 . On the other hand, 4 is assumed to isomerize to the β,γ-unsaturated aldehyde c , which could yield 6 and 7 by photodecarbonylation. The cyclo-butanone 8 is shown to be a photoisomer of the ketone 6 . Furthermore, eucarvol ( 18 ) rearranges by a thermal [1,5]-H-shift to dihydro-eucarvone ( 20 ); on UV.-irradiation 18 gives the bicyclic isomers 27 and 28 .     

Conformation of Some Anomeric O-Benzylated D-gluco-, L-Ido-, and Hex-4-enopyranoside derivatives

By use of ¹H-NMR. spectroscopy it is shown that in the anomeric tri-O-benzyl derivatives of D -gluco- and L -idopyranosides the C(5) (aliphatic) substituent has a strong tendency to assume an equatorial position. The conformer (⁴C₁ or ¹C₄) with C(6) in equatorial position is favoured, even if other bulky substituents are forced to occupy an axial position; the same effect is observed in some anomeric O-benzylated 6-deoxy-L -idopyranoside derivatives. If, however, the tetragonal configuration of the saturated C(5) is changed into a trigonal (sp²) configuration, e.g. in the anomers of 1,2,3-tri-O-benzylated L -threo-hex-4-enopyranosiduronates, the C(5)–C(6) bond no longer determines the equilibrium of (distorted) pyranoid conformations; the anomeric (‘Eduard-Lemieux’) effect then becomes important in the stabilization of the corresponding half-chair (¹H₂ or ²H₁) conformations.     

Untersuchungen zum System Te/O/Br

Investigations on the System Te/O/Br The melting point diagram of the system TeBr₄? TeO₂ was obtained by total pressure measurements and DTA measurements. A Congruent melting composition Te₆O₁₁Br₂ exists, the melting point is 570°C. The enthalpy of formation and the standard entropy of the species TeOBr₂,g was derived from measurements of the total pressure over Te₆O₁₁Br₂/TeBr₄ and from the transport behaviour of the TeO₂ with Br₂. From the decomposition-pressure measurements over Te₆O₁₁Br₂/TeO₂ follow the partial pressure. The enthalpy of formation ΔH°(Te₆O₁₁Br₂,f,298) = ?453.5 kcal/Mol was obtained from the enthalpy of solution. The transport-behaviour of TeO₂ with HBr, with Tebr₄ and Br₂ and that of Te₆O₁₁Br₂ is clear with the thermodynamic data of TeObr₂.     

Nucleophilic aromatic substitution of activated cationic groups by 18F-labeled fluoride. A useful route to no-carrier-added (NCA) 18F-labeled aryl fluorides

A method is described for the rapid preparation of no-carrier-added (NCA) ¹⁸F-labeled aryl fluorides by treatment of the corresponding aryltrimethylammonium perchlorates with ¹⁸F-labeled fluoride in DMSO. The basic features of the ¹⁸F-for-⁺NMe₃ displacement process are evaluated as a function of the experimental variables and compared with related substitution routes to NCA ¹⁸F-labeled aryl fluorides. The relative nucleofugicity of the ammonium group in the nucleophilic substitution reactions surpasses that of the best neutral leaving groups, including NO₂ and F itself. In contrast, radiofluoride incorporation into aromatic rings $\text{via}$ other cationic substrates, such as aryldimethylsulfonium perchlorates, is prevented by the fast methyl group transfer from the starting compound to the nucleophiles present. The use of the ammonium function as a leaving group in nucleophilic substitutions by ¹⁸F^? may give access to the rapid preparation of novel NCA ¹⁸F-radiopharmaceuticals by facilitating the synthesis and the purification of their labeled precursors.     

Electrochemical dimerization of 2-(2'-thienyl)pyridine adsorbed on Au(111) observed by in situ fluorescence

The study of heterodentate molecules adsorbed on metal electrodes provides an opportunity to expand the functionality of modified surfaces while offering insights into the surface and intramolecular electronic interactions of organic adsorbates. The adsorption of 2-(2'-thienyl)pyridine, a molecule containing both pyridine and thiophene moieties, on a Au(111) electrode is reported. Adsorption was characterized by electrochemistry in neutral and basic aqueous electrolyte and was compared to that of pyridine. The aqueous electrochemistry of thiophene on Au(111) was also characterized for comparison purposes. At negative potentials, in the presence of 2-(2'-thienyl)pyridine, a diffuse, pi-bonded monolayer was formed, and a phase transition to a close-packed N- and/or S-bonded configuration was observed near -0.4 V in a 1 mM solution of adsorbate, similar to that seen in pyridine on Au(111). The thiophene-like oxidative dimerization of the molecule was confirmed at positive potentials using in situ fluorescence microscopy by comparison with the spectrum of the chemically synthesized dimer.     

Über die Hölderstetigkeit schwacher Lösungen semilinearer elliptischer Systeme mit einseitiger Bedingung

This paper deals with the question if bounded weak solutions of elliptic systems