Synthesis of amphiphilic diacyl derivatives of 3,7-diazabicyclo[3.3.1]nonan-9-one

1. Download high-res image (98KB)
2. Download full-size image

     

Metathesis of ethyl 4-pentenoic acid and its cometathesis with α-olefins

Conclusions A system containing WC1₆ and l,l,3,3-tetramethyl-l,3-disilacyclobutane catalyzes the metathesis of ethyl 4-pentenoic acid and its cometathesis with 1-heptene.Translated from Izvestiya Akademii Nauk SSSR, Seriya Khimicheskaya, No. 11, pp. 2618–2619, November, 1986.     

Colossal magnetoresistance of FexMn1−xS magnetic semiconductors

The magnetic, electric, magnetoresistive, and structural properties are investigated in the sulfide solid solutions Fe_xMn_1−2x S, which are based on the antiferromagnetic semiconductor α-MnS (the fcc NaCl lattice). Colossal negative magnetoresistance (δ_H∼−83% at 160 K for x ∼ 0.29), comparable to that observed in La-Ca-Mn-O polycrystals and films (δ_H∼−90% at 100 K and 40 kOe), is observed in compounds with intermediate concentrations 0.26<x<0.4, corresponding to the region of incipient ferromagnetism. Pis’ma Zh. éksp. Teor. Fiz. 69, No. 12, 895–899 (25 June 1999)     

Synthesis, structure, and properties of supramolecular charge-transfer complexes between bis(18-crown-6)stilbene and ammonioalkyl derivatives of 4,4'-bipyridine and 2,7-diazapyrene

4,4'-Bipyridine and 2,7-diazapyrene derivatives (A) having two ammonioalkyl N-substituents were synthesized. The complex formation of these compounds with bis(18-crown-6)stilbene (D) was studied by spectrophotometry, cyclic voltammetry, (1)H NMR spectroscopy, and X-ray diffraction analysis. In MeCN, π-donor D and π-acceptors A form supramolecular 1:1 (D·A) and 2:1 (D·A·D) charge-transfer complexes. The D·A complexes have a pseudocyclic structure as a result of ditopic binding of the ammonium groups to the crown-ether fragments. The better the geometric matching between the components, the higher the stability of the D·A complexes (log K up to 9.39). A key driving force of the D·A·D complex formation is the excessive steric strain in the precursor D·A complexes. The pseudocyclic D·A complexes involving the ammoniopropyl derivative of 4,4'-bipyridine were obtained as single crystals. Crystallization of the related ammonioethyl derivative was accompanied by transition of the D·A complexes to a structure of the (D·A)(m) coordination polymer type.     

Spectral properties and supramolecular inclusion complex formation between 2-styrylbenzothiazolium dye and cyclodextrins

The effect of native and randomly methylated β-CDs on the absorption and steady-state fluorescence spectra of 2-(4-dimethylaminostyryl)-3-(2-hydroxyethyl)-benzothiazolium chloride (DHB) in aqueous buffer solutions with various pH values was studied. The inclusion with both CDs at pH 7.2 barely changed the UV spectra, whereas significant variations were produced in the emission spectra in all buffer solutions. In all cases the CDs increase guest fluorescence. The 1:1 stoichiometry of the inclusion complexes of the dye with both CDs was established according to the modified Benesi-Hildebrand method. Binding constant values were calculated using the iterative nonlinear least-squares regression approach. The pH of the solution and the type of the CD affected complex stability. The results indicate that native β-CD possesses better complexing ability towards DHB than randomly substituted β-CD and that the most stable inclusion complexes are formed in basic medium because of the structural changes in the guest molecule. In basic medium an attempt is made to interpret the proposed mechanism in terms of molecular rearrangement which take place as the dye penetrates the CD cavity.     

EPR study of the Jahn-Teller effect of Cu2+ ions in ZnGa2O4

The Jahn-Teller effect in the ZnGa₂O₄ spinel single crystal has been investigated using electron paramagnetic resonance of Cu²⁺ ions in the temperature range 110–560 K. It has been shown that copper ions occupy octahedral sites 16d in the ZnGa₂O₄ crystal with cubic symmetry O _h ⁷ (Fd-3m). At T < 560 K, the octahedra undergo tetragonal distortions (predominantly tension) and rotation around the fourfold axes by the angle θ ≈ 2.6°. The parameters of the spin Hamiltonian, which characterize the prolate (g _‖ = 2.355, g _⊥ = 2.077, A _‖ = 116 Oe, A _tp = 12 Oe) and oblate (g _‖ = 2.018, g _⊥ = 2.246, A _‖ = 75 Oe, A _⊥ = 44 Oe) octahedra, have been determined. At temperatures above 560 K, the static Jahn-Teller effect transforms into the dynamic effect and the spectrum of the magnetic resonance becomes isotropic with g = 2.116 (the experimental frequency corresponds to the X band).     

Calorimetric and x-ray diffraction studies of the (NH4)3WO3F3 and (NH4)3TiOF5 perovskite-like oxyfluorides

The heat capacity and unit cell parameters of the (NH₄)₃WO₃F₃ and (NH₄)₃TiOF₅ perovskite-like oxyfluorides were measured in the temperature interval from 80 to 300 K; the existence of two and one phase transitions in these compounds, respectively, was demonstrated, and their thermodynamic parameters were determined. The effect of a hydrostatic pressure of up to 0.5 GPa on the phase transition temperatures was studied. Triple points and high-pressure phases were found in the T vs. p diagrams. An analysis of entropy changes suggests that all the structural transformations revealed are associated with the ordering of structural blocks. __________ Translated from Fizika Tverdogo Tela, Vol. 46, No. 5, 2004, pp. 888–894. Original Russian Text Copyright ? 2004 by Flerov, Gorev, Fokina, Bovina, Laptash.     

Photophysical behaviours of some 2-styrylindolium dyes in aqueous solutions and in the presence of cyclodextrins

Host–guest inclusion type association between native β-cyclodextrin and randomly substituted methyl-β-CD and two 2-styrylindolium cationic dyes, e.g. 1,3,3-trimethyl-2-(4-diethylaminostyryl)-3H-indolium iodide (D1) and 1,3,3-trimethyl-2-[4-(N-2-cyanoethyl,N-methyl)-aminostyryl]-3H-indolium iodide (D2), are reported. The described indolium derivatives belong to the rarely investigated class of unsymmetrical polymethines. The complex formation was studied in aqueous buffer solutions with two pH values (7.2 and 3) by means of absorption and steady-state fluorescence spectroscopy. The association equilibrium constant (K), the molar absorptivity and the stoichiometry of the complexes were evaluated using the modified Benesi-Hildebrand approach. The complex stability was affected by the pH of the solution and by the type of CD. The results obtained indicate that D1 forms 1:1 complexes with both β-CD and Me-O-β-CD, whereas D2 does not form stable complexes with Me-O-β-CD and in acidic medium. The fluorescent intensity of D1 in the presence of CDs increases over four times relative to the intensity of the pure dye solutions, presumably via inclusion of the dye into the cyclodextrin cavity due to rigidity of the structure.     

Synthesis and properties of Mn1−XFeXS single-crystals at room temperature

Results of the first synthesis of Mn_1−XFe_XS single-crystals and its structural, electrical and magnetic properties at room temperature are presented. The Mn²⁺→Fe²⁺ substitution in Mn_1−XFe_XS solid solutions is accompanied by a compression of the NaCl lattice and a small deformation of the octahedral environments, and the concentration transition from dielectric to semimetal. Single-line Mossbauer spectra indicate the paramagnetic state Mn_1−XFe_XS sulfides at room temperature.