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11.
[reaction: see text] The highly strained cyclic allene 2,3-didehydro-2H-thiopyran was generated by irradiation of matrix-isolated 2-benzothienylchlorocarbene and characterized by IR and UV/vis spectroscopy, in situ trapping, and DFT modeling. Calculations indicate that the allenic moiety in this system, although less aromatic in character, is relatively more stable than in the corresponding oxa system. It is suggested that the thio ring system can more readily accommodate the allenic geometry. 相似文献
12.
Ivan Petkov Asya Petinova Stanimir S. Stoyanov Stefan Metsov Stefan I. Stoyanov 《Journal of inclusion phenomena and macrocyclic chemistry》2008,60(3-4):329-338
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. 相似文献
13.
Asya Petinova Stefan Metsov Ivan Petkov Stefan Stoyanov 《Journal of inclusion phenomena and macrocyclic chemistry》2007,59(1-2):183-190
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. 相似文献
14.
Vedernikov AI Ushakov EN Efremova AA Kuz'mina LG Moiseeva AA Lobova NA Churakov AV Strelenko YA Alfimov MV Howard JA Gromov SP 《The Journal of organic chemistry》2011,76(16):6768-6779
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. 相似文献
15.
Galina Abramova Juerg Schefer Nadir Aliouane Martin Boehm German Petrakovskiy Alexandr Vorotynov Mikhail Gorev Asya Bovina Vladimir Sokolov 《ChemInform》2015,46(22):no-no
Single crystals of the α-MnS-based FexMn1-xS (x = 0-0.3) solid solutions are prepared and shown to be new Mott materials with the rock salt structure. 相似文献