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951.
Zabula AV Spisak SN Filatov AS Grigoryants VM Petrukhina MA 《Chemistry (Weinheim an der Bergstrasse, Germany)》2012,18(21):6476-6484
Bowl-shaped mono- and dianions are prepared by reduction of corannulene (C(20)H(10), 1) with sodium and potassium metals in the presence of [18]crown-6 ether. Single-crystal X-ray diffraction studies of two sodium salts, [Na(THF)(2)([18]crown-6)](+)[1(-)] (2a) and [Na([18]crown-6)](+)[1(-)] (2b), reveal the presence of naked corannulene monoanions 1(-) in both cases. In contrast, the potassium adduct, [K([18]crown-6)](+)[1(-)] (3), shows an η(2)-binding of the K(+) ion to the convex face of 1(-). For the first time, corannulene dianions have been isolated as salts with sodium, [Na(2)([18]crown-6)](2+)[1(2-)] (4a) and [Na(THF)(2)([18]crown-6)](+)[Na([18]crown-6)](+)[1(2-)] (4b), and potassium counterions, [K([18]crown-6)](2)(+)[1(2-)] (5). Their structural characterization reveals geometry perturbations upon addition of two electrons to a bowl-shaped polyarene. It also demonstrates η(5)- or η(6)-binding of metals to the curved carbon surface of 1(2-), depending on the crystallization conditions. Both mono- and doubly-charged corannulene bowls show the preferential exo binding of Na(+) and K(+) ions in all investigated compounds. Various types of C-H···π interactions are found in the crystals of 2-5. The UV/Vis, ESR, and (1)H NMR spectroscopic studies of 2-5 indicate different coordination environment of corannulene anions in solution, depending on the metal ion. 相似文献
952.
Štrukil V Igrc MD Eckert-Maksić M Friščić T 《Chemistry (Weinheim an der Bergstrasse, Germany)》2012,18(27):8464-8473
Mechanochemical methods of neat grinding and liquid-assisted grinding have been applied to the synthesis of mono- and bis(thiourea)s by using the click coupling of aromatic and aliphatic diamines with aromatic isothiocyanates. The ability to modify the reaction conditions allowed the optimization of each reaction, leading to the quantitative formation of chiral bis(thiourea)s with known uses as organocatalysts or anion sensors. Quantitative reaction yields, combined with the fact that mechanochemical reaction conditions avoid the use of bulk solvents, enabled solution-based purification methods (such as chromatography or recrystallization) to be completely avoided. Importantly, by using selected model reactions, we also show that the described mechanochemical reaction procedures can be readily scaled up to at least the one-gram scale. In that way, mechanochemical synthesis provides a facile method to fully transform valuable enantiomerically pure reagents into useful products that can immediately be applied in their designed purpose. This was demonstrated by using some of the mechanochemically prepared reagents as organocatalysts in a model Morita-Baylis-Hillman reaction and as cyanide ion sensors in organic solvents. The use of electronically and sterically hindered ortho-phenylenediamine revealed that mechanochemical reaction conditions can be readily optimized to form either the 1:1 or the 1:2 click-coupling product, demonstrating that reaction stoichiometry can be more efficiently controlled under these conditions than in solution-based syntheses. In this way, it was shown that excellent stoichiometric control by mechanochemistry, previously established for mechanochemical syntheses of cocrystals and coordination polymers, can also be achieved in the context of covalent-bond formation. 相似文献
953.
Pridatchenko ML Perlova TY Ben Hamidane H Goloborodko AA Tarasova IA Gorshkov AV Evreinov VV Tsybin YO Gorshkov MV 《Analytical and bioanalytical chemistry》2012,402(8):2521-2529
The amino acid sequence determines the individual protein three-dimensional structure and its functioning in an organism.
Therefore, “reading” a protein sequence and determining its changes due to mutations or post-translational modifications is
one of the objectives of proteomic experiments. The commonly utilized approach is gradient high-performance liquid chromatography
(HPLC) in combination with tandem mass spectrometry. While serving as a way to simplify the protein mixture, the liquid chromatography
may be an additional analytical tool providing complementary information about the protein structure. Previous attempts to
develop “predictive” HPLC for large biomacromolecules were limited by empirically derived equations based purely on the adsorption
mechanisms of the retention and applicable to relatively small polypeptide molecules. A mechanism of the large biomacromolecule
retention in reversed-phase gradient HPLC was described recently in thermodynamics terms by the analytical model of liquid
chromatography at critical conditions (BioLCCC). In this work, we applied the BioLCCC model to predict retention of the intact
proteins as well as their large proteolytic peptides separated under different HPLC conditions. The specific aim of these
proof-of-principle studies was to demonstrate the feasibility of using “predictive” HPLC as a complementary tool to support
the analysis of identified intact proteins in top-down, middle-down, and/or targeted selected reaction monitoring (SRM)-based
proteomic experiments. 相似文献
954.
Carmona P Molina M Calero M Bermejo-Pareja F Martínez-Martín P Alvarez I Toledano A 《Analytical and bioanalytical chemistry》2012,402(6):2015-2021
Peripheral mononuclear leukocytes from Alzheimer’s disease (AD) patients were analyzed by infrared spectroscopy and their
spectroscopic properties were compared with those from age-matched healthy controls. Two-dimensional correlation analysis
of mean spectra measured at various disease stages shows that the protein secondary structure from AD patients involves β-sheet
enrichment and carbonyl intensity increase relative to healthy controls. The area percentages of β-sheets, which were obtained
by using a peak ratio second-derivative spectral treatment, were used for receiver operating characteristic (ROC) analysis
to distinguish between patients with AD and age-matched healthy controls. The critical concentration and area under the curve
(AUC) were determined by this curve analysis which showed a good performance for this quantitative assay. The results were
90% sensitivity and 90.5% specificity for determinations involving mild and moderate AD patients, and 82.1% sensitivity and
90.5% specificity for determinations involving patients at the three AD stages (mild, moderate, and severe). The AUC was greater
than 0.85 in both scenarios. Taken together these results show that healthy controls are distinguished from mild and moderate
AD patients better than from patients with severe disease and suggest that this infrared analysis is a promising strategy
for AD diagnostics. 相似文献
955.
We study the expectation value of the phase of the fermion determinant for Wilson lattice fermions with chemical potential. We use quenched SU(3) ensembles and implement a recently proposed exact dimensional reduction of the fermion determinant. Ensembles at several temperatures below and above the phase transition are studied and we analyze the role of the quark mass, the temperature, the volume and the topological sectors. We compare our numerical results to predictions from chiral perturbation theory. 相似文献
956.
Marina S. Fonari Eduard V. Ganin Wen‐Jwu Wang 《Acta Crystallographica. Section C, Structural Chemistry》2005,61(7):o431-o433
In the centrosymmetric formula unit of the title complex, C8H16O4·2C18H16S, the 1,4,7,10‐tetraoxacyclododecane molecule adopts the biangular [66] conformation, and the triphenylmethanethiol molecules are linked to the macrocycle via a long S—H⋯O hydrogen bond [S⋯O = 3.460 (2) Å and S—H⋯O = 161 (2)°]. Attractive interactions of phenyl groups in edge‐to‐face conformations combine inversion‐related formula units into chains running along the [111] direction in the crystal structure. Association of the chains into sheets is achieved via C—H⋯π interactions. 相似文献
957.
958.
Irina Malakhova Yuliya Parotkina Marina Palamarchuk Marina Eliseikina Aleksandr Mironenko Alexey Golikov Svetlana Bratskaya 《Molecules (Basel, Switzerland)》2021,26(15)
The feasibility of several approaches to the fabrication of monolith composite cryogels containing transition-metal ferrocyanides for Cs+ ion uptake has been evaluated. Although in the series of investigated metal ion precursors (Cu(II), Zn(II), Ni(II), and Co(II)), in situ formation of the sorption active phase in polyethyleneimine (PEI) cryogel was feasible only in the case of Zn(II) ferrocyanide, this approach has shown significant advantages over the immobilization of ex situ synthesized ferrocyanide nanoparticles. Nanoparticles of the mixed ferrocyanide Zn1.85K0.33[Fe(CN)6] formed in situ had an average size of 516 ± 146 nm and were homogeneously distributed in the monolith located at the polymer surface rather than embedded in the matrix. The Young modulus of the PEI cryogel increased after modification from 25 to 57 kPa, but composites maintained high permeability to the flow. Sorption of Cs+ ions has been investigated at superficial velocity up to 8 m/h. Steep breakthrough profiles and uptake efficiency of >99.5% until breakthrough point confirmed that a supermacroporous structure of the monolith composite assured good mass transfer, so that intraparticle diffusion was not the limiting stage of sorption kinetics. Application of the rate-constant distribution model (RCD model) to analyze the breakthrough curves of Cs+ sorption allowed the identification of two types of sorption sites with a difference in sorption rate constants of ~1 log unit. Most likely, sorption on “fast” sorption sites was governed by ion exchange between Cs+ ions in solution and K+ ions in the ferrocyanide lattice. Cs-137 radionuclide removal was investigated using the monolith composite columns of various geometries at superficial velocity up to the 6.6 m/h; specific gamma activity was reduced from 265 kBq/L to the background level, showing high potential of these materials for POU application. 相似文献
959.
Artem A. Zemtsov Marina I. Struchkova Pavel A. Belyakov Vladimir A. Tartakovsky 《Tetrahedron letters》2009,50(25):2998-7806
A method for the trifluoromethylation of arylidene Meldrum’s acids using Me3SiCF3 followed by transformation of the initial products to CF3-substituted esters and alcohols is described. The sequence of reactions is performed without isolation of intermediate compounds furnishing the final products in good overall yields. 相似文献
960.
Complexes of poly(propylene imine) dendrimers D8[DAB-dendr-(NH2)8] and D32 [DAB-dendr-(NH2)32] were prepared by interaction of the dendrimers with transition metal salts such as FeCl3.6H2O; CoCl2.6H2O; CuCl2.2H2O; VOSO4.5H2O; Na2MoO4.2H2O and Na2WO4.2H2O at room temperature in aqueous solutions. The content of metal ions in the complexes was found to be from 8.2 to 69.6 mg metal ion/g polymer carrier. The complexes were characterized by using IR, UV-VIS, Moessbauer spectroscopy and EPR. The anticipated co-ordination structure of the compounds was suggested. It was found that the order of the catalytic activity of the complexes of poly(propylene imine) dendrimers D8 and D32 in the reaction of epoxidation of cyclohexene with organic hydroperoxides such as tert-butyl hydroperoxide (t-BHP), ethylbenzene hydroperoxide (EBHP) and cumene hydroperoxide (CHP) was as follows: D32-MoО22+>D32-VО2+>D32-WО22+ > D32-Co2+ > D32-Cu2+>D32-Fe3+. The order of reactivity of organic hydroperoxides in the reaction studied was: t-BHP > EBHP > CHP. 相似文献