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121.
Franco Benetollo Gabriella Bombieri Giuseppe Alonzo Nuccio Bertazzi 《Journal of chemical crystallography》1995,25(2):89-92
The synthesis and the crystal and molecular structure of the difluoro(hydroxodi-2-pyridylmethoxo-NNO) antimony(III) compound determined by single crystal X-ray diffraction analysis are reported. Crystals are orthorhombic, space group Pbcn,a=12.732(2),b=12.165(2),c=15.936(2) Å. Refinement based on 1516 observed reflections led to a finalR value of 0.025 (Rw=0.028). In the crystal the di-2-pyridyl ketone behaves asfacial-(NNO)-terdentate in the Sb coordination, the square pyramid geometry around the metal is completed by the coordination of two fluorine atoms. 相似文献
122.
Markt P McGoohan C Walker B Kirchmair J Feldmann C De Martino G Spitzer G Distinto S Schuster D Wolber G Laggner C Langer T 《Journal of chemical information and modeling》2008,48(8):1693-1705
The cysteine protease cathepsin S (CatS) is involved in the pathogenesis of autoimmune disorders, atherosclerosis, and obesity. Therefore, it represents a promising pharmacological target for drug development. We generated ligand-based and structure-based pharmacophore models for noncovalent and covalent CatS inhibitors to perform virtual high-throughput screening of chemical databases in order to discover novel scaffolds for CatS inhibitors. An in vitro evaluation of the resulting 15 structures revealed seven CatS inhibitors with kinetic constants in the low micromolar range. These compounds can be subjected to further chemical modifications to obtain drugs for the treatment of autoimmune disorders and atherosclerosis. 相似文献
123.
124.
Siani G Angelini G De Maria P Fontana A Pierini M 《Organic & biomolecular chemistry》2008,6(22):4236-4241
The rates of tautomerization of 2-nitrocyclohexanone (2-NCH) have been measured spectrophotometrically at 25.0 +/- 0.1 degrees C in several organic aprotic solvents and their binary mixtures. In cyclohexane the reaction is effectively catalyzed by bases and inhibited by acids while the so-called "spontaneous reaction" appears essentially due to autocatalysis. Apparent second order rate constants (k(app)(B)) for the reaction catalyzed by triethylamine (TEA) and pyridine (Pyr) have been obtained. From the experimental k(app)(B) values rate constants for the enolization (k(1)(B)) and ketonization (k(-1)(B)) reactions have been calculated. A Kamlet-Taft type linear solvation energy relationship (LSER) adequately accounts for the observed solvent effects. Activation parameters for both reactions show that solvent effects are mainly entropic in origin and that there is a shift of the transition state from a ketone-like to an enol-like structure on passing from less to more polar solvents. 相似文献
125.
Yasser M. Loksha Daniel Globisch Erik B. Pedersen Paolo La Colla Gabriella Collu Roberta Loddo 《Journal of heterocyclic chemistry》2008,45(4):1161-1166
126.
Onel L Bourceanu G Wittmann M Noszticzius Z Szabó G 《The journal of physical chemistry. A》2008,112(46):11649-11655
A recent report on an intense CO 2 and CO evolution in the Briggs-Rauscher (BR) reaction revealed that iodination of malonic acid (MA) is not the only important organic reaction in the classical BR oscillator. To disclose the source of the gas evolution, iodomalonic (IMA) and diiodomalonic (I2MA) acids were prepared by iodinating MA with nascent iodine in a semibatch reactor. The nascent iodine was generated by an iodide inflow into the reactor, which contained a mixture of MA and acidic iodate. Some CO2 and a minor CO production was observed during these iodinations. It was found that in an aqueous acidic medium the produced I2MA is not stable but decomposes slowly to diiodoacetic acid and CO2. The first-order rate constant of the I 2MA decarboxylation at 20 degrees C was found to be k1 = 9 x 10(-5) s(-1), which is rather close to the rate constant of the analogous decarboxylation of dibromomalonic acid under similar conditions (7 x 10(-5)s(-1)). From the rate of the CO2 evolution, the I2MA concentration can be calculated in a MA-IMA-I2MA mixture as only I2MA decarboxylates spontaneously but MA and IMA are stable. Following CO2 evolution rates, it was proven that I2MA can react with MA in the reversible reaction I2MA + MA <--> 2 IMA. The equilibrium constant of this reaction was calculated as K = 380 together with the rate constants of the forward k 2 = 6.2 x 10 (-2) M (-1)s(-1) and backward k-2 = 1.6 x 10(-4) M(-1)s(-1) reactions. The probable mechanism of the reaction is I(+1) transfer from I2MA to MA. The presence of I(+1) in a I2MA solution is demonstrated by its reduction with ascorbic acid. To estimate the fraction of CO2 coming from the decarboxylation of I2MA in an oscillatory BR reaction, the oscillations were inhibited by resorcinol. Unexpectedly, all CO2 and CO evolution was interrupted for more than one hour after injecting a small amount of resorcinol (10(-5) M initial concentration in the reactor). Finally, some implications of the newly found I(+1) transfer reactions and the surprisingly effective inhibition by resorcinol regarding the mechanism of the oscillatory BR reaction are discussed. The latter is explained by the ability of resorcinol to scavenge free radicals including iodine atoms without producing iodide ions. 相似文献
127.
Let m ≥ 1 be an integer and N > 2m. Let μ be a positive Radon measure on . We study necessary and sufficient conditions on possible distributional solutions of , that guarantee the validity of the representation formula a.e. on , where and c(2m) is a positive constant depending on m and N. Several consequences are derived. In particular we prove Liouville theorems for systems of higher order elliptic inequalities
and weighted form of Hardy-Littlewood-Sobolev systems of integral equations.
Received: March 2008 相似文献
128.
Inductively coupled plasma mass spectrometry (ICP-MS) is a suitable tool for multi-element analysis at low concentration levels. Rare earth element (REE) determinations in standard reference materials and small volumes of molten ice core samples from Antarctica have been performed with an ICP-time of flight-MS (ICP-TOF-MS) system. Recovery rates for REE in e.g. SPS-SW1 amounted to ∼103%, and the relative standard deviations were 3.4% for replicate analysis at REE concentrations in the lower ng L−1 range. Analyses of REE concentrations in Antarctic ice core samples showed that the ICP-TOF-MS technique meets the demands of restricted sample mass. The data obtained are in good agreement with ICP-Quadrupole-MS (ICP-Q-MS) and ICP-Sector Field-MS (ICP-SF-MS) results. The ICP-TOF-MS system determines accurately and precisely REE concentrations exceeding 5 ng L−1 while between 0.5 and 5 ng L−1 accuracy and precision are element dependent. 相似文献
129.
Gabriella Cavallo Giancarlo Terraneo Alessandro Monfredini Marco Saccone Arri Priimagi Tullio Pilati Giuseppe Resnati Pierangelo Metrangolo Duncan W. Bruce 《Angewandte Chemie (Weinheim an der Bergstrasse, Germany)》2016,128(21):6408-6412
Unconventional ionic liquid crystals in which the liquid crystallinity is enabled by halogen‐bonded supramolecular anions [CnF2 n+1‐I⋅⋅⋅I⋅⋅⋅I‐CnF2 n+1]− are reported. The material system is unique in many ways, demonstrating for the first time 1) ionic, halogen‐bonded liquid crystals, and 2) imidazolium‐based ionic liquid crystals in which the occurrence of liquid crystallinity is not driven by the alkyl chains of the cation. 相似文献
130.
Cuccurullo M Schlosser G Cacace G Malorni L Pocsfalvi G 《Journal of mass spectrometry : JMS》2007,42(8):1069-1078
Reversible protein phosphorylation mediated by protein kinases and phosphatases is the most studied post-translational modification. Efficient characterization of phosphoproteomes is hampered by (1) low stoechiometry, (2) the dynamic nature of the phosphorylation process and (3) the difficulties of mass spectrometry to identify phosphoproteins from complex mixtures and to determine their sites of phosphorylation. Combination of the phosphopeptide enrichment method with MALDI-TOFMS, or alternatively, with HPLC-ESI-MS/MS and MS(3) analysis was shown to be a step forward for the successful application of MS in the study of protein phosphorylation. In our study we used phosphopeptide enrichment performed in a simple single-tube experiment using zirconium dioxide (ZrO(2)). A simple protein mixture containing precipitated bovine milk caseins was enzymatically digested and the mixture of tryptic fragments was analysed before and after enrichment using nanoflow HPLC-ESI-MS/MS and surface-enhanced laser desorption/ionization (SELDI)-MS/MS on QqTOF instruments to compare the efficiency of the two methods in the determination of phosphorylation sites. Both approaches confirm the high selectivity obtained by the use of batch-wise, ZrO(2)-based protocol using di-ammonium phosphate as the eluting buffer. More phosphorylation sites (five for beta-casein and three for alpha(S1)-casein) were characterized by SELDI-MS/MS than by nanoflow HPLC-ESI-MS/MS. Therefore, ZrO(2)-based phosphopeptide enrichment combined with SELDI-MS/MS is an attractive alternative to previously reported approaches for the study of protein phosphorylation in mixtures of low complexity with the advance of fast in situ peptide purification. The method was limited to successful analysis of high-abundance proteins. Only one phosphorylation site was determined for the minor casein component alpha(S2)-casein by ESI-MS/MS and none for kappa-casein. Therefore an improvement in enrichment efficiency, especially for successful phosphoproteomic applications, is needed. 相似文献