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181.
R. Alan Aitken Nouria A. Al‐Awadi Graham Dawson Osman El‐Dusouqui Kamini Kaul Ajith Kumar 《国际化学动力学杂志》2007,39(1):6-16
A series of five [(acetyl)(arylcarbabmoyl)methylene]triphenyl‐phosphoranes 1a–e and their thiocarbamoyl analogues 2a–e , [(alkoxycarbonyl)(arylcarbamoyl)methylene]triphenylphosphoranes 3a–e and their thiocarbamoyl analogues 4a–e were prepared and fully characterized. All ylides are found under conditions of flash vacuum pyrolysis to fragment giving arylisocyanate or isothiocyanate and acetyl ylides or alkoxy ylides which undergo thermal extrusion of Ph3PO. A kinetic study shows that these reactions are unimolecular and are of first‐order nature with no significant substituent effect. The thiocarbamoyl ylides 2 react from 4.6 to 42 times faster than their carbamoyl ylides 1 , while the thiocarbamoyl ylides 4 react from 6.6 to 20.9 times faster than their carbamoyl ylides 3 . © 2006 Wiley Periodicals, Inc. Int J Chem Kinet 39: 6–16, 2007 相似文献
182.
The synthesis and characterization of nine coordination networks based on 1,3-bis(phenylthio)propane, L(3), and silver(I) salts of PF(6)(-) (1), CF(3)COO(-) (2), CF(3)CF(2)COO(-) (3), CF(3)CF(2)CF(2)COO(-) (4), p-TsO(-) (5, 6), and CF(3)SO(3)(-) (7-9) are reported. Only 1 and other "isostructural" complexes with weakly coordinating anions such as ClO(4)(-) and SbF(6)(-) are of the host-guest type. In all the other complexes, the anions and the acetone molecules, when present, are coordinated to the metal. Most of the complexes studied here form a 2D-coordination network. Only 4 and 5 adopt a polymer-like chain structure. The packing of the chains of 4 is pseudohexagonal compact, while that of 5 is of the centered type. In complex 1, the silver atom is tetrahedrally coordinated to the sulfur atoms of four different ligands. The PF(6)(-) anions and acetone molecules, sandwiched between silver-ligand cationic sheets, are held through van der Waals interactions. In each of the three perfluorocarboxylates (2-4), two silver atoms are joined by the anions in a diatomic bridging mode. The Ag...Ag distances are sufficiently short to indicate weak metal...metal interactions. The dimeric units in 2 and 3 are interconnected through the ligands, thereby generating a 2D-network of neutral sheets, while, in 4, the dimeric units are bound to four ligands and a 1D-coordination polymer is generated. In the case of the sulfonate anions (p-TsO(-) and CF(3)SO(3)(-)), the crystallization solvent influences the structure adopted. Thus, in 5, 7, and 9 obtained from petroleum ether, or other nonpolar solvents, two silver atoms are bound in a double-bridge fashion, while a monobridge mode is noted for 6 and 8, both recrystallized from diethyl ether. In 8, both bridging types are observed. The thermogravimetric investigation, in the room temperature-450 degrees C interval, of complexes 1, 3, and 7, which incorporate acetone molecules in their crystal structures, reveals a two-step weight loss for 1 (the acetone molecules are lost first followed by the ligands, leaving behind the silver salt), while complexes 3 and 7 decompose in a single step to metallic silver. 相似文献
183.
Summary. The reaction of 3,3-diphenylindan-1,2-dione with trimethyl phosphite in dry benzene at room temperature for about 15 h led
to the formation of a mixture containing dimethyl (3,3-diphenyl-2-methoxy-1-indenyl)phosphate and dimethyl (3,3-diphenyl-1H-2-oxo-1-indanyl)phosphate, whereas with triisopropyl phosphite, diisopropyl (3,3-diphenyl-2-isopropoxy-1-indenyl)phosphate
is the only product. Treatment of the dione with dialkyl phosphites under different experimental conditions gave dialkyl (3,3-diphenyl-1-hydroxy-2-oxo-1-indanyl)phosphates.
Reaction mechanisms are presented which account for the experimental results. Structural assignments of the new compounds
are based on the spectroscopic evidences and two examples were elucidated by X-ray crystallography. 相似文献
184.
Imamoglu Mustafa Aydin Ali Osman Dundar Mustafa S. 《Central European Journal of Chemistry》2005,3(2):252-262
A preconcentration method of gold, palladium and copper based on the sorption of Au (III), Pd (II) and Cu (II) ions on a column
packed with 3-(2-aminoethylamino)propyl bonded silica gel is described. The modified silica gel was synthesized and characterized
by FT-IR and C, H, N elemental analysis. At column preconcentration, the effects of parameters such as pH, volume, flow rate,
matrix constituents of solutions and type of eluent on preconcentration of gold, palladium and copper were studied. The recoveries
of Au (III), Pd (II) and Cu (II) were 98.93±0.51, 98.81±0.36 and 99.21±0.42 % at 95 % confidence level, respectively. The
detection limits (δ) of the elements were 0.032, 0.016 and 0.012 μg ml−1, respectively. The preconcentration method was applied for determination of gold and palladium in certified reference material
SARM 7B and copper in river and synthetic seawater by FAAS. Gold, palladium and copper were determined with relative error
lower than 10 %. 相似文献
185.
The X-ray crystal structure analysis of the title compound, exo,exo-2,3-endo,endo-5,6-tetrabromobicycloheptane, C7H8Br4, which is a product of high temperature bromination of norbornadiene, shows that the skeleton of the molecule is not changed after two bromine molecules are added via successive bromination reactions. The addition of Br2 to both double bonds occurs (contrary to our expectation) in a syn fashion. It crystallizes in the orthorhombic space group Pbca with a = 15.688(2), b = 13.345(2), c = 9.461(1) Å, V = 1980.7(3) Å3, Z = 8 and Dx = 2.762 gcm–3. 相似文献
186.
Arnaud J. A. Soirat Chung F. Wong Roman Osman Harel Weinstein 《Journal of computational chemistry》1997,18(7):888-901
As a first step toward developing simulation models for studying the indirect mechanism of radiation damage to DNAs, we have carried out Brownian dynamics simulations to study the reactions of hydrated electrons with a 12-base-pair B-DNA, (dA)12(dT)12, and with bases, monodeoxynucleotides, and polydeoxynucleotides. We first studied in detail the sensitivity of diffusion reaction rate constants to different model and simulation parameters. Based on the sensitivity studies, a set of model and simulation parameters was obtained for the final production runs. The use of this set of parameters reduced the computational costs but delivered reasonably reliable results. The calculated reaction rate constants were in qualitative agreement with experiments. For the DNA double-helix, (dA)12(dT)12, the simulations demonstrated that hydrated electrons preferred to attack the two ends of the double-helix. Electrostatic interactions between the DNA and the hydrated electrons make the T strand more susceptible to attack than the A strand. The increased reactivity of the T strand due to electrostatic interactions results from the increased reactivity of the C6 sites of the thymine bases, at the expense of the reactivity of the C8 sites of the adenine bases. The reactivity of the relatively buried reactive sites of the adenine and thymine bases are less affected by electrostatic interactions. © 1997 by John Wiley & Sons, Inc. J Comput Chem 18: 888–901, 1997 相似文献
187.
The rates of gas-phase elimination reactions of methyl benzoylformate ( 1 ) and 3-hydroxy-3-methyl-2-butanone ( 2 ) were obtained at T = 600 K. The two substrates undergo unimolecular first-order elimination for which the Arrhenius equations are, respectively, log k = 13.2 − 53270/(4.574 × 600) for ( 1 ) and log k = 12.4 − 53060/(4.574 × 600) for ( 2 ). The products of pyrolysis of ( 1 ) are benzaldehyde, formaldehyde and CO, while those of ( 2 ) are acetaldehyde and acetone. The kinetics of the elimination reactions show benzoylformic acid to be 106-fold more reactive than ( 1 ), and pyruvic acid ca. 105-fold more reactive relative to ( 2 ); an indication of the rate-controlling part played by the acidity of the hydrogen atom involved in the elimination process of the present compounds in this particular type of reaction. © 1997 John Wiley & Sons, Inc. Int J Chem Kinet 29: 295–298, 1997. 相似文献
188.
Effects of the three-nucleon forces on the triton binding energy are investigated using different models for which the xN scattering amplitudes for the off-mass-shell pions are extrapolated from the on-mass-shell data. In the independent model potential, the threenucleon forces are constructed using the chiral symmetry through partial conservation of the axial current vectors and current algebra. On the other hand, the three-nucleon forces in the dependent model potential are derived from an effective Lagrangian which is constrained by chiral and gauge symmetry. The effect of the long range 2π and the repulsive ap-exchange three-nucleon forces on the triton binding energy are investigated. The bound state triton binding energies are then calculated by solving the Faddeev equations with a Hamiltonian including the three-nucleon forces, using different nucleon-nucleon interactions. The pionic form factors are considered with different sets of the form factor cutoff,parameter Λ. The 2π-exchange forces with S- and P-wave amplitudes are found to overbind the triton binding energy by about 0.4~Y 1.6 MeV. However, xp-exchange forces are found to reduce the 2π exchange forces by about 18% of its contribution, to the triton binding energy. 相似文献
189.
Tamera D. Hughes Osman F. Güner Emma Carine Iradukunda Robert S. Phillips J. Phillip Bowen 《Molecules (Basel, Switzerland)》2022,27(1)
Under normal physiological conditions, the kynurenine pathway (KP) plays a critical role in generating cellular energy and catabolizing tryptophan. Under inflammatory conditions, however, there is an upregulation of the KP enzymes, particularly kynurenine 3-monooxygenase (KMO). KMO has garnered much attention due to its production of toxic metabolites that have been implicated in many diseases and disorders. With many of these illnesses having an inadequate or modest treatment, there exists a need to develop KMO inhibitors that reduce the production of these toxic metabolites. Though prior efforts to find an appropriate KMO inhibitor were unpromising, the development of a KMO crystal structure has provided the opportunity for a rational structure-based design in the development of inhibitors. Therefore, the purpose of this review is to describe the kynurenine pathway, the kynurenine 3-monooxygenase enzyme, and KMO inhibitors and their potential candidacy for clinical use. 相似文献
190.
Sayed E. El-Sayed Neveen A. Abdelaziz Hosam-Eldin Hussein Osman Ghadir S. El-Housseiny Ahmed E. Aleissawy Khaled M. Aboshanab 《Molecules (Basel, Switzerland)》2022,27(1)
Resistance to antifungal agents represents a major clinical challenge, leading to high morbidity and mortality rates, especially in immunocompromised patients. In this study, we screened soil bacterial isolates for the capability of producing metabolites with antifungal activities via the cross-streak and agar cup-plate methods. One isolate, coded S6, showed observable antifungal activity against Candida (C.) albicans ATCC 10231 and Aspergillus (A.) niger clinical isolate. This strain was identified using a combined approach of phenotypic and molecular techniques as Lysinibacillus sp. . The purified metabolite displayed fungicidal activity, reserved its activity in a relatively wide range of temperatures (up to 60 °C) and pH values (6–7.8) and was stable in the presence of various enzymes and detergents. As compared to fluconazole, miconazole and Lamisil, the minimum inhibitory concentration of the metabolite that showed 90% inhibition of the growth (MIC90) was equivalent to that of Lamisil, half of miconazole and one fourth of fluconazole. Using different spectroscopic techniques such as FTIR, UV spectroscopy, 1D NMR and 2D NMR techniques, the purified metabolite was identified as terbinafine, an allylamine antifungal agent. It is deemed necessary to note that this is the first report of terbinafine production by Lysinibacillus sp. MK212927, a fast-growing microbial source, with relatively high yield and that is subject to potential optimization for industrial production capabilities. MK212927相似文献