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991.
Daniele Cauzzi Roberto Giordano Enrico Sappa Antonio Tiripicchio Marisa Tiripicchio Camellini 《Journal of Cluster Science》1993,4(3):279-296
The title complex (complex1) was the first alkyne-substituted triruthenium dihydrido cluster to be reported and was characterized by spectroscopy as a triangular cluster with the alkyne parallel to a Ru-Ru edge. Recently, we have found that1 is a key intermediate in the homogeneous hydrogenation of diphenylacetylene catalyzed by tetrahedral Ru4 and FeRu3 clusters. Since the discovery of1, a great number of complexes with alkynes parallel to a cluster edge have been reported; at present this is the more common bonding mode for alkynes on trinuclear clusters. The structural features of1 allow a comparison with those of other ruthenium-containing derivatives and help to draw suggestions of the role of1 in hydrogenation catalysis. 相似文献
992.
Guidoboni E de los Rios I Ienco A Marvelli L Mealli C Romerosa A Rossi R Peruzzini M 《Inorganic chemistry》2002,41(4):659-668
Reaction of [(triphos)Re(CO)(2)(OTf)] (1) [triphos = MeC(CH(2)PPh(2))(3); OTf = OSO(2)CF(3)] with P(4)S(3) and P(4)Se(3) yields pairs of coordination isomers, namely, [(triphos)Re(CO)(2)[eta(1)-P(apical)-P(4)X(3)]](+) (X = S, 2; Se, 5) and [(triphos)Re(CO)(2)[eta(1)-P(basal)-P(4)X(3)]](+) (X = S, 3; Se, 6). The latter represent the first examples of the eta(1)-P(basal) coordination achieved by the P(4)X(3) molecular cage. Further reaction of 2/3 and 5/6 mixtures with 1 affords the dinuclear species [[(triphos)Re(CO)(2)](2)[mu,eta(1:1)-P(apical,)P(basal)-P(4)X(3)]](2+) (X = S, 4; Se, 7) in which the unprecedented M-eta(1)-P(basal)/eta(1)-P(apical)-M' bridging coordination of the P(4)X(3) molecule is accomplished. A theoretical analysis of the bonding properties of the two coordination isomers is also presented. The directionality of apical vs basal phosphorus lone pairs is also discussed in terms of MO arguments. 相似文献
993.
994.
Vincenza Bruno Anna Castaldo Roberto Centore Augusto Sirigu Felice Sarcinelli Mauro Casalboni Roberto Pizzoferrato 《Journal of polymer science. Part A, Polymer chemistry》2002,40(10):1468-1475
The synthesis of the new chromophores 2‐{4‐[4‐(N,N‐dihydroxyethylamino)‐phenylazo]‐phenyl}‐6‐nitrobenzoxazole ( 1 ) and 4‐[4‐(N,N‐dihydroxyethylamino)phenylazo]‐benzoic acid ( 2 ) is described. Three homopolymers obtained by the polycondensation of 1 with propyloxy‐terephthalic acid and 1 and 2 with 2,4‐tolylenediisocianate as well as two copolymers obtained by polycondensation of appropriate mixtures of chromophores 1 and 2 with 2,4‐tolylene‐diisocianate were prepared and characterized. All as‐prepared polymers but one (homopolyurethane of 1 ) were amorphous and exhibited good optical clarity, good thermal stability above the glass transition, and solubility in organic solvents. The second‐order nonlinear optical behavior of the amorphous polymers was investigated on spin‐coated corona‐poled films through second harmonic generation (SHG) experiments at 1064 nm. At this wavelength, resonance‐enhanced values of the SHG coefficient d33 were found in the range between 6 and 34 pm/V where higher values were observed for polymers with a higher molar content of 1 . © 2002 Wiley Periodicals, Inc. J Polym Sci Part A: Polym Chem 40: 1468–1475, 2002 相似文献
995.
Mussardo P Corda E González-Ruiz V Rajesh J Girotti S Martín MA Olives AI 《Analytical and bioanalytical chemistry》2011,400(2):321-327
The interaction between DNA and several newly synthesized derivatives of the natural anticancer compound luotonin A has been
studied. The results from our work reveal an effective and selective alkaloid/double-stranded DNA (ds-DNA) interaction. In
the presence of increasing amounts of ds-DNA, a noticeable fluorescence quenching of the luotonin A derivatives under study
was observed. However, this effect did not take place when single-stranded DNA (ss-DNA) was employed. The association constant
alkaloids/ds-DNA was calculated by quantitation of such a quenching effect. The influence of other quenchers, namely Co2+ and Br− on the native fluorescence of luotonin A and derivatives was also studied, and a remarkable quenching effect was observed
for both ions. We have also investigated how by binding DNA the alkaloids could get protected from the external Co2+ and Br− quenchers. The Stern–Volmer constants (K
SV) for Co2+ and Br− quenching effect on the studied alkaloids were considerably reduced (10–50%) after incubation of the compounds in the presence
of DNA with regard to the K
SV values in absence of DNA. An increase in the fluorescence anisotropy values of luotonins was also produced only in the presence
of ds-DNA but not in the case of ss-DNA. To better characterize the nature of that interaction, viscosimetry assays and ethidium
bromide displacement studies were conducted. With regard to DNA reference solutions, the viscosity of solutions containing
DNA and luotonin A derivatives was reduced or not significantly increased. It was also observed that the studied compounds
were unable to displace the intercalating agent ethidium bromide. All of these results, together with the obtained association
constants values (K
ass = 2.2 × 102 – 1.3 × 103), support that neither covalent nor intercalating interactions luotonin A derivatives/ds-DNA are produced, leading to the
conclusion that these alkaloids bind ds-DNA through the minor groove. The specific changes in the fluorescence behavior of
luotonin A and derivatives distinguishing between ss-DNA and ds-DNA binding, lead us to propose these compounds as attractive
turn-off probes to detect DNA hybridization. 相似文献
996.
Hortencia Silva-Jiménez Roberto Zazueta-Sandoval 《Applied biochemistry and biotechnology》2005,121(1-3):205-217
In previous work, purification procedures and zymogram analysis conducted with supernatants of crude extracts from aerobic
mycelium of the YR-1 strain of Mucor circinelloides isolated from petroleum-contaminated soils indicated the existence of only one soluble alcohol oxidase (sAO) activity. In
the present work enzymatic activity of alcohol oxidase (AO) was also detected in the mixed membrane fraction (MMF) of a high-speed
centrifugation procedure after drastic ballistic cellular homogenization to break the mycelium from strain YR-1. When mycelial
cells were gently broken by freezing the mycelium with liquid nitrogen, smashing in a mortar, and submitting the samples to
an isopycnic sucrose gradients (10–60% sucrose), AO activity was detected in particular and discrete fractions of the gradient,
showing specific density values quite different from the density of peroxisomes. The results suggest that there could be a
different intracellular pattern of distribution of the microsomal fraction in aerobically grown mycelium depending on the
carbon source used in the culture media, including alcohols and hydrocarbons, but not in glucose. In working with particulate
fractions, we found two AO activities: a new membrane alcohol oxidase (mAO) activity and the sAO. Both activities appear to
be located in the inner of the cells in specific compartments different from the peroxisomes, so mAO could be in the membrane
of these compartments and sAO in the lumen of the vesicles. We also assayed other enzymatic activities involved in hydrocarbon
biodegradation to establish its intracellular location and other enzymatic activities such as peroxidase to use them as intracellular
markers of different organelles. In the case of monooxygenase, the first enzymatic step in the hydrocarbon biodegradation
pathway, its location was in the same fractions where AOs were located, suggesting the existance of a specific organelle that
contains the enzymatic activities involved in hydrocarbon biodegradation. 相似文献
997.
Fleming Martínez Abolghasem Jouyban William E. Acree Jr. 《Physics and Chemistry of Liquids》2017,55(4):432-443
The preferential solvation parameters of phenobarbital in aqueous binary mixtures of 1,4-dioxane, t-butanol, n-propanol, ethanol, propylene glycol and glycerol were derived from solution thermodynamic properties by using the IKBI method. This drug is sensitive to preferential solvation effects in all these mixtures. The preferential solvation parameter by the cosolvent (δx1,3) is negative in almost all the water-rich mixtures but positive in mixtures with similar proportions of solvents and cosolvent-rich mixtures, except in 1-propanol + water mixtures, where negative values are also found in mixtures with x1 ≥ 0.70. Hydrophobic hydration around the non-polar ethyl and phenyl groups of this drug in water-rich mixtures could play a relevant role in drug solvation. Otherwise, in mixtures of similar solvent compositions and in cosolvent-rich mixtures the preferential solvation by cosolvent could be due to the acidic behaviour of the drug. 相似文献
998.
Campillo N Viñas P Martínez-Castillo N Hernández-Córdoba M 《Journal of chromatography. A》2011,1218(14):1815-1821
Microwave-assisted extraction (MAE) and dispersive liquid-liquid microextraction (DLLME) coupled with gas chromatography-mass spectrometry (GC-MS) were evaluated for use in the extraction and preconcentration of volatile nitrosamines in meat products. Parameters affecting MAE, such as the extraction solvent used, and DLLME, including the nature and volume of the extracting and disperser solvents, extraction time, salt addition and centrifugation time, were optimized. In the MAE method, 0.25g of sample mass was extracted in 10mL NaOH (0.05M) in a closed-vessel system. For DLLME, 1.5mL of methanol (disperser solvent) containing 20μL of carbon tetrachloride (extraction solvent) was rapidly injected by syringe into 5mL of the sample extract solution (previously adjusted to pH 6), thereby forming a cloudy solution. Phase separation was performed by centrifugation, and a volume of 3μL of the sedimented phase was analyzed by GC-MS. The enrichment factors provided by DLLME varied from 220 to 342 for N-nitrosodiethylamine and N-nitrosopiperidine, respectively. The matrix effect was evaluated for different samples, and it was concluded that sample quantification can be carried out by aqueous calibration. Under the optimized conditions, detection limits ranged from 0.003 to 0.014ngmL(-1) for NPIP and NMEA, respectively (0.12-0.56ngg(-1) in the meat products). 相似文献
999.
José W. D. Coutinho André M. B. S. Sampaio Iranaldo S. da Silva Flávio Colmati Roberto B. de Lima 《Journal of Solid State Electrochemistry》2018,22(10):3147-3159
The electrooxidation of ethylene glycol was studied using platinum–cadmium electrocatalysts supported on high surface area carbon Vulcan XC-72. This is the first instance of Cd being used as an electrocatalyst for glycol oxidation reaction. The catalysts were prepared with various Pt:Cd atomic ratios of 90:10, 80:20, and 70:30. All the catalysts prepared were synthesized by the alcohol reduction method with 20 wt.% metal on carbon. These materials were characterized morphologically by X-ray diffraction (XRD) and Transmission Electron Microscopy (TEM) and electrochemically by cyclic voltammetry and chronoamperometry. The electrochemical measurements were carried out at 25, 35, 45, and 55 °C, and the products of the electrochemical reaction were monitored by high-performance liquid chromatography (HPLC). The XRD patterns of all the PtCd catalysts presented cubic face-centered structures, and TEM revealed a homogeneous particle distribution on the carbon support with low agglomeration. The average particle size was assumed to be the maximum of the Gaussian distribution curve of particle size, at close to 2.5 nm. The presence of Cd results in an improvement in the glycol oxidation reaction, as observed by cyclic voltammetry; linear sweep voltammetry shows a lower onset potential compared to that of pure platinum. At a constant potential of 0.50 V (vs. RHE) at ambient temperature, HPLC showed glycolaldehyde to be the main byproduct formed from ethylene glycol oxidation at potential constant of 0.50 V. 相似文献
1000.
Martín M Torres O Oñate E Sola E Oro LA 《Journal of the American Chemical Society》2005,127(51):18074-18084
In the presence of ligands such as acetonitrile, ethylene, or propylene, the Ir(I) complex [Ir(1,2,5,6-eta-C8H12)(NCMe)(PMe3)]BF4 (1) transforms into the Ir(III) derivatives [Ir(1-kappa-4,5,6-eta-C8H12)(NCMe)(L)(PMe3)]BF4 (L = NCMe, 2; eta2-C2H4, 3; eta2-C3H6, 4), respectively, through a sequence of C-H oxidative addition and insertion elementary steps. The rate of this transformation depends on the nature of L and, in the case of NCMe, the pseudo-first-order rate constants display a dependence upon ligand concentration suggesting the formation of five-coordinate reaction intermediates. A similar reaction between 1 and vinyl acetate affords the Ir(III) complex [Ir(1-kappa-4,5,6-eta-C8H12){kappa-O-eta2-OC(Me)OC2H3}(PMe3)]BF4 (7) via the isolable five-coordinate Ir(I) compound [Ir(1,2,5,6-eta-C8H12){kappa-O-eta2-OC(Me)OC2H3}(PMe3)]BF4 (6). DFT (B3LYP) calculations in model complexes show that reactions initiated by acetonitrile or ethylene five-coordinate adducts involve C-H oxidative addition transition states of lower energy than that found in the absence of these ligands. Key species in these ligand-assisted transformations are the distorted (nonsquare-planar) intermediates preceding the intramolecular C-H oxidative addition step, which are generated after release of one cyclooctadiene double bond from the five-coordinate species. The feasibility of this mechanism is also investigated for complexes [IrCl(L)(PiPr3)2] (L = eta2-C2H4, 27; eta2-C3H6, 28). In the presence of NCMe, these complexes afford the C-H activation products [IrClH(CH=CHR)(NCMe)(PiPr3)2] (R = H, 29; Me, 30) via the common cyclometalated intermediate [IrClH{kappa-P,C-P(iPr)2CH(CH3)CH2}(NCMe)(PiPr3)] (31). The most effective C-H oxidative addition mechanism seems to involve three-coordinate intermediates generated by photochemical release of the alkene ligand. However, in the absence of light, the reaction rates display dependences upon NCMe concentration again indicating the intermediacy of five-coordinate acetonitrile adducts. 相似文献