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排序方式: 共有498条查询结果,搜索用时 281 毫秒
241.
Francesco Dondi Yassin Du Ale Kahie Gaetano Lodi Maurizio Remelli Pierluigi Reschiglian Corrado Bighi 《Analytica chimica acta》1986
Optimization of the chromatographic separation of flavonoid compounds in camomile extracts by the simplex method and the Monte Carlo method is described. Evaluation fo the number of peaks at unit resolution (Rs = 1) is used as the criterion of separation quality. The Davis-Giddings theory is applied in calculating the number of components and the results are validated by numerical simulations. Peak-purity checks for three identified compounds in commercial sample extracts are reported. Capacity factor patterns for 18 flavonoid and phenolic compounds over an extended range of methanol/aqueous buffer (pH 2.8) mobile phases are described. 相似文献
242.
Roda B Cioffi N Ditaranto N Zattoni A Casolari S Melucci D Reschiglian P Sabbatini L Valentini A Zambonin PG 《Analytical and bioanalytical chemistry》2005,381(3):639-646
Biocompatible methods capable of rapid purification and fractionation of analytes from complex natural matrices are increasingly in demand, particularly at the forefront of biotechnological applications. Field-flow fractionation is a separation technique suitable for nano-sized and micro-sized analytes among which bioanalytes are an important family. The objective of this preliminary study is to start a more general approach to field-flow fractionation for bio-samples by investigation of the correlation between channel surface composition and biosample adhesion. For the first time we report on the use of X-ray photoelectron spectroscopy (XPS) to study the surface properties of channels of known performance. By XPS, a polar hydrophobic environment was found on PVC material commonly used as accumulation wall in gravitational field-flow fractionation (GrFFF), which explains the low recovery obtained when GrFFF was used to fractionate a biological sample such as Staphylococcus aureus. An increase in separation performance was obtained first by conditioning the accumulation wall with bovine serum albumin and then by using the ion-beam sputtering technique to cover the GrFFF channel surface with a controlled inert film. XPS analysis was also employed to determine the composition of membranes used in hollow-fiber flow field-flow fractionation (HF FlFFF). The results obtained revealed homogeneous composition along the HF FlFFF channel both before and after its use for fractionation of an intact protein such as ferritin. 相似文献
243.
Piero Dalla Croce Pierluigi Gariboldi Concetta La Rosa 《Journal of heterocyclic chemistry》1987,24(6):1793-1797
The cycloaddition reaction of symmetrically and unsymmetrically substituted munchnones with arylsulfonyl alkynes has been studied. The reaction affords pyrrole derivatives whose structures were assigned on the basis of spectroscopic data. The distribution of regioisomers observed in the case of unsymmetrically substituted munchnones is discussed. 相似文献
244.
245.
Dražen Adamović Victor G. Kac Pierluigi Möseneder Frajria Paolo Papi Ozren Perše 《Communications in Mathematical Physics》2016,343(2):445-476
We revisit two old and apparently little known papers by Basuev (Teoret Mat Fiz 37(1):130–134, 1978, Teoret Mat Fiz 39(1):94–105, 1979) and show that the results contained there yield strong improvements on current lower bounds of the convergence radius of the Mayer series for continuous particle systems interacting via a very large class of stable and tempered potentials, which includes the Lennard-Jones type potentials. In particular we analyze the case of the classical Lennard-Jones gas under the light of the Basuev scheme and, using also some new results (Yuhjtman in J Stat Phys 160(6): 1684–1695, 2015) on this model recently obtained by one of us, we provide a new lower bound for the Mayer series convergence radius of the classical Lennard-Jones gas, which improves by a factor of the order 105 on the current best lower bound recently obtained in de Lima and Procacci (J Stat Phys 157(3):422–435, 2014). 相似文献
246.
Kallol K. Ghosh Sancheeta Kolay Sunita Bal Manmohan L. Satnami Pierluigi Quagliotto P. R. Dafonte 《Colloid and polymer science》2008,286(3):293-303
The kinetics of the hydrolysis of p-nitrophenyl acetate (PNPA) and p-nitrophenyl diphenyl phosphate (PNPDPP) by hydroxamate ions mediated by gemini surfactants with quaternary ammonium bromide
(16-n-16,2Br−, n = 3, 4, 6, 12) and pyridinium chloride (12py-n-py12,2Cl−, n = 3, 4) head group have been investigated at 27 °C. The gemini surfactant with the pyridinium head group, 12-py-4-py12,2Cl− (tetramethylene-1,4 bis dodecylpyridinium chloride) shows a large rate acceleration effect than that with an ammonium head group, 16-12-16,2Br−, relative to those in water. The apparent pK
a of the hydroxamic acids have been determined in the presence of gemini surfactants. Catalytic system N-phenylbenzohydroxamate/12py-4-py12,2Cl− demonstrated over ~1,590-fold and ~255-fold rate enhancement in the hydrolysis of PNPA and PNPDPP, respectively, for the
identical reaction performed in buffer aqueous media at 27 °C. The second order rate constant and binding constants for reactions
were determined employing pseudophase model for micellar catalysis. 相似文献
247.
Zattoni A Rambaldi DC Roda B Parisi D Roda A Moon MH Reschiglian P 《Journal of chromatography. A》2008,1183(1-2):135-142
Hollow-fiber flow field-flow fractionation is here applied to untreated, whole human blood serum. Matrix-assisted, laser desorption/ionization time-of-flight-mass spectrometry (MALDI-TOF-MS) of serum fractions shows mass signals in the <30,000 M(r) range where low-abundance, serum protein components are known to be present, though a membrane of nominal 30,000 Da cutoff was employed for the fractionation device. Using diluted sera spiked with low amounts (0.06-0.1%, w/w) of an artificial mixture constituted the human adrenocorticotropic hormone fragments 18-39 (M(r)=2465.7) and 7-38 (M(r)=3659.2), and of bovine insulin (M(r)=5734), horse cytochrome c (M(r)=12384) and chicken lysozyme (M(r)=14388), a hybrid fractionation/microfiltration mechanism shows to govern the separation of the low-M(r) components. 相似文献
248.
249.
Gensty T Becker K Fischer I Elsässer W Degen C Debernardi P Bava GP 《Physical review letters》2005,94(23):233901
We report the onset of wave chaos in a real-world vertical-cavity surface-emitting laser. In a joint experimental and modeling approach we demonstrate that a small deformation in one layer of the complicated laser structure changes the emission properties qualitatively. Based on the analysis of the spatial emission profiles and spectral eigenvalue spacing distributions, we attribute these changes to the transition from regular behavior to wave chaos, and justify the full analogy to two-dimensional billiards by model calculations. Hence, these lasers represent fascinating devices for wave chaos studies. 相似文献
250.
An XeCl laser beam has been used to investigate stimulated Raman scattering in H2 and in various H2-foreign gas mixtures. Helium, neon, argon, and nitrogen have been tested as foreign gases. In all the investigated mixtures with 50% of H2, the energy conversion efficiency to the first Stokes (353 nm) was more than 70% higher than that obtained in H2 at the same total pressure (40 bar) and pump energy (60 mJ). The dependence of the energy conversion efficiency on pump beam divergence has also been investigated. 相似文献