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991.
Reviriego F Navarro P García-España E Albelda MT Frías JC Domènech A Yunta MJ Costa R Ortí E 《Organic letters》2008,10(22):5099-5102
The synthesis and steady-state fluorescence studies on the interaction with AMPH, METH, MDMA, and DA of two diazatetraester pyrazole crowns containing appended N-(9H-fluoren-9-yl) and N-(naphth-2-ylmethyl) functions, in a water/ethanol 70:30 mixture at physiological pH, are described. 相似文献
992.
An RP-HPLC method for the determination of four phenolic compounds: gallic acid (GA), pyrogallol (PY), resorcinol (RE) and ellagic acid (EA), derived from hydrolysable tannins is reported. Separation was achieved on a SunFire C18 (250 x 4.6 mm id, 5 microm) column at 40 degrees C with gradient elution. UV detection at 280 nm was applied. The developed method was validated in terms of linearity, accuracy and precision. Satisfactory repeatability and between day precision were noticed with RSD values lower than 3%. Recoveries from different biological samples ranged from 91.50 to 105.25%. The LODs were estimated as 1.70 mg/L for PY, 1.68 mg/L for GA, 1.52 mg/L for RE and 0.98 mg/L for EA with a 20 microL injection volume. The method was applied for the determination of these compounds in oak leaves and in ruminal fluid and urine samples taken from beef cattle fed with oak leaves. The proposed method could be used in ruminant nutrition studies to verify the effect that a diet rich in tannins have on ruminal fermentation and to determine the toxicity of these compounds. 相似文献
993.
Trends and recent applications of matrix solid-phase dispersion 总被引:1,自引:0,他引:1
Matrix solid-phase dispersion (MSPD) is a sample-preparation technique with increasing acceptance in trace analysis of organic
compounds using chromatographic and electro-driven separation techniques. It has been applied to the extraction and fractionation
of a large number of substances from solid, semi-solid, and liquid matrices. Low sample and solvents consumption, straightforward
application, and reduced cost, and its ability to simultaneously perform extraction and clean-up in a single step, are some
of its major advantages. This review attempts to provide an updated, concise and critical overview on the latest trends and
applications of MSPD, placing emphasis on comparison of its performance with that of other techniques, besides focusing on
practical features to take into account depending on the nature of the sample and the properties of the analytes. Achievements,
advantages, and limitations are discussed. The paper also highlights future challenges to be faced. 相似文献
994.
Rodríguez-Castrillón JA Moldovan M García Alonso JI Lucena JJ García-Tomé ML Hernández-Apaolaza L 《Analytical and bioanalytical chemistry》2008,390(2):579-590
Isotope pattern deconvolution is a mathematical technique for isolating distinct isotope signatures from mixtures of natural
abundance and enriched tracers. In iron metabolism studies measurement of all four isotopes of the element by high-resolution
multicollector or collision cell ICP–MS allows the determination of the tracer/tracee ratio with simultaneous internal mass
bias correction and lower uncertainties. This technique was applied here for the first time to study iron uptake by cucumber
plants using 57Fe-enriched iron chelates of the o,o and o,p isomers of ethylenediaminedi(o-hydroxyphenylacetic) acid (EDDHA) and ethylenediamine tetraacetic acid (EDTA). Samples of root, stem, leaves, and xylem sap,
after exposure of the cucumber plants to the mentioned 57Fe chelates, were collected, dried, and digested using nitric acid. The isotopic composition of iron in the samples was measured
by ICP–MS using a high-resolution multicollector instrument. Mass bias correction was computed using both a natural abundance
iron standard and by internal correction using isotope pattern deconvolution. It was observed that, for plants with low 57Fe enrichment, isotope pattern deconvolution provided lower tracer/tracee ratio uncertainties than the traditional method
applying external mass bias correction. The total amount of the element in the plants was determined by isotope dilution analysis,
using a collision cell quadrupole ICP–MS instrument, after addition of 57Fe or natural abundance Fe in a known amount which depended on the isotopic composition of the sample. 相似文献
995.
Iraís A. Quintero‐Ortega Gabriel Jaramillo‐Soto Pedro R. García‐Morán M. Luz Castellanos‐Cárdenas Gabriel Luna‐Bárcenas Eduardo Vivaldo‐Lima 《大分子反应工程》2008,2(4):304-320
A comparison of kinetic models for dispersion polymerization of MMA and styrene in supercritical CO2 is presented. The limiting case of solution polymerization, as a simplified case, was also addressed. Calculation of the partition of components between the continuous and dispersed phases was emphasized. Experimental data for the solution and dispersion polymerizations of styrene and MMA, using different types of stabilizers, were used to guide the study. Although all the models analyzed can be considered as “adequate” in representing the behavior of the system, some of their strengths and drawbacks have been highlighted.
996.
Alejandro Ortíz Braulio Insuasty Justo Cobo John N. Low Christopher Glidewell 《Acta Crystallographica. Section C, Structural Chemistry》2008,64(9):o505-o507
In the title compound, C6H18N22+·2C2H2ClO2−, the cation lies across an inversion centre in the P space group. The ions are linked by two two‐centre N—H...O hydrogen bonds and by one three‐centre N—H...(O)2 hydrogen bond to form a three‐dimensional framework structure. The significance of this study lies in the analysis of the complex hydrogen‐bonded structure and in the comparison of this structure with those of other simple hexamethylenediammonium salts. 相似文献
997.
Andreas Defant Domingo García Manuel Maestre David Pérez-García 《Mathematische Annalen》2008,342(3):533-555
Bohr showed that the width of the strip (in the complex plane) on which a given Dirichlet series , converges uniformly but not absolutely, is at most 1/2, and Bohnenblust-Hille that this bound in general is optimal. We
prove that for a given infinite dimensional Banach space Y the width of Bohr’s strip for a Dirichlet series with coefficients a
n
in Y is bounded by 1 - 1/Cot (Y), where Cot (Y) denotes the optimal cotype of Y. This estimate even turns out to be optimal, and hence leads to a new characterization of cotype in terms of vector valued
Dirichlet series.
The first, second and third authors were supported by MEC and FEDER Project MTM2005-08210. 相似文献
998.
A sufficient condition for the strict insertion of a continuous function between two comparable upper and lower semicontinuous
functions on a normal space is given. Among immediate corollaries are the classical insertion theorems of Michael and Dowker.
Our insertion lemma also provides purely topological proofs of some standard results on closed subsets of normal spaces which
normally depend upon uniform convergence of series of continuous functions. We also establish a Tietze-type extension theorem
characterizing closed G
δ
-sets in a normal space.
This research was supported by the Ministry of Education and Science of Spain and FEDER under grant MTM2006-14925-C02-02.
The first named author also acknowledges financial support from the University of the Basque Country under grant UPV05/101. 相似文献
999.
J. García-Melián C. Morales-Rodrigo J. D. Rossi A. Suárez 《Annali di Matematica Pura ed Applicata》2008,187(3):459-486
In this paper we perform an extensive study of the existence, uniqueness (or multiplicity) and stability of nonnegative solutions
to the semilinear elliptic equation − Δu = λ u − u
p
in Ω, with the nonlinear boundary condition ∂u/∂ν = u
r
on ∂Ω. Here Ω is a smooth bounded domain of with outward unit normal ν, λ is a real parameter and p, r > 0. We also give the precise behavior of solutions for large |λ| in the cases where they exist. The proofs are mainly
based on bifurcation techniques, sub-supersolutions and variational methods.
相似文献
1000.
Granados AM Fracaroli AM de Rossi RH Fuertes P Torroba T 《Chemical communications (Cambridge, England)》2008,(4):483-485
A phenylethynyl Fischer carbene complex was used as a traceless directing group for the regioselective cycloaddition of dithiolethiones to arylacetylene, which constitutes the first synthesis of E-dithiafulvene thione or dithioesters. 相似文献