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101.
Canosa P Morales S Rodríguez I Rubí E Cela R Gómez M 《Analytical and bioanalytical chemistry》2005,383(7-8):1119-1126
The degradation of 2-(2,4-dichlorophenoxy)-5-chlorophenol (triclosan) in chlorinated water samples was investigated. Sensitive
determination of the parent compound and its transformation products was achieved by gas chromatography with mass spectrometry
detection after sample concentration, using a solid-phase extraction sorbent and silylation of the target compounds. Experiments
were accomplished using ultrapure water spiked with chlorine and triclosan concentrations in the low mg/l and ng/ml ranges
respectively. Chlorination of the phenolic ring and cleavage of the ether bond were identified as the main triclosan degradation
pathways. Both processes led to the production of two tetra- and a penta-chlorinated hydroxylated diphenyl ether, as well
as 2,4-dichlorophenol. The formation of 2,3,4-trichlorophenol was not detected in any experiment; however, significant amounts
of 2,4,6-trichlorophenol were noticed. All of these five compounds were also identified when triclosan was added to tap-water
samples with free chlorine concentrations below 1 mg/l. Minor amounts of three di-hydroxylated phenols, containing from one
to three atoms of chlorine in their structures, were also identified as unstable triclosan chlorination by-products. The analysis
of several raw wastewater samples showed the co-existence of important concentrations of triclosan and its most stable by-products
(2,4-dichlorophenol and 2,4,6-trichlorophenol), reinforcing the potential occurrence of the described transformations when
products containing triclosan are mixed with chlorinated tap water. 相似文献
102.
Hernández-Borges J Rodríguez-Delgado MA García-Montelongo FJ Cifuentes A 《Electrophoresis》2005,26(20):3799-3813
Chiral separation of enantiomers is one of the most challenging tasks for any analytical technique including CE. Since the first report in 1985 showing the great possibilities of CE for the separation of chiral compounds, the amount of publications concerning this topic has quickly increased. Although chiral electromigration methods have mainly been used for enantioseparation of drugs and pharmaceuticals, they have also been applied to analyze chiral pollutants. This article intends to provide an updated overview, including works published till January 2005, on the principal applications of CE to the chiral analysis of pollutants and their metabolites, with special emphasis on articles published in the last 10 years. The main advantages and drawbacks regarding the use of CE for chiral separation of pollutants are addressed including some discussion on the foreseen trends of electromigration procedures applied to chiral analysis of contaminants. 相似文献
103.
Rodríguez Flores J Berzas Nevado JJ Durán Merás I Rodríguez Gómez MJ 《Journal of separation science》2005,28(7):658-664
A capillary zone electrophoresis (CZE) method using a fused-silica capillary (60.2 cm x 75 microm ID) was investigated for the determination of triamterene (TRI), methotrexate (MTX), and creatinine (CREA) in human urine. The separation was performed using a hydrodynamic injection time of 7 s (0.5 psi), a voltage of 25 kV, a capillary temperature of 30 degrees C, and 40 mM phosphoric acid adjusted to pH 2.25 by addition of triethanolamine as separation electrolyte. Under these conditions, analysis takes about 15 min. A linear response over the 0.5-15.0 mg L(-1) concentration range was found for TRI and MTX, and 0.5-80.0 mg L(-1) for CREA. Dilution of the sample (water:urine, 1:1 for TRI and MTX, and 1:25 for CREA determination) was the only step necessary prior to analysis by electrophoresis. The developed method is easy, rapid, and sensitive and has been applied to determine triamterene,methotrexate, and creatinine in urine samples with satisfactory results. 相似文献
104.
M. T. Fernández-Díaz J. Rodríguez-Carvajal J. L. Martínez G. Fillion F. Fernández R. Saez-Puche 《Zeitschrift für Physik B Condensed Matter》1991,82(2):275-282
Neutron powder diffraction and magnetization measurements have been performed in stoichiometric Pr2NiO4+(0), which at room temperature (RT) is orthorhombic (Bmab). Ni2+ becomes three dimensionally (3D) antiferromagnetically ordered atT
N
325K, with a propagation vectork=[100], and spins oriented along thea axis (parallel to the propagation vector). The magnetic structure belongs to the
7g
(––+)-representation (g
x
mode, Shubnikov groupB
pmab') ofBmab, and a magnetic moment of 1.5
B
is measured at 155K. This compound undergoes two different structural phase transitions. First, going down in temperature, Pr2NiO4 transforms by a first order phase transition from orthorhombic (Bmab) to tetragonal (P42/ncm) atT
c1115K. At high temperature, we can predict a transformation from orthorhombic (Bmab) to tetragonal (I4/mmm) in a continuous way. The extrapolated temperature for this second structural transition isT
c21500±100K. The low temperature structural transformation allows a change in the magnetic structure which forT<T
c1 is better described in the orthorhombic symmetry. Just belowT
c1 the magnetic structure is described by the:
3g
(–+)-representation ofPccn(gxcyfz mode, Shubnikov groupPccn), this magnetic phase begins to disappear going down in temperature and at the same time a new magnetic phase grows. This new magnetic structure is described by the
1g
ofPccn (c
xgyaz mode, Shubnikov groupPccn). Both magnetic structures coexist in a certain temperature range. At 1.5 K thec
xgyaz mode represents the total of the magnetic ordering. To reproduce the observed magnetic intensities we are forced to consider that Pr3+ is polarized below 40 K, with a magnetic structure which is coupled to the Ni sublattices (i.e.
1g
and
3g
). The magnetic moment at low temperature for Pr is about 1.28
B
. 相似文献
105.
A. Villares S. Rodríguez C. Lafuente F. M. Royo M. C. López 《Journal of solution chemistry》2004,33(9):1119-1133
Experimental viscosities and the corresponding viscosity deviations for the binary mixtures of a cyclic ether (tetrahydrofuran, tetrahydropyran, 2-methyltetrahydrofuran, or 2,5-dimethyltetrahydrofuran) with benzene, toluene, fluorobenzene, or chlorobenzene are given at 25°C. The kinematic viscosities and the corresponding densities were measured with an uncertainty of ±10– 4 mm2-s– 1 and ±(5×10– 3) kg-m– 3, respectively. The viscosity data were correlated by the equations of Grunberg–Nissan, McAllister, and Heric. On the other hand, the results have been compared to the predictions, by the method proposed by Asfour. 相似文献
106.
García-Río L Hervés P Mejuto JC Pérez-Juste J Rodríguez-Dafonte P 《Journal of colloid and interface science》2000,225(2):259-264
We carried out an investigation on the influence of several alkylamines, frequently present in reactions carried out in microemulsions, on the properties of the water/AOT/isooctane system. The presence of alkylamines has an important effect on the electrical percolation phenomena. This effect of amines on the electrical percolation of microemulsions of AOT/isooctane/water can be explained by taking into account the ability of these substrates to associate with the AOT film in the microemulsion, the basicity of the amine, and the different solubility of the amine in the three pseudophases of the system. Copyright 2000 Academic Press. 相似文献
107.
Nicolaou KC Rodríguez RM Mitchell HJ Suzuki H Fylaktakidou KC Baudoin O van Delft FL 《Chemistry (Weinheim an der Bergstrasse, Germany)》2000,6(17):3095-3115
In this first of a series of four articles we introduce everninomicin 13,384-1 (1), a powerful antibiotic effective against drug resistant bacteria, as a target for total synthesis and discuss its retrosynthetic analysis. From the three defined fragments required for the synthesis (2: A1B(A)C fragment; 4: DE fragment; 5: FGHA2 fragment), we describe herein two approaches to the A1B(A)C block. The first strategy relied on an olefin metathesis reaction to construct a common intermediate for rings B and C, but was faced with final protecting group problems. The second, and successful approach, involved a 1,2-phenylsulfeno migration and a sulfur directed glycosidation procedure to link rings B and C, as well as an acyl fluoride intermediate to install the sterically hindered aryl ester moiety (ring A1). The final stages of the synthesis of the required 2-phenylseleno glycosyl fluoride 2 required introduction of a phenylseleno group at C-1 of ring C followed by a novel, DAST-promoted 1,2-migration to produce the desired 2-beta-phenylseleno glycosyl fluoride moiety. 相似文献
108.
Mogolloń L. Rodríguez R. Larrota W. Ortiz C. Torres R. 《Applied biochemistry and biotechnology》1998,(1):765-777
Asphaltenes from a crude oil rich in heavy metals (Castilla crude oil) were fractionated and partially characterized. Biocatalytic
modifications of these fractionated asphaltenes by three different hemoproteins: chloro-peroxidase (CPO), cytochrome C peroxidase
(Cit-C), and lignin peroxi-dase (LPO) were evaluated in both aqueous buffer and organic solvents. The reactions were carried
out in aqueous buffers, ternary systems of toluene: isopropanol: water, and aqueous-miscible organic solvent solutions with
petroporphyrins as substrate. The petroporphyrins were more soluble in the ternary systems and aqueous miscible-organic solvent
systems than in the aqueous buffer systems. However, only the CPO-mediated reactions were effective in eliminating the Soret
peak in both aqueous and organic solvent systems. The effects of CPO-mediated reactions on the release of the metals complexed
with the porphyrins and asphaltenes were also determined. Chloroperoxidase was able to alter components in the heavy fractions
of petroleum and remove 53 and 27% of total heavy metals (Ni and V, respectively) from petroporphyrin-rich fractions and asphaltenes 相似文献
109.
110.
R. Rodríguez G. Rojas M. Estevez S. Vargas 《Journal of Sol-Gel Science and Technology》2002,23(2):99-105
The fractal characterization of silica particles prepared by the sol-gel method was obtained; from the beginning of the sol-gel synthesis to the aggregation process of these particles by adding metal ions in solution, the fractal dimension was determined. At the beginning of the sol-gel process, unstable structures were formed due, essentially, to the auto-catalytic nature of the sol-gel condensation reactions; these particles are fractal structures with a fractal exponent corresponding to a reaction limited aggregation regime. As the time proceeds, the reactants are consumed approaching the system to equilibrium, stabilizing the size of the silica particles. The silica sol can be flocculated by adding metal ions in solution. The fractal exponent for the aggregation process was determined, obtaining a value corresponding to a diffusion limited aggregation regime. 相似文献