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41.
D. Zorrilla Cuenca J. Sánchez Márquez M. Fernández Núñez R. Rodríguez Huertas 《International journal of quantum chemistry》2007,107(4):879-893
This project consists of two parts. In the first part, a series of test calculations is performed to verify that the integrals involved in the determination of atomic and molecular properties by standard self‐consistent field (SCF) methods can be obtained through Halton, Korobov, or Hammersley quasi‐random integration procedures. Through these calculations, we confirm that all three methods lead to results that meet the levels of precision required for their use in the calculation of properties of small atoms or molecules at least at a Hartree–Fock level. Moreover, we have ensured that the efficiency of quasi‐random integration methods that we have tested is Halton=Korobov>Hammersley?pseudo‐random. We also find that these results are comparable to those yielded by ordinary Monte Carlo (pseudo‐random) integration, with a calculation effort of two orders of smaller magnitude. The second part, which would not have been possible without the integration method previously analyzed, contains a first study of atoms constrained in spherical boxes through SCF calculations with basis functions adapted to the features of the problem: Slater‐type orbitals (STOs) trimmed by multiplying them by a function that yields 1 for 0 < r < (R‐δ), polynomial values for (R‐δ) < r < R and null for r > R, R being the radius of the box and δ a variationally determined interval. As a result, we obtain a equation of state for electrons of small systems, valid just in the limit of low temperatures, but fairly simple. © 2006 Wiley Periodicals, Inc. Int J Quantum Chem, 2007 相似文献
42.
Guillena G Rodríguez G Albrecht M van Koten G 《Chemistry (Weinheim an der Bergstrasse, Germany)》2002,8(23):5368-5376
Arylplatinum(II) complexes have been covalently bonded to the N and C termini and to the alpha-carbon of various amino acid derivatives. These organometallic-functionalized amino acid compounds can be converted into the corresponding free amino acids under both basic and acidic conditions; this demonstrates the excellent stability properties of these biomolecules. Due to the NMR activity displayed by the 195Pt nucleus (natural abundance 33.8%, I = 1/2) these compounds are functional bio-markers. Furthermore, the ability of the arylplatinum functional group to bind SO2 gas, selectively and reversibly as indicated by changes in the spectroscopic properties (1H, 13C, 195Pt NMR and UV spectra) of these compounds, allows for the potential use of these complexes as in vitro biosensors. 相似文献
43.
D. Rodríguez P. Fernández C. Pérez-Conde A. Gutiérrez C. Cámara 《Fresenius' Journal of Analytical Chemistry》1994,349(6):442-446
A rapid and sensitive method has been developed for the determination of lead in water samples by flame atomic absorption spectrometry using on-line preconcentration on a microcolumn packed with silica gel treated with a mixture of Aliquat 336 and nitroso-R-salt. The lead is retained at pH 5.5. The preconcentrated lead is directly eluted from the column to the nebulizer-burner system using 150 L of 0.1 mol/L hydrochloric acid. The optimum preconcentration conditions are given and the retention efficiency achieved is higher than 80%. The enrichment factor is 37 and 100 for sample volumes of 5 and 30 mL, respectively. The limits of detection are 10.0, 6.0 and 4.0 ng/mL when 5, 10 and 30 mL of water is preconcentrated. 相似文献
44.
Otero A Fernández-Baeza J Antiñolo A Carrillo-Hermosilla F Tejeda J Lara-Sánchez A Sánchez-Barba L Fernández-López M Rodríguez AM López-Solera I 《Inorganic chemistry》2002,41(20):5193-5202
The preparation of new "scorpionate" ligands in the form of the lithium derivatives [(Li(bdmpzdta)(H(2)O))(4)] (1) [bdmpzdta = bis(3,5-dimethylpyrazol-1-yl)dithioacetate], [Li(bdphpza)(H(2)O)(THF)] (2) [bdphpza = bis(3,5-diphenylpyrazol-1-yl)acetate], and [Li(bdphpzdta)(H(2)O)(THF)] (3) [bdphpzdta = bis(3,5-diphenylpyrazol-1-yl)dithioacetate] has been carried out. Furthermore, a series of titanium complexes has been prepared by reaction of TiCl(4)(THF)(2) with the lithium reagents [(Li(bdmpza)(H(2)O))(4)] (4) [bdmpza = bis(3,5-dimethylpyrazol-1-yl)acetate] and 1. Under the appropriate experimental conditions neutral complexes, namely [TiCl(3)(kappa(3)-bdmpza)] (5), [TiCl(3)(kappa(3)-bdmpzdta)] (6), and [TiCl(2)(kappa(2)-bdmpzdta)(2)] (7), and cationic complexes, namely [TiCl(2)(THF)(kappa(3)-bdmpza)]Cl (8) and [TiCl(2)(THF)(kappa(3)-bdmpzdta)]Cl (9), were isolated. Complexes 8 and 9 undergo an interesting nucleophilic THF ring-opening reaction to give the corresponding alkoxide-containing species [TiCl(2)(kappa(3)-bdmpza)(O(CH(2))(4)Cl)] (10) and [TiCl(2)(kappa(3)-bdmpzdta)(O(CH(2))(4)Cl)] (11). A family of alkoxide-containing complexes of general formulas [TiCl(2)(kappa(3)-bdmpza)(OR)] [R = Me (12); R = Et (14); R = (i)Pr (16); R = (t)Bu (18)] and [TiCl(2)(kappa(3)-bdmpzdta)(OR)] [R = Me (13); R = Et (15); R = (i)Pr (17)] was also prepared. The structures of these complexes have been determined by spectroscopic methods, and in addition, the X-ray crystal structures of 3, 7, 10, and 11 were also established. 相似文献
45.
Transformation
of dynamic DSC results into isothermal data for the curing kinetics study
of the resol resins 总被引:1,自引:0,他引:1
M. V. Alonso M. Oliet J. García F. Rodríguez J. Echeverría 《Journal of Thermal Analysis and Calorimetry》2006,86(3):797-802
Kinetics of thermosetting polymers curing is difficult to study by isothermal
methods based on the differential scanning calorimetry (DSC) technique. The
difficulty is due to the low sensitivity of the equipment for total reaction
heat measurements during high temperature process. The aim of this paper is
to display the equivalence between a dynamic model, the Ozawa method, and
an isothermal isoconversional fit, which allows predicting the isothermal
behavior of the resol resins cure through dynamic runs by DSC. In this work,
lignin–phenol–formaldehyde and commercial phenol–formaldehyde
resol resins were employed. In addition, the isothermal kinetic parameters
for both resins were performed by means of transformation of the data obtained
from the dynamic Ozawa method. 相似文献
46.
J. Hernández-Borges M. A. Rodríguez-Delgado F. J. García-Montelongo 《Chromatographia》2006,63(3-4):155-160
Several improvements in sample pretreatment for the determination of organic pollutants (i.e. n-alkanes, polycyclic aromatic hydrocarbons, PAHs) in marine biota (mussels) are presented. The use of liquid nitrogen and
homogenization of the samples are shown to be an alternative to the time consuming liophilization step required for the analysis
of biota samples. Microwave-assisted hydrolysis and extraction are combined to isolate organic pollutants (19 n-alkanes and 27 PAHs) from biota matrices. Experimental design (ED) and artificial neural networks (ANNs) were used to optimize
the experimental conditions. NIST-CRM 2978 was used to test the validity of the developed method which shows a good agreement
with certified values. 相似文献
47.
The development of methodologies for the formation of carbon-carbon double bonds could be considered one of the most important challenges in organic synthesis. To this end, beta-elimination reactions in 1,2-difunctionalised substrates have been one of the most important means of generating C=C bonds.This review is intended to highlight the use of SmI2 in beta-elimination procedures, such that the organization of this revision highlights conventional beta-elimination processes which are promoted by samarium diiodide. The synthetic applications of SmI2 will be covered, and 1,2-elimination reactions which are involved in sequential reactions promoted by samarium diiodide, will also be illustrated. These methodologies along with the more recent developments in the area are discussed in this tutorial review. 相似文献
48.
Micellar electrokinetic capillary chromatography for the determination of Viagra and its metabolite (UK-103,320) in human serum 总被引:1,自引:0,他引:1
Berzas Nevado JJ Rodríguez Flores J Castañeda Peñalvo G Rodríguez Fariñas N 《Electrophoresis》2001,22(10):2004-2009
Micellar electrokinetic capillary chromatography (MEKC) was investigated for the determination of Viagra (sildenafil citrate, SC) and its metabolite (UK-103,320) in human serum in a concentration range of clinical interest. For MEKC, human serum samples spiked with SC and UK were obtained directly after elution with methanol from a tC18 cartridge. The extract was evaporated and regenerated in a solution 1 mM of phosphate buffer (pH 12.3) which contained a methanol percentage of 20% that was analyzed using phosphate buffer (pH 12.3, 10 mM) containing 30 mM sodium dodecyl sulfate (SDS) as separation electrolyte and a fused-silica capillary. This method gave satisfactory interday precision with respect to migration times relative standard deviation (RSD < 1%) and linear responses for the concentration ranges investigated (0.50-3.50 mg L(-1) for the compound SC and 0.90-4.60 mg L(-1) for UK). An intraday RSD (n = 5 graphs) between the slopes of the calibration graphs was acceptable (6.40%) for SC and (3.37%) for UK. A satisfactory interday precision between slopes was also obtained (RSD 4.10% for SC and a RSD 2.72% for UK) which demonstrated the ruggedness of this method. Detection limits (S/N = 3) were about 200 ng/mL for both compounds in human serum. MEKC was shown as a good method with regards to simplicity, precision and sensitivity. 相似文献
49.
Gracia CA Gómez-Barreiro S González-Pérez A Nimo J Rodríguez JR 《Journal of colloid and interface science》2004,276(2):408-413
Static (SLS) and dynamic (DLS) light-scattering techniques were applied to the study of the aggregation of dodecyl- (C12DBACl), tetradecyl- (C14DBACl), and hexadecyldimethylbenzylammonium (C16DBACl) chlorides in water and in 0.01 and 0.05 m NaCl aqueous solutions at 25 degrees C. Results of SLS measurements yielded critical micelle concentration (cmc) values for aqueous and NaCl solutions. The aggregation numbers of the micelles for the homologous surfactants are low but increase with chain length and ionic strength of the solution. Various patterns of changes of the diffusion coefficient, D, as a function of chain length, molality, and with ionic strength were found for the studied surfactants. Transformations in the structure of micelles of C14DBACl in 0.01 m NaCl occur at a concentration of surfactant of about 0.01 m. Such transformations, presumably due to rodlike structure, are the more extensive the higher the concentration of NaCl. The concentration of C16DBACl in 0.05 m NaCl covers the range where already repulsive interactions between micelles occur, as judged by the strongly negative slope of the D versus molality plot. To provide additional information on the suggested transformations, complementary viscosity measurements for C14DBACl in 0.01 m of NaCl have been performed. 相似文献
50.
Rodríguez-Cea A de la Campa MR Sanz-Medel A 《Analytical and bioanalytical chemistry》2005,381(2):388-393
Cytochromes P-450 are members of a superfamily of hemoproteins involved in the oxidative metabolism of various physiological and xenobiotic compounds in eukaryotes and prokaryotes. The multiplicity of this group of enzymes has been widely studied by chromatographic techniques, mainly high-performance liquid chromatography (HPLC). Because these enzymes are membrane-bound proteins, sample preparation for chromatographic separation of P-450 enzymes requires a solubilization step. The sample-preparation procedures are critical, because detergents affect not only the efficiency of protein solubilization but also their further chromatographic resolution. Trout liver microsomes have been taken here as a model sample to investigate iron speciation in cytochrome P-450. Trouts were treated intraperitoneally with -naphthoflavone, a potent inducer of some P-450 enzymes, and a microsomal suspension containing 7.4±0.1 nmol mL–1 P-450 enzymes was obtained by ultracentrifugation. Lubrol PX was selected as detergent for solubilization, resulting in about 90% solubilization recovery. The solubilized cytochromes P-450 were further separated by AE–FPLC, with UV detection, or coupled to ICP–MS with an octapole reaction system, ICP–(ORS)MS (monitoring Fe signals at masses 54, 56, and 57). A sampling procedure and chromatographic conditions are developed and were successfully applied to iron speciation in trout liver P-450 enzymes. ICP–(ORS)MS detection of P-450 enzymes is Fe-specific and so will give accurate information on the prosthetic group of the protein, which can constitute an advantageous alternative to classical methods for detection of these hemoproteins. 相似文献