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排序方式: 共有185条查询结果,搜索用时 15 毫秒
31.
N.M. Peruchenaa L. Sosa G.A. Aucar R.H. Contreras 《Journal of Molecular Structure》1995,330(1-3):211-216
Vicinal J(SnCCSn) and J(SnCCC) spin-spin coupling constants are calculated within the RPA MNDO method for different dihedral angles, θ, determined by the intervening bonds, in model compounds. For both types of couplings, calculated values closely follow Karplus-like dependences. Results are discussed in terms of experimental values, and the effects of substituents attached to the coupled atoms are briefly analyzed for the θ = 0 ° and θ = 180 ° conformations. These last values were also calculated using the RPA AM1 method. Results indicate that the RPA MNDO and RPA AM1 approaches show interesting potential for studying the structural dependences of 3J(SnSn) and 3J(SnC) couplings in tin-containing compounds. 相似文献
32.
Summary The determinations of phenol is studied by means of a carbon paste electrode modified with 10% sepiolite using DPV. A 10 min preconcentration step was performed at pH 1.5 under open circuit conditions. Measurements were made in another cell by DPV with E=100 mV (sweep rate = 40 mV/s) in 0.02 mol/l KNO3 medium at pH 2. Detection limits (3 ) of 30 ng/ml were achieved for determinations in orange, lemon and cola drinks.
Phenolbestimmung durch Differentialpuls-Voltammetrie mit einer Sepiolit-modifizierten Kohlepaste-Elektrode相似文献
33.
Perez Gutierrez RM Rosario Vargas S Martinez Martinez F Garcia Baez E Figueroa Torres G 《Natural product research》2006,20(3):305-310
Antispasmodic activity-guided fractionation together with chemical analysis led to the isolation of one novel delta-lactone named oedogonolide from Oedogonium capillare. Identification was based on spectroscopic methods. The oedogonolide produces a significant antispasmodic effect on the contractions of the rat ileum induced by acetylcholine, histamine and barium chloride. 相似文献
34.
Wilfredo Sosa 《Journal of Optimization Theory and Applications》2013,159(3):795-804
In this work, we introduce a Representation of continuous real-valued functions defined over a real Hilbert space. As a consequence, we can introduce a Sandwich Theorem for semi-continuous functions, a Separation Theorem for closed sets and a representation Theorem of lower semi-continuous functions. 相似文献
35.
The main purpose of this paper is the study of sufficient and/or necessary conditions for existence of solutions of equilibrium problems. We discuss some of the assumptions of the problem, under which the introduced conditions are sufficient and/or necessary, and also analyze the effect of these assumptions on the connection between the solution sets of the equilibrium problem and of a related convex feasibility problem. 相似文献
36.
Microwave assisted micellar extraction (MAME) coupled with solid phase microextraction (SPME) and HPLC-UV determination have been used for the determination of five organochlorine pesticides from agricultural soil samples. A non-ionic surfactant, Polyoxyethlylene 10 Lauryl Ether was used, and the different variables for the optimization of MAME and SPME procedures were studied. This method was applied successfully to the determination of these pesticides in several kinds of agricultural soil samples with different characteristics. Most of the compounds studied can be recovered in good yields with R.S.D. lower than 9% and detection limit ranged between 56-96 ng g−1 for the pesticides studied. 相似文献
37.
Halko R Padrón Sanz C Sosa Ferrera Z Santana Rodríguez JJ 《Journal of AOAC International》2006,89(5):1403-1409
A simple and fast analytical method was developed for the determination of benzimidazole fungicides (benomyl, carbendazim, thiabendazole, and fuberidazole) in soil samples. The analytes were extracted from the soil samples by means of conventional microwave-assisted extraction, using the non-ionic surfactants polyoxyethylene 10 lauryl ether (POLE) and oligoethylene glycol monooalkyl ether (Genapol X-080) as extractants. Determinations were made by using liquid chromatography with direct fluorescence detection. The use of an analytical column Symmetry C-18 offered short retention times of analytes without the need of any pH regulators with mobile phase methanol-water (50 + 50, v/v). The best results were obtained using 5% (v/v) POLE as extractant with recoveries of the fungicides in spiked soil samples between 71 and 105%. The results were compared with those obtained when Soxhlet extraction was applied to the same soil samples. 相似文献
38.
Background
Presenilin-1 (PS1) is a transmembrane protein first discovered because of its association with familial Alzheimer’s disease. Mice with null mutations in PS1 die shortly after birth exhibiting multiple CNS and non-CNS abnormalities. One of the most prominent features in the brains of PS1?/? embryos is a vascular dysgenesis that leads to multiple intracerebral hemorrhages. The molecular and cellular basis for the vascular dysgenesis in PS1?/? mice remains incompletely understood. Because the extracellular matrix plays key roles in vascular development we hypothesized that an abnormal extracellular matrix might be present in endothelial cells lacking PS1 and examined whether the lack of PS1 affects expression of fibronectin a component of the extracellular matrix known to be essential for vascular development.Results
We report that primary as well as continuously passaged PS1?/? endothelial cells contain more fibronectin than wild type cells and that the excess fibronectin in PS1?/? endothelial cells is incorporated into a fibrillar network. Supporting the in vivo relevance of this observation fibronectin expression was increased in microvascular preparations isolated from E14.5 to E18.5 PS1?/? embryonic brain. Reintroduction of PS1 into PS1?/? endothelial cells led to a progressive decrease in fibronectin levels showing that the increased fibronectin in PS1?/? endothelial cells was due to loss of PS1. Increases in fibronectin protein in PS1?/? endothelial cells could not be explained by increased levels of fibronectin RNA nor based on metabolic labeling studies by increased protein synthesis. Rather we show based on the rate of turnover of exogenously added biotinylated fibronectin that increased fibronectin in PS1?/? endothelial cells results from a slower degradation of the fibronectin fibrillar matrix on the cell surface.Conclusions
These studies show that PS1 regulates the constitutive turnover of the fibronectin matrix in endothelial cells. These studies provide molecular clues that may help to explain the origin of the vascular dysgenesis that develops in PS1?/? embryonic mice.39.
Teodoro Cordova-Fraga Modesto Sosa Martha Alicia Hernandez-Gonzalez Jose Antonio Reyes-Aguilera Sergio Solorio Chystian Ramirez Evelia Bautista-Flores Guadalupe Reynaga Mario Avila-Rodriguez Jose Maria De la Roca-Chiapas 《Applied magnetic resonance》2012,42(2):161-167
Magnetic resonance imaging (MRI) of the gastrointestinal (GI) tract is still limited due to the lack of widely available oral
contrast agents (OCA). The availability of OCA for MRI of the GI tract is a necessity; different fruits might be implemented
as OCA in order to solve this need throughout the year. The objective of this study is to present an alternative fruit as
a clinical OCA for MRI of the GI tract, Achras sapota L. (common medlar). Both physical and chemical characterization of the medlar was performed. It was also tested in situ and
in vivo as an OCA for MRI of the GI tract. Results showed that this fruit had a diamagnetic behavior, although it has enough
iron, manganese and copper to contrast the GI tract in T
1- and T
2-weighted images. Thus we conclude that the medlar fruit has shown a potential as an OCA in GI evaluation by MRI, so it can
be considered as an alternative in complementation of natural OCA. 相似文献
40.
Daura Vega Zoraida Sosa 《International journal of environmental analytical chemistry》2013,93(3):185-197
Abstract A sequential injection analysis method for the simultaneous spectrophotometric determination of phosphate and silicate has been developed. The method is based on the different reaction rates of the heteropolymolybdate formation reactions. Concentrations within the range 0.026—0.485 mmol P l?1 and 0.125—2.848 mmol Si l?1 have been determined at a frequency of 30 samples per hour. An R.S.D. of 2.1% was obtained for 0.162 mmol P l?1 and of 1.1% for 1.424 mmol Si l?1. The method was found to be suitable for the determination of phosphate and silicate in wastewater. 相似文献