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311.
Yolanda Pérez Isabel Sierra Mariano Fajardo 《Journal of organometallic chemistry》2006,691(13):3053-3059
A variety of bisalkoxo titanium dichloride THF adducts [Ti(OR)2Cl2(thf)2] {OR = adamantanoxo (9), (1R,2S,5R)-(−)-menthoxo (10), (1S-endo)-(−)-borneoxo (11)} have been prepared and characterized by spectroscopic techniques. The molecular structure of 11 has been determined by single-crystal X-ray diffraction studies. The parent Lewis acid bisalkoxo titanium dichloride derivatives and related alkoxo complexes [Ti(OR)2(OPri)2]2 have been tested as initiators in ring-opening polymerization of ε-caprolactone and l-lactide. 相似文献
312.
Felipe Gómez-de la Torre Yolanda Gutiérrez Félix A. Jalón Blanca R. Manzano Ana Rodríguez 《Monatshefte für Chemie / Chemical Monthly》2000,131(12):1267-1280
Summary. Partial removal of chloride anions from the dimer [Pd(η3-2-CH3*C3H4)(μ-Cl)]2 with AgTf(Tf = CF3SO3) followed by addition of dppm affords [Pd2(η3-Me*C3H4)2(μ-Cl)(μ-dppm)]Tf (1). The substitution of Cl− by X− (X = pz, SC6F5, S
py
) using the appropriate salts yields the new derivatives [Pd2(η3-Me*C3H4)2(μ-X)(μ-dppm)]Tf (2–4). All complexes exhibit a dinuclear half-A-frame structure with two isomers present in solution. The isomers differ in the
relative orientation of the two allyl groups (cis or trans). The isomer interconversion was studied by variable temperature 1H NMR spectroscopy. The molecular structures of 2 and 4 were solved by X-ray diffraction studies. A distorted boat conformation of the seven- or six-membered metallacycle was found
in both cases.
Received June 7, 2000. Accepted June 20, 2000 相似文献
313.
Kananat Naksomboon Yolanda Álvarez-Casao Michiel Uiterweerd Nick Westerveld Beatriz Maciá M. Ángeles Fernández-Ibáñez 《Tetrahedron letters》2018,59(4):379-382
An efficient catalytic system for the C–H olefination of arenes with different allylic substrates is reported. The catalytic system is based on Pd(OAc)2 and a readily accessible bidentate S,O-ligand. The methodology shows high activity with a wide range of arenes, including bulky and, electron-rich and -poor arenes. The applicability of this catalyst is demonstrated in the late-stage functionalization of the complex molecule O-methylestrone. 相似文献
314.
David K.W. Yeung Kunwar S. Bhatia Yolanda Y.P. Lee Ann D. King Philippe Garteiser Ralph Sinkus Anil T. Ahuja 《Magnetic resonance imaging》2013
Purpose
The purpose was to describe the design and fabrication of a driver suitable for magnetic resonance elastography (MRE) of the head and neck and to assess its performance in evaluating human parotid gland, lymph nodes and thyroid at 3.0 T.Materials and methods
A head and neck driver was fabricated using a commercial transducer, headrest mould and piston extension. Driver performance was tested using a motion-sensitized spin-echo MRE pulse sequence. Six healthy volunteers and three patients (two metastatic nodes and one papillary carcinoma) were evaluated using MRE. Viscoelastic maps were computed to obtain storage modulus (G’) and loss modulus (G”) of the normal parotid and thyroid, metastatic node and thyroid cancer. Reproducibility was assessed by coefficient of variation.Results
All subjects completed MRE examination without discomfort. Initial G’ and G” values were as follows: normal parotid gland, 1.12 kPa and 0.48 kPa; thyroid, 0.58 kPa and 0.42 kPa; metastatic node, 0.66 kPa and 0.58 kPa; and thyroid cancer, 0.17 kPa and 0.28 kPa. Based on parotid data, the coefficient of variation for G’ and G” was 4.7% and 9.8%.Conclusion
A new MRE driver for head and neck was successfully implemented, and our initial results suggested the device was suitable for the mechanical assessment of tissues in the head and neck. 相似文献315.
Nataly Carolina Rosero-Navarro Pawel Figiel Roman Jedrzejewski Anna Biedunkiewicz Yolanda Castro Mario Aparicio Sergio Antonio Pellice Alicia Durán 《Journal of Sol-Gel Science and Technology》2010,54(3):301-311
The aim of this work was to study the effect of the incorporation of cerium nitrate in a silica-methacrylate sol–gel hybrid
matrix reinforced with silica nanoparticles. Sols, coatings and powders have been studied, focusing specially in the determination
of the redox ratio Ce3+/Ce4+ and films structure. Sols have been characterised using viscosity measurements and FT-IR spectroscopy, and powders and coatings
obtained with different Ce contents through UV–Vis and FT-IR spectroscopy, TGA, TEM, AFM and FE-SEM. The goal was to reach
the best compromise between maximum cerium concentration and coating stability to better understand the mechanisms acting
in active anti-corrosive processes. 相似文献
316.
The pentadentate ligand N,N′-bis(2-hydroxyphenyl)-pyridine-2,6-dicarboxamide (POPYH4) has been used to prepare a variety of new complexes [HNEt3]2[Zn4Cl(POPYH)3] (2), [HNEt3][PdCl(POPYH2)] (3), [HNEt3][Ni(POPYH)] (4) and K[Ni(POPYH)] (5) which show the versatility of this multidentate ligand. The complexes have been characterised spectroscopically and their molecular and crystal structures have been determined by single crystal X-ray diffraction techniques. In these complexes the ligand exhibits different modes of coordination towards different transition metal ions. The structure of triethylammonium salt of the Zn(II) dianion 2 consists of an unusual tetra-zinc core supported by three POPYH ligands each one of which links two adjacent zinc centres through two oxygen and two nitrogen donor atoms. The salt of the square planar Pd(II) anion 3 contains one POPYH2 ligand which coordinates in a tridentate fashion through the two deprotonated amido groups and by the central pyridine nitrogen donor. The two Ni(II) salts 4 and 5 contain the same [Ni(POPYH)]− anion in which the square planar Ni(II) centre is chelated by a POPYH ligand through the two deprotonated amido nitrogen atoms, the pyridine nitrogen and a deprotonated hydroxyl group. 相似文献
317.
318.
Determination of pesticides and veterinary drug residues in food by liquid chromatography-mass spectrometry: A review 总被引:1,自引:0,他引:1
Ana Masiá Maria Morales Suarez-Varela Agustin Llopis-Gonzalez Yolanda Picó 《Analytica chimica acta》2016
Monitoring of pesticides and veterinary drug residues is required to enforce legislation and guarantee food safety. Liquid chromatography-mass spectrometry (LC-MS) is the prevailing technique for assessing both types of residues because LC offers a versatile and universal separation mechanism suitable for non-gas chromatography (GC) amenable and the majority of GC-amenable compounds. This characteristic becomes more relevant when LC is coupled to MS because the high sensitivity and specificity of the detector allows to apply generic sample preparation procedures, which simultaneously extract a wide variety of residues with different physico-chemical properties. Determination of metabolites and degradation products, non-target suspected screening of an increasing number of residues, and even unknowns identification are also becoming inherent LC-MS advantages thanks to the latest advances. For routine analysis and, in particular, for official surveillance purposes in food control, analytical methods properly validated following strict guidelines are needed. After a brief introduction and an outline of the legislation applicable around the world, aspects such as improvement of specificity of high-throughput methods, resolution and mass accuracy of identification strategies and quantitative accuracy are critically reviewed in this article. In them, extraction, separation and determination are emphasized. The main objective is to offer an assessment of the state of the art and identify research needs and future trends in determining pesticide and veterinary drug residues in food by LC-MS. 相似文献
319.
Ultra-high-performance liquid chromatography-quadrupole time-of-flight mass spectrometry (UPLC-QqTOF-MS) is an emerging technique offering more rapid and efficient separation, as well as the possibility to obtain accurate mass measurement and tandem mass spectrometry (MS/MS). This paper deals with the use of UPLC-QqTOF-MS to identify the pesticide residues present in complex pear extracts. Carbendazim, imazalil, and ethoxyquin were successfully identified because of the accurate mass determination of their protonated molecule and their major fragments in the product ion mass spectra. A few plastic and latex additives were also found, most of them probably coming from the packaging transfer to the fruits. The potential of the UPLC-QqTOF-MS and UPLC-QqTOF-MS/MS techniques as a quantification tool is also discussed taking imazalil as example. For quantification, calibration curves were linear over a dynamic range of 2 orders of magnitude, whereas higher calibration ranges are better adjusted to polynomial curves of second and third order. Quantification using different mass windows was also assessed. Accurate quantification required mass windows as wide as 20 mDa, narrower mass windows of 5 mDa provided erroneous quantification, probably because the low ion abundance. The mean recoveries and percentage relative standard deviation (RSD) of 35 determinations for imazalil were 76% (13% RSD) by MS and 77% (14% RSD) by MS/MS. The theoretical limit of detection was 0.4 microg kg(-1), with a validated limit of quantification of 2 microg kg(-1). The quantitative data obtained using UPLC-QqTOF-MS were compared with those obtained using conventional liquid chromatography (LC)-MS/MS with a triple quadrupole (QqQ). It was concluded that UPLC-QqTOF-MS might become a powerful analytical tool for both, unknown's identification and quantification of target pesticides. 相似文献
320.
Alkylidenation of arylmethyl, dialkyl, and cyclic ketones with 2-( p-toluenesulfinyl)benzyl iodide in the presence of NaN(SiMe3)2 takes place with a high or complete control of the facial selectivity at the carbonyl group (up to 98% de) and the carbanion (>98% de), respectively, yielding mixtures of only two optically pure trisubstituted epoxides ( E/Z ratio ranges between 2:1 and >50:1). Removal of the p-tolylsulfinyl group with t-BuLi provides the corresponding (E)-3-phenyl-2,2-disubstituted epoxides without affecting their optical purity. 相似文献