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排序方式: 共有533条查询结果,搜索用时 15 毫秒
491.
Effect of a Carboxylic Group on the Conformational Properties of Some Gemini Surfactants 总被引:1,自引:0,他引:1
Paweł Misiak Bożenna Różycka-Roszak Anna Mozrzymas Emilia Fisicaro 《Journal of solution chemistry》2007,36(7):845-851
Molar volumes of derivatives of N,N-bisdimethyl-1,2-ethanediamine of general formula [C
n
H2n+1OOCCH2(CH3)2N+CH2CH2N+(CH3)2CH2COOC
n
H2n+1]2Cl− (bis-C
n
BEC), and betaine ester derivatives of general formula N+(CH3)3CH2COOC
n
H2n+1Cl− (C
n
BEC), were calculated by means of molecular connectivity indices and an additivity scheme. The COO group contribution in the
β-position to the molar volume of bis-C
n
BEC was found from experimental data to be significantly lower from that for C
n
BEC and was estimated to be 13.5 cm3⋅mol−1. It is suggested that this effect is due to hydrogen bonding between the carboxyl groups via water molecules. Molecular dynamics
simulations of bis-C12BEC and 14–2–14 molecules in water were performed and suggest that the upper part of the bis-C12BEC, containing the carboxyl groups, is stiffened by its hydration shell. 相似文献
492.
A new chiral derivatizing agent for ee determination of 1,2-diols via (1)H NMR is described. (S)-(+)-N-acetylphenylglycineboronic acid (1) is synthesized in enantiomerically pure form; its reaction with chiral diols quantitatively yields cyclic boronic esters 5a-g. The latter show a remarkably high diastereodifferentiation of proton NMR signals useful for de determination. [reaction: see text] 相似文献
493.
Pichini S Abanades S Farré M Pellegrini M Marchei E Pacifici R Torre Rde L Zuccaro P 《Rapid communications in mass spectrometry : RCM》2005,19(12):1649-1656
A gas chromatography method with mass spectrometric detection is described for the determination of Salvinorin A, the main active ingredient of the hallucinogenic mint Salvia divinorum. The method was validated in plasma, urine, saliva and sweat using 17-alpha-methyltestosterone as internal standard. The analytes were extracted from biological matrices with chloroform/isopropanol (9:1, v/v). Chromatography was performed on a 5% phenyl methyl silicone capillary column and analytes were determined in the selected ion monitoring mode. The method was validated over the concentration range 0.015-5 microg/mL plasma, urine and saliva and 0.01-5 microg/patch in the case of sweat. Mean recoveries ranged between 77.1 and 92.7% for Salvinorin A in different biological matrices, with precision and accuracy always better than 15%. The method was applied to the analysis of urine, saliva and sweat from two consumers after smoking 75 mg plant leaves to verify the presence of the active ingredient of S. divinorum in human biological fluids as a biomarker of plant consumption. Salvinorin A was detected in urine (2.4 and 10.9 ng/mL) and saliva (11.1 and 25.0 ng/mL), but not in sweat patches from consumers. 相似文献
494.
Virgil Brboiu Emilia Streba Cornelia Luca Cristofor I. Simionescu 《Journal of polymer science. Part A, Polymer chemistry》1995,33(3):389-398
The reactions of vinylpyridine polymers with α,β-unsaturated carboxylic acids such as acrylic, methacrylic, crotonic, itaconic, cinnamic, fumaric, and maleic acids were studied. It was found that, when reacted with acrylic, itaconic and fumaric acids. poly(4-vinylpyridine) gave macromolecular betaine products while with maleic acid, betaine as well as the corresponding salt was obtained. Poly(2-vinylpyridine) reacted with the same acids as poly(4-vinylpyridine) gave only the salts. No significant changes were observed with the two polymers when reacted with methacrylic, crotonic, and cinnamic acids. To attempt to rationalize these observations with the two macromolecular tertiary amines, the reactions of 4-methyl and 2-methylpyridines with the same carboxylic acids were investigated. The 1H-NMR methodology was generally applied to elucidate the chemical structure obtained. © 1995 John Wiley & Sons, Inc. 相似文献
495.
N. Majcen E. Bulska I. Leito Emilia Vassileva Ioannis Papadakis Philip Taylor 《Accreditation and quality assurance》2002,7(10):419-422
In 2000, the European Commission-Joint Research Centre, Institute for Reference Materials and Measurements (EC-JRC-IRMM) set
up a project to improve the scientific basis for metrology in chemistry (MiC) in EU candidate countries. Several activities
were initiated (training, fellowships, sponsoring seminars, conferences and participation in the International Measurement
Evaluation Programme – IMEP). A particular initiative, discussed here, was to assist each of the national measurement institutes
of these countries to write a status report on MiC. Most importantly, the report was intended to be the end-product of a process
to document the current status of MiC. Intentionally, this process involved not only the providers of services in MiC but
all the major stakeholders in this activity (e.g. major field laboratories, accreditation bodies, regulatory bodies, educators,
professional bodies). The status reports are intended to be the first step of the future improvement process. In those countries
where writing of the status reports has been started (Slovenia, Poland, Bulgaria and Estonia) the first signs are that this
process leads to better co-operation and particularly a better understanding of what the future role and activities of each
of these stakeholders should be.
Correspondence to N. Majcen 相似文献
496.
Mariana Emilia Ghica 《Analytica chimica acta》2005,532(2):145-151
A new methyl viologen-mediated amperometric enzyme electrode sensitive to glucose has been developed using carbon film electrode substrates. Carbon film electrodes from resistors fabricated by pyrolytic deposition of carbon were modified by immobilization of glucose oxidase through cross-linking with glutaraldehyde in the presence of bovine serum albumin. The mediator, methyl viologen, was directly immobilised with the enzyme together with Nafion cation-exchange polymer. The electrochemistry of the glucose oxidase/methyl viologen modified electrode was investigated by cyclic voltammetry and by electrochemical impedance spectroscopy. The biosensor response to glucose was evaluated amperometrically; the detection limit was 20 μM, the linear range extended to 1.2 mM and the reproducibility of around 3%. When stored in phosphate buffer at 4 °C and used every day, the sensor showed good stability over more several weeks. 相似文献
497.
Mononuclear macrocyclic complexes of manganese(II ), cobalt(II ) and nickel(II ) perchlorate using 10 different oxaazamacrocyclic ligands (L1 — L10) have been prepared and characterized. The complexation reactions with the diiminic ligands were obtained by template condensation of the appropriate dialdehyde and diamine precursors; the reduced macrocycle complexes were synthesized using a direct route. The complexes have been characterized by elemental analyses, molar conductivity, mass spectrometry, IR, UV‐vis spectroscopy, diffuse reflectance and magnetic susceptibility measurements. 相似文献
498.
The paper provides an explanation for altruistic behavior based on the matching and learning technology in the population.
In a infinite structured population, in which individuals meet and interact with their neighbors, individuals learn by imitating
their more successful neighbors. We ask which strategies are robust against invasion of mutants: A strategy is unbeatable if when all play it and a finite group of identical mutants enters then the learning process eliminates the mutants with
probability 1. We find that such an unbeatable strategy is necessarily one in which each individual behaves as if he is related
to his neighbors and takes into account their welfare as well as his. The degree to which he cares depends on the radii of
his neighborhoods.
Received June 1996/Revised version October 1998 相似文献
499.
Josep M Oliva M Emilia D G Azenha Hugh D Burrows Rita Coimbra J Serxio Seixas de Melo L Moisés Canle M Isabel Fernández J Arturo Santaballa Luis Serrano-Andrés 《Chemphyschem》2005,6(2):306-314
We report a joint computational and luminescence study on the low-lying excited states of sym-triazines, namely, 1,3,5-triazine (1) and the ubiquitous herbicides atrazine [6-chloro-N2-ethyl-N4-isopropyl-1,3,5-triazine-2,4-diamine (2)] and ametryn [6-methylthio-N2-ethyl-N4-isopropyl-1,3,5-triazine-2,4-diamine (3)]. Geometrical structures, energetics, and transition and state properties of I and 2 were computed at the TD-DFT, CASSCF, and CASPT2 levels of theory. The fluorescence and phosphorescence emission spectra, lifetimes, and fluorescence quantum yields were measured for the three compounds, and from these, the energies of the lowest excited states and their corresponding radiative rates were determined. The predictions from CASPT2 calculations are in good agreement with the experimental results obtained from the luminescence studies and allow the interpretation of different absorption and emission features. 相似文献
500.
Diego Cesario Mariagrazia Fortino Tiziana Marino Francesca Nunzi Nino Russo Emilia Sicilia 《Journal of computational chemistry》2019,40(8):944-951
The effects on the activity of thyroxine (T4) due to the chalcogen replacement in a series of peri-substituted naphthalenes mimicking the catalytic function of deiodinase enzymes are computationally examined using density functional theory. In particular, T4 inner-ring deiodination pathways assisted by naphthyl-based models bearing two tellurols and a tellurol-thiol pair in peri-position are explored and compared with the analogous energy profiles for the naphthalene mimic having two selenols. The presence of a halogen bond (XB) in the intermediate formed in the first step and involved in the rate-determining step of the reaction is assumed to facilitate the process increasing the rate of the reaction. The rate-determining step calculated energy barrier heights allow rationalizing the experimentally observed superior catalytic activity of tellurium containing mimics. Charge displacement analysis is used to ascertain the presence and the role of the electron density charge transfer occurring in the rate-determining step of the reaction, suggesting the incipient formation or presence of a XB interaction. © 2019 Wiley Periodicals, Inc. 相似文献