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101.
Mitch K.P Leung 《Analytica chimica acta》2003,491(1):15-25
A covalent interaction-based molecularly imprinted polymer (MIP) material for 3-chloro-1,2-propanediol (3-MCPD), a post-testicular anti-fertility agent and possible carcinogen and mutagen in food products containing acid-hydrolyzed vegetable proteins, has been successfully fabricated using 4-vinylphenylboronic acid as the functional monomer. Rebinding assay revealed that the binding constant, KB, for the receptor sites and non-specific sites are 1.93±0.1×104 and 2.74±0.7×102 M−1, respectively. The estimated number of receptor site, Bmax, imprinted is 123.3±3 μmol/g of MIP. The MIP material is able to act as a potentiometric chemosensor for 3-MCPD via increase in Lewis acidity of the receptor sites upon reaction of the arylboronic acid with 3-MCPD to form the more acidic arylboronic acid esters. A simple pH glass electrode is sufficient to monitor the analyte-specific rebinding. In unbuffered aqueous media, linear potentiometric response from 0 to 350 ppm of 3-MCPD can be achieved. The MIP-based chemosensing in a soya sauce matrix has also been attempted. It is found that the dynamic range of the potentiometric chemosensing response of the MIP material is much reduced, probably due to the blocking or deactivation of receptor sites by interferents in soya sauces. Nevertheless, the present work demonstrated the feasibility of using MIP-based chemosensors as semi-quantitative analytical tools for screening purposes in quality control of food products. 相似文献
102.
Cyrille Ceugniet Ltitia Lepetit Nancy Lauth De Viguerie Henry Jammes Nicole Peyrot Monique Rivire 《Journal of chromatography. A》1998,810(1-2):237-240
A high-performance liquid chromatographic (HPLC) procedure was developed to allow the rapid separation, in a single run, of a mixture of the main retinal isomers (all-trans, 13-cis, 9-cis), all-trans-retinol, and of the two major photooxygenated photoproducts (5,8-peroxyretinal and 5,6-epoxyretinal). The mixture was separated by HPLC on an octadecyl (ODS) column with 16% (v/v) diethyl ether in hexane as mobile phase and anthracene as the internal standard. A commercial type cosmetic formulation containing 0.05% all-trans-retinal was analyzed successfully for this analyte. 相似文献
103.
David M. Dastrup Steven M. Weinreb James R. Henry Andrew J. Lechleiter 《Tetrahedron》2004,60(4):901-906
β-Tosylethylhydrazine (6) can be prepared efficiently in one step from commercially available p-tolyl vinyl sulfone (7) and hydrazine hydrate. This hydrazine reacts with both 1,3-diketones and conjugated ynones in glacial acetic acid to provide a variety of N-tosylethyl-protected (TSE) pyrazoles in good yields. The TSE group can be removed from the pyrazoles using potassium t-butoxide in THF at −30 °C-rt. In addition, hydrazine 6 condenses with β-ketonitriles and β-aminoacrylonitriles to afford 5-aminopyrazoles, which can be deprotected by brief treatment with NaOEt in EtOH/DMSO at 45 °C. 相似文献
104.
The oxidation of uric acid has been studied by thin-layer spectroelectrochemistry using an optically transparent gold minigrid electrode and enzymatically using peroxidase. Under both enzymatic and electrochemical conditions a u.v.-absorbing intermediate (λmax=302–304 nm between pH 7–9.3) is observed. This intermediate is proposed to be an imine-alcohol species formed by rapid hydration of the primary reaction product which is a diimine. Under the conditions employed in both the enzymatic electrochemical studies the imine-alcohol intermediate is hydrated in a first order reaction with an observed rate constant of 3.5×10?3s?1 between pH 7–9.3. This study establishes the similarity between the electrochemical and enzymatic oxidation of uric acid and indicates that electrochemical investigations of the redox behavior of purines can provide unique insights into their biological redox properties. 相似文献
105.
Jakub Kołacz Henry G. Gotjen Robel Y. Bekele Jason D. Myers Jesse A. Frantz Michael Ziemkiewicz 《Liquid crystals》2020,47(4):531-539
ABSTRACTIn a planar dielectric waveguide, weak confinement of a propagating mode in a high index core leads to a measurable evanescent interaction with the cladding. In this work, we study the effect of a reorientable anisotropic cladding on the behaviour of Transverse Electric (TE) and Transverse Magnetic (TM) mode polarisations using a liquid crystal (LC)-clad waveguide architecture. The polarised evanescent field of a guided mode interacts with a voltage-tunable birefringent LC cladding to deflect an out-coupled beam. Experimental measurements are coupled with a theoretical framework and show good consistency with simulation results. We isolate the effect of mode confinement by changing the thickness of the high index core. Interactions between the LC index ellipsoid and the mode polarisation are probed by changing the initial alignment of the LC. Finally, we examine the difference in deflection between TE and TM modes, which incorporates both a change in mode confinement and a difference in LC index components. 相似文献
106.
A flame photometric method of determining calcium in phosphate, carbonate, and silicate locks has been developed Aluminum and phosphate interference was overcome by the addition of a large excess of magnesium. The method is rapid and suitable for routine analysis Results obtained are within ± 2% of the calcium oxide content. 相似文献
107.
Clifford Henry Taubes 《Communications in Mathematical Physics》1985,97(4):473-540
In each monopole sector there exist an infinite number of finite energy solutions to the Prasad-Sommerfield limit of the SU(2) Yang-Mills-Higgs equations on 3 whose energy is greater than any finite number.National Science Foundation Postdoctoral Fellow in Mathematics 相似文献
108.
Development of high-performance liquid chromatographic fingerprints for distinguishing Chinese Angelica from related umbelliferae herbs 总被引:6,自引:0,他引:6
Lu GH Chan K Liang YZ Leung K Chan CL Jiang ZH Zhao ZZ 《Journal of chromatography. A》2005,1073(1-2):383-392
A high-performance liquid chromatographic (HPLC) fingerprint of Chinese Angelica (CA) was developed basing on the consistent chromatograms of 40 CA samples (Angelica sinensis (Oliv.) Diels). The unique properties of this HPLC fingerprints were validated by analyzing 13 related herbs including 4 Japanese Angelicae Root samples (JA, A. acutiloba Kitagawa and A. acutiloba Kitagawa var. sugiyame Hikino), 6 Szechwan Lovage Rhizome samples (SL, Ligusticum chuanxiong Hort.) and 3 Cnidium Rhizome samples (CR, Cnidium officinale Makino). Both correlation coefficients of similarity in chromatograms and relative peak areas of characteristic compounds were calculated for quantitative expression of the HPLC fingerprints. The amount of senkyunolide A in CA was less than 30-fold of that in SL and CR samples, which was used as a chemical marker to distinguish them. JA was easily distinguished from CA, SL and CR based on either chromatographic patterns or the amount of coniferyl ferulate. No obvious difference between SL and CR chromatograms except the relative amount of some compounds, suggesting that SL and CR might have very close relationship in terms of chemotaxonomy. Ferulic acid and Z-ligustilide were unequivocally determined whilst senkyunolide I, senkyunolide H, coniferyl ferulate, senkyunolide A, butylphthalide, E-ligustilide, E-butylidenephthalide, Z-butylidenephthalide and levistolide A were tentatively identified in chromatograms based on their atmospheric pressure chemical ionization (APCI) MS data and the comparison of their UV spectra with those published in literatures. 相似文献
109.
M. Chatry M. Henry M. In C. Sanchez J. Livage 《Journal of Sol-Gel Science and Technology》1994,1(3):233-240
The hydrolysis and condensation of zirconium n-propoxide in n-propanol have been chemically controlled via the complexation of the zirconium precursor with acetylacetone. The size of the zirconium oxide-based particles is mainly controlled by the complexation ratio x=[acac]/[Zr]. the mean size increases from nanometric to submicronic range when x decreases from 1 to 0.1. Amorphous colloidal particles are obtained at room temperature. They result from a competitive growth/termination mechanism of zirconium-oxo species in the presence of acac surface capping agents. However non-aggregated nanocrystalline particles of tetragonal zirconia, about 2 nm in diameter are formed upon aging at 60°C when hydrolysis is performed in the presence of paratoluene sulfonic acid (PTSA). 相似文献
110.