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81.
Vanesa Guillén-Casla María Eugenia León-González Luis Vicente Pérez-Arribas Luis María Polo-Díez 《Analytical and bioanalytical chemistry》2010,397(1):63-75
Changes in free amino acids content and its potential racemization in ready-to-eat foods treated with E-beam irradiation between
1 and 8 kGy for sanitation purposes were studied. A simple heart cut two-dimensional high performance liquid chromatographic
method (LC–LC) for the simultaneous enantiomeric determination of three pairs of amino acids used as markers (tyrosine, phenylalanine,
and tryptophan) is presented. The proposed method involves the use of two chromatographs in an LC–LC achiral–chiral coupling.
Amino acids and their decomposition products were firstly separated in a primary column (C18) using a mixture of ammonium acetate buffer (20 mM, pH 6) (94%) and methanol (6%) as the mobile phase. Then, a portion of
each peak was transferred by heart cutting through a switching valve to a teicoplanin-chiral column. Methanol (90%)/water
(10%) was used as the mobile phase. Ultraviolet detection was at 260 nm. Detection limits were between 0.16 and 3 mg L−1 for each enantiomer. Recoveries were in the range 79–98%. The LC–LC method combined with the proposed sample extraction procedure
is suitable for complex samples; it involves an online cleanup, and it prevents degradation of protein, racemization of L-enantiomers,
and degradation of tryptophan. Under these conditions, D-amino acids were not found in any of the analyzed samples at detection
levels of the proposed method. 相似文献
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Miriam A. Martins Alho Maria I. Errea Vanesa L. Sguerra Norma B. D'Accorso Laura B. Talarico Cybele C. García Elsa B. Damonte 《Journal of heterocyclic chemistry》2005,42(5):979-983
1,2‐O‐Isopropylidene‐α‐L‐threofuranosyl heterocyclic derivatives were synthesized from 1,2‐O‐iso‐propylidene‐α‐D‐xilopentadialdo‐1,4‐furanose and tested for antiviral activity against herpes simplex virus type 1, dengue virus type 2 and Junin virus. For comparative propose, the antiviral activity of some of their pyranosyl analogues were also tested. The furanosyl derivatives showed to be moderate inhibitors of Junin virus and, in general, proved to be more effective than the pyranosyl analogues. 相似文献
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Rocio Cuervo‐Rodriguez Vanesa Bordeg Maria Carmen Fernndez‐Monreal Marta Fernndez‐García Enrique L. Madruga 《Journal of polymer science. Part A, Polymer chemistry》2004,42(17):4168-4176
Controlled free‐radical copolymerization of styrene (S) and butyl acrylate (BA) was achieved by using a second‐generation nitroxide, N‐tert‐butyl‐N‐[1‐diethylphosphono‐(2,2‐dimethylpropyl)] nitroxide (DEPN), and 2,2‐azobisisobutyronitrile (AIBN) at 120 °C. The time‐conversion first‐order plot was linear, and the number‐average molecular weight increased in direct proportion to the ratio of monomer conversion to the initial concentration, providing copolymers with low polydispersity. The monomer reactivity ratios obtained were rS = 0.74 and rBA = 0.29, respectively. To analyze the convenience of applying the Mayo–Lewis terminal model, the cumulative copolymer composition against conversion and the individual conversion of each monomer as a function of copolymerization time were studied. The theoretical values of the propagating radical concentration ratio were also examined to investigate the copolymerization rate behavior. © 2004 Wiley Periodicals, Inc. J Polym Sci Part A: Polym Chem 42: 4168–4176, 2004 相似文献
87.
The jet-cooled rotational spectrum of uracil has been investigated using laser ablation molecular beam Fourier transform microwave (LA-MB-FTMW) spectroscopy. The quadrupole structure originated by the two 14N nuclei of uracil has been completely resolved and assigned. This provides a definitive method to establish the pyrrolic or pyrimidinic nature of the N nuclei and allows us to conclude that the observed tautomer of uracil in the gas phase is the diketo form. From the rotational constants of the isotopic species detected, a structure of uracil has been determined. 相似文献
88.
Lillo V Mata JA Segarra AM Peris E Fernandez E 《Chemical communications (Cambridge, England)》2007,(21):2184-2186
Stable N-heterocyclic platinum-carbene complexes are the first example of platinum-mediated regioselective H-B addition to vinylarenes and alkynes, allowing consecutive cross coupling reactions with the same catalytic system. 相似文献
89.
This paper demonstrates that the spectrophotometric properties of blood hemoglobin (Hb) can be used for the direct determination of biochemical compounds in blood. Glucose is used as a model, but the methodology can be applied to many other compounds (only a previous enzymatic reaction producing H(2)O(2) is needed). In order to develop the method, a model relating the Hb absorbance variation during the reaction with the glucose concentration has been developed to provide theoretical support for the method and to predict its application to other compounds. In addition, clear blood samples need to be prepared without pre-treatment and lateral reactions of H(2)O(2) with other blood constituents need to be blocked; this has been achieved with 100 : 1 v/v blood dilution in bi-distilled water and azide addition. The linear response range of the method can be fitted between 2 and 540 mg dL(-1) glucose relative to the original blood sample (RSD about 4%, 70 mg dL(-1)). The analyte concentration can be obtained by an absolute calibration method or by the standard addition method; both have been applied for direct glucose determination in several blood samples and good correlations with those obtained by an automatic analyzer have been obtained. 相似文献
90.
Lillo V Fructos MR Ramírez J Braga AA Maseras F Díaz-Requejo MM Pérez PJ Fernández E 《Chemistry (Weinheim an der Bergstrasse, Germany)》2007,13(9):2614-2621
The complexes [Cu(NHC)(NCMe)]BF4 (NHC=N-heterocyclic ligand), with bis(catecholato)diboron (B2(cat)2) as the boron source, efficiently catalyze the diboration of styrene with very high degrees of conversion. With the appropriate NHC ligand, the reaction proceeds quantitatively toward the diborated derivative PhCH(Bcat)--CH2(Bcat). The [styrene]/[B2(cat)2] ratio also has a strong effect on the selectivity: the use of an excess of styrene allows modification of the selectivity toward the formation solely of the monoborated derivative, PhCH2--CH2(Bcat). DFT calculations suggest that no oxidative addition processes take place at copper, but that intermediates containing coordinated sigma-bonds are involved in the catalytic cycle. 相似文献