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91.
The essential oil from aerial parts (stems and leaves) of Atriplex undulata (Moq) D. Dietr. (Chenopodiaceae) has been studied for its in vitro antioxidant activity. The chemical composition of the oil obtained by hydrodistillation was determined by GC and GC-MS. The major constituents were p-acetanisole (28.1%), beta-damascenone (9.3%), beta-ionone (5.1%), viridiflorene (4.7%) and 3-oxo-alpha-ionol (2.2%). The antioxidant activity of the oil was determined by two methods: Crocin bleaching inhibition (Krel = 0.72 +/- 0.15) and scavenging of the DPPH radical (IC50 = 36.2 +/- 1.6 microg/mL). The presence of active compounds like p-acetanisole, carvone, vanillin, 4-vinylguaiacol, guaiacol, terpinen-4-ol and alpha-terpineol could explain the antioxidant activity observed for this oil. 相似文献
92.
We characterize the hereditary torsion pairs of finite type in the functor category of a ring R that are associated to tilting torsion pairs in the category of R-modules. Moreover, we determine a condition under which they give rise to TTF triples. 相似文献
93.
Overwhelming evidence has been previously reported for the existence of the so‐called “dimer nucleophile mechanism” in aromatic nucleophilic substitutions by amines in aprotic solvents, for which the most prominent feature is the fourth‐order kinetics (third order in amine) that has been observed with many different substrate–nucleophile systems, especially those in which departure of the nucleofuge is the rate‐determining step. The mechanism has been confirmed by several other features, although other alternative mechanisms were suggested to explain the fourth‐order kinetics, no one has been able to explain the other above‐mentioned features. The present paper affords additional experimental evidence and derivation of the kinetic expressions for reactions with good nucleofugues, where the first step is rate determining. The work involves studies of the reactions of 2,4‐dinitrofluorobenzene and 2,4‐dinitrochlorobenzene with aniline and with alkyldiamines in toluene. The novelty of this work lies in the selection of substrate–nucleophile systems exhibiting kinetic behavior that allows estimations of the different k's involved. The satisfactory agreement between the quotients of k's calculated from sets of data obtained under different reaction conditions hereby reported indicates that the assumptions made are correct and that the whole treatment applied to the kinetic data is justified. All together, the results fit well with the reaction scheme involving the dimer nucleophile mechanism, adding new evidence to this mechanism that it is well established in the current literature. © 2010 Wiley Periodicals, Inc. Int J Chem Kinet 42: 735–742, 2010 相似文献
94.
Barreca ML Gitto R Quartarone S De Luca L De Sarro G Chimirri A 《Journal of chemical information and computer sciences》2003,43(2):651-655
A three-dimensional pharmacophore model for the binding of noncompetitive AMPA receptor antagonists was developed in order to map common structural features of highly active compounds. This hypothesis, which consists of two hydrophobic regions, one hydrogen bond acceptor and one aromatic region, was successfully used as framework for the design of a new class of allosteric modulators containing a tetrahydroisoquinoline skeleton and for in silico screening. The promising biological results suggested that the identified molecules might be useful "lead compounds" for future drug development. 相似文献
95.
Luppi G Lanci D Trigari V Garavelli M Garelli A Tomasini C 《The Journal of organic chemistry》2003,68(5):1982-1993
The liquid-phase synthesis and the conformational analysis of a small library of fully protected tetramers containing L-pyroglutamic acid (L-pGlu), (4S,5R)-4-methyl-5-carboxybenzyloxazolidin-2-one (L-Oxd), or (4R,5S)-4-methyl-5-carboxybenzyloxazolidin-2-one (D-Oxd) as residue i + 1 are reported to test the tendency of these oligomers to assume a -hairpin conformation. The most promising molecule is Boc-L-Val-D-Oxd-Gly-L-Ala-OBn, which assumes a preferential -turn conformation in CDCl3, as shown by IR and 1H NMR analysis. These findings have been confirmed by DFT calculations, which provide an interpretation for the available experimental data and agree with the reported observations. 相似文献
96.
Dalmora SL Júnior LB Schmidt CA Vaccari SF Oliveira PR Codevilla CF 《Journal of AOAC International》2004,87(6):1305-1308
Enoxaparin is a low-molecular weight heparin used clinically for the prevention and treatment of venous and arterial thrombosis. An anti-factor Xa assay was used to evaluate the potency of the final drug preparation. Method validation investigated parameters such as the range, linearity (r2 = 0.9971), precision, accuracy, and robustness; the biological assay incorporated a chromogenic endpoint and detection at 405 nm. The method yielded good results with a quantitation limit of 0.037 IU/mL and a detection limit of 0.011 IU/mL. The results demonstrated the validity of the anti-factor Xa assay for the determination of enoxaparin. 相似文献
97.
Elena Belluso Donata Bellis Elisa Fornero Silvana Capella Giovanni Ferraris Sergio Coverlizza 《Mikrochimica acta》2006,154(1-2):95-100
A method based on cloud point extraction (CPE) separation/preconcentration of trace cadmium as a prior step to its determination
by graphite furnace atomic absorption spectrometry (GFAAS) has been developed. If the system temperature is higher than the
cloud point temperature (CPT) of the nonionic surfactant of p-octyl polyethyleneglycolphenyether (Triton X-100), the complex
of Cd2+ with 1-(2-pyridylazo)-2-naphthol (PAN) could be extracted into surfactant-rich phase. The chemical variables affecting CPE
were evaluated and optimized. Under the optimum conditions, preconcentrating 10.0 mL of water samples permitted a limit of
detection of 5.9 ng · L−1 (3σ) for cadmium with an enhancement factor of 50 and a relative standard deviation of 2.1% (n = 11, c = 2.0 ng · mL−1). The method was applied to the determination of cadmium in reference material and water samples with satisfactory results. 相似文献
98.
Francesco Ghetti Silvana Fuoco Giovanni Checcuccii 《Photochemistry and photobiology》1998,68(3):276-280
The effect of monochromatic UVB (280–315 nm) irradiation on the photosynthetic activity of the marine green alga Dunaliella salina was investigated by monitoring the rate of oxygen exchange. Samples were irradiated with narrow bands centered at different UV wavelengths (281, 290, 300, 310 and 322 nm). In a first set of experiments the samples were preirradiated keeping constant the irradiance and varying exposure time. By increasing UVB fluence, a wavelength-dependent decrease in the rate of oxygen production was observed. In a second set of experiments oxygen exchange was monitored simultaneously to UVB irradiation. The decline in the rate of oxygen production was sharper at short wavelengths and faster with increasing UVB photon flux density. The photon fluence action spectra derived from the two sets of experiments are in good agreement and indicate a decrease in the UVB-inhibiting effectiveness of two orders of magnitude from about 0.2 (mmol m-2)-1 at 281 nm to about 0.003 (mmol m-2)-1 at 322 nm. The photon flux density action spectrum derived from the second set of experiments indicates a smoother decrease from about 0.2 (pmol s-l m-2)-1 at 281 nm to about 0.05 (pmol s-l m-z)-l at 310 nm. 相似文献
99.
A screen-printed biosensor for the detection of pesticides in water miscible organic solvents is described based on the use of p-aminophenyl acetate as acetylcholinesterase substrate. The oxidation of p-aminophenol, product of the enzymatic reaction was monitored at 100 mV vs. Ag/AgCl screen-printed reference electrode. Miscible organic solvents as ethanol and acetonitrile were tested. The acetylcholinesterase (AChE) was immobilised on a screen-printed electrode surface by entrapment in a PVA-SbQ polymer and the catalytic activity of immobilised AChE was studied in the presence of different percentages of organic solvents in buffer solution. The sensor shows good characteristics when experiments were performed in concentrations of organic solvents below 10%. No significant differences were observed when working with 1 and 5% acetonitrile in the reaction media. Detection limits as low as 1.91x10(-8) M paraoxon and 1.24x10(-9) M chlorpyrifos ethyl oxon were obtained when experiments are carried out in 5% acetonitrile. 相似文献
100.
Débora de Oliveira Marco Di Luccio Carina Faccio Clarissa Dalla Rosa João Paulo Bender Nádia Lipke Silvana Menoncin Cristiana Amroginski José Vladimir de Oliveira 《Applied biochemistry and biotechnology》2004,115(1-3):771-780
We studied the production of fatty acid ethyl esters from castor oil using n-hexane as solvent and two commercial lipases, Novozym 435 and Lipozyme IM, as catalysts. For this purpose, a Taguchi experimental
design was adopted considering the following variables: temperature (35–65°C), water (0–10 wt/wt%), and enzyme (5–20 wt/wt%)
concentrations and oil-to-ethanol molar ratio (1∶3 to 1∶10). An empirical model was then built so as to assess the main and
cross-variable effects on the reaction conversion and also to maximize biodiesel production for each enzyme. For the system
containing Novozym 435 as tatalyst the maximum conversion obtained was 81.4% at 65°C, enzyme concentration of 20 wt/wt%, water
concentration of 0 wt/wt%, and oil-to-ethanol molar ratio of 1∶10. When the catalyst was Lipozyme IM, a conversion as high
as 98% was obtained at 65°C, enzyme concentration of 20 wt/wt%, water concentration of 0 wt/wt%, and oil-to-ethanol molar
ratio of 1∶3. 相似文献