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991.
L. C. R. Andrade J. A. Paixo M. J. M. de Almeida C. Siquet F. Borges 《Acta Crystallographica. Section C, Structural Chemistry》2006,62(2):o95-o97
The molecule of the title compound, C23H40O4Si2, features an approximate non‐crystallographic C2 symmetry axis. The aldehyde group is disordered over two positions with similar occupancies. The geometry of the isolated molecule was studied by ab initio quantum mechanical calculations employing a molecular orbital Hartree–Fock method. The calculations reproduce well the equilibrium geometry but slightly overestimate the value of the Si—O bond lengths of the trioxadisilepine ring. 相似文献
992.
Feng G Mareque-Rivas JC Torres Martín de Rosales R Williams NH 《Journal of the American Chemical Society》2005,127(39):13470-13471
The activity of a Zn(II) complex of a tetradentate, tripodal ligand for catalyzing phosphodiester cleavage is enhanced 750-fold by introducing three hydrogen bond donors to the ligand. Inhibition studies show that the Zn-aqua complex is the kinetically active form and that it binds the transition state with a formal dissociation constant of 3 x 108 M-1. The effect of these ligand modifications on the transition-state affinity is comparable to the rate acceleration provided by the metal ion itself. Overall, this mononuclear complex is more active than the most reactive dinuclear Zn(II) complexes reported to date. 相似文献
993.
994.
A solid-phase microextraction (SPME) sampling method is developed to evaluate indoor exposure to benzene, toluene, ethylbenzene, xylene, and styrene with gas chromatography and flame ionization detection for quantitative analysis. An SPME holder with a 100-pm polydimethylsiloxane (PDMS) and 65-pm PDMS-divinylbenzene fiber coating is tested in different air relative humidity conditions. The method gives good resolution, shows a linear response, is repeatable, and presents high sensitivity. This method is compared with National Institute of Occupational Safety and Health (NIOSH) active sampling. 相似文献
995.
In this study, an analytical procedure for the determination in sediment of the most abundant and/or physiological active estrogens (estradiol, estriol, estrone, ethynyl estradiol, and diethylstilbestrol) and progestogens (progesterone, norethindrone. and levonorgestrel) is described. The procedure includes ultrasonic extraction of the lyophilized sediment, clean-up with octadecylsilica cartridges, and analysis by liquid chromatography-diode array detection-mass spectrometry (LC-DAD-MS). MS detection is performed with an electrospray interface in the positive ion mode for determination of the progestogens and in the negative ion mode for determination of the estrogens. The method was applied to the determination of the target compounds in river sediments from the area of Catalonia. Estrogens and progestogens were found at concentrations usually in the low ng g(-1) range. Estriol and norethindrone were the compounds most frequently found whereas maximum concentrations in all sediment samples were obtained for ethynyl estradiol (22.8 ng g(-1)) and estrone (11.9 ng g(-1)). Detection limits were in the range of 0.04-1.00 ng g(-1). Preliminary conjectures with regards to the environmental behavior and impact of estrogens and progestogens in rivers are made. To the authors' knowledge, this is the first work reporting a detailed method for the analysis of estrogens and progestogens in river sediments and data on the environmental occurrence of both groups of compounds. 相似文献
996.
Theodoridis G Haasnoot W Cazemier G Schilt R Jaziri M Diallo B Papadoyannis IN de Jong GJ 《Journal of chromatography. A》2002,948(1-2):177-185
The application of immunoaffinity chromatography for the purification of Taxus plant and cell extracts prior to the HPLC analysis is described. Polyclonal antibodies raised against 10-deacetylbaccatin III (10-DAB III), paclitaxel's main precursor in plant, were characterised by enzymed-linked immunosorbent assay. Immunoglobulins from selected antisera were immobilised on CNBr-activated Sepharose 4B. The immunoaffinity column was used for the purification of plant and plant cell culture extracts prior to their analysis by HPLC. Immunoaffinity chromatography enabled the selective concentration of taxoids and enhanced sample clean-up. 相似文献
997.
Elenise Bannwart de Moraes Patricia Fazzio Martins César Benedito Batistella Mario Eusebio Torres Alvarez Rubens Maciel Filho Maria Regina Wolf Maciel 《Applied biochemistry and biotechnology》2006,132(1-3):1066-1076
Molecular distillation was studied for the separation of tocopherols from soya sludge, both experimentally and by simulation,
under different operating conditions, with good agreement. Evaporator temperatures varied from 100°C to 160°C and feed flow
rates ranged from 0.1 to 0.8 kg/h. The process pressure was maintained at 10−6 bar, the feed temperature at 50°C, the condenser temperature at 60°C, and the stirring at 350 rpm. For each process condition,
samples of both streams (distillate and residue) were collected and stored at −18°C before tocopherols analyses. Owing to
the differences between molecular weights and vapor pressures of free fatty acids and tocopherols, tocopherols preferentially
remained in the residue at evaporator temperatures of 100°C and 120°C, whereas for higher temperatures (140°C and 160°C) and
lower feed flow rate, tocopherols tended to migrate to the distillate stream. 相似文献
998.
H. T. Matsuda B. F. de Araujo J. A. de Araujo 《Journal of Radioanalytical and Nuclear Chemistry》1995,199(6):453-463
Celeste-1 is a lab-scale hot cell intended for R&D work in reprocessing of low burn-up spent fuel elements. The studies are concerned with head-end, first separation cycle by Purex Process using mini mixer-settlers and development of analytical techniques. The analytical monitoring for process control purposes is based on several off-line techniques, such as X-ray fluorescence spectrometry, potentiometric titration, -and -spectroscopy, spectrophotometry, fluorimetry, density measurement and gas chromatography. The analytical treatment takes place in a shielded working place analytical hot cell, glove boxes and hoods and some final measurements are made in the associated analytical laboratory. A pneumatic system is used for transporting analytical samples. All analytical procedures are ready and in operation. 相似文献
999.
Gerard de Leeuw John S. Field Raymond J. Haines Beth McCulloch Elsie Meintjies Christiaan Monberg Gillian M. Olivier Praveen Ramdial Clifford N. Sampson Beate Sigwarth Nick D. Steen Kandasamy G. Moodley 《Journal of organometallic chemistry》1984,275(1):99-111
Reaction of [Fe2(CO)9] with a half molar amount of R2PYPR2 (Y = CH2, R = Ph, Me, OMe or OPri; Y = N(Et), R = OPh, OMe or OCH2; Y = N(Me), R = OPri or OEt) leads to the ready formation of a product which on irradiation with ultraviolet light rapidly decarbonylates to the heptacarbonyl derivative [Fe2(μ-CO)(CO)6{μ-R2PYPR2}]. Treatment of the latter with a slight excess of the appropriate ligand results, under photochemical conditions, in the formation of the dinuclear pentacarbonyl complex [Fe2(μ-CO)(C))4{μ-R2PYPR2}2] but under thermal conditions in the formation of the mononuclear species [Fe(CO)3{R2PYPR2}]. Reaction of [Ru3(CO)12] with an equimolar amount of (RO)2PN(R′)P(OR)2 (R′ = Me, R = Pri or Et; R′ = Et, R = Ph or Me) under either thermal or photochemical conditions produces [Ru3(CO)10{μ-(RO)2PN(OR)2}] which reacts further with excess (RO)2PN(R′)P(OR)2 on irradiation with ultraviolet light to afford the dinuclear compound [Ru2(μ-CO)(CO4{μ-(RO)2PN(R′)P(OR)2}2]. The molecular structure of [Ru2(μ-CO)(CO)4{μ-(MeO)2PN(Et)P(OMe)2}2], which has been determined by X-ray crystallography, is described. 相似文献
1000.
Romeiro NC Albuquerque MG de Alencastro RB Ravi M Hopfinger AJ 《Journal of computer-aided molecular design》2005,19(6):385-400
The p38-mitogen-activated protein kinase (p38-MAPK) plays a key role in lipopolysaccharide-induced tumor necrosis factor-alpha (TNF-alpha) and interleukin-1 (IL-1) release during the inflammatory process, emerging as an attractive target for new anti-inflammatory agents. Four-dimensional quantitative structure-activity relationship (4D-QSAR) analysis [Hopfinger et al., J. Am. Chem. Soc., 119 (1997) 10509] was applied to a series of 33 (a training set of 28 and a test set of 5) pyridinyl-imidazole and pyrimidinyl-imidazole inhibitors of p38-MAPK, with IC50 ranging from 0.11 to 2100 nM [Liverton et al., J. Med. Chem., 42 (1999) 2180]. Five thousand conformations of each analogue were sampled from a molecular dynamics simulation (MDS) during 50 ps at a constant temperature of 303 K. Each conformation was placed in a 2 angstroms grid cell lattice for each of three trial alignments. 4D-QSAR models were constructed by genetic algorithm (GA) optimization and partial least squares (PLS) fitting, and evaluated by leave-one-out cross-validation technique. In the best models, with three to six terms, the adjusted cross-validated squared correlation coefficients, Q2adj, ranged from 0.67 to 0.85. Model D (Q2adj = 0.84) was identified as the most robust model from alignment 1, and it is representative of the other best models. This model encompasses new molecular regions as containing pharmacophore sites, such as the amino-benzyl moiety of pyrimidine analogs and the N1-substituent in the imidazole ring. These regions of the ligands should be further explored to identify better anti-inflammatory inhibitors of p38-MAPK. 相似文献