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81.
82.
The described radiochromatographic method permits fast and high-sensitivity monitoring of soil biodegradation products of an insect growth regulator for its environmental risk assessment. We analyzed and compared two diastereoisomers of ethyl N-(2-(4-[(2-hydroxycyclohexyl) methyl]phenoxy)ethyl)carbamate, namely its cis-(1S,2S) isomer JN-W330 and a trans-(1R,2S) isomer JN-W331. Microbial conversion of the cis-isomer to the trans-isomer was proved by mass spectrometry analyzer. Among the chromatographic columns tested, the best separation was found with a 125 mm x 4 mm i.d. column packed with Supersphere 100 RP-C18, 5 microm and an acetonitrile-water gradient. The detection limit for the both isomers was in the range of 120-250 Bq (0.3-0.8 ng) at a concentration of 2 ng/ml with radiometric detection. The calibration curves for standard solutions were linear in the range of 150Bq-150kBq (r = 0.996). The method enabled us to compare the analyzed juvenoids with biologically active oostatic peptides in terms of their environmental safety. 相似文献
83.
Baeza A Nájera C Sansano JM Saá JM 《Chemistry (Weinheim an der Bergstrasse, Germany)》2005,11(13):3849-3862
The enantioselective synthesis of cyanohydrin O‐phosphates by using in situ generated bifunctional catalysts (R)‐ or (S)‐3,3′‐bis(diethylaminomethyl)‐1,1′‐binaphthol–aluminium chloride (binolam–AlCl) is reported. The reaction, which can be described as an overall cyano‐O‐phosphorylation of aldehydes, has a wide scope and applicability. Evidence is also provided, including ab initio and DFT calculations, in support of supported by the Lewis acid/Brønsted base (LABB) dual role of the catalyst in inducing first the key enantioselective hydrocyanation, which is then followed by O‐phosphorylation. A brief screening of the synthetic usefulness of the resulting cyanohydrin O‐phosphates unveiles some interesting applications. Among them, chemoselective hydrolysis, reduction and palladium‐catalysed nucleophilic allyl substitution, thereby leading to enantiomerically enriched α‐O‐phosphorylated α‐hydroxy esters, β‐amino alcohols and γ‐cyanoallyl alcohols, respectively. Naturally occurring (?)‐tembamide and (?)‐aegeline are synthesised accordingly. 相似文献
84.
Frédéric Blanc Christophe Copéret Bernard Fenet 《Journal of organometallic chemistry》2005,690(23):5014-5026
The reaction of Mo(N)(CH2tBu)3 (1) and SiO2-(700) generates (SiO)Mo(NH)(CHtBu)(CH2tBu) (2) when performed in C6H6 (material [1/SiO2-(700)]C6H6). The grafting occurs presumably by protonation of the nitrido ligand to form an intermediate (SiO)Mo(NH)(CH2tBu)3 (3), a pentacoordinated complex, which decomposes into 2 and 2,2-dimethylpropane. While [1/SiO2-(700)]C6H6 is highly active in olefin metathesis, [1/SiO2-(700)]CH2Cl2 and [1/SiO2-(700)]THF are poorly active or inactive catalysts respectively. In contrast, when Mo(N)(CH2tBu)3 reacts with a molecular silanol derivative, a soluble model of the surface of SiO2-(700), it yields a very stable complex, (c-C5H9)7Si7O12SiO-Mo(NH)(CH2tBu)3 (3m), which does not spontaneously generate 2,2-dimethylpropane and an alkylidene complex in contrast to the surface complex. Moreover, 3m does not catalyse olefin metathesis at room temperature as it does not already contain the initiating carbene ligand, and it is necessary to heat up the reaction mixture to 110 °C to obtain low catalytic activity. Nevertheless, the complex 3m generates well-defined metallocarbenes when heated in the presence of PMe3: (c-C5H9)7Si7O12SiO-Mo(N)(CHtBu)(P(CH3)3)2 (4m) as a 10:1 mixture of its syn and anti rotamers with the loss of 2 equiv. of 2,2-dimethylpropane. 相似文献
85.
A new method of HPLC column retentivity testing utilizes polymeric probes instead of conventional sets of low molar mass substances. The procedure allows at least semiquantitative, separate and independent evaluation of adsorption and partition properties of column packings. In this present work, the method is applied for comparison of the polar interactivities of selected silica gel C18 HPLC columns. It is shown that free silanols which remained on the surface of the end-capped silica C18 column packings are accessible for interaction with highly polar macromolecules. High molar mass polymeric test probes are adsorbed on the surface silanols and their retention volumes increase. As result, deviations from regular size-exclusion chromatographic (SEC) behavior are observed. The extent of retention volume changes depends on both the nature of polymer probes and on column packing type. Adsorption of macromolecules can be suppressed by addition of a highly polar substance to the mobile phase. The amount of polar additive which is needed to attain regular SEC elution of the polymer probe depends on the column packing type and can be used as a characteristic of silanophilic column interactivity. Courses of dependences of retention volumes on sizes of macromolecules indicate the presence of "U-turn" adsorption which allows two and more silanols situated among C18 groups to be occupied simultaneously with the same macromolecule. 相似文献
86.
Kvasnicková L Glatz Z Sterbová H Kahle V Slanina J Musil P 《Journal of chromatography. A》2001,916(1-2):265-271
Capillary electrochromatography (CEC) using polymer-based monolithic stationary phase has been developed as a promising method for the determination of lignans of Schisandra chinensis. The columns were prepared by in situ copolymerisation of acrylamide, N,N'-methylenebisacrylamide, vinylsulfonic acid and lauryl acrylate in presence of poly(ethylene glycol) as a porogenic agent. The columns [33 cm (24.5 cm effective length) x 75 microm I.D.] were successfully used to analyse and quantify the major lignans in extract of the seeds of Schisandra chinensis. Good separations were achieved in less than 35 min. The calibration graphs were linear in the range 0.025-1.0 mg/ml of given lignan with correlation coefficients between 0.9951 and 0.9996. The inter-day reproducibility of the peak area were below 3.9% and the inter-day reproducibility of the migration time were below 4.2%. The results of quantitative CEC analyses were compared with those obtained by reversed-phase HPLC, the levels of schizandrin, gomisin A, gomisin N and wuweizisu C determined by CEC were in a good agreement with those determined by HPLC. 相似文献
87.
The lattice energies of a series of organic dihydrogenphosphate salts capable of second harmonic generation (SHG) have been calculated. These calculations, coupled with empirical data, indicate that a minimum of 20–25% of the lattice energy arises from hydrogen-bond interactions. Hydrogen bonding is shown to be a strong enough force to have a profound effect on the overall packing and crystal geometry of such ionic materials, and is thus an important factor to consider for crystal engineering. 相似文献
88.
Equilibrium constants for oxidations of cyclanols by cyclohexanone in benzene have been determined in the presence of aluminium isopropoxide. The free energies of the equilibrium (ΔGox) are correlated with equilibrium constants for dissociation of cyanohydrins, rate constants for cyclanol oxidation with chromic acid, ketone reduction with sodium borohydride and trifluoroethanolysis of tosylates. 相似文献
89.
This work presents a study of the thermal
degradation of ultra-high molecular mass polyethylene (UHMWPE) stabilized
with natural (α-tocopherol and carvacrol) and synthetic antioxidants.
Thermogravimetric analysis in dynamic mode was used to determine the apparent
activation energies of different samples. The stabilization of UHMWPE with
low concentrations (around 0.3%) of α-tocopherol is enough to obtain
an efficient thermal performance of the polymer. Carvacrol is also a good
stabilizer for UHMWPE, but at higher concentration than in the case of α-tocopherol.
The comparison of apparent activation energy between samples with natural
and synthetic antioxidants in similar concentration shows that α-tocopherol
is a better stabilizer in terms of their thermal performance. 相似文献
90.
The sensitive reactions between 4-(2-pyridylazo)resorcinol (PAR) and yttrium, lanthanum and the lanthanides can be used for the spectrophotometric determination of these elements. The method has no advantage over other methods for the determination of aluminium and lanthanum. Only M(PAR)H and M(PAR) complexes are formed in solutions where the molarity of the metal ion is greater than or nearly equal to the molarity of the ligand at pH < 7-5. If there is molar excess of PAR, 1:2 complexes may be formed but this is certain only for the yttrium-PAR system. Errors in analysis may result from the simultaneous occurrence of optically different complexes; close control of pH and reagent concentration is essential. Optical and equilibrium data are given for the systems investigated. 相似文献