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121.
Reaction of 2-Chloromethyl-3-hydroxy-4(3H)quinazolinone ( 1 ) with aliphatic amines and hydroxide follows two different routes affording substituted methyl quinazolinones and a dimer 2 derived from 1 . The former were formed by SN2 reactions while the latter was formed by an inter-molecular nucleophilic displacement. Second-order and third-order rate constants, respectively, were determined, and the kinetic factors influencing both parallel reactions were analysed.  相似文献   
122.
A new procedure for the determination of sterols in serum samples is proposed. The system consists of coating a Solid Phase Microextraction (SPME) microfiber in headspace mode with the derivatizing agent N,O-bis(trimethylsilyl)trifluoracetamide (BSTFA) and then applying this coated fiber to the simultaneous extraction and derivatization of three precursors in the cholesterol biosynthesis pathway (desmosterol, lathosterol and lanosterol) and two phytosterols (sitosterol and sitostanol) in serum samples. Optimization of the analytical procedure via the application of an experimental design, a study of matrix effects, and an analysis of serum pool samples are all described and discussed.  相似文献   
123.
N,N‐bis(carboxymethyl)‐1‐adamantylamine acid (H2BCAA) or N‐(1‐adamantyl)‐iminodiacetic acid forms zwitterions that are intra‐stabilized by a ‘bifurcated’ N+‐H···O(carboxyl)2 interaction. In the crystal, both half‐protonated carboxyl groups of H2BCAA± are involved in linear O‐H···O inter‐molecular bridges of 2.46Å. In the studied BCAA‐CuII derivatives, the iminodiacetate‐moiety of the BCAA chelating ligand exhibits a mer‐NO2 conformation in [Cu(BCAA)(H2O)2] ( 1 ) and [Cu(BCAA)(Him)]2 ( 2 ), but a fac‐O2+N(apical) conformation in [Cu(BCAA)(bpy)(H2O)]·3.5H2O ( 3 ) [Him = imidazole, bpy =2,2′‐bipyridine]. In clear contrast, dipyridylamine (dpya), as auxiliary ligand, seems to be unable to promote the fac‐O2+N(apical) conformation in BCAA, as reveal the structures of two new salts with the trinuclear cation [(dpya)2Cu‐μ2‐Cu(BCAA)2‐Cu(dpya)2]2+ and the anions [Cu(BCAA)2]2? ( 4 ) or NO3? ( 5 ), respectively.  相似文献   
124.
Although it is quite obvious that an increasing amount of energy is required to remove more and more electrons from an atom, the proof of this observation seems to be a remarkably difficult problem in mathematical physics. Here, by using well-known energy bounds, we show the monotonicity of ionization energies for the simplest nontrivial system, i.e., a nucleus (with infinite mass) and three electrons, which physically corresponds to ionization in the lithium isoelectronic series via the para-channel.PHYMAT, Dept. de math. Univ. de Toulon et du Var F-83130 La Garde, France.On leave from Stranski Institut, TEL 33 Tech. Univ. Berlin D-1000 Berlin 10, F.R.G.Laboratoire propre du Centre Nationale de la Recherche Scientifique.  相似文献   
125.
Current approaches to mercury speciation and total trace element analysis require separate extraction/digestions of the sample. Ecologically important aquatic organisms--notably primary consumers such as zooplankton, polychaetes and amphipods--usually yield very low biomass for analysis, even with significant compositing of multiple organisms. Individual organisms in the lower aquatic food chains (mussels, snails, oysters, silversides, killifish) can also have very low sample mass, and analysis of whole single organisms is important to metal uptake studies. A method for the determination of both methyl Hg and total heavy metal concentrations (Zn, As, Se, Cd, Hg, Pb) in a single, low-mass sample of aquatic organisms was developed. Samples (2 to 50 mg) were spiked with enriched with (201)MeHg and (199)Hg, then leached in 4 M HNO(3) at 55 degrees C for extraction of MeHg. After 16 h, an aliquot (0.05 mL) was removed to determine mercury species (methyl and inorganic Hg) by isotope dilution gas chromatography inductively coupled plasma mass spectrometry (ICP-MS). The leachate was then acidified to 9 M HNO(3) and digested in a microwave at 150 degrees C for 10 min, and total metal concentrations were determined by collision cell ICP-MS. The method was validated by analyzing five biological certified reference materials. Average percent recoveries for Zn, As, Se, Cd, MeHg, Hg(total) and Pb were 99.9%, 103.5%, 100.4%, 103.3%, 101%, 97.7%, and 97.1%, respectively. The correlation between the sum of MeHg and inorganic Hg from the speciation analysis and total Hg by conventional digestion of the sample was determined for a large sample set of aquatic invertebrates (n = 285). Excellent agreement between the two measured values was achieved. This method is advantageous in situations where sample size is limited, and where correlations between Hg species and other metals are required in the same sample. The method also provides further validation of speciation data, by corroborating the sum of the Hg species concentrations with the total Hg concentration.  相似文献   
126.
Vapour–liquid equilibria (VLE), liquid–liquid equilibria (LLE), and excess enthalpies (HE) of binary mixtures of perfluoro-n-hexane plus an ether (diethyl, dipropyl, dibutyl, butyl methyl, and butyl ethyl ether), have been determined using a head-space gas-chromatographic technique, a turbidimetric apparatus, and a heat-flow calorimeter, respectively. A recently designed titration technique and calculation procedure have been used to obtain HE from heats of solution. The observed liquid–liquid coexistence curves have been compared with those predicted by the activity coefficients γi and their temperature dependence. All mixtures are strongly endothermic (HE > 0) and show large positive deviations from ideality (GE > 0), which increase with the size of the ether. Molecular interactions have been examined by calculating and discussing solvation functions and Kirkwood–Buff (KB) integrals. Perfluorohexane proved to be an inert molecule that interacts with ethers more weakly than hexane.  相似文献   
127.
Horizontal nondenaturing electrophoresis of proteins in polyacrylamide gels was used to observe specific interactions between membrane proteins. The method was particularly well suited for solubilized transporters of the outer membrane of Gram-negative bacteria, and allowed specific complexes of transporter and the inner-membrane protein TonB to be isolated. We have used this method to investigate the interactions between four different outer-membrane transporters, and the TonB proteins from two different organisms. The results show that a stable complex can be isolated on gels for all the proteins studied, but can depend in some cases of the detergent used for solubilization. Furthermore, we observe cross-species interaction as TonB from a given organism can interact with transporters from another organism.  相似文献   
128.
[reaction: see text] Chiral 2-acyl-3-allyl- or 2-acyl-3-benzyl-substituted perhydro-1,3-benzoxazines readily cyclized under irradiation to azetidin-3-ol derivatives. The diastereoselectivity of the cyclization is dependent on the nature of the substituents at the nitrogen atom. N-allyl-substituted derivatives yielded only two of the four possible diastereomers in moderate to good diastereomeric excess. The cyclization of N-benzyl derivatives was totally diastereoselective leading to a single diastereomer. The elimination of the menthol appendage lead to enantiopure 2,3-disubstituted azetidin-3-ol derivatives.  相似文献   
129.
130.
A new method to compute effects of tunneling in one-dimensional multiple well is developed. A tunneling parameter built with physical quantities is introduced to measure the splitting between eigenvalues due to tunneling. These splittings are given by convergent series in term of this tunneling parameter for a wide class of double well.  相似文献   
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