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11.
The method is based on formation of the fluorescent condensation products with o-phthaldialdehyde; 0.5–2000 ng ml?1 histamine and 3–700 ng ml?1 spermidine can be quantified, with relative standard deviations of 2–3%. Histamine/spermidine ratios of 2.5:1–1:30 can be handled. A selectivity study is reported. 相似文献
12.
Mario H. Gutierrez Warren T. Ford 《Journal of polymer science. Part A, Polymer chemistry》1986,24(4):655-663
Glass transition temperatures have been determined for polystyrenes crosslinked with 1–10% divinylbenzene and swollen with toluene, chloroform, N,N-dimethylformamide, and tetrahydrofuran to as high as 0.7 weight fraction solvent. The Tg′s depend approximately on the weight fractions and the Tg′s of the components according to the empirical equation 1nTg = m1 1nTg1 + m2 1nTg2 of Pochan. The Tg′s of the networks swollen with toluene also fit approximately a quasithermodynamic equation of Karasz based on the Tg′s and the ΔCp′s at Tg of the components. 相似文献
13.
The characteristics of the ternary complexes formed by fluoride, bromide, iodide and thiocyanate with tin(IV) and 5,7-dichloro-8-quinolinol (HCQ) have been studied. A spectrophotometric method is proposed for the determination of tin(IV) (1–20 μg ml?1), based on the extraction into chloroform of the tin/iodide/HCQ complex. Aluminium, bismuth and lead do not interfere, but antimony, copper, iron(III) and fluoride do. Copper and iron can be eliminated by preliminary extraction in the absence of iodide. 相似文献
14.
Lei Liu Wes Lee Cassandra R. Youshaw Mingbin Yuan Michael B. Geherty Peter Y. Zavalij Osvaldo Gutierrez 《Chemical science》2020,11(31):8301
A highly chemoselective iron-catalyzed three-component dicarbofunctionalization of unactivated olefins with alkyl halides (iodides and bromides) and sp2-hybridized Grignard reagents is reported. The reaction operates under fast turnover frequency and tolerates a diverse range of sp2-hybridized nucleophiles (electron-rich and electron-deficient (hetero)aryl and alkenyl Grignard reagents), alkyl halides (tertiary alkyl iodides/bromides and perfluorinated bromides), and unactivated olefins bearing diverse functional groups including tethered alkenes, ethers, protected alcohols, aldehydes, and amines to yield the desired 1,2-alkylarylated products with high regiocontrol. Further, we demonstrate that this protocol is amenable for the synthesis of new (hetero)carbocycles including tetrahydrofurans and pyrrolidines via a three-component radical cascade cyclization/arylation that forges three new C–C bonds.A highly selective iron-catalyzed three-component dicarbofunctionalization of unactivated alkenes with alkyl halides and sp2-hybridized Grignard reagents is reported. 相似文献
15.
Corey D. Gutierrez 《Tetrahedron letters》2005,46(20):3595-3597
Sodium triacetoxyborohydride, NaBH(OAc)3 with tri-isopropoxytitanium chloride, TiCl(OiPr)3 is a useful reagent combination for reductive amination. Electron-deficient amines and heteroaromatic amines such as 2-aminopyrimidine and 2-aminothiazole can be reductively alkylated at room temperature to afford the corresponding secondary amines in good yields. 相似文献
16.
Lei Liu Wes Lee Mingbin Yuan Chris Acha Michael B. Geherty Brandon Williams Osvaldo Gutierrez 《Chemical science》2020,11(12):3146
Design and implementation of the first (asymmetric) Fe-catalyzed intra- and intermolecular difunctionalization of vinyl cyclopropanes (VCPs) with alkyl halides and aryl Grignard reagents has been realized via a mechanistically driven approach. Mechanistic studies support the diffusion of alkyl radical intermediates out of the solvent cage to participate in an intra- or intermolecular radical cascade with a range of VCPs followed by re-entering the Fe radical cross-coupling cycle to undergo (stereo)selective C(sp2)–C(sp3) bond formation. This work provides a proof-of-concept of the use of vinyl cyclopropanes as synthetically useful 1,5-synthons in Fe-catalyzed conjunctive cross-couplings with alkyl halides and aryl/vinyl Grignard reagents. Overall, we provide new design principles for Fe-mediated radical processes and underscore the potential of using combined computations and experiments to accelerate the development of challenging transformations.Design and implementation of the first (asymmetric) Fe-catalyzed intra- and intermolecular difunctionalization of vinyl cyclopropanes (VCPs) with alkyl halides and aryl Grignard reagents has been realized via a mechanistically driven approach. 相似文献
17.
The intramolecular Diels-Alder reaction of N-3,5-hexadienoyl ethyl acrylimidates provides an efficient method for the synthesis of cis-fused hexahydroisoquinolones. As a demonstration of the stereochemical control offered by this cycloaddition, two approaches to the construction of the DE rings of reserpine are reported. In the second entry, N-((4-(trimethylsilyl)ethoxymethoxy)methyl-6-benzyloxy-3Z,5E-hexadienoyl)-1-aza-2-ethoxy-1,3-butadiene (40) undergoes cycloaddition to produce as the major product (4aS,7R,8aS)-7-benzyloxy-5-((2-trimethylsilyl)ethoxymethoxy)methyl-3,4,4a,7,8,8a-hexahydroisoquinol-3-one (41). Cycloadduct 41 is then stereospecifically elaborated to (4aS,5S,6R,7R,8aR)-6-methoxy-5-methoxycarbonyl-7-(3,4,5-trimethoxy)benzoyldecahydroisoquinoline-2-carboxylic acid methyl ester (3), a key intermediate previously transformed to reserpine. 相似文献
18.
Nonlinear Dynamics - In this paper, type V intermittency is studied using the M function methodology developed in the last years. This methodology is applied on two different maps to evaluate the... 相似文献
19.
Two negative minima of the first normal stress difference in a cellulose‐based cholesteric liquid crystal: Helix uncoiling 下载免费PDF全文
Coro Echeverria Pedro L. Almeida Oscar F. Aguilar Gutierrez Alejandro D. Rey Maria Helena Godinho 《Journal of Polymer Science.Polymer Physics》2017,55(10):821-830
The shear rate dependence of material functions such as shear viscosity (η) and the first normal stress difference (N1) were given and interpreted earlier by Kiss and Porter. Their widely accepted work revealed the possibility of having a negative minimum of N1 for polymeric liquid crystals. In this work, we disclose for the first time the evidence of two negative N1 minima on a sheared cellulosic lyotropic system. The lower shear rate minimum is ascribed to the uncoiling of the cholesteric helix, as theoretically predicted earlier. Our findings contribute also to the understanding of the other minimum already reported in the literature and attributed to the nematic director tumbling mode. Moreover, the elastic change that the LC‐HPC sample undergoes during the helix unwinding of the cholesteric structure is also by means of oscillatory measurements. This study is a contribution for the understanding of the structure‐properties relationship linked with the complex rheological behavior of chiral nematic cellulose‐based systems and may help to improve their further processing. © 2017 Wiley Periodicals, Inc. J. Polym. Sci., Part B: Polym. Phys. 2017 , 55, 821–830 相似文献
20.
We provide an affirmative answer to the C
r
-Closing Lemma, r ≥ 2, for a large class of flows defined on every closed surface. 相似文献