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541.
[reaction: see text] Nineteen Mn(II) complexes were screened for the catalytic epoxidation of terminal olefins using peracetic acid. Few of these complexes are efficient catalysts at pH < 2, but many are effective at 1 mol % catalyst loading at pH 4. With 0.1 mol % loading, four complexes epoxidize 1-octene in approximately 80% yield in 5 min. The relative reactivity of the catalysts toward different olefins was probed using a multicomponent intermolecular competition reaction. 相似文献
542.
Giuseppina Negri Concetta Kascheres Albert J. Kascheres 《Journal of heterocyclic chemistry》2004,41(4):461-491
Enaminoketones and esters are gaining increased interest, particularly cyclic‐β‐enaminoesters, which are known as important intermediates for the synthesis of heterocycles and natural products, because the enantioselective preparation of highly functionalized compounds is of central importance in synthetic chemistry. Enaminones are versatile synthetic intermediates that combine the ambident nucleophilicity of enamines with the ambident eletrophilicity of enones. Enaminoketones and enaminonitriles have proven to be versatile building blocks for the synthesis of various heterocycles such as pyridine, pyrimidine and pyrrole deriva tives. Enaminones systems have “enone” character, and may act as acceptors in both 1,2 and 1,4‐additions. In this way the enaminone serves as a scaffold for annulation, and can gain access to systems such as pyrroles indolizidines, quinolizidines and perhydroindoles, all of which are common motifs in alkaloid structures. Enaminones are frequently employed as building blocks for the preparation of a variety of bicyclic compounds of biological interest and have been recently recognized as potential anticonvulsant compounds. Since a large number of developments in the use of enaminones in heterocyclic synthesis have occurred, a review of the recent developments in the synthetic approaches, covering the literature since 1995 until 2004, to these interesting molecules and their useful chemical transformations and biological activity can be considered of considerable value. 相似文献
543.
Electron nuclear double resonance (ENDOR) spectra of free radicals produced by ultraviolet (UV) photolysis of polycrystalline and single crystal dimethylnitramine (or N-methyl-N-nitromethanamine) [DMN; (CH3)2NNO2 were studied atca. ?30°C. Results suggest that multiple radical species are formed during UV photolysis of DMN, perdeutero-DMN-d6, and15N-labeled DMN. Proton ENDOR spectra are consistent with assignment of a cation radical (CH3)2NNO 2 + as the major DMN radical species. Proton hyperfine coupling anisotropy, which is observed from the ENDOR spectra, is attributed to inequivalence of the two DMN methyl groups. 相似文献
544.
545.
Loredana De Bartolo Maria Rende Sabrina Morelli Giuseppina Giusi Simona Salerno Antonella Piscioneri Amalia Gordano Anna Di Vito Marcello Canonaco Enrico Drioli 《Journal of membrane science》2008
Membranes have become of great interest for tissue engineering application, since they offer the advantage of developing neuronal tissue that may be used in implantable or in vitro hybrid systems for the simulation of brain function. The behaviour of neurons isolated from the hippocampus on membranes with different surface properties was investigated. 相似文献
546.
Giuseppina Barbieri Dikran Dikranjan Chiara Milan Hans Weber 《Mathematische Nachrichten》2008,281(7):930-950
For a recursively defined sequence u : = (un) of integers, we describe the subgroup tu (??) of the elements x of the circle group ?? satisfying limn unx = 0. More attention is dedicated to the sequences satisfying a secondorder recurrence relation. In this case, we show that the size and the free‐rank of tu (??) is determined by the asymptotic behaviour of the ratios qn = (un /un –1) and we extend previous results of G. Larcher, C. Kraaikamp, and P. Liardet obtained from continued fraction expansion. (© 2008 WILEY‐VCH Verlag GmbH & Co. KGaA, Weinheim) 相似文献
547.
548.
Sarah L. Newberry Ulrich E. Prechsl Matthew Pace Ansgar Kahmen 《Isotopes in environmental and health studies》2017,53(4):368-381
Cryogenic vacuum extraction is the well-established method of extracting water from soil for isotopic analyses of waters moving through the soil–plant–atmosphere continuum. We investigate if soils can alter the isotopic composition of water through isotope memory effects, and determined which mechanisms are responsible for it. Soils with differing physicochemical properties were re-wetted with reference water and subsequently extracted by cryogenic water distillation. Results suggest some reference waters bind tightly to the soil and not all of this tightly bound water is removed during cryogenic vacuum extraction. Kinetic isotopic fractionation occurring when reference water binds to the soil is likely responsible for the 18O-depletion of re-extracted reference water, suggesting an enrichment of the tightly bound soil water pool. Further re-wetting of cryogenically extracted soils indicates an isotopic memory effect of tightly bound soil water on water added to the soil. The data suggest tightly bound soil water can influence the isotopic composition of mobile soil water. Findings show that soils influence the isotope composition of soil water by (i) kinetic fractionation when water is bound to the soil and (ii) equilibrium fractionation between different soil water pools. These findings could be relevant for plant water uptake investigations and complicate ecohydrological and paleohydrological studies. 相似文献
549.
Antonio Palumbo Piccionello Luca Menichetti Paolo Armanetti Alessandra Flori Ilaria Monaco Mirko Maturi Andrea Pace Erica Locatelli 《Journal of nanoparticle research》2018,20(10):259
A selective functionalization of dopamine amino group with the photoluminescent 7-nitroben-zofurazan was achieved through a one-pot protection-functionalization-deprotection sequence. The resulting fluorescent catecholic ligand was used as a capping agent for iron oxide nanoparticles thus obtaining photoluminescent magnetic nanoparticles (PL-MNPs). The PL-MNPs were then embedded into PLGA-b-PEG polymeric nanocarriers which quenched the emission of the capping agent. Full recovery of fluorescence was observed after disassembling the polymeric layer of the nanoparticle, thus supporting the use of PL-MNPs as a multifunctional system for targeted drug delivery. 相似文献
550.
Giuseppina Autuori Patrizia Pucci Maria Cesarina Salvatori 《Archive for Rational Mechanics and Analysis》2010,196(2):489-516
In this paper we consider the problem of non-continuation of solutions of dissipative nonlinear Kirchhoff systems, involving
the p(x)-Laplacian operator and governed by nonlinear driving forces f = f (t, x, u), as well as nonlinear external damping terms Q = Q(t, x, u, u
t
), both of which could significantly dependent on the time t. The theorems are obtained through the study of the natural energy Eu associated to the solutions u of the systems. Thanks to a new approach of the classical potential well and concavity methods, we show the nonexistence
of global solutions, when the initial energy is controlled above by a critical value; that is, when the initial data belong
to a specific region in the phase plane. Several consequences, interesting in applications, are given in particular subcases.
The results are original also for the scalar standard wave equation when p ≡ 2 and even for problems linearly damped. 相似文献