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51.
Valentina Bleve Christian Schäfer Dr. Paola Franchi Dr. Serena Silvi Prof. Dr. Elisabetta Mezzina Prof. Dr. Alberto Credi Prof. Marco Lucarini 《ChemistryOpen》2015,4(1):2-21
An acid–base switchable molecular shuttle based on a [2]rotaxane, incorporating stable radical units in both the ring and dumbbell components, is reported. The [2]rotaxane comprises a dibenzo[24]crown-8 ring (DB24C8) interlocked with a dumbbell component that possesses a dialkylammonium (NH2+) and a 4,4′-bipyridinium (BPY2+) recognition site. Deprotonation of the rotaxane NH2+ centers effects a quantitative displacement of the DB24C8 macroring to the BPY2+ recognition site, a process that can be reversed by acid treatment. Interaction between stable 2,2,6,6-tetramethylpiperidine-1-oxyl (TEMPO) radicals connected to the ring and dumbbell components could be switched between noncoupled (three-line electron paramagnetic resonance (EPR) spectrum) and coupled (five-line EPR spectrum) upon displacement of the spin-labelled DB24C8 macroring. The complete base- and acid-induced switching cycle of the EPR pattern was repeated six times without an appreciable loss of signal, highlighting the reversibility of the process. Hence, this molecular machine is capable of switching on/off magnetic interactions by chemically driven reversible mechanical effects. A system of this kind represents an initial step towards a new generation of nanoscale magnetic switches that may be of interest for a variety of applications. 相似文献
52.
53.
Competitive Gold‐Promoted Meyer–Schuster and oxy‐Cope Rearrangements of 3‐Acyloxy‐1,5‐enynes: Selective Catalysis for the Synthesis of (+)‐(S)‐γ‐Ionone and (−)‐(2S,6 R)‐cis‐γ‐Irone 下载免费PDF全文
Dr. Serena Bugoni Dr. Valentina Merlini Dr. Alessio Porta Dr. Sylvain Gaillard Prof. Giuseppe Zanoni Prof. Dr. Steven P. Nolan Prof. Giovanni Vidari 《Chemistry (Weinheim an der Bergstrasse, Germany)》2015,21(40):14068-14074
We report a simple, highly stereoselective synthesis of (+)‐(S)‐γ‐ionone and (‐)‐(2S,6R)‐cis‐γ‐irone, two characteristic and precious odorants; the latter compound is a constituent of the essential oil obtained from iris rhizomes. Of general interest in this approach are the photoisomerization of an endo trisubstituted cyclohexene double bond to an exo vinyl group and the installation of the enone side chain through a [(NHC)AuI]‐catalyzed Meyer–Schuster‐like rearrangement. This required a careful investigation of the mechanism of the gold‐catalyzed reaction and a judicious selection of reaction conditions. In fact, it was found that the Meyer–Schuster reaction may compete with the oxy‐Cope rearrangement. Gold‐based catalytic systems can promote either reaction selectively. In the present system, the mononuclear gold complex [Au(IPr)Cl], in combination with the silver salt AgSbF6 in 100:1 butan‐2‐one/H2O, proved to efficiently promote the Meyer–Schuster rearrangement of propargylic benzoates, whereas the digold catalyst [{Au(IPr)}2(μ‐OH)][BF4] in anhydrous dichloromethane selectively promoted the oxy‐Cope rearrangement of propargylic alcohols. 相似文献
54.
Interplay of Hole Transfer and Host–Guest Interaction in a Molecular Dyad and Triad: Ensemble and Single‐Molecule Spectroscopy and Sensing Applications 下载免费PDF全文
Dr. Xiangyang Wu Dr. Fang Liu Dr. Kym L. Wells Serena L. J. Tan Prof. Dr. Richard D. Webster Prof. Dr. Howe‐Siang Tan Prof. Dr. Dawei Zhang Prof. Dr. Bengang Xing Prof. Dr. Edwin K. L. Yeow 《Chemistry (Weinheim an der Bergstrasse, Germany)》2015,21(8):3387-3398
A new molecular dyad consisting of a Cy5 chromophore and ferrocene (Fc) and a triad consisting of Cy5, Fc, and β‐cyclodextrin (CD) are synthesized and their photophysical properties investigated at both the ensemble and single‐molecule levels. Hole transfer efficiency from Cy5 to Fc in the dyad is reduced upon addition of CD. This is due to an increase in the Cy5‐Fc separation (r) when the Fc is encapsulated in the macrocyclic host. On the other hand, the triad adopts either a Fc‐CD inclusion complex conformation in which hole transfer quenching of the Cy5 by Fc is minimal or a quasi‐static conformation with short r and rapid charge transfer. Single‐molecule fluorescence measurements reveal that r is lengthened when the triad molecules are deposited on a glass substrate. By combining intramolecular charge transfer and competitive supramolecular interaction, the triad acts as an efficient chemical sensor to detect different bioactive analytes such as amantadine hydrochloride and sodium lithocholate in aqueous solution and synthetic urine. 相似文献
55.
Garramone G Pietrangeli D Ricciardi G Conoci S Guascito MR Malitesta C Cesari D Casilli S Giotta L Giancane G Valli L 《The journal of physical chemistry. B》2008,112(37):11517-11528
Thin films of a newly synthesized iron(III) porphyrazine, LFeOESPz ( L = ClEtO, OESPz = ethylsulfanylporphyrazine), have been deposited by the Langmuir-Schafer (LS) technique (horizontal lifting) on ITO or gold substrates. Before deposition, the floating films have been investigated at the air-water interface by pressure/area per molecule (pi/ A) experiments, Brewster angle microscopy (BAM) and UV-vis reflection spectroscopy (RefSpec). The complex reacts with water subphase (pH 6.2) forming the mu-oxo dimer, which becomes the predominant component of the LS films ( LS-Fe) as indicated by optical, IR, XPS, and electrochemical data. LS-Fe multilayers exhibit, between open circuit potential (OCP) and +0.90 V (vs SCE), two independent peak pairs with formal potentials, E surf (I) and E surf(II) of +0.56 V and +0.78 V, respectively. According to dynamic voltammetric and coulometric experiments the peak pair at +0.56 V is attributed to one-electron process at the iron(III) centers on the monomer, while the peak pair at +0.78 V is associated to a four-electron process involving mu-oxo-dimer oligomers. LS-Fe films prove to be quite stable electrochemically between OCP and +0.90 V. The electrochemical stability decreases, however, when the potential range is extended both anodically and cathodically outside these limits, due to formation of new species. Upon incubation with TCA solutions, LS-Fe films show remarkable changes in the UV-vis spectra, which are consistent with a significant mu-oxo dimer --> monomer conversion. Addition of TCA to the electrochemical cell using a LS-Fe film as working electrode, results in a linear increase of a cathodic current peak near -0.40 V as the TCA concentration varies in the 0.1-2.0 mM range. This behavior is interpreted in terms of TCA inducing a progressive change in the composition of the LS-Fe films in favor of the monomeric iron(III) porphyrazine, which is responsible for the observed increase in the cathodic current near -0.40 V. 相似文献
56.
Rapid microchip-based electrophoretic immunoassays for the detection of swine influenza virus 总被引:1,自引:0,他引:1
Reichmuth DS Wang SK Barrett LM Throckmorton DJ Einfeld W Singh AK 《Lab on a chip》2008,8(8):1319-1324
Towards developing rapid and portable diagnostics for detecting zoonotic diseases, we have developed microchip-based electrophoretic immunoassays for sensitive and rapid detection of viruses. Two types of microchip-based electrophoretic immunoassays were developed. The initial assay used open channel electrophoresis and laser-induced fluorescence detection with a labeled antibody to detect influenza virus. However, this assay did not have adequate sensitivity to detect viruses at relevant concentrations for diagnostic applications. Hence, a novel assay was developed that allows simultaneous concentration and detection of viruses using a microfluidic chip with an integrated nanoporous membrane. The size-exclusion properties of the in situ polymerized polyacrylamide membrane are exploited to simultaneously concentrate viral particles and separate the virus/fluorescent antibody complex from the unbound antibody. The assay is performed in two simple steps--addition of fluorescently labeled antibodies to the sample, followed by concentration of antibody-virus complexes on a porous membrane. Excess antibodies are removed by electrophoresis through the membrane and the complex is then detected downstream of the membrane. This new assay detected inactivated swine influenza virus at a concentration four times lower than that of the open-channel electrophoresis assay. The total assay time, including device regeneration, is six minutes and requires <50 microl of sample. The filtration effect of the polymer membrane eliminates the need for washing, commonly required with surface-based immunoassays, increasing the speed of the assay. This assay is intended to form the core of a portable device for the diagnosis of high-consequence animal pathogens such as foot-and-mouth disease. The electrophoretic immunoassay format is rapid and simple while providing the necessary sensitivity for diagnosis of the illness state. This would allow the development of a portable, cost-effective, on-site diagnostic system for rapid screening of large populations of livestock, including sheep, pigs, cattle, and potentially birds. 相似文献
57.
Takabayashi Y McDonald MT Papanikolaou D Margadonna S Wu G Liu RH Chen XH Prassides K 《Journal of the American Chemical Society》2008,130(29):9242-9243
The superconducting transition temperature of the high-Tc SmO1-xFxFeAs superconductors increases monotonically as the F-doping level x increases to 0.20. High-pressure magnetization experiments reveal a strong sensitivity of Tc to interatomic distances in the underdoped regime (x = 0.12) with the pressure coefficient of Tc, d(ln Tc)/dP being strongly positive. However, as the doping level increases further to x = 0.15, we find that this sensitivity is strongly suppressed and at the same time, d(ln Tc)/dP sharply switches over to assume negative values with Tc decreasing with increasing applied pressure. The abrupt change in the pressure response of the superconducting properties of the SmO1-xFxFeAs phases coincides with the putative existence of a quantum critical point (QCP) near x approximately 0.14, as proposed by resistivity and Hall effect measurements. 相似文献
58.
Margadonna S Takabayashi Y McDonald MT Kasperkiewicz K Mizuguchi Y Takano Y Fitch AN Suard E Prassides K 《Chemical communications (Cambridge, England)》2008,(43):5607-5609
The newly discovered superconductor FeSe(1-x) (x approximately 0.08, T(c)(onset) approximately 13.5 K at ambient pressure rising to 27 K at 1.48 GPa) exhibits a structural phase transition from tetragonal to orthorhombic below 70 K at ambient pressure-the crystal structure in the superconducting state shows remarkable similarities to that of the REFeAsO(1-x)F(x) (RE = rare earth) superconductors. 相似文献
59.
Serena Coiai Elisa Passaglia Francesco Ciardelli Diego Tirelli Franco Peruzzotti Emiliano Resmini 《Macromolecular Symposia》2006,234(1):193-202
The synthesis of polystyrene chains covalently bound to the surface of cross-linked rubber particles from recycled tires (ground tire rubber, GTR) was investigated via free radical polymerization in situ by using azobisisobutyronitrile (AIBN) and dibenzoyl peroxide (BPO) as initiators. Indeed, the graft polymerization provides a significant route to modify the physical and chemical properties of these particles allowing to improve their compatibility with other polymers. Polymerization reactions were carried out in bulk by changing the styrene/GTR ratio as well as the amount of free radical initiator. Appreciable amounts of polystyrene (PS) were grafted on GTR when BPO was used as confirmed by particle characterizations. 相似文献
60.
Gilbert Mercieca Sara Odoardi Serena Mestria Marisa Cassar Sabina Strano‐Rossi 《Journal of separation science》2020,43(14):2858-2868
The constant emergence of new psychoactive substances is a challenge to clinical and forensic toxicologists who need to constantly update analytical techniques to detect them. A large portion of these substances are synthetic cannabinoids. The aim of this study was to develop a rapid and simple method for the determination of synthetic cannabinoids and their metabolites in urine and blood using gas chromatography–mass spectrometry. The method involves an ultrasound‐assisted dispersive liquid–liquid microextraction that implies a rapid procedure, giving excellent extraction efficiencies with minimal use of toxic solvents. This is followed by silylation and analysis with gas chromatography–mass spectrometry. The chromatographic method allows for the separation and identification of 29 selected synthetic cannabinoids and some metabolites. The method was validated on urine and blood samples with the ability to detect and quantify all analytes with satisfactory limits of detection (from 1 to 5 ng/mL), limits of quantification (5 ng/mL), and selectivity and linearity (in the range of 5–200 ng/mL). The developed assay is highly applicable to laboratories with limited instrumental availability, due to the use of efficient and low‐cost sample preparation and instrumental equipment. The latter may contribute to enhance the detection of new psychoactive substances in clinical and forensic toxicology laboratories. 相似文献