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241.
J. W. Mcfarland B. M. Howe J. D. Lehmkuhler D. C. Myers 《Journal of heterocyclic chemistry》1995,32(6):1747-1750
Formylation of 2,2′,5′,2′-terfuran ( 1 ) with N-methylformanilide and phosphorus oxychloride gave 5-formyl-2,2′,5′,2′-terfuran ( 2 ) and 5,5′-diformyl-2,2′5′,2′-terfuran ( 3 ). Reduction of 2 and 3 afforded 5-hydroxymethyl-2,2′,5′,2′-terfuran ( 4 ) and 5,5′ dihydroxymethyl-2,2′,5′,2′-terfuran ( 5 ), respectively. Terfuran 1 reacted with phenylmagnesium bromide to give 5-(phenylhydroxymethyl)-2,2′,5′,2′-terfuran ( 6 ), and was carbonated to 5-carboxy 2,2′,5′,2′-terfuran ( 7 ) and 5,5′-dicarboxy-2,2′,5′,2′-terfuran ( 8 ). Bromination of 1 with N-bromosuccinimide gave 5,5′-dibromo 2,2′,5′,2′-terfuran ( 9 ). 相似文献
242.
The unimolecular mass-analysed ion kinetic energy (MIKE) spectra of 9 pairs of hydrocarbon and ketone steroid isomers, differing only in the stereochemistry at the A/B and C/D ring junctions, have been measured and are discussed with a view to unambiguous structural identification. Reproducible differences in the MIKE spectra are observed, which are large enough in certain instances to suggest that MIKE spectrometry may be used for determining the stereochemistry of the A/B and C/D ring junctions in steroidal isomers, even if the second isomer is not available. This fortunate situation is rarely observed in conventional mass spectrometry of stereoisomeric steroids. Furthermore, these differences in the MIKE spectra may be correlated with differences in strain energy between configurational isomers. The sensitivity of MIKE spectrometry to differences in strain energies makes it a potentially powerful stereochemical probe. 相似文献
243.
Shanmugasundaram Veerabahu Bajorath Jürgen Christoffersen Ralph E. Petke James D. Howe W. Jeffrey Johnson Mark A. Agrafiotis Dimitris K. Lee Pil Kuhn Leslie A. Goodwin Jay T. Holloway M. Katharine Doman Thompson N. Walters W. Patrick Schreyer Suzanne Medina-Franco José L. Martinez-Mayorga Karina Restifo Linda L. 《Journal of computer-aided molecular design》2022,36(9):623-638
Journal of Computer-Aided Molecular Design - In May 2022, JCAMD published a Special Issue in honor of Gerald (Gerry) Maggiora, whose scientific leadership over many decades advanced the fields of... 相似文献
244.
Yutong Wu Po‐Wei Huang Joshua D. Howe Yu Yan Jose Martinez Anna Marianchuk Yamin Zhang Hang Chen Nian Liu 《Angewandte Chemie (Weinheim an der Bergstrasse, Germany)》2019,131(43):15372-15378
Zinc–bromine flow batteries are promising for stationary energy storage, and bromine‐complexing agents have been used to form phase‐separated liquid polybromide products. However, an understanding of the dynamics of polybromide nucleation is limited due to the beam sensitivity and complexity of polybromides. Here we report an in operando platform composed of dark‐field light microscopy and a transparent electrochemical cell to reveal the dynamics of polybromide formation in their native environment. Using our platform, we confirm and reveal the liquid nature, chemical composition, pinning effect (strong interaction with Pt), residual effect (residual charge products on the surface), self‐discharging, and over‐oxidation of the polybromide products. The results provide insights into the role of complexing agents and guide the future design of zinc–bromine flow batteries. Furthermore, our in operando platform can potentially be used to study sensitive species and phases in other electrochemical reactions. 相似文献
245.
Thanh Nhut Do M. Faisal Khyasudeen Pawe J. Nowakowski Zhengyang Zhang Howe‐Siang Tan 《化学:亚洲杂志》2019,14(22):3992-4000
The frequency fluctuation correlation function (FFCF) measures the spectral diffusion of a state's transition while the frequency fluctuation cross‐correlation function (FXCF) measures the correlation dynamics between the transitions of two separate states. These quantities contain a wealth of information on how the chromophores or excitonic states interact and couple with its environment and with each other. We summarize the experimental implementations and theoretical considerations of using two‐dimensional electronic spectroscopy to characterize FFCFs and FXCFs. Applications can be found in systems such as the chlorophyll pigment molecules in light‐harvesting complexes and CdSe nanomaterials. 相似文献
246.
Susan E. Howe C. M. Davidson Martin McCartney 《Analytical and bioanalytical chemistry》1999,363(5-6):582-584
Uranium was determined in extracts of inter-tidal sediment, obtained from a contaminated harbour, using the three-stage sequential extraction procedure recommended by BCR. The element was found mainly in association with reducible, or reducible and oxidisable, phases and the overall concentration was enhanced (up to 6.7 μg g–1 dry weight) with respect to typical, UK levels. The 238U/235U ratio has been measured in digests of stream sediments obtained from the vicinity of a uranium enrichment plant. Significant enhancement in 235U with respect to the natural 238U/235U ratio (137.88:1) was observed at some locations. 相似文献
247.
A review is given of recent work in the authors' laboratory on the characterization of different forms of nanostructured titania.
It is shown that nanocrystalline anatase powders and nanocrystalline anatase thin films differ significantly in their optical
properties, due primarily to differences in sintering behaviour on drying. It is argued that the electronic properties of
these systems are determined by surface phenomena rather than quantum size effects. The novel titanosilicate zeolite ETS-10
which contains one dimensional “quantum wires” of titania provides an alternative system for studying quantum size effects
which has considerable potential for photocatalysis. 相似文献
248.
Paulo Vieira Margarida Q. Miranda Dr. Igor Marques Dr. Sílvia Carvalho Dr. Li-Jun Chen Dr. Ethan N. W. Howe Carl Zhen Claudia Y. Leung Dr. Michael J. Spooner Bárbara Morgado Prof. Odete A. B. da Cruz e Silva Prof. Cristina Moiteiro Prof. Philip A. Gale Prof. Vítor Félix 《Chemistry (Weinheim an der Bergstrasse, Germany)》2020,26(4):888-899
The anion-binding and transport properties of an extensive library of thiophene-based molecules are reported. Seventeen bis-urea positional isomers, with different binding conformations and lipophilicities, have been synthesized by appending α- or β-thiophene or α-, β-, or γ-benzo[b]thiophene moieties to an ortho-phenylenediamine central core, yielding six subsets of positional isomers. Through 1H NMR, X-ray crystallography, molecular modelling, and anion efflux studies, it is demonstrated that the most active transporters adopt a pre-organized binding conformation capable of promoting the recognition of chloride, using urea and C−H binding groups in a cooperative fashion. Additional large unilamellar vesicle-based assays, carried out under electroneutral and electrogenic conditions, together with N-methyl-d -glucamine chloride assays, have indicated that anion efflux occurs mainly through an H+/Cl− symport mechanism. On the other hand, the most efficient anion transporter displays cytotoxicity against tumor cell lines, while having no effects on a cystic fibrosis cell line. 相似文献
249.
A theory is proposed for the design of a uniform tunnel-entrance hood whose cross-sectional area
exceeds the tunnel area
. A train entering the tunnel produces a low-frequency compression wave that can be subject to nonlinear steepening in a long tunnel. An optimized hood of length ℓh increases the initial thickness of the compression wave front from R/M to ℓh/M, where Rℓh is the nominal radius of the tunnel and M is the train Mach number. In addition, the pressure rise should be linear across the wave front to obtain an overall minimum value of the subjectively important pressure gradient. This is achieved in a uniform hood by distributing windows along the hood wall to vent away high-pressure air displaced by the train. We consider the problem of determining the distribution and sizes of these windows and the magnitude of the area ratio
to ensure that the hood behaves optimally at low-train Mach numbers (M<0.2), when the hood can be regarded as being acoustically compact. At the projected higher Mach numbers of advanced high-speed trains (0.4, say) recent analysis for hoods of uniform cross-section by Howe in 2003 indicates that a hood optimized for low Mach number operations continues to produce an essentially linear pressure rise across a compression wave of thickness ℓh/M except for a low-amplitude oscillation at the very front of the wave. 相似文献
250.