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71.
A survey of conditions for the palladium catalyzed intramolecular Heck cyclization of protected amines has shown that the Herrmann-Beller palladacycle can be exploited under ‘cationic’ conditions to provide a robust and rapid route (<2 h) to the synthesis of single double bond isomer phenanthridines in excellent yield (76-99%). In addition, the same cyclization can be performed under ‘neutral’ conditions to provide phenanthridines with a double bond isomer profile suitable for exploitation in diversity-based applications. We have also shown that the highly reactive (tBu3P)2Pd catalyst can induce cyclization at low temperatures (≤50 °C), giving similar results to the ‘neutral’ conditions, and offering an alternative pathway for sensitive substrates. 相似文献
72.
Donaldson PM Guo R Fournier F Gardner EM Barter LM Barnett CJ Gould IR Klug DR Palmer DJ Willison KR 《The Journal of chemical physics》2007,127(11):114513
We show that it is possible to both directly measure and directly calculate Fermi resonance couplings in benzene. The measurement method used was a particular form of two-dimensional infrared spectroscopy (2D-IR) known as doubly vibrationally enhanced four wave mixing. By using different pulse orderings, vibrational cross peaks could be measured either purely at the frequencies of the base vibrational states or split by the coupling energy. This capability is a feature currently unique to this particular form of 2D-IR and can be helpful in the decongestion of complex spectra. Five cross peaks of the ring breathing mode nu13 with a range of combination bands were observed spanning a region of 1500-4550 cm(-1). The coupling energy was measured for two dominant states of the nu13+nu16 Fermi resonance tetrad. Dephasing rates were measured in the time domain for nu13 and the two (nu13+nu16) Fermi resonance states. The electronic and mechanical vibrational anharmonic coefficients were calculated to second and third orders, respectively, giving information on relative intensities of the cross peaks and enabling the Fermi resonance states of the combination band nu13+nu16 at 3050-3100 cm(-1) to be calculated. The excellent agreement between calculated and measured spectral intensities and line shapes suggests that assignment of spectral features from ab initio calculations is both viable and practicable for this form of spectroscopy. 相似文献
73.
Spectroscopic probes of the quasi-liquid layer on ice 总被引:1,自引:0,他引:1
Raman spectra of the water OH-stretch region were acquired at air-ice and air-water interfaces at a glancing angle, which allowed observation of surface characteristics. The shapes of the OH-stretch bands indicate that the environment at the air-ice interface is different from that at the air-water interface and from that seen in bulk water. Water spectra measured at the surface of dodecane under low relative humidity indicate that this method is sensitive to fewer than 50 monolayers of water. Changes in the local environment of the surfacial water molecules may be induced by the presence of different solute species, giving rise to changes in the shape of the band. Dissolved sodium chloride disrupts hydrogen bonding in liquid water and has the same effect at the air-ice interface. However, when either HCl or HNO(3) is adsorbed from the gas phase onto an ice surface, the opposite effect is seen: Their presence appears to increase the extent of hydrogen bonding at the ice surface. At the same time, shifts in the laser-induced fluorescence spectra of acridine, a fluorescent pH-probe present at the air-ice interface, indicate that dissociation of acids occurs there. These observations suggest that the formation of hydronium ions at the air-ice interface enhances the hydrogen bonding of surfacial water molecules. 相似文献
74.
Generation of Molecular Complexity from Cyclooctatetraene: Preparation of Aminobicyclo[5.1.0]octitols
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Dr. Mohamed F. El‐Mansy Matthew Flister Dr. Sergey Lindeman Kelsey Kalous Prof. Daniel S. Sem Prof. William A. Donaldson 《Chemistry (Weinheim an der Bergstrasse, Germany)》2015,21(30):10886-10895
A series of eight stereoisomeric N‐(tetrahydroxy bicyclo‐[5.1.0]oct‐2S*‐yl)phthalimides were prepared in one to four steps from N‐(bicyclo[5.1.0]octa‐3,5‐dien‐2‐yl)phthalimide (±)‐ 7 , which is readily available from cyclooctatetraene (62 % yield). The structural assignments of the stereoisomers were established by 1H NMR spectral data as well as X‐ray crystal structures for certain members. The outcomes of several epoxydiol hydrolyses, particularly ring contraction and enlargement, are of note. The isomeric phthalimides as well as the free amines did not exhibit β‐glucosidase inhibitory activity at a concentration of less than 100 μM . 相似文献
75.
Enzymatic Oxygen Microsensor Based on Bilirubin Oxidase Applied to Microbial Fuel Cells Analysis
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Matteo Grattieri Sofia Babanova Carlo Santoro Edoardo Guerrini Stefano PM Trasatti Pierangela Cristiani Massimiliano Bestetti Plamen Atanassov 《Electroanalysis》2015,27(2):327-335
A selective oxygen biosensor based on bilirubin oxidase (BOx) was developed. The sensor was used for determining oxygen profiles in a membraneless, single‐chamber microbial fuel cell (SCMFC), fed with raw wastewater. The linear response of the sensor was optimized by a diffusion layer of silica gel. A computer‐controlled stage was used to obtain accurate and precise measurements. Oxygen concentration in biofilms covering electrodes was measured, showing 3 mg L?1 of O2 in the bulk solution, decreasing to 0 mg L?1 in the cathodic biofilm. The MFC generated power in the range of 0–0.08 mW, associated to the oxygen content. 相似文献
76.
Glancing angle laser-induced fluorescence was used to investigate the effects of organic monolayer coatings on the ozonation kinetics of pyrene at the air-aqueous interface. Fluorescence spectra show that both 1-octanol and octanoic acid coatings give rise to similar decreased polarity at the interface relative to the uncoated surface and show a similar propensity of pyrene to partition to the interface. Ozonation kinetics follow a Langmuir-Hinshelwood mechanism, indicating a surface reaction. At high ozone concentrations, a monolayer coating of 1-octanol enhances the rate relative to the uncoated surface and a coating of octanoic acid decreases the rate. Pyrene fluorescence is most efficiently quenched by ozone in the presence of a 1-octanol coating, followed by the uncoated surface, and least efficiently quenched by ozone in the presence of octanoic acid. In agreement with earlier work, a significant photoenhancement of the ozonation is observed at the uncoated surface; however, no enhancement is observed with monolayer coatings of either organic. Quantum chemical calculations indicate a reasonable binding of ozone by the carboxylic acid group (in both its dissociated and undissociated forms). We suggest that the inhibition of the water surface reaction by a monolayer of octanoic acid is due to the sequestration of ozone by the carboxylic acid group. 相似文献
77.
We propose an answer to a question raised by F. Burstall: Is there any interesting theory of isothermic submanifolds of ? n of dimension greater than two? We call an n-immersion f(x) in ? m isothermic k if the normal bundle of f is flat and x is a line of curvature coordinate system such that its induced metric is of the form $\sum_{i=1}^{n} g_{ii}\,\mathrm{d} x_{i}^{2}$ with $\sum_{i=1}^{n} \epsilon_{i} g_{ii}=0$ , where ?? i =1 for 1??i??n?k and ?? i =?1 for n?k<i??n. A smooth map (f 1,??,f n ) from an open subset ${\mathcal{O}}$ of ? n to the space of m×n matrices is called an n-tuple of isothermic k n-submanifolds in ? m if each f i is an isothermic k immersion, $(f_{i})_{x_{j}}$ is parallel to $(f_{1})_{x_{j}}$ for all 1??i,j??n, and there exists an orthonormal frame (e 1,??,e n ) and a GL(n)-valued map (a ij ) such that $\mathrm{d}f_{i}= \sum_{j=1}^{n} a_{ij} e_{j}\,\mathrm {d} x_{j}$ for 1??i??n. Isothermic1 surfaces in ?3 are the classical isothermic surfaces in ?3. Isothermic k submanifolds in ? m are invariant under conformal transformations. We show that the equation for n-tuples of isothermic k n-submanifolds in ? m is the $\frac{O(m+n-k,k)}{O(m)\times O(n-k,k)}$ -system, which is an integrable system. Methods from soliton theory can therefore be used to construct Christoffel, Ribaucour, and Lie transforms, and to describe the moduli spaces of these geometric objects and their loop group symmetries. 相似文献
78.
During this study, flow visualization through the use of imaging provided visual data of the events that occurred as the flame
oscillated. Imaging was performed in two different ways: 1) the first method was phase-locked imaging to capture a detailed
history by simply advancing the phase angle during each image capture, 2) the second method involved high-speed imaging to
gather visual image data of a natural or forced oscillating flame. For visualization, two items were considered. The first
one was the shape of the flame envelope as it evolved during one oscillation cycle. From the data gathered, it was confirmed
that the flame stretched in the vertical direction before quenching in the region near its center. The second consideration
was imaging of the oxidizer (air) in the region immediately outside the flame. This was done by imaging the laser light reflected
from particles seeded into the flow, which revealed formation of vortical structures in those regions where quenching had
occurred. It was noted that quenching took place primarily by the entrainment of fresh non-reacting air into the flame. The
quenching process was in turn responsible for the oscillatory behavior. 相似文献
79.
The effect of row depth on Strouhal numbers derived from peaks in the turbulence spectra measured in an in-line tube bank and on the excitation of acoustic standing waves in the duct containing the bank has been investigated. The results indicate significant variations with bank depth and location in the bank although common features are evident. A buffeting type frequency predicted by Owen [1] is clearly shown beyond the fifth row of deeper banks whilst peaks evident in the turbulence spectra at the front of these banks and for less deep banks are assumed to be generated by vortex action and interaction in the wakes of tube rows. For the geometrical configuration tested, acoustic resonance is generated by the coincidence of a vorticity peak frequency with the standing wave frequency for all cases but the two row deep bank in which the excitation source was most probably in the wake of the bank. Finally, a modification of Owen's theory yields an equation which predicts a Strouhal number of the correct order. 相似文献
80.
When treated with concentrated hydrochloric acid or heated beyond its melting point, the versatile thioimine 2 2-mercaptobenzhydrylidenamine was unexpectedly converted to the title ring system. Also, this imine can be converted to 3-phenyl-1,2-benzisothiazoles by prolonged exposure to air. 相似文献