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1.
[reaction: see text] The TiCl4-mediated reaction of an ester with benzoyl chloride results in high yields of the alpha-benzoylated ester. Diazo transfer of the benzoylated ester utilizing p-acetoamidobenzenesulfonyl azide affords the alpha-diazo ester in good yield. Using this simplified procedure, it is easy to prepare gram quantities of alpha-diazo esters. 相似文献
2.
ABSTRACT Copolymers of 1,5-dioxepan-2-one (DXO) and e-caprolactone (?-CL), δ-valerolactone (δ-VL) or L-lactide (LLA) have been synthesized and characterized. High molecular weight copolymers were obtained using stannous-2-ethyl hexanoate as catalyst in bulk. Reactivity ratios for the copolymerization of DXO and δ-VL were determined at 110°C as rVL=0.5 and rDXO=2.3. At high conversion, depolymerization of δ-VL occurred, resulting in lower molecular weight and variations in the copolymer composition. Physical properties, such as crystallinity and melting temperature of the DXO-copolymers proved to be strongly dependent on the choice of comonomer and on the molar composition of the copolymers. DXO appears to be incorporated into the poly-?-caprolactone (PCL) crystals and to some extent into the poly-δ-valerolactone (PVL) crystals, resulting in a more gradual decrease in crystallinity with increasing amount of DXO. 相似文献
3.
We report here on differential linear scan voltammetry, DLSV, that combines the working principles of linear scan voltammetry, LSV, and the numerous existing pulsed voltammetry techniques. DLSV preserves the information from continuous interrogation in voltage and high accuracy that LSV provides about electrochemical processes, and the much better sensitivity of differential pulsed techniques. DLSV also minimizes the background current compared to both LSV and pulsed voltammetry. An early version of DLSV, derivative stationary electrode polarography, DSEP, had been proposed in the 1960s but soon abandoned in favor of the emerging differential pulsed techniques. Relative to DSEP, DLSV takes advantage of the flexibility of discrete smoothing differentiation that was not available to early investigators. Also, DSEP had been explored in pure solutions and with reversible electrochemical reactions. DLSV is tested in this work in more challenging experimental contexts: the measurement of oxygen with a carbon fiber microelectrode in buffer, and with a gold microdisc electrode exposed to a live biological preparation. This work compares the analytical performance of DLSV and square wave voltammetry, the most popular pulsed voltammetry technique. Figure
Square wave voltammetry and differential linear scan voltammetry, DLSV. Measurement protocols and analytical results on dissolved oxygen levels obtained with a gold microdisc electrode at a live biological preparation 相似文献
4.
Gupta R Sheth DM Boone TK Sevilla AB Fréchette J 《Langmuir : the ACS journal of surfaces and colloids》2011,27(24):14923-14929
Pinning of the triple contact line adversely affects electrowetting on dielectric. Electrowetting response of substrates with contact angle hysteresis ranging from 1° to 30° has been characterized, and the results are interpreted within the framework of electromechanics corrected for pinning. The relationship between contact angle hysteresis, threshold potential for liquid actuation, and electrowetting hysteresis is quantified. Our results demonstrate that a modified electrowetting equation, based on balance of forces (including the pinning forces) acting on the triple contact line and on the drop, describes the electrowetting response of substrates with significant contact angle hysteresis. Finally, the surface properties of PDMS Sylgard 184 were found to be influenced by the electric field. 相似文献
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6.
Sheth AR Lubach JW Munson EJ Muller FX Grant DJ 《Journal of the American Chemical Society》2005,127(18):6641-6651
Structural and solid-state changes of piroxicam in its crystalline form under mechanical stress were investigated using cryogenic grinding, powder X-ray diffractometry, diffuse-reflectance solid-state ultraviolet-visible spectroscopy, variable-temperature solid-state (13)C nuclear magnetic resonance spectroscopy, and solid-state diffuse-reflectance infrared Fourier transform spectroscopy. Crystalline piroxicam anhydrate exists as colorless single crystals irrespective of the polymorphic form and contains neutral piroxicam molecules. Under mechanical stress, these crystals become yellow amorphous piroxicam, which has a strong propensity to recrystallize to a colorless crystalline phase. The yellow color of amorphous piroxicam is attributed to charged piroxicam molecules. Variable-temperature solid-state (13)C NMR spectroscopy indicates that most of the amorphous piroxicam consists of neutral piroxicam molecules; the charged species comprise only about 8% of the amorphous phase. This ability to quantify the fractions of charged and neutral molecules of piroxicam in the amorphous phase highlights the unique capability of solid-state NMR to quantify mixtures in the absence of standards. Other compounds of piroxicam, which are yellow, are known to contain zwitterionic piroxicam molecules. The present work describes a system in which proton transfer accompanies both solid-state disorder and a change in color induced by mechanical stress, a phenomenon which may be termed mechanochromism of piroxicam. 相似文献
7.
RD Harris WS Baker Van Stipdonk MJ RM Crooks EA Schweikert 《Rapid communications in mass spectrometry : RCM》1999,13(14):1374-1380
A suite of keV polyatomic or 'cluster' projectiles was used to bombard unoxidized and oxidized self-assembled monolayer surfaces. Negative secondary ion yields, collected at the limit of single ion impacts, were measured and compared for both molecular and fragment ions. In contrast to targets that are orders of magnitude thicker than the penetration range of the primary ions, secondary ion yields from polyatomic projectile impacts on self-assembled monolayers show little to no enhancement when compared with monatomic projectiles at the same velocity. This unusual trend is most likely due to the structural arrangement and bonding characteristics of the monolayer molecules with the Au(111). Copyright 1999 John Wiley & Sons, Ltd. 相似文献
8.
A Mukherjee M Dasgupta DJ Hinde CR Morton AC Berriman RD Butt JO Newton H Timmers 《Pramana》2001,57(1):195-198
Fusion cross-sections for the 7Li + 12C reaction have been measured at energies above the Coulomb barrier by the direct detection of evaporation residues. The heavy
evaporation residues with energies below 3 MeV could not be separated out from the α-particles in the spectrum and hence their
contribution was estimated using statistical model calculations. The present work indicates that suppression of fusion cross-sections
due to the breakup of 7Li may not be significant for 7Li + 12C reaction at energies around the barrier. 相似文献
9.
Recent calculations of the energetic barriers for diffusion of Au atoms on the Au(110) surface have shown that for moves perpendicular to the close-packed atomic rows, concerted, or multi-atom movements are energetically favorable over single-atom movements for the same displacement. Entropic hindrances, however are expected to limit concerted moves. In the present paper this competition is investigated via simulation techniques based on model potentials that reproduce the relevant energtic and entropic features of the Au(110) situation. Apparently non-Arrhenius behavior is found for the concerted motions. A new scheme, which avoids the necessity of long simulation runs to determine the “hop” rate at several temperatures, for determining entropic barriers directly is proposed and tested. Though this method is applied in the present context to a simplified model for the interatomic potentials, it can be straightforwardly extended to realistic treatments of those interactions. 相似文献
10.
Raj Gandhi Subhendra Mohanty Tarun Souradeep S Agarwalla K Bhattacharya B Brahmachari R Crittenden S Goswami P Ghoshal M Lindner H S Mani S Mitra S Pascoli S Panda R Rangarajan S Ray T Roy Choudhury R Saha S Sarkar A Srivastava R Sheth S Uma Sankar U Yajnik 《Pramana》2006,67(4):735-742
The working group on astroparticle and neutrino physics at WHEPP-9 covered a wide range of topics. The main topics were neutrino
physics at INO, neutrino astronomy and recent constraints on dark energy coming from cosmological observations of large scale
structure and CMB anisotropy. 相似文献