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71.
R. E. Lutz W. M. Hankins M. G. Hankins W. J. Welstead C. L. Dickerson 《Journal of heterocyclic chemistry》1970,7(3):569-573
2,5-Diphenyl-3-morpholinofuran ( 1 ) reacts with bromine and trifluoroacetic acid, giving respectively 2-bromo and 2-hydro furylium salts ( 2,3 ). The 2-hydroxy furylium bromide ( 4 ) was obtained by reaction of cis-morpholino-1,2-dibenzoylethylene ( 5 ) with hydrogen bromide. The nmr spectra of these salts show differences between the two morpholino dimethylene moieties of each caused by restricted rotation at the 3-immonium group. Chemical relationships studied include reductions to the morpholinofuran, conversions to 3-furanones, and the slow reaction of morpholinodibenzoylethylene with phenylmagnesium bromide to give cis-dibenzoylstyrene (13). 相似文献
72.
Dickerson TJ Lovell T Meijler MM Noodleman L Janda KD 《The Journal of organic chemistry》2004,69(20):6603-6609
The recent discovery that nornicotine 1, a minor nicotine metabolite, can catalyze the aldol reaction under physiologically relevant conditions has initiated research efforts into the potential chemical roles of nicotine metabolites. Herein, we disclose studies aimed at determining the origin and thus mechanism of the nornicotine-catalyzed aqueous aldol reaction. Conformationally constrained compounds designed to mimic the low-energy conformations of nornicotine were synthesized and tested for aldol catalysis; however, none showed rate enhancements on par with nornicotine. To further explore the mechanism of this process, a density functional theory (DFT) study was performed by using a variety of compounds previously tested for catalysis. These in silico studies have uncovered an unprecedented mechanistic subtlety of aqueous aldol reactions. Unlike the single transition state model observed for aldol reactions in organic solvent, the nornicotine-catalyzed reaction in water proceeds via a two-step mechanism in which a water molecule is utilized in both steps and a stable intermediate is generated. In total, these studies validate the proposed enamine-based mechanism of nornicotine-catalyzed aqueous aldol reactions and also provide the basis for future studies into the stereoelectronic nature of individual catalyst structures. 相似文献
73.
We study the effect of the zero- to one-dimensional (1D) transformation on multiparticle Auger recombination using a series of elongated semiconductor nanocrystals (quantum rods). We observe a transition from the three- to two-particle recombination process as the nanocrystal aspect ratio is increased. This transition indicates that in the 1D confinement limit, Auger decay is dominated by Coulomb interactions between 1D excitons that recombine in a bimolecular fashion. One consequence of this effect is strongly reduced decay rates of higher multiparticle states that lead to increased optical-gain lifetimes and efficient light amplification due to involvement of excited electronic states. 相似文献
74.
Brogan AP Eubanks LM Koob GF Dickerson TJ Janda KD 《Journal of the American Chemical Society》2007,129(12):3698-3702
Marijuana abuse continues to plague society and the lack of effective treatments warrants concern. Catalytic antibodies capable of oxidatively degrading the major psychoactive component of marijuana, Delta9-tetrahydrocannabinol (Delta9-THC), are presented. The antibodies generate reactive oxygen species from singlet oxygen (1O2*), using riboflavin (vitamin B2) and visible light as the 1O2* source. Cannabitriol was identified as the major degradation product of this reaction, demonstrating the ability of an antibody to catalyze a complex chemical transformation with therapeutic implications for treating marijuana abuse. 相似文献
75.
Jason M. Hogan David M. S. Johnson Susannah Dickerson Tim Kovachy Alex Sugarbaker Sheng-wey Chiow Peter W. Graham Mark A. Kasevich Babak Saif Surjeet Rajendran Philippe Bouyer Bernard D. Seery Lee Feinberg Ritva Keski-Kuha 《General Relativity and Gravitation》2011,43(7):1953-2009
We propose an atom interferometer gravitational wave detector in low Earth orbit (AGIS-LEO). Gravitational waves can be observed by comparing a pair of atom interferometers separated by a 30 km baseline. In the proposed configuration, one or three of these interferometer pairs are simultaneously operated through the use of two or three satellites in formation flight. The three satellite configuration allows for the increased suppression of multiple noise sources and for the detection of stochastic gravitational wave signals. The mission will offer a strain sensitivity of ${<10^{-18}/\sqrt{{\rm Hz}}}$ in the 50mHz?C10Hz frequency range, providing access to a rich scientific region with substantial discovery potential. This band is not currently addressed with the LIGO, VIRGO, or LISA instruments. We analyze systematic backgrounds that are relevant to the mission and discuss how they can be mitigated at the required levels. Some of these effects do not appear to have been considered previously in the context of atom interferometry, and we therefore expect that our analysis will be broadly relevant to atom interferometric precision measurements. Finally, we present a brief conceptual overview of shorter-baseline $({\lesssim100\,{\rm m}})$ atom interferometer configurations that could be deployed as proof-of-principle instruments on the International Space Station (AGIS-ISS) or an independent satellite. 相似文献
76.
Hogan JM Hammer J Chiow SW Dickerson S Johnson DM Kovachy T Sugarbaker A Kasevich MA 《Optics letters》2011,36(9):1698-1700
We built an ultra-low-noise angle sensor by combining a folded optical lever and a Sagnac interferometer. The instrument has a measured noise floor of 1.3 prad/√Hz at 2.4 kHz. We achieve this record angle sensitivity using a proof-of-concept apparatus with a conservative N=11 bounces in the optical lever. This technique could be extended to reach subpicoradian/√Hz sensitivities with an optimized design. 相似文献
77.
Swearingen KE Dickerson JA Turner EH Ramsay LM Wojcik R Dovichi NJ 《Journal of chromatography. A》2008,1194(2):249-252
The fluorogenic reagent Chromeo P465 is considered for the analysis of proteins by capillary electrophoresis with laser-induced fluorescence detection. The reagent was first used to label alpha-lactalbumin; the product was analyzed by capillary zone electrophoresis in a sub-micellar sodium dodecyl sulfate (SDS) buffer. The product generated a set of equally spaced but poorly resolved peaks that formed a broad envelope with a net mobility of 4 x 10(-4)cm(2) V(-1) s(-1). The components of the envelope were presumably protein that had reacted with different numbers of labels. The mobility of these components decreased by roughly 1% with the addition of each label. The signal increased linearly from 1.0 nM to 100 nM alpha-lactalbumin (r(2)=0.99), with a 3sigma detection limit of 70 pM. We then considered the separation of a mixture of ovalbumin, alpha-chymotrypsinogen A, and alpha-lactalbumin labeled with Chromeo P465; unfortunately, baseline resolution was not achieved with a borax/SDS buffer. Better resolution was achieved with N-cyclohexyl-2-aminoethanesulfonic acid/Tris/SDS/dextran capillary sieving electrophoresis; however, dye interactions with this buffer system produced a less than ideal blank. 相似文献
78.
Willis B Eubanks LM Dickerson TJ Janda KD 《Angewandte Chemie (International ed. in English)》2008,47(44):8360-8379
In the classic novella "The Strange Case of Dr. Jekyll and Mr. Hyde", Robert Louis Stevenson paints a stark picture of the duality of good and evil within a single man. Botulinum neurotoxin (BoNT), the most potent known toxin, possesses an analogous dichotomous nature: It shows a pronounced morbidity and mortality, but it is used with great effect in much lower doses in a wide range of clinical scenarios. Recently, tremendous strides have been made in the basic understanding of the structure and function of BoNT, which have translated into widespread efforts towards the discovery of biomacromolecules and small molecules that specifically modulate BoNT activity. Particular emphasis has been placed on the identification of inhibitors that can counteract BoNT exposure in the event of a bioterrorist attack. This Review summarizes the current advances in the development of therapeutics, including vaccines, peptides, and small-molecule inhibitors, for the prevention and treatment of botulism. 相似文献
79.
Gonzalo-Juan I Krejci AJ Dickerson JH 《Langmuir : the ACS journal of surfaces and colloids》2012,28(11):5295-5301
The controlled electrophoretic deposition of monolayers and ultrathin films of 4.0 nm TiO(2) nanocrystals from stable, nonpolar solvent-based suspensions is reported. Stable suspensions were prepared in hexane, and the electrophoretic mobility of the nanocrystals was enhanced by a combination of a liquid-liquid extraction followed by mechanical surfactant removal by high-speed centrifugation. The controlled evolution of the density of TiO(2) nanocrystal monolayers was studied by transmission electron microscopy and optical transmittance spectroscopy. Ultrathin films were assembled while maintaining monolayer-by-monolayer growth and uniform density of the film. A time-dependent, equivalent circuit model has been proposed to characterize the electrophoretic current that was recorded during our experiments. Further, we demonstrate that the proposed model, coupled with the mobility, provides a means to estimate the deposition rate and, hence, the time necessary to fabricate a submonolayer, a monolayer, and multilayers of nanocrystals. 相似文献