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141.
Hamura T Ibusuki Y Uekusa H Matsumoto T Siegel JS Baldridge KK Suzuki K 《Journal of the American Chemical Society》2006,128(31):10032-10033
We report herein the syntheses of dodecamethoxytricyclobutabenzene (TCBB) 1 and hexaoxo-TCBB 2, a class of molecules with structural and theoretical interest. The preparation is based on the 3-fold [2 + 2] cycloadditions of benzyne and ketene silyl acetals (KSAs), where the selectively protected 2-iodophloroglucinol derivative served as a synthetic equivalent of benztriyne I, allowing rapid and regioselective annulation of fully functionalized four-membered rings. Structural study on the former compound showed that the C-C bond lengths in the central benzene ring were essentially the same. 相似文献
142.
Dewald S Lang T Schröter CD Moshammer R Ullrich J Siegel M Morgner U 《Optics letters》2006,31(13):2072-2074
A Ti:sapphire oscillator with an extended cavity generates pulses with 0.5 microJ energy at a repetition rate of 6 MHz and pulse durations of 50 fs. Tight focusing creates peak intensities exceeding 10(14) W/cm2, which is sufficient for ionizing helium, a nonlinear process where at least 17 photons are absorbed simultaneously. 相似文献
143.
A novel prototype gel oscillator that functions by dissipating the chemical energy of glucose by an enzyme-mediated reaction is proposed. The product of the reaction modulates the degree of swelling and hence the permeability of a poly(N-isopropylacrylamide-co-methacrylic acid) gel membrane which in turn regulates the flow of substrate to the enzyme. No external energy is required aside from the chemical energy of glucose present externally at constant concentration. A negative chemomechanical feedback loop is established which, coupled with hysteresis in the membrane permeability characteristics, produces pulsing oscillations. In this study, we introduce a simple model which provides guidelines for experimental design, and report preliminary experimental evidence for oscillation. Application of this prototype system to the episodic delivery of drugs and hormones is envisaged. (c) 1999 American Institute of Physics. 相似文献
144.
Using dynamic low-coherence interferometry to image Brownian motion within highly scattering media 总被引:1,自引:0,他引:1
Dynamic low-coherence interferometry was used to measure Brownian motion of submicrometer particles within highly scattering media. Strong rejection of multiply scattered light was obtained by combination of a coherence gate with a confocal microscope, thus allowing particle characterization methods generally reserved for optically dilute materials to be applied to optically concentrated suspensions. The Brownian diffusion coefficient of highly scattering media was determined with an accuracy better than 5%. Furthermore, we show that spatial variations in the Brownian diffusion coefficient can be imaged with an axial resolution determined by the coherence length of the light source (~30 mum) . The experiments also show broadening of the power spectrum as a function of depth into the sample, most likely as a result of detecting multiply scattered light. 相似文献
145.
Siegel W 《Physical review D: Particles and fields》1994,50(4):2799-2805
146.
Über die Darstellung von m-Hydroxybenzonitrilen durch Reaktion von Alkalicyaniden mit Chinolacetaten
Zusammenfassung Die Einwirkung von Kaliumcyanid in alkoholischer Lösung auf o- und p-Chinolacetate mit freier 5-Stellung führt unter 1,4-Addition des Cyanids zur Bildung entsprechend substituierter m-Hydroxybenzonitrile. In manchen Fällen scheint dieser Bildungsweg anderen Darstellungsmethoden dieser Verbindungen überlegen zu sein. *** DIRECT SUPPORT *** A3615062 00004 相似文献
147.
A. R. Martin S. H. Kim G. W. Peng G. V. Siegel T. J. Yale 《Journal of heterocyclic chemistry》1978,15(8):1331-1334
1,2-Dihydro-3-hydroxy-3H-pyrido[3,2,1-kl]phenothiazines and 1H-pyrido[3,2,1-kl]phenothiazines undergo acid catalyzed disproportionation with intermolecular hydride transfer to form pyrido[3,2,1-kl]phenothiazinium salts and 1,2-dihydro-3H-pyrido[3,2,1-kl]phenothiazines. Sodium borohydride reduction of 3-alkyl- or 3-arylpyrido[3,2,1-kl]phenothiazinium salts gives 3-alkyl- or 3-aryl-1H-pyrido[3,2,1-kl]phenothiazines. In the presence of a proton source, borohydride reduction of pyrido[3,2,1-kl]phenothiazinium fluoroborate or 3-chloropyrido-[3,2,1-kl]phenothiazinium perchlorate gives 1,2-dihydro-3H-pyrido[3,2,1-kl]phenothiazine, while 1H-pyrido[3,2,1-kl]phenothiazine is formed in aprotic solvents with pyridine present. 相似文献
148.
V. Švorčík J. Siegel P. Slepička V. Kotál J. Švorčíková M. Špirková 《Surface and interface analysis : SIA》2007,39(1):79-85
Polyethyleneterephtalate (PET) and polytetrafluorethylene (PTFE) foils were modified by plasma discharge. The effect of plasma modification on polymer surface wettability and on properties of gold coatings were studied as a function of time from plasma exposure (aging time) and polymer substrate temperature. Thickness, sheet resistance, and surface topology of gold layers were studied. Aging of the plasma‐exposed samples is accompanied by increase in contact angle, which is explained by rearrangement of the polymer segments in the polymer surface monolayer, and a decrease in the concentration of polar groups. The aging also leads to a decline in surface roughness Ra measured by atomic force microscopy (AFM). Under deposition conditions, comparable thicknesses of deposited Au layers were prepared on pristine PET and plasma‐treated PET and PTFE samples. The thinnest Au layers were evaporated onto pristine PTFE. The sheet resistance decreases with increasing thickness of Au layer. Plasma treatment leads to an increase of PTFE surface roughness, which becomes even more pronounced after Au deposition. A higher roughness shows that the PET samples are deposited with the Au layer at temperatures above the glassy transition temperature Tg. Copyright © 2006 John Wiley & Sons, Ltd. 相似文献
149.
The adsorption of a number of lipoproteins, i.e., low-density lipoprotein (LDL), oxidized LDL (oxLDL), high-density lipoprotein (HDL), and lipoprotein (a), at silica and methylated silica as well as at the latter surface modified through adsorption of proteoheparan sulfate, was investigated with in situ ellipsometry at close to physiological conditions. It was found that LDL, oxLDL, HDL, and lipoprotein (a) all adsorbed more extensively at silica than at methylated silica. Upon exposure of the methylated silica surface to proteoheparan sulfate, this proteoglycan adsorbs through its hydrophobic moiety, thereby forming a layer similar to that in the biological system, with the polysaccharide chains forming brushes oriented toward the aqueous solution. Analogous to the biological system, both lipoprotein (a) and LDL were found to deposit at such surfaces, the latter particularly in the simultaneous presence of Ca(2+). After HDL pre-exposure, however, no LDL deposition was observed, even at high LDL and Ca(2+) concentrations. These findings correlate well with those obtained from clinical investigations on risk factors for atherosclerosis. Copyright 2000 Academic Press. 相似文献
150.
Marshall M. Siegel Rushung Tsao Allan Wissner 《Journal of mass spectrometry : JMS》1993,28(11):1297-1308
A series of substituted bisaryl phosphate compounds, (R1CH2)+ ArOP = O(O?)(OArR2R3), was analyzed and characterized by fast atom bombardment mass spectrometry. Abundant fragment ions were observed and correlated with the proposed structures. From fragmentation pattersn, ‘ortho effect’ reactions were demonstrated to have occurred when the phosphoryl oxygen reacted with the (CH2R1)+ and C?O(OCH3) substituents in the ortho position, relative to the phosphate group, and displaced the R1 and OCH3 groups, respectively, to produce phosphorus containing six-membered rings fused to the aryl moiety. When the (CH2R1)+ substituents were in the meta position relative to the phosphate group, the ‘ortho effect’ reactions were not observed. However, when the C?O(OCH3) substituent was in the meta position relative to the phosphate group, an abundant fragment ion containing a five-membered phosphate ring fused to the aryl ring was detected with the original phosphoryl oxygen ortho to both the phosphate oxygen and a formyl group, formed from the original C?O(OCH3) substituent. All other fragmentations not involving the ‘ortho effect’ reactions were nearly identical for the different structural isomers of the substituted bisaryl phosphate compounds. 相似文献