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71.
Different stereoisomers of active molecules often cause different physiological responses and hence pose a challenge for their identification. This study involves perceptive fragmentation behavior of newly isolated cassane butenolides, caesalpinolide A [1] and caesalpinolide B [2] (epimeric at the hemiketal position) by tandem MS. The electrospray ionization-mass spectrometry (ESI-MS)/collision-induced dissociation (CID; ESI-MS(2) and ESI-IT-MS(n)) were investigated. The effect of orientations of hemiketal hydroxyl at C-12 was clearly observed in the mass spectrum. Tandem mass spectra of 1, 1(A) or 2, 2(A) show stereospecific fragmentation resulting in significant abundance dissimilarity of [MH - H(2)O](+) as well as differences in fragmentation pathway. Both of these pathways seem to be influenced by the stereochemistry of the molecule. The differentiation can be clearly visualized from the [M + H - H(2)O](+)/[M + H](+) ratio of the two isomers where beta-isomer 2 was found to be five times higher than that of alpha-isomer 1 in full scan liquid chromatography-electrospray ionization mass spectrometry(LC-ESI-MS). In high-energy CID, the mass fingerprint of 1, 2, 1(A), and 2(A) was found to be different from one another. 相似文献
72.
Chemical vapor discrimination using a compact and low-power array of piezoresistive microcantilevers
A compact and low-power microcantilever-based sensor array has been developed and used to detect various chemical vapor analytes. In contrast to earlier micro-electro-mechanical systems (MEMS) array sensors, this device uses the static deflection of piezoresistive cantilevers due to the swelling of glassy polyolefin coatings during sorption of chemical vapors. To maximize the sensor response to a variety of chemical analytes, the polymers are selected based on their Hildebrand solubility parameters to span a wide range of chemical properties. We utilize a novel microcontact spotting method to reproducibly coat a single side of each cantilever in the array with the polymers. To demonstrate the utility of the sensor array we have reproducibly detected 11 chemical vapors, representing a breadth of chemical properties, in real time and over a wide range of vapor concentrations. We also report the detection of the chemical warfare agents (CWAs) VX and sulfur mustard (HD), representing the first published report of CWA vapor detection by a polymer-based, cantilever sensor array. Comparisons of the theoretical polymer/vapor partition coefficient to the experimental cantilever deflection responses show that, while general trends can be reasonably predicted, a simple linear relationship does not exist. 相似文献
73.
M. G. Kotresh K. S. Adarsh M. A. Shivkumar Sanjeev R. Inamdar 《Journal of fluorescence》2016,26(4):1249-1259
This article highlights some physical studies on the relaxation dynamics and Förster resonance energy transfer (FRET) of semiconductor quantum dots (QDs) to proximal dye molecule and the way these phenomena change with core to core-shell QD is discussed. Efforts to understand the optical and carrier relaxation dynamics of CdSe and CdSe/ZnS QDs are made by using absorption, steady-state fluorescence and time-resolved fluorescence (TCSPC) techniques. Steady-state as well as time-resolved fluorescence measurements were employed to evaluate the QD PL quenching induced by the proximal Rhodamine 101 dye molecule and to examine the influence of deep trap states on energy transfer efficiency. The FRET parameters such as spectral overlap, Förster distance, intermolecular distance for each donor-acceptor pair are determined and variation of these parameters from core to core-shell QD is discussed. 相似文献
74.
Microgels were prepared within reverse micelles via photocrosslinking. Gelation resulted from the [2 + 2] photodimerization reaction of nitrocinnamoyl (NC) groups on multi-arm polyethylene glycol (PEG) or gelatin. Because of the potential for biomedical and chemical applications, immobilization capacity within the microgels was investigated. Quantum dots (QDs), for example, share a similar size scale with proteins and can be physically trapped within the microgels. In addition, the optoelectronic properties of QDs could be utilized for analytical, imaging, and therapeutic purposes. Small molecules and recognition sequences (e.g. biotin) can also be covalently immobilized within the microgel networks through the photodimerization reaction. In the presence of biotin-PEG-NC, the resulting microgels added to streptavidin-coated plates. The microgel properties such as biodegradability and degree of swelling may be engineered for particular applications including targeted monitoring and controlled drug delivery systems. 相似文献
75.
It is useful to state propagation laws for a self-focusing laser beam or a soliton in group-theoretical form to be called
Lie-optical form for being able to predict self-focusing dynamics conveniently and amongst other things, the geometrical phase.
It is shown that the propagation of the gaussian laser beam is governed by a rotation group in a non-absorbing medium and
by the Lorentz group in an absorbing medium if the additional symmetry of paraxial propagation is imposed on the laser beam.
This latter symmetry, however, needs care in its implementation because the electromagnetic wave of the laser sees a different
refractive index profile than the laboratory observer in this approximation. It is explained how to estimate this non-Taylor
paraxial power series approximation. The group theoretical laws so-stated are used to predict the geometrical or Berry phase
of the laser beam by a technique developed by one of us elsewhere. The group-theoretical Lie-optic (or ABCD) laws are also
useful in predicting the laser behavior in a more complex optical arrangement like in a laser cavity etc. The nonlinear dynamical
consequences of these laws for long distance (or time) predictions are also dealt with. Ergodic dynamics of an ensemble of
laser beams on the torus during absorptionless self-focusing is discussed in this context. From the point of view of new physics
concepts, we introduce a stroboscopic invariant torus and a stroboscopic generating function in classical mechanics that is
useful for long-distance predictions of absorptionless self-focusing. 相似文献
76.
An approach for photonic generation of an arbitrary chirped microwave waveform with an increased time-bandwidth product (TBWP) is proposed and experimentally demonstrated. In the proposed model, light from the mode locked laser is splitted into two parts by using 1 × 2 power splitter: one is sent to linearly chirped fiber Bragg grating (LCFBG) through circulator and the other is time delayed by fiber delay line. The optical pulse in upper arm is time stretched by the LCFBG. Meanwhile, the optical pulse in lower arm experiences a time delay and then stretched by the dispersive single mode fiber. Temporal interference pattern is generated with an increasing or decreasing free spectral range by combination of two time-stretched optical pulses. Finally, the temporal interference pattern which is obtained at the output of optical coupler is transformed into an arbitrary chirped microwave waveform by using a photo-detector. The main advantage of this proposed model is high TBWP in the range of 750–1000 which ultimately results in an increased range resolution of radio detection and ranging. 相似文献
77.
A modified phonon confinement model considering the size distribution, an improved phonon dispersion curve and a confinement function is developed for the calculation of size dependent Raman spectra of the silicon (Si) nanocrystals. The model is capable of simultaneous calculations of the Raman shift, intensity and linewidth. The calculated size dependent redshift and linewidth of Raman spectra are in good agreement with the available experimental data in literature and better than previously reported theoretical results. The rapid rise in the redshift and linewidth for relatively smaller Si nanocrystals are well reproduced. The asymmetric behavior of Raman spectra is also obtained from the present model. 相似文献
78.
Abstract Xanthobilirubinic acid, a model dipyrrinone for one-half of the bilirubin molecule in photochemical and metabolism studies,
is more polar than bilirubin and insoluble in water and in chloroform. Replacing the β-alkyl substituents on the lactam ring
of xanthobilirubinic acid with methyl-capped ethylene glycol, diethylene glycol, and triethylene glycol (PEG) groups steadily
increased the water solubility of the pigment so that the last is completely soluble in both water and chloroform. Synthesized
by base-catalyzed condensation of the corresponding methyl-capped 3,4-diPEG-pyrrolin-2-one with 3,5-dimethyl-4(2-ethoxycarbonylethyl)-2-formyl-1H-pyrrole, these new PEGylated analogs of xanthobilirubinic acid are yellow-colored dipyrrinones that form intermolecular hydrogen-bonded
dimers in chloroform solution but are monomeric in methanol and water, as revealed by 1H NMR spectroscopy and vapor pressure osmometry. Methyl xanthobilirubinate has served as a synthetic precursor to bilirubinoids;
its amphiphilic PEGylated analogs suggest a route to water-soluble bilirubinoids and biliverdinoids.
Graphical abstract
相似文献
79.
Sanjeev Gautam Anup Thakur D.K. Shukla H.J. Shin Keun Hwa Chae K.P. Singh Navdeep Goyal 《Journal of Non》2011,357(11-13):2340-2343
This paper reports the effect of proton irradiation on the electrical properties of a-As2S3 in the temperature range of 323–418 K and frequency range 0.1–100 kHz. The variation of transport property is studied with proton irradiation dose (1 × 1013 ions/cm2 and 1 × 1015 ions/cm2). It has been observed that proton irradiation changes the dc conductivity (σdc), dc activation energy (ΔEdc) and ac conductivity (σac(ω)). The σdc and σac(ω) increases with dose of proton irradiation. The value of frequency exponent (s) decreases with the temperature and irradiation dose. These results are explained in terms of change in density of defect states in these glasses. 相似文献
80.
Sanjeev Gautam Shanshank N. Kane B.–G. Park J.–Y. Kim L.K. Varga J.–H. Song Keun Hwa Chae 《Journal of Non》2011,357(11-13):2228-2231
This paper reports x-ray absorption spectroscopy (XAS) and x-ray magnetic circular dichroism (XMCD) studies at Fe L3,2 and Co L3,2-edges to investigate the electronic structure of (Fe100 ? xCox)78Si9Nb3B9Cu1 (0 < x < 95) alloys. The influence of controlled Co addition on electronic structural and magnetic properties of (Fe100 ? xCox)78Si9Nb3B9Cu1 (x = 0, 20, 40, and 60) alloys has been investigated and it has been observed that Co exists as Co2+/Co3+, while Fe exists as a mixture of Fe0 (metallic) and Fe2+. The XMCD studies confirm these results and reveal that Co-ions are responsible for the room temperature ferromagnetism (RTFM) in the system, while at Fe L3,2-edge it shows a diamagnetic behavior. 相似文献