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91.
92.
Nitric oxide (NO) is an important mediator responsible for numerous physiological phenomena. Transient levels of NO in biological systems usually range from nanomolar to micromolar concentrations, with a rapid return to basal levels normally seen following these increases. Because NO can diffuse only over a local area in limited time due to such low levels of production and due to its short life-time prior to degradation, high spatial and temporal resolutions are required for direct and continuous NO measurement if the physiological role of NO is to be investigated in any system. For such purposes, analytical methods based on bio-imaging and electrochemical techniques for the measurement of NO are useful. In this paper, we describe the successful application of these methods to a number of biological systems. Specifically, complementary application of these methods demonstrate that it is possible to detect real-time NO production from nervous tissue with high spatial and temporal resolutions. 相似文献
93.
Miyuki Narita Fumio Hamada Mayumi Sato Iwao Suzuki Tetsuo Osa 《Journal of inclusion phenomena and macrocyclic chemistry》1999,34(4):421-430
Flexible hosts, 6A,6B-; 6A,6C-; 6A,6D-; and 6A,6E-bis dansylglycine-modified -cyclodextrins (-1, -2, -3, and -4, respectively) have been synthesized as a sensing molecule for organic guests including terpenoids and bile acids. These host compounds show a pure monomer fluorescence whose intensity is decreased or enhanced upon addition of guest species. The value I/I0, where I and I0 are fluorescence intensities in the presence and absence of a guest and I is I0- I, was used as a parameter of sensitivity. These hosts exhibit highly sensitive and selective molecular recognition ability, particularly, for lithochoic acid, chenodeoxycholic acid, and ursodeoxycholic acid. The behaviors of the appended moieties of these hosts when host–guest complexation occurs are studied by induced circular dichroism (ICD) spectra and fluorescence spectral change on accommodation of a guest. The ICD pattern of these hosts alone or on accommodation of a guest is very similar, indicating that the behavior of the appended moieties are very similar. The guest-induced variations in the fluorescence or ICD intensity suggest that the appended moieties act as a hydrophobic cap that enables the cyclodextrin to form 1 : 1 host–guest complexes. 相似文献
94.
95.
《Journal of separation science》2002,25(18):1317-1324
Multidimensional gas chromatography (2D GC) is demonstrated as a way to improve limits of detectability of spectrophotometric detectors. UV and IR detectors are generally less sensitive than mass spectrometers or other GC detectors. This has placed some limitations on the useful capabilities provided by spectrophotometric detectors, such as the ability to provide structure‐related information for a particular analyte. In this paper, we report results from interfacing a 2D GC instrument to a UV detector. Symmetry factor and the ratio of retention time divided by peak width did not show deterioration of the quality of chromatography when a megabore column was used with this detector. Furthermore, an increase in the limits of detectability over that attainable in a single‐column system was realized by using the 2D GC system. However, the low flow (1 mL/min) imposed by the use of a microbore column (250 μm ID) caused significant tailing when the UV detector was used. 相似文献
96.
Summary The retention, selectivity and elution order of fluorescent 1,N6-etheno derivatives of diadenosine polyphosphates and their enzymatic degradation products on octadecyl and phenyl-bonded
silica columns have been studied as a function of mobile phase pH, ionic strength and organic modifier content. Good separations
of the compounds of interest were achieved using mobile phases of around 0.1M potassium phosphate buffers at neutral pH containing
approximately 10% methanol or 4% acetonitrile for C18 columns and 5% methanol or 1.5% acetonitrile for phenyl columns. The data obtained were used to establish isocratic assays
for diadenosine polyphosphate cleaving activities from chromaffin cells using Di(1,N6-ethenoadenosine) polyphosphates as fluorogenic substrate analogues followed by fluorescence detection. 相似文献
97.
Lin Jia Hui Yang Jun Deng Junmei Chen Yuan Zhou Pan Ding Leigang Li Na Han Yanguang Li 《中国化学》2019,37(5):497-500
Electrocatalytic carbon dioxide reduction holds great promise for reducing the atmospheric CO2 level and alleviating the energy crisis. High‐performance electrocatalysts are often required in order to lower the high overpotential and expedite the sluggish reaction kinetics of CO2 electroreduction. Copper is a promising candidate metal. However, it usually suffers from the issues of poor stability and low product selectivity. In this work, bimetallic Cu‐Bi is obtained by reducing the microspherical copper bismuthate (CuBi2O4) for selectively catalyzing the CO2 reduction to formate (HCOO–). The bimetallic Cu‐Bi electrocatalyst exhibits high activity and selectivity with the Faradic efficiency over 90% in a wide potential window. A maximum Faradaic efficiency of ~95% is obtained at –0.93 V versus reversible hydrogen electrode. Furthermore, the catalyst shows high stability over 6 h with Faradaic efficiency of ~95%. This study provides an important clue in designing new functional materials for CO2 electroreduction with high activity and selectivity. 相似文献
98.
The cationization of poly(ethylene glycol)s, PEG 4000 and PEG 6000, under matrix-assisted laser desorption/ionization conditions was studied by using different concentration ratios of the sodium ion, as the reference ion, and another alkali metal ion (Li(+), K(+), Rb(+), Cs(+)). A linear correlation was found between the intensity ratio of the sodiated PEGs and PEGs cationized with alkali metal ions versus the initial concentration ratio of sodium and alkali metal ions. The slopes of these straight lines are proposed as a novel selectivity ratio for the ionization process. The intensity distribution of the cationized PEGs was also investigated. It was found that the cationized oligomers follow Poisson statistics. The M(n) and M(w) values were also evaluated. An explanation for the observed effects is given. 相似文献
99.
Data on the kinetics, selectivity, kinetic isotope effect, and the effect of the acidity of the medium on the rate of the
reactions of benzene and alkylbenzenes in sulfuric acid (59–78 wt.% H2SO4) solutions of 1-adamantanol at 30 °C indicate that the direct reagents are the adamantyl carbocations (Ad+) that alkylate the arenes. The ortho positions of the benzene ring are not accessible on account of steric hindrances. The
rate of attack by the Ad+ cation on the accessible para and meta positions of the ring is controlled by the formation of a σ complex.
__________
Translated from Teoreticheskaya i éksperimental’naya Khimiya, Vol. 42, No. 1, pp. 14–18, January–February, 2006. 相似文献
100.
QiongCHENG TuZhiPENG XiaoBoHU CatherineF.YANG 《中国化学快报》2004,15(12):1473-1476
A novel fibroin modified electrode with ion recognition was reported. The membrane with isoelectric point of pH 4.5, was modified on graphite and carbon fiber electrodes. The pH-responsive ion recognition of the modified electrode was investigated by use of some neurocompounds. The fibroin carbon fiber electrode has been used for in-vivo determination. 相似文献