Nitric oxide (NO) is a powerful vasodilator in different vascular beds and NO-donors are widely used in clinical practice. Early data suggested that NO and NO-donors activate vascular smooth muscle high-conductance, calcium-activated potassium channels (BK channels). There exist two hypotheses explaining the effect of NO and NO-donors on BK channels—one stating that protein kinase G (PKG) mediates the effect of NO, and the other one stating that NO acts directly on the channel. Thus, the degree of contribution of PKG to the NO-induced activation of the BK channel is still not completely clear. This study tested the hypothesis that the sodium nitroprusside (SNP)-induced activation of vascular smooth muscle BK channels is fully mediated by PKG. This hypothesis was investigated using the patch-clamp technique and freshly isolated smooth muscle cells from rat tail artery. In whole-cell experiments, SNP considerably increased the outward current compared with the addition of the bath solution. SNP did not alter the current in the presence of iberiotoxin, the specific blocker of BK channels, during co-application with hydroxocobalamin, an NO-scavenger, and in the presence of Rp-8-Br-PET-cGMPS, the specific PKG-inhibitor. In inside-out patches, the activity of BK channels was increased by SNP, SNAP, and DEA-NO. However, these effects did not differ from the effect of the application of drug-free bath solution. Furthermore, a similar increase in single BK channel activity was induced by Rp-8-Br-PET-cGMPS, Rp-8-Br-PET-cGMPS together with SNP, hydroxocobalamin, and hydroxocobalamin together with SNP or DEA-NO. Finally, the activity of excised BK channels did not change in the absence of any application but was considerably increased by PKG compared with the addition of drug-free bath solution. These results suggest that NO released from NO-donors stimulates the BK current only through activation of PKG. 相似文献
Silver nanoparticles were synthesized in a chitosan biopolymer by an in situ ‘green’ chemical procedure, using d-glucose as the reducing agent. The reaction intermediates (silver–chitosan complexes) as well as the obtained nanocomposites were investigated using transmission electron microscopy, UV–vis, FTIR and photoluminescence spectroscopy. The theoretical analysis of the UV–vis absorption of the Ag–chitosan complexes suggested that the significant contribution to the complex spectrum arises from clusters of silver containing 4–9 atoms. The absorption spectrum of the nanocomposite exhibited a strong surface plasmon resonance band at 406 nm. The photoluminescence behavior of the pure chitosan, the silver–chitosan complexes and the nanocomposites were discussed in terms of morphology and silver weight content. 相似文献
This paper presents an analysis of some measures leading to intensification of the combustion process in a biomass-fuelled fluidized-bed combustor with a cone-shape bed (or ‘conical FBC’). Two combustors firing rice husks with elevated fuel-ash content were the focus of this study. Compared to the pilot 350-kWth conical FBC exhibiting combustion efficiency of up to 96%, the newly constructed 400-kWth combustor included geometrical and design modifications aimed at improving the combustion efficiency and emission performance of the reactor. Differences between the air distributors and Δp–u diagrams (accounting for the total pressure drop across the air distributor and gas–solid fluidized bed) for the two reactors are discussed. Axial temperature and gas concentration (O2, CO and NOx) profiles in the combustors were compared for similar operating conditions (excess air and heat release rate per unit cross-sectional area). At excess air of 40–60%, the bed temperature in the advanced conical FBC was substantially, by about 180 °C, higher than that in the pilot combustor, mainly, due to better fuel–air mixing and higher residence time of reactants. The formation and decomposition of CO and NO in the bed region as well as in the freeboard of these two combustors showed quite different trends under similar operating conditions. At excess air of 40–60%, the CO emission from the advanced conical FBC was found to be much (7–8 times) lower than that from the pilot combustor, while the NOx emissions were represented by almost the same values. High (over 99%) combustion efficiency was achieved when firing rice husk in the advanced 400 kWth conical FBC for the range of excess air. 相似文献
Highly uniform NiO nano-particles with a crystallite size of about 3 nm were obtained by room-temperature ball-milling of the parent Ni(OH)2, which was derived using a sol-gel method. The obtained nano-structured NiO precursor was then utilized for the fabrication of NiO-sensing electrodes (SEs), which were further examined in the mixed-potential-type YSZ-based planar NO2 sensor. The obtained results revealed the attractive advantages for the application of mechanochemical approach in regard to achieve high NO2 sensitivity, NO2 selectivity and reproducibility. All of the evaluated sensors attached with the nano-structured NiO-SEs, regardless of its sintering temperature, were found to exhibit high NO2 sensitivity at 800 °C under the wet condition (5 vol.% water vapor). In addition to high NO2 sensitivity, the sensor attached with 1100 °C-sintered NiO-SE showed highly selective properties towards NO2. The observed improvement in NO2-sensing characteristics as well as the attainment of highly reproducible behavior for different sensor devices is discussed based on morphological and electrochemical observations of the studied sensors. 相似文献
The ionic conductivity of the hafnia-scandia, hafnia-yttria, and hafnia-rare earth solid solutions with high dopant concentrations of 8, 10, and 14 mol% was measured in air at 600° to 1050°C. Impedance spectroscopy was used to obtain lattice conductivity. A majority of the investigated samples exhibited linear Arrhenius plots of the lattice conductivity as a function of temperature. For all investigated dopant concentrations the ionic conductivity was shown to decrease as the dopant radius increased. The activation enthalpy for conduction was found to increase with dopant ionic radius. The fact that the highest ionic conductivity among 14-mol%-doped systems was obtained with HfO2─Sc2O3 suggested that the radius ratio approach should be used to predict the electrical conductivity behavior of HfO2─R2O3 systems. A qualitative model based on the Kilner's lattice parameter map does not seem to apply to these systems. For the three systems HfO2─Yb2O3, HfO2─Y2O3, and Hf2O3─Sm2O3 a conductivity maximum was observed near the dopant concentration of 10 mol%. Deep vacancy trapping is responsible for the decrease in the ionic conductivity at high dopant concentrations. Formation of microdomains of an ordered compound cannot explain the obtained results. A comparison between the ionic conductivities of doped HfO2 and ZrO2 systems indicated that the ionic conductivities of HfO2 systems are 1.5 to 2.2 times lower than the ionic conductivities of ZrO2 systems. 相似文献
Coal combustion from power stations is an important anthropogenic contributor of toxic trace elements to the environment. Some trace elements may be emitted in range of valencies, often with varying toxicity and bioavailability. Hence, determination of trace element speciation in coals and their combustion products is important for conducting comprehensive risk assessments of the emissions from coal-fired power stations. This study focuses on speciation of selected trace elements, As, Cr, and Se, in coal combustion products and Hg in flue gas, which were sampled at one Australian power station. Different analytical methods such as secondary ion mass spectrometry (SIMS), ion chromatography-inductively coupled plasma mass spectrometry (IC-ICPMS) and X-ray absorption near edge structure spectrometry (XANES) were used to determine trace element speciation in coal and ash samples. Results showed that As, Cr and Se are all present in a range of valency states in coal. Concentrations of As and Se in the bottom ash as well as the more toxic hexavalent chromium were less than the detection limits. The more toxic As3+ form in fly ash was at 10% of the total arsenic, while selenium was mainly found in Se4+ form. Hexavalent chromium (Cr6+) in fly ash was 2.7% of the total fly ash chromium. Mercury speciation in flue gas was determined using the Ontario Hydro sampling train and analysis technique. Approximately 58% of the total mercury in flue gas was released in the elemental form (Hg0), which, among all mercury species, has the highest residence time in the environment due to lower solubility. This work summarises the performance of the selected analytical techniques for speciation of trace elements. 相似文献
Hydrodynamic regimes and characteristics of air–sand flow were studied in a cone-shape swirling fluidized bed for two types of air entry, or swirl generator: through a four-nozzle system (tangential entry) and using an annular-spiral air distributor (axial entry). Quartz sand of four particle sizes, 180–300, 300–500, 500–600 and 850–1180 μm, was used as the bed material in experimental tests on a cold model of a conical swirling fluidized bed combustor. During each test run, the pressure drop across the bed (Δp) was measured versus superficial velocity at the lower bed basis (u) for three static bed heights (20, 30 and 40 cm). Four regimes were found in the bed behavior for both swirl generators. The Δp–u diagrams were compared between tangential and axial air entries for different operating conditions. Mathematical models for predicting major hydrodynamic characteristics, the minimum fluidization velocity (umf) and corresponding pressure drop across the bed (Δpmf), were empirically developed. The dimensionless dependency of Δp/Δpmf on u/umf showed the apparent common trends and similarity for most of the test trials. For the two air injection systems, a Nomograph for assessment of Δp at any arbitrary superficial velocity and bed height was proposed as well. 相似文献
Reticular oxygen of Al2O3 or CeOx supported on Al2O3 was used for the epoxidation of propene without any double bond cleavage. In batch reaction, Al2O3 alone was able to convert propene into propene oxide (PO) with 100% selectivity and 2% conversion of propene with a close to 3:1 ratio with respect to the number of Al(III) reduced to elemental Al. When Ce2O3/Al2O3 or CeO2/Al2O3 was used, Al remained in its +3 oxidation state, while the Ce oxide was the oxidant as demonstrated by XPS analyses. CeOx/Al2O3 was more active (propene conversion yield of 4–5%) but the selectivity was lower (70%) as PO was isomerized into acetone and propionaldehyde.
Interestingly the use of reticular oxygen very much improves the selectivity with respect to the use of pure O2. In fact, while propene was more efficiently oxidized (10%) with O2 in presence of Al2O3 or CeOx/Al2O3, the selectivity was as low as 40% because C1 and C2 products were formed. However, the use of reticular oxygen represents a selective two-step technique for the use of molecular oxygen as oxidant of propene. The used oxides can be re-oxidized and the whole process can be further improved towards higher yields.
PO is quantitatively converted into propene carbonate by reaction with CO2 in presence of Nb2O5. 相似文献
Inhibition of the biosynthesis of complex N‐glycans in the Golgi apparatus influences progress of tumor growth and metastasis. Golgi α‐mannosidase II (GMII) has become a therapeutic target for drugs with anticancer activities. One critical task for successful application of GMII drugs in medical treatments is to decrease their unwanted co‐inhibition of lysosomal α‐mannosidase (LMan), a weakness of all known potent GMII inhibitors. A series of novel N‐substituted polyhydroxypyrrolidines was synthesized and tested with modeled GH38 α‐mannosidases from Drosophila melanogaster (GMIIb and LManII). The most potent structures inhibited GMIIb (Ki=50–76 μm , as determined by enzyme assays) with a significant selectivity index of IC50(LManII)/IC50(GMIIb) >100. These compounds also showed inhibitory activities in in vitro assays with cancer cell lines (leukemia, IC50=92–200 μm ) and low cytotoxic activities in normal fibroblast cell lines (IC50>200 μm ). In addition, they did not show any significant inhibitory activity toward GH47 Aspergillus saitoiα1,2‐mannosidase. An appropriate stereo configuration of hydroxymethyl and benzyl functional groups on the pyrrolidine ring of the inhibitor may lead to an inhibitor with the required selectivity for the active site of a target α‐mannosidase. 相似文献