Blood plasma and serum contain factors that activate inwardly rectifying GIRK1/GIRK4 K+ channels in atrial myocytes via one or more non-atropine-sensitive receptors coupled to pertussis-toxin-sensitive G-proteins. This channel is also the target of muscarinic M2 receptors activated by the physiological release of acetylcholine from parasympathetic nerve endings. By using a combination of HPLC and TLC techniques with matrix-assisted laser desorption ionization–time-of-flight MS, we purified and identified sphingosine 1-phosphate (SPP) and sphingosylphosphocholine (SPC) as the plasma and serum factors responsible for activating the inwardly rectifying K+ channel (IK). With the use of MS the concentration of SPC was estimated at 50nM in plasma and 130nM in serum; those concentrations exceeded the 1.5nM EC50 measured in guinea-pig atrial myocytes. With the use of reverse-transcriptase-mediated PCR and/or Western blot analysis, we detected Edg1, Edg3, Edg5 and Edg8 as well as OGR1 sphingolipid receptor transcripts and/or proteins. In perfused guinea-pig hearts, SPC exerted a negative chronotropic effect with a threshold concentration of 1µM. SPC was completely removed after perfusion through the coronary circulation at a concentration of 10µM. On the basis of their constitutive presence in plasma, the expression of specific receptors, and a mechanism of ligand inactivation, we propose that SPP and SPC might have a physiologically relevant role in the regulation of the heart.
Chemical looping combustion (CLC) is a promising technology for fossil fuel combustion that produces sequestration-ready CO 2 stream, reducing the energy penalty of CO 2 separation from flue gases. An effective oxygen carrier for CLC will readily react with the fuel gas and will be reoxidized upon contact with oxygen. This study investigated the development of a CeO 2 -promoted Fe 2 O 3 −hematite oxygen carrier suitable for the methane CLC process. Composition of CeO 2 is between 5 and 25 wt % and is lower than what is generally used for supports in Fe 2 O 3 carrier preparations. The incorporation of CeO 2 to the natural ore hematite strongly modifies the reduction behavior in comparison to that of CeO 2 and hematite alone. Temperature-programmed reaction studies revealed that the addition of even 5 wt % CeO 2 enhances the reaction capacity of the Fe 2 O 3 oxygen carrier by promoting the decomposition and partial oxidation of methane. Fixed-bed reactor data showed that the 5 wt % cerium oxides with 95 wt % iron oxide produce 2 times as much carbon dioxide in comparison to the sum of carbon dioxide produced when the oxides were tested separately. This effect is likely due to the reaction of CeO 2 with methane forming intermediates, which are reactive for extracting oxygen from Fe 2 O 3 at a considerably faster rate than the rate of the direct reaction of Fe 2 O 3 with methane. These studies reveal that 5 wt % CeO 2 /Fe 2 O 3 gives stable conversions over 15 reduction/oxidation cycles. Lab-scale reactor studies (pulsed mode) suggest the methane reacts initially with CeO 2 lattice oxygen to form partial oxidation products (CO + H 2 ), which continue to react with oxygen from neighboring Fe 2 O 3 , leading to its complete oxidation to form CO 2 . The reduced cerium oxide promotes the methane decomposition reaction to form C + H 2 , which continue to react with Fe 2 O 3 /Fe 3 O 4 to form CO/CO 2 and H 2 O. This mechanism is supported by the characterization studies, which also suggest that the formation of carbonaceous intermediates may affect the reaction rate and selectivity of the oxygen carrier.
The reversible adsorption of CO2 on tetraethylenepentamine (TEPA) and the polyethylene glycol (PEG)-modified amine sites were investigated using attenuated total reflection infrared (ATR-IR) spectroscopy, mass spectrometry (MS), and density functional theory (DFT). The presence of PEG at the amine site increased the rate of formation of adsorbed CO2, enhanced the formation of weakly adsorbed CO2 which can be removed from flowing inert gas at room temperature, and decreased CO2 desorption peak (i.e., sorbent regeneration) temperature. The calculated CO2 binding energy (BE) and optimized structures suggest CO2 adsorbed on TEPA primarily in the form of ammonium carbamate. The presence of PEG promoted the formation of a species which exhibited an experimental IR spectrum resembling the simulated spectrum of a low BE zwitterion species. The observation suggests PEG controlled the formation of the adsorbed intermediate species. Modeling of the transient CO2 adsorption profiles further showed PEG accelerated the rate of diffusion of adsorbed CO2 species in TEPA film by decreasing viscosity. The IR spectra of TEPA-PEG revealed PEG could assist in breaking up hydrogen bonding between amine sites, further supporting the promotion of diffusion of adsorbed CO2 through decreasing TEPA viscosity. This study unravelled the mechanism of the effects of PEG on CO2 capture kinetics and capacity on amine sites.
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