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Oxygen Exchange (oxygen + exchange)
Selected AbstractsIn Situ Time-Resolved Neutron Diffraction Investigation during Oxygen Exchange in Layered Cobaltite Cathode Materials,ANGEWANDTE CHEMIE, Issue 45 2009Lorenzo Malavasi Dr. Man achte auf den Sauerstoff: Mit dem im Titel genannten Verfahren können die beim Sauerstoffaustausch in einem Material auftretenden Strukturänderungen untersucht werden (siehe Diagramm für die Zunahme des Sauerstoffgehalts, wenn der Gasfluss von Ar auf O2 umgestellt wird). Die Methode wird an einem schichtförmigen Cobaltit demonstriert, einem vielversprechenden Kathodenmaterial für Brennstoffzellen. [source] The Nature of Oxygen Exchange in ZrW2O8 Revealed by Two-Dimensional Solid-State 17O NMR.CHEMINFORM, Issue 18 2004Matthew R. Hampson Abstract For Abstract see ChemInform Abstract in Full Text. [source] Nitric oxide bioavailability modulates the dynamics of microvascular oxygen exchange during recovery from contractionsACTA PHYSIOLOGICA, Issue 2 2010D. M. Hirai Abstract Aim:, Lowered microvascular PO2 (PO2mv) during the exercise off-transient likely impairs muscle metabolic recovery and limits the capacity to perform repetitive tasks. The current investigation explored the impact of altered nitric oxide (NO) bioavailability on PO2mv during recovery from contractions in healthy skeletal muscle. We hypothesized that increased NO bioavailability (sodium nitroprusside: SNP) would enhance PO2mv and speed its recovery kinetics while decreased NO bioavailability (l -nitro arginine methyl ester: l -NAME) would reduce PO2mv and slow its recovery kinetics. Methods:,PO2mv was measured by phosphorescence quenching during transitions (rest,1 Hz twitch-contractions for 3 min,recovery) in the spinotrapezius muscle of Sprague,Dawley rats under SNP (300 ,m), Krebs-Henseleit (Control) and l -NAME (1.5 mm) superfusion conditions. Results:, Relative to recovery in Control, SNP resulted in greater overall microvascular oxygenation as assessed by the area under the PO2mv curve (PO2 AREA; Control: 3471 ± 292 mmHg s; SNP: 4307 ± 282 mmHg s; P < 0.05) and faster off-kinetics as evidenced by the mean response time (MRToff; Control: 60.2 ± 6.9 s; SNP: 34.8 ± 5.7 s; P < 0.05), whereas l -NAME produced lower PO2 AREA (2339 ± 444 mmHg s; P < 0.05) and slower MRToff (86.6 ± 14.5 s; P < 0.05). Conclusion:, NO bioavailability plays a key role in determining the matching of O2 delivery-to-O2 uptake and thus the upstream O2 pressure driving capillary-myocyte O2 flux (i.e. PO2mv) following cessation of contractions in healthy skeletal muscle. Additionally, these data support a mechanistic link between reduced NO bioavailability and prolonged muscle metabolic recovery commonly observed in ageing and diseased populations. [source] Naturally low carbonic anhydrase activity in C4 and C3 plants limits discrimination against C18OO during photosynthesisPLANT CELL & ENVIRONMENT, Issue 9 2000J. S. Gillon ABSTRACT The 18O content of CO2 is a powerful tracer of photosynthetic activity at the ecosystem and global scale. Due to oxygen exchange between CO2 and 18O-enriched leaf water and retrodiffusion of most of this CO2 back to the atmosphere, leaves effectively discriminate against 18O during photosynthesis. Discrimination against 18O (,18O) is expected to be lower in C4 plants because of low ci and hence low retrodiffusing CO2 flux. C4 plants also generally show lower levels of carbonic anhydrase (CA) activities than C3 plants. Low CA may limit the extent of 18O exchange and further reduce ,18O. We investigated CO2,H2O isotopic equilibrium in plants with naturally low CA activity, including two C4 (Zea mays, Sorghum bicolor) and one C3 (Phragmites australis) species. The results confirmed experimentally the occurrence of low ,18O in C4, as well as in some C3, plants. Variations in CA activity and in the extent of CO2,H2O isotopic equilibrium (,eq) estimated from on-line measurements of ,18O showed large range of 0,100% isotopic equilibrium (,eq= 0,1). This was consistent with direct estimates based on assays of CA activity and measurements of CO2 concentrations and residence times in the leaves. The results demonstrate the potential usefulness of ,18O as indicator of CA activity in vivo. Sensitivity tests indicated also that the impact of ,eq< 1 (incomplete isotopic equilibrium) on 18O of atmospheric CO2 can be similar for C3 and C4 plants and in both cases it increases with natural enrichment of 18O in leaf water. [source] Gas sensing in microplates with optodes: Influence of oxygen exchange between sample, air, and plate materialBIOTECHNOLOGY & BIOENGINEERING, Issue 3 2005Sarina Arain Abstract Microplates with integrated optical oxygen sensors are a new tool to study metabolic rates and enzyme activities. Precise measurements are possible only if oxygen exchange between the sample and the environment is known. In this study we quantify gas exchange in plastic microplates. Dissolved oxygen was detected using either an oxygen-sensitive film fixed at the bottom of each well or a needle-type sensor. The diffusion of oxygen into wells sealed with different foils, paraffin oil, and paraffin wax, respectively, was quantified. Although foil covers showed the lowest oxygen permeability, they include an inevitable gas phase between sample and sealing and are difficult to manage. The use of oil was found to be critical due to the extensive shaking caused by movement of the plates during measurements in microplate readers. Thus, paraffin wax was the choice material because it avoids convection of the sample and is easy to handle. Furthermore, without shaking, significant gradients in pO2 levels within a single well of a polystyrene microplate covered with paraffin oil were detected with the needle-type sensor. Higher pO2 levels were obtained near the surface of the sample as well as near the wall of the well. A significant diffusion of oxygen through the plastic plate material was found using plates based on polystyrene. Thus, the location of a sensor element within the well has an effect on the measured pO2 level. Using a sensor film fixed on the bottom of a well or using a dissolved pO2 -sensitive indicator results in pO2 offset and in apparently lower respiration rates or enzyme activities. Oxygen diffusion through a polystyrene microplate was simulated for measurements without convection,that is, for samples without oxygen diffusion through the cover and for unshaken measurements using permeable sealings. This mathematical model allows for calculation of the correct kinetic parameters. © 2005 Wiley Periodicals, Inc. [source] | |||||||||||||