An understanding of the rate of reaction of nitric oxide (NO) with oxygen in aqueous solutions is needed in assessing the various actions of NO in the body. A novel approach was developed for studying the kinetics of this reaction, which permitted simultaneous and continuous measurements of the concentrations of NO and the principal product, nitrite (NO2-). Nitric oxide was measured using a chemiluminescence detector, with continuous sampling achieved by diffusion of NO through a membrane fitted into the base of a small, stirred reactor. The results with various initial NO and O2 concentrations confirmed that the rate of reaction is second-order in NO and first-order in O2. The rate of reaction of NO was described by the expression 4k1 [NO]2[O2], where k1 was (2.1 +/- 0.4) x 10(6) M-2 s-1 at 23 degrees C and (2.4 +/- 0.3) x 10(6) M-2 s-1 at 37 degrees C. The value of k1 was the same at pH 4.9 and 7.4. The rate of formation of NO2- equaled the rate of reaction of NO (within experimental uncertainty of a few percent), and there was no detectable formation of nitrate (NO3-). This confirmed that NO and NO2- were the only NOx species present in significant amounts and supported the validity of pseudo-steady-state assumptions for NO2 and N2O3, which are intermediates in the conversion of NO to NO2-.(ABSTRACT TRUNCATED AT 250 WORDS)

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To investigate the fate of nitric oxide (NO) synthesized by activated macrophages, the concentrations of NO and its principal reaction products, nitrite (NO2-) and nitrate (NO3-), were measured as a function of time in suspension cultures of RAW264.7 macrophages attached to microcarrier beads. Synthesis of NO became evident 2-5 h after stimulation of the cells, and steady concentrations of NO were achieved after about 9 h. The appearance of NO in the extracellular fluid coincided with the appearance of NO2- and NO3-, which were formed thereafter at approximately equal and constant rates. Using a kinetic model based on rate constants measured previously in cell-free systems, only half of the NO2- formed could be accounted for by the reaction of NO with O2. It is known that NO reacts with superoxide (O2.) to give peroxynitrite and that NO also reacts with peroxynitrite to yield NO2-, so that the latter reaction may explain the "excess" NO2- formation. Adding superoxide dismutase to the medium markedly reduced the ratio of NO3- to NO2-, consistent with the hypothesis that NO3- in the medium results primarily from the extracellular reaction of NO with O2-.. The addition of morpholine, a model amine, resulted in formation of N-nitrosomorpholine, concurrent with the other products. Measured rates of nitrosomorpholine formation were 6-fold lower than predictions based on kinetics in simple solutions, suggesting that in the cell culture system there were additional reactions that lowered the concentration of nitrous anhydride, the principal nitrosating agent formed from NO and O2.

The development of low-cost, sustainable, and renewable energy sources has been a major focus since the 1970s. Fuel-grade ethanol is one energy source that has great potential for being generated from biomass. The demonstration of the fermentation of biomass-generated producer gas to ethanol is the major focus of this article in addition to assessing the effects of producer gas on the fermentation process. In this work, producer gas (primarily CO, CO(2), CH(4), H(2), and N(2)) was generated from switchgrass via gasification. The fluidized-bed gasifier generated gas with a composition of 56.8% N(2), 14.7% CO, 16.5% CO(2), 4.4% H(2), and 4.2% CH(4). The producer gas was utilized in a 4-L bioreactor to generate ethanol and other products via fermentation using a novel clostridial bacterium. The effects of biomass-generated producer gas on cell concentration, hydrogen uptake, and acid/alcohol production are shown in comparison with "clean" bottled gases of similar compositions for CO, CO(2), and H(2). The successful implementation of generating producer gas from biomass and then fermenting the producer gas to ethanol was demonstrated. Several key findings following the introduction of producer gas included: (1) the cells stopped growing but were still viable, (2) ethanol was primarily produced once the cells stopped growing (ethanol is nongrowth associated), (3) H(2) utilization stopped, and (4) cells began growing again if "clean" bottled gases were introduced following exposure to the producer gas.