NO Release Rates Research Articles

Role of CO2 and H2O on NO Formation during Biomass Char Oxidation

We have investigated how CO2 and H2O influence NO release rates during char oxidation of biomass. In addition, the role of catalytic elements in these processes has been studied. NO release rates w...

Characterisation of NO production and consumption: new insights by an improved laboratory dynamic chamber technique

Abstract. Biogenic NOx emissions from natural and anthropogenically influenced soils are currently estimated to amount to 9 Tg a−1, hence a significant fraction of global NOx emissions (45 Tg a−1). During the last three decades, a large number of field measurements have been performed to quantify biogenic NO emissions. To study biogenic NO emissions as a function of soil moisture, soil temperature, and soil nutrients, several laboratory approaches have been developed to estimate local/regional NO emissions by suitable upscaling. This study presents an improved and automated laboratory dynamic chamber system (consisting of six individual soil chambers) for investigation and quantification of all quantities necessary to characterise biogenic NO release from soil (i.e. net NO release rate, NO production and consumption rate, and respective Q10 values). In contrast to former versions of the laboratory dynamic chamber system, the four experiments for complete characterisation can now be performed on a single soil sample, whereas former studies had to be performed on four sub-samples. This study discovered that the sub-sample variability biased former measurements of net NO release rates tremendously. Furthermore, it was also shown that the previously reported variation of optimum soil moisture (i.e. where a maximum net NO release rates occur) between individual sub-samples is most likely a methodical artefact of former versions of the laboratory dynamic chamber system. A comprehensive and detailed methodical concept description of the improved laboratory dynamic chamber system is provided. Response of all quantities (necessary to characterise net NO release) to soil temperature and NO mixing ratio of the flushing airstream are determined by automatic monitoring of these variables during one single drying-out experiment with one single soil sample only. The method requires precise measurements of NO mixing ratio at the inlet and outlet of each soil chamber; finally, four pairs of inlet/outlet NO mixing ratios are sufficient to derive all necessary quantities. Soil samples from drylands exhibit particularly low NO production, but even lower NO consumption rates. However, with the improved laboratory dynamic chamber system those low levels can be quantified, as well as corresponding NO compensation point mixing ratios and respective Q10 values. It could be shown that the NO compensation point mixing ratio seems to be generally independent of gravimetric soil moisture content, but, particularly for dryland soils, strongly dependent on soil temperature. New facilities have been included into the improved system (e.g. for investigation of net release rates of other trace gases, namely CO2 and volatile organic compounds – VOCs). First, results are shown for net release rates of acetone (C3H6O), acetaldehyde (C2H4O) and CO2. This new system is thus able to simultaneously investigate potential mechanistic links between NO, multitudinous VOC and CO2.

Biomass Char Nitrogen Oxidation—Single Particle Model

In this study, the release of NO during the combustion of single char particles of spruce bark was investigated. Modeled NO release rates were compared to experimentally determined NO rates from a single particle reactor of quartz glass. The operating conditions were between 1073 and 1323 K with 3–19 vol % O2 and with 0% NO in the surrounding gas. The NO release rates from the single particles were determined from measured molar fractions of NO at the outlet from the reactor system. In the model, the char-N is assumed to be oxidized proportionally to the char-C oxidation rate, which is measured. The formed NO is assumed to be reduced as a function of the local NO concentration inside the particle. The NO concentration profile inside the char particle is numerically calculated by taking into account the transport of NO inside and outside the particle and the reduction rates of NO inside the char particle. The modeled NO release rates were in good agreement with the measurements. The results show that the fractional conversion of char-N to NO increases as functions of decreasing particle size and conversion. The most likely explanation for this is that the formed NO diffuses away at an increasing rate as the particle decreases in size. Further, a suggested analytical model for the fractional conversion of char-N to NO is tested.

Time dependent production of NO from combustion of large biomass char particles

In this study, the NO release during the char combustion of single biomass particles was investigated. Cylindrical biomass particles of spruce bark, short rotation coppice (SRC) poplar, Danish straw, and torrefied wood were combusted in a single particle reactor of quartz glass operating between 1073 and 1323K and with 3–19vol.% O2. The initial diameter of the particles was 8mm. Molar fractions of NO and CO2 were measured at the outlet of the reactor system. During the char combustion stage, the measured molar fractions were converted into time resolved release of NO and carbon from the char particle. To model the NO release from the single char particles, the char-N was assumed to be oxidized to NO proportionally to the experimental carbon release rate. The NO reduction reactions are lumped together such that the reduction rate is modeled as a function of an apparent activation energy, pre-exponential factor, and reaction order. The results showed good agreement between the modeled and experimental NO release rates. Initially most of the formed NO was reduced inside the char particle. As the conversion proceeded, the NO release from the char particles increased although the mass and the diameter of the particle decreased. This is attributed that the fraction of char-N being released as NO increased significantly during conversion. In the final conversion stage, all char-N was released as NO.

Experimental analysis of nitric oxide‐red blood cells interactions using a novel micron scale flow system

NO consumption by RBCs in blood vessels is reported to be several folds lesser than free Hb. Mechanisms of reduced NO uptake by RBCs are under intense investigation. NO delivery to the RBCs is critical in quantification of interactions. Common methods of NO delivery include saturated NO solutions and NO‐donors that create localized NO concentration and have unsteady NO release rates, respectively. We designed a micron scale flow system in which precise amounts of gaseous NO can be delivered over longer periods through polymeric semi‐permeable membrane. The flow system simulates in vivo conditions like the constant NO flux from endothelium to the lumen, diffusional resistances for NO transport in the lumen and NO reaction with flowing RBCs. Using the flow system, we studied the effect of NO concentration, RBC flow rates and hematocrit on NO‐RBC interactions. NO‐RBC reaction products (nitrite and total nitrogen species (NOx)) were measured using chemiluminescence analyzer. Nitrite and total NOx formation increased with NO concentrations, however, nitrite and total NOx formations nearly doubled when RBC flow rate was halved. Nitrite and total NOx formations decreased with hematocrit. Results obtained from this study further enhance our understanding of the effects of hemodynamic parameters on the NO‐RBC interactions. Supported by: AHA 0530050N and NIH R01 HL084337 & R15 HL087287.

Evaluation of Nitrosyl Ruthenium Complexes Entrapped in an Oil-In-Water Emulsion as Vasodilator Agents

Several attempts have been made toward the production of oxide (NO)- releasing agents based on metallic complexes. However, many of these agents have been shown to undergo hydroxide electrophilic attack, thus generating the corresponding nitro species. Entrapped nitrosyl ruthenium species can be stabilized in an oil-in-water (o/w) emulsion and be further used for local NO delivery. This study describes the transdermal permeation of cis and trans- (RuCl(bpy)2NO)(PF6)2 complexes as NO-donor agents from a topically applied emulsion, with NO release rates of 0.042 ± 0.002 and 0.035 ± 0.003 � mol/cm 2 .h, respectively. In vitro skin permeation studies performed with the cis and trans- (RuCl(bpy)2(NO))(PF6)2 complexes in o/w emulsion showed that they tend to accumulate in the stratum corneum (SC) and viable skin, with spontaneous NO release occurring in the viable skin only. NO release was detected by using an NO- sensor when the complexes were in contact with the sonicated skin. The vascular responses to the NO released from the cis and trans-(RuCl(bpy)2(NO))(PF6)2 complexes in o/w emulsion were also evaluated by vasodilation experiments.

More lipophilic dialkyldiamine-based diazeniumdiolates: synthesis, characterization, and application in preparing thromboresistant nitric oxide release polymeric coatings.

The synthesis, characterization, and biomedical application in preparing more thromboresistant polymeric coatings for a series of lipophilic dialkyldiamine-based diazeniumdiolatesare described. Dialkylhexamethylenediamine diazeniumdiolates of the form RN[N(O)NO](-)(CH(2))(6)NH(2)(+)R, where R = CH(3), CH(2)CH(3), (CH(2))(2)CH(3), (CH(2))(3)CH(3), (CH(2))(4)CH(3,) (CH(2))(5)CH(3), and (CH(2))(11)CH(3), are prepared via reaction of the corresponding diamine with NO. The more lipophilic diazeniumdiolates [e.g., R = (CH(2))(3)CH(3)] can be incorporated into hydrophobic polymeric films (e.g., plasticized PVC), and the resulting materials release NO for extended periods of time upon exposure to PBS buffer. The mechanism of NO release from these films is examined in detail. More stable initial NO release can be achieved by adding lipophilic anionic species (e.g., tetraphenylborate derivative) to the polymeric material to buffer the activity of protons within the organic phase. It is shown that the use of these new lipophilic NO-donors in polymers provides the ability to tailor NO release rates for a variety of medical applications. As an example, polymers doped with N,N'-dibutylhexamethylenediamine diazeniumdiolate and a tetraphenylborate derivative are employed as coatings for vascular grafts in sheep. The NO release grafts exhibited enhanced performance and had an average 95% thrombus-free surface area compared to 42% for the corresponding control grafts when examined after 21d of implantation.

The Crystal Structure of Nitrophorin 2: A TRIFUNCTIONAL ANTIHEMOSTATIC PROTEIN FROM THE SALIVA OF RHODNIUS PROLIXUS

Nitrophorin 2 (NP2) (also known as prolixin-S) is a salivary protein that transports nitric oxide, binds histamine, and acts as an anticoagulant during blood feeding by the insect Rhodnius prolixus. The 2.0-A crystal structure of NP2 reveals an eight-stranded antiparallel beta-barrel containing a ferric heme coordinated through His(57), similar to the structures of NP1 and NP4. All four Rhodnius nitrophorins transport NO and sequester histamine through heme binding, but only NP2 acts as an anticoagulant. Here, we demonstrate that recombinant NP2, but not recombinant NP1 or NP4, is a potent anticoagulant; recombinant NP3 also displays minor activity. Comparison of the nitrophorin structures suggests that a surface region near the C terminus and the loops between beta strands B-C and E-F is responsible for the anticoagulant activity. NP2 also displays larger NO association rates and smaller dissociation rates than NP1 and NP4, which may result from a more open and more hydrophobic distal pocket, allowing more rapid solvent reorganization on ligand binding. The NP2 protein core differs from NP1 and NP4 in that buried Glu(53), which allows for larger NO release rates when deprotonated, hydrogen bonds to invariant Tyr(81). Surprisingly, this tyrosine lies on the protein surface in NP1 and NP4.

Lack of Tyrosine Nitration by Peroxynitrite Generated at Physiological pH

Nitration of tyrosine residues of proteins has been suggested as a marker of peroxynitrite-mediated tissue injury in inflammatory conditions. The nitration reaction has been extensively studied in vitro by bolus addition of authentic peroxynitrite, an experimental approach hardly reflecting in vivo situations in which the occurrence of peroxynitrite is thought to result from continuous generation of .NO and O-2 at physiological pH. In the present study, we measured the nitration of free tyrosine by .NO and O-2 generated at well defined rates from the donor compound (Z)-1-[N-[3-aminopropyl]-N-[4-(3-aminopropylammonio)butyl]-amino]- dia zen-1-ium-1,2-diolate] (spermine NONOate) and the xanthine oxidase reaction, respectively. The results were compared with the established nitration reaction triggered by authentic peroxynitrite. Bolus addition of peroxynitrite (1 mM) to tyrosine (1 mM) at pH 7.4 yielded 36.77 +/- 1.67 microM 3-nitrotyrosine, corresponding to a recovery of about 4%. However, peroxynitrite formed from .NO and O-2, which were generated at equal rates ( approximately 5 microM x min-1) from 1 mM spermine NONOate, 28 milliunits/ml xanthine oxidase, and 1 mM hypoxanthine was much less efficient (0.67 +/- 0.01 microM; approximately 0.07% of total product flow). At O-2 fluxes exceeding the .NO release rates, 3-nitrotyrosine formation was below the detection limit of the high performance liquid chromatography method (<0.06 microM). Nitration was most efficient (approximately 0.3%) with the .NO donor alone, i.e. without concomitant generation of O-2. Nitration by .NO had a pH optimum of 8.2, increased progressively with increasing tyrosine concentrations (0.1-2 mM), and was not enhanced by NaHCO3 (up to 20 mM), indicating that it was mediated by .NO2 rather than peroxynitrite. Our results argue against peroxynitrite produced from .NO and O-2 as a mediator of tyrosine nitration in vivo.

Measurement and modeling of nitric oxide release rates for nitric oxide donors.

An accurate model of the nitric oxide (NO)-release rate is essential for predicting the temporal NO-release rate and resulting NO concentrations for NO donors. Knowledge of the NO-release rate and/or the NO concentration is beneficial for assessing the physiological or pathological effects of NO on cell systems. This study describes a method to measure the temporal NO-release rate from NO donor compounds utilizing a modified ultrafiltration cell. For this study, the NO-release rates of spermine NONOate and diethylamine NONOate were measured and kinetically modeled at pH 7.4 and 37 degrees C. An advantage of this method is that complete dissolution of the NONOate was not necessary for modeling the NO-release rate. One model parameter, which is the number of moles of NO released per mole of decomposed NONOate, is 1.7 +/- 0.1 and 1.5 +/- 0.2 for spermine and diethylamine NONOate, respectively. The other model parameter, which is the NONOate first-order decomposition rate constant, is 0.019 +/- 0.002 min-1 and 0.47 +/- 0.10 min-1 for spermine and diethylamine NONOate, respectively, as determined from NO concentration profiles. The decomposition rate constant measured by spectrophotometry was consistent with the above value for spermine NONOate but was approximately half the above value for diethylamine NONOate. Preliminary experiments using spectrophotometry showed that for both NONOates the decomposition activation energy was approximately 100 kJ/mol. The NO-release rate model for spermine NONOate was applied to a model for predicting the NO concentration in oxygenated solution. The NO concentration was measured in phosphate buffer, culture medium, and Tyrode's solution. Excellent agreement was observed between experimental and predicted NO concentrations.

“NONOates” (1-substituted diazen-1-ium-1,2-diolates) as nitric oxide donors: Convenient nitric oxide dosage forms

1-Substituted diazen-1-ium-1,2-diolates have proved useful as tools in enzymology and other pharmacological research applications in which spontaneous generation of nitric oxide according to a reasonably well-defined time course is required. This chapter summarizes relevant physicochemical data, including the NO release rates and product profiles, for a selection of these compounds. Guidelines for quality control and a systematic nomenclature scheme are also presented. It is hoped that, in summarizing this information here, our chapter will help those contemplating new applications of diazeniumdiolate technology as they seek to capitalize on what we believe are the inherent advantages of this compound type in research on the pharmacological properties of nitric oxide.

Processes involved in uptake and release of nitrogen dioxide from soil and building stones into the atmosphere

Atmospheric NO 2 was taken up by samples of various soils and building stones. The NO 2 uptake rate constants were highest in soil samples taken during the summer months. However, the NO 2 uptake rate constants of the soils and building stones were not significantly correlated with any of the following variables: moisture, pH, ammonium, nitrite, or nitrate. NO 2 uptake by soil and stone was not abolished by autoclaving indicating a chemical uptake process. NO 2 uptake by acidic and air-dry soils and stones resulted in nearly stoichiometric reduction of NO 2 to NO. This reduction was enhanced by the addition of ferrous iron and was further enhanced by incubation under 1 ppmv SO 2. The results suggest that NO 2 reduction may be coupled to oxidation of ferrous to ferric iron which may be reduced again by atmospheric SO 2 thus regenerating the ferrous iron content of the soil or stone. Conversion of NO 2 to NO was not observed in neutral or/and moist soils and stones. NO 2 was also taken up by purified and sterilized quartz sand moistend with water. This uptake was enhanced by addition of humic material but not by addition of bacteria which both had been extracted from genuine soil. Under most conditions, only uptake but no release of NO 2 was observed. However, NO 2 was released in air-dry soils that were heated to 45–65°C, or in ammonium-fertilized soil or stone that was drying up at room temperature. Under the latter conditions mimicking field practice, the NO 2 release reached rates that were similar to the NO release rates.

Influence of oxygen on production and consumption of nitric oxide in soil

NO and N2O release rates were measured in an acidic forest soil (pH 4.0) and a slightly alkaline agricultural soil (pH 7.8), which were incubated at different O2 concentrations (<0.01 – 20% O2) and at different NO concentrations (40 – 1000 ppbv NO). The system allowed the determination of simultaneously operating NO production rates and NO uptake rate constants, and the calculation of a NO compensation concentration. Both NO production and NO consumption decreased with increasing O2. NO consumption decreased to a smaller extent than NO production, so that the NO compensation concentrations also decreased. However, the NO compensation concentrations were not low enough for the soils to become a net sink for atmospheric NO. The release of N2O increased relative to NO release when the gases were allowed to accumulate instead of being flushed out. The forest soil contained only denitrifying, but not nitrifying bacteria, whereas the agricultural soil contained both. Nevertheless, NO release rates were less sensitive to O2 in the forest soil compared to the agricultural soil.

Metabolism of nitric oxide in soil and denitrifying bacteria

Production and consumption of NO was measured under anaerobic conditions in a slightly alkaline and an acidic soil as well as in pure cultures of denitrifying Pseudomonas aeruginosa, P. stutzeri, P. fluorescens, Paracoccus denitrificans, Azospirillum brasilense, and A. lipoferum. Growing bacterial cultures reduced nitrate and intermediately accumulated nitrite, NO, N2O, but not NO2. Addition of formaldehyde inhibited NO production and NO consumption. In the presence of acetylene NO was reduced to N2O. Net NO release rates in denitrifying bacterial suspensions and in soil samples decreased hyperbolically with increasing NO up to mixing ratios of about 5 ppmv NO. This behaviour could be modelled by assuming a constant rate of NO production simultaneously with a NO consumption activity that increased with NO until Vmax was reached. The data allowed calculation of the gross rates (P) of NO production, of the rate constants (k), Vmax and Km of NO consumption, and of the NO compensation mixing ratio (mc). In soil, P was larger than Vmax resulting in net NO release even at high NO mixing ratios unless P was selectively inhibited by chlorate + chlorite or by aerobic incubation conditions. In bacteria, Vmax was somewhat larger than P resulting in net NO uptake at high NO mixing ratios. Both P and Vmax were dependent on the supply of electron donor (e.g. glucose). Both in soil (aerobic or anaerobic) and in pure culture, the Km values of NO consumption were in a similar low range of about 0.5–6.0 nM. Anaerobic soil and denitrifying bacteria exhibited mc values of 1.6–2.1 ppmv NO and 0.2–4.0 ppmv NO, respectively.

Influence of pH on the release of NO and N2O from fertilized and unfertilized soil

NO and N2O release rates were measured in an acidic forest soil (pH 4.0) and a slightly alkaline agricultural soil (pH 7.8) after the pH was adjusted to values ranging from pH 4.0 to 7.8. The total release of NO and N2O during 20 h of incubation was determined together with the net changes in the concentrations of NH4+, NO2−and NO3−in the soil. The release of NO and N2O increased after fertilization with NH4+and/or NO3−; it strongly decreased with increasing pH in the acidic forest soil; and it increased when the pH of the alkaline agricultural soil was decreased to pH 6.5. However, there was no simple correlation between NO and N2O release or between these compounds and activities such as the NO2−accumulation, NO3−reduction, or NH4+oxidation. We suggest that soil pH exerts complex controls, e.g., on microbial populations or enzyme activities involved in nitrification and denitrification.

Release of nitric oxide from building stones into the atmosphere

Stone material from the corroding surface of buildings generally released nitric oxide with rates of 0.42–4.2 ng NON h −1 g −1 d.w. despite their large range of moisture, pH and content of ammonium, nitrite and nitrate. The net release rates of NO were independent of the NO mixing ratio of the atmosphere up to 1 ppmv NO. Whereas NO 2 was taken up by all stones tested, uptake of NO was only observed in one out of five types of stone. NO release rates were highest at the stone surface and rapidly decreased in depth lower than 1 cm. NO release persisted for up to >3 months after the stone sample was removed from the building. NO was mainly produced during the biogenic oxidation of ammonium to nitrate at the stone surface which was probably due to endolithic nitrifying bacteria. Chemical decomposition of nitrite to NO and NO 2 was only observed under acidic conditions.