Electron scavenger nitrate

Figure 6 Effect of scavenging capacity for e q on the number of electrons scavenged in aqueous solutions of nitrous oxide, nitrate, and selenate. Experimental data nitrate—( ) [77], ( ) [78] ...

Many of the fast chemical reactions discussed in the preceding sections involve at least one reactant which is of low symmetry. The reactions of the solvated electron with nitrate, naphthalene or pyrene are instances where the oxidant has a mirror plane (in the molecular plane) in the accepting orbital. Hence, reaction of the solvated electron with such a scavenger when both are contained in this plane should be slower than in other configurations. Similarly, the contact quenching of fluorescence from naphthalene or 1,2-benzanthracene by carbon tetrabromide [7], or... 

In the presence of the electron scavengers there is observed some drop in the intensities of the EPR signal of the e tr and of the respective optical band and a new radical appears which is actually the product of reaction of the electron with the added substance. Thus, the appearance of the ion-radicals of N032 and N022 has been detected in the solutions of nitrate and nitrite (22, 28, 31, 33, 34), 0 in the perchlorate glasses (29),... 

Nitrate as Electron Scavenger. In the case of nitrate, a linear relationship between the D37 dose and the initial concentration of AA was found, as shown in Figure 3. The curve passes through the origin, and its slope corresponds to a G-value for total degradation nearly twice that in oxygen, namely G(-AA) = 2.2. At neutral pH, hydrated electrons and OH-radicals are both known to be formed with G-values of about 2.25. The present result would therefore suggest that hydrated electrons are transformed by nitrate into a radical which behaves as if it were stoichiometrically equivalent to OH. It may be assumed that this radical... 

Radiolysis of aqueous nitrate solution has been investigated not only from practical viewpoints in nuclear technology, but also from scientific interests in order to understand the radiolysis of water because nitrate ion is an efficient scavenger for hydrated electron [114] and even for the precursor of the hydrated electron [115]. In practical process, the concentration range of nitrate covers from millimolars to 10 M and the radiation effect not only in diluted nitrate solutions but also in concentrated ones should be considered. 

These reactions are the terminal electron-transfer reactions during anaerobic respiration, the enzymes being part of a redox loop generating a proton-motive force capable of driving ATP synthesis. Periplasmic nitrate reductase (Nap) participates in cellular redox processes, aerobic denitrification, and nitrate scavenging. ... 

NapB. NapB is a subunit of the heterodimeric periplasmic nitrate reductase (NapAB) and transfers electrons to the catalytic NapA molybdoprotein. Nap systems are found in a number of bacteria, iucluding enterobacteria, aerobic denitrifiers, and nonsulfur purple photo synthetic bacteria. Their physiological function is different in these groups of bacteria and includes redox balancing using nitrate as an electron sink to dispose of excess rednctant, aerobic denitrification, and nitrate scavenging in nitrate-limited environments. 

We have investigated in detail the parameters affecting the continuous y-radiolysis of concentrated solutions (intensity, pH, 02, scavengers, etc.). Transients were investigated by pulsed electron beam radiolysis and kinetic spectroscopy, and the reactions of the optically accessible excited states of nitrate were investigated by conventional photolysis. This paper represents a survey of our recent results which, taken in conjunction with the work of others, allows the construction of a model whereby the main features of this system may be understood and may even be predicted. Literature review is necessarily selective for the present purpose (because of doubtful relevance to liquid state processes, low temperature radiolysis, and hence ESR work has been omitted from... 

This behavior then suggests that N02 is an intermediate in the direct effect (the present behavior could be and probably is caused partly by increased formation of e from the nitrate, the electron then reacting via Reaction 1, but pulse radiolysis work show this is not a sufficient explanation). Further discussion of I" scavenging is deferred until a presentation of the results of pulse radiolysis experiments. 

The most effective additives in PAHs reduction were the nitrates. The following explanation of their effectiveness was offered. When heated, the nitrates generate nitric oxide (NO), an odd-electron componnd, capable of scavenging free radicals thermally generated from tobacco components... 

When nitric acid is irradiated with an electron pulse of 10 ns duration, two formation processes, fast and slow, are observed as clearly shown in Figure 3. The fast process is completed after the duration of the pulse but the slower one grows up to 200 ns in 3 M nitric acid. If an OH scavenger is introduced, the slow component is easily reduced without the reduction of the fast component. This finding strongly suggests that the slow process is attributable to the OH radical reaction with nitric acid or nitrate ion. When the sample is replaced... 

X 10 m s ) of 2.4 x 10 ° dm mol s and in substantial agreement with a similar determination by Aldrich et al. [117]. Both groups found that the rate coefficient was independent of acetone concentration. It is substantially activation-limited. With nitromethane, the operational rate coefficient increased with concentration from 2.9 x 10 in dilute solutions to 4.3 X 10 dm mol" s at O.Smoldm" nitromethane. Such an increase would be expected for reactions occurring before the steady-state is established. Wolff et al. [118] found that the rate coefficients for hydrated electrons reacting with NOJ, H, acetone and NO2 was independent of concentration of scavenger above 0.1 mol dm , though only nitrate reacts at the diffusion-limited rate, even if hydro-dynamic corrections are applied (Chap. 9, Sect. 4). 

Later, we will see that NO2 will again be converted to nitrite (5.206) via electron transfer processes independent of the reaction chain (5.201) to (5.203), thereby establishing dynamic equilibria. In the presence of formate HCOO , which is an efficient OH radical scavenger, it not only prevents nitrite losses via reaction (5.191), but actually converts NO2, the major product of nitrate photolysis, into additional nitrite via the following reaction sequence = 4.3 10 L mol s and ks 202 = 2.4 10 L mol s ... 

In addition to the methyl-ethyl lead alkyls, gasolines frequently contain ethylene dichloride and dibromide as scavengers. These latter compounds also give a high response in the Electron capture detector and frequently elute at the same time as one of the lead alkyls. Dawson overcame this difficulty by using a chemically active stationary phase, silver nitrate in Carbowax 400, as a precolumn... 

Kramer used an electron capture detector for the determination of lead alkyls in petroleum. He claims that a complete analysis for tetramethyllead and tetraethyllead in petrol can be achieved on a column (3 metres) of 10% of Apiezon L on Chromosorb W at 120°C with bromobenzene as internal standard. To separate the mixed alkyls (ethyltrimethyllead, diethyldimethyllead and triethylmethyHead, tetramethyllead and tetraethyllead) it is necessary to combine the above analysis with use of a pre-column (5 cm) of 20% of Carbowax 400 saturated with silver nitrate on Chromosorb W impregnated with 8% of potassium hydroxide. The pre-column retains halogen-containing scavengers in the petrol, which would otherwise mask the ethyltrimethyllead peak. As little as 0.002 g of tetramethyllead and tetraethyllead can be detected in 1 litre of petroleum in a 45 minute analysis. 

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