Electron scavenger oxygen

This reaction has been shown to be very rapid77. Sulphuric and acetic acids sup press the polymerisation. Evidently their anions are ineffective as initiators, and the enhanced proton concentration provided by them must reduce the chain lifetime. The slight retarding effect of oxygen could be due to electron scavenging. However, the authors suggest that there may be a small free radical component of the chain reaction, which is inhibited in the presence of oxygen. 

The hypothesis that electron scavenging by oxygen or other oxidants is faster than electron-hole recombination is perhaps too restrictive, as it is now recognized that this reaction, in particular with oxygen, can be rather slow (see Ref. 19 and the values of estimated rate constants in Ref. 41). When 0x2 acts as a mere electron scavenger, reaction (Ig) could be neglected. The rate... 

The photocatalytic conversion rate increases with the increase of the oxygen partial pressure. The typical explanation is that oxygen acts as an electron scavenger, thus reducing the rate of electron-hole recombination (Chen and Ray, 1999). 

However, photocatalytic reduction of organic compounds is generally less important than their oxidation because the reduction potential of a Ti02(e ) is lower than the oxidation potential of a Ti02(h ). Also, most of the reducible substrates cannot compete kinetically with oxygen as an electron scavenger [15]. 

The guanine moiety has the lowest ionization potential of any of the DNA bases or of the sugar-phosphate backbone. As a result, radiation-produced holes are stabilized as dG for hydrated DNA irradiated at 77 K There is an extensive literature describing the role of dG in the radiation chemistry of DNA as studied by pulse radiolysis, flash photolysis, and product analysis. In order to explicate the oxidative reaction sequence in irradiated DNA and to more firmly identify the relevant radical intermediates, ESR spectroscopy was employed to investigate y-irradiated hydrated DNA (T = 12 2). Some experiments were also performed on hydrated (T = 12 2) DNA in which an electron scavenger [thallium(ni) (TP )] was employed to isolate the oxidative path. Oxygen-17 isotopically enriched water was also used to confirm a proposed water addition step to G and the subsequent transformations that follow These experiments were run in oxygen-free samples under conditions for which indirect effects were unimportant. 

Trichloroacetate rapidly reacts with the solvated electrons produced by laser flash photolysis of natural organic matter isolated from the Suwannee River, and thus quenches the absorption of the electrons at 720 nm. The ibsorption is also quenched by the addition of other good electron acceptors, including oxygen, protons, or nitrous oxide. In natural waters, halocarbon concentrations are typically very low, and the dominant scavenger of solvated electrons is oxygen. 

When solutions of CdS colloids containing no additional electron and hole acceptor in the solution, are exposed to a high intensity laser flash, a rather large absorption of an intermediate is observed around 700 nm, similarto that described for the laser excitation of Ti02 in the previous section. The absorption spectrum of the intermediate is given in Fig. 9.17 [52]. It is not due to trapped electrons and holes but it is identical with to the well-known spectrum of hydrated electrons as proved by radiolysis experiments [52]. The half-life of the hydrated electrons is a few microseconds. In the presence of typical hydrated electron scavengers, such as oxygen, acetone or cadmium ions, the decay of the intermediate became much faster. 

The experiments evaluating the reactivity of the reaction of OH radical with polymer chains were performed under N20 saturation for reducing the influence of hydrated electron and oxygen. N20 reacts with hydrated electron and produces OH radical[reaction (9)]. To measure the rate constants of OH radical with polymer chains, a competition method is suitable. An absorption peak of OH radical is at UV region and the absorption coefficient is very low, so it is difficult to observe OH radical directly. In this experiment, KSCN and KI were used as a competitor scavenger. OH radical reacts with SCN or I and generates... 

In the oxygen system at approximately 50 mm. pressure (collision frequency — 109 sec. 1) half of the 02 " ions are stabilized before emission can take place (13). In the condensed phase, therefore, deactivation should compete to the exclusion of electron emission. The much higher probability of collisional deactivation in liquids may explain why compounds such as C02 and CH3C1, for which attachment is very inefficient in the gas phase, are often effective electron scavengers in liquid systems. One must be wary, therefore, of using even relative gas-phase electron attachment coefficients in liquid-phase studies. For molecules with very small electron affinities (< 0.1 e.v.) the reversibility of Reaction 3 may have to be considered even after the excitation energy of the negative ion has been removed by collision. 

Electron scavenging by oxygen species in competition with eqn. (53a) was identified as the origin of the sensitivity of this photoassisted redox-type mechanism towards added oxygen. 

Mechanism (1) is common to all electron scavengers, mechanism (2) is typical for oxygen, and mechanism (3) is typical for hydrogen peroxide, which acts according to Equation 2 ... 

Oxygen as Electron Scavenger. In the case of oxygen there is a linear relationship between D87 dose and initial concentration of AA with only a small intercept at the ordinate (Figure 3). The G-value for... 

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