Oxygen enhancement, effect

Vinicombe DA, Moss SH, Davies DJG (1978) Photo-reactivation ofy-radiation damage in Escherichia coli as evidence for the nature of the oxygen-enhancement effect. Int J Radiat Biol 33 483-492 Voityuk AA, Jortner J, Bixon M, Rosch N (2000) Energetics of hole transfer in DNA. Chem Phys Lett 324 430-434... 

As mentioned sulfonyl radicals readily add oxygen even in low temperature glasses [5,28]. The reaction has also been observed for the radicals grafted to the silica surface [44]. Sulfonyl peroxyls have been suggested to contribute to the oxygen enhancement effect known in radiobiology (discussed later) [95]. 

The Duoplasmatron (Eig. 3.18). In the Duoplasmatron, gas-discharge ion sources are used for bombardment with oxygen or argon. In dynamic SIMS, especially, the use of O2 ions is common because of the chemical enhancement effect. With a duoplasmatron ion beam currents of several microamps can be generated. The diameter of the beam can be focused down to 0.5 pm. 

The oxygen ion beam diameter is limited to 0.5 pm by the duoplasmatron source used. For mapping electropositive elements this drawback must be tolerated because of the chemical enhancement effect. 

Alkyl Esters (x), it has been observed that a conflict between I and M effects invariably takes place in the case of esters. Here, the non-bonding electrons residing on oxygen enhance the + M conjugation thereby decreasing the C = O frequency. 

These results confirmed the enhancement effect of tin on the electrocatalytic activities for the methanol oxidation. As stated before, tin has the main effect on the oxidation of eoCOad (Easily Oxidized COad) using water as the oxygen source while it has little effect on the oxidation of AoCOad (hard to-oxidize COad). which requires Ptr-OH as the oxygen source. This methanol oxidation enhancement effect is. therefore, also likely because of the enhancement of the utilization of water. Although it is not known whether this water utilization is through a path that has eoCOad as an intermediate or another path that has other active intermediates, there is no practical difference between the two because both paths proceed at more cathodic potentials than a path that has hoCOad as an intermediate. 

In vitro clonal tumor cell studies have demonstrated the severe cytotoxicity of a-particles delivered by At single exponential cell survival-dose curves were obtained, with (37% survival) values of 29-48 cGy and 57-73 cGy for Chinese hamster V-79 (5J ) and HEp2 cells, respectively (55). In both studies the oxygen enhancement ratio (OER) was found to be slightly greater than unity, probably resulting from the low-LET components of At decay (see Fig. 5). In biological systems, such a-particle emissions enable comparable cytotoxicities to be effected in both hypoxic and euoxic tumor cell populations. 

McCoy, E. C., and H. S. Rosenkranz, Activation of Polycyclic Aromatic Hydrocarbons to Mutagens by Singlet Oxygen An Enhancing Effect of Atmospheric Pollutants, Cancer Lett., 9, 35-42 (1980). 

Griffiths, R. F. et al., Proc. 18th Int. Combust. Symp., 1981, 893—901 If rapid compression of dilute ethylene oxide vapours occurs, ignition and/or decomposition may occur. Thus 5% of oxide in argon will ignite if compressed more than 11-fold, and presence of traces of oxygen enhances the effect. Even 1% or less of ethylene in the oxide in air may be hazardous if modest but rapid compression occurs. 

As noted above, the X-ray sensitization of cells using MGd has been investigated extensively and appears to operate at least in part in an oxygen dependent manner, with cytotoxic activity that is substantially enhanced upon the addition of ascorbate to the media [69], The cytotoxic activity of MGd can also be enhanced with L-buthionine-S,R-sulfoximine (BSO), an irreversible inhibitor of an enzyme involved in glutathione biosynthesis (y-glutamylcysteine synthetase), that serves to suppress the synthesis of ROS-protective glutathione. Presumably, this activity is responsible for the in vitro radiation enhancing effect of BSO [66,71],... 

As with the Maillard reaction, odorous compounds are formed, water and carbon dioxide are liberated, the pH drops during the reaction, colour formation is markedly increased by increasing the pH, oxygen has only a slight enhancing effect on colour production, and the reaction is inhibited by sulfur dioxide. 

FIGURE 7. Dependence of relative biological effect (RBE) and of oxygen enhancement ratio (OER) on the linear energy transfer (LET) of radiation. Reprinted from Brown, Appl. Radiat. Isot., 37, 789 (1986) (Reference 84) by kind permission of Elsevier Science Ltd, The Boulevard, Langford Lane, Kidlington, OX5 1GB... 

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