Gamma-radiolysis

Gamma Radiolysis of Liquid Dinitrogen Tetrox-ide , PATR 3072 (1963) 20) Anon,... 

The effect of irradiation on the extractability of sulfoxides towards plutonium, uranium and some fission products were studied by Subramanian and coworkers . They studied mainly the effect of irradiation on dihexyl sulfoxide (DHSO) and found that irradiation did not change the distribution coefficient for Ru, Eu and Ce but increases the distribution coefficient for Zr and Pu. When comparing DHSO and tributyl phosphate (TBP), the usual solvent for the recovery and purification of plutonium and uranium from spent nuclear fuels, the effect of irradiation to deteriorate the extraction capability is much larger in TBP. Lan and coworkers studied diphenyl sulfoxides as protectors for the gamma radiolysis of TBP. It was found that diphenyl sulfoxide can accept energy from two different kinds of excited TBP and thus inhibits the decomposition of the latter. 

In a related manner, gamma radiolysis of tetrazolium salts also yields formazans.256,257 Pulse radiolysis in aqueous solutions leads to tetrazole... 

Gamma radiolysis of simple carboxylic acids and N-acetyl amino acids results in loss of the carboxyl group with formation of carbon monoxide and carbon dioxide. In the carboxylic acids, the ratio of C0/C02 produced is approximately 0.1, while in the N-acetyl amino acids the ratio is much smaller. In the poly carboxylic acids and poly amino acids, radiolysis also results in the loss of the carboxyl group, but here the ratio of C0/C02 is greater than 0.1. Incorporation of aromatic groups in the poly amino acids provides some protection for the carboxyl group. The degradation of the poly acids is believed to involve radical and excited state pathways. 

ALIPHATIC CARBOXYLIC ACIDS The radiation chemistry of the simple aliphatic carboxylic acids has been widely investigated. The major products of gamma radiolysis of these compounds are typified by those found (1) for radiolysis of isobutyric acid at 273 K... 

Table I. Yields of volatile products for gamma radiolysis of isobutyric acid at 273 K...

Figure 1. ESR spectra of isobutyric acid following gamma radiolysis in the solid state at (A) 77 K (B) 195 K.

The range of products formed on gamma radiolysis of N-acetylglycine was similar to that formed on radiolysis of the aliphatic carboxylic acids, but there are some noticeable differences in the yields of products. Carbon dioxide is by far the major volatile product of radiolysis and the corresponding product of the decarboxylation reaction, N-methyl acetamide, is also present in large yield, but the yield of this product was not quantitatively determined. By contrast, carbon monoxide is found in very small yield. The yield of acetamide, the product of N-Ca bond scission, is found in much greater yield. 

A variety of radical products is observed following gamma radiolysis of the N-acetyl amino acids at 77 K (6), depending on the nature of the side chain of the parent amino acid. In the case of N-acetyl alanine, for example, the intermediates are (i) the anion radical IV (ii) the decarboxylation radical V (iii) the deamination radical VI and (iv) the alpha carbon radical VII. 

Table IV. G-values for the volatile products formed on gamma radiolysis of N-acetylglycine at 303 K...

A similar behaviour has been found to occur with the other N-acetyl amino acids. In each case, the most stable radical observed at 303 K was the alpha carbon radical, as was also observed for the aliphatic carboxylic acids. In Table VI the radical yields observed following gamma radiolysis of a series of N-acetyl amino acids at 303 K are reported, together with the stable radical intermediates observed at this temperature (5). 

POLYCARBOXYLIC ACIDS The gamma radiolysis of the homopolymers of acrylic, methacrylic and itaconic acids have been investigated in the solid state at 303 K, and in each case the yields of carbon monoxide, carbon dioxide and of radical intermediates have been measured. These are reported in Tables VII and VIII respectively. 

Table VIII. 6-values for radical formation for gamma radiolysis of poly acids at 303 K...

As with the aliphatic carboxylic acid model compounds, the major volatile product observed on gamma radiolysis of the poly acids is carbon dioxide. However, the carbon dioxide yields are somewhat larger than those observed for the model compounds. 

The only radical intermediate observed for poly methacrylic acid was the propagating radical formed by main chain scission. This observation is similar to that noted for gamma radiolysis of poly methylmethacrylate, where the propagating radical is also found as the only stable radical intermediate following radiolysis at 303 K. In both cases the propagating radical is formed by -scission following the loss of the side chain, resulting in formation of the unstable tertiary radical. 

Thus, polymethacrylic acid undergoes net scission on gamma radiolysis with a G-value of approximately 4, while polyacrylic acid, on the other hand, undergoes net crosslinking with a G-value of approximately 1.2 (7). Crosslinking in polyacrylic acid is favourable because of the formation of main chain radicals. These can react to form crosslinks between polymer chains. 

POLYAMINO ACIDS Aliphatic polyamino acids irradiated in the solid state have been reported to undergo N-Ctf, main-chain, bond scission on gamma radiolysis (9) and the stable radical intermediates formed following radiolysis at 303 K are alpha carbon radicals, as observed in the N-acetyl amino acids. 

Two stable radical intermediates are observed following gamma radiolysis at 303 K. The alpha carbon radical VIII and the side chain radical IX are formed in approximately equal yields, with the total G-value for radical production equal to 3.2. This value is similar to that observed for the poly acids. The observed radicals are those which would be expected on the basis of the aliphatic carboxylic acids and previous studies of the poly amino acids with aliphatic side chains. 

Sawasaki T, Tanabe T, Yoshida T, Ishida R (2003) Application of gamma radiolysis of water for H2 production. J Radioanal Nucl Chem 255 271-274... 

Petrik NG, Alexandrov AB, Vail AI (2001) Interfacial energy transfer during gamma radiolysis of water on the surface of Zr02 and some other oxides. J Phys Chem B 105 5935-5944... 

Hi. Lysine. Gamma radiolysis of aerated aqueous solution of lysine (94) has been shown, as inferred from iodometric measurements, to give rise to hydroperoxides in a similar yield to that observed for valine and leucine. However, attempts to isolate by HPLC the peroxidic derivatives using the post-column derivatization chemiluminescence detection approach were unsuccessful. This was assumed to be due to the instability of the lysine hydroperoxides under the conditions of HPLC analysis. Indirect evidence for the OH-mediated formation of hydroperoxides was provided by the isolation of four hydroxylated derivatives of lysine as 9-fluoromethyl chloroformate (FMOC) derivatives . Interestingly, NaBILj reduction of the irradiated lysine solutions before FMOC derivatization is accompanied by a notable increase in the yields of hydroxylysine isomers. Among the latter oxidized compounds, 3-hydroxy lysine was characterized by extensive H NMR and ESI-MS measurements whereas one diastereomer of 4-hydroxylysine and the two isomeric forms of 5-hydroxylysine were identified by comparison of their HPLC features as FMOC derivatives with those of authentic samples prepared by chemical synthesis. A reasonable mechanism for the formation of the four different hydroxylysines and, therefore, of related hydroperoxides 98-100, involves initial OH-mediated hydrogen abstraction followed by O2 addition to the carbon-centered radicals 95-97 thus formed and subsequent reduction of the resulting peroxyl radicals (equation 55). 

Figure 11 Effect of temperature on the yield of OH radicals from gamma radiolysis. Experiments (A) Kent and Sims [100], ( ) Elliot et al. [101] Calculation (solid line) IRT modeling using track structure simulation.

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