Recoil labelling

Chemical effects of nuclear reactions do not only cause rupture of chemical bonds, they also lead to formation of new chemical bonds, a result that may be used for preparation of labelled compounds. Recoil labelling and self-labelling both involve radiation-induced reactions and also belong to the field of radiation chemistry. 

Recoil labelling was first observed by Reid in 1934. After neutron irradiation of a mixture of ethyl iodide and pentane, 1-labelled amyl iodide was found. It is produced by substitution of an H atom by an hot atom. 

Labelling of organic compounds with " I is performed by exchange of halogen atoms or by iodination. Decay of Xc in the presence of organic compounds also leads to formation of labelled compounds (recoil labelling). 

Direct recoil labeling of organic molecules with atoms has been attempted without success. Studies of reactions with liquid-phase acetic acid, acetaldehyde, and ethanol (35) as well as with larger biologic molecules like -chymotrypsin (57) led only to radiolysis and labeled fragmentation products. It is imlikely that this approach to labeling will ever be successful for preparation of radiochemicals due to the multivalency of nitrogen. 

Effect of Radiation Dose on Recoil Labeled Species Tritium and Cyclopropane"... 

Effect of Scavengers on Recoil-Labeled Species Products normalized to parent = 100... 

A detailed study of the products and intramolecular tritium distribution in the parent, when liquid phenylacetic acid was recoil-labeled, was made by Elatrash and Johnson (1961). They concluded that distribution in the excited parent was essentially random with little or no steric elfect being involved. They explain the exceptionally low activity observed in the methylene group of the labeled parent by suggesting that tritium substitution at the methylene position leads to an excited intermediate whose probability of de-excitation to labeled parent is considerably lower than when other positions in the molecule undergo substitution consequently a greater number of the methylene-substitution intermediates fragment rather than stabilize. The mechanistic emphasis here is on the excitation in the intermediate. 

T. Braun et al. Hungary Recoil labeling of fullerenes by implosion... 

For the production of C-labeled tracers, four main approaches have been employed (1) Biosynthetic methods, (2) Recoil labeling, (3) Organic synthetic methods, and (4) Enzyme catalysis. 

Biosynthetic methods using plant leaves or algae (lifton and Welch 1971) and recoil labeling (e.g., via the spallation reaction 0(p,3p3n) C) are today of little importance. Presently, the only labeling methods of practical interest are organic synthesis and enzymatic catalysis. 

---