Radioactive decay in a labelled molecule leads to specific chemical and biological consequences which are due to local transmutation effects such as recoil, electronic excitation, build-up of charge states and change of chemical identity, as well as to internal radiolytic effects. In the present paper these effects are reviewed emphasizing the relation of the chemical alterations on a molecular level to the biological manifestation. Potential importance of this type of research for biomedical applications is pointed out. In part 1 we review the underlying physical and chemical principles and consequences of beta-decay of 3H, 14C, 32P, 33P, 35S and 125I for gaseous and simple condensed organic systems. Part 2 which will appear in the next issue will include the discussion of biological effects associated with beta-decay.

In Part 1 of this article physical and chemical effects of beta-decay in labelled molecules were reviewed and their potential importance for breaking predetermined and specific bonds were pointed out. After incorporation of labelled biomolecules in living systems, such as viruses, phages or cells, the radioactive decay of the label alters the biological behaviour of the system, in the extreme case causing loss of the ability to reproduce, the extent of these consequences depending strongly on the type of radioisotope. Now Part 2 includes a brief discussion of biological effects associated with beta-decay emphasizing the relative importance of local transmutation and internal radiation effects from the decay of 3H, 14C, 32P, 33P, 35S and 125I. Attempt is also made, whenever possible at the present stage of understanding, to correlate biological effects with chemical processes on a molecular level.

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Band 7, Heft 1 1967 J. NARBUTT et al., Thermal Annealing of 82 Br in Neutron-Irradiated p-Dibromobenzene 55 stets entgegengebrachte Interesse und die großzügige Förderung. Dem Bundesministerium für Wissenschaftliche Forschung, Bad Godesberg und der Kommission für Transuranforschung der Bayrischen Akademie der Wissenschaften sind wir für die finanzielle Unterstützung dieser Arbeiten zu Dank verpflichtet. Frl. P. SCHILZ, Herrn M. FOCHLER und Frau U. JAAKSOH danken wir für die Unterstützung bei den experimentellen Arbeiten.

of 82 Br 51 extremely low quantum yield 10~3) [6] in photolysis (2537 Â) of benzene where one deals with 1 B 21i exclusively and PPO is a known efficient acceptor of energy from state. 25-IOr 1 5.0-10~3 75-IO' 2 Concentration of PPO WW 2 M Fig. 1. Effect of PPO on G (biphenyl) in «°Co-y radiolysis of benzene Table 1. Effect of addition of organic scintillators on θ (biphenyl) Concentration of scintillators G (biphenyl) pure benzene 0.062 1.36 X 10" 2 M PPO 0.050 1.18 X 10~2 M p-terphenyl 0.053Earlier, 2-butene has been successfully employed by C und all and Griffiths [4] to demonstrate that at ~ 0.125 mole/1, most of the triplets produced in γradiolysis of benzene are quenched. A concentration of ca. 0.11 M trans 2-butene employed in the present investigation decreased G (biphenyl) to the extent of 0.012 only. This result suggests that triplets may play only a minor part. G (biphenyl) was also found to decrease with addition of naphthalene. For a concentration of ca. 0.1 M naphthalene G (biphenyl) was found to be 0.040 as compared to a value of 0.043 for a corresponding concentration of PPO. This is interpreted to mean that these solutes are acting in a non specific way and perhaps some unknown mode of preferential energy localisation is involved in these cases. Acknowledgement