Origin of asymmetry in biomolecules

Abstract

ONE of the most exciting hypotheses put forward to explain the molecular asymmetry of living beings is based on a physical concept, the ‘parity nonconservation law’¹. According to this, matter is intrinsically asymmetric (β particles are always spin polarised) and the molecular asymmetry on Earth is a reflection of the structure of matter itself^2–5. Though the theory is attractive, experimental results are controversial. Some people have reported differences in the radiation susceptibility of the two enantiomers (D and L forms) of a molecule if irradiated with β⁻ particles and/or their associated circularly polarised γ rays (bremsstrahlung)⁶, whereas others have failed to detect any differential radiolysis in similar experiments⁷. One possible explanation for the controversial data may be that the decomposition of molecules depends on many factors which may mask the expected differential interaction between β⁻ particles and optical isomers. To avoid these disturbing factors, we studied the annihilation of β⁺ particles in optical isomers, exploiting the great advantage of this technique that it gives information about the interaction process itself rather than about the products of interaction.