γ-Radiation Induced Polymerization of a Chiral Monomer: A New Way to Produce Chiral Amplification

The treatment of the terpene β(−)pinene with γ radiation (at dose level: 150, 300 and 600 kGy) causes its polymerization into a resin and into a dimer. The yield of the resin and of the dimer appears to be linearly dependent to the radiation dose. The structure of the products was studied by FT–IR spectroscopy also in comparison to a reference β(−)pinene resin prepared by cationic polymerization. A highly ordered structure was found in the case of the radiopolymer in comparison to the resin from cationic polymerization. Polarimetric measurements have shown astonishing enhancement in the optical activity of the radiopolymer and radiodimer in comparison to the starting optical activity of the β(−)pinene monomer. Also DSC (differential scanning calorimetry) data supports the unexpected highly ordered structure for the β(−)pinene radiopolymer in comparison to the resin prepared by cationic polymerization. The results have been discussed in terms of amplification of chirality caused by γ radiation and the implications of this fact on the mechanism of chiral amplification on prebiotic molecules. Presented at: National Workshop on Astrobiology: Search for Life in the Solar System, Capri, Italy, 26 to 28 October, 2005.