Differential interaction of helical beta particles with liquid enantiomers

Abstract

Two hypotheses exist to explain the origin of biomolecular homochirality; (i) that the selection of D-sugars and L-amino acids was determined by chance, a "frozen accident" or (ii) that the asymmetry of biomolecules is related to the intrinsic asymmetry of matter. Experiments designed to investigate a differential interaction between the parity violating weak interactions and chiral molecules have been conducted for thirty years; however, results are inconclusive. Electrons or positrons emitted during beta decay of radioactive nuclides are spin polarized; data presented here indicate that the helical particles travel further in one liquid enantiomer than in its mirror image isomer. Five chiral pairs were examined by Cerenkov pulse height spectroscopy; radiation originated with β- from ³²P or β+ from ²²Na, and the Bethe equation solved. Measured and calculated differences for ³²P in R and S 2-phenylbutyric acid (PBA) were significant to 2 sigma; differences for R and S α-pinene were significant to 1 sigma. The other enantiomers were on the brink of significance for β- form ³²P. Non-polarized Compton electrons gave superimposable spectra. Significance was reached for ²²Na in PBA; for the other isomers differences may be obscured by concomitant Compton electrons from gamma irradiation. The aromatic PBA was also measured by scintillation pulse height spectroscopy; additional nuclides included ³H and ³⁵S. Artifical contamination studies indicated that the displacement of the pulse height spectra of one enantiomer with respect to the other was not due to the presence of an impurity. The analogy between pulse height spectroscopy and circular dichroism is discussed; bombardment of chiral molecules by electrons from dissolved nuclides probes the absolute sense of the helical potential field of enantiomers. The results presented here favor the second hypothesis; chiral molecules are recognized by spin polarized β particles form parity violating radioactive decay.