India, Oct. 7 -- Some molecules can exist in either of two different variants, and many chemical reactions generate near-equal proportions of the two. The amino acids in living organisms, on the other hand, follow a curious asymmetry: although many of them can exist in two variants, only one dominates.

Engineering chemical reactions with similar asymmetry has implications in therapeutics. Many drug molecules can exist in forms that are mirror images of each other. If a pharmaceutical contains a mix of both variants, it is not always ideal: one variant has the desired therapeutic effect, but the other can sometimes cause harmful side effects.

The underlying cause of this is linked to the asymmetry in the chemistry of living organisms. Th...