Duplex Formation and the Origins of Homochirality

The roots of biological homochirality remain unknown despite decades of study. A commonly proposed path includes an initial small enantiomeric excess that was amplified over time, but a satisfactory source of the excess and a plausible amplification process have yet to be described. We propose here a route to oligonucleotide homochirality from unactivated racemic sources based upon the facts that duplex structures are inherently homochiral and their synthesis from strands of complementary string nucleotide subunits is both uncommonly rapid and exergonic. Simulations employing available kinetic and thermochemical data in an iterated sequence of three equilibria in dry/wet cycles running from unactivated and racemic RNA monomers through oligonucleotides to duplex structures have shown that the exceptional association rate distorts the otherwise simple equilibrium string and overcomes the severe kinetic and stoichiometric barriers to the pairing of the statistically scant homochiral fractions. The simulations reveal widespread deracemization and the full conversion of racemic monomers to populations of L- and D-duplexes in a succession of growth in which the initially formed duplexes are replaced over time with increasingly larger descendants. This claim is open to experimental testing.