(308b) Microscopic Models of Chiral Amplification and Symmetry Breaking

Amino acids, sugars and other biomolecules are geometrically constrained by the machinery of life to predominantly express one enantiomer over its mirror image. Fundamental questions naturally arise about the origin of this homochirality from a presumably racemic, pre-biotic environment, and these open questions provide an active area of research. One unsolved question is whether homochirality is a prerequisite for life or merely incidental. Novel mechanisms of asymmetric synthesis and chiral amplification of biomolecules are also of great practical interest, for example in the pharmaceutical industry. Therapeutic compounds often must be synthesized with a particular chirality, and in extreme cases the mirror image may be harmful. We formulate two-dimensional lattice models to study equilibrium phase behavior that leads to liquid-phase chiral amplification, and another lattice model to study spontaneous chiral symmetry breaking with asymmetric autocatalysis. The equilibrium model suggests a possible thermodynamic scenario for liquid-phase emergence of chiral imbalance in a prebiotic and presumably nearly racemic world [1]. For the kinetic model, starting from a chirally unbiased initial condition, spontaneous symmetry breaking with chiral amplification occurs [2]. We are not aware of another model with molecularly-explicit chirality, microscopic degrees of freedom, autocatalysis and inhibition that exhibits symmetry breaking. This suggests a useful role for theory and modeling in elucidating the possible conditions that may have given rise to the emergence of chirality in a pre-biotic world, and for identifying strategies for the rational design of industrial chiral synthesis processes.

[1] T.G. Lombardo and F.H. Stillinger and P.G. Debenedetti, Thermodynamic mechanism for solution phase chiral amplification via a lattice model. Proc. Nat'l. Acad. Sci. USA, 106, 15131, 2009.

[2] H.W. Hatch and F.H. Stillinger and P.G. Debenedetti, Chiral symmetry breaking in a microscopic model with asymmetric autocatalysis and inhibition. In submission, 2010.