The Evolution of Multicomponent Systems at High Pressures: IV. The Genesis of Optical Activity in High-density, Abiotic Fluids

TL;DR

This paper develops a thermodynamic framework linking molecular chirality to excess volume and Gibbs free energy, demonstrating that high-density conditions can induce optical activity in abiotic fluids through racemic to scalemic transitions.

Contribution

It extends existing equations of state to include chiral hard bodies and shows how high-pressure conditions can lead to optical activity in abiotic fluids.

Findings

Chiral mixtures can evolve into optically active scalemic states at high densities.

Monte Carlo simulations confirm pressure-induced racemic-scalemic transitions.

The phase behavior of similar molecules is complex and pressure-dependent.

Abstract

A thermodynamic argument has been developed which relates the chirality of the constituents of a mixture of enantiomers to the system excess volume, and thereby to its Gibbs free enthalpy. A specific connection is shown between the excess volume and the statistical mechanical partition function. The Kihara-Steiner equations, which describe the geometry of convex hard bodies, have been extended to include also chiral hard bodies. These results have been incorporated into an extension of the Pavlicek-Nezbeda-Boubik equation of state for convex, aspherical, hard-body systems. The Gibbs free enthalpy has been calculated, both for single-component and racemic mixtures, for a wide variety of hard-body systems of diverse volumes and degrees of asphericity, prolateness, and chirality. The results show that a system of chiral enantiomers can evolve to an unbalanced, scalemic mixture, which must manifest optical activity, in many circumstances of density, particle volume, asphericity, and degree of chirality. The real chiral molecules fluorochloroiodomethane, CHFClI, and 4-vinylcyclohexene, C8H12, have been investigated by Monte Carlo simulation, and observed to manifest, both, positive excess volumes (in their racemic mixtures) which increase with pressure, and thereby the racemic-scalemic transition to unbalanced distributions of enantiomers. The racemic-scalemic transition, responsible for the evolution of an optically active fluid, is shown to be one particular case of the general, complex phase behavior characteristic of "closely-similar" molecules (either chiral or achiral) at high pressures.