Enantioselective radical reactions can be induced by electron spin polarization: A quantum mechanism for Nature's emergent homochirality?

TL;DR

This paper proposes a quantum mechanism where enantioselective radical reactions driven by electron spin polarization could explain the origin of biological homochirality, supported by a theoretical model consistent with experimental data.

Contribution

It introduces a quantum-based theory of enantioselectivity in radical reactions driven by spin polarization, offering a new mechanistic insight into the emergence of homochirality in nature.

Findings

Quantum coherent dynamics induce enantioselectivity in radical pair reactions.

The theory bounds maximum enantiomeric excess consistent with experiments.

Suggests spin-polarized electrons as a mechanism for biological homochirality.

Abstract

Biomolecules that constitute life on Earth are chiral, but the precise mechanism by which homochirality emerged remains a mystery. In this work it is demonstrated that reactions of radical pairs, where one of the radical electron spins is polarised, can be enantioselective. This phenomenon arises from transient coherent quantum dynamics of the radical pair electron spins, which is known to occur even in warm and noisy condensed phase environments, where energetic perturbations much smaller than thermal energy can have large effects on reactivity. A quantitative theory is presented based on the molecular theory of chirality induced spin selectivity (CISS), where electron exchange interactions and chirality-dependent spin-orbit coupling effects control enantioselectivity. This theory provides useful bounds on the maximum enantiomeric excess for these reactions, which are found to be consistent with previous experiments. The enantioseletive radical pair mechanism presented here provides an alternative mechanistic basis to a recent proposal that spin-polarised photoelectrons from magnetite provided the initial chiral symmetry breaking necessary for the inception of homochirality in Nature, as well as suggests a new strategy for asymmetric synthesis using spin-polarised electrons.