Cross-Catalysis and Weak Interactions: Keys to the Chiral Polarization of the Biosphere

Molecular homochirality - the uniformity of chirality in biological molecules - is a fundamental feature of life, yet its origins remain unresolved. The correspondence between the chirality of biological monomers on Earth and that observed in ancient meteorites implies a systematic selection of chirality sign in prebiotic chemistry, rather than a stochastic process. While classical theories attribute symmetry breaking to chiral autocatalysis, such self-amplifying processes are rare and have not been empirically demonstrated in the synthesis of amino acids and carbohydrates. In contrast, chiral cross-catalysis between amino acids and carbohydrates - a mechanism consistent with known chemical behavior - could similarly amplify chiral purity. However, cross-catalysis alone cannot determine the chirality sign due to its inherent symmetry, leaving the origin of the initial bias unexplained. Although weak interactions have been proposed as a potential source of this bias, their effects are theoretically negligible, raising questions about their sufficiency. Our kinetic analysis of cross-catalytic systems reveals that even an infinitesimal preference for left-handed amino acids and right-handed carbohydrates could be sufficient to establish the homochirality observed in life. This mechanism provides a plausible link between prebiotic chemistry and the homochirality of the biosphere, offering a potential resolution to this longstanding enigma.