Enantiomeric discrimination by UV–Vis-absorption chiral anisotropy of chiral nanostructured Au particles

Enantiomeric discrimination plays a crucial role in various scientific domains, including analytical chemistry, chemical biology, pharmaceuticals, and pesticide research. A variety of theoretical frameworks and chiroptical spectroscopic methods, including optical rotation and circular dichroism, have been devised to identify and quantify enantiomers. Generally, circularly polarized light is utilized to determine the absolute configuration and composition of enantiomers. However, these techniques are not suitable for racemic mixtures or substances with minimal optical activity. Herein, we propose that ultraviolet–visible-absorption chiral anisotropy (UV–Vis-ChA) of chiral nanostructured Au particles (CNAPs) can be utilized for enantiomeric discrimination, using amino acids as a model system. The CNAPs, synthesized via a seed-mediated method using chiral glutathione as the symmetry-breaking agent, exhibit a helical nanocubic structure. Upon the addition of amino acid enantiomers to the CNAPs solution, the decrease in the UV–Vis absorbance of CNAPs solution, with varying rates, was induced by enantiomers with different enantiomeric excess (ee) values. The rate constant of absorbance decrease (k_Δ) was proportional to the ee values, regardless of polarity, size, or chromophore type. It is speculated that the UV–Vis-ChA results from the selective aggregation of CNAPs due to the formation of coordination bonds with enantiomers which is driven by their spin polarizations. This work provides a cost-effective, broad-spectrum, and quantitative approach to enantiomeric discrimination.