Interparticle chiral recognition of enantiomers: a nanoparticle-based regulation strategy

The ability to regulate how molecular chirality of enantiomeric amino acids operates in biological systems constitutes the basis of drug design for specific targeting. We report herein a nanoparticle-based strategy to regulate interparticle chiral recognition of enantiomers using enantiomeric cysteines (l and d) and gold nanoparticles as a model system. A key element of this strategy is the creation of a nanoscale environment either favoring or not favoring the preferential configuration of the pairwise zwitterionic dimerization of the enantiomeric cysteines adsorbed on gold nanoparticles as a footprint for interparticle chiral recognition. This recognition leads to interparticle assembly of the nanoparticles which is determined by the change in the nanoparticle surface plasmonic resonance. While the surface density and functionality of cysteines on gold nanoparticles are independent of chirality, the interparticle chiral recognition is evidenced by the sharp contrast between the interparticle homochiral and heterochiral assembly rates based on a first-order kinetic model. The structural properties for the homochiral and heterochiral assemblies of nanoparticles depend on the particle size, the cysteine chirality, and other interparticle binding conditions. The structural and thermodynamic differences between the homochiral and heterochiral interactions for the interparticle assemblies of nanoparticles were not only substantiated by spectroscopic characterizations of the adsorbed cysteine species but also supported by structures and enthalpies obtained from preliminary density functional theory calculations. The experimental-theoretical correlation between the interparticle reactivity and the enantiomeric ratio reveals that the chiral recognition is tunable by the nanoscale environment, which is a key feature of the nanoparticle-regulation strategy for the interparticle chiral recognition.