Enantioselective Recognition of Chiral Guests by the Water-Soluble Chiral Keplerate {Mo132} Spherical Capsule with 30 Inner Lactate Ligands

Investigations of chiral host guest chemistry are important to explore recognition in confined environments. Here, by synthesizing water-soluble chiral porous nanocapsule based on the inorganic metal-oxo Keplerate-type cluster, {Mo₁₃₂} with chiral lactate ligands with the composition [Mo₁₃₂O₃₇₂(H₂O)₇₂(x-Lactate)₃₀]^42- (x = D or L), it was possible to study the interaction with a chiral guest, L/D-carnitine and (R/S)-2-butanol in aqueous solution. The enantioselective recognition was studied by quantitative ¹H NMR and ¹H DOSY NMR which highlighted that the chiral recognition is regulated by two distinct sites. Differences in the association constants (K) of L- and D-carnitine, which, due to their charge, are generally restricted from entering the interior of the host, are observed, indicating that their recognition predominantly occurs at the surface pores of the structure. Conversely, a larger difference in association constants (K_S/K_R = 3) is observed for recognition within the capsule interior of (R)- and (S)-2-butanol.