Enantioselective recognition of racemic amino alcohols in aqueous solution by chiral metal-oxide keplerate {Mo132} cluster capsules

Determining the relative configuration or enantiomeric excess of a substance may be achieved using NMR spectroscopy by employing chiral shift reagents (CSRs). Such reagents non-covalently interact with the chiral solute, resulting in each chiral form experiencing different magnetic anisotropy, which is reflected in their NMR spectra. The Keplerate polyoxometalate (POM) is a molybdenum-based, water-soluble, discrete inorganic structure with a pore-accessible inner cavity, decorated by differentiable ligands. Through ligand exchange from the self-assembled nanostructure we have synthesized a set of chiral Keplerate host molecules. By exploiting interactions of analyte molecules at the surface pores we establish the relative configuration of chiral amino alcohol guests (phenylalaninol and 2-amino-1-phenylethanol) in aqueous solvent and determine their enantiomeric excess by 1 H NMR. The use of POMs as chiral shift reagents represents an application of the class that is yet to be well established and opens avenues into aqueous host-guest chemistry with self-assembled recognition agents