Experimental and computational studies of enantioseparation of structurally similar chiral compounds on amylose tris(3,5-dimethylphenylcarbamate).

The enantioseparation of 14 structurally similar chiral solutes, with one or two chiral centers, are studied for a commercially important polysaccharide-based chiral stationary phase, amylose tris(3,5-dimethylphenylcarbamate) (ADMPC). Among these solutes, only two solutes show significant enantioresolutions of 2 to 2.5 in n-hexane/2-propanol (90/10, v/v) at 298 K. The retention factors of the chiral solutes vary significantly from 0.7 to 7.0, and they are compared with those of simpler nonchiral solutes having similar but fewer functional groups. The sorbent-solute H-bonding interactions between the solute functional groups and the polymer C=O and NH functional groups are probed with attenuated total reflection infrared spectroscopy (ATR-IR). The H-bonding interactions of the polymer C=O and NH groups with the solutes result in changes in the IR amide band wavenumbers of ADMPC upon solute adsorption. The nanostructure of an ADMPC cavity and the potential interactions with the chiral solutes are proposed based on the sorbent-solute-solvent HPLC data, the sorbent-solute IR data, and the sorbent-solute molecular dynamics (MD) simulations. The results are consistent with the three point attachment hypothesis and indicate that a significant enantioresolution in ADMPC requires at least three different interaction sites for simultaneous H-bonds and phenyl-phenyl interactions for phenylpropylamine (PPA) and various structurally similar chiral solutes.