| Abstract
| - A method to selectively probe the different adsorption ofenantiomers at chiral solid−liquid interfaces is applied,which combines attenuated total reflection infrared spectroscopy and modulation spectroscopy. The spectralchanges on the surface are followed while the absoluteconfiguration of the adsorbate is changed periodically.Demodulated spectra are calculated by performing asubsequent digital phase-sensitive data analysis. Themethod is sensitive solely to the difference of the interaction of the two enantiomers with the chiral surface, andthe small spectral changes are amplified by the phase-sensitive data analysis. Its potential is demonstrated byinvestigating an already well-studied system in liquidchromatography, namely, the enantiomer separation ofN-3,5-dinitrobenzoyl-(R,S)-leucine (DNB-(R,S)-Leu) using tert-butylcarbamoyl quinine (tBuCQN) as the chiralselector immobilized on the surface of porous silicaparticles. The performed experiments and density functional theory calculations confirm an interaction modelthat was proposed earlier based on solution NMR andXRD in the solid state. It emerges that the ionic interactionis the strongest one, but the main reason for the potentialfor enantioseparation of the chiral stationary phase (CSP)is the distinct formation of a hydrogen bond of the (S)-enantiomer with the chiral selector. This H-bond isestablished between the amide N−H of DNB-(S)-Leu withthe carbamate CO of the CSP. The (R)-enantiomerinstead shows no specific hydrogen bonds. Only theunspecific ionic bonding between the protonated quininepart of the tBuCQN and the carboxylate of the DNB-(R)-Leu (holds also for DNB-(S)-Leu) is observed.
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