Chiral Self-Selectivity in Two Model Dinitrobenzoyl-Derivatized Brush-Type Chiral Stationary Phases

Abstract

A study of chiral self-discrimination in two model chiral stationary phases, N- (3,5-dinitrobenzoyl-phenylglycine and N-(3,5-dinitrobenzoyl)leucine, is described. "Brush-type" chiral interfaces are obtained by attaching these compounds onto oxidized Si(111) samples and atomic force microscopy tips by using two sample preparation procedures: a direct and a two-step surface deposition of the chiral stationary phase onto the substrate. By using AFM, the morphologies of the resulting chiral interfaces are obtained. XPS and FTIR provide information regarding the relative distribution of the compounds on the surface. We analyze the N 1s peaks using XPS to ensure that all the NH 2 groups on the surface are capped. Chemical force spectrometric measurements of the chiral self-selectivity in 2-propanol demonstrate that chiral discrimination is present in both systems, but larger forces are observed for N-(3,5-dinitrobenzoyl)phenylglycine, consistent with a previous molecular dynamics study that demonstrated much weaker solvent interactions with this species.

Chiral Discrimination of a Proline-Based Stationary Phase: Adhesion Forces and Calculated Selectivity Factors

“…We have previously reported on the self-selectivity of N -(3,5-dinitrobenzoyl)phenylglycine and N -(3,5-dinitrobenzoyl)leucine CSPs in a series of protic and aprotic solvents. − We found that the less sterically hindered and more flexible leucine moiety led to increased hydrogen bonding with the solvent. This interaction with the solvent occurred at the carbonyl and amide groups within the selector and reduced chiral discrimination because the sites were not available for interactions with the analyte.…”