Chromatographic approach to the measurement of the interstrand distance for some chiral bonded phases

Abstract

A series of homologous IV ,/V'-bls(2,4-dinltrophenyI )-a,<v-dlamlnoalkanes (bls-DNP's) was chromatographed at various temperatures on -baslc chiral stationary phases derived from /V-(2-naphthyl)alanlne In order to determine the enthalpy and entropy of adsorption. The number of methylene groups in the bis-DNP's Influences the ability of the terminal ir-acidlc groups to interact simultaneously with neighboring strands of stationary phase, a process termed "bridging". When the number of methylene groups Is optimal for bridging, the enthalpy of adsorption Is most exothermic. The length of the bis-derlvatlve required for optimal bridging is related to the interstrand distance. Optimal bridging occurs for the bls-DNP's having five methylene groups regardless of the extent of surface coverage of the silica for the surface coverage range Investigated. This suggests that the strands are not randomly spaced on the silica, with Interstrand distance being Influenced only by surface coverage, but are Instead clustered, the clusters having similar distributions of Interstrand distances. Adsorption Is more exothermic for phases of high surface coverages than for low. If interstrand spacing is Independent of surface coverage but surface coverage affects the enthalpy of adsorption, then surface coverage must influence the cluster size, which then Influences the average extent of solvation of a strand of bonded phase.

Investigation of monovalent and bivalent enantioselective molecular recognition by electrospray ionization-mass spectrometry and tandem mass spectrometry

“…These results indicate that the bivalent receptor with a C 6 tether unit possesses the ability to interact with multiple selector sites on the CSP surface simultaneously, thus increasing interaction affinity by a factor of two, and enantioselectivity more than 5-fold. The data successfully demonstrate the concept first illustrated by Pirkle and coworkers, a technique that was used originally to study the distance between selector sites on CSPs [22,23].…”

“…Thus, the study of multivalency effects in the cinchonane-type chiral selector systems were pursued to investigate (1) whether tethering guest enantiomers to create bivalent forms would show increased retention and enantioselectivity in "chiral HPLC" (indicating the use of stationary phases to which is bound the chiral selector 1 for the purpose of differential retention of guest enantiomers), in a similar manner to that reported by Pirkle and coworkers [22,23]; and (2) if mass spectrometric methods can offer complementary information in terms of interaction affinity, selectivity, and energetics of enantioselective multivalent chiral recognition systems.…”

“…Pirkle and coworkers demonstrated this advantage when they studied the inter-functional distance between enantioselective recognition motifs on a chiral stationary phase (CSP) using synthesized bivalent analyte stereoisomers [22,23]. Bis(amide) linked 3,5-dinitrobenzoyl-leucine (DNB-Leu) enantiomers, incorporating a homologous series of spacer units, were chromatographed on N-(2-naphthyl)alanine-derived CSPs.…”

Design of Chromatographic and Electrophoretic Separation Based on Ion-Pair Formation of Aromatic Disulfonates with Polyammonium Ions

“…Table lists the distances between sulfur atoms in ADS molecules and those between nitrogen atoms in PAs. According to the concept of supramolecular chemistry (molecular ruler), the match of span between interacting sites in a host molecule with that in a guest molecule is essential for stable complexation …”

The Reciprocal Principle of Selectand-Selector-Systems in Supramolecular Chromatography †

“…The manner of immobilization, for example, has some bearing upon the efficacy of the chiral recognition process [19]. Thus deviations from the reciprocal principle may arise from the environment of the selector in the stationary phase, e.g., as the result of immobilization and the presence of a spacer linking the selector to a chromatographic matrix [21].…”