Single Isomer N-Heterocyclic Cyclodextrin Derivatives as Chiral Selectors in Capillary Electrophoresis

In order to better understand the chiral recognition mechanisms of positively charged cyclodextrin (CD) derivatives, synthesis, pKa determination by 1H nuclear magnetic resonance (NMR)-pH titration and a comparative capillary electrophoretic (CE) study were performed with two series mono-substituted cationic single isomer CDs. The first selectors mono-(6-N-pyrrolidine-6-deoxy)-β-CD (PYR-β-CD), mono-(6-N-piperidine-6-deoxy)-β-CD (PIP-β-CD), mono-(6-N-morpholine-6-deoxy)-β-CD (MO-β-CD) mono-(6-N-piperazine-6-deoxy)-β-CD (PIPA-β-CD), carrying pH-adjustable moiety at narrower rim cavity, while second set represented their quaternarized, permanently counterparts: mono-(6-N-(N-methyl-pyrrolidine)-6-deoxy)-β-CD (MePYR-β-CD), mono-(6-N-(N-methyl-piperidine)-6-deoxy)-β-CD (MePIP-β-CD), mono-(6-N-(N-methyl-morpholine)-6-deoxy)-β-CD (MeMO-β-CD) mono-(6-N-(4,4-N,N-dimethyl-piperazine)-β-CD (diMePIPA-β-CD). Based on pH-dependent selector concentration-dependent studies these N-heterocyclic CDs presented herein, it can be concluded that all could successfully applied as for enantiodiscrimination several negatively zwitterionic model racemates. substituent-dependent enantiomer migration reversal dansylated-valine using PIP-β-CD contrary PYP-β-CD, MO-β-CD PIPA-β-CD was also studied 1H- 2D ROESY NMR experiments.