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

Exploring inclusion complexes of cyclodextrins with quinolinone based gastro protective drug for enhancing bioavailability and sustained dischargement

Solid rebamipide based inclusion complexes were achieved by freeze-dry method and characterized by FTIR, UV–visible, 1H-NMR, 2D-ROESY, fluorescence spectroscopy, SEM and conductance. The enzyme substituted emission spectrum of the two comparative inclusion complexes with β-cyclodextrin (β-CD) and HP-β-CD in the diverse solvent systems determined the controlled release of the drug were the mid of interest. Amylase increased the stability of the inclusion complexation, proved that if it is taken together with the inclusion complex, the effectiveness and impact of the inclusion complexes will have a prolonged effect in the body. It could significantly improve the bioavailability of rebamipide.

Linkage of α-cyclodextrin-terminated poly(dimethylsiloxanes) by inclusion of quasi bifunctional ferrocene

We report the noncovalent linkage of terminally substituted oligo(dimethylsiloxanes) bearing α-cyclodextrins (α-CD) as host end groups for the cyclopentadienyl rings of ferrocene. This double complexation of unsubstituted ferrocene leads to a supramolecuar formation of the siloxane strands. Structural characterization was performed by the use of 1H NMR and IR spectroscopy and by mass spectrometry. Electron microscopy studies and dynamic light scattering measurements show a significant decrease of the derivative size after the complexation with ferrocene. In addition, further evidence for the successful complexation of the end groups was verified by the shifts of the protons in the 1H NMR spectra and in the correlation signals of the 2D ROESY NMR spectra.

Binding of Coumarin 334 withβ-Cyclodextrin and with C-Hexylpyrogallol[4]arene: Opposite Fluorescence Behavior

We report here the structure of the host-guest complexes of Coumarin 334 (C334) withβ-cyclodextrin (β-CD) and with C-hexylpyrogallol[4]arene (C-HPA) and the effect of acidity on the neutral-cation equilibrium of C334 in water and in the presence of the host molecules. The structures of the host-guest complexes are proposed on the basis of the change of fluorescence on the addition ofβ-CD or C-HPA to C334 and by 2D ROESY spectroscopy. Opposite fluorescence behaviors, that is, quenching of fluorescence inβ-CD and enhancement of fluorescence in C-HPA are observed. Time-resolved fluorescence analysis is done for the complexation, and biexponential decay pattern is observed. The possible strong inclusion complexation with C-HPA is explained. The ground and the excited statepKavalues for the protonation equilibrium of C334 in water and the difficulty of protonation in the presence of the host molecules are discussed.

Synthesis and 2D NMR characterization of Ni(II), Pd(II), and Cu(II) complexes with H2cdsalen (methyl-2{N-[2-(2′-hydroxyphenyl)methylidenenitrilo]ethyl}amino-1-cyclopentenedithiocarboxylate)

In this study we report on the preparation of Ni(II), Pd(II), Co(II), and Cu(II) complexes with H2cdsalen (methyl-2{N-[2-(2′-hydroxyphenyl)methylidenenitrilo]ethyl}amino-1-cyclopentenedithiocarboxylate)salicylaldehyde. The products were characterized using 1D NMR (1H and 13C) and 2D NMR (COSY, NOESY, and ROESY) techniques. The conformational studies of the complexes with Ni and Pd in solution have been performed with help of the nuclear Overhauser effect (NOE) and 2D ROESY experiments.