Facile synthesis of positively charged monosubstituted α- and γ-cyclodextrins for chiral resolution of anionic racemates

Mono-6-Substituted Cyclodextrins-Synthesis and Applications

Cyclodextrins are well known supramolecular hosts used in a wide range of applications. Monosubstitution of native cyclodextrins in the position C-6 of a glucose unit represents the simplest method how to achieve covalent binding of a well-defined host unit into the more complicated systems. These derivatives are relatively easy to prepare; that is why the number of publications describing their preparations exceeds 1400, and the reported synthetic methods are often very similar. Nevertheless, it might be very demanding to decide which of the published methods is the best one for the intended purpose. In the review, we aim to present only the most useful and well-described methods for preparing different types of mono-6-substituted derivatives. We also discuss the common problems encountered during their syntheses and suggest their optimal solutions.

Single isomer cyclodextrins as chiral selectors in capillary electrophoresis

Since decades, cyclodextrins are one of the most powerful selectors in chiral capillary electrophoresis for the enantioseparation of diverse organic compounds. This review concerns papers published over the last decade (from 2009 until nowadays), dealing with the capillary electrophoretic application of single isomer cyclodextrin derivatives in chiral separations. Following a brief overview of their synthetic approaches, the inventory of the neutral, negatively and positively charged (including both permanently ionic and pH-tunable ionizable substituents) and zwitterionic CD derivatives is presented, with insights to underlying structural aspects by NMR spectroscopy and molecular modeling. CE represents an ideal tool to study the weak, non-covalent supramolecular interactions. The published methods are reviewed in the light of enantioselectivity, enantiomer migration order and the fine-tuning of enantiodiscrimination by the substitution pattern of the single entity selector molecules, which is hardly possible for their randomly substituted counterparts. All the reviewed publications herein support that cyclodextrin-based chiral capillary electrophoresis seems to remain a popular choice in pharmaceutical and biomedical analysis.

Properties of cationic monosubstituted tetraalkylammonium cyclodextrin derivatives - their stability, complexation ability in solution or when deposited on solid anionic surface

The thermal stability of the monosubstituted cationic cyclodextrin (CD) derivatives PEMEDA-β-CD and PEMPDA-β-CD, which differ in their substituent linker length (ethylene and propylene, respectively), was studied via ¹H NMR experiments. PEMPDA-β-CD exhibited higher resistance towards the Hofmann degradation and was chosen as a more suitable host molecule for further studies. Inclusion properties of PEMPDA-β-CD in solution with a series of simple aromatic guests (salicylic acid, p-methoxyphenol and p-nitroaniline) were determined by isothermal titration calorimetry (ITC) and compared to the native β-CD. Permanently charged cationic CD derivatives were successfully deposited on the anionic solid surface of polymeric Nafion^® 117 membrane via electrostatic interactions. Deposition kinetics and coverage of the surface were determined by ELSD. Finally, the ability of the CD derivatives bound to the solid surface to encapsulate aromatic compounds from aqueous solution was measured by UV–vis spectroscopy. The obtained results are promising for future industrial applications of the monosubstituted β-CD derivatives, because the preparation of cationic CD derivatives is applicable in large scale, without the need of chromatographic purification. Their ionic deposition on a solid surface is simple, yet robust and a straightforward process as well.

Revisit to imidazolium receptors for the recognition of anions: highlighted research during 2006-2009

In this tutorial review we discuss imidazolium receptors for anion recognition and recent contributions between 2006-2009 are reviewed according to target analytes, such as ATP and DNA, as well as structural classification, including cage type imidazoliums, imidazolium calixarenes, ferrocenyl imidazoliums, chiral systems, fluorescent or colorimetric imidazoliums, imidazolium cyclophane, nano assembled structures, bile acid-imidazolium, and tripodal-imidazolium systems.

Selectively functionalized cyclodextrins and their metal complexes

Cyclodextrins (CDs) are cyclic oligomers of alpha-1,4-linked D-glucopyranose. Due to their unique structure, marked by a chiral and hydrophobic cavity, CDs have been extensively used as chiral selectors and drug delivery systems. The functionalization both improve the CD applications and widen their use in many other fields, such as molecular recognition and enzyme mimicking. Moreover, the functionalization highly increases the metal binding properties of the CDs. This critical review is a report of recent applications concerning the CD derivatives and their metal complexes. The metal ion assists the host-guest interaction often increasing the properties of CDs to act as chiral receptors. Furthermore, it can act as a catalytic center in the mimicking of metalloenzymes based on functionalized CDs (164 references).