Novel methoxypropylimmidazolium β-cyclodextrin for improved enantioseparation of amino acids

Polysaccharides as separation media for the separation of proteins, peptides and stereoisomers of amino acids

Reliable separation of peptides, amino acids and proteins as accurate as possible with the maximum conformation and biological activity is crucial and essential for drug discovery. Polysaccharide, as one of the most abundant natural biopolymers with optical activity on earth, is easy to be functionalized due to lots of hydroxyl groups on glucose units. Over the last few decades, polysaccharide derivatives are gradually employed as effective separation media. The highly-ordered helical structure contributes to complex, diverse molecular recognition ability, allowing polysaccharide derivatives to selectively interact with different analytes. This article reviews the development, application and prospects of polysaccharides as separation media in the separation of proteins, peptides and amino acids in recent years. The chiral molecules mechanism, advantages, limitations, development status and challenges faced by polysaccharides as separation media in molecular recognition are summarized. Meanwhile, the direction of its continued development and future prospects are also discussed.

Supramolecular assembly induced chiral interface for electrochemical recognition of tryptophan enantiomers

The β-CD@PEI-Fc chiral interface was prepared based on the supramolecular host-guest interaction between ferrocene (Fc) grafted polyethyleneimine (PEI-Fc) and chiral β-cyclodextrin (β-CD). SEM results show that β-CD@PEI-Fc interface has a regular spatial structure, which can effectively distinguish tryptophan (Trp) enantiomers. Under the optimal conditions, differential pulse voltammetry shows that the peak current ratio (Id/Il) of Trp enantiomers can reach 2.84 at 15 °C. More interestingly, the β-CD@PEI-Fc/GCE exhibited chiral recognition of d-Trp and l-Trp via water contact angle measurements. There was a good linear relationship between the peak current and the concentration of Trp enantiomers in the range from 0.005 mM to 0.10 mM. Finally, the chiral interface can be applied for quick detection of the proportion of isomers in Trp racemic solution, which is very important for chiral recognition in racemic mixture of chiral compounds. Meanwhile, the β-CD@PEI-Fc/GCE showed good stability and reproducibility.

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.

Fluorescent Thrombin Binding Aptamer-Tagged Nanoparticles for an Efficient and Reversible Control of Thrombin Activity

Progress in understanding and treatment of thrombotic diseases requires new effective methods for the easy, rapid, and reversible control of coagulation processes. In this framework, the use of aptamers, and particularly of the thrombin binding aptamer (TBA), has aroused strong interest, due to its enormous therapeutic potential, associated with a large number of possible applications in biotechnological and bioanalytical fields. Here, we describe a new TBA analogue (named tris-mTBA), carrying three different pendant groups: a dansyl residue at the 3'- and a β-cyclodextrin moiety at the 5'-end-providing a host-guest system which exhibits a marked fluorescence enhancement upon TBA G-quadruplex folding-and a biotin tag, allowing the attachment of the aptamer onto biocompatible streptavidin-coated silica nanoparticles (NPs) of 50 nm hydrodynamic diameter (Sicastar). The use of nanoparticles for the in vivo delivery of TBA, expected to induce per se increased nuclease resistance and improved pharmacokinetic properties of this oligonucleotide, offers as an additional advantage the possibility to exploit multivalency effects, due to the presence of multiple copies of TBA on a single scaffold. In addition, the selected fluorescent system allows monitoring both the presence of TBA on the functionalized NPs and its correct folding upon immobilization, also conferring enhanced enzymatic resistance and bioactivity. The anticoagulant activity of the new tris-mTBA, free or conjugated to Sicastar NPs, was evaluated by dynamic light scattering experiments. Highly effective and reversible inhibition of thrombin activity toward fibrinogen was found for the free tris-mTBA and especially for the tris-mTBA-conjugated NPs, demonstrating great potential for the biomedical control of blood clotting.

Improving the sensitivity in chiral capillary electrophoresis

CE is known for being one of the most powerful analytical techniques when performing enantioseparations due to its numerous advantages such as excellent separation efficiency and extremely low solvents and reagents consumption, all of them derived from the capillary small dimensions. Moreover, it is worth highlighting that unlike in chromatographic techniques, in CE the chiral selector is generally within the separation medium instead of being attached to the separation column which makes the method optimization a more versatile task. Despite its numerous advantages, when using UV-Vis detection, CE lacks of sensitivity detection due to its short optical path length derived from the narrow separation capillary. This issue can be overcome by means of different approaches, either by sample treatment procedures or by in-capillary preconcentration techniques or even by employing detection systems more sensitive than UV-Vis, such as LIF or MS. The present review assembles the latest contributions regarding improvements of sensitivity in chiral CE published from June 2013 until May 2015, which follows the works included in a previous review reported by Sánchez-Hernández et al. [Electrophoresis 2014, 35, 12-27].