Supramolecular assembly induced chiral interface for electrochemical recognition of tryptophan enantiomers

A signal amplification for Trp isomers electrochemical recognition based on PEDOT:PSS and CS/PAA multilayers

In this work, enhanced tryptophan (Trp) isomers recognition was successfully demonstrated on (CS/PAA)3.5@PEDOT:PSS/GCE, a multilayer chiral sensor with good stability and reproducibility. The (CS/PAA)n multilayers chiral interface was first fabricated via alternating self-assembly of chiral chitosan (CS) and achiral polyacrylic acid (PAA). Conductive PEDOT:PSS was then compounded with (CS/PAA)n multilayers to obtain the chiral sensor for the electrochemical recognition of Trp isomers. The structure of the sensor and its chirality properties for Trp isomers were characterized by fourier transform infrared spectroscopy (FT-IR)，scanning electron microscopy (SEM) and electrochemical methods. The SEM images showed uniform distribution of PEDOT:PSS in the multilayer films, which changed the internal structure of the (CS/PAA)3.5. Consequently, (CS/PAA)3.5@PEDOT:PSS multilayers rendered more chiral centers in addition to improved good conductivity, which significantly amplified the oxidation peak current ratio of D-Trp to L-Trp (ID/IL) up to 6.71 at 25 °C. In addition, a linear relationship was observed between the peak current and Trp enantiomer concentration in the range of 0.002-0.15 mM, and the detection limits of D-Trp and L-Trp were 0.33 and 0.67 μM, respectively. More importantly, the percentage of D-Trp in non-racemic Trp enantiomers mixture solutions were successfully determined on the chiral interface, showing its effectiveness and promising potential in practical applications.

Study on Quality Control of Tenofovir Disoproxil Fumarate Enantiomers by High-Performance Liquid Chromatography–Mass Spectrometry

This study aims at developing a high-performance liquid chromatography–mass spectrometry (LC–MS) method to analyze tenofovir disoproxil fumarate (TDF) and its pharmaceutical preparations. Several cyclodextrin mobile-phase additives were applied to reversed-phase and normal-phase chromatography, and the effects of three chiral stationary phases on the TDF separation were investigated in this study. The R-type and S-type of TDF tablets were quantitatively analyzed in the single ion monitoring (SIM) scanning mode with a Unichiral CMD column. This method has been successfully applied to the separation and quantification of TDF and its isomers. The linear ranges of (R)-TDF and (S)-enantiomer were 1–20 and 0.2–16 μg/mL, respectively. The limit of detection for (R)-TDF and (S)-enantiomer was 0.0015 and 0.0012 μg/mL, respectively. (S)-enantiomer was not detected in the formulas from all the seven manufacturers, and the drug content of each took more than 98.5% of the labeled amount, which complies with the regulations. The method shows its advantages on high sensitivity, low detection limit, good practicability, and repeatability. The proposed method may provide a novel platform for separation of TDF enantiomers and quality control of TDF raw materials and preparations.

Chirality Discrimination at Binary Organic|Water Interfaces Monitored by Interfacial Tension Measurements with Preliminary Comparison with Molecular Dynamics Simulations

Chirality discrimination at a binary toluene (organic)/water(aqueous) interface between R- or S-Tol-BINAP (2,2'-Bis(di-p-tolylphosphino)-1,1'-binaphthyl) molecules and the water-soluble serine chiral specie is examined for the first time, using a combination of interfacial tension measurements and molecular dynamic simulations. Experimental interfacial measurements exhibit a clear chirality-controlled difference when a homochiral versus a heterochiral enantiomeric pairs are introduced at the interfaces. The related molecular dynamics simulations support the experimental results and provide further molecular insight of intermolecular interactions at the interfaces. The results indicate that interfacial tension measurements can capture the preferential interactions which exist between different pairs of enantiomers at the binary interfaces, opening up a new way for probing chirality discrimination at liquid-liquid interfaces.