Enantioselective recognition of chiral acids by supramolecular interactions with chiral AIEgens

Enantioselective Fluorescence Recognition of Free α-Amino Acids by Ion-Type Ammonium Salt-Based Sensors

Optically pure amino acids have extensive applications in pharmaceuticals, pesticides, food, materials, and other fields. Enantiomers recognition of chiral amino acids using optical methods with synthetic chiral sensors has attracted extensive attention. Most reported sensors typically identify guests by covalent or hydrogen bonding or hydrophobic interaction with amino acids and their derivatives. In this paper, a series of ion-type quaternary ammonium salt-based enantioselective fluorescent sensors were synthesized for chiral recognition of free α-amino acids via electrostatic interaction. The fluorescence intensity ratios ID/IL (ID, IL, fluorescence intensity of sensor when treated with D- or L-amino acid) were up to 2.1 and enantioselective fluorescence enhancement ratios ef (ef=[IL-I0]/[ID-I0] or [ID-I0]/[IL-I0]. (I0, fluorescence intensity of the sensor)) were up to 5.0. Among them, sensor 3 showed best enantioselective recognition performance toward tryptophan (Trp), and L-Trp significantly quenched the fluorescence of sensor 3, but D-Trp greatly enhanced the fluorescence of sensor 3, its ID/IL was 2.11 and ef was 1.8. The mechanistic investigation by NMR spectrum revealed that a tight three-point interaction, including electrostatic interaction, hydrogen bond, and π-π stacking, between sensor 3 and D-Trp was formed.

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.

Light-triggered Modulation of Supramolecular Chirality

Dynamically controlling the supramolecular chirality is of great significance in development of functional chiral materials, which is thus essential for the specific function implementation. As an external energy input, light is remote and accurate for modulating chiral assemblies. In non-polarized light control, some photochemically reactive units (e. g., azobenzene, ɑ-cyanostilbene, spiropyran, anthracene) or photo-induced directionally rotating molecular motors were designed to drive chiral transfer or amplification. Besides, photoexcitation induced assembly based physical approach was also explored recently to regulate supramolecular chirality beyond photochemical reactions. In addition, circularly polarized light was applied to induce asymmetric arrangement of organic molecules and asymmetric photochemical synthesis of inorganic metallic nanostructures, in which both wavelength and handedness of circularly polarized light have effects on the induced supramolecular chirality. Although light-triggered chiral assemblies have been widely applied in photoelectric materials, biomedical fields, soft actuator, chiral catalysis and chiral sensing, there is a lack of systematic review on this topic. In this review, we summarized the recent studies and perspectives in the constructions and applications of light-responsive chiral assembled systems, aiming to provide better knowledge for the development of multifunctional chiral nanomaterials.

Enantioselective determination of chiral acids and amino acids by chiral receptors with aggregation-induced emissions

The chiral AIEgens showed satisfying enantiomer discrimination not only for amino acids but also for chiral acids.