Chiral Chemosensors Research Articles

Chiral Mechanically Interlocked Molecules – Applications of Rotaxanes, Catenanes and Molecular Knots in Stereoselective Chemosensing and Catalysis

Interlocked molecules, such as rotaxanes, catenanes, and molecular knots, offer conceptually new possibilities for the generation of chiral chemosensors and catalysts. Due to the presence of the mechanical or topological bond, interlocked molecules can be used to design functional systems with unprecedented features, such as switchability and deep binding cavities. In addition, classical elements of chirality can be supplemented with mechanical or topological chirality, which have so far only scarcely been employed as sources of chirality for stereoselective applications. This minireview discusses recent examples in this emerging area, showing that the application of chiral interlocked molecules in sensing and catalysis offers many fascinating opportunities for future research.1 Introduction2 Interlocked Molecules with Chiral Subcomponents2.1 Point Chirality2.2 Axial Chirality3 Mechanically Chiral Interlocked Molecules4 Topologically Chiral Interlocked Molecules5 Outlook

A Chiral Recognition System Orchestrated by Self‐Assembly: Molecular Chirality, Self‐Assembly Morphology, and Fluorescence Response

AbstractThe newly developed oligophenylenevinylene (OPV)‐based fluorescent (FL) chiral chemosensor (OPV‐Me) for the representative enantiomeric guest, 1,2‐cyclohexanedicarboxylic acid (1,2‐CHDA: RR‐ and SS‐form) showed the high chiral discrimination ability, resulting in the different aggregation modes of OPV‐Me self‐assembly: RR‐CHDA directed the fibrous supramolecular aggregate, whereas SS‐CHDA directed the finite aggregate. The consequent FL intensity toward RR‐CHDA was up to 30 times larger than that toward SS‐CHDA. Accordingly, highly enantioselective recognition was achieved. Application to the chirality sensing was also possible: OPV‐Me exhibited a linear relationship between the FL intensity and the enantiomeric excess through the morphological development of stereocomplex aggregates. These results clearly show that the chiral recognition ability is manifested by the amplification cascade of the chirality difference through self‐assembly.

A Chiral Recognition System Orchestrated by Self-Assembly: Molecular Chirality, Self-Assembly Morphology, and Fluorescence Response.

The newly developed oligophenylenevinylene (OPV)-based fluorescent (FL) chiral chemosensor (OPV-Me) for the representative enantiomeric guest, 1,2-cyclohexanedicarboxylic acid (1,2-CHDA: RR- and SS-form) showed the high chiral discrimination ability, resulting in the different aggregation modes of OPV-Me self-assembly: RR-CHDA directed the fibrous supramolecular aggregate, whereas SS-CHDA directed the finite aggregate. The consequent FL intensity toward RR-CHDA was up to 30 times larger than that toward SS-CHDA. Accordingly, highly enantioselective recognition was achieved. Application to the chirality sensing was also possible: OPV-Me exhibited a linear relationship between the FL intensity and the enantiomeric excess through the morphological development of stereocomplex aggregates. These results clearly show that the chiral recognition ability is manifested by the amplification cascade of the chirality difference through self-assembly.

Simultaneous chirality sensing of multiple amines by (19)F NMR.

The rapid detection and differentiation of chiral compounds is important to synthetic, medicinal, and biological chemistry. Palladium complexes with chiral pincer ligands are demonstrated to have utility in determining the chirality of various amines. The binding of enantiomeric amines induces distinct (19)F NMR shifts of the fluorine atoms appended on the ligand that defines a chiral environment around palladium. It is further demonstrated that this method has the ability to evaluate the enantiomeric composition and discriminate between enantiomers with chiral centers several carbons away from the binding site. The wide detection window provided by optimized chiral chemosensors allows the simultaneous identification of as many as 12 chiral amines. The extraordinary discriminating ability of this method is demonstrated by the resolution of chiral aliphatic amines that are difficult to separate using chiral chromatography.

Anthracene-labeled pyridinium-based symmetrical chiral chemosensor for enantioselective recognition of l-tartrate

A new anthracene-based chiral chemosensor 1 has been designed and synthesized. l-Valine has been used as the chiral source in the design. The chemosensor 1 has been established as an efficient enantioselective sensor for l-tartrate. While in the presence of l-tartrate the fluorescent sensor 1 in DMSO exhibits considerable increase in emission, the isomeric tartrate brings relatively small change. The enantiomeric fluorescence difference ratio (ef) has been determined to be 29.38.

A fluorescent chiral chemosensor for the recognition of the two enantiomers of chiral carboxylates

A new 7-nitrobenz-2-oxa-1,3-diazole (NBD)-based fluorescent chiral chemosensor (NBD-1) was prepared and applied to the recognition of the two enantiomers of the tetrabutylammonium salts of N-t-Boc-α-amino acids and chiral carboxylic acids including naproxen. In particular, the chiral recognition by the new fluorescent chiral chemosensor for the two enantiomers of N-t-Boc-threonine (tetrabutylammonium salt) was quite excellent, the Stern-Volmer constant ratio (K(D)/K(L)) for the two enantiomers being as high as 4.89.

Enantioselective Recognition of Tartaric Acids with Ethynylated Carbazole-Based Chiral Bisboronic Acid Chemosensors with Improved Response at Acidic pH

Chiral bisboronic acid chemosensors based on ethynylated carbazole were prepared. The chiral chemosensors show red-shifted emission than the chemosensors with unsubstituted carbazole fluorophore. a-PET effect was found for the chemosensors, which is different from our previous observation of the d-PET effect for boronic acid chemosensors based on carbazole. Enantioselective recognition of tartaric acids was implicated with these chemosensors. Consecutive fluorescence emission enhancement/diminishment were observed with increasing the concentration of the tartaric acids, which is tentatively assigned to the transition of the binding stoichiometry from 1:1 binding to 1:2 binding. In particularly interesting is the improved fluorescence response at acidic pH for recognition of tartaric acids, which is rarely observed for a-PET chemosensors. We propose that the sensing is due to hybrid mechanism of a-PET/d-PET and conformational restriction upon binding. Our results will be useful for design of chiral boronic acid chemosensors with improved fluorescence response at acidic pH, which are rarely reported.

Colorimetric detection of achiral anions and chiral carboxylates by a chiral thiourea—phthalimide dyad

The chiral chemosensor 1, based on a thiourea-activated phthalimide, is available by four reaction steps from 4-nitrophthalimide. 1 detects fluoride, chloride, acetate, and dihydrogen phosphate anions by changes in UV-vis absorption. Fluoride in excess induces deprotonation whereas the other anions show only complex formation in the ground state. (1)H-NMR studies confirm the formation of these H-bonded complexes and the fluoride-induced receptor deprotonation in the recognition process. Moderate chiral recognition was observed for sodium D/L-lactate with K(ass)(D)/K(ass)(L) = 1.93.

Novel chiral fluorescent chemosensors for malate and acidic amino acids based on two-arm thiourea and amide

The charge neutral anthracene based chiral fluorescent receptors 4a and 4b containing thiourea and amide groups were synthesized by simple steps in good yields, and their enantioselective recognition for chiral dicarboxylic anions (L/D-malate, L/D-aspartate, and L/D-glutamate) were examined by UV–vis, fluorescence, and 1H NMR spectroscopy. The sensor 4a exhibited an excellent enantioselective recognition ability towards malate (Kass (L)/Kass (D) = 9.65).Key words: enantioselective recognition, chiral chemosensor, fluorescence, malate.

Enantioselective Analysis of an Asymmetric Reaction Using a Chiral Fluorosensor

An axially chiral 1,8-dipyridylnaphthalene N,N'-dioxide has been employed in enantioselective fluorescence analysis of the enzymatic kinetic resolution of trans-1,2-diaminocyclohexane. The procedure eliminates cumbersome purification and derivatization steps required by traditional methods. The results demonstrate the potential of fluorescence spectroscopy using suitable chiral chemosensors for real-time analysis of the enantiomeric composition of chiral compounds and for high-throughput screening of asymmetric reactions. [structure: see text]

Amidine-based molecularly imprinted polymers-new sensitive elements for chiral chemosensors.

Using the optical measurement technique reflectometric interference spectroscopy (RIfS), the interaction of molecularly imprinted polymers (imprinted with either (R, R)- or (S, S)-2,3-di- O-benzoyltartraric acid) with the corresponding templates and template antipodes were investigated. With these sensors chiral separation with a separation factor of 1.2 could be achieved whereas a reference polymer resulted in no separation. RIfS signals were of opposite sign for imprinted polymer layers containing phenylboronic acid binding site monomers.