From MonoBINOL to BisBINOL: Expanded Enantioselective Fluorescent Recognition of Amino Acids

Self-Assembled Nanotubes Based on Chiral H8-BINOL Modified with 1,2,3-Triazole to Recognize Bi3+ Efficiently by ICT Mechanism

A novel fluorescent "off" probe R-β-D-1 containing a 1,2,3-triazole moiety was obtained by the Click reaction with azidoglucose using H8-BINOL as a substrate, and the structure was characterized by 1H NMR and 13C NMR and ESI-MS analysis. The fluorescence properties of R-β-D-1 in methanol were investigated, and it was found that R-β-D-1 could be selectively fluorescently quenched by Bi3+ in the recognition of 19 metal ions and basic cations. The recognition process of Bi3+ by R-β-D-1 was also investigated by fluorescence spectroscopy, SEM, AFM, etc. The complex pattern of R-β-D-1 with Bi3+ was determined by Job's curve as 1 + 1, and the binding constant Ka of R-β-D-1 and Bi3+ was valued by the Benesi-Hildebrand equation as 1.01 × 104 M-1, indicating that the binding force of R-β-D-1 and Bi3+ was medium. The lowest detection limit (LOD) of the self-assembled H8-BINOL derivative for Bi3+ was up to 0.065 µM. The mechanism for the recognition of Bi3+ by the sensor R-β-D-1 may be the intramolecular charge transfer effect (ICT), which was attributed to the fact that the N-3 of the triazole readily serves as an electron acceptor while the incorporation of Bi3+ serves as an electron donor, and the two readily undergo coordination leading to the quenching of fluorescence. The recognition mechanism and recognition site could be verified by DFT calculation and CDD (Charge Density Difference).

Synthesis of novel fluorescence probes and their application in the enantioselective recognition of arginine

Arginine (Arg) plays a crucial and multifaceted role in various biological processes, encompassing cell division, wound healing, immune system modulation, and plant signaling. This study introduced a pair of novel chiral fluorescent probes, (R)-5 and (S)-5, constructed upon the BINOL framework, which exhibited enantiomeric selectivity and sensitivity to d-Arg/l-Arg in fluorescence experiments. These probes offered a simple, rapid, low-cost, and highly selective method for detecting Arg enantiomers, thereby providing a highly sensitive approach for their qualitative and quantitative analysis. The enantioselective fluorescence enhancement ratios {ef = [(I1 - I0)/(I2 - I0) = ΔI1/ΔI2]} of (R)-5 and (S)-5 to Arg were 1694 and 5163, respectively. Moreover, the probes demonstrated the capability to detect the concentration of d-Arg and l-Arg with a limit of detection of 4.84 × 10-7 M and 3.35 × 10-7 M, respectively, as well as determine the enantiomeric excess. These probes exhibited high chemical selectivity and enantioselectivity, enabling the identification of different configurations of Arg, quantification of Arg concentrations, and determination of the enantiomeric composition of Arg. This study provides valuable insights for the development of sensitive and selective chiral molecular detection methods, significantly advancing our comprehension of the relationship between Arg concentration and probe fluorescence response.

Enantioselective and Chemoselective Optical Detection of Chiral Organic Compounds without Resorting to Chromatography

Enantiorecognition and resolution are of essential importance in many diverse areas of science. Whenever there arises a need to analyze/investigate enantiomers in different situations chromatography stands up in our minds immediately. Nevertheless, chemoselective and enantioselective recognition/discrimination (without going for separation) constitutes a different perception and requirement. The techniques using chiroptical sensing cause detection based on molecular interactions induced in different manners. Enantioselective sensing of monosaccharides in γ-cyclodextrin assembly and by diboronic acid based fluorescent sensors, application of bi-naphthol and H8 BINOL based sensors and dendrimers, metal-to-ligand charge transfer transitions in CD, exciton-coupled circular dichroism, surface enhanced Raman spectroscopy, and enantioselective indicator displacement sensor arrays for enantioselective recognition/detection of chiral organic compounds, such as amines, amino acids/alcohols, and hydroxycarboxylic acids have been discussed in progressive manner with mechanistic explanations, wherever available. Besides, the chiroptical vs LC approach has been discussed. The present paper is focused on certain different non-chromatographic optical techniques and aims to extend an understanding and a view to consider such techniques which have been successful in selective detection, and determination of absolute configuration and enantiomeric excess, (without resorting to separation vis-à-vis LC) and that have potential use in high-throughput chiral assay and combinatorial search for asymmetric catalysts and reagents.

Effective enantioselective recognition by steady-state fluorescence spectroscopy: Towards a paradigm shift to optical sensors with unusual chemical architecture

A series of amino acid-derived 1,2,3-triazoles presenting the amino acid residue and the benzazole fluorophore connected by a triazole-4-carboxylate spacer was studied for enantioselective recognition using only steady-state fluorescence spectroscopy in solution. In this investigation, the optical sensing was performed with D-(-) and L-(+)-Arabinose and (R)-(-) and (S)-(+)-Mandelic acid as chiral analytes. The optical sensors showed specific interactions with each pair of enantiomers, allowing photophysical responses, which were used for their enantioselective recognition. DFT calculations confirm the specific interaction between the fluorophores and the analytes corroborating the observed high enantioselectivity of these compounds with the studied enantiomers. Finally, this study investigated nontrivial sensors for chiral molecules by a mechanism different than turn-on fluorescence and has the potential to broad chiral compounds with fluorophoric units as optical sensors for enantioselective sensing.

Synthesis of amylose and cellulose derivatives bearing bulky pendants for high-efficient chiral fluorescent sensing

Three novel amylose and cellulose phenylcarbamate derivatives bearing bulky para-substituted benzothienyl or benzofuranyl pendants were successfully synthesized as chiral fluorescent sensors through carbamoylation followed by Suzuki-Miyaura coupling reactions. The bulky derivatives showed good enantioselective fluorescent sensing properties toward a total of eight chiral quenchers in this study. Especially, a high enantiomeric fluorescence difference ratio (ef = 164.35) was achieved on amylose benzofuranylphenylcarbamates (Amy-2) to the 3-amino-3-phenylpropan-1-ol (Q5), an important chiral drug intermediate. It indicated that a favorable chiral environment was effectively constructed by arrangement of bulky π-conjugated benzothienyl or benzofuranyl pendants on the phenylcarbamate moieties surrounding the helical backbone, which is crucial for high-efficient chiral fluorescent sensing. As chiral stationary phases for high-performance liquid chromatography, the bulky benzothienylphenylcarbamates of amylose and cellulose also showed good resolution powers to thirteen racemates, including metal tris(acetylacetonate) complexes, chiral drugs, analytes with axial chirality and chiral aromatic amines, which were difficult to be efficiently separated even on the popular Chiralpak AD and Chiralcel OD. The excitation-dependent chiral fluorescent sensing probably followed different mechanisms from that for chromatographic enantioseparation relying on the dynamic collision of molecules in the ground state. The structure of the bulky derivatives was also investigated by CD spectra and POM microscopy.

Enantioselective Recognition of Lysine and Phenylalanine Using an Imidazole Salt-Type Fluorescent Probe Based on H8-BINOL

An imidazole bromide fluorescent probe (R)-1 based on chiral H₈-BINOL was synthesized with a high yield; it was found to have good enantioselective recognition of lysine and phenylalanine using fluorescence analysis. When L-lysine was recognized, the enantioselective fluorescence enhancement ratio was 2.7 (ef = I_L - I₀/I_D - I₀, ef = 2.7, 20 eq Lys); as the amount of L-Lys increased, a distinct red shift was observed (the wavelength varied by 55.6 nm, 0-100 eq L-Lys), whereas D-Lys had a minimal red shift. The generation of this red shift phenomenon was probably due to the ICT effect; the probe's intramolecular charge transfer was affected after (R)-1 bound to L-Lys, and this charge transfer was enhanced, leading to a red shift in fluorescence. In addition to the enantioselective recognition of lysine, phenylalanine was also recognized; the enantioselective fluorescence enhancement ratio was 5.1 (ef = I_L - I₀/I_D - I₀, ef = 5.1, 20 eq Phe).

Biomimetic Self-Assembled Chiral Inorganic Nanomaterials: A New Strategy for Solving Medical Problems

The rapid expansion of the study of chiral inorganic structures has led to the extension of the functional boundaries of inorganic materials. Nature-inspired self-assembled chiral inorganic structures exhibit diverse morphologies due to their high assembly efficiency and controlled assembly process, and they exhibit superior inherent properties such as mechanical properties, chiral optical activity, and chiral fluorescence. Although chiral self-assembled inorganic structures are becoming more mature in chiral catalysis and chiral optical regulation, biomedical research is still in its infancy. In this paper, various forms of chiral self-assembled inorganic structures are summarized, which provides a structural starting point for various applications of chiral self-assembly inorganic structures in biomedical fields. Based on the few existing research statuses and mechanism discussions on the chiral self-assembled materials-mediated regulation of cell behavior, molecular probes, and tumor therapy, this paper provides guidance for future chiral self-assembled structures to solve the same or similar medical problems. In the field of chiral photonics, chiral self-assembled structures exhibit a chirality-induced selection effect, while selectivity is exhibited by chiral isomers in the medical field. It is worth considering whether there is some correspondence or juxtaposition between these phenomena. Future chiral self-assembled structures in medicine will focus on the precise treatment of tumors, induction of soft and hard tissue regeneration, explanation of the biochemical mechanisms and processes of its medical effects, and improvement of related theories.

Visualization of Enantiorecognition and Resolution by Chiral AIEgens

Enantioselective recognition and separation have attracted much attention in pharmaceutical analysis, food chemistry, and life science. Herein, we propose an efficient strategy to achieve such purposes using optically active luminogens with aggregation-induced emission (AIE) characteristics. These AIE luminogens (AIEgens) show strong enantiomeric discrimination for 12 kinds of chiral acids and unprotected amino acids. In particular, an exceptionally high enantioselectivity for d/l-Boc-glutamic acid was observed, as demonstrated by the large difference between the formed AIEgen/acid complexes. Due to the AIE effect, enantioselective separation was achieved by aggregation of the AIEgens with one enantiomer in the mixed acid solution. Through analysis of the fluorescence standard curve, the aggregates of AIEgen/chiral acid possessed 90% d-analyte, from which the enantiomeric excess (ee) value was assessed to be 80% ee. Such a result is in good agreement with that (91% d-analyte and 82% ee) by chiral HPLC analysis. Thus, this simple one-step aggregation method can serve as a preliminary screening tool for high-throughput analysis or separation of chiral chemicals.

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.

Enantioselective recognition of chiral acids by supramolecular interactions with chiral AIEgens

Novel chiral AIEgens bearing optically pure amino groups were synthesized and showed excellent discrimination for a series of chiral acidic compounds and amino acids. Interestingly, after supramolecular assembly with 4-sulfocalix[4]arene, the obtained complexes showed enhanced enantioselectivity for chiral acids.