Chiral Fluorescence Research Articles

Chiral Conjugated Microporous Polymers as Novel Chiral Fluorescence Sensors for Amino Alcohols

Novel (R)‐(+)‐1,1′‐bi‐2‐naphthol ((R)‐(+)‐BINOL)‐based conjugated microporous polymers (CMP1–4) with high Brunauer–Emmett–Teller (BET) surface area are synthesized through Sonogashira–Hagihara cross‐coupling of di‐/tetra‐bromo‐substituted (R)‐(+)‐BINOL derivatives and 1,3,5‐triethynylbenzene. Fluorescence studies find that CMP4 can act as a sensitive and enantioselective sensor for chiral amino alcohols, such as 2‐amino‐1‐propanol (AA1), 2‐amino‐3‐methyl‐1‐butanol (AA2), and 2‐amino‐2‐phenylethanol (AA3), which expands the application scope of conjugated microporous polymers. image

Chiral anthracene fluorescence system using achiral 1-naphthylmethylamine

A chiral anthracene fluorescence system was developed from achiral 2-anthracenecarboxylic acid and 1-naphthylmethylamine. Although chiral functional organic materials are usually prepared using chiral molecules, in this system, a chiral supramolecular organic fluorophore, which exhibited fluorescence in the solid state, was prepared from achiral molecular components.

A coumarin-based chiral fluorescence sensor for the highly enantioselective recognition of phenylalaninol

A chiral host L1 incorporating (S)-BINOL and substituted coumarin moieties was synthesized via a nucleophilic addition–elimination reaction, and ligand L2 could be obtained by the reduction reaction of the imine-based L1 with NaBH4. The fluorescence responses of chiral compounds L1 and L2 on (L)-/(D)-phenylalaninol were investigated by fluorescence spectra. The fluorescence intensity of L1 in cooperation with (L)-/(D)-phenylalaninol shows a gradual enhancement upon addition of (L)-/(D)-phenylalaninol and keeps a nearly linear correlation with the concentration molar ratios from 1 : 10 to 1 : 180. Stoichiometries and association constants of L1 with (L)-/(D)-phenylalaninol were calculated. The results indicate that chiral sensor L1 can exhibit a remarkable “turn-on” fluorescence enhancement response and excellent enantioselective behaviour for (L)-phenylalaninol by direct visual observation at low concentration, and the value of the enantiomeric fluorescence difference ratio (ef) is 3.07. On the contrary, no obvious fluorescence response and enantioselective recognition effect can be detected for L2 towards either (L)-/(D)-phenylalaninol.

Large stokes shift chiral polymers containing (R,R)-salen-based binuclear boron complex: Synthesis, characterization, and fluorescence properties

Two novel chiral fluorescence polymers P-1 and P-2 incorporating (R,R)-salen-based binuclear boron complex in the main chain backbone were synthesized by (R,R)-salen-based boron complex (M-1) with 9,9-dibutyl-2,7-diethynyl-9H-fluorene (M-2) and 1,4-dibutoxy-2,5-diethynylbenzene (M-3) via Pd-catalyzed Sonogashira coupling reaction, respectively. The chiral polymers were characterized by 1H NMR, UV–vis spectroscopy, photoluminescence (PL), gel permeation chromatography (GPC), TGA, DSC, cyclic voltammetry (CV), and theoretical calculation using density-functional theory (DFT) method. P-1 and P-2 show anisotropic fluorescence property with emission spectral maxima at 474 nm and 514 nm, respectively. Both two chiral polymers can exhibit high fluorescence quantum yields (up to 44% and 52%) with large Stokes shifts over 90 nm. The DFT theoretical calculation of the polymer repeating units indicates that the optical band gaps of P-1 is higher than that of P-2, which was consistent with the CV determination results.

Salen-Based Chiral Fluorescence Polymer Sensor for Enantioselective Recognition of α-Hydroxyl Carboxylic Acids

(R,R)-Salen-based chiral polymer P-1 was synthesized by the polymerization of 5,5'-((2,5-dibutoxy-1,4-phenylene)bis(ethyne-2,1-diyl))bis(2-hydroxy-3-(piperidin-1-ylmethyl) benzaldehyde (M-1) with (1R,2R)-cyclohexane-1,2-diamine (M-2) via nucleophilic addition- elimination reaction, and (R,R)-salan-based polymer P-2 could be obtained by the reduction reaction of P-1 with NaBH(4). (R,R)-Salen-based chiral polymer P-1 can exhibit greater fluorescence enhancement response toward (l)-α-hydroxyl carboxylic acids, and the value of enantiomeric fluorescence difference ratio (ef) can reach as high as 8.41 for mandelic acid and 6.55 for lactic acid. On the contrary, (R,R)-salan-based chiral polymer P-2 shows obvious fluorescence quenching response toward α-hydroxyl carboxylic acids. Most importantly, (R,R)-salen-based polymer P-1 can display bright blue fluorescence color change in the presence of (l)-α-hydroxyl carboxylic acids under a commercially available UV lamp, which can be clearly observed by the naked eyes.

Coumarin-based chiral fluorescence sensor incorporating a thiourea unit for highly enantioselective recognition of N-Boc-protected proline

New coumarin-based chiral thiourea sensor 1 was found to be an enantioselective fluorescent chemosensor for N-Boc-protected proline. The chiral sensor shows lower background fluorescence, and higher fluorescence enhancement with 18 nm blue shifts. Job plot analysis result indicates that sensor 1 can form a 1 : 1 stoichiometric complex and it could be used as a fluorescence sensor for the determination of enantiomer composition of N-Boc-protected proline.

In Situ Evaluation of Kinetic Resolution Catalysts for Nitroaldol by Rationally Designed Fluorescence Probe

Development of effective chemical catalysts is a key concern in organic chemistry. Therefore, convenient screening systems for chemical catalysts are required, and although some fluorescence-based HTS systems have been developed, little attempt has been made to apply them to asymmetric catalysts. Therefore, we tried to develop a chiral fluorescence probe which can evaluate the reactivity and enantioselectivity of asymmetric catalysts. We focused on kinetic resolution catalysts as a target of our novel fluorescence probe, employing β-elimination following acylation of nitroaldol. Once the hydroxyl group of nitroaldol is acylated, β-elimination occurs immediately, affording nitro olefin. Therefore, we designed and synthesized a fluorescence probe with an asymmetric nitroaldol moiety. Its fluorescence intensity decreases dramatically upon β-elimination, so the fluorescence decrease is an indicator of the reaction yield. Thus, the enantioselectivity of kinetic resolution catalysts can be assessed simply by measuring the fluorescence intensities of the reaction mixtures of the two enantiomers; it is not necessary to purify the product. This fluorescence probe revealed that benzotetramisole is a superior catalyst for kinetic resolution of nitroaldol. Furthermore, we established an HTS system for asymmetric catalysts, using a fluorescence probe and benzotetramisole. To our knowledge, this is the first fluorescence-based HTS system for asymmetric catalysts.

Highly enantioselective recognition of a wide range of carboxylic acids based on enantioselectively aggregation-induced emission

A new chiral fluorescence receptor, designed to exploit aggregation-induced emission (AIE), exhibited not only an exceptionally high enantioselectivity but was also applicable to a wide range of chiral carboxylic acids. The fluorescence intensity ratio of two enantiomers ranged from 10 to 1.6 × 10(4) and could be used to determine the purity of the enantiomers.

Metal ion based chiral fluorescence sensor selective for dihydrogenphosphate

A Cu(II) based conformationally restricted chiral fluorescence sensor (receptor 2) has been designed and synthesized for selective sensing of anions. The anion recognition property of the Cu2+-complex has been studied in acetonitrile by fluorescence methods which show remarkable sensitivity toward dihydrogen phosphate via fluorescence modulation of the Cu2+-complex over the other anions examined.

Separation of tyrosine enantiomer derivatives by capillary electrophoresis with light-emitting diode-induced fluorescence detection

Capillary electrophoresis (CE) coupled with fiber-optic light-emitting diode-induced fluorescence detection has been developed for the separation of tyrosine (Tyr) enantiomers. R(−)-4-(3-isothiocyanatopyrrolidin-1-yl)-7-( N, N-dimethylaminosulfonyl)-2,1,3-benzoxadiazole was used as a chiral fluorescence tagged reagent for derivatization of Tyr. The effect of pH, running buffer concentration and applied voltage on enantioselectivity has been investigated. The optimum CE conditions are 15 mmol/L borate running buffer (pH 10.5) and 14-kV applied voltage. Good reproducibility was obtained with coefficient of variation ( n = 7) of migration time and peak area less than 0.2 and 2.0%, respectively. The limits of detection of d- and l-Tyr derivatives were 2.9 and 2.2 μmol/L (S/N = 3), respectively. The proposed method has been successfully applied to the determination of Tyr in a commercial amino acid oral solution.

A Solid-state Chiral Fluorophore Obtained from Achiral Fluorescent Biphenyl-4-carboxylic Acid and rac-Phenylmethylamine Derivatives

Abstract A chiral supramolecular organic fluorophore is developed by using achiral biphenyl-4-carboxylic acid and rac-1-phenylethylamine. This fluorophore is a spontaneously resolved chiral fluorescence system.

Enantioselective Fluorescent Recognition of Amino Alcohol Based on Calix[4]arenes Bearing Diphenylethylenediamine Units

Two novel chiral fluorescence calix[4]arenes functionalized at the lower rim with diphenylethylenediamine and thiourea units were synthesized and examined for their enantioselective recognition abilities by the fluorescence and 1H NMR spectra in DMSO. The results indicate that 1 and 2 both formed a 1:1 complex with amino alcohol and exhibit good enantioselective fluorescent responses for phenylglycinol (receptor 1 K L/K D = 4.85, ΔΔG0 = − 3.90 kJ mol− 1).

Synthesis and Enantioselective Discrimination of Chiral Fluorescence Receptors Bearing Amino Acid Units

AbstractTwo chiral fluorescence receptors (1, 2) were synthesized, and their structures were characterized by IR, 1H NMR, 13C NMR, mass spectra and elemental analysis. The chiral recognition of receptors was studied by 1H NMR and fluorescence spectra. The results demonstrate that receptors and dibenzoyl tartrate anion formed a 1:1 complex. The receptor 1 exhibited a good enantioselective recognition ability toward the enantiomers of dibenzoyl tartrate anion.

Sensitive fluorescent sensors for malate based on calix[4]arene bearing anthracene

Two chiral fluorescence receptors 3a and 3b based on calix[4]arenes were synthesized, and their chiral recognition properties for enantiomeric malate were studied by fluorescence and 1H NMR spectra in CHCl 3. The addition of either l- or d-malate caused obvious fluorescence quenching of the host solution. Different fluorescent responses demonstrate that the two receptors have good enantioselective recognition abilities towards malate.

Novel chiral fluorescent macrocyclic receptors: synthesis and recognition for amino acid anions

New chiral fluorescence macrocycles 1 and 2 containing naphthalene and amino acid units were synthesized. The binding properties for amino acid anions were examined by the fluorescence and 1H NMR spectra. The results indicated good enantioselectivity of 1 toward the N-protected phenylalanine anions.

Enantioselective recognition by optically active chiral fluorescence sensors bearing amino acid units

Chiral fluorescence receptors 1 and 2 were synthesized and their structures characterized by IR, 1H NMR, 13C NMR, MS spectra, and elemental analysis. The chiral recognition abilities of 1 and 2 were studied by 1H NMR and fluorescence spectra. The results demonstrate that receptors 1 and 2 with bis(tetrabutylammonium) dibenzoyl tartrate formed a 1:1 complex. Receptor 2 exhibits an excellent enantioselective recognition ability toward the enantiomers of bis(tetrabutylammonium) dibenzoyl tartrate.

Capillary Electrophoresis for Diastereomers of (R,S)-Tetrahydroisoquinoline-3-Carboxylic Acid Derivatized with (R)-4-Nitro-7-(3-Aminopyrrolidin-1-yl)-2,1,3-Benzoxadiazole: Effect of Molecular Geometries

Diastereomers derived from (R,S)-tetrahydroisoquinoline-3-carboxylic acid (Tic), a potential neurotoxin with a chiral fluorescence tagging reagent, (R)-4-nitro-7-(3-aminopyrrolidin-1-yl)-2,1,3-benzoxadiazole (NBD-APy), are well resolved by capillary electrophoresis (CE). For a better understanding of the separation mechanism, a semiempirical computational method (i.e., AM1 method) is used to study the molecular geometry, relative energy, and size of the derivatives. The molecular sizes are estimated to be 216.3 and 240.6 cm3/mol for (R)-NBD-APy-(R)-Tic and (R)-NBD-APy-(S)-Tic, respectively. The CE elution order of the diastereomeric derivatives confirms the AM1 computational results: (R)-NBD-APy-(R)-Tic elutes before (R)-NBD-APy-(S)-Tic. The effects of running buffer pH and the addition of a chiral selector, beta-cyclodextrin (beta-CD), on the separation are studied. In the presence of beta-CD, the migration behavior of the diastereomers is changed because of the formation of CD inclusion complexes. Study of the space-filling models for optimized conformations of the diastereomeric derivatives and beta-CD suggests that the geometries of the diastereomers decides that the diastereomers are incorporated into the CD cavity to form CD inclusion complexes with different volumes. Experimental results from CE separations conclude the same.

Synthesis and chiral recognition of novel chiral fluorescence receptors bearing 9-anthryl moieties

Two chiral fluorescence receptors 1 and 2 have been synthesized, and their structures characterized by IR, 1H NMR, MS spectra and elemental analysis. The chiral recognition of the receptors was studied by 1H NMR and fluorescence spectra. The results demonstrate that the receptors and tetrabutylammonium mandelate formed a 1:1 complex. Two receptors exhibit good chiral recognition abilities towards the enantiomers of tetrabutylammonium mandelate.

Development of Highly PotentD-Glucosamine-Based Chiral Fluorescent Labeling Reagents and a Microwave-Assisted β-Selective Glycosidation of a Methyl Glycoside Reagent

We synthesized new chiral fluorescence labeling reagents having a 2,3-anthracenedicarboximide group from D-glucosamine, and it was possible to introduce target alcohols at the anomeric positions of the reagents with beta-selectivity by glycosidations. Especially, it was possible to use methyl glycoside reagent as a glycosyl donor with a Lewis acid and microwave irradiation, and it gave selectively beta-glycoside while the reaction without microwave irradiation gave alpha- and beta-mixed glycosides. Those reagents showed very high chiral discrimination ability, and they made it possible to separate the eight stereoisomers of 4,8,12,16-tetramethylheptadecanol by HPLC after derivatizations.

Microenvironmental properties and chiral discrimination abilities of bile salt micelles by fluorescence probe technique.

The microenvironmental properties as well as the chiral discrimination abilities of four kinds of bile salt micelles were investigated by the fluorescence probe technique. A new fluorescence probe, 1,1'-bi-2-naphthol, was exploited to study the aggregation of bile salts, size, micropolarity, and microrigidity of the micelles with or without the presence of inorganic salts. Based on these results, the chiral discrimination abilities of bile salt micelles were further investigated by using (R)- and (S)-1,1'-bi-2-naphthol as chiral fluorescence probes. Different chiral discrimination ability was revealed by fluorescence spectra, fluorescence increase rate, and fluorescence quenching constants. The chiral discrimination mechanism of bile salt micelles was discussed.