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.     

Preparation of a metal–ligand fluorescent chemosensor and enantioselective recognition of carboxylate anions in aqueous solution

Two chiral fluorescent chemosensors 1 and 2 were synthesized, and the structure characterized by IR, ¹H NMR, ¹³C NMR, MS spectra and elemental analysis. Their recognition ability was studied in aqueous solution (Tris–HCl buffer pH 7.4, MeOH/H₂O = 1:1) through fluorescence spectra. Receptors 1 and 2 showed a good binding ability to the copper ion. The host 1-Cu²⁺ complex showed a chiral recognition ability to mandelate anions with a preferable binding to l-mandelate than d-mandelate anions. The host 1-Cu²⁺ complex and l- or d-mandelate anions formed 1:1 stoichiometric complex. The binding constant for l-mandelate is 576 M⁻¹, whereas that for d-mandelate is only 38 M⁻¹, which can be distinguished by the different change of fluorescence intensity.     

基于(R)-1,1’-联萘硫脲的手性荧光受体: 合成与手性识别

Two chiral fluorescent receptors 1 and 2 based on (R)-1,1‘-binaphthylene-2,2‘-bisthiourea were synthesized, and their chiral recognition properties for enantiomeric mandelate anions were studied by fluorescence spectra and molecular modeling. Addition of the L- and D-mandelate anions caused considerable fluorescent increases in the fluorescent intensity of the host solution. The L-enantiomer can enhance the fluorescence intensity of 1 much more than the D-enantiomer can do, and 1 shows a better enantioselective recognition ability than 2.     

Fluorescent enantioselective receptor for S-mandelate anion based on cholic acid

A chiral fluorescent receptor 1 based on cholic acid was designed and synthesized. The enantioselective recognition ability of 1 to mandelate anion was studied by the fluorescence in CH₃CN and a ¹H NMR spectroscopic method. The results indicate that 1 exhibited a good enantioselectivity to the enantiomer of the mandelate anion in CH₃CN.     

Convenient synthesis and anion recognition properties of N-flurobenzoyl-N′-phenylthioureas in water-containing media

Novel artificial anionic receptors N-flurobenzoyl-N′-phenylthioureas were synthesized by simple steps in good yields. The binding properties for anions of these N-flurobenzoyl-N′-phenylthioureas and 2N-benzoyl-N′-phenyl thiourea were examined by UV-vis and ¹H NMR spectroscopy. By fluorination of the benzoyl chromophore, the receptors had higher binding affinity for tested anions than the receptor 2. Especially, we studied the anion binding efficiency of the receptors 1N-(3-flurobenzoyl)-N′-phenylthiourea and 2 in dimethyl and dimethyl sulfoxide-water binary solutions in detail respectively. In pure dimethyl sulfoxide, the receptors 1 and 2 had higher binding affinity for F⁻ over AcO⁻. However, as the ratio of water to dimethyl sulfoxide increases, we found the binding properties for tested anions of 1 and 2 changed in dimethyl sulfoxide-water binary solutions. The receptor 1 showed high binding affinity and selective ability for AcO⁻ in dimethyl sulfoxide containing water with varied ratios.     

The anion recognition properties of Schiff base or its reductive system based on 2,2′-bipyridine derivatives

Two novel artificial receptors, 2,2′-bipyridine derivatives containing phenol group, have been designed and synthesized. The interaction of the receptors containing Schiff base or its reductive system with biologically important anions was determined by UV–vis and ¹H NMR titration experiments. Results indicate that receptors 1 and 2 show the strong binding ability for dihydrogen phosphate (H₂PO₄⁻), fluoride (F⁻), acetate (AcO⁻) and almost no binding ability for chloride (Cl⁻), bromide (Br⁻), iodide (I⁻). At the same time, the strongest binding ability of receptor 1 for H₂PO₄⁻ among studied anions is not influenced by the existence of other anions; as well as receptor 2 for F⁻. In addition, the binding ability of receptor 1 (Schiff base system) with various anions is stronger than that of receptor 2 (the reductive Schiff base system) due to the difference of electronic effect.     

Development of colorimetric receptors for selective discrimination between isomeric dicarboxylate anions

Three new chromogenic receptors (1, 2, and 3) containing p-nitrophenyl or p-nitronaphthyl group appended to the thiourea units or containing p-nitrophenyl group appended to the urea moiety were synthesized and characterized. Upon addition of a series of isomeric dicarboxylate anions to receptor 1 in DMSO/H₂O (80:20 v/v), the appearance of the solution of receptor 1 with maleate or phthalate showed color changes from blue to green or blue to dark-green, respectively, which those can be detected by naked eye at parts per million. Similar experiments were repeated using 2, the solution showed a distinct color change from blue to pink only when 2 is formed as a complex with maleate. Whereas, the addition of the same isomeric dicarboxylate anions to receptor 3, did not induce any color change. Thus, for unique color change, both receptors 1 and 2 can act as optical chemosensors for recognition of maleate versus fumarate. In addition, the receptor 1 can also be a colorimetric receptor for selective discrimination between aromatic isomeric dicarboxylate anions.     

Enantioselective fluorescent sensor for dibenzoyl tartrate anion based on chiral binaphthyl derivatives bearing an amino acid unit

The fluorescent photoinduced electron transfer (PET) chemosensors 1–3 based on (S)-1,1′-bi-2-naphthol were designed for their recognition of dibenzoyl tartrate anions. The binding properties for hydroxy acid anions were examined by the fluorescence and ¹H NMR spectra. The results indicated that receptor 1 exhibit excellent enantioselectivity toward the enantiomers of dibenzoyl tartrate anion.     

Synthesis of colorimetric receptors for dicarboxylate anions: a unique color change for malonate

Three new chromogenic receptors (1, 2, and 3) containing p-nitrophenyl or p-nitronaphthyl or methyl groups appended to the thiourea groups were synthesized and characterized. Upon addition of a series of dicarboxylate anions to receptor 1 in DMSO, only the appearance of the solution of receptor 1 with malonate showed a color change from blue to yellow which can be detected by the naked eye at parts per million. With the addition of the series of dicarboxylate anions to receptor 2, the solutions showed an indistinct intense dark-red color. Whereas the addition of the same dicarboxylate anions to receptor 3, the solutions did not induce any color change. Thus, for the unique color change, the receptor 1 can act as an optical chemosensor for the malonate anion even in the presence of other dicarboxylate anions.     

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.     

Amino alcohol based chiral solvating agents: synthesis and applications in the NMR enantiodiscrimination of carboxylic acids

Four optically active amino alcohols were synthesized via the ring opening of (R)-N-(2,3-epoxypropyl)phthalimide with (R)-2-phenyl glycinol, (1R,2S)-cis-1-amino-2-indanol, (R)-2-amino-1-butanol and (S)-phenyl ethylamine in 73-93% yields. The enantioselective recognition of these receptors towards the enantiomers of racemic carboxylic acids was studied by ¹H NMR spectroscopy. The molar ratio and the association constants of the chiral compounds with each of the enantiomers of the guests were determined by using Job plots and a non-linear least-squares fitting method, respectively. Large non-equivalent chemical shifts (up to 30.0 Hz) can be achieved in the presence of chiral amino alcohols 2 and 5. Amongst the chiral receptors used, compound 5 was found to be the best chiral shift reagent, and was effective in the determination of the enantiomeric excess of chiral carboxylic acids.     

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.     

Fluorescent sensors for amino acid anions based on calix[4]arenes bearing two dansyl groups

Two novel types of chiral calix[4]arenes containing hydrazide and dansyl groups were synthesized and examined for their enantioselective recognition abilities by the fluorescence and ¹H NMR spectra in CHCl₃. The results indicate that both 4a and 4b have excellent enantioselectivities to the N-protected alanine or phenylalanine anions.     

Ni(dmit)2 salts with chiral stilbazolium- and ferrocenyl-based chromophores as countercations

Four 1:1, two-component salts combining the [Ni(dmit)₂]⁻ anion (dmit²⁻ = 2-thioxo-1,3-dithiole-4,5-dithiolato) and chiral stilbazolium-based countercations (HPMS⁺ = 4′-[2-(hydroxymethyl)pyrrolidinyl]-1-methylstilbazolium and MPMS⁺ = 4′-[2-(methoxy-methyl)pyrrolidinyl]-1-methylstilbazolium), or chiral ferrocenyl-based countercations (2⁺ = (E)-1-((R)-2-methylferrocenyl)-2-(1-methyl-4-pyridiniumyl)ethene; 3⁺ = (E)-1-((S)-2-trimethylsilylferrocenyl)-2-(1-methyl-4-pyridiniumyl)ethene) were prepared. Semiconducting behaviour (2·10⁻⁴ S·cm⁻¹ measured on compressed pellets for [Ni(dmit)₂] (MPMS), for example) is secured by the presence of the [Ni(dmit)₂]⁻ anions. The chiral nature of the countercations ensures non-centrosymmetry of the structures (space group P1 for [Ni(dmit)₂](2) and [Ni(dmit)₂](3), for example). A ubiquitous antiparallel arrangement of the cations, which are thus packed in a pseudo-centrosymmetrical environment, results in almost vanishing second-order susceptibilities χ⁽²⁾, and therefore zero efficiencies in second harmonic generation.     

Diphenylmethane-based anion receptors bearing bis(p-toluenesulfonyl urea) groups

Diphenylmethane-based receptors (1) bearing urea units were prepared for anion recognition. Analogous anion receptors based on biphenyl (2), diphenylsulfide (3), cyclophane (4) and phenyl (5) were also synthesized as control compounds. Their anion recognition ability was evaluated by ¹H-NMR spectroscopy in CDCl₃ at 297 K. The association constants for the complexation between receptors and anions are strongly dependent on the framework of the receptors and the urea moiety substituent. The much stronger binding of a chloride anion by the diphenylmethane-based receptor (1a) having two p-toluenesulfonyl urea groups was observed. It is rationalized by the stronger hydrogen bond donor strength of the p-toluenesulfonyl urea group and the moderate flexibility of the diphenylmethane framework and is explained in terms of the complex geometry.     

Naked eye sensing of anions using thiourea based chemosensors with real time application

Novel chromogenic sensors with thiourea moiety as receptor unit were synthesized and characterized using IR and NMR spectroscopic techniques. The receptors 1 and 2 bearing hydrogen bonding site demonstrate visually striking color change, UV–vis, and fluorescence responses for F⁻, AcO⁻, and OH⁻ over other anions such as Cl⁻, Br⁻, H₂PO₄⁻ and HSO₄⁻. Both the receptors 1 and 2 demonstrate detection limit at micro molar level. Further insight to the nature of interaction between receptors and anions was studied using ¹H NMR titration experiment. In particular, the fluoride of tooth paste and mouthwash in water phase can be detected by receptor 2.     

Anion recognition by d-ribose-based receptors

Anion recognition properties of d-ribose-based receptors α- and β-1 were measured by ¹H NMR in CDCl₃ and MeCN-d₃. Receptor β-1 showed effective binding with anions by cooperative hydrogen bonds of cis-diol. The anomeric isomer α-1 is a less effective anion receptor which has similar cis-diol as a recognition site, indicating that the stereo configuration of the anomeric position is of significant influence on the anion recognition ability.     

Synthesis, structure and anion binding properties of lower rim α-hydroxyamide calix[4]arene derivatives

A new family of p-tert-butylcalix[4]arenes functionalized at the lower rim with α-ketoamide or α-hydroxyamide functions has been prepared. The ¹H and ¹³C NMR spectra indicate that the macrocycles preferably adopt a cone conformation. X-ray crystal study of the α-ketoamide derivative 4a shows the flattened cone conformation in the solid state. Reduction of α-ketoamide 4ab has produced the α-hydroxyamide derivatives 6ab. The introduction of chiral moieties on the lower rim position of the calix[4]arene allowed the synthesis of the chiral derivatives 7 and 8. Host-guest complexation properties towards various anions of the chiral α-hydroxyamide 8 have been examined by ¹H NMR spectroscopy. This new receptor has shown promising selectivity for and N-tosyl-(L)-alaninate.     

Effective receptors for fluoride and acetate ions: synthesis and binding study of pyrrole- and cystine-based cyclopeptido-mimetics

Two conformationally constrained pseudo-cyclopeptides (1, 2) consisting of pyrrole-, pyridine-, and cystine-moieties were designed and synthesized as neutral receptors for anionic guests. The anion recognition abilities of these two receptors were examined photometrically in acetonitrile solution. The UV-vis study revealed that the [1+1] receptor (1) formed 1:1 complexes with anions, whereas the [2+2] receptor (2) led to 1:2 mode binding with anions. Both receptors displayed good affinity and selectivity for fluoride and acetate ions.     

Study on the selectivity of anion receptors by adjusting the distance of two urea fragments and their analytical application

Three anion receptors based on urea: 1 N, N??-bis-(p-nitrophenylaminocarbonyl)-Hydrazine, 2 N, N??-bis-(p-nitrophenylaminocar-bonyl)-ethylenediamine and 3 N, N??-bis-(p-nitrophenylaminocarbonyl)-1, 3-propane-diamine are designed and synthesized. Studies of UV?Cvis spectra presented that 1 was an excellent sensor of F^? and 2 was sensitive to H₂PO₄ ^?. Unfortunately, 3 can not distinguish the anions investigated in this paper. The color changes of the hosts upon the addition of a variety of structurally different anions were also utilized as naked-eye detection which is very convenient. It also revealed significantly that the distance between two recognition sites of receptor had an immediate effect on the selectivity of receptor for anions, which had been confirmed by the ¹H NMR titration and IR.