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.     

Bile acid based receptors for multiple metal ion recognition

A series of bile acid based receptors having triazole unit along with some additional heteroatom containing moieties as coordinating units for transition metal ion recognition has been synthesized. The UV–Vis studies revealed that these receptors show significant multiple binding affinity for Hg²⁺, Cd²⁺, Pb²⁺ and Cu²⁺ ions.     

Aminobenzohydrazide based colorimetric and ‘turn-on’ fluorescence chemosensor for selective recognition of fluoride

Chemosensors based on aminobenzohydrazide Schiff bases bearing pyrene/anthracene as fluorophores have been designed and synthesized for F⁻ ion recognition. The addition of fluoride ions to the receptors causes a dramatically observable colour change from pale yellow to brown/red. ¹H NMR studies confirm that the F⁻ ion facilitates its recognition by forming hydrogen bond with hydrogens of amide and amine groups. Moreover these sensors have also been successfully applied to detection of fluoride ion in commercial tooth paste solution.     

Synthesis of novel cone-configurated hexa-tert-butyl-trimethoxy-calix[6]arenes bearing tris(bipyridyl) pendants and their use in recognition and ionic speciation

A series of novel cone-configurated p-tert-butyl-trimethoxycalix[6]arenes bearing three 2,2′-bipyridyl units at their lower rim have been synthesized. The ¹H NMR and ¹³C NMR spectra of synthesized derivatives revealed that the ring inversion in calix[6]arene could be suppressed by the introduction of three 2,2′-bipyridyl moieties at the lower rim of calix[6]arene scaffold which fixes it into its cone configuration. The complexation ability of the synthesized receptors (5a–d) towards Fe(II) ion was investigated by UV-Visible titration to reveal that the synthesized receptors interact with Fe(II) in a 1:1 binding stoichiometry and respond to a specific oxidation state of the metal ion. The observations have significance for studies directed at the design of molecular receptors for ionic speciation through molecular recognition.     

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

Two 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.     

Triazole-based chromogenic and non-chromogenic receptors for halides

We designed and synthesized a series of triazole-based receptors for anion recognition. Our studies demonstrated that an amide-linked triazole unit is a promising moiety for anion recognition. We synthesized various chromogenic and non-chromogenic receptors based on this moiety. Receptor 11 binds very strongly (K = 102,750 M⁻¹) to fluoride. Receptor 18 changes color from faint yellow to orange upon binding to fluoride.     

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 CHCl₃. 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.     

Benzene-based tripodal isothiouronium compounds as sulfate ion receptors

Novel benzene-based tripodal isothiouronium receptors are synthesized for the selective recognition of tetrahedral oxoanions. The binding study by isothermal titration calorimetry indicates that the cationic receptors bind sulfate ions preferably in a tripodal mode, while they show a mixed binding mode toward phosphate ion. The tripodal isothiouronium receptors show large ΔG⁰ values toward sulfate ions in methanol, which are entropy driven. The results demonstrate that a subtle structural constraint can lead to different binding modes toward structurally similar 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.     

Synthesis of novel chiral bis-N-substituted-hydrazinecarboxamide receptors and probing their solution-phase recognition to chiral carboxylic guests by ESI-TOF/MS and tandem ESI-MS

Seven novel bis-N-substituted-hydrazinecarboxamide receptors were synthesized in good to excellent yields by reacting chiral dicarbohydrazides, obtained from commercially available tartaric acid, with substituted aromatic isocyanates. The newly synthesized hydrazinecarboxamides formed structurally unique supramolecular aggregates, which have been confirmed by ESI-TOF/MS and tandem ESI-MS. They also showed molecular recognition to a selection of chiral carboxylic guests and oligopeptides, which mimic the backbone structure of the bacterial cell wall. The structures of the novel compounds were verified by various spectroscopic techniques including FTIR, ¹H NMR, ¹³C NMR, ESI-TOF/MS, tandem ESI-MS, 2D ROESY NMR, and CD spectroscopy.     

Enantioselective Fluorescent Sensors for N-Boc-Protected Amino Acid Anions Based on BINOL

The four novel derivatives of BINOL have been prepared and the structures of these compounds characterized by IR, MS, ¹H and ¹³C NMR spectroscopy and elemental analysis. The enantioselective recognition of these receptors has been studied by fluorescence titration and ¹H NMR spectroscopy. The receptors exhibited different chiral recognition abilities towards N‐Boc‐protected amino acid anions and formed 1:1 complexes between host and guest. Receptor s exhibit excellent enantioselective fluorescent recognition ability towards the amino acid derivatives.     

Synthesis and crystal structures of fluorescent receptors for 9-butyladenine

Two pyrene containing fluorescent receptors, 2-(1-pyrenyl)benzoic acid (FR-1) and 8-(1-pyrenyl)-1-naphthoic acid (FR-2), have been designed and synthesized to mimic a pyrene dinucleotide for molecular recognition of 9-butyladenine (9-BuA). The X-ray crystal structures of the receptors FR-1 and FR-2 along with the binding substrate 9-BuA have been determined. FR-1 has the carboxyl group in the same plane as the phenyl group whereas the pyrenyl group is perpendicular to the phenyl group. However, both carboxyl and pyrenyl groups in FR-2 are parallel to each other but perpendicular to the naphthyl group. The binding constant for FR-2 to 9-BuA was found to be 7896±2187 M⁻¹, which is 8.3-fold greater than that for FR-1 (953±129 M⁻¹). The results indicate that the complex of 9-BuA with FR-2 is more stable than that with FR-1 by 1.2 kcal/mol. In addition, the molecular recognition of 9-BuA with the receptors can also be observed using fluorescence spectroscopy.     

芳酰基硫脲受体的合成及对阴离子识别研究

设计合成了3种芳酰基硫脲受体分子. 利用紫外-可见吸收光谱考察了其与F^－, Cl^－, Br^－, AcO^－, HSO₄^－, H₂PO₄^－等阴离子的作用. 结果表明该类受体分子与阴离子形成氢键配合物. 加入F^－, AcO^－时, 溶液立刻由无色变为黄色, 而加入其它阴离子则无变化, 从而实现对这两种阴离子的裸眼识别. 结果表明受体分子与阴离子间形成1∶1型的配合物. ¹H NMR滴定及质子溶剂效应为受体分子与阴离子间的氢键作用本质提供了直接依据.     

Synthesis and enantioselective recognition of an (S)-BINOL-based colorimetric chemosensor for mandelate anions

New chiral receptors 1 and 2 based on (S)-BINOL and thiourea units were synthesized. The chiral recognition of receptors for chiral anions were studied by fluorescence, UV–vis, and ¹H NMR spectra. The results of the non-linear curve fitting indicated that the receptors and guest anions formed a 1:1 stoichiometric complex. The obvious color change of receptor 2 can be observed by the naked eye when the enantiomers of mandelate anions were added, which demonstrates that receptor 2 may be used as a colorimetric sensor for mandelate anions.     

Enantioselective fluorescent sensors for amino acid derivatives based on BINOL bearing benzoyl unit

The derivatives of BINOL, (S)-1 and (R)-1, and their analogues have been prepared and the structures of these compounds have been characterized by IR, MS, ¹H, and ¹³C NMR spectroscopy and elemental analysis. The enantioselective recognition of these receptors has been studied by fluorescence titration and ¹H NMR spectroscopy. The receptors exhibited different chiral recognition abilities toward some enantiomers of chiral materials and formed 1:1 complexes between host and guest. Receptor (S)-1 or (R)-1 exhibits excellent enantioselective fluorescent recognition abilities toward amino acid derivatives.     

Synthesis and anion recognition properties of pyrrole-bearing acyclic receptors

A new series of acyclic anion receptors (1-4) based on methyl 5-(aminomethyl)-1H-pyrrole-2-carboxylate were designed and synthesized. The anion recognition properties of these receptors were examined by ¹H NMR spectroscopy and rationalized by density functional theoretical calculation. Receptor 1 displays the highest affinity and selectivity for anionic guests mainly due to the intramolecular hydrogen bonds and rigid molecular geometry.     

Anion,cation and ion-pair recognition by bis-urea based receptors containing a polyether bridge

Two bis-urea type receptors were synthesized containing a polyether bridge and two 4-nitrophenyl groups as chromogenic units, R1 and R2. Molecular recognition studies of receptors towards different tetraalkylammonium and alkali metal salts were carried out in DMSO by UV-Vis and ¹H-NMR spectroscopy. The receptors were found to have high affinity for diverse anions and ion-pairs, showing the highest affinities towards the tetramethylammonium and sodium salts. The cation binding ability of the receptors was evidenced by means ¹H NMR, mass spectrometric ESI⁺ studies and the crystal structures of some precursors. Additionally, the molecular modelling at the DFT level of the tetramethylammonium acetate complexes illustrates the potential ion-pair binding ability of the receptors: the anion is recognized through strong hydrogen bonds from the NH─ groups from the two urea sites, while the cation is bound by a combination of cation─π, C-H···O and C-H···π interactions.     

Experimental and computational studies of anion recognition by pyridine-functionalised calixarenes

Calix[4]arene-based receptors linked to amide and pyridine moieties have been synthesised in four steps from calix[4]arene, and characterised by ¹H and ¹³C NMR spectroscopy. The recognition properties of these receptors towards different anions were evaluated using ¹H NMR and computational studies. The receptors show modest selectivities towards dihydrogen phosphate versus carboxylates.     

Fluoride anion sensing using colorimetric reagents containing binaphthyl moiety and urea binding site

Four 1,1′-binaphthalene based bis-urea derivatives bearing aryl groups at end-on nitrogen atoms IIIa–d were synthesized as potential sensor molecules. These receptors show characteristic UV-VIS spectral changes on complexation with anions and they exhibit selective recognition of F⁻ over other halide anions. Interaction of a fluoride anion with urea NH groups was confirmed by ¹H NMR data. The presence of an electron-withdrawing nitro group in N′-aryls (receptors IIIa and IIIb) appeared to be necessary for naked-eye colorimetric detection. These receptors show dramatic color change from light-yellow to orange (IIIa) or to orange-red (IIIb) in the presence of guest fluoride anions already at concentrations of 10⁻⁵ mol dm⁻³ of the receptor and host.     

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.