A novel C3v-symmetric molecular clip with tris(diamide) recognition sites on trindane platform for H2PO4− recognition

To avoid the deprotonation events occurred in the receptor upon recognition of basic anions, a novel C_3v-symmetric anion receptor 2 with two amide groups appended in each arm was designed and synthesized by using the trindane tricarboxylic acid as tripodal molecular framework. The anion recognition ability by 2 was examined by ¹H NMR titration study in DMSO-d₆, which revealed that the addition of H₂PO₄^? guests caused substantial downfield shifts of the amide-NH protons peaks due to the formation of a host-guest complex in 1:1 binding stoichiometry with the estimated binding constant (K_a) of 244?M^?1. No noticeable binding of 2 was observed with other tested anions such as F^?, Cl^?, Br^?, I^?, NO₃^? and HSO₄^? under similar conditions.     

Coumarin-based tripodal chemosensor for selective detection of Cu(II) ion and resultant complex as anion probe through a Cu(II) displacement approach

In this paper, a novel tripodal fluorescent receptor based on naturally occurring coumarin was synthesized and its ionic recognition properties were fully investigated by spectroscopic techniques. As revealed by the results, tripodal 1 exhibits excellent selectivity toward copper(II) by forming a 1:1 complex with triazole N as the main binding sites. And the resulted 1·Cu²⁺ complex shows recognition ability toward H₂PO₄^? by metal displacement approach. The recognition mechanism was further investigated by computer calculation.     

Fluorescent detection of amidinium-carboxylate and amidinium formation using anthracene-based diamidine: an application for the analysis of dicarboxylic acid binding

An anthracene-based diamidine (1) ‘turn-on’ fluorescent probe for the detection of dicarboxylic acids has been designed and synthesized. The fluorescence spectra of the diamidine 1 with carboxylic acids that showed two different fluorescence bands, which corresponded to the amidinium-carboxylate (λ_em=430-440 nm), and amidinium (λ_em=460-470 nm as a broad band) formation, were confirmed by DOSY NMR and TD-DFT calculations. These different fluorescence bands showed the binding mode of carboxylic acids and the stability of formed complexes toward diamidine 1. The fluorescent detection of amidinium-carboxylate formation using diamidine 1 was applicable to the detection of α,ω-dicarboxylic acids (C₆-C₁₃) and succeeded in the detection of α,ω-dicarboxylic acid (adipic acid) in human urine.     

Colorimetric and fluorescence sensing of anions using thiourea based coumarin receptors

Thiourea-containing coumarins 1, 2 have been designed and synthesized via reaction of 6-aminomethylcoumarin and the corresponding isothiocyanates. Their anion-binding ability has been examined using UV-vis, fluorescence and ¹H NMR. The anion recognition takes place through charge neutral thiourea receptor sites with concomitant fluorescence quenching of the coumarin moiety with 1 showing a strong binding to C₆H₅COO⁻ over F⁻ with a distinct change in color.     

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.     

β-Carbonylsilanes with a silacyclohexane skeleton and additional C-functionalized organyl groups at the silicon atom: synthesis, reactivity, and NMR-spectroscopic characterization

A series of novel β-carbonylsilanes, with a silacyclohexane skeleton and additional C-functionalized organyl groups at the silicon atom, were synthesized, their reactivity was explored, and they were structurally characterized by multinuclear NMR spectroscopy. The aim of these investigations was to provide the basis for the development of novel silicon-based drugs containing a silacyclohexane skeleton, with a CH₂C(O)R substituent and an additional C-functionalized organyl group at the silicon atom.     

Formyl MIDA Boronate: C1 Building Block Enables Straightforward Access to α-Functionalized Organoboron Derivatives

Formyl MIDA boronate has been known to be an elusive type of acylboronate that has not been obtained to date. In this work, an approach to the one-pot preparation and chemical transformations of formyl MIDA boronate were developed to provide new types of α-functionalized organoboron compounds. Among them are acylboronate reagents which present boron-substituted analogues of ynones and β-dicarbonyl compounds. The developed synthetic procedures, utilizing formyl MIDA boronate, are tolerant to diverse functional groups, making this reagent an advantageous C₁ building block for extending the scope of organoboron chemistry.     

6,6′-Bis-substituted BINOL boronic acids as enantioselective and chemoselective fluorescent chemosensors for d-sorbitol

A new chiral fluorescent BINOL boronic acid 1 has been synthesized. The chiral recognition properties of 1 are drastically different from BINOL boronic acid c. Sensor 1 shows improved enantioselectivity as well as chemoselectivity toward sugar alcohols, such as d-sorbitol and d-mannitol.The enantioselectivity of sensor 1 toward d-sorbitol (K_R/K_S) is 1:35 (pH 9.0), and the chemoselectivity for d-sorbitol/d-mannitol is 20:1.     

Fluorescent sensing of anions using a bis-quinoxaline amidothiourea based supramolecular cleft; an example of an anion-induced deprotonation event

The quinoxaline 1, possessing a 2,6-pyridyl-based amidothiourea moiety, with the view of forming a pre-organised molecular cleft, was developed as a fluorescent anion sensor. The sensing ability of 1 was evaluated in organic solution where both the ground and the excited state of 1 was affected upon recognition of anions such as acetate [as tetrabutylammonium salt (TBAAc) solution] at the amiodothiourea moieties in MeCN. The fluorescence of 1, with λ_max at 477 nm, was, on all occasions quenched, upon anion recognition. Using TBAOH, we also show that the same anion-induced changes occurred; demonstrating that for this particular sensor, the anion-sensing takes place via a deprotonation mechanism. This anion-induced deprotonation event was further investigated by carrying out ¹H NMR titrations on 1, using both AcO⁻ and OH⁻ in DMSO-d₆.     

Synthesis of cholate-based pyridinium receptor and its recognition toward l-tryptophan

Four cholate-based pyridinium compounds were synthesized and their binding abilities toward unmodified amino acids were investigated by UV spectroscopy and fluorescence emission spectroscopy. Studies revealed that the recognition process involved hydrogen bonding, electrostatic force, and π–π interaction. The receptor 4a was found to recognize l-tryptophan specifically, and the complex was studied by ¹H NMR spectroscopy. The receptors 4b and 4c showed very little recognition ability toward l-tryptophan, indicating the important role of the benzyl group at pyridinium ring.     

Molecular Recognition and Cooperative Binding Ability of Fluorescent Dyes by Bridged Bisβ-cyclodextrin)s Tethered with Aromatic Diamine

A novel bridged bis(β-cyclodextrin),m-phenylenediimino-bridged bis(6-imino-6-deoxy-β-cyclodextrin) (2), was synthesized by the reaction of m-phenylenediamine and 6-deoxy-6-formyl-β-cyclodextrin. The inclusion complexation behavior of the novel bridged bis(β-cyclodextrin) 2,as well as native β-cyclodextrin (1),p-phenylenediamino-bridged bis(6-amino-6-deoxy-β-cyclodextrin) (3) and 4,4'-bianilino-bridged bis(6-amino-6-deoxy-β-cyclodextrin) (4) with representative fluorescent dye molecules, i.e., acridine red (AR), neutral red (NR), Rhodamine B (RhB), ammonium 8-anilino-1-naphthalenesulfonate (ANS) and sodium 6-toluidino-2-naphthalenesulfonate (TNS), was investigated at 25 °C in aqueous phosphate buffer solution (pH 7.20) by means of fluorescence, and circular dichroism, as well as 2D NMR spectrometry. The spectrofluorometric titrations have been performed to calculate the complex stability constants (K_S) and Gibbs free energy changes (Δ G°) for the stoichiometric 1 : 1 inclusion complexation of 1–4 with fluorescent dye molecules. The results obtained demonstrated that bis(β-cyclodextrin)s 2–4 showed much higher affinities toward these guest dyesthan native β-cyclodextrin 1. Typically, dimer 2 displayed the highest binding ability upon inclusion complexation with ANS, affording 35 times higher K_S value than native β-cyclodextrin. The significantlyenhanced binding abilities of these bis(β-cyclodextrin)s are discussed from thebinding mode and viewpoints of size/shape-fit concept and multiple recognition mechanism.     

A novel strapped porphyrin receptor for molecular recognition

A novel strapped porphyrin receptor Zn1, in which two electron-rich bis(p-phenylene)-34-crown ether-10 units are incorporated, has been designed and synthesized from the newly developed intermediate 7 for investigating new chemistry of molecular recognition. ¹H NMR and UV-Vis studies revealed that Zn1 displays relatively weak binding abilities to neutral electron deficient naphthalene-1,8,4,5-tetracarboxydiimide (NDI) derivatives 13 (no simple complexing stoichiometry was observed), 19 (K_a=48(±5) M⁻¹) and 30 (K_a=46(±5) M⁻¹) in chloroform-d, strong binding ability to pyridine derivative 25, (K_a=1.5(±0.12)×10³ M⁻¹) in chloroform, moderately strong binding ability to tetracationic compound 35·4PF₆ (K_a=475(±50) M⁻¹) in acetone-d₆, and very strong binding affinity to compound 22 (K_a=6.5(±0.7)×10⁵ M⁻¹), which consists of one pyridine and two NDI units, in chloroform. Remarkable cooperative effect of the intermolecular metal-ligand coordination and donor-acceptor interactions in complex Zn1·22 was observed by comparing the complexing behaviors between Zn1 and the appropriately designed guests. Complex Zn1·22 possesses an unique three-dimensional tri-site binding feature. For comparison, the complexing affinity of 1 toward compounds 13, 19, and 30 in chloroform-d and 35·4PF₆ in acetone-d₆ has also been investigated and the binding patterns in different complexes were explored. The results demonstrate that strapped porphyrin derivatives are ideal precursors for constructing new generation of three-dimensional multi-site artificial receptors for molecular recognition and host-guest chemistry.     

A multi-responsive diarylethene-rhodamine 6G derivative for sequential detection of Cr3+ and CO32−

A new unsymmetrical diarylethene derivative (1o) with rhodamine 6G as a functional group has been designed and synthesized. It displayed good physicochemical properties induced by lights and chemical stimuli. 1o could sensitively detect towards Cr³⁺ with a 1:1 stoichiometry, and exhibit an obviously fluorescence (from dark to light cyan) and color (from colorless to pink) changes during the recognition process. The limit of detection was determined to be 27?nM and 8.5?nM via UV/vis and fluorescence methods, respectively. More importantly, the resulting complex 1o-Cr³⁺ (1o') could be served as a potential fluorescent probe to selectively and sensitively recognize toward CO₃^2?, the limit of detection was determined to be 0.88?μM and 0.26?μM via UV/vis and fluorescence methods, respectively. Moreover, the quenching of fluorescence intensity can reach 95% due to the perfect FRET processes between the excited open-ring rhodamine 6G moiety and the closed-ring diarylethene unit.     

Fluorescent detection of amidinium-carboxylate and amidinium formation using a 1,8-diphenylnaphthalene-based diamidine: dicarboxylic acid recognition with high fluorescence efficiency

A 1,8-diphenylnaphthalene-based diamidine (1) ‘turn-on’ fluorescent probe for the detection of dicarboxylic acids has been designed and synthesized. The fluorescence spectra of the diamidine 1 with carboxylic acids that showed two different fluorescence bands, which corresponded to the amidinium-carboxylate (λ_em=410–430 nm) and amidinium (λ_em=440–470 nm as a broad band, which consisted from two peaks) formation, were confirmed by DOSY NMR and TD-DFT calculations. The complexation of diamidine 1 with dicarboxylic acids, which have sufficient distances between the two carboxylic groups for binding to the diamidine 1 (dicarboxylic acids 3, 4, and α,ω-dicarboxylic acids 6 (C₆–C₂₀)), showed the formation of 1:1 complexes (i.e., amidinium-carboxylate formation). On the other hand, for the complexation with monocarboxylic acids and dicarboxylic acids having insufficient distances between the two carboxylic groups (benzoic acid 5, acetic acid 7, and α,ω-dicarboxylic acids 6 (C₃–C₅)), formation of the amidinium (1·2H⁺) was observed. Relatively similar binding constants (10⁻⁵) for the complexation of the diamidine 1 with dicarboxylic acids 6, which depend on their chain length (strain), were observed due to the flexibility of the 1,8-diphenylnaphthalene unit. Additionally, for the complexation of the diamidine 1 with dicarboxylic acids, higher fluorescence quantum yields (Φ_fl: up to 80%) were observed when compared to the binding of the diamidine 2 (Φ_fl: up to 35%).     

Synthesis and estimation of gelation ability of C3-symmetry tris-urea compounds

C₃-Symmetry tris-urea low molecular weight gelator (LMWG) (1), which shows chemical stimuli responsible for a sol-gel phase transition, was divided into five regions. Based on the division, 22 derivatives were synthesized. The gelation ability of these derivatives was tested in nine organic solvents with a wide range of values for relative static permittivity (?_r=47.2-1.89). Some derivatives showed a better performance as LMWGs than the original tris-urea LMWG (1). For example, the critical gelation concentration (CGC) in acetone was improved from 1.5 wt % to 0.5 wt % by changing the core substituent (18). Highly versatile LMWG for a variety of solvents was obtained by changing the linker moiety (23). Structural information to design tris-urea LMWGs is important to create rationally a functional supramolecular gel.     

Synthesis of novel C2-symmetric chiral crown ethers and investigation of their enantiomeric recognition properties

A series of new C₂-symmetric chiral aza crown ether macrocycles 1–4 have been synthesized from (S)-3-aryloxy-1,2-propanediol and (S)-1,2-propanediol for the enantiomeric recognition of amino acid ester derivatives. These new macrocycles have been shown to be strong complexing agents for primary organic ammonium salts (with K up to 176.93 M^?1 and ΔG° up to 12.81 kJ mol^?1) by ¹H NMR titration. These macrocyclic host exhibited enantioselective bonding toward the d-enantiomer of phenylalanine methyl ester hydrochloride with K_D/K_L up to 6.87 in CDCl₃ with 0.25% CD₃OD.     

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.     

Pyrenyl-appended imidazolium receptor for selective fluorescence sensing of oxalic acid

A new fluorescent imidazolium-based cholestane receptor 4 bearing a pyrene moiety was synthesized. The binding ability of 4 toward various dicarboxylic acids was examined by UV-vis and fluorescence spectroscopy. Receptor 4 showed the highest binding constant for oxalic acid among all the tested dicarboxylic acids (K_a = 5.06 × 10⁴ M⁻¹). Oxalic acid formed a complex with 4 with a 1:2 ratio in ethanol.     

Alkyne oligomerization catalyzed by molybdenum(0) complexes

Three new molybdenum(0) complexes, [Mo(CO)₃(Hpz)₃] (1), [Mo(CO)₂(Hpz)₂(DMAD)₂] (2), (DMAD=dimethyl acetylenedicarboxylate) and [Mo(CO)₃(1-Me-imidazole)₃] (3) were synthesized and characterized. Their activity and selectivity in alkyne cyclotrimerization and co-trimerization reactions was investigated. The molecular structures of 1 and 2 have been determined by unconventional powder and standard single-crystal diffraction methods, respectively. 1 consists of a pseudo-octahedral complex of C₃ symmetry, with the ligands in fac disposition; complex 2, of idealized C₂ symmetry, is obtained by substitution of one CO and one pyrazole in 1 by two DMAD ligands, and shows the rare trans configuration of π-bound acetylenic moieties.