351 research outputs found
Synthesis and structures of O-anthrylmethyl-substituted hexahomotrioxacalix[3]arenes
O-Alkylation of 7,15,23-tri-tert-butyl-25,26,27-trihydroxy-2,3,10,11,18,19-hexahomo-3,11,19-trioxacalix[3]arene (1Hā) with 9-chloromethylanthracene 5 was carried out under different reaction conditions. Variation of the number of anthrylmethyl group introduced at the phenolic rim of hexahomotrioxacalix[3]arene 1Hā was achieved through selective O-alkylation using stoichiometric amounts of 9-chloromethylanthracene 5 in acetone to afford the mono-O-alkylated product 2HāAn, the di-O-alkylated product 3HAnā and the tri-O-alkylated product partial-cone-4Anā, respectively. Interestingly, by using an acetone/benzene (1:1 v/v) mixed solvent system, the cone-4Anā was successfully synthesized. These results suggest that the solvent can also control the conformation of the O-alkylation products. The possible reaction routes of the cone-4Anā and partial-cone-4Anā are also discussed
A study of allosteric binding behaviour of a 1,3-alternate thiacalix[4]arene-based receptor using fluorescence signal
A novel heteroditopic thiacalix[4]arene receptor L possessing 1,3-alternate conformation, which contains two pyrene moieties attached to the lower rim via urea linkages together with a crown ether moiety appended at the opposite side of the thiacalix[4]arene cavity, has been synthesized. The complexation behaviour of receptor L was studied by means of fluorescence spectra and Ā¹H NMR titration experiments in the presence of Kāŗ ions and a variety of other anions. The results suggested that receptor L can complex efficiently via the urea cavity or the crown ether moiety, and a positive/negative allosteric effect operating in receptor L was observed
Positive allosteric binding behavior of pyrene-appended triazole-modified thiacalix[4]arene-based fluorescent receptors
The novel heteroditopic receptors 5aā¼c have been synthesized, which bear a thiacalix[4]arene in the 1,3-alternate conformation. Two urea moieties possessing various aryl groups with either electron-donating or -withdrawing groups at their p-positions function as anion-binding sites. At the opposite side of the cavity are two pyrene-appended triazole rings, which act as cation-binding sites. The binding property of receptor 5c was investigated by means of 1H NMR and UVāvis spectroscopy and by fluorescence titration experiments in the presence of various transition metal cations and anions in CH2Cl2āDMSO (10:1, v/v) solution. Interestingly, it was found that receptor 5c possessing two p-nitrophenyl ureido moieties, most efficiently complexes in the urea cavity or bistriazoles; the plausible allosteric effect of receptor 5c was also investigated
Synthesis and inclusion behavior of a heterotritopic receptor based on hexahomotrioxacalix[3]arene
A heterotritopic hexahomotrioxacalix[3]arene receptor with the capability of binding two alkali metals and a transition metal in a cooperative fashion was synthesized. The binding model was investigated by using Ā¹H NMR titration experiments in CDClāāCDāCN (10:1, v/v), and the results revealed that the transition metal was bound at the upper rim and the alkali metals at the lower and upper rims. Interestingly, the alkali metal ions Liāŗ and Naāŗ bind at the lower and upper rim respectively depending on the dimensions of the alkali metal ions versus the size of the cavities formed by the calix[3]arene derivative. The hexahomotrioxacalix[3]arene receptor acts as a heterotritopic receptor, binding with the transition metal ion Agāŗ and the alkali metals ions Liāŗ and Naāŗ. These findings were not applicable to other different sized alkali metals, such as Kāŗ and Csāŗ
A pyrene-armed hexahomotrioxacalix[3]arene as a multi-sensor via synergistic and demetallation effects
A new pyrene-armed hexahomotrioxacalix[3]arene L has been synthesized, which exhibits a pronounced fluorescence enhancement response toward CuĀ²āŗ ions via a ZnĀ²āŗ or CdĀ²āŗ triggered synergistic effect. Additionally, the LĀ·CuĀ²āŗ+ complex can subsequently serve as a sensor for Fā» via anion-induced demetallation. The fluorescence responses by the input of CuĀ²āŗ, ZnĀ²āŗ/CdĀ²āŗ and Fā» can be constructed as a combinational logic gate which mimics a set of molecular traffic signals
A pyrene-functionalized triazole-linked hexahomotrioxacalix[3]arene as a fluorescent chemosensor for ZnĀ²āŗ ions
A new pyrenyl appended hexahomotrioxacalix[3]arene L featuring 1,2,3-triazole linkers was synthesized as a fluorescent chemosensor for ZnĀ²āŗ in mixed aqueous media. It exhibited high affinity toward ZnĀ²āŗ, and the monomer and excimer emission of the pyrene moieties could be adjusted. The binding stoichiometry of the LĀ·ZnĀ²āŗ complex was determined to be 1:1, and the association constant (Ka) was found to be 7.05 Ć 10ā“ Mā»Ā¹. The binding behavior with ZnĀ²āŗ has been confirmed by Ā¹H NMR spectroscopic analysis
Fluorescent turn-on sensors based on pyrene-containing Schiff base derivatives for Cu2+ recognition: spectroscopic and DFT computational studies
A new fluorescent chemosensor L1, pyrene containing long chain Schiff base derivative in 1-position has been synthesized. Similarly, the receptors L2 and L3 are also designed in order to compare the binding ability for detection of Cu2+. The receptors exhibit very weak fluorescence (Ī¦ = 0.01) due to the photoinduced electron transfer (PET). Upon addition of 10 equiv. of Cu2+, the emission intensity of ligands L1 and L2 are increased 65-fold (Ī¦ = 0.31) and 25-fold (Ī¦ = 0.08) in CH3CN/CH2Cl2 solvents system respectively. NMR titration experiments, spectroscopic and DFT computational studies confirmed the binding phenomena and sensitivity of Cu2+
Synthesis and evaluation of a novel fluorescent sensor based on hexahomotrioxacalix[3]arene for ZnĀ²+ and CdĀ²+
A novel type of selective and sensitive fluorescent sensor having triazole rings as the binding sites on the lower rim of a hexahomotrioxacalix[3]arene scaffold in a cone conformation is reported. This sensor has desirable properties for practical applications, including selectivity for detecting ZnĀ²āŗ and CdĀ²āŗ in the presence of excess competing metal ions at low ion concentration or as a fluorescence enhancement type chemosensor due to the cavity of calixarene changing from a āflattened-coneā to a more-upright form and inhibition of PET. In contrast, the results suggested that receptor 1 is highly sensitive and selective for CuĀ²āŗ and FeĀ³āŗ as a fluorescence quenching type chemosensor due to the photoinduced electron transfer (PET) or heavy atom effect
Synthesis and evaluation of a novel ionophore based on a thiacalix[4]arene derivative bearing imidazole units
O-Alkylation of the flexible thiacalix[4]arene 1 with 2-chloromethyl-1-methyl-1H-imidazole 2 in the presence of NaāCOā or KāCOā afforded mono-O-alkylation product 3 in 29ā51% yield, along with recovery of the starting compound. In contrast, the same reaction in the presence of CsāCOā gave only one pure stereoisomer, namely 1,3-alternate-4; other possible isomers were not observed. Alkali metal salts such as NaāCOā and CsāCOā can play an important role in the conformer distribution via a template effect. The conformations of the receptors, mono-O-alkylation product 3 and that of 1,3-alternate-4, have been confirmed by X-ray crystallography. Furthermore, the complexation properties of the receptor 1,3-alternate-4 toward selected alkali/transition metal cations are reported. The two-phase solvent extraction data indicated that 1,3-alternate-4 exhibited a stronger extraction efficiency for transition metals over alkali metals. The dichromate anion extraction ability of 1,3-alternate-4 showed that it could serve as an efficient extractor of HCrāOāā»/CrāOāĀ²ā» anions at low pH
Click-modified hexahomotrioxacalix[3]arenes as fluorometric and colorimetric dual-modal chemosensors for 2,4,6-trinitrophenol
A new type of chemosensor-based approach to the detection of 2,4,6-trinitrophenol (TNP) is described in this paper. Two hexahomotrioxacalix[3]arene-based chemosensors 1 and 2 were synthesized through click chemistry, which exhibited high binding affinity and selectivity toward TNP as evidenced by UVāvis and fluorescence spectroscopy studies. Ā¹H NMR titration analysis verified that CHāÆO hydrogen bonding is demonstrated as the mode of interaction, which possibly facilitates effective charge-transfer
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