P-sulfonated Calix Research Articles

Spectrofluorimetric study on the inclusion interaction between lomefloxacin and p-sulfonated calix[4]arene and its analytical application

The characteristics of host–guest complexation between p-sulfonated calix[4]arene (SC4A) and lomefloxacin (LMFX) were investigated by fluorescence spectrometry. A 1:1 stoichiometry for the complexation was established and an association constant of 6.48 × 10 4 l mol −1 at 25 °C was calculated by applying a deduced equation. The interaction mechanism of the inclusion complex was discussed and the various factors affecting the inclusion process were examined in detail. It was found that an appropriate amount of cationic surfactant cetyltrimethylammonium bromide (CTAB) can remarkably enhance the fluorescence intensity of the supramolecular complex system. Based on the obtained results, a novel sensitive spectrofluorimetric method for the determination of lomefloxacin based on supramolecular complex was developed with a linear range of 0.01–3.0 μg ml −1 and a detection limit of 0.008 μg ml −1, for the first time. The method was applied for the determination of lomefloxacin in pharmaceutical preparations successfully.

A novel spectrofluorimetric method for determination of lomefloxacin based on supramolecular inclusion complex between it and p-sulfonated calyx[4]arene

The characteristics of host–guest complexation between p-sulfonated calix[4]arene (SC4A) and lomefloxacin (LFLX) were investigated by fluorescence spectrometry. 1:1 stoichiometry for the complexation was established and their association constant at 25 °C was calculated by applying a deduced equation. The interaction mechanism of the inclusion complex was discussed. It was found that an appropriate amount of cationic surfactant cetyltrimethylammonium bromide (CTAB) could remarkably enhance the fluorescence intensity of the supramolecular complex system. Based on the obtained results, a novel sensitive spectrofluorimetric method for the determination of lomefloxacin was developed with a linear range of 0.01–3.0 μg ml −1 and a detection limit of 0.008 μg ml −1. The proposed method was applied satisfactorily to determine lomefloxacin in pharmaceutical preparations.

Synthesis of p-sulfonated calix[4]arene-intercalated layered double hydroxides and their adsorption properties for organic molecules

Calixarenes are macrocyclic organo anions, which cavity is capable of molecular recognition, while layered double hydroxides (LDHs) are widely known as hydrotalcite-like compounds, anion exchangers and host–guest materials. In this study, the intercalation of water-soluble p-sulfonated calix[4]arene (CS4) in the interlayer of the Mg–Al and Zn–Al LDHs (M 2+/Al ratio = 3) by the coprecipitation method has been investigated as well as the adsorption property of the resulting CS4/LDHs for benzyl alcohol (BA) and p-nitrophenol (NP). It was found that the CS4/LDHs with the molar ratio of CS4/Al = 0.25 (Mg–Al LDH) and 0.12 (Zn–Al LDH) were obtained as a single phase. The arrangement of CS4 in the LDH interlayer was different by the kind of the host metal ions as CS4 cavity axis perpendicular (Mg–Al LDH) and parallel (Zn–Al LDH) to the basal layer, influencing strongly on the BET surface area, N 2 adsorbed volume and adsorption property for BA and NP.

Potentiometric sensors based on poly(3,4-ethylenedioxythiophene) (PEDOT) doped with sulfonated calix[4]arene and calix[4]resorcarenes

Potentiometric ion sensors have been prepared by galvanostatic electrosynthesis of the conducting polymer poly(3,4-ethylenedioxythiophene) (PEDOT) doped with p-sulfonated calix[4]arene (C[4]S) and p-methylsulfonated calix[4]resorcarenes (Rn[4]S) with alkyl substituents of different chain length (R1=CH3; R2=C2H5; R3=C6H13). The bowl-shape of these doping ions makes them suitable as ionic recognition sites, and their bulky character is expected to prevent them from leaching out of the conducting polymer membrane. For comparison, sensors based on PEDOT doped with poly(styrene sulfonate) (PSS) and poly(vinyl sulfonate) (PVS) were also constructed. The resulting GC/PEDOT electrodes were conditioned in 0.01 mol L−1 AgNO3 and their performance as Ag+ ion-selective electrodes (ISEs) studied. Results reveal that selectivity and lifetime of the electrodes is affected by the doping anion structure, although all electrodes show selectivity towards Ag+ ions. Interaction of Ag+ with sulfur atoms present in the conducting polymer backbone is considered to be the main reason for this behavior. A second set of electrodes was constructed and conditioned in 0.1 mol L−1 KCl. These electrodes were tested in chloride solutions of quaternary ammonium cations, showing that C[4]S and R2[4]S exhibit significant sensitivity towards pyridinium.

The electrochemical behavior of p-sulfonated calix[4]arene

The electrochemical behavior of p-sulfonated calix[4]arene was studied. In aqueous solution, p-sulfonated calix[4]arene can be oxidized when the potential is more than 0.7 V versus SCE. It is confirmed that the reaction is an irreversible two-electron transfer electrochemical reaction. The anodic peak potential, E p, is affected by the acidity of the solution. E p shifts in the negative direction when the pH increases. The electron transfer coefficient, α, is 0.65. At 25 °C, the diffusion coefficient of p-sulfonated calix[4]arene is 3.1 × 10 −5 cm 2 s −1. The activation energy, E a, for the electrochemical reaction is (18.8 ± 0.2) kJ mol −1.

A New Fluorometric Method for the Detection of the Neurotransmitter Acetylcholine in Water Using a Dansylcholine Complex with p-Sulfonated Calix[8]arene

A new method for the fluorometric detection of the neurotransmitter acetylcholine (ACh) in water is presented. Use of the fluorescence of dansylcholine (DANCh) bound to p-sulfonated calix[8]arene affords a new fluorometric method for the detection of ACh (>10-4 M) inaqueous solution (pH = 6.9). The fluorescence intensity of DANCh in aqueous solution was enhanced 1.8 fold after the complexation with p-sulfonated calix[8]arene. The addition of ACh to the aqueous solution of the DANCh-calix[8]arene complex significantly decreased the fluorescence intensity, which results from the replacement of DANCh in the complex with ACh. The effects of other synaptic neurotransmitters on the fluorescence of the DANCh complex were examined for dopamine, histamine, ATP, GABA, glycine, l-glutamic acid, and l-aspartic acid. Among the neurotransmitters studied, ACh was most effective in changing the fluorescence of the DANCh complex. Possible application of the DANCh complex dye for the detection of ACh in biological systems is discussed.

Mutually induced formation of host-guest complexes between p-sulfonated calix[8]arene and photolabile cholinergic ligands.

Adaptive systems: The conformationally flexible p-sulfonated calix[8]arene and photolabile cholinergic ligands adapt to each other and select the right conformers to form ditopic binding complexes (see schematic representation), thus mimicking ligand binding in biological receptors or enzymes.

Capillary electrophoresis separation of p-sulfonated calix[ n]arenes, n=4, 6, 8

The CE separation of p-sulfonated calix[ n]arenes, where n=4, 6 and 8, was investigated. Under positive potential conditions optimum separation was found to be borate buffer modified with sodium dodecyl sulfate. Under these conditions separation was achieved in less than 10 min. The effect on the separation of the addition of divalent cations: Mg 2+, Ca 2+ and Ba 2+ was studied. p-Sulfonatedcalixarenes were detected in the anodic side of the capillary. There was an improvement in the reproducibility and analysis time although efficiency did not improve significantly.

Thermodynamic study of p-sulfonated calixarene complexes in aqueous solution

Association equilibrium constants and thermodynamic parameters (i.e., ΔH and ΔS) for complexation between N,N-dimethylindoaniline and p-sulfonated calix[n]arenes in aqueous solution have been determined by means of UV–VIS spectroscopy. Equilibrium constants corresponding to calix[n]arene-p-sulfonates increase in the order [4] < [6] ≈ [8]. ΔH and ΔS values, which are interpreted in terms of the importance of the various interactions responsible for complexation, lead to a linear ΔH – TΔS relationship. Such a linear correlation is interpreted in terms of the extent of calixarene conformational change and of host and guest desolvation involved in the complexation process.