Spectroscopic studies on the inclusion interaction of p-sulfonatocalix[6]arene with vitamin B6

The formation of the inclusion complex of p-sulfonatocalix[6]arene (SCX6) with different forms of vitamin B₆ (VB₆) was studied by using fluorescence spectroscopy. VB₆ can exist in one of three forms (the acidic form, neutral zwitterionic form and basic form) depending on pH. The fluorescence intensities of acidic and basic forms of VB₆ remarkably decreased in presence of SCX6. SCX6 preferred to form 1:1 inclusion complexes with acidic and basic forms of VB₆ but hardly form inclusion complex with neutral zwitterionic form. According to the nonlinear curve fitting method, the inclusion constant (K) for the formation of inclusion complexes of acidic and basic forms of VB₆ with SCX6 were evaluated to be 1.4?×?10⁴ and 9?×?10³ L/mol, respectively. The binding affinity of SCX6 towards acidic form is attributed to hydrogen bonds and hydrophobic interaction, furthermore, additional electrostatic interaction also plays a crucial role. The possible inclusion mode was given by ¹H NMR technique.     

Baylis-Hillman reaction in [bdmim][PF6] ionic liquid

A new use of ionic liquid [bdmim][PF₆] as solvent for the Baylis-Hillman reaction is presented. Unlike the commonly used [bmim][PF₆] that evidently reacts with electrophilic aldehydes under basic conditions, ionic liquid [bdmim][PF₆] is inert and the Baylis-Hillman reaction in [bdmim][PF₆] proceeds smoothly with better yield.     

5,11,17,23-四叔丁基-25,26,27,28-四[3-(甲氧基羰基)苄氧基]杯[4]芳烃包合性能的研究

杯芳烃是继冠醚和环糊精后的第三代主体化合物 .这类主体分子不仅可以识别和络合阳离子 ,而且还具有包合中性有机分子的性能 [1～ 5] .杯 [4]芳烃类包合物的晶体结构测定表明 ,它们可分为分子内和分子间包合两种类型 [3 ,5] ,前者是客体分子被包合在主体分子的空穴内 ,后者是客体分子被包合在主体分子之间 .对叔丁基杯 [4]芳烃的下沿酚氧基与上沿均可进行化学修饰得到不同的杯 [4]芳烃衍生物 .最早报道的对叔丁基杯 [4]芳烃及其衍生物的分子内包合物是与甲苯或乙腈的 1∶ 1包合物 [4 ,5] ,客体分子依靠 CH3 -π的作用被包结在主体分子内[6]…     

Calix[8]arene anions: solid state structure of an inclusion compound with a tetrabutylammonium cation

Octakis(dimethylsiloxy)-octa-p-tert-butylcalix[8]arene was prepared from the parent p-tert-butylcalix[8]arene and 1,1,3,3-tetramethyldisilazane. Desilylation of the siloxy-calix[8]arene with tetrabutylammonium fluoride hydrate under different conditions afforded di- and tetraanionic derivatives. Determination of the solid state structure of the dianion revealed the formation of an inclusion compound with one tetrabutylammonium cation inside the macrocyclic cavity.     

Calix[6]arene acetic acid extraction behavior and specificity with respect to nucleobases

The extraction behavior of various nucleobases was investigated with a series of calixarene derivatives. A calix[6]arene acetic acid was found to extract around 80% of adenine from an aqueous phase, and showed the highest specificity for adenine among all the nucleobases tested. The important factors influencing the recognition properties of calixarene were discovered to be its cyclic structure, its cavity size, and the functional carboxylic acid groups. The carbonyl group and the position of the amino group in the guest molecules also affect the extraction efficiency. Calix[6]arene forms a stable 1:1 complex with adenine by entrapping it into the cavity. Adenine was readily recovered from the organic phase by contacting with a fresh acidic solution.     

The complexation of ferrocene derivatives by a water-soluble calix[6]arene

The complexation of several ferrocene derivatives by the water-soluble hostp-sulfonato-calix[6]arene was investigated using electrochemical and¹H-NMR spectroscopic techniques. The electrochemical results indicate that both oxidation states of the guests are bound to the calixarene host, although the oxidized (ferrocenium) forms are complexed more strongly than the reduced (ferrocene) species.¹H-NMR spectroscopic data indicate that the complexation phenomena involves the inclusion of the guest's ferrocene moiety into the flexible calixarene cavity.This paper is dedicated to the commemorative issue on the 50th anniversary of calixarenes.     

Nonaqueous microemulsion-containing ionic liquid [bmim][PF6] as polar microenvironment

The phase behavior of toluene/Triton X-100 (TX-100)/1-butyl-3-methylimidazolium hexafluorophosphate([bmim][PF6]) was studied. It was demonstrated that the single-phase microemulsion area covered about 75% of the phase diagram at 25 °C. Electrical conductivities of the system with different w ([bmim][PF6]-to-TX-100 molar ratio) values were determined, and the results were used to locate the sub-regions of the single-phase microemulsion. The results showed that a transform from [bmim][PF6]-in-oil ([bmim][PF6]/O) microstructure via a bicontinuous region to an oil-in-[bmim][PF6] (O/[bmim][PF6]) microstructure occurred with the increase of Φ (weight fraction of TX-100 and [bmim][PF6] in the system). The aggregate size of the reverse microemulsions of [bmim][PF6]/O was determined using small-angle X-ray scattering. The results showed that the size of the reverse microemulsions depended markedly on the w values.     

Dominant factors affecting extraction behavior of amino compounds by a calix[6]arene carboxylic acid derivative

A calix[6]arene carboxylic acid derivative was utilized as an extractant for various amino compounds including amino acids. The host compound exhibited a high extractability compared to that of commercially available extractants such as di(2-ethylhexyl)phosphoric acid (D2EHPA). The important factors for amino acid extraction were found to be its cyclic structure and its cavity size, the functional carboxylic groups, and the length of the alkyl chains. The hydrophobicity and the ionic property of guest molecules also affect the extraction efficiency. Calix[6]arene forms a stable complex with a guest molecule by entrapping it into the cavity. The molecular geometries of calixarene before and after extraction were also discussed using computational calculations with the PM3 type of semi-empirical method.     

Hydrogen substitution effect on the solubility of perhalogenated compounds in ionic liquid [bmim][PF6]

Solubility behaviors of binary mixtures of CFCl₃ (R-11), CFCl₂-CF₂Cl (R-113), CHCl₃ (R-20), CDCl₃ (R-20-d), CHCl₂–CF₃ (R-123) with room-temperature ionic liquid [bmim][PF₆] (1-butyl-3-methylimidazolium hexafluorophosphate) have been investigated using the volumetric and cloud-point methods, since all the systems show liquid–liquid equilibria (LLE). Large immiscibility (LLE) gaps of the perhalogenated compounds (R-11 and R-113) in the ionic liquid have been drastically reduced by the addition of only one hydrogen (or deuterium) in these compounds. The R-123 + [bmim][PF₆] binary system belongs to the Type-V fluid behavior. Noticeably large negative values (−2 to −8 cm³ mol⁻¹) of the excess molar volume in the ionic liquid-rich side solution have been observed for all the present systems. Experimental LLE data have been well correlated by the use of the NRTL (non-random two liquid) activity coefficient model.     

Fluorimetric properties of a 2-hydroxypropyl-beta-cyclodextrin: 9-methyl-benzo[a]phenothiazine inclusion complex in aqueous media. Analytical usefulness

The formation of an inclusion complex between 9-methyl-12H-benzo[a]phenothiazine (MeBPHT) and 2-hydroxypropyl-β-cyclodextrin (HP-β-CD) was investigated in aqueous medium. A 12-fold fluorescence emission intensity enhancement was found for the complexed relative to the free analyte. MeBPHT forms a 1:1 stoichiometry complex with HP-β-CD. A formation constant of 460 (±100) M⁻¹ was calculated using the Benesi-Hildebrand method and fluorimetric data. The limit of detection was 7 ng ml⁻¹ for MeBPHT in the presence of HP-β-CD instead of 60 ng ml⁻¹ in the absence of HP-β-CD.     

Preconcentration of aqueous dyes through phase-transfer liquid-phase microextraction with a room-temperature ionic liquid

In this study, we employed the room-temperature ionic liquid [bmim][PF₆] as both ion-pair agent and an extractant in the phase-transfer liquid-phase microextraction (PTLPME) of aqueous dyes. In the PTLPME method, a dye solution was added to the extraction solution, comprising a small amount of [bmim][PF₆] in a relatively large amount of CH₂Cl₂, which serves as the disperser solvent to an extraction solution. Following extraction, CH₂Cl₂ was evaporated from the extractant, resulting in the extracted dyes being concentrated in a small volume of the ionic liquid phase to increase the enrichment factor. The enrichment factors of for the dye Methylene Blue, Neutral Red, and Methyl Red were approximately 500, 550 and 400, respectively; their detection limits were 0.014, 0.43, and 0.02 μg L⁻¹, respectively, with relative standard deviations of 4.72%, 4.20%, and 6.10%, respectively.     

Voltammetric behavior of C60-p-tert-butylcalix[8]arene inclusion complex film

The C₆₀-p-tert-butylcalix[8]arene inclusion complex film has been directly formed on the surface of a glassy carbon electrode, and its electrochemical behavior in acetonitrile containing tetra-n-butylammonium hexafluorophosphate as the supporting electrolyte studied. The film has a two-electron reduction wave at −1.0 V (vs Ag/AgCl), but limits to the first cathodic potential scan. Received: 16 September 1997 / Accepted: 27 October 1997     

Removal of 2,4-dichlorophenol using ionic liquid [BMIM]+[PF6]- encapsulated PVDF membrane

2,4-Dichlorophenol (2,4-DCP) is one of the toxic chlorophenol compounds found in aquatic environments. Chlorophenols are priority pollutants, due to their high toxicity, mutagenicity and carcinogenicity. In this study, experiments were carried out for the removal of 2,4-Dichlorophenol (Cl₂C₆H₃OH) from aqueous solution using commercial grade PVDF membrane immobilised with 1-Butyl-3-methyl imidazolium hexafluorophosphate [BMIM]⁺[PF6]^- ionic liquid. Scanning Electron Microscopy (SEM) and Fourier Transform Infrared Spectroscopy (FT-IR) used to identify and to confirm the surface morphology, functional groups and operational stability of Ionic Liquid [BMIM]⁺[PF₆]^- encapsulated PVDF membrane. The effect of various factors such as feed phase pH, initial 2,4-DCP concentration, operation time and stirring speed along with different stripping agents such as NaOH, KOH and NH₄OH on the removal of chlorophenols has been investigated. The maximum permeation rate of 85.52% was achieved over an experimental run of 24 at pH 4 with a strip flux of 8.18323 × 10^?09 mol m^?2s^?1 in 0.1 M NaOH strip phase.     

Metallic macrocycle with a 1,3-alternate calix[4]arene salicylideneamine ligand

The calix[4]arene-based podand which incorporates two salicylideneamine units in 1,3-alternate positions of the lower rim has been prepared and subjected to complexation studies with transition metal ions. The nickel and copper complexes form a 2 : 2 stoichiometric metallic macrocyclic framework.     

Ionic liquid pillar[5]arene: its ionic conductivity and solvent-free complexation with a guest

A room-temperature ionic liquid containing macrocyclic compound pillar[5]arene in its core was synthesized. The ionic liquid showed high thermal stability, moderate ionic conductivity and solvent-free complexation ability with the guest tetracyanoethylene.     

γ-Radiation effect on ionic liquid [bmim][BF4]

The effect of γ radiation on 1-butyl-3-methylimidazolium tetrafluoroborate ([bmim][BF₄]) was investigated in detail. It was found that radiation induced an increase of UV absorption of the ionic liquid but no change in its glass transition point. Raman spectroscopy analysis indicates that the radiolysis of [bmim][BF₄] induces detectable destruction of alkyl-chain and scission of H-atoms of ring of imidizolium cation, and the relatively small changes of BF₄⁻ anion. Viscosities of irradiated [bmim][BF₄] samples were measured at different shear rates and temperatures, and compared with irradiated [bmim][PF₆] samples. The plots of shear stress against shear rate indicates that [bmim][BF₄] is a Newtonian fluid, no matter with irradiation. The viscosity of irradiated [bmim][BF₄] decreased with increasing of temperature and followed an Arrhenius equation. However, radiation caused no change in the viscosity of [bmim][BF₄], but a decrease in the viscosity of [bmim][PF₆] by up to 10%. We conclude that the radiation stability of [bmim][BF₄] is higher than [bmim][PF₆].     

Spectrofluorimetric determination of benzoimidazolic pesticides: effect of p-sulfonatocalix[6]arene and cyclodextrins

The effect of the addition of a macrocyclic host (H) such as p-sulfonatocalix[6]arene (C6S), native and modified cyclodextrins (CDs), on the fluorescence of benzoimidazolic fungicides (P), like Benomyl (BY) and Carbendazim (CZ), has been studied. The fluorescence of BY in water at pH 1.000 and 25.0 degrees C was increased in the presence of C6S, alphaCD and hydroxypropyl-beta-CD (HPCD). The association constants determined by fluorescence enhancement showed weak interactions (K(A) approximately 10(1) to 10(2) M(-1)) between the fungicide with both CDs, whereas they were stronger with C6S (K(A) approximately 10(5) M(-1)). Molecular recognition of BY for C6S was mainly attributed to electrostatic interactions, and for CDs to the hydrophobic effect and hydrogen bond formation. On the other hand, the fluorescent behaviour of CZ in the presence of C6S at pH 6.994 was interpreted as the formation of two complexes with 1:1 (P:H) and 1:2 (P:H(2)) stoichiometry, the latter being less fluorescent than the free analyte. Relative fluorescence quantum yield ratios between the complexed and free BY (phi(P:H)/phi(P)) were 2.00+/-0.05, 1.40+/-0.03 and 2.8+/-0.4 for C6S, alphaCD and HPCD, respectively. The analytical parameters improved in the presence of C6S and CDs. The best limit of detection (L(D), ng mL(-1)) was 17.4+/-0.8 with HPCD. The proposed method with C6S and HPCD was successfully applied to fortified samples of tap water and orange flesh extract with good recoveries (91-106%) and R.S.D. (< or = 2%) by triplicate analysis. The method is rapid, direct and simple and needs no previous degradation or derivatization reaction.     

Extraction and DFT study on the complexation of H3O with hexaethyl p-tert-butylcalix[6]arene hexaacetate

From extraction experiments and γ-activity measurements, the extraction constant corresponding to the equilibrium H₃O⁺(aq) + 1· Na⁺(nb)  1·H₃O⁺(nb) + Na⁺(aq) taking place in the two-phase water–nitrobenzene system (1 = hexaethyl p-tert-butylcalix[6]arene hexaacetate; aq = aqueous phase, nb = nitrobenzene phase) was evaluated as log K_ex (H₃O⁺, 1·Na⁺) = −0.6 ± 0.1. Further, the stability constant of the 1·H₃O⁺ complex in water saturated nitrobenzene was calculated for a temperature of 25 °C as log β_nb (1·H₃O⁺) = 6.8 ± 0. 2. By using quantum mechanical DFT calculations, the most probable structure of the 1·H₃O⁺ complex species was predicted. In this complex, the hydroxonium ion H₃O⁺ is bound partly to three carbonyl oxygen atoms by strong hydrogen bonds and partly to three alternate phenoxy oxygens by somewhat weaker hydrogen bonds.