Assembly of a novel supramolecular synthon of calix[4]arene presenting four carboxylic acids

An extremely complex solid state structure described by two virtual channels and a 2-D square grid of hydrogen bonds is generated by four carboxylic acids groups of calix[4]arene tetrabutyroxycarboxylic acid.     

去叔丁基杯[8]芳烃乙酸钠对紫杉醇包合作用的研究

采用紫外分光光度法和荧光光谱法研究去叔丁基杯[8]芳烃乙酸钠对紫杉醇的包合和释放过程,考察了二者物质的量之比、温度等因素对包合作用的影响.结果显示去叔丁基杯[8]芳烃乙酸钠在一定条件下与紫杉醇可形成稳定的超分子包合物,包合后水溶性明显提高,且随着去叔丁基杯[8]芳烃乙酸钠/紫杉醇物质的量之比的增加,荧光强度明显增强.去叔丁基杯[8]芳烃乙酸钠今后有望成为紫杉醇类抗肿瘤药物的良好载体.     

新型杯[4]芳烃衍生物的合成及其氨基酸萃取性能

杯[4]-1,3-二乙酸乙酯衍生物(1)与水合肼反应生成杯[4]芳烃酰肼衍生物(2),化合物(2)与异硫氰酸苯酯反应得到含酰胺和硫脲单元的新型杯[4]芳烃衍生物(3).总产率达70%.系列氨基酸萃取实验表明化合物(3)对异亮氨酸有较好的选择性萃取能力.     

Complexation of amino acids derivatives in water by calix[4]arene phosphonic acids

Series of the calix[4]arene phosphonic acids with various substituents at the lower rim was synthesized. Complexing properties of these receptors towards methyl esters of six amino acids strongly depended on the calix[4]arene conformation flexibility. The complex formation processes were monitored using ¹H NMR spectroscopy (deuterated phosphate buffer at pD 7.3, 22 °C) and association constant values were evaluated. Inherently mobile calix[4]arene molecule 3 occurred in cone conformation in aqueous solution turned out to be more effective in complexation of the basic amino acids methyl esters compared to the rigid 2 and flexible 4. Mixed 1:2 and 2:1 (host–guest) complexes were observed for compound 1 with all amino acids methyl esters.     

Networked calix[4]arene polymers with unusual mechanical properties

Polymeric networks built from calix[4]arenes that form a three dimensional folded structure have been predicted to exhibit negative Poisson's ratios (auxetic), an unusual property which makes them superior to conventional materials in many practical applications.     

Study on thermal decomposition of calix[6]arene and calix[8]arene

Thermal decomposition kinetics of calix[6]arene (C6) and calix[8]arene (C8) were studied by Thermogravimetry analysis (TG) and Differential thermal analysis (DTA). TG was done under static air atmosphere with dynamic heating rates of 1.0, 2.5, 5.0, and 10.0 K min⁻¹. Model-free methods such as Friedman and Ozawa–Flynn–Wall were used to evaluate the kinetic parameters such as activation energy (E _a) and pre-exponential factors (ln A). Model-fitting method such as linear regression was used for the evaluation of optimum kinetic triplets. The kinetic parameters obtained are comparable with both the model-free and model-fitting methods. Within the tested models, the thermal decomposition of C6 and C8 are best described by a three dimensional Jander’s type diffusion. The antioxidant efficiency of C6 and C8 was tested for the decomposition of polypropylene (PP).     

Thermodynamic study of functionalized calix[n]arene and resorcinol[n]arene monolayers spreaded at an aqueous pendant drop

The behavior of insoluble calix[n]arene and resorcinol[n]arene derivatives monolayers were studied through the use of a constant surface Langmuir balance based on Axisymmetric Drop Shape Analysis (ADSA). In each case, a stable monolayer was obtained and different transitions (induced for lateral compression) could be identified. Thermodynamic parameters were computed through two dimensional Clausius–Clayperon equations and used to valuate the monolayer stability. A noticeable reduction of thermodynamic parameters occurred at highly tested temperatures (328 and 338 K) for those compounds that had hydrocarbon tails or benzene rings attached to one side of macrocyclic rim. Such fact was related to a monolayer rearrangement where the macrocyclic ring changed from a parallel to a perpendicular orientation. In this orientation the hydrophobic interactions between hydrocarbon chains and benzene rings were maximized. At highly temperature, where vigorous molecular motion existed, those interactions were superior to the stabilization effect through hydrogen bond.     

Complexation and extraction of non-ferrous metals by calix[n]arene phosphine oxides

The extraction of non-ferrous metal (M²⁺) nitrates by the calix[4,6]arenes (L), bearing four or six phosphine oxide donor groups at the upper or at the lower rim, was quantitatively described in the form of [M_n(NO₃)_2nL] (n = 1, 2) complexes. The extraction constants (Zn²⁺ > Cu²⁺ > Co²⁺ > Ni²⁺) for the both types of L coincide with Irving-Williams sequence. Calix[4]arenes, phosphorylated at the lower (narrow) rim, provide better stability of ML complexes because of the best spatial fitting of M²⁺ by the donor groups. For the upper (wide) rim phosphorylated calix[4]arenes M₂L and ML₂ complexes are more stable. Unusual zwitterionic [Co₂(NO₃)₄L] complex of the lower rim tetraphosphorylated calix[4]arene 1 was determined by X-ray structural analysis.     

Synthesis and binding properties of calix[4]arene telomers

Two calix[4]arene derivatives (5 and 8) and their telomers are synthesized to estimate selective extraction of alkali and transition metal cations from the aqueous to the organic phase (chloroform). Compound 5 shows selectivity toward Hg²⁺. Compound 8 and telomers 6 and 9 are not selective but are good extractants for all used transition metal ions. The observations suggest that ethylene glycol bridges are efficient for carrying transition metal cations in a two-phase solvent system. © 1999 John Wiley & Sons, Inc. J Polym Sci A: Polym Chem 37: 4351–4355, 1999     

Nonlinear optical properties in calix[n]arenes: orientation effects of monomers

We investigate the nonlinear optical (NLO) polarizations for various geometric arrangements of the dipolar chromophores in a calix[n]arene geometry. The interactions were studied by using (HF)3 as model compounds both in parallel and frustrated orientations. The interdipolar angle between the monomer molecules is varied so that many different arrangements of the dipoles can be realized which is associated with the opening up of the calix[n]arene rings. Quantum-chemical calculations at both ab initio and semiempirical levels, show that the all-parallel arrangement of the dipoles exhibit the maximum magnitude for the nonlinear optical coefficients at small interdipolar angles for all interdipolar distances. In the frustrated orientations however, the NLO response is maximum at large interdipolar angles corresponding to the flattened calix[n]arene rings. The role of hydrogen bonding in stabilizing these assemblies in various conformations has been investigated. Crystallographic database analysis for calix[3]arenes shows that optical properties in real molecular systems can be modeled based on our simple interaction theory.     

Thermal behaviour of some ester derivatives of p-tert-butyl calix[n]arene

The thermal behaviour of three ester derivatives of p-tert-butyl calix[n]arene (n?=?4, 6 and 8) in comparison with the parent calixarene was investigated by means of the thermogravimetric (TG) and differential thermogravimetic (DTG) analysis and differential scanning calorimetry (DSC). The thermal stability domains, the composition of the pyrolysis products and the thermal effects, were determined on the basis of TG, DTG and DSC plots registered in nitrogen flow. Attempts to analyse the evolved gases by TG-FTIR coupling were also performed. It was demonstrated that the stability of the calix[n]arene derivatives depends on both the size of the hydrophobic cavity and number of the substituting groups grafted on the calix[n]arene skeleton.     

Effect of conformation on metal ion extraction by calix[4]arene dicarboxylic acids

Synthetic routes to four calix[4]arene stereoisomers with two distal methoxycarboxy groups and two distal butoxy groups are reported. Conformations of cone, partial cone (butyl up), partial cone (acid up), and 1,3-alternate were established by ¹H and ¹³C-NMR spectroscopy. To probe the influence of ligand conformation on metal ion complexation, extractions from aqueous solutions into 1,2-dichloroethane were performed. These included competitive alkali metal cation extractions, competitive alkaline earth metal cation extractions, and single species extractions of Pb²⁺ and of Hg²⁺. Comparisons are also made with the results for a conformationally mobile analogue in which the two butoxy groups are replaced with methoxy groups.     

Unique inclusion properties of crystalline powder p-tert-butylthiacalix[4]arene toward alcohols and carboxylic acids

Powdery crystals of p-tert-butylthiacalix[4]arene (2) selectively include EtOH from 1:1 mixtures of MeOH-EtOH and EtOH-PrOH, and EtCO(2)H from HCO(2)H-EtCO(2)H. On the other hand, no acid is included from HCO(2)H-MeCO(2)H, even though MeCO(2)H is included from the neat acid. The origins of these phenomena are discussed based on X-ray analysis of inclusion crystals prepared separately by crystallization.     

Percolation model of conductivity of calix[n]arene-p-sulfonic acids

Proton conductivity of special class of aromatic sulfonic acids is described, in particular, calixarene sulfonic acids that consist of flat anionic layers interlinked by labile two-dimensional hydrogen-bond network. High proton conductivity of their hydrates was observed earlier. The dependence of their transport characteristics (the proton conductivity, the activation energy of conductivity) was shown to have threshold character. The studied systems’ behavior is described on basis of percolation model that assumes changing of the proton transport mechanism at low water content in the structure.     

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.     

Chromogenic calix[4]arene as ionophore for potentiometric and optical sensors

Chromogenic calix[4]arene derivative was synthesized and tested as an ionophore for potentiometric and optical sensors. Distinct sodium selectivity was observed with this ionophore based, plasticized PVC membranes in potentiometric measurements suggesting their utility for biological applications. Optode membranes exhibited sodium sensitivity in the 5 x 10(-2) -10(-4)M concentration range. The optical sensitivity was improved by the use of an internal, lipophilic base (TDDA). The operation of the optical sensor is in accordance with the ion-exchange theory.     

Supramolecular structures formed by calix[8]arene derivatives

Octamethoxy calix[8]arenes substituted in the para position by amide, urea, and imide functions were synthesized from the octamethyl ether of tert-butylcalix[8]arene by ipso nitration, reduction, and acylation. Scanning force microscopy of spin coated samples on graphite suggests that these derivatives self-organize into tubular nanorods via hydrogen bonds between p-amide functions. A single-crystal X-ray structure reveals a centrosymmetric conformation for the octanitro derivative. [structure: see text]     

Synthesis by ring closing metathesis and properties of an electroactive calix[6]arene [2]catenane

Abstract

Tris-(N-phenylureido)-calix[6]arenes are heteroditopic non-symmetric molecular wheels that, in apolar media, bind viologen-based molecular axles in a pseudorotaxane-type fashion. Because of the precise kinetic requirements associated with the threading process, in apolar solvents, the dicationic portion of the axle enters the calixarene annulus exclusively from the upper rim. With the general aim to develop new prototypes of molecular devices and machines whose functions could be governed through a wider set of control elements, we envisaged that the unique properties of these calixarene wheels could be transferred to the synthesis of new catenanes for the construction of unidirectional rotary motors. Herein, we describe the synthesis of a tris(N-phenylureido)calix[6]arene-based catenane by applying the intramolecular ring-closing metathesis reaction for the catenation step on a pre-formed pseudorotaxane.