Sulfur-containing hetero-calix[4]pyrroles as mercury(II) cation-selective receptors: thermodynamic aspects

Two sulfur-containing hybrid calix[4]pyrrole derivatives (III and IV) have been synthesized and fully characterized. Several analytical techniques (1H NMR, conductance measurements, UV-vis spectrophotometry, titration potentiometry, and titration calorimetry) have been used to assess the interaction between these hybrid calixpyrrole receptors and metal cations in acetonitrile and dimethylsulfoxide. The partition constants of calix[4]pyrrole, I, II, and IV in the acetonitrile-hexane solvent system and the solubilities of the ligands in various solvents at 298.15 K were determined. 1H NMR measurements reveal the sites of interaction of calixpyrrole ligands with metal cations in CD3CN. Conductance and UV-vis spectrophotometric measurements were performed to establish the composition of mercury(II) calixpyrrole complexes in acetonitrile at 298.15 K. Titration calorimetry was used to quantitatively assess Hg(II)-calixpyrrole interactions. Thus the thermodynamics of complexation of calixpyrrole ligands with the mercury(II) cation in acetonitrile at 298.15 K are reported. Potentiometric titrations were also used to establish the stepwise stability constants for the complexation of calix[3]thieno[1]pyrrole with the Hg(II) cation in acetonitrile at 298.15 K. The results show that replacement of one or more pyrrole units by thiophene rings in calix[4]pyrrole has tuned significantly the discrimination ability of these ligands between anions and enables the produced hybrid calixpyrroles to bind selectively with Hg(II) in acetonitrile. No interaction was observed between these ligands and other metal cations in acetonitrile.     

Missing-link macrocycles: hybrid heterocalixarene analogues formed from several different building blocks

The synthesis and structural characterization of hybrid heterocalix[4]arene analogues containing pyrrole, benzene, methoxy-substituted benzene, and pyridine subunits is described. Macrocycles 1 and 2, examples of calix[2]benzene[2]pyrrole and calix[1]benzene[3]pyrrole systems, respectively, are synthesized by the condensation of pyrrole and an appropriate phenylbis(carbinol). Macrocycles 3 and 7, examples of calix[2]benzene[1]pyridine[1]pyrrole and calix[1]pyridine[3]pyrrole, respectively, are synthesized by the use of a carbene-based pyrrole-to-pyridine ring-expansion procedure. Single-crystal X-ray analysis reveals that compounds 1a, 1b, and 2b adopt 1,3-alternate conformations in the solid state, whereas compounds 3 and 7 display structures that are best described as "flattened partial cones" in terms of their conformation. (Series a refers to pure benzene-derived systems, whereas series b indicates macrocycles containing 5-methoxyphenyl subunits). In the solid state, the methoxy-functionalized macrocycles 1b and 2b, and the chloropyridine-containing macrocycle 7 exist as dimers. In the case of 1a and 7, these compounds interact with neutral solvent in the solid state. The conformations of the macrocycles in solution were explored by temperature-dependent proton NMR and NOESY spectral analysis. At 188 K, macrocycles 1a and 2a adopt flattened 1,3-alternate conformations, whereas macrocycles 3 and 7 exist in the form of flattened partial-cone conformations. Standard proton NMR titration analyses were carried out in the case of macrocycles 1a and 2a, and reveal that at least the second of these systems is capable of binding fluoride and chloride anions in CD(2)Cl(2) solution at room temperature (K(a)=571 and 17M(-1) in the case of 2a and F(-) and Cl(-), respectively).     

Strapped and other topographically nonplanar calixpyrrole analogues. Improved anion receptors

Calixpyrroles and related macrocycles are non-aromatic synthetic anion receptors that have attracted considerable attention in recent years. The unfunctionalized, parent calix[4]pyrrole system, also known as octamethylporphyrinogen, may be prepared in one step and in high yield from pyrrole and acetone, and is an effective anion receptor, showing a preference for fluoride, phosphate, carboxylate and chloride anions in organic media. Efforts to improve the anion binding affinity of calix[4]pyrrole and to modify its inherent selectivity have led to the synthesis of a variety of new, modified calixpyrroles. Among the most effective of these are derivatives that contain bridging "straps". In this Feature Article, the preparation and properties of these and other topographically nonplanar calixpyrrole analogues are reviewed from the perspective of the anion recognition chemist.     

Synthesis and Properties of Functionalized Schiff Bases of 5α,10α-Di（4-hydroxylphenyl）calix[4]pyrrole and 5α,15β-Di（4-hydroxylphenyl）calix｜4] pyrrole

A series of calix[4]pyrrole meso-substituted Schiff bases was synthesized with 5α,10α-di（4- hydroxylphenyl）calix[4]pyrrole or 5α,15β-di（4-hydroxylphenyl）calix[4]pyrrole as starting materials. The synthetic routes included alkylation with methyl a-chlroroaceate, ammonolysis with alkylene diamine, and condensation with salieylladehyde or 2-hydroxynaphthaldehyde. The crystal structures of the new calix[4]pyrroles and their Schiff bases were determined by X-ray diffraction. The coordination properties of the representative ealix[4]pyrrole Sehiff bases to transition metal ions were also investigated by UV-Vis spectra.     

A new calix[4]pyrrole derivative and its anion (fluoride)/cation (mercury and silver) recognition

A new calix[4]pyrrole-based macrocycle, meso-tetramethyl-tetrakis{4-[2-(ethylthio)ethoxy]phenyl}calix[4]pyrrole, 7, has been synthesized and fully characterized. Unlike other calixpyrrole derivatives that show selective interaction with anions, calixpyrrole 7 described in the present work forms stable complexes with both metal cations and anions. The thermodynamics of complexation of this ditopic calixpyrrole derivative with metal cations (Hg2+ and Ag+) and the fluoride anion in nonaqueous solutions have been determined by titration calorimetry, and the host-guest composition has been investigated by using conductance measurements at 298.15 K. 1H NMR studies provide clear evidence about the sites of complexation of 7 with the ionic species, which show that the NH groups are taking part in the complexation of this ligand with the fluoride anion while the sulfur donor atoms are responsible for the interaction with metal cations. Using the present data on 7 and structurally related analogues (1-6), the complexation behavior is discussed comparatively from the thermodynamic point of view. Possessing four sulfur-containing pendent arms, 7 displays an enhanced hosting ability for Hg2+ in acetonitrile. As compared with 1, the calixpyrrole derivative, 7, shows a unique interaction with fluoride among the anions investigated in acetonitrile and dimethyl sulfoxide. As far as the fluoride complex is concerned, the medium effect is assessed in terms of the thermodynamics of the transfer of reactants and product from acetonitrile (reference solvent) to dimethyl sulfoxide.     

N-Confused Calix

Next to the "normal" calix[4]pyrrole 1, the N-confused calix[4]pyrrole 2 is formed in substantial amounts (up to 22 % yield) as side product in the acid-catalyzed condensation reaction of ketones and pyrrole. In some cases, doubly N-confused calix[4]pyrroles are also formed.     

Tetrakis(bicyclo[2.2.2]oct‐2‐ene)‐Fused Calix[4]pyrrole

Tetrakis(bicyclo[2.2.2]oct‐2‐ene)‐fused calix[4]pyrrole, 5 , was obtained starting from (E)‐1,2‐bis(phenylsulfonyl)ethylene. This new calixpyrrole derivative is the prospective precursor of tetrabenzocalix[4]pyrrole, a potential ion‐pair receptor and an attractive species as a possible deep‐walled ‘molecular container’.     

Calix[6]pyrrole and hybrid calix[n]furan[m]pyrroles (n+m=6): syntheses and host-guest chemistry

Calix[6]pyrrole 2 and the "hybrid systems" calix[3]furan[3]pyrrole 12, calix[2]furan[4]pyrrole 13, and calix[1]furan[5]pyrrole 14, have been synthesized by increasing conversion of the furan units present in the readily accessible calix[6]furan 3 to pyrroles. The host-guest chemistry of these novel macrocycles towards a number of anions, including halogen ions, dihydrogen phosphate, hydrogen sulfate, nitrate, and cyanide has been investigated in solution by (1)H NMR titration techniques and/or phase transfer experiments. The solid-state structures of the free receptors 2, 12, and 13, the 1:1 complexes of calix[6]pyrrole 2 with chloride and bromide, and the 1:1 complex of 14 with chloride are also reported.     

Modified calix[4]pyrrole receptor: solution thermodynamics of anion complexation and a preliminary account on the phosphate extraction ability of its oligomer

A modified calix[4]pyrrole, namely meso-tetramethyl-tetrakis-(4-hydroxyphenyl) calix[4]pyrrole, 1, has been synthesized and characterized. (1)H NMR investigations in various deuterated solvents seems to indicate that this receptor interacts with acetone-d(6). The solution thermodynamics of 1 in various solvents is reported. Complexation studies in CD(3)CN show that the NH and OH functionalities of 1 are the active sites of its interaction with the fluoride and the dihydrogen phosphate anions. The composition of the anion complexes was established through conductance measurements. In all cases, 1:1 complexes are formed. The thermodynamics of anion complexation in acetonitrile and N,N-dimethylformamide is discussed comparatively with previous reported data for the parent calix[4]pyrrole, 2, and these anions in these solvents. The medium effect on anion complexation is discussed in terms of the solvation properties of the reactants and the product in acetonitrile and N,N-dimethylformamide. An oligomeric material containing 1 as anchor group was synthesized and characterized by mass spectrometry. Preliminary studies have been performed to assess the extracting properties of this oligomer for the removal of phosphates from aqueous solutions. The effects of pH, temperature on the extraction of this anion salt from water, as well as the kinetics of the process (fast) were investigated.     

Synthesis of meso‐tetra acid and ester functionalized calix[4]pyrroles

Novel meso‐tetracarboxylic acid and meso‐tetraester functionalized calix[4]pyrroles were synthesized by condensation of pyrrole with levulinic acid and ethyl pyruvate in sufficient yields. In addition, mixed condensation products can also be synthesized using this method. These new compounds may be useful as molecular receptors and polyfunctional starting materials for further derivatization.     

Transport of solutes through calix[4]pyrrole-containing cellulose acetate films

Films of cellulose acetate containing different concentrations of meso-octamethyl-porphyrinogen (calix[4]pyrrole) were prepared and characterized using UV-vis and FTIR spectroscopy, DSC and SEM. Incorporation of calix[4]pyrrole into cellulose acetate leads to a decrease in the degree of hydrophilicity of the polymeric matrix. However, a slight increase in the percentage of water uptake of the polymer is found with an increase of the initial amount of calix[4]pyrrole in the composite composition. This effect can be related to the plasticizing effect that the calix[4]pyrrole provokes in the cellulose acetate. A comparative study of transport parameters of oxygen and some non-associated electrolytes (sodium, copper(II) and nickel chlorides) was carried out. The diffusion coefficients of molecular oxygen through cellulose acetate films decrease with an increase of the concentration of calix[4]pyrrole in the composite films. The transport (diffusion and permeation) of the above mentioned electrolytes through a set of composite films shows a decrease of permeability and diffusion coefficients with an increase of calix[4]pyrrole concentration. Such behaviour is typical of systems where interactions between the polymer and diffusing species occur. However, from the analysis of the distribution coefficient, it was found that those interactions are only dependent on the calix[4]pyrrole content for 2:1 electrolytes.     

N-Tosylpyrrolidine calix[4]pyrrole: synthesis and ion binding studies

The synthesis and preliminary solution phase ion binding properties of the N-tosylpyrrolidine calix[4]pyrrole 2 are reported. This β-octaalkyl-substituted calix[4]pyrrole, the first to be prepared via a direct condensation reaction, was obtained by reacting the 3,4-alkyl-functionalized pyrrole 8 with acetone in the presence of an acid catalyst. On the basis of (1)H NMR spectroscopic analyses and isothermal titration calorimetry, it was concluded that, compared with the parent, β-unsubstituted calix[4]pyrrole (1), compound 2 possesses significantly enhanced binding ability for halide anions in chloroform. Furthermore, 2 proved capable of solubilizing in chloroform solution the otherwise insoluble salts, CsF and CsCl. These effects are ascribed to the interactions between the four tosyl groups present in 2 and the counter cations of the halide anion salts.     

Siloxane-functionalized calix[4]pyrrole: synthesis, characterization and modification of silica-based solid supports

A siloxane-functionalized calix[4]pyrrole derivative was synthesized starting from the corresponding alcohol-functionalized calix[4]pyrrole. Structural elucidation was carried out by using NMR spectroscopy, mass spectrometry and X-ray diffraction analysis. The use of this siloxane-functionalized calix[4]pyrrole for modification of various silica solid supports (silica gel 60, fume silica, and SiO₂ nanopowder) was studied. Characterization of the modified silica solid supports was achieved by FTIR, TGA, and elemental analysis. It was also shown that the production of silica nanoparticles is possible via a sol-gel reaction of siloxane-functionalized calix[4]pyrrole and tetraethoxysilane (TEOS). Calix[4]pyrrole modified silica solid supports were found to sense chloride anions of Azure A dye.     

(硫杂)杯[4]芳烃缩氨基(硫)脲(桥联)衍生物的合成

对叔丁基(硫杂)杯[4]芳烃-1,3-二醛基衍生物4a和4b与苯基氨基硫脲进行“1＋2”缩合反应, 合成了杯[4]芳烃缩氨基硫脲衍生物5a和5b, 产率为84%和85%. 化合物4a和4b与1,6-己基双氨基脲发生“1＋1”缩合反应, 合成了杯[4]芳烃双缩氨基脲桥联衍生物6a和6b, 产率为83%和80%. 新化合物的结构与构象经元素分析、质谱、核磁共振谱等表征证实.     

一锅法合成含两种桥联链的杯[4]双冠醚和双杯[4]冠醚

报道了"一锅法"合成含两种桥联链的新型杯[4]双冠醚和双杯[4]冠醚.杯[4]芳烃先与N,N’-乙撑基-二(2-氯乙酰胺)发生"1+1"缩合反应,然后直接加入三甘醇双对甲苯磺酸酯继续进行"2+2"缩合反应,合成了含两种桥联链的新型双杯[4]冠醚4.按照相似程序,杯[4]芳烃先后与N,N’-乙撑基-二(2-氯乙酰胺)、溴乙酸乙酯和二乙烯三胺反应,得到含两种桥联链的新型杯[4]双冠醚5.化合物5进一步与异硫氰酸苯酯反应合成带硫脲支链的杯[4]双冠醚6.所有新化合物的结构与构象经元素分析、质谱、核磁共振谱等表征证实.     

Spectroscopic study on anion recognition properties of calix[4]pyrroles: effects of tetraalkylammonium cations

The solution binding properties of calix[4]pyrroles with anion (added as tetraalkylammonium salts) were investigated using UV-vis spectroscopic techniques. The obvious red-shift of absorption maximum band of calix[4]pyrrole in EtOH in the presence of the tetramethylammonium (TMA(+)) or tetraethylammonium (TEA(+)) salts were observed. These results displayed in electronic absorption spectra indicated calix[4]pyrrole receptors linking anionic species through multiple hydrogen bonding interactions are capable of using the periphery electron-rich "walls" for selectively binding electron-deficient tetraalkylammonium cation subunits by cation-pi charge-transfer interaction. It was seen that the stability of the calix[4]pyrrole-anion complex depends strongly on the cation. The meso-alkyl groups of the calix[4]pyrrole, the affinity for the anion subunits and the structure of tetraalkylammonium cations have considerable effects on the formation of cation-pi charge-transfer interaction.     

Strain-Induced Ring Expansion Reactions of Calix[3]pyrrole-Related Macrocycles

The recent discovery of calix[3]pyrrole, a porphyrinogen-like tripyrrolic macrocycle, has provided an unprecedented strain-induced ring expansion reaction into calix[6]pyrrole. Here, we synthesized calix[n]furan[3-n]pyrrole (n=1∼3) macrocycles to investigate the reaction scope and mechanism of the ring expansion. Single crystal X-ray analysis and theoretical calculations revealed that macrocyclic ring strain increases as the number of inner NH sites increases. While calix[1]furan[2]pyrrole exhibited almost quantitative conversion into calix[2]furan[4]pyrrole within 5 minutes, less-strained calix[2]furan[1]pyrrole and calix[3]furan were inert. However, N-methylation of calix[2]furan[1]pyrrole induced a ring-expansion reaction that enabled the isolation of a linear reaction intermediate. The mechanism analysis revealed that the ring expansion consists of regioselective ring cleavage and subsequent cyclodimerization. This reaction was further utilized for synthesis of calix[6]-type macrocycles.     

1,3-indane-based chromogenic calixpyrroles with push-pull chromophores: synthesis and anion sensing

[structure: see text]. Knoevenagel condensation of 2-formyl-octamethylcalix[4]pyrrole with selected 1,3-indanedione derivatives yields calix[4]pyrrole anion sensors with push-pull chromophores displaying strong intramolecular charge transfer. The push-pull feature results in augmented signal output as well as in dramatic changes in anion selectivity exemplified by a 50-fold increase in acetate vs chloride selectivity compared to the parent calix[4]pyrrole.     

Synthesis of Flavin–Calix[4]arene Conjugate Derivatives

The synthesis of two new flavin substituted calix[4]arene derivatives, 9 and 10 , is described. The first flavin substituted calix[4]arene derivative 9 was synthesized by the reaction of 3‐methylalloxazine ( 5 ) with 25,27‐bis(3‐bromopropoxy)‐26,28‐dihydroxy‐5,11,17,23‐tetra(tert‐butyl)calix[4]arene ( 4 ) in high yield (92%). The other derivative 10 was prepared from 3‐methylalloxazine‐1‐acetic acid ( 7 ) and 25,27‐bis(3‐cyanopropoxy)calix[4]arene ( 3 ). All new compounds were characterized by a combination of FT‐IR and ¹H‐NMR spectroscopy, and elemental‐analysis techniques.     

手性杯[4]丝氨酸衍生物的合成及其催化性能

以对叔丁基苯酚为原料,经环化缩合、脱叔丁基、酚羟基醚化、甲酰化和氧化反应制得5-羧基-25,26,27,28-四正丙基杯[4]芳烃(5);5与O-苄基-N-苄氧羰基丝氨酸反应制得5-(O-丝氨酸)-25,26,27,28-四正丙基杯[4]甲酸酯(7),其结构经~1H NMR,~(13)C NMR和MS(ESI)表征。研究了溶剂和水的用量对7催化性能的影响。结果表明:水为溶剂,其用量为10 eq.时,收率和非对映选择性分别为95%和3∶97 dr;当水的用量为30 eq.时,收率和非对映选择性分别为93%和98∶2 dr。