The synthesis and characterisation of a partially substituted calix[4]arene, namely, 5,11,17,23-tetra-tert-butyl,25,27-bis[aminoethoxy] 26,28-dihydroxycalix[4]arene are reported. Its interaction with commonly used pharmaceuticals (clofibric acid, diclofenac and aspirin) was investigated by spectroscopic (1H NMR and UV), electrochemical (conductance measurements) and thermal (titration calorimetry) techniques. It is concluded on the basis of the experimental work and molecular simulation studies that the receptor interacts selectively with these drugs. Preliminary studies on the selective extraction of these pharmaceuticals from water by the calix receptor are reported and the potential for a carrier mediated sensor based on this ligand for ‘on site’ monitoring of pharmaceuticals is discussed.Download high-res image (180KB)Download full-size image

The use of calixpyrroles as cation monitoring systems is very limited. The importance of fundamental studies for providing the basis for the selection of an appropriate ionophore for use in the design of ion selective electrodes cannot be overemphasised. Thus a new ditopic receptor, namely meso-tetramethyl-tetrakis-(4N,N-diethylacetamide) phenoxymethyl]calix[4]pyrrole (CPA), bearing cation and anion recognition sites has been synthesized and characterized using NMR measurements in acetonitrile. This new receptor interacts with Ca(II), Sr(II), Ba(II), Pb(II) and Cd(II) perchlorate salts and Hg(II) (nitrate as counter-ion). Among the cations tested, 1:1: complexes were found between CPA and the above mentioned cations except Hg(II) for which a 1:2 (ligand:metal cation) complex is found. These fundamental studies provided the basis for the design of a Hg(II) ion selective electrode (ISE). A detailed investigation on possible interactions between the analyte and the individual components of the membrane in solution as well as in membranes prepared in the absence of the receptor, revealed that NaPh4B, an additive frequently used in the preparation of mercury ion selective membranes, interacts with Hg(II). The implications of these findings on previously reported (Hg(II) ISE) are discussed. The optimum working conditions of the new electrode on its potentiometric response were established. Selectivity coefficients of Hg(II) relative to other cations were calculated. The advantages of this electrode relative to others reported in the literature are discussed. Analytical applications include its use as an indicator electrode as well as for the quantitative determination of this cation in an amalgam.

Correction for ‘A ditopic calix[4]pyrrole amide derivative: highlighting the importance of fundamental studies and the use of NaPh4B as additive in the design and applications of mercury(II) ion selective electrodes’ by Angela F. Danil de Namor et al., J. Mater. Chem. A, 2015, DOI: 10.1039/c5ta02215k.

Two molecular receptors based on calix[4]arenes and their interaction with chlorophenoxy acid herbicides in solution and in the solid state have been investigated. From 1H NMR studies it is shown that the conformational changes of the receptor are directly related to the acid strength of the herbicide. Conductance data show that the interaction takes place through a proton transfer reaction from the herbicide to the receptor. This is also reflected in the solid state (X-ray crystallography). Based on these fundamental studies, these receptors were immobilised by grafting them into a silica based solid support. The extracting properties of calix[4]arene modified silica for these pollutants were investigated as a function of the pH of the aqueous solution and the capacities of these materials to remove these pollutants are reported. Titration calorimetry is for the first time explored to determine the factors (kinetics, mass/solution ratio and temperature) contributing to the optimal removal of herbicides from water. These materials can be easily recycled via a pH switching mechanism. After several recycling processes the extraction capacity of these materials remains at the level of 80–90% of the original value.

A new lower rim partially functionalized calix[4]arene, namely, 5,11,17,23-tetra-tert-butyl[25,27-bis(diethylthiocarbamoyl)oxy]calix[4]arene, 1 was synthesized and characterized by 1H NMR in different deuterated solvents to assess the degree of solvent–ligand interactions and the conformation of 1 in solution. 1H NMR, conductometric and thermodynamic investigations reveal that this receptor interacts only with silver(I) and mercury(II) in dipolar aprotic media. The complexation process has been thermodynamically characterized and the results are compared with the corresponding data (when available) involving analogous ligands and these metal cations in the appropriate solvent. Emphasis is made on the difference between ‘selective extraction’ and ‘selective ionic recognition’ by receptors. Final conclusions are given.

Following the synthesis and characterization of meso-tetramethyl tetrakis (4-phenoxy acetone) calix[4]pyrrole, 1, the solution properties of this receptor in various solvents were investigated. Particular emphasis is placed on the selection of the solvent in assessing thermodynamic selectivity in ion complexation studies involving calixpyrrole receptors. Thus, statements recently made in the literature are addressed. The interaction of 1 with anions and cations was assessed through 1H NMR in CD3CN at 298 K. Among anions, significant chemical shift changes were observed in the pyrrolic protons by the addition of halide salts to 1 in the deuterated solvent. The sequence observed in the Δδ values is that observed in the transfer Gibbs energies of these anions from a dipolar aprotic (acetonitrile) to a protic medium (representative of 1) based on the Ph4AsPh4B convention. As far as metal cations in CD3CN are concerned, the most significant changes are observed (relative to those of the ligand) in the protons of the phenoxy acetone functionality upon the addition of the mercury(II) salt to 1. Conductance measurements reveal the formation of 1:1 complexes with these ions. Thermodynamic data derived from titration calorimetry are reported and compared with available data for analogous ligands. A quantitative evaluation of the thermodynamic stability was carried out. The applications of these ligands as anchor groups in oligomeric frameworks are discussed. Final conclusions are given.

Diethyl sulfide was chemically immobilized on the surface of silica gel (0.2–0.5 and 0.06 mm) for the formation of two newly synthesized silica gel phases (S1 and S2). A new chelating resin containing meso-tetramethyl-tetrakis-(thiophene)calix[4]pyrrole, CP(I), was also synthesized via the condensation of CP(I) with formaldehyde. The selection of this receptor is based on fundamental studies. Among the cations and anions considered, CP(I) interacts only with mercury(II). The functionalized silicas and the calixpyrrole resin were characterized by elemental analysis and mass spectrometry. The batch removal of metal cations (Hg2+, Pb2+ and Cd2+) by these materials from aqueous solutions was investigated. The uptake capacities of the silica based materials (S1 and S2) and calixpyrrole polymers (R1) for the Hg2+ cation were determined. The Hg(II) cation uptake data have been found to fit both, the Langmuir and Freundlich isotherms, and the coefficients indicated favorable uptake of this cation by these materials. Parameters such as the kinetics of the uptake process, pH, temperature, silica particle size and metal-ion concentration effects were evaluated. The data obtained clearly indicate that S1 has the higher uptake capability and faster retention rate for Hg(II) ions relative to S2 and R1. In a column operation, it was observed that the Hg2+ cation was effectively removed from aqueous solution by the calixpyrrole resin, R1. The percentage of recovery of this resin for the Hg2+ cation was found to be higher than 95%. The results obtained are compared with previously reported materials for mercury removal from aqueous solutions.

The implications of environmental contamination by fluoride on human health call upon the need for the development of monitoring systems for the ‘in situ’ detection of fluoride in contaminated sources and new technologies approaches for their removal. This paper reports recent work on the design of calixpyrrole receptors selective for the fluoride anion. The various steps undertaken for the thermodynamic characterization of these receptors and their anionic complexes are discussed. Thus based on thermodynamic data, the medium and ligand effects on selectivity are quantitatively assessed using representative calixpyrrole derivatives.

The distribution of various chlorinated compounds, 2,4-dichlorophenoxyethanoic acid, 2,4-D, 2-(2,4-dichlorophenoxy)propionic acid, 2,4-DP, 2,4,5-trichlorophenoxyethanoic acid, 2,4,5-T, 2-(2,4,5-trichlorophenoxy)propionic acid, 2,4,5-TP and 2,3,6-trichlorophenylethanoic acid, 2,3,6-T, was investigated in mutually saturated water–non-aqueous solvent systems at 298.15 K. The data were used to calculate (i) the distribution constant, Kd, referred to the process involving ionic species in the aqueous phase and undissociated species in the organic phase and (ii) the dimerisation constant, Kdim, in aprotic media saturated with water. A new treatment used to derive these data is described. The Kd values in the mutually saturated solvents for the various pesticides are compared with corresponding data in the pure solvents derived from solubility measurements in water and in non-aqueous solvents. Data in water were corrected for ion-pair formation while those in the organic phase were corrected for dimerisation. Good agreement is found between the two sets of data.

•First report on calix[4]pyrrole interactions with arsenic species (solution and solid state).•Optimal conditions established for removing As(III) and As (V) from water.•High removal capacity of receptor for arsenic species and fast kinetics of extraction.•Tests on real water samples from contaminated sites with high percentages of removal.Although extensive research has been carried on anion complexation reactions involving calix[4]pyrrole, nothing has been reported regarding this receptor and its interaction with arsenic species. The fact that a single step reaction is required for the synthesis of this receptor, calls upon the need to explore its removal ability for these species from water as a starting point for the development of a new technological approach for water remediation purposes based on Supramolecular Chemistry. This paper reports a detailed study on the interactions involving calix[4]pyrrole with As(III) and As(V). The interaction of As species and calix[4]pyrrole was assessed by 1H NMR using a phase transfer approach aided by molecular simulation studies. The X-ray spectrum confirms the presence of arsenic species in the solid receptor.Optimal conditions for removing As(III) and As(V) from water were established. The kinetics of extraction is fast and calix[4]pyrrole is able to remove 15.28 and 14.29 mg/g of arsenate and arsenite respectively.Material was tested for removing arsenic species from real samples collected from different contaminated sites in Argentina. Percentages of arsenate, arsenite and organic arsenic removed from these samples are higher than 85%.Download high-res image (164KB)Download full-size image

Following the synthesis and characterization of meso-tetramethyl tetrakis (4-phenoxy acetone) calix[4]pyrrole, 1, the solution properties of this receptor in various solvents were investigated. Particular emphasis is placed on the selection of the solvent in assessing thermodynamic selectivity in ion complexation studies involving calixpyrrole receptors. Thus, statements recently made in the literature are addressed. The interaction of 1 with anions and cations was assessed through 1H NMR in CD3CN at 298 K. Among anions, significant chemical shift changes were observed in the pyrrolic protons by the addition of halide salts to 1 in the deuterated solvent. The sequence observed in the Δδ values is that observed in the transfer Gibbs energies of these anions from a dipolar aprotic (acetonitrile) to a protic medium (representative of 1) based on the Ph4AsPh4B convention. As far as metal cations in CD3CN are concerned, the most significant changes are observed (relative to those of the ligand) in the protons of the phenoxy acetone functionality upon the addition of the mercury(II) salt to 1. Conductance measurements reveal the formation of 1:1 complexes with these ions. Thermodynamic data derived from titration calorimetry are reported and compared with available data for analogous ligands. A quantitative evaluation of the thermodynamic stability was carried out. The applications of these ligands as anchor groups in oligomeric frameworks are discussed. Final conclusions are given.

Diethyl sulfide was chemically immobilized on the surface of silica gel (0.2–0.5 and 0.06 mm) for the formation of two newly synthesized silica gel phases (S1 and S2). A new chelating resin containing meso-tetramethyl-tetrakis-(thiophene)calix[4]pyrrole, CP(I), was also synthesized via the condensation of CP(I) with formaldehyde. The selection of this receptor is based on fundamental studies. Among the cations and anions considered, CP(I) interacts only with mercury(II). The functionalized silicas and the calixpyrrole resin were characterized by elemental analysis and mass spectrometry. The batch removal of metal cations (Hg2+, Pb2+ and Cd2+) by these materials from aqueous solutions was investigated. The uptake capacities of the silica based materials (S1 and S2) and calixpyrrole polymers (R1) for the Hg2+ cation were determined. The Hg(II) cation uptake data have been found to fit both, the Langmuir and Freundlich isotherms, and the coefficients indicated favorable uptake of this cation by these materials. Parameters such as the kinetics of the uptake process, pH, temperature, silica particle size and metal-ion concentration effects were evaluated. The data obtained clearly indicate that S1 has the higher uptake capability and faster retention rate for Hg(II) ions relative to S2 and R1. In a column operation, it was observed that the Hg2+ cation was effectively removed from aqueous solution by the calixpyrrole resin, R1. The percentage of recovery of this resin for the Hg2+ cation was found to be higher than 95%. The results obtained are compared with previously reported materials for mercury removal from aqueous solutions.

The use of calixpyrroles as cation monitoring systems is very limited. The importance of fundamental studies for providing the basis for the selection of an appropriate ionophore for use in the design of ion selective electrodes cannot be overemphasised. Thus a new ditopic receptor, namely meso-tetramethyl-tetrakis-(4N,N-diethylacetamide) phenoxymethyl]calix[4]pyrrole (CPA), bearing cation and anion recognition sites has been synthesized and characterized using NMR measurements in acetonitrile. This new receptor interacts with Ca(II), Sr(II), Ba(II), Pb(II) and Cd(II) perchlorate salts and Hg(II) (nitrate as counter-ion). Among the cations tested, 1:1: complexes were found between CPA and the above mentioned cations except Hg(II) for which a 1:2 (ligand:metal cation) complex is found. These fundamental studies provided the basis for the design of a Hg(II) ion selective electrode (ISE). A detailed investigation on possible interactions between the analyte and the individual components of the membrane in solution as well as in membranes prepared in the absence of the receptor, revealed that NaPh4B, an additive frequently used in the preparation of mercury ion selective membranes, interacts with Hg(II). The implications of these findings on previously reported (Hg(II) ISE) are discussed. The optimum working conditions of the new electrode on its potentiometric response were established. Selectivity coefficients of Hg(II) relative to other cations were calculated. The advantages of this electrode relative to others reported in the literature are discussed. Analytical applications include its use as an indicator electrode as well as for the quantitative determination of this cation in an amalgam.

Correction for ‘A ditopic calix[4]pyrrole amide derivative: highlighting the importance of fundamental studies and the use of NaPh4B as additive in the design and applications of mercury(II) ion selective electrodes’ by Angela F. Danil de Namor et al., J. Mater. Chem. A, 2015, DOI: 10.1039/c5ta02215k.