Fluorescence Recognition of Anions Using a Heteroditopic Receptor: Homogenous and Two-Phase Sensing

In contrast to monotopic receptor 3, the anthracene functionalized squaramide dual-host receptor 1 is capable of selectively extracting sulfate salts, as was evidenced unambiguously by DOSY, mass spectrometry, fluorescent and ion chromatography measurements. The receptors were investigated in terms of anion and ion pair binding using the UV–vis and ¹H NMR titrations method in acetonitrile. The reference anion receptor 3, lacking a crown ether unit, was found to lose the enhancement in anion binding induced by the presence of cations. Besides the ability to bind anions in an enhanced manner exhibited by ion pair receptors 2 and 4, changing the 1-aminoanthracene substituent resulted in their exhibiting a lower anion affinity than receptor 1. By using receptor 1 and adjusting the water content in organic phase it was possible to selectively detect sulfates both by “turn-off” and “turn-on” fluorescence, and to do so homogenously and under interfacial conditions. Such properties of receptor 1 have allowed the development of a new type of sensor capable of recognizing and extracting potassium sulfate from the aqueous medium across a phase boundary, resulting in an appropriate fluorescent response in the organic solution.     

Highly Efficient,Tripodal Ion-Pair Receptors for Switching Selectivity between Acetates and Sulfates Using Solid–Liquid and Liquid–Liquid Extractions

A tripodal, squaramide-based ion-pair receptor 1 was synthesized in a modular fashion, and ¹H NMR and UV-vis studies revealed its ability to interact more efficiently with anions with the assistance of cations. The reference tripodal anion receptor 2, lacking a crown ether unit, was found to lose the enhancement in anion binding induced by presence of cations. Besides the ability to bind anions in enhanced manner by the “single armed” ion-pair receptor 3, the lack of multiple and prearranged binding sites resulted in its much lower affinity towards anions than in the case of tripodal receptors. Unlike with receptors 2 or 3, the high affinity of 1 towards salts opens up the possibility of extracting extremely hydrophilic sulfate anions from aqueous to organic phase. The disparity in receptor 1 binding modes towards monovalent anions and divalent sulfates assures its selectivity towards sulfates over other lipophilic salts upon liquid–liquid extraction (LLE) and enables the Hofmeister bias to be overcome. By changing the extraction conditions from LLE to SLE (solid–liquid extraction), a switch of selectivity from sulfates to acetates was achieved. X-ray measurements support the ability of anion binding by cooperation of the arms of receptor 1 together with simultaneous binding of cations.     

The Effect of the Counter Anion on the Complexation of Alkali Metal Salts to Polyethylene Glycol

The complexation of alkali metal salts by polyethylene glycol is strongly dependent on the counter anion of the salt. In general, potassium salts are more easily complexed. In fact, sodium salts at low free energy of formation are barely complexed at all. By conductometric and index of refraction measurements it was shown that anions capable of hydrogen bonding such as OH⁻, F⁻, HSO⁻₄ and HCO⁻₃ were ion paired to the complexed potassium cation and existed as relatively “naked” anions. Other anions such as Cl⁻, Br⁻, I⁻, SCN⁻, NO⁻₃, NO⁻₂ AND HF⁻₂ existed as disassociated anions with significant solvation shells. The use of polyethylene glycol as a phase transfer catalyst considering the results found is discussed.     

Synthesis and Ion-Binding Properties of Polymeric Pseudocrown Ethers: A Molecular Dynamics Study

Abstract

A novel method for producing inexpensive polymeric pseudocrown ethers in situ during free-radical polymerizations was investigated using molecular dynamics simulations. This scheme is based upon a template ion and exploits the tendency of oligomeric ethylene glycol diacrylates to form intramolecular cycles during polymerization. In the scheme, a template ion is used to induce the poly(ethylene glycol) diacrylates (PEGDA) to assume cyclic structures before polymerization with a comonomer. Experimental studies demonstrated that certain salts that were insoluble in nonpolar solvents were solubilized upon the addition of oligomeric poly(ethylene glycol) (PEG) due to complexation. Further evidence of cation binding by oligomeric PEG was obtained by ¹H NMR studies of PEG and its complexes with metal salts. To optimize the template ion synthesis approach, molecular dynamics simulations were performed on PEGDA containing between two and ten ethylene glycol repeating units, with and without the presence of cations. Simulation results indicated that the presence of the templating cation significantly decreased the mean end-to-end distance, thereby bringing the unsaturated endgroups into close proximity. The PEGDA ligand that resulted in the most effective templatization for Na⁺ contained four ethylene glycol repeating units. Simulation times greater than 50 ps had little effect on the results for ligands containing 7 or fewer ethylene glycol repeating units.     

Synthesis and anion-sensing property of a family of Ru(II)-based receptors containing functionalized polypyridine as binding site

A family of fluoroionophores have been synthesized incorporating Ru(II)-bipyridine moiety as fluorogenic unit and amino/benzenesulphonamido functionalized 1,10-phenanthroline moiety, attached to Ru(II), as binding sites. Two of the ligands and one of the complexes have been characterized crystallographically. Anion recognition property, studied by luminescence, UV–vis and ¹H NMR spectroscopy, with a large number of anions exhibit strong complexation with F^?, H₂PO₄^? and AcO^?. Binding constants have been determined from luminescence titration and ¹H NMR study gave insight about binding site of anions. Bidentate chelating nature of the H₂PO₄^? and AcO^? anions and steric crowding created by benzenesulphonamide moiety has significantly influenced binding constants and selectivity.     

Thiacalixarenes with Sulfur Functionalities at Lower Rim: Heavy Metal Ion Binding in Solution and 2D-Confined Space

Sulfur-containing groups preorganized on macrocyclic scaffolds are well suited for liquid-phase complexation of soft metal ions; however, their binding potential was not extensively studied at the air–water interface, and the effect of thioether topology on metal ion binding mechanisms under various conditions was not considered. Herein, we report the interface receptor characteristics of topologically varied thiacalixarene thioethers (linear bis-(methylthio)ethoxy derivative L², O₂S₂-thiacrown-ether L³, and O₂S₂-bridged thiacalixtube L⁴). The study was conducted in bulk liquid phase and Langmuir monolayers. For all compounds, the highest liquid-phase extraction selectivity was revealed for Ag⁺ and Hg²⁺ ions vs. other soft metal ions. In thioether L² and thiacalixtube L⁴, metal ion binding was evidenced by a blue shift of the band at 303 nm (for Ag⁺ species) and the appearance of ligand-to-metal charge transfer bands at 330–340 nm (for Hg²⁺ species). Theoretical calculations for thioether L² and its Ag and Hg complexes are consistent with experimental data of UV/Vis, nuclear magnetic resonance (NMR) spectroscopy, and single-crystal X-ray diffractometry of Ag–thioether L² complexes and Hg–thiacalixtube L⁴ complex for the case of coordination around the metal center involving two alkyl sulfide groups (Hg²⁺) or sulfur atoms on the lower rim and bridging unit (Ag⁺). In thiacrown L³, Ag and Hg binding by alkyl sulfide groups was suggested from changes in NMR spectra upon the addition of corresponding salts. In spite of the low ability of the thioethers to form stable Langmuir monolayers on deionized water, one might argue that the monolayers significantly expand in the presence of Hg salts in the water subphase. Hg²⁺ ion uptake by the Langmuir–Blodgett (LB) films of ligand L³ was proved by X-ray photoelectron spectroscopy (XPS). Together, these results demonstrate the potential of sulfide groups on the calixarene platform as receptor unit towards Hg²⁺ ions, which could be useful in the development of Hg²⁺-selective water purification systems or thin-film sensor devices.     

Influence of metal salts in reaction medium on performance enhancement of novel aliphatic–aromatic-based polyamide thin-film composite osmosis membranes

In this study, we report an easy and novel way to develop high flux aliphatic–aromatic-based thin-film composite (TFC) polyamide osmosis membranes by addition of inorganic metal salts with amine reactants in the reaction system of polyethylene imine (PEI) and 1,3-benzene dicarbonyl chloride. Inorganic metal salts like CuSO₄, NiSO₄, MgSO₄, and Al₂(SO₄)₃ added to block some of the amine groups of PEI through complexation which in turn changes the polycondensation reaction kinetics of amine acid chloride reaction. The prepared membranes were characterized using water contact angle and atomic force microscopy studies and the performances were evaluated both in reverse osmosis and forward osmosis mode. In presence of metal salts in reaction interface, the performance of TFC membranes was greatly enhanced and the optimum metal salt concentration was identified for individual metal salts for maximum performance enhancement. The effects of different anions for same metal ion and different molecular weight of PEI were evaluated on composite polyamide membrane performances. Water permeability (flux) of 63.48 L m^?2 h^?1 was achieved upon inorganic salt addition compared to the unmodified TFC membranes with flux of 42.1 L m^?2 h^?1 at similar salt rejection of ~95%. Based on the new findings, a conceptual model was proposed to explain the role of metal ion in amine solution on the resulting characteristics of aromatic–aliphatic type polyamide–polysulfone composite membrane.     

Anion complexation by calix[4]arene-TTF conjugates

Calix[4]arenes bearing tetrathiafulvalene (TTF) moieties appended to the upper rim via the amidic functions were synthesized and used for ¹H NMR and UV/Vis complexation studies towards selected anions. It was found that the complexation affinity towards H₂PO₄⁻ dramatically depends on the substitution pattern of the calixarene moiety. As a result, the proximally disubstituted derivative has a complexation constant by two orders of magnitude higher than the distally disubstituted analogue. The differences between proximal and distal receptors were also documented by their behaviour during the oxidation of the attached TTF units.     

Sodium thiocyanate binding by a 3-aminobenzoic acid based ion pair receptor consisting of a thiourea binding domain

The ability to recognize weakly coordinating thiocyanate anion was studied using 3-aminobenzoic acid based ion pair receptor (1) consisting of thiourea and crown ether binding domains. UV–Vis and ¹H NMR spectroscopic measurements carried out in acetonitrile showed that receptor 1, unlike its urea analog 2, is able to effectively associate weakly coordinating thiocyanate anion (TBASCN) and exhibits a more than six-fold enhancement in the presence of sodium cations (NaSCN). Data obtained from in-solution measurements are in agreement with the X-ray analysis of 1·NaSCN complex and confirms effective sodium thiocyanate association by receptor 1. In the solid state, thiocyanate anion and sodium cation interact directly with the corresponding binding domains.     

含硫脲聚乙炔的合成与氟离子识别特性

设计合成了一种新颖的含硫脲的乙炔,1-（4-乙炔苯基）-3-（4-丁基苯）硫脲（1）,并采用有机铑作为催化剂对其进行聚合.通过一系列阴离子的正四丁基铵盐的DMF溶液来评价聚合物的阴离子识别性能.加入F后,poly（1）的DMF溶液颜色立即改变;而加入Cl,HSO4-,Br-,NO3-,C6H5COO-和CH3COO-后,溶液颜色不变,说明poly（1）对F具有裸眼识别能力.紫外吸收滴定光谱和Hill曲线分析确定F-的结合能力,poly（1）/F-配合的Hill系数为1.6,表观结合常数（Ka）高达1.35×104,这说明poly（1）/F-形成了稳定的配合物.     

Molecular Recognition of Phosphate Esters: A Balance of Hydrogen Bonding and Proton Transfer Interactions

The interaction of different phosphate esters with a series of hydrogen bonding receptors has been studied using UV-visible and NMR spectroscopies and X-ray crystallography. Critical for binding is a combination of an acidic proton and the potential for bidentate hydrogen bonding either between charged or uncharged components. Phosphotriesters show no binding to the receptors. Phosphodiesters bind to both bis-(2, 6–diacylaminopyridine) and mono-(2, 6–diacylaminopyridine) receptors in chlorocarbon solvent via proton transfer to form the pyridinium phosphate ion pair and bidentate hydrogen bonding between the anion and the cation. Titration experiments as well as Job's analyses show that for cyclic and acyclic bis-(2, 6–diacylaminopyridine) receptors 2 : 1 complexes can be formed. X-ray crystal structures demonstrate that in the solid state two different binding arrangements are present; either a direct bidentate interaction or intramolecular hydrogen bonding with self-assembly of an oligomeric structure. Phosphomonoesters bind to mono-(2, 6–diacylaminopyridines) in a similar way to the diesters, via proton transfer and bidentate hydrogen bonding. In this, as in the diester case, only a single acid-base interaction is possible and proton transfer is preferred. However, in the interaction of phosphomonoesters with bis-(2, 6–diacylaminopyridine) derivatives two acid-base interactions are possible between the two pyridines and two POH groups, and little proton transfer is seen. Strong binding (K_a = 1.0 × 10⁵M⁻¹) occurs via tetrahydrogen bond formation. Thus, there appears to be a balance between the occurrence of proton transfer and the number of hydrogen bonds formed between receptor and substrate.     

Channel Mimetic Sensing Membranes for Nucleotides Based on Multitopic Hydrogen Bonding

Nucleotide-induced permeability changes of oriented monolayers composed of the nucleotide receptors 4-amino-1-octadecyl-2-(1H)-pyrimidinone ( 1 ), 5-methyl-1-octadecyl-2,4(1H,3H)-pyrimidinedione ( 2 ), and 1-(2-heptylundecyl)-4-(8-(3-methylureido)-2-naphthyl)-amide-2-(1H)-pyrimidinone ( 3 ) were examined. These molecules are capable of binding guanosine, adenosine, and guanosine nucleotides, respectively, by multitopic hydrogen bonding. Monolayers were first formed at the air/water interface and then directly contacted with a highly oriented pyrolytic graphite (HOPG) electrode. The permeabilities of these membranes were evaluated with cyclic voltammetry, using [Fe(CN)₆]^4– as permeability marker. Selectively 5′-GMP-induced decreases in the permeability of the membranes based on receptor 1 or 3 were observed. On the other hand, decreases in the permeability of membranes based on receptor 2 were larger in the presence of 5′-AMP than of 5′-GMP. The permeability changes thus observed can be ascribed to repulsive electrostatic interaction between the marker anions and the negatively charged nucleotides that selectively bind to the electrically neutral membrane receptors. The ratios of the oxidation current decreases for solutions containing 3.0 mM 5′-GMP and for solutions containing 3.0 mM 5′-AMP were 1.30, 0.76, and 1.85 for monolayers based on receptors 1, 2 , or 3 , respectively. The monolayer based on receptor 3 , which is capable of binding the guanine base by five hydrogen bonds, showed a higher 5′-GMP selectivity than the monolayer of receptor 1 with the cytosine residue. Similar nucleotide-induced permeability changes were observed for mixed multilayers of receptor 1 and octadecanol ( 4 ), as well as for mixed monolayers with receptor 2 and 4.     

Evaluation of Transport Capacity through Liquid Membranes of Some Crown Ether‐Siloxane Copolymers

The complexation ability of some linear crown ether‐siloxane copolymers of ester or amide type with cations as K⁺ and NH₄⁺ was investigated spectrophotometrically in order to select the polysiloxane receptors that achieve good ion transport ability by bulk liquid membrane systems. The transport properties of the potassium picrate through a liquid membrane using siloxane‐crown ether polyamide as carrier were discussed.     

A new family of ionic liquids based on the 1-alkyl-2-methyl pyrrolinium cation

Five new salts based on 1-alkyl-2-methyl pyrrolinium ion are reported, two involving the iodide ion and three involving the bis(trifluoromethanesulfonyl) amide ion. The iodide salts have melting points around 100 °C, while the amide salts have melting points around room temperature. Two of the amide salts can be easily quenched into the glassy state and exhibit glass transition temperatures around −70 °C. The 2-methyl pyrrolinium cation bears structural similarities to the aromatic imidazolium cations on one hand and the cyclic ammonium cation family based on the pyrrolidinium cation on the other. The properties of the salts reported here are compared within these two related families of salts.     

Estimation of ion pair formation constants of lithium salts in mixtures of glymes and 1,4-dioxane

This paper presents data coming from ¹⁹F NMR spectroscopy and conductivity measurements used as two independent methods for the determination of ion pair formation constants. The studied systems were limited to lithium tetrafluoroborate and trifluoromethylsulfonate solutions in mixtures of 1,4-dioxane and glyme, diglyme or water. The systems containing glyme and diglyme have coordinating properties (donor and acceptor numbers) very similar to liquid poly(ethylene glycol) dimethyl ether and solid poly(ethylene oxide) and their composition can be tailored to have the dielectric constants similar to those of the polymeric systems. The obtained results are compared with the electrochemical and spectroscopic data found in the literature for liquid poly(ethylene glycol) dimethyl ether and solid poly(ethylene oxide). The main stress of the discussion is focused on ion-ion and ion-solvent interactions and the influence of the oligooxyethylene chain length on ionic pair formation. Additionally, on the basis of the electrochemical data for the dioxane-water solutions, the difference in behavior between water-free and water containing samples of similar polarity is discussed. To check the influence of the cation on ion pairing, a similar set of experiments was performed for tetraalkylamonium salts with identical anions.     

Quo vadis Anionenextraktion?

Quo Vadis Anion Extraction? Reactive extraction processes represent efficient and smart technologies for separation and concentration of metal ions in solution. Despite the importance of anions in biology, medicine, environment and industry, practical examples of anion extraction are relatively limited compared to metal ion separation. Anion extraction processes are mainly based on the non‐specific ion‐pair formation with hydrophobic ammonium cations. In these processes the phase transfer of anions is dominated by their lipophilicity. The specific characteristics of anions in comparison to those of cations are closely connected to the difference in extraction processes for the two ion types. Novel approaches for specific binding and selective transport of anionic components are based both on the better understanding of the biological role of anions and on the possibilities of supramolecular chemistry to built up receptor architectures with complementary binding modes for anions. In the given review the authors discuss present research tendencies and application possibilities of new extractant types for separation and concentration of anionic species in solution.     

Where is the Anion Extraction Going?

Reactive extraction processes represent efficient and smart technologies for separation and concentration of metal ions in solution, which are frequently used in industry. Despite the importance of anions in biology, medicine, environment and industry, practical examples of anion extraction are relatively limited compared to metal ion separation. Anion extraction processes are mainly based on the nonspecific ion pair formation with hydrophobic ammonium cations. In this case the phase transfer of anions is dominated by their lipophilicity. The reasons for this situation are closely connected with the specific features of anions in contrast to cations. Novel approaches for specific binding and selective transport of anionic components are based both on the better understanding of the biological role of anions and on the possibilities of supramolecular chemistry to create receptor architectures with complementary binding modes for anions. In the given review the authors discuss present research tendencies and application possibilities of new extractant types for separation and concentration of anionic species in solution.     

对羟基偶氮苯磺酸钠应用于水相中的阴离子识别研究

合成主体对羟基偶氮苯磺酸钠,并通过紫外-可见吸收光谱及最色反应研究了水作为溶剂时主体对无机盐阴离子的识别作用.结果表明,对羟基偶氮苯磺酸钠可在水中对磷酸根离子进行选择性识别,并产生显著光谱效应和颜色变化,而对其他阴离子则无明显响应,从而实现水相中对磷酸根的裸眼检测.因此该化合物可作为检测水中磷酸根的化学敏感器.     

Selection of metalloenzymes by catalytic activity using phage display and catalytic elution

The metallo-beta-lactamase betaLII from Bacillus cereus 569/H/9 was displayed on the filamentous phage fd. The phage-bound enzyme fd-betaLII was shown to be active on benzylpenicillin as substrate; it could be inactivated by complexation of the essential zinc(II) ion with EDTA and reactivated by addition of a zinc(II) salt. A selection process was designed to extract active phage-bound enzymes from libraries of mutants in three steps: 1. inactivation of active phage-bound enzymes by metal ion complexation, 2. binding to substrate-coated magnetic beads, 3. release of phages capable of transforming the substrate into product upon zinc salt addition. The selection process was first successfully tested on model mixtures containing fd-betaLII plus either a dummy phage, a phage displaying an inactive mutant of the serine beta-lactamase TEM-1, or inactive and low-activity mutants of betaLII. The selection was then applied to extract active phage-bound enzymes from a library of mutants generated by mutagenic polymerase chain reaction (PCR). The activity of the library was shown to increase 60-fold after two rounds of selection. Eleven clones from the second round were randomly picked for sequencing and to characterize their activity and stability.     

Synthesis, characterization and photophysical properties of novel fluorene-based copolymer with pendent urea group: Fluorescent response for anions through H-bonding interaction

A novel fluorene-based copolymer P₁ with diphenyl urea as pendent group, as well as its analogous copolymer P₂ without urea group for comparison, were synthesized by Suzuki-coupling reaction, and characterized by ¹H NMR, EA, IR and GPC. The polymers were brightly blue emissive in THF, DMF, or DMSO solution. Anion titration experiments carried out in THF indicate that the polymer P₁ has good selectivity for fluoride ion, acetate ion, and dihydrogen phosphate ion, and the sensitivity and selectivity of P₁ toward these anions come from the strong hydrogen-bond interaction between the anions and the urea group of the copolymer. This new system utilizing the strong luminescence property of the polyfluorene as reporter and the hydrogen-bond-forming ability of urea group may act as novel effective anions receptor and chemosensor.