Fluoride-selective colorimetric sensor based on thiourea binding site and anthraquinone reporter

A structurally simple colorimetric sensor, N-4-nitrobenzene-N'-1'-anthraquinone-thiourea (1), for anions was synthesized and characterized by (1)H NMR, ESI mass and IR methods. In acetonitrile, the addition of F(-) changed 1 solution from colorless to yellow. In the presence of other anions such as CH(3)CO(2)(-), H(2)PO(4)(-), HSO(4)(-) and Cl(-), however, the absorption spectrum of 1 was slightly red shifted with no obvious color changes observed. The association constants of anionic complexes followed the order of F(-)>CH(3)CO(2)(-)>H(2)PO(4)(-)>HSO(4)(-)>Cl(-)>Br(-), which was different from the order of anion basicity. AM1 calculation results indicated that the most stable configuration of 1 existed in the Z-E-conformation with a six-membered ring via intramolecular hydrogen bond. This made thiourea moiety of 1 in an unfavorable conformation to bond with oxygen-anionic substrates such as CH(3)CO(2)(-) and H(2)PO(4)(-), thus leading to a high selectivity and sensitivity for the detection of F(-).     

A novel colorimetric and fluorescent anion chemosensor based on the flavone quasi-crown ether-metal complex

The metal-ligand complex 1 ([Mg (L)] (2+)) (or 2 ([Ca (L)]( 2+))) was demonstrated to selectively bind HSO(4)(-) (or H(2)PO(4)(-)) over other anions by using UV-vis absorption and fluorescence spectroscopy. The studied complex exhibits the remarkable color change and fluorescence quenching upon introducing HSO(4)(-) (or H(2)PO(4)(-)) anion in acetonitrile. Both the mechanism and structure of the secondary complex of complex 1 with anion were proposed on the basis of theoretical computation.     

Fluorescent sensing of anions with acridinedione based neutral PET chemosensor

Newly synthesised fluorescent chemosensor ADDTU contains the thiourea receptor connected to the acridinedione (ADD) fluorophore via a covalent bond, giving rise to a fluorophore-receptor motif. In this fluorescent chemosensor, the anion recognition takes place at the receptor site which result in the concomitant changes in the photophysical properties of a ADD fluorophore by modulation of photoinduced electron transfer (PET) process. The binding ability of these sensor with the anions F(-), Cl(-), Br(-), I(-), HSO(4)(-), ClO(4)(-), AcO(-), H(2)PO(4)(-) and BF(4)(-) (as their tetrabutylammounium salts) in acetonitrile were investigated using UV-vis, steady state and time-resolved emission techniques. ADDTU system allows for the selective fluorescent sensing of AcO(-), H(2)PO(4)(-) and F(-) over other anions in acetonitrile.     

Imidazolium-based macrocycles as multisignaling chemosensors for anions

A series of structurally novel anion receptors , , and in which a ferrocene unit and a fluorescent moiety are linked to two imidazolium rings have been designed and prepared from 1,1'-bis(imidazolylmethyl)ferrocene. Their crystal structures revealed that these receptors are capable of incorporating anions such as PF(6)(-) and Br(-). Consequently, the anion binding studies were carried out using various techniques including electrochemistry (CV and OSWV), fluorescence, UV-vis, and (1)H NMR spectroscopy. All the receptors showed a special electrochemical response to the F(-) anion with a remarkable cathodic shift of more than 260 mV and displayed a unique selectivity for F(-) and AcO(-) anions with fluorescence enhancement over various other anions of present interest (Cl(-), Br(-), I(-), HSO(4)(-), H(2)PO(4)(-)). In addition, for receptor , obvious absorption changes were observed when the H(2)PO(4)(-) anion was added while other anions (F(-), Cl(-), Br(-), I(-), AcO(-), HSO(4)(-)) showed only a minor influence on the UV-vis spectra. (1)H NMR titrations demonstrated that receptors and can bind anions through (C-H)(+)X(-) hydrogen bonds and showed strong affinity and high selectivity for the AcO(-) anion in acetonitrile.     

Anion binding studies of fluorinated expanded calixpyrroles

The anion binding properties of fluorinated calix[n]pyrroles (n = 4-6) in aprotic solvents (acetonitrile and DMSO) and modified reaction conditions allowing for the synthesis and isolation of the hitherto missing dodecafluorocalix[6]pyrrole from the condensation of 3,4-difluoro-1H-pyrrole and acetone are described. In acetonitrile solution containing 2% water, the association constants for the 1:1 binding interaction between octafluorocalix[4]pyrrole and chloride anion obtained with isothermal titration calorimetry (ITC) and (1)H NMR titration methods were found to match reasonably well. As compared to its nonfluorinated congener, octafluorocalix[4]pyrrole was found to display enhanced binding affinities for several representative anions in pure acetonitrile as judged from ITC analyses. Similar analyses of the fluorinated calix[n]pyrroles revealed an increase in the relative affinity for bromide over chloride with increasing macrocycle size, as manifest in a decrease in the binding ratio K(a(Cl))/K(a(Br)). Anion binding studies in the solid state, involving single-crystal X-ray diffraction analyses of the chloride and acetate anion complexes of octafluorocalix[4]pyrrole and decafluorocalix[5]pyrrole, respectively, confirmed the expected hydrogen bond interactions between the pyrrolic NH protons and the bound anions.     

Influence of charge on anion receptivity in amide-based macrocycles

Binding and structural aspects of anions with tetraamido/diquaternized diamino macrocyclic receptors containing m-xylyl, pyridine, and thiophene spacers are reported. (1)H NMR studies indicate that the quaternized receptors display higher affinities for anions compared to corresponding neutral macrocycles. The macrocycles containing pyridine spacers consistently display higher affinity for a given anion compared to those with either m-xylyl or thiophene spacers. The m-xylyl- and pyridine-containing receptors exhibit high selectivity for H(2)PO(4)(-) in DMSO-d(6) with association constants, K(a) = 1.09 × 10(4) and >10(5) M(-1), respectively, and moderate selectivity for Cl(-) with K(a) = 1.70 × 10(3) and 5.62 × 10(4) M(-1), respectively. Crystallographic studies for the Cl(-) and HSO(4)(-) complexes indicate that the m-xylyl-containing ligand is relatively elliptical in shape, with the two charges at ends of the major axis of the ellipse. The anions are hydrogen bonded with the macrocycle but are outside the ligand cavity. In the solid state, an unusual low-barrier hydrogen bond (LBHB) was discovered between two of the macrocycle's carbonyl oxygen atoms in the HSO(4)(-) complex. The pyridine-containing macrocycle folds so that the two pyridine units are face-to-face. The two I(-) ions are chelated to the two amides adjacent to a given pyridine. In the structure of the thiophene containing macrocycle with two BPh(4)(-) counterions, virtually no interaction was observed crystallographically between the macrocycle and the bulky anions.     

Carboxylate anions binding and sensing by a novel tetraazamacrocycle containing ferrocene as receptor

A tetraazamacrocycle containing ferrocene moieties has been synthesized and characterized. The tetraprotonated form of this compound was evaluated as a receptor (R) for anion recognition of several substrates (S), Cl(-), PF(6)(-), HSO(4)(-), H(2)PO(4)(-) and carboxylates, such as p-nitrobenzoate (p-nbz(-)), phthalate (ph(2-)), isophthalate (iph(2-)) and dipicolinate (dipic(2-)). (1)H NMR titrations in CD(3)OD indicated that this receptor is not suitable for recognizing HSO(4)(-) and H(2)PO(4)(-), but weakly binds p-nbz(-), and strongly interacts with ph(2-), dipic(2-), and iph(2-) anions forming 1 : 2 assembled species. The largest beta(2) binding constant was determined for ph(2-), followed by dipic(2-) and finally iph(2-). The effect of the anionic substrates on the electron-transfer process of the ferrocene units of R was evaluated using cyclic voltammetry (CV) and square wave voltammetry (SWV) in methanol solution and 0.1 mol dm(-3)(CH(3))(4)NCl as the supporting electrolyte. Titrations of the receptor were undertaken by addition of anion solutions in their tetrabutylammonium or tetramethylammonium forms. The protonated ligand exhibits a reversible voltammogram, which shifts cathodically in the presence of the substrates. The data revealed kinetic constraints in the formation of the receptor/substrate entity for dipic(2-), ph(2-) and iph(2-) anions, but not for p-nbz(-). In spite of the slow kinetics of assembled species formation with the ph(2-) substrate, this anion provides the largest redox-response when the supramolecular entity is formed, followed by dipic(2-), iph(2-) and finally p-nbz(-) anions. This trend is in agreement with the (1)H NMR results and the values of the binding constants. Single crystal X-ray structures of the receptor with PF(6)(-), ph(2-), iph(2-) and p-nbz(-) were carried out and showed that supermolecules with a RS(2) stoichiometry are formed with the first three anions, but RS(4) with p-nbz(-). In all cases the binding occurs outside the macrocyclic cavity via N-H...O=C hydrogen bonds for carboxylate anions and N-H...F hydrogen bonds for the PF(6)(-) anion, which is in agreement with the solution results. The macrocyclic framework adopts different conformations in order to interact with each substrate having Fe...Fe intramolecular distances ranging from 10.125(14) to 12.783(15)A.     

Anion and carboxylic acid binding to monotopic and ditopic amidopyridine macrocycles

Binding of inorganic anions, carboxylic acids, and tetraalkylammonium carboxylates by macrocyclic compounds of different size was studied by NMR in DMSO-d6. It has been shown that at least a 15-membered ring is necessary for successful recognition of fluoride. Larger macrocycles were shown to bind HSO4(-), H2PO4(-), Cl(-), and carboxylic acid salts. Effects of binding topicity are discussed. The 30-membered macrocycles 4 and 4m selectively bind substrates that are size- and shape-complementary: maximum binding is observed for dicarboxylic acids and dicarboxylates with four-carbon chains, and the binding constant for association of fumaric acid and 4 is ca. 5 orders of magnitude higher than that of maleic acid. The 30-membered macrocycle 4m showed selectivity toward alpha-ketocarboxylic acids. Secondary amino groups were not crucial for binding of fluoride to the macrocycles; however, they proved to be very important for selectivity and strength of carboxylic acid binding. The X-ray structure of the adduct of 4 and nitrobenzoic acid confirmed the guest H-bonding with both the amide and the secondary amino groups of the 30-membered macrocyclic host.     

New chromogenic and fluorescent probes for anion detection: formation of a [2 + 2] supramolecular complex on addition of fluoride with positive homotropic cooperativity

Two new chromogenic and fluorescent probes for anions have been designed, synthesized, and characterized. These probes contain multiple hydrogen bonding donors including hydrazine, hydrazone, and hydroxyl functional groups for potential anion interacting sites. Despite the possible flexible structural framework due to the presence of sp3 carbon linkage, X-ray structure analysis of probe 2 displayed an essentially planar conformation in the solid state owing to strong crystal packing interactions comprising a combination of favorable pi-pi stacking effect and hydrogen bonding to cocrystallized CH3OH molecules. Both probes 1 and 2 display orange color in DMSO solution and show fairly weak fluorescence at room temperature. Binding studies revealed that both probes 1 and 2 show noticeable colorimetric and fluorescent responses only to F-, OAc-, and H2PO4- among the nine anions tested (F-, Cl-, Br-, I-, OAc-, H2PO4-, HSO4-, ClO4-, and NO3-). The general trend of the sensitivity to anions follows the order of F- > OAc- > H2PO4- > Cl- > Br- approximately I- approximately HSO4- approximately ClO4- approximately NO3-. A 1:2 (probe to anion) binding stoichiometry was found for probe 1 with OAc- and H2PO4- and probe 2 with F-, OAc-, and H2PO4-. The binding isotherm of probe 1 to F- was found to be complicated with apparent multiple equilibria occurring in solution. The formation of an aggregated supramolecular complex upon addition of fluoride is proposed to rationalize the observed optical responses and is supported by ESI mass spectrometry and pulsed-field gradient NMR spectroscopy. Data analysis suggests that the binding of probe 1 to F- shows positive homotropic cooperativity.     

[Ru(phen)2(H2biim)](PF6)2配合物与阴离子的选择性作用

研究了[Ru(phen)₂(H₂biim)](PF₆)₂(1)与各种阴离子之间的选择性作用, 发现配合物1与Cl^-, Br^-, I^-, NO₃^-, HSO₄^-和H₂PO₄^-阴离子之间存在氢键作用. OAc^-阴离子与配合物1作用, 由于强的氢键作用使H₂biim上的一个H转移到OAc^-上, 使配合物1脱去一个质子, 形成{[Ru(phen)₂(H₂biim)](OAc)}结合体, 溶液颜色由黄色变为橙棕色. 由于F^-能形成非常稳定的HF₂^-, 配合物1逐步脱去2个质子, 溶液颜色由黄色变为紫色, 因此可作为裸眼检测阴离子的识别剂.     

Preparation of N,N'-bisethoxyethane[12]amideferrocenophane and its application in anion recognition

Novel N,N'-bisethoxyethane[12]amideferrocenophane has been synthesized by a condensation reaction and characterized by (1)H NMR and mass spectrum. The anion recognition properties of the compound are evaluated via (1)H NMR, FT-IR, and electrochemical measurement. It is found that N,N'-bisethoxyethane[12]amideferrocenophane exhibits remarkable electrochemical response to H(2)PO(4-) anion in CH(2)C(l2) or CH(3)CN solution, and response to anions can also be observed in CH(3)CN solution containing up to 15% water. Binding constants between the compound and HSO(4-) in different solutions have been determined by UV-vis spectrum titration experiments. The results indicate that the compound shows a selective recognition trend of H(2)PO(4-) > HSO(4-) (F(-)) > Br(-).     

以黄酮冠醚金属配合物为基体的阴离子化学敏感器

合成了两种以新型黄酮类冠醚化合物(L)为配体的金属配合物[Ca(L)]²⁺(1)或[Mg(L)]²⁺(2).对其在乙腈溶液中与阴离子间的相互作用进行了研究.当这种化学敏感器和HSO₄^-或H₂PO₄^-阴离子相互作用时,可观察到强烈的颜色变化.UV光谱滴定实验表明,配合物1(或2)和HSO₄^-间形成了1:1的稳定配合物.配合物1(或2)对于HSO₄^-或H₂PO₄^-阴离子也可用荧光光谱法进行选择性检测,较UV方法有更高的灵敏度.还提出了配合物1(或2)与阴离子间通过两点结合方式,构成新的配合物可能结构的建议.通过色调变化和荧光测定的方法进行研究,结果表明,带有染料分子的金属配合物可用作为有效识别和检测阴离子的敏感器件.     

A novel colorimetric sensor of dihydrogen-phosphate based on metal complex between 8-hydroxy quinoline-5-azo-4'-nitrobenzene and cobalt

A novel colorimetric sensor based on 8-hydroxy quinoline-5-azo-4'-nitrobenzene (1) was prepared and used for recognizing anions. 1 and its metal complex (1.Co) were found to show response to anions such as CH(3)CO(2)(-), H(2)PO(4)(-), HSO(4)(-), F(-) and dramatic color changes were observed. The selectivity and sensitivity of 1 and 1.Co for sensing anions were different, which was in the order of CH(3)CO(2)(-)>F(-)>H(2)PO(4)(-)>HSO(4)(-) for 1 and H(2)PO(4)(-)>HSO(4)(-)>CH(3)CO(2)(-) approximately F(-) for 1.Co, respectively. In CH(3)CN, sensor 1.Co exhibited excellent specificity toward H(2)PO(4)(-), and the color variety was dependent on the concentration of H(2)PO(4)(-) which was attributed to anion structure and stability of anionic complex (1-anion), metal complex (1-Co) and inorganic complex (Co-anion).     

Selective anion sensing based on tetra-amide calix[6]arene derivatives in solution and immobilized on gold surfaces via self-assembled monolayers

Two anion receptors, 1 and 2, based on the calix[6]crown-4 architecture were synthesized and characterized by NMR (1H, 13C, COSY), UV-vis, and MALDI-MS. 1H NMR measurements demonstrate that receptors 1 and 2 exhibit the highest binding affinity for fluoride ions compared to other anions including Cl-, Br-, NO3-, HSO4-, H2PO4-, and AcO-. The binding constants of 1 with F- and AcO- are 326 (+/-32) and 238 (+/-23) M-1, whereas those of 2 with F- and AcO- are 222 (+/-25) and 176 (+/-21) M-1. The fluorescent titration of 2 with various anions such as Cl-, Br-, NO3-, HSO4-, and H2PO4- led to essentially no change in excimer emission and a slight enhancement of monomer emission. In contrast, a dramatic change was observed in the fluorescence spectra upon the addition of F- and AcO- to 2. Self-assembled monolayers (SAMs) of 1 were formed on gold surfaces and characterized by reductive desorption and other techniques. Cyclic voltammetry (CV) and electrochemical impedance spectroscopy were used to monitor anion recognition by the SAM-modified gold electrodes. The gold electrodes modified by SAMs of 1, upon binding with the F- anion, exhibit a dramatic increase in charge-transfer resistance (Rct) values. This is due to the repulsion between the negatively charged electrode surfaces and the negatively charged Fe(CN)6(3-/4-) redox probe in the electrolyte solution. In contrast, smaller increases in Rct values were observed in the cases of other monovalent anions investigated.     

Anion responsive TTF-appended calix[4]arenes. Synthesis and study of two different conformers

Two new cone- and 1,3-alternate-calix[4]arenes (cone-1 and 1,3-alt-1), bearing four modified TTF (tetrathiafulvalene) substituents on the upper rim, have been synthesized. The binding ability of these two sets of conformers for various anions, including F(-), Cl(-), Br(-), I(-), PF6(-), ClO4(-), HSO4(-), CH3COO(-), H2PO4(-), and HP2O7(3-), was tested in organic media by monitoring the changes in their UV/vis and (1)H NMR spectra as a function of added anion, as well as via cyclovoltammetry (CV) (all anions studied as their respective TBA salts). On the basis of the present findings, we propose that incorporation of four TTF units within an overall calix[4]arene-based recognition framework produces a preorganized receptor system that displays a modest preference for the pyrophosphate (HP2O7(3-)) anion.     

Anion binding by a tetradipicolylamine-substituted resorcinarene cavitand

Anion binding has been achieved with a resorcinarene substituted with four 2,2'-dipicolylamine moieties on the upper rim. The four dipicolylamine groups reside in proximity on one rim of the cavitand. The dipicolylamine groups were protonated with triflic acid to provide the cationic ammonium sites for anion binding. This anion receptor binds strongly to anions of different geometries, such as H(2)PO(4)(-), Cl(-), F(-), CH(3)CO(2)(-), HSO(4)(-), and NO(3)(-). The association constants for binding these anions are large, on the order of log K = 5 in CD(3)CN, a solvent of intermediate dielectric constant. These values represent significant binding compared to other cavitands with nitrogen pendant groups. Evidence suggests that the cavitand provides two identical receptor sites formed by two dipicolylamine groups, facilitating the simultaneous binding of two anions. Intramolecular binding of anions between two protonated dipicolylamine groups is indicated on the basis of the comparison to a structurally similar monomeric analogue and by semiempirical PM3 molecular modeling. Titrations with the analogue result in much weaker anion association, even at high concentrations, indicating the importance of proximity and preorganization of sites on the cavitand upper rim.     

Binding of inorganic oxoanions to macrocyclic ligands: effect of the degree of protonation on supramolecular assemblies formed by phosphate and [18]aneN(6)

Five macrocycle-oxoanion adducts have been isolated from aqueous solutions containing 1,4,7,10,13,16-hexaazacyclooctadecane ([18]aneN(6), L) and phosphoric acid whose pH had been adjusted to selected values in the 1-8 range. Four products, (H(6)L)(H(2)PO(4))(6).2H(3)PO(4) (1), (H(6)L)(H(2)PO(4))(6) (2), (H(4)L)(H(2)PO(4))(4).2H(2)O (4), and (H(4)L)(HPO(4))(2).7H(2)O (5) crystallized from aqueous solutions at pH 1, 3, 6, and 8, respectively, while (H(4)L)(H(2)PO(4))(4) (3) crystallized on diffusion of EtOH into an aqueous reaction mixture at pH 6. Single-crystal X-ray structure determinations enabled an examination of supramolecular interactions between protonated forms of [18]aneN(6), phosphoric acid and its conjugate bases, and water of solvation. The macrocycle adopts a variety of conformations in order to accommodate the supramolecular constructs formed by the oxoanions and solvent molecules as the relative proportions of interacting species are altered. At pH 1 and 3, the fully protonated macrocycle, [LH(6)](6+), is found with six H(2)PO(4)(-) anions. At pH 6 and 8, the tetraprotonated macrocycle, [LH(4)](4+), crystallizes with four H(2)PO(4)(-) and two HPO(4)(2)(-), respectively. Variations in the solute of crystallization are evident, with phosphoric acid being present at the lowest pH and water at pH 6 and 8. In 5, the seven unique water molecules form a string-of-pearls motif within which a new heptameric isomer, consisting of a water pentamer that uses a single water to interact with the other two unique water molecules, is found. Structures 1, 2, 4, and 5 exhibit eta-3 H-bonding of ammonium protons to a single oxygen of the guest phosphates located above and below the macrocyclic ring. In 3, two phosphate oxygens of the cavity anion interact with the macrocycle, one of which participates in eta-2 H-bonding with ammonium groups.     

Dipyrrolyldiketone difluoroboron complexes: novel anion sensors with C-H...X- interactions

1,3-Dipyrrolyl-1,3-propanediones, synthesized from pyrroles and malonyl chloride, form BF2 complexes, which represent a new class of naked-eye sensors for halide and oxoanions. The association mode for the interactions of both the pyrrolyl NH and bridging CH protons with anions was confirmed by 1H NMR chemical shifts in CD2Cl2 and supported by theoretical studies. The binding constants (Ka) were estimated as 8.1x10(4), 2.0x10(3), 3.3x10(2), 1.3x10(4), and 80 M(-1) for F-, Cl-, Br-, H2PO4(-), and HSO4(-) by UV/Vis absorption spectral changes in CH2Cl2. Augmentation of Ka compared with dipyrrolylquinoxaline for H2PO4(-) is much larger than those for other anions. Contrary to other anions, F- quenches the emission almost completely, which was detected by the fluorescence spectrum as well as the naked-eye. In the case of the chloride anion complex, the formation of Cl(-)-bridged 1D networks, in which anion is associated with two BF2 complexes, is observed in the solid state.     

对二甲氨基苯甲酸的阴离子识别应用研究

采用紫外分光光度法和荧光分光光度法研究了主体分子对二甲氨基苯甲酸与HPO42-、SO42-、H2PO4-、ClO4-、HSO4-、NO3-、BF4-、PF6-、F-、Cl-和Br-等11种阴离子客体的识别作用.发现在乙腈溶液中,该主体分子对二价阴离子HPO42-和SO42-表现了强亲和力和高选择性;并对一价阴离子F-和H2PO4- 具有一定的响应能力;而与一价阴离子ClO4-、HSO4-、NO3-、BF4-、PF6-、Cl-和Br-几乎没有作用.结果表明主客体分子本身的酸碱性和阴离子的负电荷数目是影响主体分子对阴离子识别性能的主要因素.     

基于蒽-苯并咪唑鎓的荧光传感器对H2PO4-的高选择性识别

设计合成了基于蒽-苯并咪唑鎓的受体分子1和2,通过荧光发射光谱研究了受体分子1和2对F^-、Cl^-、Br^-、I^-、AcO^-、HSO₄^-、H₂PO₄^-、NO₃^-、ClO₄^-等阴离子的识别性能。 研究发现,在受体分子1和2的乙腈溶液(5.0×10^-6 mol/L)中加入10倍化学计量的H₂PO₄^-时,受体分子1的荧光猝灭百分数为13%,受体分子2的荧光猝灭百分数高达94%,表明受体分子2在构型上与H₂PO₄^-更匹配,可作为H₂PO₄^-的荧光关闭型(turn-off)探针。 受体分子2与H₂PO₄^-的结合比为1:1,结合常数为(3.70±0.16)×10⁴ L/mol,检出限为3.77×10^-6 mol/L。