BF2 complex of fluorinated dipyrrolyldiketone: a new class of efficient receptor for acetate anions

The beta-fluorinated derivative (2b) of the 1,3-dipyrrolyl-1,3-propanedione BF2 complex has been prepared from 3,4-difluoropyrrole and malonyl chloride, followed by treatment with BF3.OEt2. Despite the simple, acyclic, and neutral structure, 2b exhibits efficient 1:1 binding for anions in CH2Cl2 using the bridging CH and pyrrole NH as interaction sites. The binding constant (Ka) of 2b for acetate (CH3CO(2-)), associating more effectively than anions such as F-, Cl-, Br-, H2PO(4-), and HSO(4-), is estimated to be 9.6 x 10(5) M(-1), approximately 9 times larger than that of the beta-H derivative 2a (1.1 x 10(5) M(-1)). The UV-vis and fluorescence spectral changes of 2b elucidate the effective recognition of an amino acid, such as phenylalanine, in the anionic form; this is also supported by CD spectral changes with mirror images by L- and D-isomers. Furthermore, in the solid state, BF2 complex 2b provides Cl- -bridged supramolecular networks and, in sharp contrast, deprotonated "anionic" self-assembled structures by F- binding.     

Aryl-substituted C3-bridged oligopyrroles as anion receptors for formation of supramolecular organogels

BF2 complexes of aryl-substituted dipyrrolyldiketones (3a-c, 5a-d) have been synthesized by the condensation of arylpyrroles obtained by Suzuki cross-coupling reactions with malonyl chloride, followed by treatment with BF3.OEt2. The binding constants (Ka11) of the BF2 complexes (3a-c) for various anions (Cl-, Br-, CH3CO2-, H2PO4-, and HSO4-) in CH2Cl2 decrease in the order Ph (3a) > o-tolyl (3b) > 2,6-Me2Ph (3c), possibly because of differences in the planarity and the number of interacting o-CH units at the binding sites. Aryl-substituted receptors exhibit a [1+1] binding mode with Cl- as well as a [2+1] binding mode under conditions of high concentration and low temperature, as suggested by 1H NMR studies in CD2Cl2. These receptors, especially phenyl-substituted (3a) and o-tolyl (3b), exhibit drastic colorimetric and fluorescent changes in the presence of F- due to extended pi-conjugation, as compared to 2,6-dimethylphenyl (3c) and the previously reported derivatives (1a-c). Aryl-substitution at the alpha-positions of pyrrole is an excellent means for the introduction of various substituents at the periphery of the anion receptors. For example, derivatives with long alkoxy chains at 3,4,5-positions of the substituent aryl rings (5b-d) afford emissive gel structures in hydrocarbon solvents, such as octane, based on the stacking of slipped H- and J-aggregates at the core pi-plane. The structural organization of the supramolecular gels was investigated by AFM, SEM, and XRD measurements as well as by considering the solid-state packing of crystalline derivatives. The slow transformation of the gel to the solution phase by the addition of various anions, possibly except for F-, is correlated with the unique properties of these acyclic receptors where inversions of pyrrole rings are required for anion binding. Boron complexes of 1,3-dipyrrolyl-1,3-propanediones with aryl-substituents, as a new class of acyclic anion receptors, have shown efficient binding due to the interacting o-CH units and, in the case of the derivative with long aliphatic chains, afforded the emissive supramolecular organogels using stacking of core pi-planes controlled by external chemical stimuli.     

Synthesis and evaluation of a pseudocyclic tristhiourea-based anion host

A novel methodology for the evaluation of receptor arrangement in structurally flexible anion chemosensors was developed and applied to map the binding site of a new pseudocyclic tristhiourea chemosensor (6). The syntheses of 6 and related macrocyclic chemosensor 10 (a model of the folded monomeric structure of 6) are reported. Both chemosensors were evaluated by titration with a variety of structurally different anions in CH3Cl and DMSO, showing a common preference for F-, CH3CO2-, and H2PO4-. However, within this group of anions, the binding patterns of the chemosensors differed, indicating dissimilarity in the arrangement of the binding sites of 6 and 10.     

Fluorescence sensing of anions based on inhibition of excited-state intramolecular proton transfer

Condensation of 2-(2'-aminophenyl)benzoxazole with p-toluenesulfonyl chloride and phenyl isocyanate yields two new anion sensors (TABO and PUBO), which can undergo excited-state intramolecular proton transfer (ESIPT) upon excitation. For the acid receptor TABO, the ESIPT process can be readily disturbed by basic anions such as F-, CH3COO-, and H2PO4- by deprotonating the sulfonamide unit, whereas in the case of PUBO, a good hydrogen-bonding donor, the ESIPT process is inhibited either by the fluoride-induced deprotonation of the urea unit or by the formation of a strong CH3COO--urea intermolecular hydrogen bond complex, and these two types of inhibition mechanisms consequently result in different ratiometric responses. But other anions with less hydrogen-bonding acceptor abilities cannot inhibit the ESIPT. Interestingly, the different inhibition abilities of F-, CH3COO-, and H2PO4- produce different spectral behaviors in PUBO, so this new sensor successfully distinguishes the subtle difference in these three anionic substrates of similar basicity and surface charge density.     

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 ditopic colorimetric sensor for fluoride ion based on thiourea mercury complex

A novel ditopic chromogenic receptor, N-5-(8-hydroxy)quinoline-N'-4'-nitro-phenyl thiourea (1), was synthesized. The metal complex 1-Hg(2+) showed sensitive and highly selective responses to F(-) over other anions such as CH(3)CO(2)(-), H(2)PO(4)(-), HSO(4)(-) and Cl(-). 1-Hg(2+)-F(-) complex formed, which promoted the intramolecular charge transfer and led to a dramatic spectral change. The color of 1-Hg(2+) solution changed from colorless to red upon addition of F(-). Thus, a colorimetric assay of F(-) was developed in acetonitrile by naked-eye detection. F(-) behaved linearly in the 8.0 x 10(-6) to 2.0 x 10(-5) mol L(-1) concentration range with LOD as 1.4 x 10(-6) mol L(-1).     

CH...anion interaction in BF2 complexes of C3-bridged oligopyrroles

Alkyl-substituted derivatives of 1,3-dipyrrolyl-1,3-propanedione BF2 complexes, the efficient receptors for halide and oxoanions with use of bridging CH as well as pyrrole NH, are reported. BF2 complexes with only one pyrrole NH interaction site (2d,e), which exhibit smaller affinities than the basic structure (2b), bind anions tightly, which is inferred by UV/vis absorption spectral changes, compared to the derivatives with an alkyl group at the bridging carbon (2f) or two pyrrole nitrogen sites (2c). With use of 1H NMR and theoretical studies for anion complexes of 2d and 2e, bridging CH (and one beta-CH in 2d) as well as pyrrole NH is found to interact with anions.     

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.     

Synthesis, photophysical, and anion-sensing properties of quinoxalinebis(sulfonamide) functionalized receptors and their metal complexes

We report the synthesis, characterization, and photophysical properties of a series of organic receptors and their corresponding ReI and RuII metal complexes as anion probes featuring bis(sulfonamide) interacting sites incorporating highly chromophoric pi-conjugated quinoxaline moieties. The interactions with various anions were extensively investigated. These probe molecules are capable of recognizing F-, OAc-, CN-, and H2PO4- with different sensitivities. The probe-anion interactions can be easily visualized via naked-eye colorimetric or luminescent responses. Probe 1 has the weakest acidic sulfonamide N-H protons and therefore simply forms hydrogen-bonding complexes with F-, OAc-, CN-, and H2PO4-. Probe 2 undergoes a stepwise process with the addition of F- and OAc-: formation of a hydrogen-bound complex followed by sulfonamide N-H deprotonation. Direct sulfonamide N-H deprotonation occurs upon the addition of CN-, while only a hydrogen-bound complex forms with the H2PO4- ion for probe 2 in a dimethyl sulfoxide (DMSO) solution. Similar probe-anion interactions occur in probe 3 with the addition of F-, CN-, or H2PO4-. However, only a genuine hydrogen-bound complex forms in the presence of the OAc- ion in a DMSO solution of probe 3 because of the subtle difference in the pKa values of sulfonamide N-H protons when probes 2 and 3 are compared. Coordination of probe 1 to a ReI center or probe 2 to a RuII center increases the intrinsic acidity of sulfonamide N-H protons and results in an enhanced sensitivity to anions.     

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.     

A theoretical investigation of the interactions between water molecules and ionic liquids

Quantum chemical calculations have been used to investigate the interaction between water molecules and ionic liquids based on the imidazolium cation with the anions [Cl(-)], [Br(-)], [BF(4)(-)], and [PF(6)(-)]. The predicted geometries and interaction energies implied that the water molecules interact with the Cl(-), Br(-), and BF(4)(-0 anions to form X(-)...W (X = Cl or Br, W = H(2)O), 2X-...2W, BF(4)(-)...W, and W...BF(4)(-)...W complexes. The hydrophobic PF(6)(-) anion could not form a stable complex with the water molecules at the density functional theory (DFT) level. Further studies indicate that the cation could also form a strong interaction with the water molecules. The 1-ethyl-3-methylimidazolium cation (Emim(+)) has been used as a model cation to investigate the interaction between a water molecule and a cation. In addition, the interaction between the ion pairs and the water was studied by using 1-ethyl-3-methylimidazolium chloride (Emim x Cl) as a model ionic liquid. The strengths of the interactions in these categories follow the trend anion-W > cation-W > ion pair-W.     

Ab initio electronic structure study of one-electron reduction of polychlorinated ethylenes

Polychlorethylene radicals, anions, and radical anions are potential intermediates in the reduction of polychlorinated ethylenes (C(2)Cl(4), C(2)HCl(3), trans-C(2)H(2)Cl(2), cis-C(2)H(2)Cl(2), 1,1-C(2)H(2)Cl(2), C(2)H(3)Cl). Ab initio electronic structure methods were used to calculate the thermochemical properties, (298.15 K), S degrees (298.15 K,1 bar), and DeltaG(S)(298.15 K, 1 bar) of 37 different polychloroethylenyl radicals, anions, and radical anion complexes, C(2)H(y)Cl(3)(-)(y)(*), C(2)H(y)Cl(3)(-)(y)(-), and C(2)H(y))Cl(4)(-)(y)(*)(-) for y = 0-3, for the purpose of characterizing reduction mechanisms of polychlorinated ethylenes. In this study, 8 radicals, 7 anions, and 22 radical anions were found to have stable structures, i.e., minima on the potential energy surfaces. This multitude of isomers for C(2)H(y)Cl(4)(-)(y)(*)(-) radical anion complexes are pi*, sigma*, and -H...Cl(-) structures. Several stable pi* radical anionic structures were obtained for the first time through the use of restricted open-shell theories. On the basis of the calculated thermochemical estimates, the overall reaction energetics (in the gas phase and aqueous phase) for several mechanisms of the first electron reduction of the polychlorinated ethylenes were determined. In almost all of the gas-phase reactions, the thermodynamically most favorable pathways involve -H...Cl(-) complexes of the C(2)H(y)Cl(4)(-)(y)(*)(-) radical anion, in which a chloride ion is loosely bound to a hydrogen of a C(2)H(x)Cl(2)(-)(x))(*) radical. The exception is for C(2)Cl(4), in which the most favorable anionic structure is a loose sigma* radical anion complex, with a nearly iso-energetic pi* radical anion. Solvation significantly changes the product energetics with the thermodynamically most favorable pathway leading to C(2)H(y)Cl(3)(-)(y)(*) + Cl(-). The results suggest that a higher degree of chlorination favors reduction, and that reduction pathways involving the C(2)H(y)Cl(3)(-)(y)(-) anions are high energy pathways.     

A C3-symmetric colorimetric anion sensor bearing hydrazone groups as binding sites

Tris-hydrazone (1) functioned as a colorimetric chemosensor for a variety of anions such as F(-), AcO(-) and H(2)PO(4)(-). The anion binding could be easily detected by naked-eye according to color changes. The high binding ability of the receptor 1 to anions was further investigated by UV-vis absorption spectroscopy in DMSO. The results of job plot of the receptor 1 with different anions demonstrated that the stoichiometry of the complex between 1 and F(-) was 1:1 (1:anion) and the stoichiometry of the other complexes studied was 1:3 (1:anion).     

[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.     

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.     

间苯二甲酰腙分子钳的合成及阴离子识别研究

设计合成了3种新型间苯二甲酰腙类化合物,利用UV-Vis及¹H NMR考察了其与F^-、Cl^-、Br^-、I^-、CH₃COO^-、HSO₄^-、H₂PO4-、ClO4-阴离子的相互作用。结果表明,主体分子4a(双对硝基苯并呋喃甲醛间苯二甲酰腙)在DMSO溶液中对F-和CH₃COO-有显著识别效果,溶液颜色由黄色变为深黄色和棕红色。通过¹H NMR滴定及质子溶剂效应进一步证明,主体分子与阴离子之间是以氢键作用方式相结合。Job曲线表明,主客体间形成1：1型氢键络合物。基于实验结果,探讨了主客体间形状和大小匹配对识别能力的影响以及主客体之间的识别模式。     

β-三氰基乙烯取代杯[4]吡咯与阴离子相互作用的密度泛函理论研究

采用密度泛函B3LYP方法对β-三氰基乙烯取代杯[4]吡咯主体分子及其与阴离子(F-、Cl-、CH3COO-、H2PO4-)形成的复合物进行研究。结果表明,β-三氰基乙烯取代杯[4]吡咯可与阴离子以分子间氢键相互作用形成复合物,并且其与阴离子结合能力大小的顺序为F-> CH3COO-> H2PO4-> Cl-,与实验结果基本一致;通过与杯[4]吡咯对比可见,强吸电子取代基的引入增强了主体分子对阴离子的结合能力。本文还从几何构型、振动光谱、NBO分析及前线轨道等方面来阐述β-三氰基乙烯取代杯[4]吡咯与不同阴离子氢键相互作用的本质以及吸电子取代基的引入对杯[4]吡咯与F-和Cl-之间主-客体相互作用的影响。     

Anion binding by fluorescent biimidazole diamides

Six 2,2'-biimidazoles with various amide groups at the 4- and 4'-positions were prepared from 5-propyl-1H-imidazole-4-carboxylic acid ethyl ester. In the final step of the synthesis, biimidazole C2-C2' bond formation was accomplished in 33-45% yield by palladium(0)-catalyzed homocoupling of the corresponding 2-iodoimidazoles. Four of the biimidazoles were studied by X-ray diffraction. In the solid state, all display coplanar imidazole rings, an anti relationship of amide groups, and intramolecular (NH(amide).N(imid)) and intermolecular (NH(imid).O(amide)) hydrogen bonding. In CH(2)Cl(2), the emission intensity of the biimidazoles is quenched by the presence of dihydrogenphosphate and chloride anions, but no shifts in lambda(emiss) are observed. Binding constants for 1:1 biimidazole-anion complexation (K(assoc)) are on the order of 10(4) M(-)(1) for H(2)PO(4)(-) and Cl(-). One of the receptors (bearing 3,5-difluorobenzylamides) is selective for chloride. The participation of the amide NH atoms in anion binding was established by (1)H NMR.     

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.     

Short metal-metal separations in a highly luminescent trimetallic Ag(I) complex stabilized by bridging NHC ligands

Reaction of 1,3-bis(2-pyridinylmethyl)-1H-imidazolium salt, [H(pyCH(2))(2)im]X (X = BF(4)(-) or Cl(-)), with silver oxide in acetonitrile readily yields yellow-brown [((pyCH(2))(2)im)(2)Ag]X, 1.BF(4) or 1.Cl. The chloride salt crystallizes with 3.650 A intermolecular Ag...Ag interactions while 1.BF(4) shows no short intermolecular interaction. Addition of excess Ag(BF(4)) produces the homoleptic carbene bridged trimetallic species, [(mu-NHC)(3)Ag(3)](BF(4))(3), 2. This species contains very short Ag-Ag separations between 2.7249(10) and 2.7718(9) A. In solution, these complexes are photoluminescent.