A new fluorescent chemosensor for fluoride anion based on a pyrrole-isoxazole derivative.
ABSTRACT: Molecules containing polarized NH fragments that behave as anion-binding motifs are widely used as receptors for recognition and sensing purposes in aprotic solvents. We present here a new example of a receptor, 3-amino-5-(4,5,6,7-tetrahydro-1H-indol-2-yl)isoxazole-4-carboxamide (receptor 1), which contains pyrrole, amide and amino subunits. This receptor shows both changes in its UV-vis absorption and fluorescence emission spectra upon the addition of F(-), resulting in highly selectivity for fluoride detection over other anions, such as Cl(-), Br(-), I(-), HSO(4) (-), H(2)PO(4) (-) and AcO(-) in CH(3)CN. (1)H NMR titration, time-dependent density functional theory (TDDFT) calculations and other experiments confirm that the sensing process is brought about by deprotonation of the pyrrole-NH in receptor 1.
Project description:A pyrrolyl-based triazolophane, incorporating CH and NH donor groups, acts as a receptor for the pyrophosphate anion in chloroform solution. It shows selectivity for this trianion, followed by HSO(4)(-) > H(2)PO(4)(-) > Cl(-) > Br(-) (all as the corresponding tetrabutylammonium salts), with NH-anion interactions being more important than CH-anion interactions. In the solid state, the receptor binds the pyrophosphate anion in a clip-like slot via NH and CH hydrogen bonds.
Project description:The interactions between chemosensors, 3-amino-5-(4,5,6,7-tetrahydro-1H-indol-2-yl)isoxazole-4-carboxamide (AIC) derivatives, and different anions (F(-) Cl(-), Br(-), AcO(-), and H(2)PO(4) (-)) have been theoretically investigated using DFT approaches. It turned out that the unique selectivity of AIC derivatives for F(-) is ascribed to their ability of deprotonating the host sensors. Frontier molecular orbital (FMO) analyses have shown that the vertical electronic transitions of absorption and emission for the sensing signals are characterized as intramolecular charge transfer (ICT). The study of substituent effects suggests that all the substituted derivatives are expected to be promising candidates for fluoride chemosensors both in UV-vis and fluorescence spectra except for derivative with benzo[d]thieno[3,2-b]thiophene fragment that can serve as ratiometric fluorescent fluoride chemosensor only.
Project description:This article illustrates the detailed decomposition behavior of NH<sub>4</sub>HSO<sub>4</sub> on the TiO<sub>2</sub> and TiO<sub>2</sub>-SiO<sub>2</sub> supports, along with the effect of SiO<sub>2</sub> addition on the sulfur resistance of the corresponding V<sub>2</sub>O<sub>5</sub>-based catalysts. For TiO<sub>2</sub> support, sulfate species selectively occupied its surface basic hydroxyl groups, while Si-OH groups functioned as the main sites for the accommodation of NH<sub>4</sub>HSO<sub>4</sub> over the TiO<sub>2</sub>-SiO<sub>2</sub> mixed support, enabling its surface sulfate species with higher thermal stability. Compared with NH<sub>4</sub> <sup>+</sup> on the TiO<sub>2</sub> surface, NH<sub>4</sub> <sup>+</sup> on the TiO<sub>2</sub>-SiO<sub>2</sub> mixed support was much easier to be consumed during the heating process, hence causing some variations in the decomposition behavior of NH<sub>4</sub>HSO<sub>4</sub>. Finally, adding SiO<sub>2</sub> enhanced the SO<sub>2</sub> tolerance properties of the catalysts to a certain extent. When exposed to the SO<sub>2</sub>-containing flue gas, the deposition of NH<sub>4</sub>HSO<sub>4</sub> mainly caused serious deactivation of SiO<sub>2</sub>-free catalyst, while the as-accumulated SO<sub>4</sub> <sup>2-</sup> also contributed to the declined activity of SiO<sub>2</sub>-added catalyst. These results ensured the potential commercialization of TiO<sub>2</sub>-SiO<sub>2</sub>-based catalysts in the typical low-temperature selective catalytic reduction systems in the short run and pointed out a strategy to design new catalysts with superior activity and enhanced SO<sub>2</sub>-tolerant ability.
Project description:A new set of diamide receptors containing anthracene and carbazole bridging subunits and either pyrrole or phenyl substituents were synthesized. The four systems produced in this way were shown to bind representative anions in DMSO-d(6) solution and in the solid state. A higher relative affinity for two test oxoanions, namely dihydrogen phosphate and benzoate, over chloride anion was seen in solution, with the anions in question being studied in the form of their respective tetrabutylammonium salts. However, the specifics of the anion recognition process were seen to depend on structure, with the pyrrole-containing systems displaying higher relative affinities than their corresponding phenyl-containing congeners, and the carbazole receptors proving more effective than the anthracene analogues. Such observations provide support for the notion that both the carbazole NH and the pyrrolic NH protons play an important role in stabilizing the receptor-bound anions in solution. Structural analyses of several anion complexes of the diamidopyrrole carbazole receptor reveal that this is not necessarily the case in the solid state; specifically, the pyrrole NH protons are seen to interact with the amide oxygen of another molecule. The net result is an extended a one-dimensional coordinaton polymer.
Project description:A comparative study of the halide and benzoate anion binding properties of a series of phenyl, pyrrole, and furan-strapped calixpyrroles has been carried out. These receptors, which have previously been shown to bind the chloride anion (Yoon et al., Angew. Chem., Int. Ed. 47(27):5038-5042, 2008), were found to bind bromide and benzoate anion (studied as the corresponding tetrabutyl-ammonium salts) with near equal affinity in acetonitrile, albeit less well than chloride, as determined from ITC measurements or NMR spectroscopic titrations. This stands in marked contrast to the parent octamethylcalixpyrrole, where the carboxylate anion affinities are substantially higher than those for bromide anion under identical conditions. This finding is rationalized in terms of tighter binding cavity present in the strapped systems. For all three anions for which quantitative data could be obtained (i.e., Cl(-), Br(-), PhCO(2) (-)), the pyrrole-strapped system displayed the highest affinity, although the relative enhancement was found to depend on the anion in question. In the specific case of fluoride anion binding to the pyrrole-strapped receptor, two modes of interaction are inferred, with the first consisting of binding to the calixpyrrole via NH-anion hydrogen bonds, followed by a process that involves deprotonation of the strapped pyrrolic NH proton. A single crystal X-ray diffraction analysis provides support for the first of these modes and further reveals the presence of a methanol molecule bound to the fluoride anion.
Project description:The syntheses and structures of five mol-ecular salts of protonated 4,4,7,7-tetra-methyl-3a,5,6,7a-tetra-hydro-benzo-thia-zol-2-yl-amine (C11H19N2S+) with different deprotonated carb-oxy-lic acids (4-methyl-benzoic acid, 4-bromo-benzoic acid, 3,5-di-nitro-benzoic acid, fumaric acid and succinic acid) are reported, namely 2-amino-4,4,7,7-tetra-methyl-4,5,6,7-tetra-hydro-1,3-benzo-thia-zol-3-ium 4-methyl-benzoate, C11H19N2S+·C8H7O2 -, (I), 2-amino-4,4,7,7-tetra-methyl-4,5,6,7-tetra-hydro-1,3-benzo-thia-zol-3-ium 4-bromo-benzoate, C11H19N2S+·C7H4BrO2 -, (II), 2-amino-4,4,7,7-tetra-methyl-4,5,6,7-tetra-hydro-1,3-benzo-thia-zol-3-ium 3,5-di-nitro-benzoate, C11H19N2S+·C7H3N2O6 -, (III), bis-(2-amino-4,4,7,7-tetra-methyl-4,5,6,7-tetra-hydro-1,3-benzo-thia-zol-3-ium) fumarate, 2C11H19N2S+·C4H2O4 2-,(IV), and the 1:1 co-crystal of bis-(2-amino-4,4,7,7-tetra-methyl-4,5,6,7-tetra-hydro-1,3-benzo-thia-zol-3-ium) succinate and 2-amino-4,4,7,7-tetra-methyl-4,5,6,7-tetra-hydro-1,3-benzo-thia-zol-3-ium hydrogen succin-ate 4,4,7,7-tetra-methyl-3a,5,6,7a-tetra-hydro-benzo-thia-zol-2-yl-amine, 1.5C11H19N2S+·0.5C4H4O4 2-·0.5C4H5O4 -. 0.5C11H18N2S, (V). In every case, the cation protonation occurs at the N atom of the thia-zole ring and the six-membered ring adopts a half-chair conformation (in some cases, the deviating methyl-ene groups are disordered over two sets of sites). The C-N bond lengths of the nominal -NH+=C-NH2 fragment of the cation are indistinguishable, indicating a significant contribution of the -NH-C=N+H2 resonance form to the structure. The packing for (I)-(V) features a robust local R 2 2(8) loop motif in which the cation forms two near-linear N-H⋯O hydrogen bonds from the N+-H group and syn H atom of the amine group to the carboxyl-ate group of an adjacent anion [(V) shows disorder of one of these bonds over N-H⋯O and N⋯H-O contributors but the same R 2 2(8) loop results for both disorder components]. The anti H atom of the -NH2 group also forms an N-H⋯O hydrogen bond, which results in  chains in (I) and (II), isolated centrosymmetric tetra-mers in (III) and  chains in (IV) and (V). Hirshfeld fingerprint plots and contact percentages for the different types of contacts of the cations are discussed.
Project description:The binding properties of the pyrrole-strapped calixpyrrole 2 for cesium halide ion pairs were studied via 1H NMR spectroscopic and single crystal X-ray diffraction analyses. Receptor 2 was found to bind CsF, CsCl, and CsBr in the solid state and in chloroform/methanol (4/1, v/v) solution with relatively high affinity as compared with the parent calixpyrrole 1. It was also revealed by solid-liquid extraction experiments that receptor 2 was capable of solubilizing CsF in CDCl3, a medium in which this salt is otherwise insoluble. Single crystal X-ray diffraction analyses and 1H NMR spectroscopic data recorded in 20% CD3OD in CDCl3 provide support for the suggestion that the strap pyrrolic NH proton of 2, as well as those of the calixpyrrole framework, contribute to anion recognition, thus increasing affinity for cesium halide salts relative to the parent system 1. In the solid state, receptor 2 interacts with CsF to form a two dimensional coordination polymer in the presence of methanol. A linear coordination polymer is observed in the case of CsCl and CsBr. Receptor 2 was also found to form a complex with CsF in chloroform/methanol (4/1, v/v) solution, albeit with a different binding mode than is seen in the solid state.
Project description:The asymmetric unit of the title compound, C(16)H(17)ClNO(2)S(+)·HSO(4) (-), (I) [systematic name: (+)-(S)-5-[(2-chloro-phen-yl)(meth-oxy-carbon-yl)meth-yl]-4,5,6,7-tetra-hydro-thieno[3,2-c]pyridin-5-ium hydrogen sulfate], contains two independent cations of clopidogrel and two independent hydrogensulfate anions. The two independent cations are of similar conformation; however, this differs from that observed in ortho-rhom-bic form (II) [Bousquet et al. (2003 ?). US Patent No. 6 504 030]. The H-N-C(chiral)-H fragment shows a trans conformation in both independent cations in (I) and a gauche conformation in (II). In (I), classical inter-molecular N-H?O and O-H?O hydrogen bonds link two independent cations and two independent anions into an isolated cluster, in which two cations inter-act with one anion only via N-H?O hydrogen bonds. Weak inter-molecular C-H?O hydrogen bonds further consolidate the crystal packing.
Project description:A convenient two-step preparation of NH-free 5-aryl-pyrrole-2-carboxylates is described. The synthetic route consists of catalytic borylation of commercially available pyrrole-2-carboxylate ester followed by Suzuki coupling without going through pyrrole N-H protection and deprotection steps. The resulting 5-aryl substituted pyrrole-2-carboxylates were synthesized in good- to excellent yields. This synthetic route can tolerate a variety of functional groups including those with acidic protons on the aryl bromide coupling partner. This methodology is also applicable for cross-coupling with heteroaryl bromides to yield pyrrole-thiophene, pyrrole-pyridine, and 2,3'-bi-pyrrole based bi-heteroaryls.
Project description:The binding interactions between the azide anion (N3-) and the strapped calixpyrroles 2 and 3 bearing auxiliary hydrogen bonding donors on the bridging moieties, as well as of normal calixpyrrole 1, were investigated via 1H NMR spectroscopic and isothermal titration calorimetry analyses. The resulting data revealed that receptors 2 and 3 have significantly higher affinities for the azide anion in organic media as compared with the unfunctionalized calixpyrrole 1 and other azide receptors reported to date. Single crystal X-ray diffraction analyses and calculations using density functional theory revealed that receptor 2 binds CsN3 in two distinct structural forms. As judged from the metric parameters, in the resulting complexes one limiting azide anion resonance contributor is favored over the other, with the specifics depending on the binding mode. In contrast to what is seen for 2, receptor 3 forms a CsN3 complex in 20% CD3OD in CDCl3, wherein the azide anion is bound only vertically to the NH protons of the calixpyrrole and the cesium cation is complexed within the cone shaped-calixpyrrole bowl. The bound cesium cation is also in close proximity to a naphthobipyrrole subunit present in a different molecule, forming an apparent cation-? complex.