Anion binding with urea and thiourea derivatives

A structurally simple 2-((1-hydroxynaphthalene-2-yl)methyleneamino)acetic acid ( 1 ) was used as a turn-on fluorescent sensor for both Zn 2+ and F − . This receptor 1 showed a significant fluorescence enhancement in the presence of zinc ion over most other competitive metal ions in 100% aqueous solution. In particular, this chemosensor could clearly distinguish Zn 2+ from Cd 2+ . The spectroscopic studies suggested that the selective response to zinc ion involved the disruption of the internal charge transfer (ICT), and the inhibition of the C N isomerization and the excited-state proton transfer (ESIPT). In vitro studies with fibroblasts showed fluorescence when sensor 1 and Zn 2+ were present. The receptor 1 could also sense F − selectively in DMSO. The fluorescence, UV–vis titration and 1 H NMR titration indicated that F − ion enhanced the fluorescence of 1 through deprotonation.

A single fluorescent chemosensor for multiple target ions: Recognition of Zn2+ in 100% aqueous solution and F− in organic solvent

A new highly selective colorimetric chemosensor 1 (E)-9-(((2-hydroxy-5-nitrophenyl)imino)methyl)-2,3,6,7-tetrahydro-1H,5H-pyrido[3,2,1-ij]quinolin-8-ol for CN− was developed. Receptor 1 showed exclusive response toward cyanide by a color change in aqueous solution. However, in aprotic solvents and methanol, the unique selectivity of 1 for CN− disappeared, and its nonselective color change was observed for other anions. This phenomenon could be possibly explained by the combination of the basicity and the hydrogen bonding ability of the anions. Moreover, 1 could be used as a practical, visible colorimetric test kit in an aqueous environment.

A colorimetric chemosensor based on a Schiff base for highly selective sensing of cyanide in aqueous solution: the influence of solvents

Desymmetrisation of aromatic diamines and synthesis of non-symmetrical thiourea derivatives by click-mechanochemistry

A novel bis-rhodamine derivative BRU was designed and synthesized in a simple way. In aqueous media, BRU could efficiently recognize Fe3+ and Al3+ among other metal ions with different color appearances through a turn-on colorimetric response. In the presence of Fe3+ or Al3+, BRU solution also displayed enhanced fluorescent emission. According to the detection limit, BRU had high recognition sensitivity towards Fe3+ and Al3+ based on either colorimetric absorbance or fluorescent emission. Interestingly, BRU bound to Fe3+ or Al3+ with a simple 1:1 mode in CH3OH and a 1:2 mode in CH3OH/H2O, displaying solvent-dependent binding property. In addition, the in situ generated BRU-Fe3+ and BRU-Al3+ complex exhibited fluorescence turn-off and color disappearance towards carbonate among other anions. These provide a potential application in sequential detection of Fe3+, Al3+ and carbonate with naked-eyes.

A novel turn-on colorimetric and fluorescent sensor for Fe3+ and Al3+ with solvent-dependent binding properties and its sequential response to carbonate

Two new colorimetric anion sensors have been synthesised where both a benzophenone group and a nitrophenyl group were used as signalling units and urea/thiourea moieties as binding sites. The receptors, effectively and selectively, recognised fluoride and carboxylate anions from other anions such as chloride, bromide, iodide, perchlorate, hydrogen sulphate and nitrate in DMSO.

A naked-eye detection of fluoride with urea/thiourea receptors which have both a benzophenone group and a nitrophenyl group as a signalling group

Two anion receptors 1 and 2 with a nitrophenyl group as a signaling group and urea/thiourea as a binding group were synthesized and their anion binding abilities were examined. The receptor 1 formed the hydrogen-bonded complex with various anions except fluoride. However, the receptor 2 immediately formed deprotonated receptor with various anions. Therefore, they operated based on a hydrogen bonding and an acid–base equilibrium. In addition, the receptor 1 proved to be an efficient and selective naked-eye detector for the fluoride ion.

Simple urea/thiourea sensors for the biologically important ions

Dihydrogen phosphate selective anion receptor 2 based on one carbazole and two indole moieties was designed and synthesized. Fluorescence and 1H NMR titration clearly showed that receptor 2 was a good sensor in the selective recognition for dihydrogen phosphate over other anions. Receptor 2 utilized two amide hydrogens, three amine hydrogens to bind anions. These five hydrogens formed concave structure for the selective recognition of dihydrogen phosphate.

Sung kyu Lee

Papers

A naked-eye detection of fluoride with urea/thiourea receptors which have both a benzophenone group and a nitrophenyl group as a signalling group

Simple urea/thiourea sensors for the biologically important ions

A new dihydrogen phosphate selective anion receptor utilizing carbazole and indole