A novel fluorescent and colorimetric anion sensor based on thiourea derivative in competitive media

Compatible Kinetic Model for Quantitative Description of Dual-Clock Behavior of the Complex Thiourea-Iodate Reaction

The thiourea-iodate reaction has been investigated simultaneously by ultraviolet-visible spectroscopy and high-performance liquid chromatography (HPLC). Absorbance-time traces measured at the isosbestic point of the iodine-triiodide system have revealed a special dual-clock behavior. During the first kinetic stage of the title reaction, iodine suddenly appears only after a well-defined time lag when thiourea is totally consumed due to the rapid thiourea-iodine system giving rise to a substrate-depletive clock reaction. After this delay, iodine in the system starts to build up suddenly to a certain level, where the system remains for quite a while. During this period, hydrolysis of formamidine disulfide as well as the formamidine disulfide-iodine system along with the Dushman reaction and subsequent reactions of the intermediates governs the parallel formation and disappearance of iodine, resulting in a fairly constant absorbance. The kinetic phase mentioned above is then followed by a more slowly increasing sigmoidally shaped profile that is characteristic of autocatalysis-driven clock reactions. HPLC studies have clearly shown that the thiourea dioxide-iodate system is responsible mainly for the latter characteristics. Of course, depending on the initial concentration ratio of the reactants, the absorbance-time curve may level off or reach a maximum followed by a declining phase. With an excess of thiourea, iodine may completely disappear from the solution as a result of the thiourea dioxide-iodine reaction. In the opposite case, with an excess of iodate, the final absorbance reaches a finite value, and at the same time, iodide ion will disappear completely from the solution due to the well-known Dushman (iodide-iodate) reaction. In addition, we have also shown that in the case of the formamidine disulfide-iodine reaction, unexpectedly the triiodide ion is more reactive toward formamidine disulfide than iodine. This feature can readily be interpreted by the enhancement of the rate of formation of the transition complex containing oppositely charged reactants. A 25-step kinetic model is proposed with just 10 fitted parameters to fit the 68 kinetic traces measured in the thiourea-iodate system and the second, but slower, kinetic phase of the thiourea-iodine reaction. The comprehensive kinetic model is constituted in such a way as to remain coherent in quantitatively describing all of the most important characteristics of the formamidine disulfide-iodine, thiourea dioxide-iodine, and thiourea dioxide-iodate systems.

Novel indole based dual responsive "turn-on" chemosensor for fluoride ion detection

An efficient new dual channel chemosensor 2,3-bis((E)-(1H-indole-3-yl)methyleneamino)maleonitrile (DN) which exhibits selective sensing of F(-) ions in DMSO, was synthesized by a facile one step condensation reaction of indole-3-carboxaldehyde with diaminomaleonitrile. The probe DN was characterized by elemental analysis, (1)H, (13)C-NMR, ESI-MS and IR spectral techniques. Upon addition of F(-), DN induces remarkable changes in both absorption and fluorescence spectra on the basis of charge transfer mechanism. The receptor DN serves for highly selective, sensitive detection of F(-) without the interference of other relevant anions. The Job's plot analysis indicates the binding stoichiometry to be 1:1 (host/guest).

A highly selective naked-eye colorimetric sensor for acetate ion based on 1,10-phenanthroline-2,9-dicarboxyaldehyde-di-(p-substitutedphenyl-hydrazone)

A new and simple colorimetric sensor with high selectivity for acetate ion based on 1,10-phenanthroline-2,9-dicarboxyaldehyde-di-(p-substitutedphenylhydrazone) receptor 2 has been synthesized. The selectively binding ability of receptor 2 to acetate ion over other anions tested was demonstrated by UV-vis absorption spectroscopy in DMSO. Comparing with other anions studied, the UV-vis absorption spectrum in dimethyl sulfoxide shows significant response toward acetate ion with high selectivity, and meanwhile dramatic color change is observed from yellow to green in the presence of acetate ion (5 x 10(-6)mol/L). Little UV-vis absorption spectrum change has occurred when receptor 2 was titrated with other different guest (F(-), Cl(-), Br(-), I(-), H(2)PO(4)(-) and OH(-)). In addition, the (1)H NMR spectrum titration shows deprotonation of the receptor in the presence of acetate ion.

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).