Thawatchai Tuntulani

Chromogenic anion sensors

Chromogenic sensors for anions generally consist of two parts: anion receptors and chromophores. In this review, 6 types of chromogenic anion sensors are described, namely, NH-based hydrogen bonding, Lewis acid, metal-ion template, transition metal complexes, chromogenic guest displacement and chromoreactands. The first 4 types possess anion receptors attached directly to the chromophores while the guest displacement techniques employ indicators as the ones that were replaced by specific anions. The last type has emerged recently and uses specific reactions between chromogenic hosts or indicators and particular anions to cause dramatic colour changes.

Chemically modified silica gel with aminothioamidoanthraquinone for solid phase extraction and preconcentration of Pb(II), Cu(II), Ni(II), Co(II) and Cd(II).

Silica gel chemically bonded with aminothioamidoanthraquinone was synthesized and characterized. The metal sorption properties of modified silica were studied towards Pb(II), Cu(II), Ni(II), Co(II) and Cd(II). The determination of metal ions was carried out on FAAS. For batch method, the optimum pH ranges for Pb(II), Cu(II) and Cd(II) extraction were >/=3 but for Ni(II) and Co(II) extraction were >/=4. The contact times to reach the equilibrium were less than 10min. The adsorption isotherm fitted the Langmuirs model showed the maximum sorption capacities of 0.56, 0.30, 0.15, 0.12 and 0.067mmol/g for Pb(II), Cu(II), Ni(II), Co(II) and Cd(II), respectively. In the flow system, a column packed modified silica at 20mg for Pb(II) and Cu(II), 50mg for Cd(II), 60mg for Co(II), Ni(II) was studied at a flow rate of 4 and 2.5mL/min for Ni(II). The sorbed metals were quantitatively eluted by 1% HNO(3). No interference from Na(+), K(+), Mg(2+), Ca(2+), Cl(-) and SO(4)(2-) at 10, 100 and 1000mg/L was observed. The application of this modified silica gel to preconcentration of pond water, tap water and drinking water gave high accuracy and precision (%R.S.D.</=9). The method detection limits were 22.5, 1.0, 2.9, 0.95, 1.1mug/L for Pb(II), Cu(II), Ni(II), Co(II) and Cd(II), respectively.

A-D-A Sensors Based on Naphthoimidazoledione and Boronic Acid as Turn-On Cyanide Probes in Water

Three fluorescence sensors based on naphthoquinoneimidazole and boronic acid (A-D-A system) have been developed with high selectivity for cyanide in water. The fluorescence band at 460 nm was switched on upon substitution of cyanide on sensors in the CTAB micelle.

Highly selective preconcentration of Cu(II) from seawater and water samples using amidoamidoxime silica

Chemically modified silica containing amidoamidoxime group was studied as a sorbent for solid-phase extraction (SPE) and preconcentration of Cu(II) prior to determination by flame atomic absorption spectrometry (FAAS). The sorbent showed an extremely high selectivity towards Cu(II) in the pH range of 4-6, while the extraction of Pb(II), Cd(II), Ni(II) and Co(II) was low. The adsorption isotherm followed the Langmuir model and the maximum sorption capacity of 0.0163 mmol Cu(II)g(-1) was achieved. In the flow system, Cu(II) was completely retained on a column containing 40 mg of the modified silica at the flow rate of 4.0 mL min(-1) and quantitatively eluted by 5 mL of 1% (v/v) HNO(3). No interference from Na(+), K(+), Mg(2+), Ca(2+), Cl(-) and SO(4)(2-) at 10, 100 and 1000 mg L(-1) was observed. When applied for preconcentration and determination of Cu(II) in tap water, pond water, and seawater, the recoveries were 96, 101, and 95%, respectively, with high precision (% relative standard deviation (R.S.D.)<4) and low method detection limit (9 microg L(-1)).

Synthesis of tripodal aza crown ether calix[4]arenes and their supramolecular chemistry with transition-, alkali metal ions and anions

Abstract Tripodal aza crown ether calix[4]arenes, 5a , 5b , 6a and 6b , have been synthesized. The structure of protonated 5a was elucidated by X-ray crystallography to be a self-threaded rotaxane. Complexation studies of 5a and 5b towards anions using Na+ as countercation were carried out by 1H NMR titration in dimethylsulfoxide-d6 and the mixture of chloroform-d and methanol-d4, respectively. Ligands 5a and 5b were able to form 1:1 complexes with Br−, I− and NO3− and the complexation stability varied as follows: NO3−>I−>Br−. The effect of countercation on anion complexation was also investigated. The results showed that the association constants of 5a towards Br− in the presence of various cations varied as K+>Bu4N+>Na+. The enhancement in anion complexation ability of 5a may result from the rearrangement of the tripodal ammonium unit in the presence of K+. The neutral forms, 6a and 6b , were able to form complexes with transition metal ions such as Co2+, Ni2+, Cu2+ and Zn2+. The stability of the complexes followed the sequence: Ni2+ 6a and 6b may, therefore, potentially be used as either transition metal ion or anion receptors that can be controlled by pH of the solution.

A reversible Em-FRET rhodamine-based chemosensor for carboxylate anions using a ditopic receptor strategy

A reversible rhodamine-based sensor (L1) capable of undergoing excimer-fluorescent resonance energy transfer (Em-FRET) was designed and synthesized using a ditopic receptor strategy. Addition of Cu2+ ions to a solution of L1 induced a ring-open conformation of spirolactam (Em-FRET ON), whilst ring closure was induced upon addition of CH3COO− (Em-FRET OFF).

Lower rim tetra-substituted and upper rim ferrocene amide calix[4]arenes: synthesis, conformation and anion-binding properties

Calix[4]arenes containing ferrocene amide at the upper rim and methoxy or ethoxycarbonylmethoxy (ethyl ester) groups at the lower rim (5a, 5b and 5c) have been synthesized. It was found that tetramethoxy 5a and dimethoxy diethyl ester 5c were conformationally labile and existed in both cone and partial cone conformation in solution. Anion-binding studies by 1H NMR titration in CDCl3 showed that 5b bound Cl− selectively with high stability. Compound 5c formed complexes with Cl− and H2PO4− where the former was more stable. The ratio of cone to partial cone conformation in compound 5a was found to decrease upon binding Cl− and H2PO4− and in a polar solvent.

Aza crown ether calix[4]arenes containing cation and anion binding sites: effects of metal ions towards anion binding ability

Abstract Tripodal aza crown ether calix[4]arenes containing both cation and anion binding sites ( 5a and 5b ) have been synthesized. The X-ray analysis shows that 5a forms a self-threaded rotaxane-like structure in the solid state. 1 H NMR titrations of the two ligands with various halide anions indicate that 5a and 5b can form complexes with Br − and I − but not F − . However, both compounds form more stable complexes with I − than with Br − in the presence of Bu 4 N + . The presence of K + enhances the binding ability of 5a towards Br − .

Cu2+-modulated cysteamine-capped CdS quantum dots as a turn-on fluorescence sensor for cyanide recognition

A new fluorescence sensor for detection of cyanide ions (CN(-)) in aqueous media based on the recovered fluorescence of cysteamine capped CdS quantum dots [Cys-CdS QDs]-Cu(2+) system was proposed. The fluorescence intensity of Cys-CdS QDs was quenched by Cu(2+) due to the binding of Cu(2+) to cysteamine on the surface of the QDs. The degree of fluorescence quenching was proportional to the concentration of Cu(2+). However, in the presence of CN(-), the fluorescence intensity of Cys-CdS QDs was found to be efficiently recovered. Experimental results showed that the pH of the buffer solution and the concentration of Cu(2+) affected the fluorescence intensity upon adding CN(-). Under the optimal condition, the recovered fluorescence intensity was linearly proportional to the increasing CN(-) concentration in the range 2.5-20 μM. The limit of detection and the limit of quantification were found to be 1.13 μM and 3.23 μM, respectively. In addition, among the tested ions, only CN(-) could turn on the fluorescence intensity suggesting that the [Cys-CdS QDs]-Cu(2+) system was a highly selective sensor for CN(-). Moreover, this proposed sensor was demonstrated to detect CN(-) in drinking water with satisfactory results.

Calix[4]arenes containing urea and crown/urea moieties: effects of the crown ether unit and Na+ towards anion binding ability

Calix[4]arenes containing urea and crown/urea moieties, 7 and 10, respectively have been synthesized. 1H NMR titrations of 7 and 10 with anions in DMSO-d6 showed that 7 and 10 formed complexes with Cl−, Br−, NO3− and H2PO4− to a different extent. The association constants of 7 and 10 towards anions were calculated and found to vary as H2PO4−>Cl−>Br−>NO3−. However, compared to 7 the presence of the crown unit in 10 resulted in a slightly higher affinity to Cl− and Br−, but a lower affinity to H2PO4−. Upon addition of Na+, the binding ability of 10 towards H2PO4− is increased due to ion-pair enhancement.