Dual colorimetric sensoring bis(indolyl)calix[4]crown-6

A Cr(VI) selective probe based on a quinoline-amide calix[4]arene

A new quinoline-amide calix[4]arene 3-receptor for detection of hazardous anions and cations have been synthesized. The 3-receptor was examined for its sensing properties towards several different anions (Cr₂O₇^2-, SCN^-, F^-, Cl^-, NO₃^-) and metal ions (Hg²⁺, Cd²⁺, Ag⁺) by UV-vis and fluorescence spectroscopies. It was detected that the 3-receptor has only sensing ability for Cr₂O₇^2- and Hg²⁺ ions, resulting in the association constants higher for Cr₂O₇^2- than to the Hg²⁺ ions. High selectivity towards Cr₂O₇^2- were also observed by fluorescence measurement among other ions (F^-, Cl^-_, SCN^-, Hg²⁺, Cd²⁺, Ag⁺) with a low limit of detection (7.36×10^-6moldm^-3). Proton NMR anion-binding investigations revealed a strong interaction of Cr₂O₇^2- anion with NH and CH groups of the receptor, showing that the combination with hydrogen-bonds donor groups strengthened the anion receptor association. Furthermore, remarkable association constants for dichromate anion obtained by all techniques strongly suggest the 3-receptor as a selective Cr(VI) sensor.

Inclusion complexation of phenoxyaliphatic acid derivatives of 3,3'-bis(indolyl)methanes with β-cyclodextrin

The inclusion complexation behavior of phenoxyaliphatic acid derivatives of 3,3'-bis(indolyl)methane (BIMs 1-5) with β-cyclodextrin (β-CD) were investigated in both solution and solid state by means of UV-Visible, fluorescence spectroscopy, FT-IR and (1)H NMR techniques. The nature of the host-guest inclusion complex between BIMs and β-CD has been elucidated. The experimental results confirmed the existence of 1:1 inclusion complex of BIMs with β-CD. The binding constants describing the extent of formation of the complexes have been determined using Benesi-Hildebrand plots using UV-Vis and fluorescence spectroscopy. BIMs exhibited an affinity for β-CD. The spectral studies suggested the phenyl ring along with alkyl substitutions of BIMs is present inside of β-CD cavity.

An efficient probe for rapid detection of cyanide in water at parts per billion levels and naked-eye detection of endogenous cyanide

A new molecular probe based on an oxidized bis-indolyl skeleton has been developed for rapid and sensitive visual detection of cyanide ions in water and also for the detection of endogenously bound cyanide. The probe allows the "naked-eye" detection of cyanide ions in water with a visual color change from red to yellow (Δλmax =80 nm) with the immediate addition of the probe. It shows high selectivity towards the cyanide ion without any interference from other anions. The detection of cyanide by the probe is ratiometric, thus making the detection quantitative. A Michael-type addition reaction of the probe with the cyanide ion takes place during this chemodosimetric process. In water, the detection limit was found to be at the parts per million level, which improved drastically when a neutral micellar medium was employed, and it showed a parts-per-billion-level detection, which is even 25-fold lower than the permitted limits of cyanide in water. The probe could also efficiently detect the endogenously bound cyanide in cassava (a staple food) with a clear visual color change without requiring any sample pretreatment and/or any special reaction conditions such as pH or temperature. Thus the probe could serve as a practical naked-eye probe for "in-field" experiments without requiring any sophisticated instruments.

A new selective colorimetric and fluorescent chemodosimeter for HSO4(-) based on hydrolysis of Schiff base

Two new receptors 1 and 2 were prepared, and their chromogenic and fluorogenic behaviors toward various anions were investigated. Receptors 1 and 2 show exclusive response toward HSO4(-) ion and also distinguish HSO4(-) from other anions by different color changes in aqueous solution (CH3CN/H2O=4/1, v/v). Between them receptor 1 selectively exhibits a pronounced HSO4(-)-induced fluorescence enhancement. The detection limit for the HSO4(-) ion was determined as (0.24±0.03μM). Thus, the receptor 1 can be used as a colorimetric and fluorescent sensor for the determination of HSO4(-) ion. The sensing mechanism has been suggested to proceed via a hydrolysis process. The hydrolysis product has been isolated and further identified by (1)H NMR spectroscopy, ESI-MS analysis and X-ray diffraction.

Ratiometric fluorescent receptors for both Zn2+ and H2PO4(-) ions based on a pyrenyl-linked triazole-modified homooxacalix[3]arene: a potential molecular traffic signal with an R-S latch logic circuit

A ratiometric fluorescent receptor with a C(3) symmetric structure based on a pyrene-linked triazole-modified homooxacalix[3]arene (L) was synthesized and characterized. This system exhibited an interesting ratiometric detection signal output for targeting cations and anions through switching the excimer emission of pyrene from the "on-off" to the "off-on" type in neutral solution. (1)H NMR titration results suggested that the Zn(2+) center of receptor L·Zn(2+) provided an excellent pathway of organizing anion binding groups for optimal host-guest interactions. It is thus believed that this receptor has potential application in sensing, detection, and recognition of both Zn(2+) and H(2)PO(4)(-) ions with different optical signals. In addition, the fluorescence emission changes by the inputs of Zn(2+) and H(2)PO(4)(-) ions can be viewed as a combinational R-S latch logic circuit at the molecular level.

Chromofluorescent indicator for intracellular Zn2+/Hg2+ dynamic exchange

The fluorescence of NABQ increases remarkably in the presence of Zn(2+) and is quenched by Hg(2+). As shown by confocal imaging, NABQ-Zn(2+) can penetrate cells, where the bound Zn(2+) is exchanged for Hg(2+). This results in the concomitant export of Hg(2+) from the cells, showing that NABQ can act as a Zn(2+) carrier and as a Hg(2+) extracting agent in living cells.

Extended Calix[4]arene-Based Receptors for Molecular Recognition and Sensing

Recent advances in the area of recognition and sensing have shown that artificial receptors derived from extended calix[4]arenes bearing multiple π-conjugated fluorophoric or chromophoric systems have found useful to enhance binding affinity, selectivity and sensitivity for recognition and sensing of a targeted ion or molecule. A comprehensive review of various π-conjugation-extended calyx[4]arene-based receptors with the highlight on the design and binding characterization for recognition and sensing is presented.