Rapid colorimetric sensing of cyanide anion in aqueous media with a spiropyran derivative containing a dinitrophenolate moiety

A spiropyran derivative containing a dinitrophenolate moiety (2: 1′,3′,3′-trimethyl-6,8-dinitro-spiro-[2H-1-benzopyran-2,2′-indoline]) behaves as a receptor for selective detection of cyanide anion (CN⁻) in aqueous media. Compound 2, when dissolved in aqueous media, spontaneously produces the spirocycle-opened merocyanine (MC) form even in dark condition. The absorption band of the MC form decreases selectively upon addition of CN⁻, via a nucleophilic addition of CN⁻ to the spirocarbon of the MC form. The nucleophilic addition occurs very rapidly (within 1 min) and enables rapid and selective quantification of very low levels of CN⁻ (>0.8 μM) by an absorption analysis.     

Acenaphthenequinone based simple colorimetric anion sensor with only one binding site

Quinonehydrazone compound 1 was designed to be a simple chromogenic anion sensor with one anion binding site. The sensor 1 was easily obtained in 83% yield by the condensation of acenaphthenequinone with 4-nitrophenylhydrazine in ethanol solution. In DMSO, sensor 1 could high selectively and visually detect anions with strong basicity (e.g., AcO^?, F^? and H₂PO₄ ^?) from chloride, bromide, and iodide ions with weak basicity.     

Advances in anion binding and sensing using luminescent lanthanide complexes

Luminescent lanthanide complexes have been actively studied as selective anion receptors for the past two decades. Ln(iii) complexes, particularly of europium(iii) and terbium(iii), offer unique photophysical properties that are very valuable for anion sensing in biological media, including long luminescence lifetimes (milliseconds) that enable time-gating methods to eliminate background autofluorescence from biomolecules, and line-like emission spectra that allow ratiometric measurements. By careful design of the organic ligand, stable Ln(iii) complexes can be devised for rapid and reversible anion binding, providing a luminescence response that is fast and sensitive, offering the high spatial resolution required for biological imaging applications. This review focuses on recent progress in the development of Ln(iii) receptors that exhibit sufficiently high anion selectivity to be utilised in biological or environmental sensing applications. We evaluate the mechanisms of anion binding and sensing, and the strategies employed to tune anion affinity and selectivity, through variations in the structure and geometry of the ligand. We highlight examples of luminescent Ln(iii) receptors that have been utilised to detect and quantify specific anions in biological media (e.g. human serum), monitor enzyme reactions in real-time, and visualise target anions with high sensitivity in living cells.

This minireview highlights advances in anion binding and sensing using luminescent lanthanide(iii) complexes.     

Ratiometric fluorescence and colorimetric sensing of anion utilizing simple Schiff base derivatives

Two ratiometric fluorescence and colorimetric anion sensors were designed and synthesized according to simple Schiff base reaction. Two compounds 1 and 2 were characterized by ESI–MS, elemental analyses and ¹H NMR. The sensors could give fast and visible color changes from yellow to red upon presence of the strong basic anions such as acetate ion. In particular, two compounds exhibited marked blue shifts (about 136 nm) in their emission spectra, when interacting with anions. Accordingly, the compounds 1 and 2 could act as real-time ratiometric fluorescence and colorimetric sensors for anions.     

Anion binding vs. deprotonation in colorimetric pyrrolylamidothiourea based anion sensors

A pyrrolylamidothiourea deprotonates in the presence of one equivalent of not only fluoride, but also acetate, benzoate or dihydrogen phosphate in DMSO solution with structural studies using synchrotron radiation confirming thiourea deprotonation in the solid state.     

New interlocked molecules generated from a podand containing urea units and imidazolium salts using an anion template

A podand containing urea units (L) was found to form interlocked structures with 2,5-dihexylamide imidazolium salts (3·X), 2,5-dihexyl imidazolium salts (4·X), and 2,5-dihexyl benzoimidazolium salts (5·X), where X=Cl⁻, Br⁻, and PF₆⁻ using anions as templates. The binding ability of L and guest molecules was evaluated by ¹H NMR titrations in CDCl₃. It was found that L could form complexes with guest molecules in the following order, 3·X > 5·X > 4·X. Stabilities of the complexes also depended on shape of the templated anions: Cl⁻>Br⁻?PF₆⁻. Hydrogen bonding and π-π stacking interactions played an important role in the self-assembling of these interlocked molecules.     

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.     

Thermal characterization of self-assembled monolayers of dialkyl disulfides containing the urea moiety

Thermal behaviors of urea-containing dialkyl disulfides 4-(3-octadecylureido)phenyl disulfide (ODPD) and 3-(octadecylureido)ethane disulfide (ODED) and octadecyl disulfide (ODDS) self-assembled monolayers (SAMs) were investigated by infrared reflection-absorption spectroscopy (IRRAS). Among the SAMs, the alkyl chain of ODPD is thermally reversible in the temperature region between 30 and 138 degrees C, whereas alkyl chains of ODED and ODDS are irreversible. With regard to the thermal stability of alkyl chains, ODED is superior to ODPD and ODDS. It is considered that the good thermal reversibility of the ODPD SAM is due to the rigid phenyl ring and the good thermal stability of the ODED SAM is due to the flexible ethylene linker. Moreover, 2D correlation analysis provides an enhancement of spectral resolution in amide II and CH2 antisymmetric stretching bands and suggests from the comparison of sequences of spectral events of ODPD and ODED SAMs that the last reorientation of the phenyl ring in the ODPD SAM is responsible for the good thermal reversibility.     

A selective colorimetric anion sensor based on an amide group containing macrocycle

A new colorimetric anion sensor 4 allows for selective 'naked-eye' differentiation of F-, AcO- and H2PO4- with similar basicity.     

Simple indole-based colorimetric sensors with electron-withdrawing chromophores: Tuning selectivity in anion sensing

Three simple colorimetric anion sensors (1, 2, and 3) containing anthrone, 1,3-indanedione, and malononitrile as signaling chromophores and an indole binding site have been designed and synthesized. The introduction of electron-withdrawing groups can not only provide chromogenic signal output, but also tune the sensitivity and selectivity of indole-based anion sensors by electron push–pull features. Their anion binding and sensing properties were investigated in detail by dramatic color changes, UV–vis absorption, and ¹H NMR. As results revealed, sensor 1 showed high selectivity for F⁻ over AcO⁻ and H₂PO₄⁻ with a distinct change in color due to the deprotonation of indole NH group. The excellent selectivity of 1 for F⁻ can be attributed to the fitness in the acidity of its NH-group, which is tuned to be able to distinguish the subtle difference in the affinity of F⁻, AcO⁻, and H₂PO₄⁻ to NH proton.     

Fluoride-selective colorimetric sensor based on thiourea binding site and anthraquinone reporter

A structurally simple colorimetric sensor, N-4-nitrobenzene-N'-1'-anthraquinone-thiourea (1), for anions was synthesized and characterized by (1)H NMR, ESI mass and IR methods. In acetonitrile, the addition of F(-) changed 1 solution from colorless to yellow. In the presence of other anions such as CH(3)CO(2)(-), H(2)PO(4)(-), HSO(4)(-) and Cl(-), however, the absorption spectrum of 1 was slightly red shifted with no obvious color changes observed. The association constants of anionic complexes followed the order of F(-)>CH(3)CO(2)(-)>H(2)PO(4)(-)>HSO(4)(-)>Cl(-)>Br(-), which was different from the order of anion basicity. AM1 calculation results indicated that the most stable configuration of 1 existed in the Z-E-conformation with a six-membered ring via intramolecular hydrogen bond. This made thiourea moiety of 1 in an unfavorable conformation to bond with oxygen-anionic substrates such as CH(3)CO(2)(-) and H(2)PO(4)(-), thus leading to a high selectivity and sensitivity for the detection of F(-).     

Bilirubin and hemoglobin interferences in direct colorimetric cholesterol reactions using enzyme reagents

The interferences of bilirubin and hemoglobin were tested in two cholesterol procedures in which enzymes were used as chemical reagents. Both procedures used similar approaches with cholesterol esterase to free cholesterol from its esters and cholesterol oxidase to generate hydrogen peroxide from the total free cholesterol resulting. From that common start, one procedure then used catalase to generate formaldehyde from methanol and the peroxide produced from cholesterol, and the formaldehyde was then reacted with acetylacetone to produce a yellow chromogen, while the other procedure used peroxidase to catalyze a reaction directly between peroxide and 4-aminoantipyrine plus phenol to generate a pink chromogen. Bilirubin and hemoglobin were shown to produce some interference by reacting competitively with peroxide in both systems and by contributing residual absorbance at the wavelengths of measurement of each of the chromogens. Since bilirubin showed a spectral change, static blanking with sample blanks caused overcorrections. However, the elimination of a sample blank for either procedure could result in a favorable compensating error because the residual color of bilirubin could substitute in part at least for the lost reactivity of the peroxide used up in reaction with the bilirubin of the sample.     

Selective colorimetric sensing of Cu using triazolyl monoazo derivative

Although the high sensitivity, high selectivity and fast response make emission (fluorescence) based technique as one of the most promising tool for developing the chemosensors for metal ions, the past few years have witnessed a demand for the absorption based chemosensors for paramagnetic heavy metal ions, especially Cu²⁺. Being paramagnetic, Cu²⁺ leads to the low signal outputs (“turn-off”) caused by decreased emission which may sometimes give false positive response, rendering the emission based technique less reliable for analytical purposes. Herein, we report synthesis and characterization of a hetarylazo derivative, characterized by a strong charge-transfer band which gets attenuated convincingly in the presence of Cu²⁺ leading to distinct naked-eye color change (yellow to purple), and to a lesser extent in the presence of Cd²⁺, Zn²⁺, Co²⁺, Pb²⁺, Fe²⁺, Ni²⁺, Fe³⁺ and Hg²⁺ for which the naked eye sensitivity was comparatively (w.r.t. Cu²⁺) much less. No response was observed for the other metal ions including Li⁺, Na⁺, K⁺, Mg²⁺, Ca²⁺, Ba²⁺, Mn²⁺, Ag⁺, Zn²⁺, Cd²⁺, Pb²⁺, and lanthanides Ce³⁺, La³⁺, Pr³⁺, Eu³⁺, Nd³⁺, Lu³⁺, Yb³⁺, Tb³⁺, Sm³⁺, Gd³⁺. The proposed sensing mechanism has been ascribed to the stabilization of LUMO after complexation with Cu²⁺ and a 1:1 stoichiometry has been deduced.     

Synthesis and biological evaluation of novel coumarin-chalcone derivatives containing urea moiety as potential anticancer agents

The increasing interest on new drug discovery is constantly up to date as drugs do not increase survival adequately against increasing cancer cases worldwide. Based on the reported anticancer activity of coumarin, chalcone and urea derivatives, the present investigation dealt with the design and synthesis of coumarin derivatives bearing diversely substituted chalcone-urea moieties 5a-k. Through a structure-based molecular hybridization approach, a series of novel coumarin-chalcone derivatives containing urea moiety was synthesized and screened for their in vitro antiproliferative activities against the cancer cell lines (H4IIE and HepG2). In addition, the synthesized compounds were tested on a cell line that was not cancerous (CHO) and the damage, it could give to normal cells was determined. Among the synthesized compounds, 5k exhibited better inhibition of H4IIE compared to Sorafenib. 5j also showed better inhibition against HepG2 than Sorafenib. In particular, 5k induced H4IIE apoptosis, arrested cell cycle at the S phase. Therefore, 5k and 5j may be potent antitumor agents, representing a promising lead for further optimization.     

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).     

Novel indole based colorimetric and "turn on" fluorescent sensors for biologically important fluoride anion sensing

A novel indole Hydrazone receptor 1 has been synthesized by one step of condensation, which can act as an efficient colorimetric and "turn on" fluorescent sensor for fluoride anions; Benesi-Hildebrand equation indicates that 1 associates with F(-) in a 1:1 stoichiometry; [TBA]OH and (1)H NMR titration experiments indicate that the deprotonation process involved upon addition of fluoride anions.     

Paper chromatography of some chelating reagents containing sulfonic groups in liquid-liquid anion exchange systems

Summary Chromatographic behaviour of nine chelating reagents in chloride and perchlorate systems was investigated with two methods: paper extraction chromatography and moist paper technique. It was found that the affinity of the reagents to cellulose treated with liquid anion exchangers decrease in the following orders: Eriochrome cyanine R>Chromazurol S>Pyrocatechol violet, and Alizarin S>ferron>chromotropic acid nitroso-R-salt>sulfosalicylic acid>tiron. The results obtained suggest that the retention of reagents in extraction chromatography is caused not only by anion-exchange process but also by adsorption and probably also by partition phenomena. The number of alkylammonium cations forming extracted species with reagents depends on the number of sulfonic groups in the reagent molecule but in sulfosalicylic acid carboxylic group can also be partially bound.     

Efficient and simple colorimetric fluoride ion sensor based on receptors having urea and thiourea binding sites

[structure: see text] Novel colorimetric receptors for selective fluoride ion sensing containing anthraquinone as chromogenic signaling subunit and urea (N,N' '-(9,10-dihydro-9,10-dioxo-1,2-anthracenediyl)bis[N'-phenyl])/thiourea (N,N' '-(9,10-dihydro-9,10-dihydro-9,10-dioxo-1,2-antrhacenediyl)bis[N-phenyl]) binding sites have been reported. These receptors have shown no affinity for other halide ions (Cl-, Br-, and I- ions). Well-defined color change in the visible region of the spectrum was observed upon addition of fluoride ion in DMSO/CH3CN solution of the receptors 1 and 2.     

Fluoride anion sensing mechanism of a BODIPY‐linked hydrogen‐bonding probe

The sensing mechanism of a fluoride‐anion probe BODIPY‐amidothiourea ( 1c ) has been elucidated through the density functional theory (DFT) and time‐dependent density functional theory (TDDFT) calculations. The theoretical study indicates that in the DMSO/water mixtures the fluorescent sensing has been regulated by the fluoride complex that formed between the probe 1c /two water molecules and the fluoride anion, and the excited‐state intermolecular hydrogen bond (H‐B) plays an important role in the fluoride sensing mechanism. In the first excited state, the H‐Bs of the fluoride complex 1cFH₂ are overall strengthened, which induces the weak fluorescence emission. In addition, molecular orbital analysis demonstrates that 1cFH₂ has more obvious intramolecular charge transfer (ICT) character in the S₁ state than 1cH₂ formed between the probe 1c and two water molecules, which also gives reason to the weaker fluorescence intensity of 1cFH₂ . Further, our calculated UV‐vis absorbance and fluorescence spectra are in accordance with the experimental measurements. © 2018 Wiley Periodicals, Inc.