Chromogenic and Fluorescent Recognition of Iodide with a Benzimidazole-Based Tripodal Receptor

Facile synthesis and anion binding studies of fluorescein/benzo-12-crown-4 ether based bis-dipyrromethane (DPM) receptors

Two novel fluorescein as well as benzo-12-crown-4 ether functionalized dipyrromethane receptors (DPM3 and DPM4) have successfully been synthesized. The anion (used as their TBA salts) binding studies of thus prepared DPM3 and DPM4 receptors were evaluated by the UV-visible spectrophotometric titrations. Binding affinities as well as the stoichiometry were determined through the UV-visible titrations data with the involvement of the BindFit (v0.5) package available online at https://supramolecular.org. Moreover, binding events were validated by means of the comparison of the partial 1H-NMR spectrum of the simple host molecule with that of the host-guest complex, and the 1 : 1 stoichiometry were further confirmed by the Job's method of continuous variation. From the results, we observed the binding constant (Ka) values of DPM3/DPM4 with various tested anions in the range of 516.07 M-1 to 63789.81 M-1, depending upon the nature/shape/size of the anions. Moreover, the anion-π interactions were confirmed by the partial 1H-NMR spectral data, and further supported by the literature reported systems. The authors hope that such types of valued receptors will be benefitted in future for the recognizing/binding of a variety of biologically important anions.

BINOL and triazole-containing Janus rings and 29-8-29-membered tricyclic ladder-type hybridized siloxane: application in the fluorescence sensing of anions

Tetrachloro- and tetraazide-substituted all-cis-tetraphenylcyclotetrasiloxanes (all-cis-T₄) 2 and 3 were synthesized in high yields and were fully characterized. Then the precursor 3 underwent CuAAC click reaction with monopropargyl BINOL 4 and dipropargyl BINOL 6 to give the novel BINOL and triazole-containing all-cis-T₄ cyclic siloxane 5 and the 29-8-29-membered-ring ladder-type hybrid siloxane 7. The sensing ability of compounds 5 and 7 towards anions was studied as well, and it was observed that 7 could selectively recognize iodides through synergistic C-H⋯I hydrogen bonding, resulting in an impressive fluorescence quenching with a K_sv of 8.10 × 10⁴ M^-1.

Binaphthyl-Based Chiral Macrocyclic Hosts for the Selective Recognition of Iodide Anions

In this study, we explorethe synthesis of binaphthyl-based chiral macrocyclic hosts for the first time. They exhibited the selective recognition abilities of iodide anions which can be favored over those of other anions (AcO^-, NO₃^-, ClO₄^-, HSO₄^-, Br^-, PF₆^-, H₂PO₄^-, BF₄^-, and CO₃F₃S^-), as confirmed by UV-vis, HRMS, and ¹H NMR spectroscopy experiments, as well as DFT calculations. Neutral aryl C-H···anion interactions play an important role in the formation complexes. The recognition process can be observed by the naked eye.

Rapid Evaluation of Material Surface Modification by a Dielectric Barrier Discharge Based on Fluorescence Coloring and Image Processing Technologies

In recent years, improving the surface properties of large-scale insulation by plasma modification has attracted extensive attention with the development of power systems and high-tech industries. However, routine evaluations of the modification effect and uniformity require complicated tests after the plasma is powered off, which waste a lot of time and cannot regulate the modification effect online. In this study, a novel fluorescence-assisted dielectric barrier discharge (DBD) for fabricating a functional film is developed, and a rapid evaluation method of the modification effect and uniformity is proposed based on fluorescence coloring and image processing technologies. The results show that the addition of an organic fluorescent agent in the DBD with hexamethyldisiloxane (HMDSO) has no negative effect on the plasma discharge and modification effect, and the fluorescence-assisted DBD successfully fabricates the functional films with typical chromogenic groups (N-H and S═O) that exhibit typical fluorescence under an UV lamp. According to image processing and parameter extraction, the plasma-assisted fluorescent film is converted into a two-dimensional (2D) color map with nine color levels, and three characteristic parameters are proposed to evaluate the modification effect rapidly and directly. It shows that the warmer the color of the treated sample, the better the hydrophobicity and electrical insulating properties, where the red region represents the optimally modified surface, while the blue region represents the worst one. The area, shape, and integrity of the plasma modification are clarified quantificationally, which provides the possibility of further online evaluation of the modification effect and uniformity by the plasma treatment.

Optical Chemical Sensing of Iodide Ions: A Comprehensive Review for the Synthetic Strategies of Iodide Sensing Probes, Challenges, and Future Aspects

Among several anions, iodide (I^- ) ions play a crucial role in human biological activities. In it's molecular form (I₂ ), iodine is utilized for several industrial applications such as syntheses of medicines, fabric dyes, food additives, solar cell electrolytes, catalysts, and agrochemicals. The excess or deficiency of I^- ions in the human body and environmental samples have certain consequences. Therefore, the selective and sensitive detection of I^- ions in the human body and environment is vital for monitoring their overall profile. Amongst various analytical techniques for the estimation of I^- ions, optical-chemical sensing possesses the merits of high sensitivity, selectivity, and utilizing the least amount of sensing materials. The distinctive aims of this manuscript are (i) To comprehensively review the development of optical chemical sensors (fluorescent & colorimetric) reported between 2001-2021 using organic fluorescent molecules, supramolecular materials, conjugated polymers, and metal-organic frameworks (MOFs). (ii) To illustrate the design and synthetic strategies to create specific binding and high affinity of I^- ions which could help minimize negative consequences associated with its large size and high polarizability. (iii) The challenges associated with sensitivity and selectivity of I^- ions in aqueous and real samples. The probable future aspects concerning the optical chemical detection of I^- ions have also been discussed in detail.

Fluorenone-Based Fluorescent and Colorimetric Sensors for Selective Detection of I- Ions: Applications in HeLa Cell Imaging and Logic Gate

Fluorenone-based fluorescent and colorimetric sensors 1 and 2 have been developed that displayed selective detection of iodide ions in the presence of interferences. Sensors displayed the fluorescence emission enhancement response toward I- with detection limits of 8.0 and 11.0 nM, respectively, which is accomplished through inhibition of intramolecular charge transfer and C=N isomerization. Excellent sensitivity and unique fluorescence enhancement response of sensors toward I- make them superior because most of the previously reported iodide sensors are based on the fluorescence quenching mechanism and are less sensitive. The sensing potential of sensors toward I- ions was investigated through 1H NMR titration, dynamic light scattering, Job's plots, and density functional theory analysis. Further, sensors displayed reversible behavior by the alternate addition of I- and Cu2+ ions that substantiate their role as recyclable sensors for the on-site detection of I- ions. Advantageously, fluorescence enhancement response of sensors was favorably used for fluorescence imaging of I- in live HeLa cells and the design of the logic gate. These sensors were successfully applied in diversified applications such as the preparation of sensors' coated paper strips and the determination of I- ions in blood serum, food, and real water samples.

Halogen Bonding Ionophore for Potentiometric Iodide Sensing

Iodide (I^-) is an essential micronutrient for thyroid function. Hence, rapid and portable sensing is important for I^- quantification in food and biological samples. Herein, we report the first example of a halogen bonding (XB) tripodal ionophore (XB1) which is selective for the I^- anion. NMR binding studies of XB1 and its H-triazole analog HB2 with I^- demonstrated the dominant influence of XB interactions between the ionophore and the I^- analyte. The phase boundary model was applied to formulate iodide-selective electrodes with the ionophore XB1. The optimal electrode exhibited a near-Nernstian response of -51.9 mV per decade within a large dynamic range (10^-1 to 10^-6 M) and notably anti-Hofmeister selectivity for I^- over thiocyanate (SCN^-), enabling the in situ determination of I^- in complex samples. This work establishes XB as a viable supramolecular interaction in the potentiometric sensing of anions.

Urea-doped carbon dots as fluorescent switches for the selective detection of iodide ions and their mechanistic study

A facile and green strategy for the fabrication of fluorescent urea-doped carbon dots (N-CDs) has been explored. Significantly, the fluorescent N-CDs could recognize iodide ions (I-) with high selectivity, and their photoluminescence could be efficiently quenched by the addition of I-. The sensitivity analysis for I- indicated a linear relationship in the range from 12.5 to 587 μM with the detection limit as low as 0.47 μM. Furthermore, the I- induced fluorescence (FL) quenching mechanism was investigated employing a combination of techniques, including UV-vis/fluorescence spectroscopy, Density Functional Theory (DFT) calculation, TEM and time-resolved fluorescence decay measurements. The DFT calculation results demonstrated that the amino- and amide groups of N-CDs play a significant role in iodide recognition through the formation of multiple N-H⋯I-, C-H⋯I- and C([double bond, length as m-dash]O)N-H⋯I- interactions with I-. The TEM experiment confirmed the aggregation process when I- was added to the N-CDs solution. Moreover, the radiative decay rate of N-CDs, which was first measured and reported the kinetic behaviors of the FL-quenching process, decreased from 3.30 × 107 s-1 to 1.95 × 107 s-1 after the coordination with I- ions. The reduced lifetime demonstrated that the excited energy dissipation led to a dynamic quenching process. Therefore, such carbon materials can function as effective fluorescent switches for the selective detection of I- ions.

Allosteric binding properties of a 1,3-alternate thiacalix[4]arene-based receptor having phenylthiourea and 2-pyridylmethyl moieties on opposite faces

Thiacalix[4]arene receptors with two thiourea moieties and two 2-pyridyl moieties exhibited a heteroditopic dinuclear receptor with F− and Ag+ ions by a positive allosteric effect.

Recent Advances in Luminescent Recognition and Chemosensing of Iodide in Water

This Minireview covers the latest developments of chemosensors based on transition-metal receptors and organic fluorophores with specific binding sites for the luminescent detection and recognition of iodide in aqueous media and real samples. In all selected examples within the last decade (made-post 2010), the iodide sensing and recognition is probed by monitoring real-time changes of the fluorescence or phosphorescence properties of the chemosensors. This review highlights effective strategies to iodide sensing from a structural approach where the iodide recognition/sensing process, through supramolecular interactions as coordination bonds, hydrogen bonds, halogen bonds and electrostatic interactions, is transduced into an optical change easily measurable. The selective iodide sensing is an active field of research with global interest due to the importance of iodide in biological, medicinal, industrial, environmental and chemical processes.

Porosity-Induced Selective Sensing of Iodide in Aqueous Solution by a Fluorescent Imidazolium-Based Ionic Porous Framework

Developing a chemosensor for rapid, sensitive, and visual detection of iodide (I^-) by a simple synthetic strategy is still challenging. Herein, we report a highly efficient iodide sensor by simply introducing ionic imidazolium groups into the porous network. This sensor, that is, a fluorescent ionic porous framework (IPF), was prepared by the quaternization reaction of octa((benzylchloride)ethenyl)silsesquioxane and 1,4-bis(1H-imidazole-1-yl)benzene and exhibited moderate porosity with a Brunauer-Emmett-Teller surface area of 379 m² g^-1 and blue fluorescence when excited by UV light. The IPF suspension in water can detect I^- with high sensitivity and selectivity among various anions and quick response by fluorescence quenching. In contrast to no response toward I^- by the linear model compound and the enhanced sensing performance with an increment of porosity, this finding indicates that the porosity of IPF is important for the detection of I^- and an inducement of the sensing process. A fluorescent paper sensor was further developed, which shows high efficiency for the visual detection of I^- similar to the abovementioned sensor, suggesting its potential in convenient and on-site sensing of I^-. In addition, the paper sensor is recyclable with a remarkable fluorescence resuming ratio of 83% after 10 times cycle detection. Moreover, the developed sensor is used for the analysis of real samples. This work represents the first example of the detection of I^- by an ionic porous polymer. Compared with conventional iodide sensors, the present sensor does not require unique structures to form the pseudocavity during sensing I^- and can easily achieve high efficiency by incorporating ionic hydrogen bond donors into the porous network, indicating the importance of porosity and the feasibility of replacing the pseudocavity with a real cavity (or pore). More iodide sensors with high efficiency can be designed and fabricated by this novel and simple strategy.

1,2,3-Triazolium macrocycles in supramolecular chemistry

In this short review, we describe different pathways for synthesizing 1,2,3-triazolium macrocycles and focus on their application in different areas of supramolecular chemistry. The synthesis is mostly relying on the well-known "click reaction" (CuAAC) leading to 1,4-disubstituted 1,2,3-triazoles that then can be quaternized. Applications of triazolium macrocycles thus prepared include receptors for molecular recognition of anionic species, pH sensors, mechanically interlocked molecules, molecular machines, and molecular reactors.

Facile method for iodide ion detection via the fluorescence decrease of dihydrolipoic acid/beta-cyclodextrin protected Ag nanoclusters

In this work, novel photoluminescent Ag nanoclusters (Ag NCs) with red emission are synthesized and successfully used for detecting iodide ion (I^-). The dihydrolipoic acid (DHLA) is used as the stabilizing agent and beta-cyclodextrin (β-CD) is used as the auxiliary stabilizing agent. DHLA and β-CD are combined with Ag atoms by the formation of AgS bonds and hydrophobic interaction, respectively. Functionalization of β-CD endows good photoluminescent properties and solubility in water to the Ag NCs. The obtained DHLA and β-CD-protected Ag NCs (DHLA/β-CD-Ag NCs) are spherical and display a dispersed state. However, the DHLA/β-CD-Ag NCs are aggregated in the presence of I^-, accompanied by the decrease in their fluorescence intensity. Because the integrity of β-CD cavities is retained on the surface of DHLA/β-CD-Ag NCs, which preserves their capability for I^- host-guest recognition, the DHLA/β-CD-Ag NCs combine with I^- through the formation of inclusion complexes. Based on this phenomenon, the prepared DHLA/β-CD-Ag NCs can be designed as a novel fluorescent probe for I^- detection. The limit of detection (LOD) is calculated as 0.06 μM, indicating that it is an ideal probe for I^- detection in practical applications.

Cholesterol-Appended Benzimidazolium Salts: Synthesis, Aggregation, Sensing, Dye Adsorption, and Semiconducting Properties

A series of cholesterol-appended benzimidazolium salts 1-9 have been designed and synthesized. They have been explored in gel chemistry. The gelation of the benzimidazolium salts is dependent on the nature of the counteranions. In addition, the gelation behavior of the gelators is linked with the presence of both π-stacking and cholesteryl motifs. Whereas bisbenzimidazolium salt 2 forms a gel in dimethylsulfoxide/H₂O (1:1, v/v) itself, under similar conditions, monobenzimidazolium salts 4 and 6 exhibit gelation in the presence of F^- ions and validate the visual sensing of F^-. As an application, the gel phase of 2 efficiently removes toxic dyes from waste water. Furthermore, all gels show thermally activated semiconducting property within a wide voltage window.

A G-quadruplex based fluorescent oligonucleotide turn-on probe towards iodides detection in real samples

A basket-type G-quadruplex (GQ) fluorescent oligonucleotide (OND) probe is designed to detect iodides dependent on thymine-Hg(II)-thymine (T-Hg(II)-T) base pairs and the intrinsic fluorescence quenching capacity of GQ. In the presence of Hg(II) ions (Hg²⁺), the two hexachloro-fluorescein-labeled ONDs form a hairpin structure and the fluorophores are dragged close to the GQ, leading to fluorescence quenching of the probe due to photoinduced electron transfer. Upon addition of iodide anions, Hg²⁺ are extracted from T-Hg(II)-T complexes which attributes to the stronger binding with iodide anions, resulting in the fluorescence recovery. Through performing the fluorescence quenching and recovery processes, this probe developed a fluorescence turn-on sensor for iodide anions determination over a linear range of 20-200nmol/L with a limit of detection of 5nmol/L. The practical use of the turn-on technology was demonstrated by its application in determination of iodides in water, food, pharmaceutical products and biological samples.

Perfect symmetrical cyclic aromatic trimer motif in tripodal molecule

A family of substituted benzimidazolyl-based tripodal molecules with alkyl substituted spacers was synthesized, showing perfect symmetric cyclic aromatic trimer motifs which remained intact in the solid as well as solution state.

Silver nanoclusters with enhanced fluorescence and specific ion recognition capability triggered by alcohol solvents: a highly selective fluorimetric strategy for detecting iodide ions in urine

Alcohol solvents can endow silver nanoclusters with enhanced red fluorescence and specific iodide recognition capability.

Cyclo[4]carbazole, an Iodide Anion Macrocyclic Receptor

A novel preorganized and rigid iodide anion macrocyclic receptor, cyclo[4]carbazole (Cy[4]C), is reported here. The structure of Cy[4]C was confirmed by single-crystal X-ray analysis. The binding affinity of Cy[4]C for iodide anion was investigated by UV-vis and ¹H NMR spectroscopic techniques. The crystal structure of the complex between Cy[4]C and chloroform also provided evidence for the recognition ability of Cy[4]C toward iodide anion. Furthermore, the 1:1 complexation stoichiometry between Cy[4]C and iodide anion was confirmed by high-resolution mass spectrometry and molecular modeling.

A mercuric ensemble based on a cycloruthenated complex as a visual probe for iodide in aqueous solution

A new water-soluble cycloruthenated complex Ru(bthiq)(dcbpy)2(+) (1, Hbthiq=1-(2-benzo[b]thiophenyl)isoquinoline, dcbpy=4,4'-dicarboxylate-2,2'-bipyridine) was designed and synthesized to form its mercuric ensemble (1-Hg(2+)) to achieve visual detection of iodide anions. The binding constant of 1-Hg(2+) is calculated to be 2.40×10(4)M(-1), which is lower than that of HgI2. Therefore, the addition of I(-) to the aqueous solution of 1-Hg(2+)lead to significant color changes from yellow to deep-red by the release of 1. The results showed that iodide anions could be easily detected by the naked eyes. The detection limit of iodide anion is calculated as 0.77μM. In addition, an easily-prepared test strip of 1-Hg(2+) was obtained successfully to detect iodide anions.

An NHC silver(i) macrometallocycle: synthesis, structure and selective recognition of iodide anions

An NHC silver(i) crown ether 1 has been synthesized, and the recognition of I⁻ using 1 as a receptor was studied.

A study of anion binding behaviour of 1,3-alternate thiacalix[4]arene-based receptors bearing urea moieties

Thiacalix[4]arene receptors with two urea moieties exhibited a high affinity towards all of the selected anions.

Ratiometric fluorophore for quantification of iodide under physiological conditions: applications in urine analysis and live cell imaging

The ratio of fluorescence intensity of fluorophoreI_{395 nm}/I_{475 nm}vs.log [I⁻] undergoes linear change over a broad iodide concentration range of 10⁻⁹to 10⁻⁵M and finds application in urine analysis and live cell imaging.

Potential anion sensing properties by a redox and substitution series of [Ru(bpy)3−n(Hdpa)n]2+, n = 1–3; Hdpa = 2,2′-dipyridylamine: selective recognition and stoichiometric binding with cyanide and fluoride ions

Efficient anion sensors [Ru(bpy)_3−n(Hdpa)_n]²⁺, n = 1–3 have been developed for selective recognition of cyanide and fluoride ions with remarkable stoichiometric binding.

Synthesis of “amphiphilic” carbon dots and their application for the analysis of iodine species (I2, I− and IO3−) in highly saline water

In this work, “amphiphilic” carbon dots (A-CDs) with a strong green fluorescence were synthesized by a simple and green method at room temperature, and the synthesized A-CDs could be used for the analysis of iodine species (I₂, I⁻ and IO₃⁻) in highly saline water.

Virgin silver nanoparticles as colorimetric nanoprobe for simultaneous detection of iodide and bromide ion in aqueous medium

A simple colorimetric nanoprobe based on virgin silver nanoparticles (AgNPs) was developed for the selective detection of iodide and bromide ions via aggregation and anti-aggregation mechanism. With addition of I(-) ions, virgin AgNPs, in presence of Fe(3+), showed perceptible color change from yellow to colorless along with disappearance of surface plasmon resonance (SPR) band of AgNPs at 400 nm. But in presence of Cr(3+), AgNPs turned yellow upon addition of I(-)and Br(-) anions. The developed virgin AgNPs probe showed high specificity and selectivity with the detection limits down to 0.32 μM and 1.32 μM for I(-) ions via two different mechanistic routes. Also, the designed probe detects Br(-) with a detection limit down to 1.67 μM.

Structures of NHC Hg(ii) and Ag(i) complexes and selective recognition of nitrate anion

Eight N-heterocyclic carbene Hg(ii) and Ag(i) complexes were prepared, and the selective recognition of nitrate anion was studied.

A turn-on fluorescence probe for imaging iodide in living cells based on an elimination reaction

Based on a unique elimination reaction prompted by the iodide, a turn-on fluorescent probe (HCy-OMe-Br) without containing heavy metal has been developed for the first time. The probe can monitor iodide with excellent selectivity and sensitivity and was successfully applied to visualize iodide in living cells.

Positive and negative allosteric effects of thiacalix[4]arene-based receptors having urea and crown-ether moieties

Allosteric binding behaviors of heteroditopic receptors bearing the 1,3-alternate conformation based thiacalix[4]arene have been evaluated by absorption and ¹H NMR titration experiments.

Steric group enforced aromatic cyclic trimer conformer in tripodal molecules

A family of tripodal molecules (1–6) with/without steric ethyl groups at the central benzene scaffold and with furan/thiophene/pyridyl groups at the 2-position of the benzimidazolyl unit was synthesised.

Synthesis, physical properties and ion recognition of a novel larger heteroacene with eleven linearly-fused rings and two different types of heteroatom

A novel larger stable heteroacene, 8N8O, has been synthesized and demonstrated to act as an efficient anion sensor for iodide over a wide range of other anions.