Chemodosimeters and 3D inorganic functionalised hosts for the fluoro-chromogenic sensing of anions

Synthesis, Optical Spectroscopy, and Laser and Biomedical Imaging Application Potential of 2,4,6-Triphenylpyrylium Tetrachloroferrate and Its Derivatives

Synthesis, optical spectroscopic properties, two-photon (TP) absorption-induced fluorescence, and laser and bioimaging application potentials of 2,4,6-triphenylpyrylium tetrachloroferrate (1),4-(4-methoxyphenyl)-2,6-diphenylpyrylium tetrachloroferrate (2), 2,6-bis(4-methoxyphenyl)-4-phenylpyrylium tetrachloroferrate (3), and 2,4,6-tris(4-methoxyphenyl)pyrylium tetrachloroferrate (4) are presented. The synthesis involves the conversion of pyrylium tosylates to pyrylium chlorides, followed by transformation into 1-4 on heating to reflux with FeCl3 in acetonitrile. They are characterized using 1H and 13C NMR spectra in CD3OD, and FTIR and Raman spectroscopic techniques. The salts dissolve in organic solvents and water (pH = 7 to 3) even at high concentrations (10-3 M). These solutions absorb light strongly from 500-300 nm. Solutions of 1, 3, and 4 fluoresce with high quantum yield in the 500-700 nm spectral range. Salts 1 and 4 exhibit fluorescence lifetime shortening, line width narrowing, and free-running laser action under intense pulsed laser excitation. Toxicity and cell imaging studies using human cancer cell lines reveal that salts 1 and 3 function as cellular fluorophores in vitro and have no adverse effects on cellular viability at nanomolar ranges. Furthermore, acetonitrile and methanol solutions of salts 1, 3, and 4 exhibit strong two-photon absorption-induced fluorescence, opening potential applications in biomedical imaging and microscopy.

A Bis(Acridino)-Crown Ether for Recognizing Oligoamines in Spermine Biosynthesis

Oligoamines in cellular metabolism carry extremely diverse biological functions (i.e., regulating Ca2+-influx, neuronal nitric oxide synthase, membrane potential, Na+, K+-ATPase activity in synaptosomes, etc.). Furthermore, they also act as longevity agents and have a determinative role in autophagy, cell growth, proliferation, and death, while oligoamines dysregulation is a key in a variety of cancers. However, many of their mechanisms of actions have just begun to be understood. In addition to the numerous biosensing methods, only a very few simple small molecule-based tests are available for their selective but reversible tracking or fluorescent labeling. Motivated by this, we present herein a new fluorescent bis(acridino)-crown ether as a sensor molecule for biogenic oligoamines. The sensor molecule can selectively distinguish oligoamines from aliphatic mono- and diamino-analogues, while showing a reversible 1:2 (host:guest) complexation with a stepwise binding process accompanied by a turn-on fluorescence response. Both computational simulations on molecular docking and regression methods on titration experiments were carried out to reveal the oligoamine-recognition properties of the sensor molecule. The new fluorescent chemosensor molecule has a high potential for molecular-level functional studies on the oligoamine systems in cell processes (cellular uptake, transport, progression in cancers, etc.).

Azo-hydrazone tautomerism in a simple coumarin azo dye and its contribution to the naked-eye detection of Cu2+ and other potential applications

A new tailor-made azo dye of coumarin connected to phenolic derivative is presented herein. Azo-hydrazone tautomerism in aqueous solution of the dye was observed and studied using spectroscopic assays such as ¹H NMR, absorption and emission assays, and theoretical studies. Tautomerism was attributed to the presence of a labile phenolic hydrogen in the ortho position to the azo functionality and the hydrazone was found to be the more dominant tautomer. Influence of metal ions on the azo-hydrazone chemical equilibrium and how the accompanying colour and spectroscopic changes can be exploited for various functions, especially the detection and quantification of Cu²⁺ in aqueous environments was explored. The presence of Cu²⁺ affects the azo-hydrazone equilibrium resulting in visual appearance and spectroscopic changes and the likely binding sites for Cu²⁺ were evaluated. Cu²⁺ pushes the azo-hydrazone equilibrium towards the more conjugated form and the presence of other metal ions does not have any perceivable impact on this mechanism. The dye showed potential applications as a sensor in colorimetric and spectroscopic detection and quantification of Cu²⁺ in domestic and environmental water samples, photo-imprinting and as a logic gate. The limits of detection (LOD) and quantification (LOQ) for Cu²⁺ were found to be 0.0779 mg/L and 0.236 mg/L, respectively, much lower than the World Health Organization (WHO) guideline limit for Cu²⁺ levels in drinking water.

Nucleophilic Approach to Cyanide Sensing by Chemosensors

Cyanide anion has wide use in industrial areas; however, it has a high toxic effect on the environment as waste. Moreover, plant seeds contain cyanide that is often consumed by human beings. Therefore, many studies are carried out to determine cyanide. Especially, optical sensors showing colorimetric and fluorimetric changes have been of considerable interest due to their easy, cheap, and fast responses. This review discusses recent developments in the colorimetric and fluorimetric detection of cyanide by nucleophilic addition to different types of receptors via the chemodosimeter approach. The sensitivity and selectivity of the sensors have been reviewed for changes in absorption and fluorescence, naked-eye detection, real sample application, and detection limits when interacting with cyanide.

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.

Spermine and Spermidine Detection through Restricted Intramolecular Rotations in a Tetraphenylethylene Derivative

Biogenic polyamines, especially spermine and spermidine, are associated with cell growth and development. These amines can be found at high concentrations in the tumor cells, tissues, and urine of cancer patients. In contrast, spermidine levels drop with age, and a possible connection between low endogenous spermidine concentrations and age-related deterioration has been suggested. Thus, the quantification of these amines in body fluids like urine could be used in the diagnosis of different pathological situations. Here a new fluorescent molecular probe based on a tetraphenylethylene derivative is reported. This probe is able to selectively detect these amines through the enhancement of the fluorescence emission of the resulting complex. This fluorescence enhancement may be related to restricted intramolecular rotations of TPE phenyl rings induced by the analyte. Theoretical studies were carried out to shed light on the observed selectivity. Finally, the detection of these amines in urine was performed with limits of detection of 0.70 µM and 1.17 µM for spermine and spermidine, respectively.

Simulation and experimental study of fluorescence labeled polyphosphate in microthrix parvicella

To study the binding mechanism of 4',6-diamidino-2-phenylindole (DAPI) and polyphosphate (Poly-P) and find fluorescent dyes which can dye Poly-P better, the interaction model of DAPI and Poly-P was calculated by the self-consistent-charge, density functional tight-binding (SCC-DFTB-D) method, and the binding sites of DAPI and Poly-P were analyzed. Further, Cy3, Rhodamine 6G and Fluorescein, which are structurally similar to DAPI, were selected to analyze their interactions with Poly-P. The binding energies and frontier orbital properties of the complexes were analyzed. These four fluorescent dyes were further used to dye the activated sludge smear and observe the fluorescence property. The Simulation results show that the N-containing indole ring structures in DAPI plays an important role in the interaction with Poly-P; the binding energies for DAPI, Cy3, Rhodamine 6G and Fluorescein with Poly-P are -42.6, -165.4, -34.7 and -28.9 kcal/mol, respectively. The frontier orbital properties for the complexes were studied, which further indicates that the interactions between Cy3, Rhodamine 6G and Poly-P are stronger than that of Fluorescein and Poly-P. The experimental results showed that Cy3 had excellent dyeing effect on Poly-P and could recognize them, while Fluorescein could not dye Poly-P. The experimental results were in good agreement with those predicted by simulation, which verified the correctness of our calculation method and provided a new strategy for finding more reliable, more sensitive and more economical fluorescent dyes capable of dyeing Poly-P.

Crystal structures, red-shifted luminescence and iodide-anion recognition properties of four novel D-A type Zn(ii) complexes

Four D-A type Zn(ii) coordination complexes, [Zn(C29H29N3O2)·(CH3OH)]·(CH3OH) (1), Zn2(C74H90N6O4)·(CH3OH) (2), [Zn(C30H28N4O2)·(CH3OH)]·(CH3OH) (3) and [Zn(C38H44N4O2)·(C2H5OH)]·(C2H5OH) (4), were designed, synthesized, and studied. Their fluorescence properties in the solid state and in THF solution were comprehensively analysed based on their single-crystal structures. The results showed that the red-shift of fluorescence emission from complexes 1 to 4 was successfully achieved via the strategy of enhancing intramolecular charge transfer (ICT) effects by increasing the number of electron-pulling and pushing groups gradually. Meanwhile, because of the fluorescence recognition abilities of these four complexes towards iodide anions in THF, they could be regarded as potential fluorescent sensors for I- in this organic solution in the future.

Directional Approach to Enantiomerically Enriched Functionalized [7]Oxa-helicenoids and Groove-Based Selective Cyanide Sensing

Several regioselective functionalized mono- and disubstituted [7]oxa-helicenoids have been synthesized in the enantiomerically enriched (90-99% ee) form. These functionalized helicenoids exhibited pronounced spectral and chiroptical properties suitable for sensing applications. In particular, corresponding helicenoid's mono and dialdehydes have been effectively used as chemodosimeters for selective detection of cyanide anions over other anions, while simple aromatic aldehydes do not function as cyanide sensors. The groove available in the helical host plays a crucial role in the sensing. The enantiomerically enriched nature of the sensors allows the use of electronic circular dichroism as an uncommon detection tool for cyanide anions, along with conventional fluorescence and NMR methods.

Triazole derived azo-azomethine dye as a new colorimetric anion chemosensor

In the pursue of developing anion sensors, an efficient triazole derived azo-azomethine dye chemosensor (S) that differentially senses F‾ and AcO‾ ions has been reported. The ions recognition ability of S was investigated by colorimetric and UV-visible spectroscopic methods. Interestingly, this chemosensor molecule is virtually inactive in presence of other anions such as Cl‾, Br‾ and I‾ and HSO₄‾. We have further presented a ratiometric approach to differentiate F‾ and AcO‾ ions. The reversibility of F‾ ion binding with S was established by the addition of Ca(NO₃)₂ to the fluoride bound S, which led to the regeneration of S. The quantum chemical calculation of energies of unbound and bound S has been employed using Density Functional Theory (DFT) to understand the interaction between chemosensor and anions. Evidence in support of fluoride-induced deprotonation of a O-H bond during the detection of F⁻ ion has been demonstrated by employing ¹H NMR titration experiments.

Overview of the Evolution of Silica-Based Chromo-Fluorogenic Nanosensors

This review includes examples of silica-based, chromo-fluorogenic nanosensors with the aim of illustrating the evolution of the discipline in recent decades through relevant research developed in our group. Examples have been grouped according to the sensing strategies. A clear evolution from simply functionalized materials to new protocols involving molecular gates and the use of highly selective biomolecules such as antibodies and oligonucleotides is reported. Some final examples related to the evolution of chromogenic arrays and the possible use of nanoparticles to communicate with other nanoparticles or cells are also included. A total of 64 articles have been summarized, highlighting different sensing mechanisms.

Azaindole-BODIPYs: Synthesis, fluorescent recognition of hydrogen sulfate anion and biological evaluation

The synthesized and sensing capability of two novel azaindole substituted mono and distyryl BODIPY dyes against bisulfate anion were reported. Structural characterizations of the targeted compounds were conducted by using matrix-assisted laser desorption/ionization time-of-flight mass spectrometry, ¹H and ¹³C NMR spectroscopies. Photophysical properties of the azaindole substituted BODIPY compounds were investigated employing absorption and fluorescence spectroscopies in acetonitrile solution. It was found that the final compounds 3 and 4 exhibited exclusively selective and sensitive turn-off sensor behavior on HSO₄^- anion. Additionally, the stoichiometry ratio of the targeted compounds to bisulfate anion was measured 0.5 by Job's method. Also, density function theory was performed to the optical response of the sensor for targeted compounds. Furthermore, the cytotoxicity of Azaindole-BODIPYs was examined against living human leukemia K562 cell lines.

Selective detection of fluoride via amplified donor-acceptor interaction of 6H-indolo[2,3-b]quinoline

In this report, 6H-indolo[2,3-b]quinoline (hereafter 2a) was synthesized and employed as an optical chemosensor for fluoride. The sensitivity of 2a towards fluoride was established from the change in both the absorption and emission signals. The various in-situ¹H NMR, UV-Vis, and density functional studies indicate that the 1:2 binding interaction between 2a and fluoride followed by deprotonation to its corresponding di-anion (2a^2-), which in turn boosted the donor-acceptor interaction between indole and quinoline moiety in 2a^2-via expansion of torsion angle by 10.2° as compared to 2a. Consequently the significant changes in both the absorption and emission signal of 2a allow us to detect and estimate the concentration of fluoride up to 0.2 μM from the mixture of different anions.

Design and application of a fluorogenic receptor for selective sensing of cations, small neutral molecules, and anions

An unprecedented single multi-analyte fluorogenic receptor, a sodium salt of N-(methyl-2-thiophenyl)-tyrosine (NaHTyrthio), is reported for the selective sensing of cations (Cu²⁺), small neutral molecules (nitrobenzene and aniline) and anions (F⁻) by variable spectral responses.

Self-assembly and anion sensing of metal–organic [M6L2] cages from fluorescent triphenylamine tri-pyrazoles with dipalladium(ii,ii) corners

Three supramolecular metallo-cages are synthesized from the fluorescent triphenylamine functionalized tri-pyrazoles via a directed self-assembly process in aqueous solution.

A colorimetric and fluorescence enhancement anion probe based on coumarin compounds

In this paper, anion probe 1 was designed and synthesized by using phenprocoumon containing acyl hydrazine with p-nitro azo salicylaldehyde reaction Dickson et al. (2008) Dickson et al. (2008) [1]. In the anion probe 1, the nitro moiety is a signaling group and the phenolic hydroxyl moiety is anion binding site. Then the anion probe 1 was characterized by mass spectra (MS) and infrared spectra (IR). The binding properties of the anion probe 1 for anions such as F(-), AcO(-), H2PO4(-), OH(-), Cl(-), Br(-) and I(-) were investigated by ultraviolet-visible (UV-Vis) spectra and fluorescence spectra Shao et al. (2008) Shao et al. (2008) [2]. Furthermore, the color of anion probe 1 after addition of F(-), AcO(-), H2PO4(-) and OH(-) in DMSO changed from yellow to blue, while no obvious color changes were observed by addition of other tested anions. Accordingly, the anion probe 1 could sense visually F(-), AcO(-), H2PO4(-) and OH(-) without resorting to any spectroscopic instrumentation Amendola et al. (2010) Amendola et al. (2010) [3].

Metal-based optical chemosensors for CN- detection

This critical review focuses on recent advances (2010-2015) in the detection of cyanide anion via metal-based optical chemosensors in which a change in colour and/or fluorescence intensity (or emission wavelength) of a molecular metal complex is determined by the direct interaction of the metal centre with this anion.

A novel tripodal colorimetric and fluorescence "turn on" chemosensor for AcO(-) and F(-) anions in CH3CN

A novel chemosensor, 3',3‴,3‴″-(((nitrilotris(ethane-2,1-diyl))tris(azanylylidene))tris(methanylylidene))tris(4-hydroxy-4'-biphenylcarbonitrile) (L) was synthesized and characterized by the combination of (1)H,(13)C, APT, COSY NMR, FT-IR, and elemental analysis. The behavior of the receptor (L) toward different anions was investigated using UV-visible and fluorescence spectroscopy. The receptor (L) indicated an efficient colorimetric "naked-eye" and "turn on" fluorescent response for fluoride and acetate in CH3CN, respectively.

A water-soluble and retrievable ruthenium-based probe for colorimetric recognition of Hg(II) and Cys

A new ruthenium-based complex 1 [(bis(4,4'-dimethylphosphonic-2,2'-bipyridine) dithiocyanato ruthenium (II))] was developed as a colorimetric probe for the detection of Hg(II) and Cys (Cysteine). The obtained compound 1 can give interconversional color changes upon the alternating addition of Hg(II) and Cys in 100% aqueous solution. The specific coordination between NCS groups with Hg(II) can lead to the formation of 1-Hg(2+) complex, which can induce a remarkable spectral changes of probe 1. Afterwards the formed 1-Hg(2+) complex can act as effective colorimetric sensor for Cys. Owing to the stronger binding affinity of sulfhydryl group to Hg(2+), Cys can extract Hg(2+) from 1-Hg(2+) complex resulting in the release of 1 and the revival of absorption profile of the probe 1. By introducing the hydrophilic phosphonic acid groups, the proposed probe exhibited excellent water solubility. The limits of detection (LODs) of the assay for Hg(2+) and Cys are calculated to be 15nM and 200nM, respectively.

A Highly Selective Chemosensor for Cyanide Derived from a Formyl-Functionalized Phosphorescent Iridium(III) Complex

A new phosphorescent iridium(III) complex, bis[2',6'-difluorophenyl-4-formylpyridinato-N,C4']iridium(III) (picolinate) (IrC), was synthesized, fully characterized by various spectroscopic techniques, and utilized for the detection of CN(-) on the basis of the widely known hypothesis of the formation of cyanohydrins. The solid-state structure of the developed IrC was authenticated by single-crystal X-ray diffraction. Notably, the iridium(III) complex exhibits intense red phosphorescence in the solid state at 298 K (ΦPL = 0.16) and faint emission in acetonitrile solution (ΦPL = 0.02). The cyanide anion binding properties with IrC in pure and aqueous acetonitrile solutions were systematically investigated using two different channels: i.e., by means of UV-vis absorption and photoluminescence. The addition of 2.0 equiv of cyanide to a solution of the iridium(III) complex in acetonitrile (c = 20 μM) visibly changes the color from orange to yellow. On the other hand, the PL intensity of IrC at 480 nm was dramatically enhanced ∼5.36 × 10(2)-fold within 100 s along with a strong signature of a blue shift of the emission by ∼155 nm with a detection limit of 2.16 × 10(-8) M. The cyanohydrin formation mechanism is further supported by results of a (1)H NMR titration of IrC with CN(-). As an integral part of this work, phosphorescent test strips have been constructed by impregnating Whatman filter paper with IrC for the trace detection of CN(-) in the contact mode, exhibiting a detection limit at the nanogram level (∼265 ng/mL). Finally, density functional theory (DFT) and time-dependent density functional theory (TD-DFT) calculations were performed to understand the electronic structure and the corresponding transitions involved in the designed phosphorescent iridium(III) complex probe and its cyanide adduct.

Reaction-based probe for hydrogen sulfite: dual-channel and good ratiometric response

We designed and synthesized a new series of intramolecular charge transfer (ICT) molecules (compounds T1, T2 and T3) by attaching various electron-donating thiophene groups to the triphenylamine backbone with aldehyde group as the electron acceptor. Based on the nucleophilic addition reaction between hydrogen sulfite and aldehyde, all compounds could act as ratiometric optical probe for hydrogen sulfite and displayed efficient chromogenic and fluorogenic signaling. Upon the addition of hydrogen sulfite anions, probe T3 displayed apparent fluorescent color changes from yellowish-green to blue, with a large emission wavelength shift (Δλ = 120 nm). T3 responded to hydrogen sulfite with high sensitivity and the detection limit was determined to be as low as 0.9 μM. At the same time, apparent changes in UV-vis spectra could also be observed. By virtue of the special nucleophilic addition reaction with aldehyde, T3 displayed high selectivity over other anions. Copyright © 2016 John Wiley & Sons, Ltd.

Colorimetric detection of fluoride ions by anthraimidazoledione based sensors in the presence of Cu(ii) ions

A thioimidazole bearing anthraimidazoledione detects fluoride selectively in the presence of Cu²⁺with a detection limit of 0.04 ppm. The results show that the change of thioimidazole to imidazole leads to no detection.

An overwhelmingly selective colorimetric sensor for Ag(+) using a simple modified polyacrylonitrile fiber

A carboxymethyl-dithiocarbamate immobilized polyacrylonitrile fiber colorimetric sensor has been synthesized. This fiber sensor exhibits excellent selectivity and sensitivity for Ag(+) in aqueous solution with a remarkable color change from light pink to red-brown over a wide pH range of 2-12. The sensor responds selectively to Ag(+) in the presence of other ions, including Mg(2+), Al(3+), Ca(2+), Cr(3+), Mn(2+), Co(2+), Ni(2+), Cu(2+), Zn(2+), Cd(2+), Hg(2+) and Pb(2+). The colorimetric sensor has an extremely fast response time (10s) and a low visual limit of detection (5.53×10(-12) mol/L). The fiber sensor also undergoes an obvious color change in the presence of Ag(+) solutions containing EDTA, NaCl or NaBr. Density functional theory optimization reveals that the sensor and Ag(+) interact via a seven-membered ring complexation mechanism.

Solvent effect on neutral chiral supramolecular assemblies and their distinct receptor behaviour towards anions

We describe the distinct receptor behaviour of a neutral chiral Cu(ii) complex in dimethylsulfoxide or methanol towards anions, such as F(-), Cl(-), Br(-), I(-) or OAc(-), where F(-) and OAc(-) show the most colorimetric change, through various spectroscopic techniques. Further insights into this at the molecular level come from the single crystal X-ray structures of both dimethylsulfoxide and methanol solvates which show a solvent effect on their supramolecular network formation. Both chromogenic and fluorogenic sensing of the anions indicate a 2 : 1 receptor-anion formation via anion-π as well as hydrogen bonding interactions.

Evidence for halogen bond covalency in acyclic and interlocked halogen-bonding receptor anion recognition

The synthesis and anion binding properties of novel halogen-bonding (XB) bis-iodotriazole-pyridinium-containing acyclic and [2]catenane anion host systems are described. The XB acyclic receptor displays selectivity for acetate over halides with enhanced anion recognition properties compared to the analogous hydrogen-bonding (HB) acyclic receptor. A reversal in halide selectivity is observed in the XB [2]catenane, in comparison to the acyclic XB receptor, due to the interlocked host's unique three-dimensional binding cavity, and no binding is observed for oxoanions. Notable halide anion association constant values determined for the [2]catenane in competitive organic-aqueous solvent mixtures demonstrate considerable enhancement of anion recognition as compared to the HB catenane analogue. X-ray crystallographic analysis of a series of halide catenane complexes reveal strong XB interactions in the solid state. These interactions were studied using Cl and Br K-edge X-ray Absorption Spectroscopy (XAS) indicating intense pre-edge features characteristic of charge transfer from the halide to its bonding partner (σ(AX←X(-))(*) ← X1s), and providing a direct measure of the degree of covalency in the halogen bond(s). The data reveal that the degree of covalency is similar to that which is observed in transition metal coordinate covalent bonds. These results are supported by DFT results, which correlate well with the experimental data.

Anion sensing by small molecules and molecular ensembles

This Tutorial Review provides a short survey of anion sensing by small molecule anion receptors, molecular ensembles and chemodosimeters.

Detecting biologically relevant phosphates with locked salicylaldehyde probes in water

This communication describes a disassembly based approach for the detection of biologically relevant di- and tri-phosphates in water using locked fluorescent salicylaldehyde probes.

Color-tunable luminescent CdTe quantum dot membranes based on bacterial cellulose (BC) and application in ion detection

Color-tunable luminescent membranes of CdTe QDs on bacterial cellulose (BC) nanofibers were successfully fabricated by in situ synthesis in aqueous solution.

A catalytic chemodosimetric approach for detection of nanomolar cyanide ions in water, blood serum and live cell imaging

The nano-molar detection of cyanide in live cell imaging and blood serum has been achieved through cyanide catalysed fluorescence enhancement with a TON between 70 and 360.