Simple bis-thiocarbono-hydrazones as sensitive, selective, colorimetric, and switch-on fluorescent chemosensors for fluoride anions

Perylenemonoimide-Based Colorimetric Probe with High Contrast for Naked-Eye Detection of Fluoride Ions

Excessive fluoride ions (F^-) in drinking water are harmful to the environment and human health. However, most reported probes of F^- can only detect fluorocarbons rather than aqueous F^-. Herein, a colorimetric and fluorescent probe (PMI-OH) based on perylenemonoimide is designed and synthesized for the detection of aqueous F^-, with high sensitivity, good selectivity, and reversibility. The F^- causes deprotonation of PMI-OH, leading to a significant red shift of 222 nm (from 520 to 742 nm) of the absorption band. Upon the addition of fluorocarbons, the fluorescence intensities of PMI-OH show good linearity against the concentrations of F^-, realizing the quantitative detection of fluorocarbons with a limit of detection as low as 0.495 μM. Finally, PMI-OH is applied to detect F^- in drinking water. The color of PMI-OH solution shows remarkable response from pink to green when the concentrations of F^- exceed the upper limit set by the World Health Organization (WHO), realizing rapid and naked-eye detection of aqueous F^-.

Microwell Fluoride Screen for Chemical, Enzymatic, and Cellular Reactions Reveals Latent Microbial Defluorination Capacity for -CF3 Groups

The capacity to defluorinate polyfluorinated organic compounds is a rare phenotype in microbes but is increasingly considered important for maintaining the environment. New discoveries will be greatly facilitated by the ability to screen many natural and engineered microbes in a combinatorial manner against large numbers of fluorinated compounds simultaneously. Here, we describe a low-volume, high-throughput screening method to determine defluorination capacity of microbes and their enzymes. The method is based on selective binding of fluoride to a lanthanum chelate complex that gives a purple-colored product. It was miniaturized to determine biodefluorination in 96-well microtiter plates by visual inspection or robotic handling and spectrophotometry. Chemicals commonly used in microbiological studies were examined to define usable buffers and reagents. Base-catalyzed, purified enzyme and whole-cell defluorination reactions were demonstrated with fluoroatrazine and showed correspondence between the microtiter assay and a fluoride electrode. For discovering new defluorination reactions and mechanisms, a chemical library of 63 fluorinated compounds was screened in vivo with Pseudomonas putida F1 in microtiter well plates. These data were also calibrated against a fluoride electrode. Our new method revealed 21 new compounds undergoing defluorination. A compound with four fluorine substituents, 4-fluorobenzotrifluoride, was shown to undergo defluorination to the greatest extent. The mechanism of its defluorination was studied to reveal a latent microbial propensity to defluorinate trifluoromethylphenyl groups, a moiety that is commonly incorporated into numerous pharmaceutical and agricultural chemicals. IMPORTANCE Thousands of organofluorine chemicals are known, and a number are considered to be persistent and toxic environmental pollutants. Environmental bioremediation methods are avidly being sought, but few bacteria biodegrade fluorinated chemicals. To find new organofluoride biodegradation, a rapid screening method was developed. The method is versatile, monitoring chemical, enzymatic, and whole-cell biodegradation. Biodegradation of organofluorine compounds invariably releases fluoride anions, which was sensitively detected. Our method uncovered 21 new microbial defluorination reactions. A general mechanism was delineated for the biodegradation of trifluoromethylphenyl groups that are increasingly being used in drugs and pesticides.

The sensing mechanism of a flavone-based ESIPT fluorescent chemodosimeter for selective recognition towards fluoride: a theoretical

The sensing mechanism of 3-hydroxyflavone-based (3-HF) fluorescent chemodosimeter 3-triisopropylsilylflavone (3-TPSF) for detecting fluoride (F-) has been theoretically investigated. The calculated Laplacian bond order confirms that the Si-O bond of 3-TPSF is the reaction site of F-. The free energy barrier of 18.33 kcal mol-1 indicates that F-triggered desilylation reaction can occur and then form the anionic state of 3-HF (3-HF-) with a fluorescence peak at 545 nm. 3-HF- captures H+ of the mixed aqueous medium to be transformed into 3-HF with an intramolecular hydrogen bond (O1-H⋯O2). The energy barrier of 1.86 kcal mol-1 in the S1 state obtained from the constructed potential energy curves confirms that the excited state intramolecular proton transfer (ESIPT) in 3-HF occurs to form a tautomer structure, which produces a long-wavelength emission of 549 nm. The fluorescence emitted from both 3-HF- and 3-HF agrees with the experimental value of 530 nm appearing after adding F-. Charge transfer analyses indicate that the extent of intramolecular charge transfer in 3-HF- is more intense than that of 3-TPSF, which induces a large Stokes shift of 180 nm. Therefore, the sensing mechanism is attributed to the combination of a large charge transfer feature and ESIPT that are caused by desilylation reaction. The significant fluorescence change makes 3-TPSF a chemodosimeter for detecting F-.

Colorimetric and fluorimetric detection of fluoride ion using thiazole derived receptor

Thiazole based receptor 3, was designed and synthesized by condensation reactionof5-chlorosalicylaldehyde with 4-(4-phenylthiazol-2-yl)semicarbazide for colorimetric and fluorimetric detection of fluoride ion. Receptor 3 was characterized by ¹H NMR, ¹³C NMR, and HRMS, and shows absorption in 280-400 nm region with emission at 442 nm in tetrahydrofuran (THF). Addition of fluoride ion to the THF solution of receptor 3 results in color change from colorless to yellow with significant change in UV-Visible absorption. The receptor-anion interaction occurs via hydrogen bonding followed by deprotonation which results in large bathochromic shift in absorption spectra and naked-eye color change. The colorimetric changes show selective response for fluoride ions over other anions. Fluorescence studies exhibit remarkable enhancement in emission intensity upon addition of fluoride ion with a limit of detection (LOD) of 8.6 nM. The ¹H NMR titration studies exhibit deprotonation of the -OH proton of the salicylaldimine moiety resulting significant colorimetric and fluorimetric changes.

Synthesis and Characterization of a Mg2+-Selective Probe Based on Benzoyl Hydrazine Derivative and Its Application in Cell Imaging

A simple benzoyl hydrazine derivative P was successfully synthesized and characterized as Mg2+-selective fluorescent probe. The binding of P with Mg2+ caused an obvious fluorescence enhancement at 482 nm. The fluorescent, UV-vis spectra, 1H-NMR, and IR spectra confirmed the formation of P-Mg2+ complex, and the formation of a 1:1 stoichiometry complex was proved by Job's plot and mass spectrometry. The recognition mechanism of P to Mg2+ was owing to the photoinduced electron transfer effect (PET). The fluorescent response was linear in the range of 0.9-4.0 µM with the detection limit of 0.3 µM Mg2+ in water-ethanol solution (1:9, v:v, pH10.0, 20 mM HEPES). In addition, the results of cell imaging of Mg2+ in Hl-7701 cells was satisfying.

Sensing mechanism of fluorogenic urea with fluoride in solvent media: A new fluorescence quenching mechanism

The interaction of 1-Phenyl-3-(pyren-1-yl) urea (LH) and fluoride anion (F^-) with a unique ON¹-OFF-ON² fluorescent response has been investigated by the density functional theory (DFT) and time-dependent density functional theory (TDDFT) calculations. The hydrogen-bonding dynamics and photophysical properties of the complex LH-F, as well as its isolated receptor LH and anion form L-H₁, have been studied in detail. We demonstrate that the intermolecular hydrogen bond (N-H…F) of the complex LH-F is greatly enhanced in the electronically excited state. The nonradiative deactivation via electron transfer and internal conversion rather than excited-state intramolecular proton transfer (ESIPT) can be facilitated by the excited state hydrogen bond strengthening. The results have been cross-validated by molecular structure, electronic spectra, frontier molecular orbitals, and infrared spectra as well as hydrogen bond binding energy. These results indicate that the current calculations completely reproduce the experimental results and provide compelling evidence for the sensing mechanism of LH for F^-.

Hydrazone-Based Small-Molecule Chemosensors

The hydrazone functional group is widely applied in several fields. The versatility and large use of this chemotype are attributed to its easy and straightforward synthesis and unique structural characteristics which is useful for different chemical and biological purposes. Recently hydrazone scaffold has been widely adopted in the design of small-molecule fluorescent and colorimetric chemosensors for detecting metals and anions because of its corresponding non-covalent interactions. This chapter provides an overview of hydrazone-based fluorescent and colorimetric chemosensors for anions and metals of biological interest, with their representative rational designs in the last 15 years. We hope this chapter inspires the development of novel and powerful fluorescent and colorimetric chemosensors for a broad range of applications.

Theoretical study on the sensing mechanism of an ON1-OFF-ON2 type fluoride fluorescent chemosensor

A density functional theory (DFT) and time-dependent density functional theory (TDDFT) calculations have been used to study the sensing mechanism of an ON¹-OFF-ON² type fluoride anion fluorescent chemosensor (Bis[[7-(diethylamino)-2-oxo-2H-chromene]methyl-ene]‑carbonothioic dihydrazide (CTC). The current theoretical calculation presents a different sensing mechanism from the experimentally proposed one (Sensor and Actuators B 2016, 222, 823-828). Instead of the combination of CTC deprotonation and poorly emissive excited state tautomer or ICT mechanism, the theoretical results predict the sensing mechanism based on dissociation reaction and excited-state proton transfer (ESPT). The calculated vertical excitation energies both in the ground states and first excited states of different forms of CTC, as well as the potential-energy curves, have completely reproduced the experimental results, providing powerful evidence for our proposed CTC sensing mechanism for fluoride anion.

Efficient Colorimetric Fluoride Anion Chemosensors With Varied Colors Based on Simple Aminobenzodifuranone Organic Π-Conjugated Dyes

High selectivity and sensitivity detection of fluoride anions (F⁻) in an organic solution by the naked eye has always been a challenge. In this investigation, a simple compound based on aminobenzodifuranone (ABDF) was designed and synthesized. Deprotonation of the amino moiety caused by F⁻ is responsible for a color change from dark blue to various colors (colorless, yellow, orange, and red) in different common organic solvents due to a blue shift over 200 nm in the UV/Vis spectrum. The color change is quite visible to the naked eye under ambient light. The detection limit for F⁻ can reach a concentration of as low as 5.0 × 10⁻⁷ M with high selectivity, even in a solution containing multiple anions.

Design and synthesis of malonohydrazide based colorimetric receptors for discrimination of maleate over fumarate and detection of F-, AcO- and AsO2- ions

In this study, we have designed and synthesized two new organic receptors R1 and R2 based on malonohydrazide for the recognition of biologically important anions. The receptor R1 capable of colorimetric discrimination of maleate over fumarate ion, exhibit significant color change from pale yellow to wine red due to intermolecular hydrogen bond between the R1 and maleate ion, supported by ¹HNMR titration, where the peak at δ12.0 ppm attributed to the NH proton experiences a downfield shift upon binding with maleate ion. Receptor R1, equipped with two electron-withdrawing NO₂ moieties as the chromogenic signaling unit enhance the hydrogen bonding tendency and acidity, and thus when comparing with receptor R2, R1 displayed substantial higher redshift (∆λ_max) of 148 nm, 143 nm, and 140 nm towards F^-, AcO^-, and maleate anion in the DMSO. In addition, the synthesized receptors R1 and R2 are able to detect F^-, AcO^-, and AsO₂^- ions as their sodium salts in an aqueous solution with visual color change. Receptor R1 exhibit electrochemical response towards F^- and AcO^- ions. The receptors R1 and R2 are successfully applied for quantitative detection of F^- ion in the toothpaste solution in an aqueous medium. Additionally, R1 and R2 exhibit fluorescence enhancement towards F^- and AcO^- ions in the DMSO. As well, R1 and R2 demonstrate to be potentially useful colorimetric chemosensor for sensing maleate ion using the test strip. The theoretical calculation based on TD-DFT corroborates well with the experimental results of the receptors R1 and R2 with fluoride, acetate and maleate.

N-(Cyano(naphthalen-1-yl)methyl)benzamides: synthesis, crystal structures, and colorimetric sensing of fluoride anions

An N-(cyano(naphthalen-1-yl)methyl)benzamide derivative was developed as a colorimetric sensor that shows a dramatic colorless-to-black response to fluoride anions.

"Turn-on" Pb2+ sensing and rapid detection of biothiols in aqueous medium and real samples

Detection of lead has continued to be of immense interest in the present industrial as well as environmental diaspora. To this end, we report a prudent Schiff base which enables the sensitive detection of Pb2+ ions in mixed aqueous medium. The probe is afforded by simple synthetic and purification processes. Further, the probe employs simple mechanistic detection of Pb2+ and also successively detects a host of biothiols. The sensor is also used to detect Pb2+ ions in real water samples and consecutive detection of a variety of biothiols, including functionalized thiouracils, in onion and garlic extract. The fact that the Pb2+-L ensemble is 'non-selective' towards any particular thiol substituted analyte in real samples could as well prove to be an interesting contribution for chemical and biological detoxification processes.

A targetable fluorescent probe for real-time monitoring of fluoride ions in mitochondria

Fluorion are pivotal anions in biology because they play an important role in dental care, treating osteoporosis, preventing tooth decay and promoting the healthy growth of bone. Studies have shown that high levels of fluoride will lead to the inactivation of the mitochondria. Therefore, it is urgent to develop a method to detect the fluoride anions in the mitochondria. Herein, we have developed a novel mitochondrial-target fluorescent probe for detecting F^- in living cells. The probe exhibited excellent sensitivity and high selectivity for F^- over the other relative species. With changing fluoride ions, the fluorescence spectrum of the probe changed significantly with a large turn-on fluorescence signal. Cell imaging indicated that the probe can penetrate viable cell membranes and rapidly detects and images fluorion over other anions in the mitochondria.

Al(iii)-responsive "off-on" chemosensor based on rhodamine derivative and its application in cell imaging

In this work, a new rhodamine chemosensor (P) with excellent photochromic properties upon vis irradiation was designed and synthesized. The fabricated chemosensor P could detect Al3+ via the opening of the spirolactam ring of the rhodamine unit with high selectivity and sensitivity. The spirolactam ring opening was confirmed by NMR and infrared spectroscopy. Upon binding with Al3+, the generated 1 : 1 P-Al3+ complex, confirmed by Job's plot titrations and mass spectrometry analysis, could exhibit a remarkable fluorescence enhancement with a limit of detection (LOD) of 0.16 μM. Furthermore, the sensing of P to Al3+ in vivo was also studied quantitatively and qualitatively in detail, and the results showed that the coordination between P with Al3+ was reversible in living cells.

Calix[5]phyrin for Fluoride Ion Sensing with Visible and Near Infrared Optical Responses

Fluoride (F- ) ion sensing is an important topic due to its roles in health, medical, and environmental sciences. In this regard, colorimetric sensors with a near infrared (NIR) optical response are useful in biological systems because they can avoid interference from endogenous chromophores. Although calix[n]phyrins are highly attractive as sensors with the NIR optical response, studies on calix[n]phyrins are still limited owing to their intrinsic instability against ambient light and air. In this study, we report the synthesis and characterization of a new calix[5]phyrin bearing one sp3 -hybridized carbon atom as a π-expanded calix[n]phyrin. Upon addition of tetrabutylammonium fluoride, the calix[5]phyrin exhibited distinct NIR absorptions at 908 and 1064 nm as well as a visible color change. Importantly, it revealed an excellent selectivity for F- ion. These results demonstrate that calix[5]phyrins are promising colorimetric and NIR sensors of F- ion.

Simple Bisthiocarbonohydrazone as a Sensitive, Selective, Colorimetric, and Ratiometric Fluorescent Chemosensor for Picric Acids

A bisthiocarbonohydrazone-based chemosensor molecule (R1) containing a tetrahydro-8-hydroxyquinolizine-9-carboxaldehyde moiety has been synthesized and characterized as a new ratiometric fluorescent probe for picric acid (PA). The ratiometric probe R1 is a highly selective and sensitive colorimetric chemosensor for PA. The association between the chemosensor and PA and the ratiometric performance enabled by the key role of excited state intramolecular proton transfer in the detection process are demonstrated. Selectivity experiments proved that R1 has excellent selectivity to PA over other nitroaromatic chemicals. Importantly, the ratiometric probe exhibited a noteworthy change in both colorimetric and emission color, and this key feature enables R1 to be employed for detection of PA by simple visual inspection in silica-gel-coated thin-layer chromatography plates. Probe R1 has been shown to detect PA up to 3.2 nM at pH 7.4. Microstructural features of R1 and its PA complex have been measured by a field emission scanning electron microscope, and it clearly proves that their morphological features differ dramatically both in shape and size. Density function theory and time-dependent density function theory calculations were performed to establish the sensing mechanism and the electronic properties of probe R1. Furthermore, we have demonstrated the utility of probe R1 for the detection of PA in live Vero cells for ratiometric fluorescence imaging.

Quantitative determination of fluoride in pure water using luminescent europium complexes

Two luminescent probes [Eu.L¹⁻²]⁺ are reported for the rapid detection of fluoride in water. Probes [Eu.L¹⁻²]⁺ exhibit exceptional enhancements in Eu emission in the presence of fluoride, permitting its selective determination within the environmentally relevant concentration range (20-210 μM).

Electrospun Nanofibers from a Tricyanofuran-Based Molecular Switch for Colorimetric Recognition of Ammonia Gas

A chromophore based on tricyanofuran (TCF) with a hydrazone (H) recognition moiety was developed. Its molecular-switching performance is reversible and has differential sensitivity towards aqueous ammonia at comparable concentrations. Nanofibers were fabricated from the TCF-H chromophore by electrospinning. The film fabricated from these nanofibers functions as a solid-state optical chemosensor for probing ammonia vapor. Recognition of ammonia vapor occurs by proton transfer from the hydrazone fragment of the chromophore to the ammonia nitrogen atom and is facilitated by the strongly electron withdrawing TCF fragment. The TCF-H chromophore was added to a solution of poly(acrylic acid), which was electrospun to obtain a nanofibrous sensor device. The morphology of the nanofibrous sensor was determined by SEM, which showed that nanofibers with a diameter range of 200-450 nm formed a nonwoven mat. The resultant nanofibrous sensor showed very good sensitivity in ammonia-vapor detection. Furthermore, very good reversibility and short response time were also observed.

Benzothiazole based multi-analyte sensor for selective sensing of Zn2+and Cd2+and subsequent sensing of inorganic phosphates (Pi) in mixed aqueous medium

A multi-analyte sensor selectively senses Zn²⁺and Cd²⁺ions and subsequently responds to phosphates in mixed aqueous medium.

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.

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.

Coumarin functionalized thiocarbonohydrazones as a new class of chromofluorescent receptors for selective detection of fluoride ion

Thiocarbonohydrazone receptors selectively recognize fluoride ionsviaH-bond interactions and subsequent deprotonation to elicit a distinct visual and fluorescence colour change.

A cyanide-selective colorimetric “naked-eye” and fluorescent chemosensor based on a diketopyrrolopyrrole–hydrazone conjugate and its use for the design of a molecular-scale logic device

A novel diketopyrrolopyrrole (DPP)–hydrazone based receptor was designed and synthesized as a selective fluorescent and colorimetric chemosensor for cyanide in aqueous media via deprotonation between the hydrazide moiety of the probe and cyanide.

Lighting up fluoride ions in cellular mitochondria using a highly selective and sensitive fluorescent probe

We report a highly selective and sensitive fluorescent probe () for detecting fluoride ions, for the first time, lighting up the fluoride ions in mitochondria with a strong green fluorescence. could be easily prepared as fluoride paper test strips to detect fluoride ions in aqueous solutions with a detection limit as low as 19 ppb.

Nanomolar Zn(ii) sensing and subsequent PPi detection in physiological medium and live cells with a benzothiazole functionalized chemosensor

Nanomolar zinc detection and subsequent pyrophosphate sensing in physiological media using a benzothiazole modified conjugated ligand and their application in paper strip and live cell imaging is demonstrated.

Fluorescent sensing of fluoride in cellular system

Fluoride ions have the important roles in a lot of physiological activities related with biological and medical system, such as water fluoridation, caries treatment, and bone disease treatment. Great efforts have been made to develop new methods and strategies for F(-) detection in the past decades. Traditional methods for the detection of F(-) including ion chromatography, ion-selective electrodes, and spectroscopic techniques have the limitations in the biomedicine research. The fluorescent probes for F(-) are very promising that overcome some drawbacks of traditional fluoride detection methods. These probes exhibit high selectivity, high sensitivity as well as quick response to the detection of fluoride anions. The review commences with a brief description of photophysical mechanisms for fluorescent probes for fluoride, including photo induced electron transfer (PET), intramolecular charge transfer (ICT), fluorescence resonance energy transfer (FRET), and excited-state intramolecular proton transfer (ESIPT). Followed by a discussion about common dyes for fluorescent fluoride probes, such as anthracene, naphalimide, pyrene, BODIPY, fluorescein, rhodamine, resorufin, coumarin, cyanine, and near-infrared (NIR) dyes. We divide the fluorescent probes for fluoride in cellular application systems into nine groups, for example, type of hydrogen bonds, type of cleavage of Si-O bonds, type of Si-O bond cleavage and cylization reactions, etc. We also review the recent reported carriers in the delivery of fluorescent fluoride probes. Seventy-four typical fluorescent fluoride probes are listed and compared in detail, including quantum yield, reaction medium, excitation and emission wavelengths, linear detection range, selectivity for F(-), mechanism, and analytical applications. Finally, we discuss the future challenges of the application of fluorescent fluoride probes in cellular system and in vivo. We wish that more and more excellent fluorescent fluoride probes will be developed and applied in the biomedicine field in the future.

Anion complexation with cyanobenzoyl substituted first and second generation tripodal amide receptors: crystal structure and solution studies

Solid and solution state anion binding via a side cleft and pseudocapsular fashion by two cyanophenyl substituted first (L1) and second (L2) generation tripodal amides has been demonstrated along with a selective anion induced conformational change of L2 from open C_2v to folded C_3v symmetry.

Colorimetric and ratiometric fluorescent chemosensor for fluoride ions based on phenanthroimidazole (PI): spectroscopic, NMR and density functional studies

Phenanthro-imidazole conjugate of biscarbanohyrazone, probe PI was designed, synthesized and characterized for selective detection of fluoride ion.

Highly selective colorimetric/fluorometric dual-channel fluoride ion probe, and its capability of differentiating cancer cells

A dual-channel naphthalimide-based chemosensor for rapid and sensitive detection of fluoride ion has been developed. Upon addition of F(-), it undergoes deprotonation reaction through H-bonding interactions, and its maximum absorption wavelength is red-shifted for 214 nm to the far-red region, together with drastically quenched fluorescence. In addition, it shows high selectivity toward F(-) anion, thus could be used for practical applications to detecting F(-) in both solution and solid state. Furthermore, the fluorescence of NIM could be enhanced in protein-containing acidic environments, hence NIM could act as lysosome marker to differentiate cancer cells from normal ones in cell imaging.

Efficient synthesis of 1,5-disubstituted carbohydrazones using K₂CO₃ as a carbonyl donor

A novel reaction that generates 1,5-disubstituted carbohydrazones via the carbonylation of tosylhydrazones has been developed. For the first time, the inexpensive, readily available, environmentally friendly, and nongaseous potassium carbonate is used as the carbonyl donor for the transformation. The reaction system exhibited tolerance with various functional groups and affords the desired products in good to excellent yields. This reaction is expected to be a powerful tool for the synthesis of carbohydrazone compounds.

Dipicrylamine as a colorimetric sensor for anions: experimental and computational study

Dipicrylamine exhibited colorimetric sensing of F⁻, OAc⁻ and H₂PO₄⁻, detectable by bared-eye, out of a large number of anions. Interestingly, F⁻ binds with one of the phenyl carbon of dipicrylamine.