Phenolate-thiazole based reversible "turn-on" chemosensor for the selective detection of carbonate anion: X-ray crystallography, DFT/TDFT, and cell study

A new phenolate-thiazole derivative (L) has been synthesized and structurally characterized.The chemo-sensing activity of L is detected by the naked eye for the aqueous carbonate anion in the pH range of 4 to 8. The selective 'turn-on' fluorescence occurs through the formation of a stable intermediate L∙CO32-(1) following the PET mechanism. The limit of detection (LOD) is found 0.18 µM based on the absorbance-based assay.The quinonoid form of bromophenol unit binds strongly with CO32- through thiazole nitrogen and hydrazinic nitrogen. Further, the selective holding of CO32- anion over other planar tetranuclear anions (e.g., SO32-, NO3-) happens with several intra and intermolecular hydrogen bonds as envisaged by the DFT/TDFT study. The formation mechanism of L∙CO32- is proposed based on experimental and theoretical studies. The biological experiments (MTT and cell imaging)reveal the non-cytotoxicity nature of L and the biocompatible uptake of L mostly in the cytoplasm at physiological pH.

Selective turn-on fluorescence sensing of Fe2+ in real water samples by chalcones

The design of fluorescence sensor for selective detection of Fe²⁺ is very important as it is part of different biochemical redox system related to a number of diseases. In many occasion sensors are unable to distinguish Fe²⁺ from Fe³⁺ ions. In the present work, we report simple chalcone type sensors for sensing Fe²⁺ ions in semi aqueous system. The receptors R1 and R2 have showed excellent sensing properties at pH 7 in CH₃OH-H₂O (1:1, v/v) solvent system. The fluorescence emission intensity of the complexes between hosts and Fe²⁺ is least affected by the other competitive metal ions leading to the formation of very tight host-guest complex. The LOD for the R1 and R2 for Fe²⁺ are 1.91 μM and 3.54 μM respectively, which is quite low in compared to the many other reported sensors. The practical applicability of these sensors is determined by the detection of Fe²⁺ in real water samples. So chalcones would be cost effective PET inhibited fluorescence sensor for Fe²⁺.

The detection of selectivity and sensitivity towards TNP by a new Zn(II)-coordination polymer as luminescent sensor in aqueous solution

Nitroaromatic compounds (NACs) can lead to various environmental pollution healh problems. In order to effectively recognize and sense NACs, a novel coordination polymers (CPs) with fluorescent characteristic [Zn₃(btc)₂(tpt)(H₂O)₂]·4H₂O (1) (tpt = tris(4-pyridyl)triazine, H₃btc = 1,3,5-benzenetricarboxylic acid) has been triumphantly prepared as an fluorescence probe by solvothermal method. 1 possesses remarkable PH stability ranging from 2.0 to 12.0 and is also stable in different pure organic solvents. It should be noted that 1 manifests a fluorescence quenching response against the detection of selectivity and sensitivity towards 2,4,6-trinitrophenol (TNP) in aqueous solution. It also makes analysis on the limit of detection towards TNP, which is as low as 0.94 µM compared with most reported CPs sensors for TNP. Therefore, 1 can become a satisfactory sensor for TNP detection with remarkable selectivity, strong anti-interference and favorable recyclability. In addition, the quenching mechanisms were also discussed. It was supposed that the mechanisms of photoinduced electron transfer (PET) as well as resonance energy transfer (RET) might be the main influencing factors.

Fluorescein Based Three-channel Probe for the Selective and Sensitive Detection of CO32- Ions in an Aqueous Environment and Real Water Samples

We have constructed a novel fluorescein-based fluorescent chemosensor, FL-In, functionalised with an indole moiety and capable of sensing by both the optical "turn-on" and electrochemical detection of carbonate ions (CO₃^2-) in aqueous media. The probe exhibits excellent selectivity and a low detection limit (0.27 µM) regarding carbonate ions by a possible coordination and hydrolysis reaction mechanism. The developed probe successfully detected CO₃^2- ions in different samples of water. Also, in a simple filter paper experiment, we documented its ability to allow the monitoring of CO₃^2- with the naked eye.

Selective, pH sensitive, "turn on" fluorescence sensing of carbonate ions by a benzimidazole

Anions play crucial roles in the sustenance of life on earth in many ways. Selective detection of specific anions is important in developing new diagnostic tools and therapeutics. A pH-sensitive & selective benzimidazole-based fluorescent sensor has been developed for rapid detection of carbonate ions which can detect carbonate ions in low nanomolar concentrations. NMR based experiments indicate direct interaction of benzimidazole imino protons with the carbonate ions leading to 1:1 ligand carbonate ion complexation events. This is one of the first reports of benzimidazole sensing carbonate ions with high selectivity which may have implications in disease prevention and toxicity assessment.

Fabrication and sensing properties of phenolphthalein based colorimetric and turn-on fluorogenic probe for CO32- detection and its living-cell imaging application

Herein, an easy assembled colorimetric and ''turn-on'' fluorescent sensor (probe P4SC) based on phenolphthalein was developed for carbonate ion (CO₃^2-) sensing in a mixture of EtOH/H₂O (v/v, 80/20, pH = 7, Britton-Robinson buffer) media. The probe P4SC demonstrated high sensitive and selective monitoring toward CO₃^2- over other competitive anions. Interaction of CO₃^2- with the probe P4SC resulted in a significant increment in emission intensity at λ_em = 498 nm (λ_ex = 384 nm) due to the strategy of blocking the photo induced electron transfer (PET) mechanism. ¹H NMR titration and Job's methods, as well as the theoretical study were carried out to support the probable stoichiometry of the reaction (1:2) between P4SC and CO₃^2-. The binding constant of the probe P4SC with CO₃^2- was calculated as 2.56 × 10¹⁰ M^-2. The probe P4SC providing rapid response time (~0.5 min) with a satisfactorily low detection limit (14.7 nM) may be useful as a valuable realistic sensor. The imaging studies on the liver cancer cells (HepG2) shows the great potential of the probe P4SC for the sensation of intracellular CO₃^2- anions. Furthermore, the satisfactory recovery and RSD values obtained for water application confirming that the probe P4SC could be applied to sensing of CO₃^2- ion.

A novel voltammetric method for the sensitive and selective determination of carbonate or bicarbonate ions by an azomethine-H probe

Our study involved a simple, sensitive voltammetric method of determining either carbonate or bicarbonate ions independently with azomethine-H and a disposable pencil graphite electrode. The reduction of azomethine-H-carbonate complexes at approximately -930 mV formed in acetic acid-acetate buffer solution (pH: 4.25) was evaluated as a response. Among the results, the limits of detection and analytical ranges for carbonate ions were 3.7 μg L^-1 and 9.9-700.0 μg L^-1 and for bicarbonate ions were 9.0 μg L^-1 and 35.0-700.0 μg L^-1, and the relative standard deviations for carbonate and bicarbonate ions ranged from 1.33% and 6.93% at different concentrations. After the proposed method was applied to water, sparkling water, seawater and baking powder samples, the results were statistically evaluated and compared with those obtained from the potentiometric auto-titration system. Last, the complex stoichiometry of both carbonate and bicarbonate ions was comprehensively investigated with fluorescence and ¹H-NMR spectroscopy.

Lansoprazole-Based Colorimetric Chemosensor for Efficient Binding and Sensing of Carbonate Ion: Spectroscopy and DFT Studies

The new benzimidazole based receptor Lansoprazole has been used to detect carbonate anion by naked-eye and Uv-Vis spectroscopy. This receptor revealed visual changes withCO 3 2 - anion in ethanol. No detectable color changes were observed upon the addition of any other tested anions. The lansoprazole chemosensor selectively recognizesCO 3 2 - ion over the other interference anions in the ethanol, followed by deprotonation and reflected 1:1 complex formation between the receptor and the carbonate ion. Lansoprazole exhibits splendid selectivity toward carbonate ion via a visible color change from colorless to yellow with a detection limit of 57 μM. The binding mode ofCO 3 2 - to receptor L is supported by Density Functional Theory calculation. Moreover, this receptor shows a practical visible colorimetric test strip for the detection of carbonate ions. The transition states calculation demonstrates the occurrence of reaction from L to L-CO 3 2 - after overcoming an energy barrier of 10.1 kcal/mol, and there is considerable interaction energy between L andCO 3 2 - (94.9 kJ/mol), both of which confirmed that receptor L has high sensitivity and selectivity to the carbonate ion. The theoretical studies were performed to acquire an electronic description of the complexation mechanism byCO 3 2 - as well as to study bonding and structure in the complex. The optimized structures and binding mechanisms were supported with a high correlation and agreement by spectroscopy and DFT calculations.

A dual emission metal-organic framework for rapid ratiometric fluorescence detection of CO3 2- in seawater

A dual emission metal-organic framework (IRMOF-10-Eu) was prepared and used as a ratiometric fluorescent sensor for CO₃ ^2- detection. IRMOF-10-Eu had good stability and excellent luminescence in aqueous solution. IRMOF-10-Eu showed dual fluorescence emission from the ligand and Eu³⁺ with single excitation. Upon treatment with CO₃ ^2-, the fluorescence ratio (I ₆₂₄/I ₃₅₈) of the probe displayed significant change. The relative fluorescence intensity ratio (I ₆₂₄/I ₃₅₈) and CO₃ ^2- concentration had a linear relationship in 50-300 μM range with a low detection limit of 9.58 μM. And the luminescence probe of CO₃ ^2- showed a fast detection time. The possible mechanism was investigated. CO₃ ^2- changed the structure of IRMOF-10-Eu and interrupted the energy transfer process. Thus, the fluorescence emission intensity of the ligand was increased and Eu³⁺ was decreased with the addition of CO₃ ^2-. IRMOF-10-Eu was used to detect CO₃ ^2- in seawater, which showed good prospect in practical application. Subsequently, a highly selective and sensitive probe, IRMOF-10-Eu, may pave an efficient way for CO₃ ^2- detection in seawater.

Cellulose-based fluorescent sensor for visual and versatile detection of amines and anions

It is practical and challenging to construct ultrasensitive and multi-responsive sensors for visual and real-time monitoring of the environment. Herein, a cellulose-based multi-responsive fluorescent sensor (Phen-MDI-CA) is fabricated, and realizes a visual and ultrasensitive detection of not only various amines but also three anions based on the change of the fluorescence and/or visible colors. Once exposure to various amines in both the solution and vapor state, the Phen-MDI-CA solution and test paper exhibit different fluorescence colors, which can be used to distinguish triethylamine, ethylenediamine, methylamine, aniline, hydrazine and pyrrolidine from other amines. Moreover, via combining the Phen-MDI-CA with the Phen-MDI-CA/malachite green ratiometric system, phosphate (PO₄^3-), carbonate (CO₃^2-) and borate (B₄O₇^2-) can be visually and accurately recognized depending on the change of the visible and fluorescence colors. In fluorescent mode, the LOD for B₄O₇^2-, PO₄^3- and CO₃^2- ions is as low as 0.18 nmol, 0.69 nmol and 0.86 nmol, respectively. Significantly, the Phen-MDI-CA can readily make a qualitative and quantitative detection of B₄O₇^2-, PO₄^3- and CO₃^2- anions in the mixture of anions. The state-of-the-art responsive behavior of Phen-MDI-CA originates from the amplification effect of cellulose polymer chain and the differentiated interactions between the sensor and analytes.

An unprecedented oxidised julolidine-BODIPY conjugate and its application in real-time ratiometric fluorescence sensing of sulfite

Reaction of a julolidine-based BODIPY compound with silver(i) ions in the presence of white light produced the oxidised julolidine version (OXJUL) containing a quaternary nitrogen. The oxidation of one ring at the julolidine site is highly unusual and there is no other reported literature example. The fluorescence maximum of OXJUL is altered from 648 nm to 608 nm by the addition of an aqueous solution of Na2SO3 over several minutes. In the presence of a large excess of sulfite a further slower reaction is observed which further shifts the emission maximum to 544 nm. The alterations form the basis of a real-time ratiometric sensor for sulfite and its detection in a white wine.

Sequential Fluorescence Recognition of Molybdenum(VI), Arsenite, and Phosphate Ions in a Ratiometric Manner: A Facile Approach for Discrimination of AsO2 - and H2PO4. ACS OMEGA 2019;4:10877-10890. [PMID: 31460185 PMCID: PMC6648501 DOI: 10.1021/acsomega.9b00377]

An amide-based smart probe (L) is explored for nanomolar detection of Mo(VI) ion in a ratiometric manner, involving hydrogen-bond-assisted chelation-enhanced fluorescence process through inhibition of photoinduced electron transfer process. The recognition of Mo(VI) is associated with a 17-fold fluorescence enhancement and confirmed by single-crystal X-ray diffraction of the resulting Mo(VI) complex (M1). Further, M1 selectively recognizes arsenite through green emission of their adduct (C1) with an 81-fold fluorescence enhancement. Interestingly, dihydrogen phosphate causes dissociation of C1 back to free L having weak fluorescence. The methods are fast, highly selective, and allow their bare eye visualization at physiological pH. All of the interactions have been substantiated by time-dependent density functional theory calculations to rationalize their spectroscopic properties. The corresponding lowest detection limits are 1.5 × 10-8 M for Mo(VI), 1.2 × 10-10 M for AsO2 -, and 3.2 × 10-6 M for H2PO4 -, whereas the respective association constants are 4.21 × 105 M-1 for Mo(VI), 6.49 × 104 M-1 for AsO2 -, and 2.11 × 105 M-1 for H2PO4 -. The L is useful for efficient enrichment of Mo(VI) from aqueous solution, while M1 efficiently removes AsO2 - from environmental samples by solid-phase extraction.

Tuning the recognition properties of urea based receptor towards cyanide in aqueous medium: Effect of fluorine substitution on strength and selectivity of the anion receptor

In this report, we have successfully tuned the selectivity and sensitivity of an anion receptor L¹ by substituting electron withdrawing natured fluorine atoms directly on to the rim of the phenyl ring. Despite the fact that, we have two electron withdrawing natured nitro substituents on the other side of receptor L¹; two fluorine substitutions made dramatic change in the sensing ability as well as the selectivity of the receptor L¹ towards anions. The acetonitrile solution contains L¹ with tetrabutyl ammonium salts of fluoride, cyanide, acetate and dihydrogen phosphate results sudden color changes from yellow to brown; almost negligible spectral/color change for azide and bifluoride, where as there is no color change observed with any other anionic guests with L¹. Solution state binding studies of L¹ are carried out by UV-Vis spectrometry titration in 100% acetonitrile and it is found to be the receptor L¹ selectively binds cyanide, phosphate and fluoride stronger than acetate; it is also found that receptor binds fluoride 100 times stronger than that of the receptor L and L¹ has almost similar efficiency in binding towards acetate ion (AcO^-). The strength of the receptor L¹ towards fluoride, cyanide, acetate and dihydrogen phosphate bindings are found to be in the order of 1.271 × 10⁵ M^-1 > 1.245 × 10⁵ M^-1 > 1.368 × 10³ M^-1, 1.23 × 10³ M^-1 respectively. When we used aqueous environment (10% of water in acetonitrile) as testing solvent system, the receptor L¹ selectively sense cyanide ion. Over all, strength of the receptor is increased towards anions with an increasing the number of fluorine atom onto the receptors. Here in we have also prepared a reference compound L² in which the receptor molecule is substituted with only one fluoride atom. The acetonitrile solution of reference receptor L² with help of naked-eye colorimetric experiment and spectrometric ammonium salts of fluoride, cyanide, acetate and bifluoride results sudden color changes from faint-yellow to brown in color. Unlike receptor L¹, receptor L² does not recognize H₂PO₄^-, but instead of H₂PO₄^-, it recognizes bifluoride as evidenced from UV-Vis spectroscopic and naked-eye colorimetric studies.

Simple and highly electron deficient Schiff-base host for anions: First turn-on colorimetric bifluoride sensor

Here in, we have designed, synthesized and isolated sensor L, as a turn-on colorimetric chemo sensor for bifluoride ion. The acetonitrile solution contains L with tetrabutyl ammonium salts of bifluoride, cyanide and fluoride results sudden color changes from yellow to dark brown where as there is no color change observed with any other anionic guests with L. Solution state binding studies of L are carried out by UV-Vis spectrometry titration and the strengths of the chemosensor L towards bifluoride, cyanide and fluoride bindings are found to be 2.67 × 10⁵ M^-1, 4.78 × 10⁵ M^-1_, 4.45 × 10⁵ M^-1 respectively. The strength and sensitivity of the absorbance based assay with L for bifluoride ion, are found to be 2.67 × 10⁵ M^-1 and 0.7 μM respectively, which is the best (highest binding constant and lowest LOD) ever reported in the literature. In order to use this sensor in practical application, we also prepared a cassette which is fabricated with sensor L and we succeeded to sense bifluoride ion.

A water-stable terbium-MOF sensor for the selective, sensitive, and recyclable detection of Al3+ and CO32− ions

A layered Tb-MOF structure exhibits high sensitivity, selectivity, and concurrently low limits of detection in relation to Al³⁺ and CO₃²⁻ ions.

Selective and sensitive fluorescent and colorimetric chemosensor for detection of CO32- anions in aqueous solution and living cells

A new colorimetric and fluorescent chemosensor for visual determination of carbonate ions was developed by the microwave assisted solvent free synthesis of 7,8-dihydroxy-3-(4-methylphenyl) coumarin (DHMC). The structural characterization of DHMC was confirmed by microanalysis and spectroscopy methods (MALDI-TOF, FT-IR, ¹H NMR, ¹³C NMR, and 2D HETCOR). The binding behaviors of DHMC were investigated towards various anions by UV-vis and fluorescence spectroscopy. DHMC showed a selective and sensitive fluorometric and colorimetric responses towards carbonate ion over other anions. The detection limit of CO₃^2- was found to be 1.03 µM. Moreover, the fluorescence imaging in living cells suggests that DHMC has a great potential in the biological imaging application. It has been demonstrated that DHMC can be used as a rapid and reliable sensor for the determination of carbonate anion in a variety of practical applications.

Hydrazinylpyridine based highly selective optical sensor for aqueous source of carbonate ions: Electrochemical and DFT studies

A series of new receptors PDZ1-3 based on 2-(arylidenehydrazinyl)pyridines have been designed and synthesized for the detection of biologically and environmentally important ions. The colorimetric detection of CO₃^2- using neutral organic receptor PDZ-1 has been achieved with characteristic visual colour change from yellow to green accompanied by a large redshift of 215nm in absorption maxima. UV-Vis spectroscopic and cyclic voltammetric studies reveal the stoichiometry of binding and electrochemistry of host-guest complex formation. The binding constant was found to be 0.77×10⁴M^-2. In addition, electrochemical studies provide an insight into the stability of the complex. DFT studies performed on the PDZ-1 and PDZ-1-CO₃^2- complex reveal the binding mechanism involved in the anion detection process. PDZ-1 is highly selective for carbonate and does not show any colorimetric response towards any other anions or cations, while PDZ-2 and PDZ-3 remain inactive in the ion detection process. The limit of detection (LOD) and limit of quantification (LOQ) of PDZ-1 for carbonate was found to be 0.11mM and 0.36mM respectively. Considerable binding constant and limit of detection make PDZ-1 to be used as a real time sensor for the detection of carbonate in environmental and biological samples.

A dipodal molecular probe for naked eye detection of trivalent cations (Al3+, Fe3+and Cr3+) in aqueous medium and its applications in real sample analysis and molecular logic gates

A dipodal reversible colorimetric trivalent metal ion chemosensor (L) has been designed and synthesized. The chemosensor L successfully detects Al³⁺, Fe³⁺ and Cr³⁺ based on binding site-signaling approach and it has practical application.

Rapid naked-eye luminescence detection of carbonate ion through acetonitrile hydrolysis induced europium complexes

[Eu₂(Hhpip)₂(OAc)₆] in DMSO shows a specific and prompt photoluminescence colour change in response to CO₃²⁻ detectable with naked eyes.

The maiden report of a fluorescent-colorimetric sensor for expeditious detection of bifluoride ion in aqueous media

A fluorescent-colorimetric chemosensor L, for rapid detection of bifluoride ion has been developed based on a simple bis-Schiff base.

A new Schiff base and its metal complex as colorimetric and fluorescent–colorimetric sensors for rapid detection of arginine

A new Schiff base (L) and its Pb²⁺-complex have been utilized for rapid detection of arginine in aqueous medium.Lexhibits an excellent selective colorimetric response whereas its Pb²⁺-complex exploits fluorescent-colorimetric response towards arginine with very low detection limits.

Solvent-dependent fluorescent-colorimetric probe for dual monitoring of Al3+ and Cu2+ in aqueous solution: an application to bio-imaging

A solvent-dependent reversible fluorescent-colorimetric bis-iminopyridyl Schiff base receptor (N¹E,N⁴E)-N¹,N⁴-bis(quinolin-4-ylmethylene)benzene-1,4-diamine (L) has been developed for the first time for sensitive and selective determination of Al³⁺ and Cu²⁺ in aqueous solution.