Aqueous Fluorometric and Colorimetric Sensing of Phosphate Ions by a Fluorescent Dinuclear Zinc Complex

An aggregation induced emission active bis-heteroleptic ruthenium(II) complex for luminescence light-up detection of pyrophosphate ions

A red emissive ruthenium(II) complex 1[PF6]2 of an amino ethanol substituted 1,10-phenanthroline-based ligand (L1) has been developed and characterized by spectroscopic analysis and single-crystal X-ray diffraction. Complex 1 shows an aggregation-induced emission (AIE) enhancement and forms nano-aggregates in the poor solvent water and highly dense polyethylene glycol (PEG) media. The possible reason behind the AIE properties may be the rigidity gained through weak supramolecular interactions between neighbouring phenanthroline ligands and PF₆^- counterions. The AIE properties were supported by UV-vis and photoluminescence (PL) spectroscopy and dynamic light scattering (DLS) studies to substantiate the formation of nano-aggregates and to understand the morphology of the aggregated particles, scanning electron microscopy (SEM) and transmission electron microscopy (TEM) studies were performed. Compound 1[PF6]2 was highly selective towards pyrophosphate ions (PPi) over other phosphates such as ATP, ADP, AMP and H₂PO₄^- ions and other competitive anions in the PL spectroscopic channel in acetonitrile. The PL titrations of 1[PF6]2 with PPi in CH₃CN furnished the association constant K_a = 1.08 × 10⁴ M^-1 and the detection limit was calculated as low as 1.54 μM. The PPi detection has been established through the unique H-bonding interaction, supported by ¹H NMR titration. Finally, the cytotoxicity study and bioimaging were carried out for biological application. The complex shows very low cytotoxicity and good biocompatibility and is suitable for intracellular PPi imaging.

Cyclometalated iridium(III) complex of a 1,2,3-triazole-based ligand for highly selective sensing of pyrophosphate ion

A new cyclometalated Ir(III) complex of a methylene-bridged benzimidazole-substituted 1,2,3-triazole methanol ligand has been synthesized for the photoluminescent detection of pyrophosphate (H₂P₂O₇^2-) anions. The solution structure of 1[PF6] was fully characterized by 1D (¹H, ¹³C) and 2D (¹H-¹H COSY, ¹H-¹³C HSQC, and ¹H-¹³C HMBC) NMR spectroscopy, and ESI-HRMS. The 1[PF6] acted as a highly selective luminescent sensor for H₂P₂O₇^2- in CH₃CN over other competitive ions, including H₂PO₄^-, ATP, ADP and AMP. The PL titration of 1[PF6] with H₂P₂O₇^2- in CH₃CN furnished the association constant K_a = 8.6 × 10⁷ M^-1 and a low detection limit of ∼127 nM. The structure of the analyte interacting ligand renders the Ir(III) complex-based probe highly selective for H₂P₂O₇^2- ions. The PL enhancement with H₂P₂O₇^2- is due to the hydrogen bonding interaction of H₂P₂O₇^2- with the triazole C-H, imidazole N-H, methylene hydrogen and hydroxyl groups of the ligand that has been supported by ¹H NMR titration. Further, the PL enhancement of 1·H₂P₂O₇^2- adducts was supported by triplet-state TDDFT calculations. In 1·H₂P₂O₇^2-, the ³MLCT-³MC energy gap is increased, and the 1·H₂P₂O₇^2- emits efficiently from the ³MLCT and ³ILCT excited states. Finally, a cytotoxicity study and live-cell imaging were performed. The probe showed low cytotoxicity against HeLa cells and was suitable for intracellular pyrophosphate imaging.

Enhanced Ultrasensitive Photoelectrochemical Probe for Phosphate Detection in Water Based on a Zirconium-Porphyrin Framework

Excessive phosphate poses a serious ecological and human health risk, and thereby, monitoring its trace concentration is of great significance to environmental protection and human health. In this work, a zirconium-porphyrin framework (PCN-222) with excellent stability and unique luminescence properties was designed to modify the surface of the indium tin oxide electrode, which was first used as a photoelectrochemical (PEC) probe for phosphate detection. The PCN-222-modified PEC probe demonstrated an excellent selectivity and stability and indicated a linear response to phosphate in the range of 0-10⁶ nM with a limit of detection (LOD) as low as 1.964 nM. To the best of our knowledge, this is the phosphate probe with the lowest LOD, and this is also the first signal-on PEC probe toward phosphate based on PCN-222. More importantly, the PEC probe can be validated for the good applicability of trace phosphate detection in real water samples, indicating a good application prospect. Finally, a series of electrochemical and spectroscopic studies have proved that phosphate can bind to the indium tin oxide (ITO)/PCN-222 electrode, which shortens the distance of the space charge region while reducing the bandwidth and thus facilitates the transfer of photogenerated electrons across the energy band barrier to reduce O₂ in the electrolyte, producing an enhanced cathodic photocurrent signal. The proposed strategy of the highly sensitive PEC probe provides a promising platform for more effective label-free phosphate monitoring in the environment and organisms.

Effect of O-substitution in imidazole based Zn(II) dual fluorescent probes in the light of arsenate detection in potable water: a combined experimental and theoretical approach

Efficient detection of arsenate (AsO₄^3-) from contaminated drinking water extracted from underground has become a matter of utmost necessity and an exquisite challenge owing to the growing public health issue due to arsenicosis. In order to combat this we planned to detect arsenate with the naked eye under UV light using a novel chemosensor material whose structure and functioning as a sensor could be certified mechanistically. Hence we were encouraged to synthesize two differently O-substituted imidazole based homologous ligands: C1 (HL¹ = 2-((E)-(3-(1H-imidazole-1-yl)propylimino)methyl)-6-ethoxyphenol) and C2 (HL² = 2-((E)-(3-(1H-imidazole-1-yl)propylimino)methyl)-6-methoxyphenol). To accomplish the purposeful exploration of the luminescent sensor, we considered Chelation Enhanced Fluorescence (CHEF) and kept on searching for a metal cation that would be able to turn on the fluorescence of the ligands. Considering Zn(II) as the most suitable candidate, luminescent complexes D1 and D2 ({[Zn₂(L¹)₂(I)₂](DMF)} and [Zn₂(L²)₂(I)₂](DMF), respectively) were synthesized and characterized by SXRD, UV-Vis, FT-IR, and photoluminescence spectroscopy. In spite of the resemblance in the solid state structures of D1 and D2, the selective response of D1 towards arsenate with high quenching constants (2.13 × 10⁶), unlike D2, has been demonstrated mechanistically with steady state and time resolved fluorescence titration, solution phase ESI-MS spectral analysis and DFT studies. The selectivity and sensitivity of the sensor D1 explicitly make this material a potent candidate for arsenate detection due to its very low detection limit (8.2 ppb), low cost and user friendly characteristics. Real life implementation of this work in a test strip is expected to prove beneficial for public health to identify arsenate polluted water.

Influence of Triazole Substituents of Bis-Heteroleptic Ru(II) Probes toward Selective Sensing of Dihydrogen Phosphate

A series of seven new bis-heteroleptic Ru(II) probes (1[PF₆]₂-7[PF₆]₂) along with two previously reported probes (8[PF₆]₂ and 9[PF₆]₂) containing a similar anion binding triazole unit (hydrogen bond donor) functionalized with various substituents are employed in a detailed comparative investigation for the development of superior selective probes for H₂PO₄^-. Various solution- and solid-state studies, such as ¹H-DOSY NMR, dynamic light scattering (DLS), single-crystal X-ray crystallography, and transmission electron microscopy (TEM), have established that the selective sensing of H₂PO₄^- by this series of probes is primarily due to supramolecular aggregation driven enhancement of ³MLCT emission. Intestingly, 1[PF₆]₂ and 7[PF₆]₂, having an electron-deficient (π-acidic) aromatic pentafluorophenyl substituent are found to be superior probes for H₂PO₄^- in comparison to the other aryl- and polyaromatic-substituted analogues (2[PF₆]₂-6[PF₆]₂, 8[PF₆]₂, and 9[PF₆]₂), in terms of a higher enhancement of the ³MLCT emission band, a greater binding constant, and a lower detection limit. The superiority of 1[PF₆]₂ and 7[PF₆]₂ could be due to better supramolecular aggregation properties in the cases of pentafluorophenyl analogues via both hydrogen bonding and anion-fluorine/anion-π noncovalent interactions.

Smartphone-based ratiometric fluorescent definable system for phosphate by merged metal-organic frameworks

Phosphate plays an important role in a wide range of chemical and biological processes, so the development of a new phosphate optical sensor with high sensitivity, specificity and visual recognition function has important practical significance. Herein, a ratiometric fluorescent (RF) probe and a smartphone-integrated colorimetric test paper sensing platform for assay phosphate was fabricated using hybrid fluorescent UiO-66-NH₂ and Eu³⁺@MOF-808 metal-organic frameworks. After continuous addition of phosphate, the blue fluorescence emission of UiO-66-NH₂ and the red emission of Eu³⁺@MOF-808 were regularly enhanced and quenched respectively, and the fluorescence response of the detection platform to phosphate exhibited a clear color change process (red → pink → blue). More importantly, the probe solution and test paper of the integrated smartphone are converted to digital values through RGB channels and successfully used to visualize semi-quantitative recognition of phosphate. In addition, an RF probe and a smartphone integrated fluorescent test paper were developed separately to devise logic gate devices for detecting phosphate. The multifunctional ratio sensing platform integrated by the smartphone furnishes a new strategy and broad prospects for the intelligent online identification of important targets in biological samples and environmental samples.

Protonation of cyclen-based chelating agents containing fluorescent moieties

The fluorescence emission properties of 1,4,7,10-tetraazacyclododecane-based receptors with appended heteroaromatic fluorophores are tuned by photoinduced electron and proton transfer processes.

TICT fluorescent probe for Al3+: Sequential detection of PPi, ATP and ADP in semi-aqueous medium and real-life applications

A ditopic Schiff base ligand, H₂L has been synthesized and characterized by all spectroscopic techniques. It is highly selective and specific towards Al³⁺ in semi aqueous medium (DMF/H₂O mixture) by exhibiting a drastic increase in the fluorescence intensity. The emission studies, spectroscopic data, life time and quantum yield results have been used to understand its binding mode, explore its specificity and establish its efficacy. The intensity difference is remarkable in physiological pH range. Due to its reversible behavior this ditopic fluorescent chemosensor can be used multiple times to make it cost effective. Detection limit for this chemosensor was found to be 0.65 μM. Experiments with TLC plates show that it can be used as a practical and portable sensor for studying environmental samples in real life. The L-Al³⁺ complex generated in the solution acts as a sensor to sequentially detect pyrophosphate groups present in inorganic pyrophosphates, ATP and ADP among other anions by turning off the fluorescence. Inhibit logic gate and its corresponding truth table has been developed to aid in further exploiting its multidimensional applications.

A Chemodosimetric Approach for Fluorimetric Detection of Hg2+ Ions by Trinuclear Zn(II)/Cd(II) Schiff Base Complex: First Case of Intermediate Trapping in a Chemodosimetric Approach

The present work discloses the application of two fluorescent zinc and cadmium complexes (1 and 2) for sensing of Hg(II) ions through a chemodosimetric approach. The ligand under consideration in this work is a N₂O donor Schiff base ligand (E)-4-bromo-2-(((2-morpholinoethyl)imino)methyl)phenol (HL), which has been harnessed to generate complexes [Zn₃L₂(OAc)₄] (1) and [Cd₃L₂(OAc)₄] (2). X-ray single crystal diffraction studies unveil the trinuclear skeleton of complexes 1 and 2. Both complexes have been found to be highly fluorescent in nature. However, the quantum efficiency of Zn(II) complex (1) dominates over the Cd(II) analogue (2). The absorption and emission spectroscopic properties of the complexes have been investigated by density functional theory. Complexes 1 and 2 can detect Hg²⁺ ions selectively by fluorescence quenching, and it is noteworthy to mention that the mechanism of sensing is unique as well as interesting. In the presence of Hg²⁺ ions, complexes 1 and 2 are transformed to mononuclear mercuric intermediate complex (3) and finally to a trinuclear mercuric complex (4) by hydrolysis. We have successfully trapped the intermediate complex 3, and we characterized it with the aid of X-ray crystallography. Transformation of complexes 1 and 2 to intermediate complex 3 and finally to 4 has been established by UV-vis spectroscopy, fluorescence spectroscopy, ESI-MS spectroscopy, ¹H NMR spectroscopy, and X-ray crystallography. The spontaneity of the above conversion is well supported by thermodynamic aspects as reflected from density functional theoretical calculations.

A new half-condensed Schiff base platform: structures and sensing of Zn2+ and H2PO4- ions in an aqueous medium

A newly designed and synthesized half-condensed organic moiety 2-hydroxy-5-methyl-3-[(2-phenylamino-phenylimino)-methyl]-benzaldehyde (HL') and a Zn₂L₄ complex sequentially detect Zn²⁺ and H₂PO₄^- ions as low as 1.13 nM and1.23 μM, respectively. HL' and a dinuclear Zn(ii) complex of in situ generated L^- in a solution formulated as Zn₂L₄ under investigation were characterized by physicochemical and spectroscopic studies along with detailed structural analyses by single-crystal X-ray crystallography. The selectivity and sensitivity of HL' towards Zn²⁺ ions and of the Zn₂L₄ complex towards H₂PO₄^- ions are based on CHEF and via displacement pathways, respectively. Dual sensing of Zn²⁺ ions and H₂PO₄^-ions in an aqueous medium via "Green-Blue-Green" emission with the reversible transformation of in situ formed HL' to HL was established by detailed electronic absorption and emission spectroscopic studies. This non-cytotoxic probe (HL', i.e. produced HL in solution) and Zn₂L₄ complexes are able to monitor the subcellular distribution changes of Zn²⁺ and H₂PO₄^- ions, respectively, by fluorescence microscopy using the human semen sample.

CdS quantum dots embedded in PVP: Inorganic phosphate ion sensing in real sample and its antimicrobial activity

Polyvinyl-pyrrolidone capped spherical cadmium sulphide quantum dots (CdS-PVP QDs), 2-6 nm in size, were developed as a selective turn-on fluorescence nanosensor for monohydrogen phosphate ion (HPO₄^2-) in aqueous medium. Fluorescence intensity of CdS-PVP QDs significantly increased with addition of HPO₄^2- ions, whereas the other common inorganic ions had very little effect on the fluorescence intensity. The proposed sensor may be efficiently used for the detection of HPO₄^2- ions at a low level of concentration up to 213 nM in real urine sample. Cell imaging study indicates that the CdS-PVP QDs are cell permeable and can detect the intracellular distribution of HPO₄^2- ions under fluorescence microscope. The CdS-PVP QDs showed considerable activity against Staphylococcus aureus also.

Chemosensing of Guanosine Triphosphate Based on a Fluorescent Dinuclear Zn(II)-Dipicolylamine Complex in Water

Guanosine triphosphate (GTP) is a key biomarker of multiple cellular processes and human diseases. The new fluorescent dinuclear complex [Zn₂(L)(S)][OTf]₄, 1 (asymmetric ligand, L = 5,8-Bis{[bis(2-pyridylmethyl)amino] methyl}quinoline, S = solvent, and OTf = triflate anion) was synthesized and studied in-depth as a chemosensor for nucleoside polyphosphates and inorganic anions in pure water. Additions at neutral pH of nucleoside triphosphates, guanosine diphosphate, guanosine monophosphate, and pyrophosphate (PPi) to 1 quench its blue emission (λ_em = 410 nm) with a pronounced selectivity toward GTP over other anions, including adenosine triphosphate (ATP), uridine triphosphate (UTP), and cytidine triphosphate (CTP). The efficient quenching response by the addition of GTP was observed in the presence of coexisting species in blood plasma and urine with a detection limit of 9.2 μmol L^-1. GTP also shows much tighter binding to the receptor 1 on a submicromolar level. On the basis of multiple spectroscopic tools (¹H, ³¹P NMR, UV-vis, and fluorescence) and DFT calculations, the binding mode is proposed through three-point recognition involving the simultaneous coordination of the N⁷ atom of the guanosine motif and two phosphate groups to the two Zn(II) atoms. Spectroscopic studies, MS-ESI, and DFT suggested that GTP bound to 1 in 1:1 and 2:2 models with high overall binding constants of log β_1 (1:1) = 6.05 ± 0.01 and log β₂ = 10.91 ± 0.03, respectively. The optical change and selectivity are attributed to the efficient binding of GTP to 1 by the combination of a strong electrostatic contribution and synergic effects of coordination bonds. Such GTP selectivity of an asymmetric metal-based receptor in water is still rare.

Embedding dual fluoroprobe in metal-organic frameworks for continuous visual recognition of Pb2+ and PO43- via fluorescence 'turn-off-on' response: Agar test paper and fingerprint

A novel dual-emissive ratiometric fluorescence (RF) probe CDs/QDs@ZIF-8 has been successfully constructed by employing a simple and effective strategy for in situ encapsulating carbon dots (CDs) and thioglycolic acid-modified CdTe quantum dots (QDs) into porous metal-organic frameworks (MOFs) "cage". The dual responsive colorimetric fluorescence probe was developed for the ultra-high selectivity and sensitivity continuous detection of Pb²⁺ (turn OFF) and PO₄^3- (turn ON) in biological samples. Blue CDs acts as a stable internal standard emission, the emission color of CDs/QDs@ZIF-8 changes from red to blue with introducing Pb²⁺, fluorescence of probe is quenched because of the binding of Pb²⁺ ions to thioglycolic acid on the surface of probe and e- transfer from the photoexcited QDs to Pb²⁺ ions, color can be recovered after the adding PO₄^3- to CDs/QDs@ZIF-8-Pb²⁺ system, which could take away Pb²⁺ ions from the surface of CDs/QDs@ZIF-8. More importantly, fabricated agar test papers was also successfully applied in visual detection of Pb²⁺ and PO₄³- in real samples, which can implement without instrument-specific calibration.

Selective sensing of ATP by hydroxide-bridged dizinc(ii) complexes offering a hydrogen bonding cavity

This work illustrates the highly selective fluorescence detection of ATP in the presence of other competing anions, such as AMP, ADP, PPi and other phosphates by using a set of hydroxide-bridged dizinc(ii) complexes offering a cavity lined with hydrogen bonds and other interactive forces. ATP, as a whole, was recognized by the synergic combination of Zn-phosphate bonding, ππ stacking between the adenine ring of ATP and the pyridine ring of the dizinc complex and hydrogen bonding interactions that modulate the cavity structure of the dizinc complexes.

A terbium(III)-functionalized zinc(II)-organic framework for fluorometric determination of phosphate

A terbium(III)-functionalized zinc(II)-organic framework (Tb-MOF-Zn) is shown to be a viable fluorescent probe for phosphate. The organic ligands 4,4',4″-[((2,4,6-trimethylbenzene-1,3,5-triyl)tris(methylene))tris(oxy)]tribenzoic acid (H₃L³) contains multiple carboxyl groups that can react with zinc(II) to yield tubular MOF-Zn. The MOF-Zn was further functionalized with Tb(III) to produce a lanthanide composite of type Tb-MOF-Zn which displays strong fluorescence with excitation/emission maxima at 285/544 nm. Fluorescence is quenched by phosphate because of the specific interaction with Tb(III) in Tb-MOF-Zn. The concentration of Tb-MOF-Zn, reaction time and pH value of the solution were optimized. Fluorescence drops linearly in the 0.01 to 200.0 μM phosphate concentration range, and the detection limit is 4.0 nM. The fluorescent probe was also used to prepare a microdot array on a glass slide for visual detection of phosphate under illumination with UV light. Graphical abstractA terbium(III) functionalized zinc(II)-organic framework was synthesized and used as fluorescent probe for determination of phosphate ions.

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.

A cationic tetrahedral Zn(ii) cluster based on a new salicylamide imine multidentate ligand: synthesis, structure and fluorescence sensing study

We present here a monocationic Zn^II tetrahedral cluster which is extremely stable and exhibits highly sensitive and selective recognition of phosphates against other common anions in water containing media.

Reaction-based ratiometric fluorescent probe for selective recognition of sulfide anions with a large Stokes shift through switching on ESIPT

Ratiometric fluorescent probe BNPT has been synthesized and characterized for S²⁻ sensing via ESIPT mechanism.

Supramolecular Aggregation of a New Substituted Bis(salicylaldiminato)zinc(II) Schiff-Base Complex Derived from trans-1,2-Diaminocyclohexane

In this contribution is reported the synthesis, characterization, and aggregation properties in solution of a novel Zn(II) complex, (R)-2, derived from the enantiopure chiral trans-1,2-diaminocyclohexane and a substituted salicylaldehyde. Detailed 1H NMR, DOSY NMR, optical absorption, and circular dichroism spectroscopic studies and chemical evidence allowed to investigate the nature of aggregate species in solution. The high solubility of (R)-2 in solution of the non-coordinating chloroform solvent leads to formation of various aggregates, some of them consisting of large oligomers estimated to contain up to 27 monomeric units. The chiral trans-stereochemistry of the bridging diamine favors a different aggregation mode in these complexes, both in the oligomers and dimers, involving a tetrahedral coordination geometry around the metal center. Overall data suggest the formation of helical oligomers, (ZnL)n, in freshly prepared chloroform solutions which, by standing or heating, evolve towards a more thermodynamically stable, dinuclear double-helicate Zn2L2 dimer.

A hexa-quinoline basedC3-symmetric chemosensor for dual sensing of zinc(ii) and PPi in an aqueous mediumviachelation induced “OFF–ON–OFF” emission

“OFF–ON–OFF” luminescence switching behavior of a hexa-quinoline based sensor towards Zn²⁺and PPi in an aqueous buffer medium is demonstrated.

Balancing the acidity of the pendant urea arm of bis-heteroleptic ruthenium(ii) complex containing pyridyl triazole for improved oxyanion recognition

The effect of the acidity of the pendant urea –NH protons on oxyanion recognition, luminiscence OFF–ON sensing and extraction is demonstrated.

Combined experimental and theoretical studies on selective sensing of zinc and pyrophosphate ions by rational design of compartmental chemosensor probe: Dual sensing behaviour via secondary recognition approach and cell imaging studies

A compartmental chemosensor probe HL was designed and synthesized for dual sensing of zinc ions and PPi via secondary recognition approach.

Rhodamine-based sensor for real-time imaging of mitochondrial ATP in living fibroblasts

Mitochondria are essential for the production and maintenance of ATP in the eukaryotic cell. To image and monitor intracellular ATP level without cell breakage, biological and chemical sensors were developed in the last years. Here, we have internalized a rhodamine-based sensor RSL⁺ into living cells and monitored the mitochondrial ATP levels in cultured mouse embryonic fibroblasts. To evaluate the robustness of the sensor we imaged the changes of the mitochondrial ATP levels under non-physiological conditions upon incubation with FCCP, oligomycin, azide, deoxyglucose or phosphoenolpyruvate; all compounds that interfere with ATP homeostasis of the cell. The ATP sensor allowed us to determine the mitochondrial ATP levels in human skin fibroblasts where we observe a similar amount of ATP compared to mouse embryonic fibroblasts. We propose the RSL⁺ to be a valuable tool for the assessment of mitochondrial dysfunction in human cells derived from mitochondrial OXPHOS patients and for basic studies on bioenergetics metabolism.

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The rhodamine-based sensor RSL⁺ permeates efficiently eukaryotic plasma membrane and accumulates in mitochondria.

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RSL⁺ detects mitochondrial ATP levels in human and mouse skin fibroblasts.

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RSL⁺ detects real-time variations of mitochondrial ATP levels under non-physiological conditions.

A coumarin based Schiff base probe for selective fluorescence detection of Al3+ and its application in live cell imaging

A new coumarin based Schiff base compound, CSB-1 has been synthesized to detect metal ion based on the chelation enhanced fluorescence (CHEF). The cation binding properties of CSB-1 was thoroughly examined in UV-vis and fluorescence spectroscopy. In fluorescence spectroscopy the compound showed high selectivity toward Al³⁺ ion and the Al³⁺ can be quantified in mixed aqueous buffer solution (MeOH: 0.01M HEPES Buffer; 9:1; v/v) at pH7.4 as well as in BSA media. The fluorescence intensity of CSB-1 was enhanced by ~24 fold after addition of only five equivalents of Al³⁺. The fluorescence titration of CSB-1 with Al³⁺ in mixed aqueous buffer afforded a binding constant, K_a=(1.06±0.2)×10⁴M^-1. The colour change from light yellow to colourless and the appearance of blue fluorescence, which can be observed by the naked eye, provides a real-time method for Al³⁺ sensing. Further the live cell imaging study indicated that the detection of intracellular Al³⁺ ions are also readily possible in living cell.

Lewis basicity of relevant monoanions in a non-protogenic organic solvent using a zinc(ii) Schiff-base complex as a reference Lewis acid

The Lewis basicity of relevant anions is reported for the first time and compared with that of neutral bases.

On the Lewis acidic character of bis(salicylaldiminato)zinc(ii) Schiff-base complexes: a computational and experimental investigation on a series of compounds varying the bridging diimine

The electronic effects induced by the geometry of the 1,2-diimine bridge control the Lewis acidic character in a series of Zn^II Shiff-base complexes.

A turn-on green channel Zn2+ sensor and the resulting zinc(ii) complex as a red channel HPO42− ion sensor: a new approach

A turn-on green channel Zn²⁺ sensor and the resulting zinc(ii) complex as a red channel HPO₄²⁻ ion sensor: a new approach.

A new fluorescent sensor containing glutamic acid for Fe3+ and its resulting complex as a secondary sensor for PPi in purely aqueous solution

A new fluorescence sensor L with benzimidazo[2,1-α]benz[de]isoquinoline-7-one as the fluorophore and glutamic acid moiety as the receptor was synthesized and characterized.

Triazole-Linked Quinoline Conjugate of Glucopyranose: Selectivity Comparison among Zn2+, Cd2+, and Hg2+ Based on Spectroscopy, Thermodynamics, and Microscopy, and Reversible Sensing of Zn2+ and the Structure of the Complex Using DFT

A water-soluble triazole-linked quinoline conjugate of glucopyranose (L) has been synthesized and characterized, and its single-crystal X-ray diffraction (XRD) structure has been established. Binding of L toward different biologically relevant metal ions has been studied using fluorescence and absorption spectroscopy in HEPES buffer at pH 7.4. The conjugate L detects Zn2+ and Cd2+ with 30 ± 2 and 14 ± 1-fold fluorescence enhancement, respectively, but in the case of Hg2+, only a fluorescence quench was observed. The stoichiometry of the complex is 1:2 metal ion to the ligand in the case of Zn2+ and Cd2+ resulting in [Zn(L)2] and [Cd(L)2], and it is 1:1 in the case of Hg2+, as confirmed from their electrospray ionization mass spectrometry (ESIMS) spectra. Zn2+ shows greater exothermicity over Cd2+, whereas Hg2+ shows endothermicity , which supports the differences in their binding strength and the nature of the corresponding complex. L exhibits rod-shaped particles and upon complexation with Zn2+, it exhibits sphere-like morphological features in scanning electron microscopy (SEM) images. However, clustered aggregates are observed in Cd2+, whereas the [HgL] complex exhibits small fused spherical structures, and therefore the signature of these ions is seen in microscopy images. The computational studies revealed that the syn-[Zn(L)2] complex is stabilized by 9.7 kcal mol-1 more than that in the case of anti-[Zn(L)2] owing to the formation of hydrogen bonds between the two glucosyl moieties within the syn-complex. Among the anions studied, [Zn(L)2] is sensitive and selective toward the phosphate ion (H2PO4 -) with a minimum detection limit of 16 ± 2 ppb. Similarly, the [HgL] can act as a secondary sensor for CN- while also exhibiting reversibility. Based on the input-output characteristics, INHIBIT logic gate was built in the case of Zn2+ vs H2PO4 - and IMPLICATION logic gate was built in the case of Hg2+ vs CN-.

Di- and Triphosphate Recognition and Sensing with Mono- and Dinuclear Fluorescent Zinc(II) Complexes: Clues for the Design of Selective Chemosensors for Anions in Aqueous Media

The synthesis of a new ligand (L1) containing two 1,4,7-triazacyclononane ([9]aneN₃ ) moieties linked by a 4,5-dimethylenacridine unit is reported. The binding and fluorescence sensing properties toward Cu²⁺ , Zn²⁺ , Cd²⁺ , and Pb²⁺ of L1 and receptor L2, composed of two [9]aneN₃ macrocycles bridged by a 6,6''-dimethylen-2,2':6',2''-terpyridine unit, have been studied by coupling potentiometric, UV/Vis absorption, and emission measurements in aqueous media. Both receptors can selectively detect Zn²⁺ thanks to fluorescence emission enhancement upon metal binding. The analysis of the binding and sensing properties of the Zn²⁺ complexes toward inorganic anions revealed that the dinuclear Zn²⁺ complex of L1 selectively binds and senses the triphosphate anion (TP), whereas the mononuclear Zn²⁺ complex of L2 displays selective recognition of diphosphate (DP). Binding of TP or DP induces emission quenching of the Zn²⁺ complexes with L1 and L2, respectively. These results are exploited to discuss the role played by pH, number of coordinated metal cations, and binding ability of the bridging units in metal and/or anion coordination and sensing.

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.

Imine-functionalized thioether Zn(ii) turn-on fluorescent sensor and its selective sequential logic operations with H2PO4−, DFT computation and live cell imaging

Thioether Schiff base (H₂L), a nontoxic Zn²⁺-sensor (LOD, 0.050 μM) has shown selective ON–OFF emission following INHIBIT logic circuit with H₂PO₄⁻and useful agent for the identification of Zn²⁺and H₂PO₄⁻in intracellular fluid in living cells.