Fluorescent and electrochemical sensing of polyphosphate nucleotides by ferrocene functionalised with two Zn(II)(TACN)(pyrene) complexes

Coordination-Induced Multivalent Self-Assembling Catalysts for Spectral Sensing Zn2+ with High Selectivity and Sensitivity

The introduction of signal amplification to molecular spectral sensing systems is an intriguing topic in supramolecular analytical chemistry. In this study, click chemistry was used to generate a triazole moiety to bridge with a long hydrophobic alkyl chain (C_n) and another short alkyl chain (C_m) bearing a 1,4,7-triazacyclonane (TACN) group for efficiently generating a self-assembling multivalent catalyst, C_n-triazole-C_m-TACN·Zn²⁺ (n and m represent the carbon numbers of both alkyl chains, respectively; n = 16, 18, and 20; m = 2 and 6), to catalyze the hydrolysis of 2-hydroxypropyl-4-nitrophenyl phosphate (HPNPP) when Zn²⁺ was added. The triazole moiety introduced adjacent to the TACN group plays an important role in improving the selectivity of Zn²⁺ because the triazole moiety can participate in the coordination interaction between the Zn²⁺ and neighboring TACN group. The supplementary triazole complexing increases the space requirement for coordinated metal ions. This catalytic sensing system also shows high sensitivity, with a favorable limit of detection down to 350 nM, even if only UV-vis absorption spectra rather than more sensitive fluorescence techniques were used for signaling, and can be used to determine the concentration of Zn²⁺ in tap water, which demonstrates the practical application feasibility.

Fluorescent chemosensors containing redox-active ferrocene: a review

The redox-active ferrocene containing two cyclopentadienyl rings and iron was extensively employed in the field of sensing, catalysis, medicine, biotechnology etc., due to the structural stability, solubility in common solvents and easy structural modification to make a wide variety of ferrocene derivatives. The ferrocene moiety can be linked suitably with fluoro-chromogenic units and applied for the multichannel (fluorescent, chromogenic and redox) sensing of various bioactive and toxic analytes. This review was narrated to compile some important ferrocene based fluorescent chemosensors developed for the detection of metal ions, anions and neutral analytes. The analytical novelty and sensing mechanisms of the summarized chemosensors are discussed to open new scopes for future research.

Good-Practice Non-Radioactive Assays of Inorganic Pyrophosphatase Activities

Inorganic pyrophosphatase (PPase) is a ubiquitous enzyme that converts pyrophosphate (PP_i) to phosphate and, in this way, controls numerous biosynthetic reactions that produce PP_i as a byproduct. PPase activity is generally assayed by measuring the product of the hydrolysis reaction, phosphate. This reaction is reversible, allowing PP_i synthesis measurements and making PPase an excellent model enzyme for the study of phosphoanhydride bond formation. Here we summarize our long-time experience in measuring PPase activity and overview three types of the assay that are found most useful for (a) low-substrate continuous monitoring of PP_i hydrolysis, (b) continuous and fixed-time measurements of PP_i synthesis, and (c) high-throughput procedure for screening purposes. The assays are based on the color reactions between phosphomolybdic acid and triphenylmethane dyes or use a coupled ATP sulfurylase/luciferase enzyme assay. We also provide procedures to estimate initial velocity from the product formation curve and calculate the assay medium’s composition, whose components are involved in multiple equilibria.

Silk Fibroin-Confined Star-Shaped Decahedral Silver Nanoparticles as Fluorescent Probe for Detection of Cu2+ and Pyrophosphate

A green, one-step method for the fabrication of silk fibroin (SF) protected silver decahedral nanoparticles (SF@AgNPs) has been developed. High-resolution transmission electron microscopy characterization demonstrated that the silver decahedral nanoparticles can provide more binding sites with (111) facets. Moreover, a facile strategy based on Cu²⁺ mediated SF@AgNPs was reported as an on-off-on fluorescent system for the detection of Cu²⁺, and the SF@AgNPs can be also used for the determination of pyrophosphate ion (P₂O₇^4-, PPi). The fluorescence of SF@AgNPs was quenched by Cu²⁺ as a complex formed between SF and Cu²⁺ and was restored when PPi was introduced into the system due to the higher binding affinity between PPi and Cu²⁺. Herein, a novel SF@AgNPs-Cu²⁺ fluorescent probe for Cu²⁺ and PPi detection is presented. The proposed assay shows a linear relationship at a Cu²⁺ concentration range from 1 to 6 μM with a detection limit of 33.3 nM. This simple, reliable, selective, and environmentally friendly fluorescent probe also has a wide concentration range from 100 to 700 μM with a detection limit of 6.7 μM for PPi. The 16 types of anions lead to negligible changes in the SF@AgNPs-Cu²⁺ complexes, while restoring the fluorescence intensity of the complexes when added with PPi. Additionally, it is demonstrated that the SF@AgNPs-based fluorescent assay works in real biological samples. It suggests that this proposed method has the potential for application in the clinical detection of Cu²⁺ and PPi.

A Coumarin-Benzothiazole Derivative as a FRET-Based Chemosensor of Adenosine 5′-Triphosphate

A coumarin-benzothiazole ratiometric probe of ATP was designed and synthesized. The probe is based on incorporation of benzothiazole scaffold as a donor and coumarin nucleus as an acceptor in a single Förster resonance energy transfer/fluorescence resonance energy transfer (FRET) sensing platform. The sensor can detect ATP in aqueous solution with high selectivity over other nucleotide polyphosphate (NPP) anions. Binding of ATP to the sensor results in modulation of FRET efficiency between the donor and the acceptor which afforded a linear relationship between FRET signal and ATP (0.1–10 μM). A limit of detection (LOD) of 94.5 nM was quantified for FRET sensing of ATP by the probe. In addition, Job plot analysis revealed 1:1 binding interaction between the probe and ATP. The FRET probe was successfully utilized in monitoring ATP hydrolysis by apyrase in aqueous solution.

Carbon nanospheres with dual-color emission and their application in ratiometric pyrophosphate sensing

Herein, we employ pH-dependent solubility equilibrium to develop the one-pot aqueous synthesis of dual-color emission fluorescent carbon nanosphere (DFCSs) with novel physicochemical properties.

An AIE-based metallo-supramolecular assembly enabling an indicator displacement assay inside living cells

We report a novel metallo-supramolecular assembly (Z/E-TPE2CyZn-PV), which consists of a tetraphenylethene (TPE)-based dinuclear Zn2+-cyclen complex and pyrocatechol violet (PV). The assembly is developed for indicator-displacement assays (IDAs) inside living cells.

Macrocycles Bearing Ferrocenyl Pendants and their Electrochemical Properties upon Binding to Divalent Transition Metal Cations

Metal complexes of Cu²⁺ , Co²⁺ , Cd²⁺ , Zn²⁺ , and Ni²⁺ formed with the ligands [Fc(cyclen)] (1) and [Fc(cyclen)₂ ] (2) (Fc=ferrocene, cyclen=1,4,7,10-tetraazacyclododecane) are synthesised and characterised. The X-ray structure of the Cu²⁺ complex of 2, Fc([Cu(cyclen)(CH₃ CN)]₂ (ClO₄ )₄ , is reported, and shows that the two positively charged Cu²⁺ -cyclen units have a coordination number of five, adopting a distorted trigonal-bipyramidal configuration. The Cu²⁺ -cyclen units are arranged in a trans-like configuration with respect to the Fc group, presumably to minimise electrostatic repulsion. The voltammetric oxidation of the free ligands 1 and 2 in a CH₂ Cl₂ /CH₃ CN (1:4) solvent mixture yields two closely spaced oxidation processes. Both electron-transfer steps are associated with the ferrocenyl moiety, implying strong communication between the cyclen nitrogen atoms and the ferrocenyl group. In contrast, cyclic voltammograms display only a simple reversible one-electron process if 1 and 2 are complexed with Cd²⁺ , Cu²⁺ , Zn²⁺ , Ni²⁺ , or Co²⁺ . Binding of these metal ions produces a significant shift in the reversible midpoint potential (E_m ). Except for Ni²⁺ , E_m is linearly proportional to the charge density of the transition metal ion, demonstrating that 1 and 2 may undergo redox switching. The diffusion coefficients of Fc, DmFc, 1 and 2, and their metal ion complexes correlate well with their molecular weights.

Pyrophosphate-Induced Intramolecular Excimer Formation in Dinuclear Zinc(II) Complexes with Tetrakisquinoline Ligands

Dinuclear Zn²⁺ complexes with HTQHPN ( N,N,N' ,N'-tetrakis(2-quinolylmethyl)-2-hydroxy-1,3-propanediamine) derivatives have been prepared, and their pyrophosphate (PPi, P₂O₇^4-) sensing properties were examined. The ligand library includes six HTQHPN derivatives with electron-donating/withdrawing substituents, an extended aromatic ring, and six-membered chelates upon zinc binding. Complexation of ligand with 2 equiv of Zn²⁺ promotes small to moderate fluorescence enhancement around 380 nm, but in the cases of HTQHPN, HT(6-FQ)HPN ( N,N,N' ,N'-tetrakis(6-fluoro-2-quinolylmethyl)-2-hydroxy-1,3-propanediamine), and HT(8Q)HPN ( N,N,N' ,N'-tetrakis(8-quinolylmethyl)-2-hydroxy-1,3-propanediamine), subsequent addition of PPi induced a significant fluorescence increase around 450 nm. This fluorescence enhancement in the long-wavelength region is attributed to the conformational change of the bis-(quinolylmethyl)amine moiety which promotes intramolecular excimer formation between adjacent quinolines upon binding with PPi. The structures of PPi- and phosphate-bound dizinc complexes were revealed by X-ray crystallography utilizing phenyl-substituted analogues. The zinc complex with HT(8Q)HPN exhibits the highest signal enhancement ( I_PPi/ I₀ = 12.5) and selectivity toward PPi sensing ( I_ATP/ I_PPi = 20% and I_ADP/ I_PPi = 25%). The fluorescence enhancement turned to decrease gradually after the addition of more than 1 equiv of PPi due to the removal of zinc ion from the ligand-zinc-PPi ternary complex, allowing the accurate determination of PPi concentrations at the fluorescence maximum composition. The practical application of the present method was demonstrated monitoring the enzymatic activity of pyrophosphatase.

Multiplexed ratiometric photoluminescent detection of pyrophosphate using anisotropic boron-doped nitrogen-rich carbon rugby ball-like nanodots

B-doped N-rich carbon rugby ball-like nanodots have been synthesized by a heterophase polymerization route and can act not only as a ratiometric sensor for Hg²⁺ but also as a dual-mode PPi-selective sensor.

A new FRET-based ratiometric probe for fluorescence and colorimetric analyses of adenosine 5′-triphosphate

A new ratiometric probe for ATP was designed based on the binding-induced modulation of FRET coupled with the ACQ sensing mechanism.

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.

Spirolactone and spirothiolactone rhodamine-pyrene probes for detection of Hg²⁺ with different sensing properties and its application in living cells

Two new rhodamine B-based fluorescent probes PyRbS and PyRbO containing pyrene moiety were designed and synthesized. Both of the probes showed colorimetric and fluorometric sensing abilities for Hg(2+) with high selectivity over other metal ions. The binding analysis using Job's plot suggested 1:1 stoichiometry for the complexes formed for Hg(2+). Compared with PyRbO, the PyRbS showed higher selectivity and sensitivity due to the thiophilic property of Hg(2+) ion. The PyRbS exhibited the linear fluorescence quenching to Hg(2+) in the range of 0.3 to 4.8 μM (λ(ex)=365 nm) and 0.3 to 5.4 μM (λ(ex)=515 nm), and the detection limit was 0.72 μM. Moreover, ratiometric changes of PyRbS with Hg(2+) in absorption spectrum were observed, which could not be obtained in the combination of PyRbO with Hg(2+). In addition, the methyl thiazolyl tetrazolium (MTT) assay demonstrated that RbPyS had low cytotoxicity and was successfully used to monitor intracellular Hg(2+) levels in living cells.

Phosphate binding by a novel Zn(II) complex featuring a trans-1,2-diaminocyclohexane ligand. Effective anion recognition in water

In this work we have investigated the binding properties of a new synthetic receptor for phosphate anions that combines metal ion coordination with electrostatic and H-bonding interactions. The described receptor is obtained by assembling an iminodiacetic (IDA) fragment, as a Zn(II) binding site, with a polyamine macrocyclic portion containing two trans-1,2-diaminocyclohexane (DAC) units and a pyrrole ring, as a cationic binding site, into an adaptive structure appropriately spanning the length of di- and tridentate phosphates. Potentiometric measurements together with (1)H and (31)P NMR investigation showed that, in a wide pH range including values of physiological interest, the Zn(II) complex of the receptor binds di- and triphosphates, such as ADP, ATP, pyrophosphate (PP) and triphosphate (TP), far better than monophosphate (MP), and that TP is poorly bound by methyliminodiacetate (MIDA) as a model for the Zn(II) binding site. Besides the excellent selectivity over other phosphates, the affinity for TP is the largest reported to date for Zn(II) complexes in water.

Macrocyclic metal complexes for metalloenzyme mimicry and sensor development

Examples of proteins that incorporate one or more metal ions within their structure are found within a broad range of classes, including oxidases, oxidoreductases, reductases, proteases, proton transport proteins, electron transfer/transport proteins, storage proteins, lyases, rusticyanins, metallochaperones, sporulation proteins, hydrolases, endopeptidases, luminescent proteins, iron transport proteins, oxygen storage/transport proteins, calcium binding proteins, and monooxygenases. The metal coordination environment therein is often generated from residues inherent to the protein, small exogenous molecules (e.g., aqua ligands) and/or macrocyclic porphyrin units found, for example, in hemoglobin, myoglobin, cytochrome C, cytochrome C oxidase, and vitamin B12. Thus, there continues to be considerable interest in employing macrocyclic metal complexes to construct low-molecular weight models for metallobiosites that mirror essential features of the coordination environment of a bound metal ion without inclusion of the surrounding protein framework. Herein, we review and appraise our research exploring the application of the metal complexes formed by two macrocyclic ligands, 1,4,7-triazacyclononane (tacn) and 1,4,7,10-tetraazacyclododecane (cyclen), and their derivatives in biological inorganic chemistry. Taking advantage of the kinetic inertness and thermodynamic stability of their metal complexes, these macrocyclic scaffolds have been employed in the development of models that aid the understanding of metal ion-binding natural systems, and complexes with potential applications in biomolecule sensing, diagnosis, and therapy. In particular, the focus has been on "coordinatively unsaturated" metal complexes that incorporate a kinetically inert and stable metal-ligand moiety, but which also contain one or more weakly bound ligands, allowing for the reversible binding of guest molecules via the formation and dissociation of coordinate bonds. With regards to mimicking metallobiosites, examples are presented from our work on tacn-based complexes developed as simplified structural models for multimetallic enzyme sites. In particular, structural comparisons are made between multinuclear copper(II) complexes formed by such ligands and multicopper enzymes featuring type-2 and type-3 copper centers, such as ascorbate oxidase (AO) and laccase (Lc). Likewise, with the aid of relevant examples, we highlight the importance of cooperativity between either multiple metal centers or a metal center and a proximal auxiliary unit appended to the macrocyclic ligand in achieving efficient phosphate ester cleavage. Finally, the critical importance of the Zn(II)-imido and Zn(II)-phosphate interactions in Zn-cyclen-based systems for delivering highly sensitive electrochemical and fluorescent chemosensors is also showcased. The Account additionally highlights some of the factors that limit the performance of these synthetic nucleases and the practical application of the biosensors, and then identifies some avenues for the development of more effective macrocyclic constructs in the future.

Making pyrophosphate visible: the first precipitable and real-time fluorescent sensor for pyrophosphate in aqueous solution

An in situ generated Zn²⁺ complex of di-2-(picoly) amine BINOL–DPA was presented as a precipitable and real-time fluorescent sensor for PPi with a detection limit of 95 nm, and it could be successfully applied in imaging PPi in living cells.

Fluorescent and colorimetric chemosensors for pyrophosphate

In this review, we will cover the fluorescent and colorimetric chemosensors developed for the detection of pyrophosphate (PPi) since 2010.

A highly selective SBA-15 supported fluorescent “turn-on” sensor for the fluoride anion

TSBA (or ASBA) remained stable upon prolonged exposure to UV light (losing ∼0.12% of its fluorescence intensity), and was highly selective towards F⁻ over other common anions (Cl⁻, Br⁻, I⁻, HPO₄²⁻, ACO⁻, and NO₃⁻).

Highly sensitive and selective detection of the pyrophosphate anion biomarker under physiological conditions

Self-assembled monolayers on gold of a multidentate adsorbate bearing a bis(carbazolyl)urea unit are prepared and used as a surface resonance plasmon sensor for the detection of hydrogen pyrophosphate anions under physiological conditions.

Chromogenic and fluorogenic chemosensors and reagents for anions. A comprehensive review of the years 2010-2011

This review focuses on examples reported in the years 2010-2011 dealing with the design of chromogenic and fluorogenic chemosensors or reagents for anions.

A PEGylated fluorescent turn-on sensor for detecting fluoride ions in totally aqueous media and its imaging in live cells

Owing to the considerable significance of fluoride anions for health and environmental issues, it is of great importance to develop methods that can rapidly, sensitively and selectively detect the fluoride anion in aqueous media and biological samples. Herein, we demonstrate a robust fluorescent turn-on sensor for detecting the fluoride ion in a totally aqueous solution. In this study, a biocompatible hydrophilic polymer poly(ethylene glycol) (PEG) is incorporated into the sensing system to ensure water solubility and to enhance biocompatibility. tert-Butyldiphenylsilyl (TBDPS) groups were then covalently introduced onto the fluorescein moiety, which effectively quenched the fluorescence of the sensor. Upon addition of fluoride ion, the selective fluoride-mediated cleavage of the Si-O bond leads to the recovery of the fluorescein moiety, resulting in a dramatic increase in fluorescence intensity under visible light excitation. The sensor is responsive and highly selective for the fluoride anion over other common anions; it also exhibits a very low detection limit of 19 ppb. In addition, this sensor is operative in some real samples such as running water, urine, and serum and can accurately detect fluoride ions in these samples. The cytotoxicity of the sensor was determined to be Grade I toxicity according to United States Pharmacopoeia and ISO 10993-5, suggesting the very low cytotoxicity of the sensor. Moreover, it was found that the senor could be readily internalized by both HeLa and L929 cells and the sensor could be utilized to track fluoride level changes inside the cells.

Highly selective colorimetric sensing pyrophosphate in water by a NBD-phenoxo-bridged dinuclear Zn(II) complex

A novel NBD-phenoxo-bridged dinuclear Zn(II) complex is found to be an effective colorimetric sensor for pyrophosphate (PPi) in pure aqueous solution over a wide pH range. This sensor shows high binding affinity (K(a)≈ 3 × 10(8) M(-1)) and high selectivity for PPi, and can be also used to assay the activity of pyrophosphatase in real time.

Zn(II)-cyclam based chromogenic sensors for recognition of ATP in aqueous solution under physiological conditions and their application as viable staining agents for microorganism

Two chromogenic complexes, L.Zn (where L is (E)-4-((4-(1,4,8,11-tetraazacyclotetradecan-1-ylsulfonyl)phenyl)diazenyl)-N,N-dimethylaniline) and its [2]pseudorotaxane form (α-CD.L.Zn), were found to bind preferentially to adenosine triphosphate (ATP), among all other common anions and biologically important phosphate (AMP, ADP, pyrophosphate, and phosphate) ions in aqueous HEPES buffer medium of pH 7.2. Studies with live cell cultures of prokaryotic microbes revealed that binding of these two reagents to intercellular ATP, produced in situ, could be used in delineating the gram-positive and the gram-negative bacteria. More importantly, these dyes were found to be nontoxic to living microbes (eukaryotes and prokaryotes) and could be used for studying the cell growth dynamics. Binding to these two viable staining agents to intercellular ATP was also confirmed by spectroscopic studies on cell growth in the presence of different respiratory inhibitors that influence the intercellular ATP generation.