Phosphate ion targeted colorimetric and fluorescent probe and its use to monitor endogeneous phosphate ion in a hemichannel-closed cell

Fluorescent probe 1, the first inorganic phosphate (Pi) targeted colorimetric and fluorescent probe to detect endogenous Pi in hemichannel-closed cells, has been developed. Probe 1 undergoes a unique Pi induced hydrolytic reaction in DMSO-HEPES (V/V = 9:1) buffered (0.02 M, pH 7.4) solutions that produces a colorimetric change associated with a 62 nm red-shift in the UV-vis absorption maximum and up to a 780-fold enhancement in the fluorescence intensity. The mechanistic proposal that these spectroscopic changes are associated with reaction Pi with 1 to form coumarin gains support from the results of theoretical calculations and mass spectrometry studies. Observations made in fluorescence imaging studies with HeLa cells and C. elegans show that 1 can be employed to monitor Pi production in vivo caused by apyrase-catalyzed ATP hydrolysis. Moreover, probe 1 was utilized to show that apoptosis of hemichannel-closed Sf9 cells is caused by Inx3 promoted dephosphorylation of Akt (RAC serine/threonine-protein kinase), leading to an elevation of the concentration of Pi. Overall, the study has produced the first fluorescent sensor 1 for endogenous inorganic phosphate. Moreover, the utility of 1 for measuring Pi release in vitro has been demonstrated and utilized to elucidate the mechanism of Inx3 action in hemichannel-closed Sf9 cells.

Radiolabeled apoptosis imaging agents for early detection of response to therapy

Since apoptosis plays an important role in maintaining homeostasis and is associated with responses to therapy, molecular imaging of apoptotic cells could be useful for early detection of therapeutic effects, particularly in oncology. Radiolabeled annexin V compounds are the hallmark in apoptosis imaging in vivo. These compounds are reviewed from the genesis of apoptosis (cell death) imaging agents up to recent years. They have some disadvantages, including slow clearance and immunogenicity, because they are protein-based imaging agents. For this reason, several studies have been conducted in recent years to develop low molecule apoptosis imaging agents. In this review, radiolabeled phosphatidylserine targeted peptides, radiolabeled bis(zinc(II)-dipicolylamine) complex, radiolabeled 5-fluoropentyl-2-methyl-malonic acid (ML-10), caspase-3 activity imaging agents, radiolabeled duramycin, and radiolabeled phosphonium cation are reviewed as promising low-molecular-weight apoptosis imaging agents.

Selective recognition of anionic cell membranes using targeted liposomes coated with zinc(ii)-bis(dipicolylamine) affinity units

Zinc(ii)-bis(dipicolylamine) (Zn2BDPA) coated liposomes are shown to have high recognition selectivity towards vesicle and cell membranes with anionic surfaces. Robust synthetic methods were developed to produce Zn2BDPA-PEG-lipid conjugates with varying PEG linker chain length. One conjugate (Zn2BDPA-PEG2000-DSPE) was used in liposome formulations doped with the lipophilic near-infrared fluorophore DiR. Fluorescence cell microscopy studies demonstrated that the multivalent liposomes selectively and efficiently target bacteria in the presence of healthy mammalian cells and cause bacterial cell agglutination. The liposomes also exhibited selective staining of the surfaces of dead or dying human cancer cells that had been treated with a chemotherapeutic agent.

Ternary complex formation and competition quench fluorescence of ZnAF family zinc sensors

Our current understanding of the intracellular thermodynamics and kinetics of Zn(ii) ions is largely based on the application of fluorescent sensor molecules, used to study and visualize the concentration, distribution and transport of Zn(ii) ions in real time. Such agents are designed for high selectivity for zinc in respect to other biological metal ions. However, the issue of their sensitivity to physiological levels of low molecular weight Zn(ii) ligands (LMWLs) has not been addressed. We followed the effects of eight such compounds on the fluorescence of ZnAF-1 and ZnAF-2F, two representatives of the ZnAF family of fluorescein-based zinc sensors containing the N,N-bis(2-pyridylmethyl)ethylenediamine chelating unit. Fluorescence titrations of equimolar Zn(ii)-ZnAF-1 and Zn(ii)-ZnAF-2F solutions with acetate, phosphate, citrate, glycine, glutamic acid, histidine, ATP and GSH demonstrated strong fluorescence quenching. These results are interpreted in terms of an interplay of the formation of the [ZnAF-Zn(ii)-LMWL] ternary complexes and the competition for Zn(ii) between ZnAF and LMWLs. UV-vis spectroscopic titrations revealed the existence of supramolecular interactions between the fluorescein moiety of ZnAF-1 and ATP and His, which, however, did not contribute to fluorescence quenching. Therefore, the obtained results show that the ZnAF sensors, other currently used zinc sensors containing the N,N-bis(2-pyridylmethyl)ethylenediamine unit, and, in general, all sensors that do not saturate the Zn(ii) coordination sphere may co-report cellular metabolites and Zn(ii) ions, leading to misrepresentations of the concentrations and fluxes of biological zinc.

Using protein-encapsulated gold nanoclusters as photoluminescent sensing probes for biomolecules

In this study, we generated gold nanoclusters (AuNCs) using inexpensive chicken egg white proteins (AuNCs@ew) as reagents. AuNCs@ew were generated by reacting aqueous tetrachloroauric acid with diluted chicken egg white under microwave heating (90W) through subsequent heating cycles (5 min/cycle). Within 10 cycles, red photoluminescent AuNCs@ew with maximum emission wavelength at ~640 nm (λex=370 nm) were obtained. The quantum yield of the as-generated AuNCs was ~6.6%. The intact and the tryptic digest of AuNCs@ew were characterized by mass spectrometry. The results showed that the AuNCs@ew were mainly derived from ovalbumin, i.e., the major protein in egg white, encapsulated AuNCs. The AuNCs@ew also has the common features found in AuNCs@protein, which is sensitive to the presence of heavy metal ions such as Cu(2+). The photoluminescence of the AuNCs@ew was quenched with the addition of Cu(2+). Furthermore, the photoluminescence of the quenched AuNCs@ew can be restored in the presence of the molecules containing phosphate functional groups because of the strong binding affinity between Cu(2+) and phosphates. We used the AuNCs@ew-Cu(2+) conjugates as switch-on sensing probes for the detection of phosphate containing metabolites such as adenosine-5'-triphosphate (ATP) and pyrophosphate (PPi). The results showed that the photoluminescence of the sensing probes increased as the concentration of the phosphate-containing molecules in the sample solution increased. The limits of detection achieved using the AuNCs@ew-Cu(2+) for ATP and PPi were ~19 and ~5 μM, respectively. Additionally, we also demonstrated the feasibility of using the AuNCs@ew as the sensing probes for lectins such as concanavalin A (Con A) based on the molecular recognitions between the glycan ligands on the AuNCs@ew and glycan binding sites on Con A.

Discrimination of adenine nucleotides and pyrophosphate in water by a zinc complex of an anthracene-based cyclophane

Combining metal-anion coordination and π-π stacking interactions, a zinc complex of a novel anthracene-based cyclophane was designed to recognise adenine nucleoside polyphosphates. This complex was found to show selective fluorescence enhancement for ATP, ADP, AMP and PPi in neutral aqueous solution. Among them, ADP induced the largest fluorescence change to the complex, while ATP showed the strongest binding affinity to the complex. This property was used to sense ATP in the presence of excess amounts of other phosphates such as ADP, AMP, PPi and Pi.

Supramolecular clippers for controlling photophysical processes through preorganized chromophores

A novel supramolecular clipping design for influencing the photophysical properties of functional molecular assemblies, by the preorganization (clipping) of chromophores, is described. Several chromophores end functionalized with molecular recognition units were designed. These molecular recognition units serve as handles to appropriately position these systems upon noncovalent interactions with multivalent guest molecules (supramolecular clippers). Towards this goal, we have synthesized 1,5-dialkoxynaphthalene (DAN) and naphthalenediimide (NDI) functionalized with dipicolylethylenediamine (DPA) motifs. These molecules could preorganize upon noncovalent clipping with adenosine di- or triphosphates, which resulted in preassociated excimers and mixed (cofacial) charge-transfer (CT) assemblies. Chiral guest binding could also induce supramolecular chirality, not only into the individual chromophoric assembly but also into the heteromeric CT organization, as seen from the strong circular dichroism (CD) signal of the CT transition. The unique ability of this design to influence the intermolecular interactions by changing the binding strength of the clippers furthermore makes it very attractive for controlling the bimolecular photophysical processes.

Cysteamine CdS quantum dots decorated with Fe3+ as a fluorescence sensor for the detection of PPi

A new sensitive and selective fluorescence sensor for the detection of pyrophosphate (PPi) in aqueous media based on the Fe(3+) decorated cysteamine CdS QDs ([Cys-CdS QDs]-Fe(3+)) was proposed. The presence of PPi can induce the fluorescence quenching of [Cys-CdS QDs]-Fe(3+) due to the high formation constants between the phosphate group and Fe(3+). Because the complex between Fe(3+) and PPi acts as an efficient quencher, the concentration of PPi can be evaluated by tracking the degree of fluorescence quenching. The fabricated sensor was optimized to obtain the best sensor selectivity and sensitivity. Under optimal conditions, a linear relationship between the fluorescence response and the concentration of PPi was established in the range of 0.5-10 μM. The limits of detection and quantitation for PPi were found to be 0.11 and 2.78 μM, respectively. Furthermore, the proposed sensor exhibited high selectivity toward PPi relative to other common anions. The proposed sensor was successfully applied to the detection of PPi in urine samples with satisfactory results.

A bispyrene derivative as a selective fluorescent probe for RNA

A novel bispyrene compound was synthesized to selectively detect RNA through excimer emission “turn-on” at physiological pH.

Detection of CREB phosphorylation via Zr (IV) ion mediated signal amplification

Phosphorylation of protein plays a vital regulatory role in a variety of biological processes. We herein report a novel method to assay the level of phosphorylated cAMP-response element binding protein (CREB) via Zr(4+) mediated signal amplification using gold nanoparticle/DNA/methylene blue (GNP/DNA/MB) nanocomposites. In this method the probe DNA immobilized at a gold electrode surface can specifically and efficiently recognize the phosphorylated target protein CREB. Then Zr(4+) links the phosphorylated CREB with GNP/DNA/MB nanocomposites by coordinating the phosphate groups on both CREB and the nanocomposites. Since the nanocomposites can provide high sensitivity (limit of detection: 0.25 nM) for the detection, efficient and highly sensitive bioanalysis of the expression level of phosphorylated protein CREB in human placenta tissues has also been conducted in this work. Our method is reported which shows acceptable stability, reproducibility for assaying of the protein phosphorylation states in real biosamples under physiological and pathological conditions with great potential for clinical applications in future.

In-situ generation of differential sensors that fingerprint kinases and the cellular response to their expression

Mitogen-activated protein (MAP) kinases are responsible for many cellular functions, and their malfunction manifests itself in several human diseases. Usually, monitoring the phosphorylation states of MAP kinases in vitro requires the preparation and purification of the proteins or Western blotting. Herein, we report an array sensing approach for the differentiation of MAP kinases and their phosphorylated counterparts in vitro. This technique utilizes a library of differential receptors created in situ containing peptides known for affinity to MAP kinases, and a Zn(II)-dipicolylamine complex that binds phosphate groups on proteins. An indicator-displacement assay signals the binding of the individual receptors to the kinases, while chemometrics is used to create a fingerprint for the kinases and their state of activity. For example, linear discriminant analysis correctly identified kinase activity with a classification accuracy of 97.5% in vitro, while the cellular response to kinase expression was classified with 100% accuracy.

Magnetite nanoparticle-induced fluorescence quenching of adenosine triphosphate-BODIPY Conjugates: application to adenosine triphosphate and pyrophosphate sensing

We report that magnetite nanoparticles (Fe3O4 NPs) act as an efficient quencher for boron dipyrromethene-conjugated adenosine 5'-triphosphate (BODIPY-ATP) that is highly fluorescent in bulk solution. BODIPY-ATP molecules attached to the surface of Fe3O4 NPs through the coordination between the triphosphate group of BODIPY-ATP and Fe(3+)/Fe(2+) on the NP surface. The formed complexes induced an apparent reduction in the BODIPY-ATP fluorescence resulting from an oxidative-photoinduced electron transfer (PET) from the BODIPY-ATP excited state to an unfilled d shell of Fe(3+)/Fe(2+) on the NP surface. A comparison of the Stern-Volmer quenching constant between Fe(3+) and Fe(2+) suggests that Fe(3+) on the NP surface dominantly controls this quenching process. The efficiency for Fe3O4 NP-induced fluorescence quenching of the BODIPY-ATP was enhanced by increasing the concentration of Fe3O4 NPs and lowering the pH of the solution to below 6.0. We found that pyrophosphate and ATP compete with BODIPY-ATP for binding to Fe3O4 NPs. Thus, we amplified BODIPY-ATP fluorescence in the presence of increasing the pyrophosphate and ATP concentration; the detection limits at a signal-to-noise ratio of 3 for pyrophosphate and ATP were determined to be 7 and 30 nM, respectively. The Fe3O4 NP-based competitive binding assay detected ATP and pyrophosphate in only 5 min. The selectivity of this assay for ATP over metal ions, amino acids, and adenosine analogues is particularly high. The practicality of using the developed method to determine ATP in a single drop of blood is also validated.

Novel reversible Zn2+-assisted biological phosphate "turn-on" probing through stable aryl-hydrazone salicylaldimine conjugation that attenuates ligand hydrolysis

A novel reversible zinc(II) chemosensing ensemble (2·Zn(2+)) allows for selective "turn-on" fluorescence sensing of ATP and PPi in aqueous media (detection limits: 2.4 and 1.0 μM, respectively) giving selective binding patterns: ATP ∼ PPi > ADP ≫ AMP > monophosphates ≈ remaining ions tested. The conjugated hydrazone [C═N-NH-R] resists hydrolysis considerably, compared to the imine [C═N-CH2-R, pyridin-2-ylmethanamine] functionality, and generalizes to other chemosensing efforts. Prerequisite Zn(2+)·[O(phenol)N(imine)N(pyr)] binding is selective, as determined by UV-vis and NMR spectroscopy; ATP or PPi extracts Zn(2+) to regenerate the ligand-fluorophore conjugate (PPi: turn-on, 512 nm; detection limit, 1.0 μM). Crystallography, 2-D NMR spectroscopy, and DFT determinations (B3LYP/631g*) support the nature of compound 2. 2-Hydrazinyl-pyridine-salicylaldehyde conjugation is unknown, as such; a paucity of chemosensing-Zn(2+) binding reports underscores the novelty of this modifiable dual cation/anion detection platform. A combined theoretical and experimental approach reported here allows us to determine both the potential uniqueness as well as drawbacks of this novel conjugation.

Fluorine NMR reporter for phosphate anions

A fluorine-labelled zinc(II)-dipicolylamine coordination complex reports the presence of phosphate anions in aqueous solution, especially pyrophosphate and ADP, and is used to monitor the enzymatic hydrolysis of ATP.

Effect of Bridging Anions on the Structure and Stability of Phenoxide Bridged Zinc Dipicolylamine Coordination Complexes

A series of four related phenol derivatives, with 2,2'-dipicolylamine substituents at the ortho positions, were prepared and their Zn2+ coordination complexes studied by spectroscopic methods. X-ray crystal diffraction analysis of a dinuclear zinc complex with two bridging acetate anions showed a ternary structure with highly charged interior and lipophilic exterior, which helps explain why this class of water-soluble complexes can effectively diffuse through cell membranes. The stability of the dinuclear zinc complexes in aqueous solution was found to be strongly anion dependent; that is, bridging oxyanions, such as acetate and pyrophosphate, lock the two Zn2+ cations to the surrounding ligand and greatly enhance ligand/zinc affinity. Overall, the results provide new insight into the structural and mechanistic factors that control the recognition and chemosensing performance of phenoxide bridged dipicolylamine molecular probes.

Glutathione-functionalized graphene quantum dots as selective fluorescent probes for phosphate-containing metabolites

Bright blue fluorescent glutathione-functionalized graphene quantum dots (GQDs@GSH) were prepared by a one-step pyrolysis method with a fluorescence quantum yield as high as 33.6%. Futhermore, the obtained GQDs@GSH can be used as a probe to estimate the ATP level in cell lysates and human blood serum.

Convenient Synthesis of Multivalent Zinc(II)-Dipicolylamine Complexes for Molecular Recognition

A pair of novel dipicolylamine ligands bearing isothiocyanate groups were used as conjugation reagents to prepare multivalent molecules with anionic recognition capability. The isothiocyanates were reacted with two classes of dendritic scaffolds bearing primary amines, squaraine rotaxanes and PAMAM dendrimers, and the products were converted into water soluble zinc(II) coordination complexes. The multivalent squaraine rotaxanes exhibit high fluorescence quantum yields in water and are very well suited for biological imaging applications.

Detection of phosphorylation states by intermolecular sensitization of lanthanide-peptide conjugates

The luminescence of a designed peptide equipped with a coordinatively-unsaturated lanthanide complex is modulated by the phosphorylation state of a serine residue in the sequence. While the phosphorylated state is weakly emissive, even in the presence of an external antenna, removal of the phosphate allows coordination of the sensitizer to the metal, yielding a highly emissive supramolecular complex.

Lanthanide(III) complexes of bis-semicarbazone and bis-imine-substituted phenanthroline ligands: solid-state structures, photophysical properties, and anion sensing

Phenanthroline-based hexadentate ligands L(1) and L(2) bearing two achiral semicarbazone or two chiral imine moieties as well as the respective mononuclear complexes incorporating various lanthanide ions, such as La(III), Eu(III), Tb(III), Lu(III), and Y(III) metal ions, were synthesized, and the crystal structures of [ML(1)Cl(3)] (M=La(III), Eu(III), Tb(III), Lu(III), or Y(III)) complexes were determined. Solvent or water molecules act as coligands for the rare-earth metals in addition to halide anions. The big Ln(III) ion exhibits a coordination number (CN) of 10, whereas the corresponding Eu(III), Tb(III), Lu(III), and Y(III) centers with smaller ionic radii show CN=9. Complexes of L(2), namely [ML(2)Cl(3)] (M=Eu(III), Tb(III), Lu(III), or Y(III)) ions could also be prepared. Only the complex of Eu(III) showed red luminescence, whereas all the others were nonluminescent. The emission properties of the Eu derivative can be applied as a photophysical signal for sensing various anions. The addition of phosphate anions leads to a unique change in the luminescence behavior. As a case study, the quenching behavior of adenosine-5'-triphosphate (ATP) was investigated at physiological pH value in an aqueous solvent. A specificity of the sensor for ATP relative to adenosine-5'-diphosphate (ADP) and adenosine-5'-monophosphate (AMP) was found. (31)P NMR spectroscopic studies revealed the formation of a [EuL(2)(ATP)] coordination species.

Organelle-localizable fluorescent chemosensors for site-specific multicolor imaging of nucleoside polyphosphate dynamics in living cells

ATP and its derivatives (nucleoside polyphosphates (NPPs)) are implicated in many biological events, so their rapid and convenient detection is important. In particular, live cell detection of NPPs at specific local regions of cells could greatly contribute understanding of the complicated roles of NPPs. We report herein the design of two new fluorescent chemosensors that detect the dynamics of NPPs in specific regions of living cells. To achieve imaging of NPPs on plasma membrane surfaces (2-2Zn(II)), a lipid anchor was introduced into xanthene-based Zn(II) complex 1-2Zn(II), which was previously developed as a turn-on type fluorescent chemosensor for NPPs. Meanwhile, for subcellular imaging of ATP in mitochondria, we designed rhodamine-type Zn(II) complex 3-2Zn(II), which possesses a cationic pyronin ring instead of xanthene. Detailed spectroscopic studies revealed that 2-2Zn(II) and 3-2Zn(II) can sense NPPs with a several-fold increase of their fluorescence intensities through a sensing mechanism similar to 1-2Zn(II), involving binding-induced recovery of the conjugated form of the xanthene or pyronin ring. In live cell imaging, 2-2Zn(II) containing a lipid anchor selectively localized on the plasma membrane surface and detected the extracellular release of NPPs during cell necrosis induced by streptolysin O. On the other hand, rhodamine-type complex 3-2Zn(II) spontaneously localized at mitochondria inside cells, and sensed the local increase of ATP concentration during apoptosis. Multicolor images were obtained through simultaneous use of 2-2Zn(II) and 3-2Zn(II), allowing detection of the dynamics of ATP in different cellular compartments at the same time.

Fluorescence detection of adenosine triphosphate in an aqueous solution using a combination of copper(II) complexes

Fluorescent ligands have been designed to form ternary complexes with a Cu(II) cation and phosphates in a buffer solution at physiological pH 7.4. It has been shown that a combination of two different ligands and CuCl(2) allows one to achieve high adenosine triphosphate/adenosine diphosphate, adenosine 5'-monophosphate selectivity, and ratiometric fluorescence sensing, while separately each ligand complex does not have such properties.

Using gold nanoclusters as selective luminescent probes for phosphate-containing metabolites

Glutathione-bound gold nanoclusters (AuNCs@GSH) can emit reddish photoluminescence under illumination of ultraviolet light. The luminescence of the AuNCs@GSH is quenched when chelating with iron ions (AuNCs@GSH-Fe(3+)), presumably resulting from the effective electron transfer between the nanoclusters and iron ions. Nevertheless, we found that the luminescence of the gold nanoclusters can be restored in the presence of phosphate-containing molecules, which suggested the possibility of using AuNCs@GSH-Fe(3+) complexes as the selective luminescent switches for phosphate-containing metabolites. Phosphate-containing metabolites such as adenosine-5'-triphosphate (ATP) and pyrophosphate play an important role in biological systems. In this study, we demonstrated that the luminescence of the AuNCs@GSH-Fe(3+) is switched-on when mixing with ATP and pyrophosphate, which can readily be observed by the naked eye. It results from the high formation constants between phosphates and iron ions. When employing fluorescence spectroscopy as the detection tool, quantitative analysis for phosphate-containing metabolites such as ATP and pyrophosphate can be conducted. The linear range for ATP and pyrophosphate is 50 μM to sub-millimolar, while the limit of detection for ATP and pyrophosphate are ∼43 and ∼28 μM, respectively. Additionally, we demonstrated that the luminescence of the AuNCs@GSH-Fe(3+) can also be turned on in the presence of phosphate-containing metabolites from cell lysates and blood plasma.

Bis- and tris-naphthoimidazolium derivatives for the fluorescent recognition of ATP and GTP in 100% aqueous solution

Naphthoimidazolium groups can form unique ionic hydrogen bonds with anions as imidazolium moieties, and in addition, they are fluorescent, so no further elaborative synthesis is needed to introduce a fluorescent group. In this paper, three naphthoimidazolium derivatives were synthesized and studied for the recognition of nucleotides. Compound 1 composed of a single naphthoimidazolium group and quaternary ammonium group did not show any significant fluorescent changes with various anions and nucleotides, such as ATP, GTP, CTP, TTP, UTP, ADP and AMP. A tripodal compound 3 bearing three naphthoimidazolium groups and three quaternary ammonium groups, respectively, showed large fluorescence enhancements with UTP, CTP and TTP and moderate fluorescence enhancements with ATP and pyrophosphate and a fluorescence quenching effect with GTP. On the other hand, compound 2 bearing two naphthoimidazolium groups and two quaternary ammonium groups displayed a selective fluorescence enhancement with ATP and a selective fluorescence quenching effect with GTP in 100% aqueous solution.

Conversion of molecular information by luminescent nanointerface self-assembled from amphiphilic Tb(III) complexes

A novel amphiphilic Tb(3+) complex (TbL(+)) having anionic bis(pyridine) arms and a hydrophobic alkyl chain is developed. It spontaneously self-assembles in water and gives stable vesicles that show sensitized luminescence of Tb(3+) ions at neutral pH. This TbL(+) complex is designed to show coordinative unsaturation, i.e., water molecules occupy some of the first coordination spheres and are replaceable upon binding of phosphate ions. These features render TbL(+) self-assembling receptor molecules which show increase in the luminescence intensity upon binding of nucleotides. Upon addition of adenosine triphosphate (ATP), significant amplification of luminescent intensity was observed. On the other hand, ADP showed moderately increased luminescence and almost no enhancement was observed for AMP. Very interestingly, the increase in luminescence intensity observed for ATP and ADP showed sigmoidal dependence on the concentration of added nucleotides. It indicates positive cooperative binding of these nucleotides to TbL(+) complexes preorganized on the vesicle surface. Self-assembly of amphiphilic Tb(3+) receptor complexes provides nanointerfaces which selectively convert and amplify molecular information of high energy phosphates linked by phosphoanhydride bonds into luminescence intensity changes.

Mononuclear Zn(II)- and Cu(II)-complexes of a hydroxynaphthalene-derived dipicolylamine: fluorescent sensing behaviours toward pyrophosphate ions

Mononuclear Zn(II)-DPA and Cu(II)-DPA complexes crafted on 2-hydroxy-6-cyanonaphthalene fluorophore selectively recognize PPi over ATP and other anions including inorganic phosphates in aqueous medium, showing turn-on type fluorescence enhancements. Coordination of a hydroxyl group of the fluorophore, directly or in alkoxy form, to the central metal ion is crucial for the sensing processes. Both the complexes elicit a fluorescence increase in a time-dependent fashion.