Simple but Effective Way to Sense Pyrophosphate and Inorganic Phosphate by Fluorescence Changes

A change in metal cation switches selectivity of a phospholipid sensor from phosphatidic acid to phosphatidylserine

Phosphatidic acid and phosphatidylserine are anionic phospholipids with emerging signalling roles in cells. Determination of how phosphatidic acid and phosphatidylserine change location and quantity in cells over time requires selective fluorescent sensors that can distinguish these two anionic phospholipids. However, the design of such synthetic sensors that can selectively bind and respond to a single phospholipid within the complex membrane milieu remains challenging. In this work, we present a simple and robust strategy to control the selectivity of synthetic sensors for phosphatidic acid and phosphatidylserine. By changing the coordination metal of a dipicolylamine (DPA) ligand from Zn(II) to Ni(II) on the same synthetic sensor with a peptide backbone, we achieve a complete switch in selectivity from phosphatidic acid to phosphatidylserine in model lipid membranes. Furthermore, this strategy was largely unaffected by the choice and the position of the fluorophores. We envision that this strategy will provide a platform for the rational design of targeted synthetic phospholipid sensors to probe plasma and intracellular membranes.

Kinetically Inert Macrocyclic Europium(III) Receptors for Phosphate

The significant role that phosphate plays in environmental water pollution and biomedical conditions such as hyperphosphatemia highlights the need to develop robust receptors that can sequester the anion effectively and selectively from complex aqueous media. Toward that goal, four macrocyclic tris-bidentate 1,2-hydroxypyridonate (HOPO) europium(III) complexes containing either a cyclen, cyclam, TACN, or TACD ligand cap were synthesized and evaluated as phosphate receptors. The solubility of EuIII-TACD-HOPO in water was insufficient for luminescent studies. Whereas EuIII-cyclen-HOPO is eight coordinate with two inner-sphere water molecules, both EuIII-cyclam-HOPO and EuIII-TACN-HOPO are nine coordinate with three inner-sphere water molecules, suggesting that the two coordination states are very close in energy. As observed previously with linear analogues of tripodal HOPO complexes, there is no relationship between the number of inner-sphere water molecules and the affinity of the complex for phosphate. Whereas all three complexes do bind phosphate, EuIII-cyclen-HOPO has the highest affinity for phosphate with the anion displacing both of its inner-sphere water molecules. On the other hand, only one or two of the three inner-sphere water molecules of EuIII-TACN-HOPO and EuIII-cyclam-HOPO are displaced by phosphate, respectively. All three complexes are highly selective for phosphate over other anions, including arsenate. All three complexes are highly stable. EuIII-cyclen-HOPO and, to a lesser extent, EuIII-TACN-HOPO are more kinetically inert than the linear EuIII-Ser-HOPO. EuIII-cyclam-HOPO, on the other hand, is not. This study highlights the significant effect that minor changes in the ligand cap can have on both the ligand exchange rate and affinity for phosphate of tripodal 1,2-dihydroxypyridinonate complexes.

A pyridine dicarboxylate based hydrazone Schiff base for reversible colorimetric recognition of Ni2+ and PPi

A pyridine dicarboxylate Schiff-base DAS was synthesized for cascade colorimetric recognition of Ni²⁺ and PPi. The selectivity and sensitivity of chemosensor DAS was investigated through colorimetric and UV-vis studies in MeOH-PBS (5 : 1, v/v, pH = 7.4). The chemosensor formed a 2 : 1 complex with Ni²⁺ metal ions with a binding constant of K_a = 3.07 × 10³ M^-2. Besides, a plausible sensing mechanism is confirmed by single crystal X-ray diffraction (SC-XRD), Job's plot and Benesi-Hildebrand plot (B-H plot) experiments. Furthermore, the DAS-Ni²⁺ ensemble formed 'in situ' was used to selectively recognise PPi. The limit of detection (LOD) of DAS for Ni²⁺ was found to be 0.14 μM and that of the DAS-Ni²⁺ ensemble for PPi was found to be 0.33 μM. Also, the potential of the chemosensor has been applied for solid state detection of Ni²⁺ as well as to mimic the 'INHIBIT' logic gate on the addition of Ni²⁺ ions and PPi.

A novel AIE-active imidazolium macrocyclic ratiometric fluorescence sensor for pyrophosphate anion

An imidazolium bridged macrocyclophane was synthesized as a ratiometric fluorescence sensor with aggregation-induced emission (AIE) characteristic to detect pyrophosphate anion with high selectivity among various anions. In the presence of zinc ion, macrocyclophane can form aggregates through complexation with pyrophosphate anion and emit ratiometric fluorescence, resulting from an enhancement in its aggregate-state emission and a reduction in its monomer emission. This AIE-active macrocycle showed great potential as a ratiometric fluorescence receptor.

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.

Design and applications of metal-based molecular receptors and probes for inorganic phosphate

Inorganic phosphate has numerous biomedical functions. Regulated primarily by the kidneys, phosphate reaches abnormally high blood levels in patients with advanced renal diseases. Since phosphate cannot be efficiently removed by dialysis, the resulting hyperphosphatemia leads to increased mortality. Phosphate is also an important component of the environmental chemistry of surface water. Although required to secure our food supply, inorganic phosphate is also linked to eutrophication and the spread of algal blooms with an increasing economic and environmental burden. Key to resolving both of these issues is the development of accurate probes and molecular receptors for inorganic phosphate. Yet, quantifying phosphate in complex aqueous media remains challenging, as is the development of supramolecular receptors that have adequate sensitivity and selectivity for use in either blood or surface waters. Metal-based receptors are particularly well-suited for these applications as they can overcome the high hydration enthalpy of phosphate that limits the effectiveness of many organic receptors in water. Three different strategies are most commonly employed with inorganic receptors for anions: metal extrusion assays, responsive molecular receptors, and indicator displacement assays. In this review, the requirements for molecular receptors and probes for environmental applications are outlined. The different strategies deployed to recognize and sense phosphate with metal ions will be detailed, and their advantages and shortfalls will be delineated with key examples from the literature.

Masking Phosphate with Rare-Earth Elements Enables Selective Detection of Arsenate by Dipycolylamine-ZnII Chemosensor

Functional reassessment of the phosphate-specific chemosensors revealed their potential as arsenate detectors. A series of dipicolylamine (Dpa)-ZnII chemosensors were screened, among which acridine Dpa-ZnII chemosensor showed the highest capability in sensing arsenate. The presence of excess ZnII improved sensitivity and strengthened the binding between acridine Dpa-ZnII complex to arsenate as well as phosphate. However, due to their response to phosphate, these sensors are not suited for arsenate detection when phosphate is also present. This study demonstrated for the first time that rare-earth elements could effectively mask phosphate, allowing the specific fluorescence detection of arsenate in phosphate-arsenate coexisting systems. In addition, detection of arsenate contamination in the real river water samples and soil samples was performed to prove its practical use. This sensor was further employed for the visualization of arsenate and phosphate uptake in vegetables and flowering plants for the first time, as well as in the evaluation of a potent inhibitor of arsenate/phosphate uptake.

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.

Signal-on fluorescence assay for pyrophosphate ions based on DNA-stabilized silver nanoclusters

Pyrophosphate anion (P₂ O₇ ^4- , PPi) is considered as a potential biomarker for arthritic diseases because high levels of PPi may result in calcium pyrophosphate dehydrate crystal deposition diseases. In this study, a simple fluorescence method for PPi was demonstrated by organic integration of the efficient fluorescence quenching ability of copper ions to DNA-scaffolded silver nanoclusters and the strong affinity of PPi towards copper ions. This simple fluorescence sensor showed a low detection limit (0.28 μM based on signal/noise = 3) towards the detection of PPi. Practical application of this method was also validated by detection of PPi in the synovial fluid.

A Conjugated Polymer Fluorescent Sensor for Continuous Identification of Copper(II) and Pyrophosphate in Blood Serum and Synovial Fluid

A novel "on-off-on" super-sensitive conjugated polymer fluorescence sensor (PPE-DPA) was developed and it was applied to realize the continuous recognition of Cu²⁺ and pyrophosphate (PPi). The fluorescence intensity decreased linearly with the change of Cu²⁺ from 0.05 to 5.0 μmol L^-1 and the limit of detection was 24 nmol L^-1. The fluorescence intensity was linearly enhanced with the increase of PPi from 0.5 to 12.0 μmol L^-1 and the limit of detection was 230 nmol L^-1. In addition, this method was applied to detect PPi in the blood serum and synovial fluid of patients with arthritis and satisfactory results were obtained. Thus, the PPE-DPA is not only an effective tool for detecting Cu²⁺ and PPi in samples, but also presents a potential way to diagnose arthritis.

Fluorescent Chemosensors for Various Analytes Including Reactive Oxygen Species, Biothiol, Metal Ions, and Toxic Gases

The development of fluorescent chemosensors for various analytes has been actively pursued by chemists. Since their inception, these efforts have led to many new sensors that have found wide applications in the fields of chemistry, biology, environmental science, and physiology. The search for fluorescent chemosensors was initiated by a few pioneering groups in the late 1970s and 1980s and blossomed during the last two decades to include more than hundreds of research groups around the world. The targets for these sensors vary from metal ions, anions, reactive oxygen/nitrogen species, biothiols, and toxic gases. Our group has made contributions to this area in last 18 years. In this perspective, we briefly introduce the history of chemosensors and review studies that we have carried out.

Acridine-based fluorescence chemosensors for selective sensing of Fe3+ and Ni2+ ions

Two novel acridine-based fluorescence chemosensors (L1 and L2) were prepared and their metal ions sensing properties were investigated. L1 (L2) exhibited an excellent selective fluorescence response toward Fe³⁺ (Ni²⁺) and the stoichiometry ratio of L1-Fe³⁺ and L2-Ni²⁺ were 1:1. The detection limits of L1 and L2 were calculated by the fluorescence titration to be 4.13μM and 1.52μM, respectively, which were below the maximum permissive level of Fe³⁺ and Ni²⁺ ions in drinking water set by the EPA. The possible mechanism of the fluorescence detection of Fe³⁺ and Ni²⁺ had been proposed according to the analysis of Job's plot, IR spectra and ESI-MS. The determination of Fe³⁺ and Ni²⁺ ions in living cells had been applied successfully.

Fluorenone based fluorescent probe for selective "turn-on" detection of pyrophosphate and alanine

To sense biologically important entities with different size and dimensions, a fluorenone based fluorescent receptor was designed and synthesized. Probe 1 displayed a distinct fluorescence enhancement emission at 565nm for pyrophosphate and 530nm for alanine in polar solvent. The fluorescence titration experiments confirm 1:1 stoichiometric ratio with high-binding constant and very low limit of detection (LoD) values. Receptor 1 showed a highly selective and sensitive recognition to HP₂O₇^3- and to alanine over other competitive anions and amino acids. In addition, the fluorescence lifetime measurement and reversible binding study results support the practical importance of 1.

Fluorescence and chemiluminescence behavior of distyrylbenzene bearing two arms of dipicolylaminomethyl groups: Interactions with zinc ion and ATP

The absorption and fluorescence spectral study of the distyrylbenzene bearing two arms of the dipicolylaminomethyl groups, the effective ligands for Zn²⁺, was studied in the presence of Zn²⁺ and ATP. Upon complexation of the distyrylbenzene with zinc ions in acetonitrile, enhancement of the fluorescence intensity was observed due to inhibition of intramolecular PET (photo-induced electron transfer) quenching, but no effect was found in aqueous media because the equilibrium laid to the free form of the ligands. In contrast, the addition of ATP disodium salt was effective to enhance the fluorescence intensity of the combination of the distyrylbenzne and Zn²⁺ in aqueous media. This assembly was applied to the peroxyoxalate chemiluminescence system and a significant increase in the intensity was observed, which provides a potential detection for ATP by chemiluminescence.

Are two better than one? Comparing intermolecular and intramolecular indicator displacement assays in pyrophosphate sensors

Peptide receptors with Zn(ii)-DPA units and a covalently bound fluorescent coumarin indicator on an oxazole-containing scaffold are shown to function as more selective pyrophosphate sensors than the analogous chemosensing ensembles in indicator displacement assays.

A hydrazone based probe for selective sensing of Al(iii) and Al(iii)-probe complex mediated secondary sensing of PPi: framing of molecular logic circuit and memory device and computational studies

A hydrazone-based conjugate acts as a dual channel sensor towards Al³⁺and PPi in H₂O–MeOH with excellent sensing capability in live cells.

Fluorescence Sensing of Inorganic Phosphate and Pyrophosphate Using Small Molecular Sensors and Their Applications

The aim of this contribution is to provide an introduction and a brief summary of the principle of fluorescence molecular sensors specific to inorganic phosphate (Pi) and inorganic pyrophosphate (PPi) as well as their applications. In our introduction we describe the impact of both Pi and PPi in the living organism and in the environment, followed by a description of the principle of fluorescence molecular sensors and the sensing mechanism in solution. We then focus on exciting research which has emerged in recent years on the development of fluorescent sensors specific to Pi and PPi, categorized by chemical interactions between the sensor and the target molecule, such as hydrogen bonding, coordination chemistry, displacement assay, aggregation induced emission or quenching, and chemical reactions.

A multi-state fluorescent switch based on a diarylethene with an acridine unit

A new asymmetrical fluorescent diarylethene derivative with an acridine unit was synthesized by Schiff base condensation. The derivative was sensitive to lights and special metal ions. Stimulated by UV/vis lights and Zn²⁺, distinct changes were observed in UV-vis and fluorescent spectra. Upon addition of Zn²⁺, the derivative emission peak was blue-shifted by 34nm and the emission intensity was enhanced by 16 fold, accompanied by the fluorescent color changed from red to light yellow, due to the formation of a 1:1 metal/ligand complex. The complex exhibited excellent fluorescence switching upon irradiation with UV light. Taking advantage of the lights and Zn²⁺ stimuli (inputs), and fluorescence intensity at 580nm (output), a molecular logic gate was constructed. Moreover, a new absorption band centered at 420-450nm emerged upon exposure to Zn²⁺. The dramatic color change of the solution made the 'naked-eyes' detection of Zn²⁺ possible.

Selective detection of inorganic phosphates in live cells based on a responsive fluorescence probe

A new activatable fluorescence probe has been designed and synthesized for inorganic phosphate detection in buffer and live cells.

Pyrophosphate Sensor Based on Principal Component Analysis of Conjugated Polyelectrolyte Fluorescence

The pyrophosphate anion (PPi) plays an important role in biochemical processes. Therefore, a simple but reliable analytical technique is essential for selective detection of PPi in biochemical systems. Here, we present a principal component analysis (PCA) method for analytical determination of PPi concentration using a fluorescent conjugated polyelectrolyte (CPE) combined with a polyamine modifier. The CPE has anionic side chains and dissolves molecularly in water, as indicated by its structured fluorescence emission spectrum. However, addition of tris(3-aminoethyl)amine (tetraamine or N4) quenches the CPE fluorescence emission. Tetraamine, which is a polycation at neutral pH, binds multiple anionic CPE chains, leading to aggregate formation, resulting in aggregation-induced fluorescence quenching. Addition of PPi to the polymer-amine aggregate reverses the process, resulting in fluorescence recovery. The relatively higher concentration of PPi compared to that of the polymer allows it to effectively compete to bind the amine, thus releasing molecularly dissolved polymer chains. Fluorescence correlation spectroscopy of the P1/N4 complex and of P1/N4/PPi confirms the change in size of the CPE aggregates that occurs upon reversible aggregation. Application of PCA to the fluorescence emission data set of standard samples yields two principal components, which are used to create a predictive model for PPi analysis. The PCA method is able to directly determine the concentration of PPi with approximately 95% accuracy within the concentration range from 100 μM to 3 mM, without the need for a reference state as is typically needed for ratiometric fluorescence assays.

Understanding Stacking Interactions between an Aromatic Ring and Nucleobases in Aqueous Solution: Experimental and Theoretical Study

Stacking interactions between aromatic compounds and nucleobases are crucial in recognition of nucleotides and nucleic acids, but a comprehensive understanding of the strength and selectivity of these interactions in aqueous solution has been elusive. To this end, model complexes have been designed and analyzed by experiment and theory. For the first time, stacking free energies between five nucleobases and anthracene were determined experimentally from thermodynamic double mutant cycles. Three different experimental methods were proposed and evaluated. The dye prefers to bind nucleobases in the order (kcal/mol): G (1.3) > T (0.9) > U (0.8) > C (0.5) > A (0.3). The respective trend of interaction free energies extracted from DFT calculations correlates to that obtained experimentally. Analysis of the data suggests that stacking interactions dominate over hydrophobic effects in an aqueous solution and can be predicted with DFT calculations.

A Disassembly Strategy for Imaging Endogenous Pyrophosphate in Mitochondria by Using an Fe(III) -salen Complex

Inorganic pyrophosphate (PPi) is produced from nucleoside triphosphates in important biosynthetic reactions and is considered a diagnostic marker for various diseases, such as cancer, crystal deposition disease, and arthritis. Traditional methods for biological PPi detection rely on off-line analytics after sample destruction. Molecular probes for imaging this biologically important analyte with temporal and spatial control in living cells are currently in demand. Herein, we report an Fe(III) -salen complex as the first small reaction-based probe for endogenous mitochondrial PPi following a disassembly approach. Significantly, we successfully applied this complex for the detection of increased cellular PPi levels, and its performance was not affected by the presence of mitochondrial ATP in living cells.

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.

A Fluorescent Sensor and Gel Stain for Detection of Pyrophosphorylated Proteins

The design and synthesis of a fluorescent sensor of diphosphate esters along with its application for in-gel detection is described. Dinuclear zinc complex 1 selectively binds diphosphate esters in the presence of various other functional groups, including monophosphate esters. Complex 1 also constitutes a competent stain for visualization of pyrophosphorylated proteins in polyacrylamide gels. This reagent will facilitate the validation and exploration of protein pyrophosphorylation.

A simple-structured acridine derivative as a fluorescent enhancement chemosensor for the detection of Pd2+ in aqueous media

4,5-Bis(hydroxymethyl) acridine (sensor 1) has been discovered and synthesized as a simple-structured Pd(2+) fluorescent probe. Sensor 1 showed highly selective recognition toward Pd(2+) over other examined metal ions in aqueous solution. Under the optimized condition, fluorescence intensity was linearly proportional to the concentration of Pd(2+) in the 0-1 μM concentration range with detection limits of 0.021 μM. The EDTA-adding and stoichiometry experiments indicated that sensor 1 was a reversible chemosensor for Pd(2+) with a 2:1 ligand/metal complex at neutral pH. Moreover, the sensor 1 was also successfully applied to determination of Pd(2+) in water samples and palladium-containing catalyst, which made it attractive for sensing applications.

A new fluorescent chemosensor for highly selective and sensitive detection of inorganic phosphate (Pi) in aqueous solution and living cells

A new fluorescein-based chemosensor, FP-Fe³⁺, was developed for the detection of inorganic phosphate (Pi) in aqueous solution and living cells.

Tetraphenylethylene imidazolium macrocycle: synthesis and selective fluorescence turn-on sensing of pyrophosphate anions

A novel tetraphenylethylene imidazolium macrocycle was found to be able to form an aggregate with a pyrophosphate anion in water, which gives a characteristic aggregation-induced emission fluorescence.

Detecting biologically relevant phosphates with locked salicylaldehyde probes in water

This communication describes a disassembly based approach for the detection of biologically relevant di- and tri-phosphates in water using locked fluorescent salicylaldehyde probes.

The phenanthroimidazole-based dizinc(ii) complex as a fluorescent probe for the pyrophosphate ion as generated in polymerase chain reactions and pyrosequencing

The phenanthroimidazole-based dizinc(II) complex is an efficient fluorescent probe for the pyrophosphate ion (PPi) in water with a very low detection limit, and also used to detect PPi released from DNA polymerization chain reaction.

Dual channel selective fluorescent detection of Al3+ and PPi in mixed aqueous media: DFT studies and cell imaging applications

A new, easily synthesizable chemosensor, DFC-EN-p-Ph-NO2, acts as a dual channel (colori- and fluorimetric) sensor for Al³⁺ and PPi.

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.

The synthesis of UDP-selective fluorescent probe and its imaging application in living cells

A perylene-based probe was developed for uridine diphosphate (UDP) sensing and cell imaging. The probe presented about 4-fold fluorescence enhancement in the presence or absence of 100equiv UDP. The selectivity toward UDP over other phosphor-containing anions was observed. The selective UDP sensing was speculated to be related to the binding affinities of Zn(2+) ions in sensor with the uridine and phosphate moieties of UDP. Furthermore, this probe was also applied to image of UDP in living cells.

Identification and characterization of an ecto-pyrophosphatase activity in intact epimastigotes of Trypanosoma rangeli

In this study, we performed the molecular and biochemical characterization of an ecto-enzyme present in Trypanosoma rangeli that is involved with the hydrolysis of extracellular inorganic pyrophosphate. PCR analysis identified a putative proton-pyrophosphatase (H⁺-PPase) in the epimastigote forms of T. rangeli. This protein was recognized with Western blot and flow cytometry analysis using an antibody against the H⁺-PPase of Arabidopsis thaliana. Immunofluorescence microscopy confirmed that this protein is located in the plasma membrane of T. rangeli. Biochemical assays revealed that the optimum pH for the ecto-PPase activity was 7.5, as previously demonstrated for other organisms. Sodium fluoride (NaF) and aminomethylenediphosphonate (AMDP) were able to inhibit approximately 75% and 90% of the ecto-PPase activity, respectively. This ecto-PPase activity was stimulated in a dose-dependent manner by MgCl₂. In the presence of MgCl₂, this activity was inhibited by millimolar concentrations of CaCl₂. The ecto-PPase activity of T. rangeli decreased with increasing cell proliferation in vitro, thereby suggesting a role for this enzyme in the acquisition of inorganic phosphate (Pi). Moreover, this activity was modulated by the extracellular concentration of Pi and increased approximately two-fold when the cells were maintained in culture medium depleted of Pi. All of these results confirmed the occurrence of an ecto-PPase located in the plasma membrane of T. rangeli that possibly plays an important role in phosphate metabolism of this protozoan.

Pyrophosphate selective recognition by a Zn2+ complex of a 2,2′-binaphthalene derivative bearing di(2-pyridylmethyl)aminomethyl groups in aqueous solution

A dinuclear zinc complex of a 2,2′-binaphthalene derivative selectively recognized a pyrophosphate anion.