Design of dual-emission chemosensors for ratiometric detection of ATP derivatives

A turn-on two-photon fluorescent probe for ATP and ADP

An acedan derivative containing Zn(II)-DPA has been developed as a two-photon probe for nucleoside phosphates, which shows enhanced fluorescence toward ATP and ADP at physiological pH 7.4 among other competing anions including AMP; the probe is permeable to cell membranes and thus can be directly used for two-photon imaging of ATP and ADP in live cells.

A highly selective fluorescent chemosensor for guanosine-5'-triphosphate via excimer formation in aqueous solution of physiological pH

A new water-soluble and fluorescent imidazolium-anthracene cyclophane 1 effectively recognizes and differentiates the biologically important GTP and ATP in 100% aqueous solution of physiological pH 7.4. Fluorescence, (1)H-NMR spectra and ab initio calculations demonstrate that excimer formation and fluorescence enhancement occur upon GTP and ATP binding, respectively, through (C-H)(+)···A(-) hydrogen bond interactions.

Labile zinc-assisted biological phosphate chemosensing and related molecular logic gating interpretations

Herein, molecular fluorescence 'OFF-ON' behavior with aqueous addition of biological phosphate and Zn(2+) is studied with Zn(2)(slys)(2)Cl(2) [H(2)slys = 6-amino-2-{(2-hydroxybenzylidene)amino}hexanoic acid], a fluorescent water-soluble complex, using various spectroscopic tools (e.g., (31)P NMR, UV-vis, emission, and CD spectroscopy) at the micromolar level. Adduct-dependent fluorescence intensity changes can be interpreted as a two-input (cation/anion) implication molecular logic gating system. A displacement study of PPi from the dizinc complex is also reported. Diphosphate and triphosphate addition/displacements were also studied. (31)P NMR spectroscopy shows gradual NMR peak shifts from bound ADP/GDP to free ADP/GDP with increasing [PPi]. In the emission spectrum, fluorescence quenching is shown: CD signal maxima decrease with addition of PPi. These displacement events are also tested with triphosphates (ATP, GTP), and their binding strength/displacement ability over ADP/GDP is quantified: PPi > ATP ≈ GTP (3.35 ± 0.77 × 10(4) M(-1) for PPi, 7.73 ± 1.79 × 10(3) M(-1) for ATP, 9.21 ± 2.88 × 10(3) M(-1) for GTP over 1·ADP). Many anions and cations were also screened for selectivity. Tubulin polymerization was assayed in the presence of 1 and its copper analogue which reflected a slight inhibition in polymerization.

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.

Fluorescent and colorimetric chemosensors for detection of nucleotides, FAD and NADH: highlighted research during 2004-2010

Due to the biological importance of nucleotides and related species, such as XNP (where X = adenosine (A), uridine (U), cytidine (C), guanosine (G), and N = mono, di, tri), FAD and NADH, the development of optical probes for these molecules has recently been an active area of research. This tutorial review focuses on the contributions between 2004-2010 concerning the fluorescent or colorimetric sensors for these biomolecules, and is organized according to their target molecule's structural classification.

Functionalization of methyl orange using cationic peptide amphiphile: colorimetric discrimination between ATP and ADP at pH 2.0

A solvatochromic and non-fluorescent acid-base indicator, methyl orange (MO) was applied to colorimetric discrimination between adenosine triphosphate (ATP) and the corresponding diphosphate (ADP) at pH 2.0 in the presence of L-glutamic acid-derived cationic peptide amphiphile 1. This method is based on the fact that the amphiphile 1 can prevent MO from protonation even at pH 2.0. No similar colour change was observed when ADP was added instead of ATP under the same conditions. The effect of the molecular structure of several peptide amphiphiles and dyes was also investigated.

Supramolecular hydrogel-based protein and chemosensor array

The development of protein and sensor arrays is crucial for rapid and high-throughput assays of biological events, markers, environmental pollutants, and others. We describe supramolecular hydrogel as a unique material for use as a matrix for immobilizing proteins, peptides, substrates, chemosensors, and mesoporous silica particles, and thereby array them on solid supports. The semi-wet conditions provided by the gel, which consists of 3D supramolecular nanofiber network structure, are suitable for entrapping such substances whilst retaining their activity and function. Moreover, the hydrophobic interior of the nanofibers of the supramolecular hydrogel can reversibly entrap hydrophobic molecules, which allows the development of various read-out systems, such as fluorescence enhancement and fluorescence resonance energy transfer (FRET), by which one can monitor the signal changes associated with, for instance, molecular recognition and enzyme activity.

Recognition and sensing of nucleoside monophosphates by a dicopper(II) cryptate

The dimetallic cryptate [Cu(2)(II)(1)](4+) selectively recognizes guanosine monophosphate with respect to other nucleoside monophosphates (NMPs) in a MeOH/water solution at pH 7. Recognition is efficiently signaled through the displacement of the indicator 6-carboxyfluorescein bound to the receptor, monitoring its yellow fluorescent emission. Titration experiments evidenced the occurrence of several simultaneous equilibria involving 1:1 and 2:1 receptor/NMP and receptor/indicator complexes. It was demonstrated that the added NMP displaces the indicator from the 2:1 receptor/indicator complex, forming the 1:1 receptor/analyte inclusion complex. Recognition selectivity is thus ascribed to the nature of nucleotide donor atoms involved in the coordination and their ability to encompass the Cu(II)-Cu(II) distance within the cryptate.

Unique sandwich stacking of pyrene-adenine-pyrene for selective and ratiometric fluorescent sensing of ATP at physiological pH

A pincer-like benzene-bridged sensor 1 with a pyrene excimer as a signal source and imidazolium as a phosphate anion receptor was synthesized and investigated for ATP sensing. A unique switch of excimer vs monomer pyrene fluorescence of 1 is observed in the presence of ATP due to the charcteristic sandwich pi-pi stacking of pyrene-adenine-pyrene. On the other hand, four other bases of nucleoside triphosphates such as GTP, CTP, UTP, and TTP can interact only from the outside with the already stabilized stacked pyrene-pyrene dimer of 1, resulting in excimer fluorescence quenching. The fluorescent intensity ratio of monomer-to-excimer for 1 upon binding with ATP (I(375)/I(487)) is much larger than that upon binding with ADP and AMP. This difference is large enough to discriminate ATP from ADP and AMP. As one of the biological applications, sensor 1 is successfully applied to the ATP staining experiments. Sensor 1 is also applied to monitor the hydrolysis of ATP and ADP by apyrase. The results indicate that 1 is a useful fluorescent sensor for investigations of ATP-relevant biological processes.

Pyrophosphate selective fluorescent chemosensors based on coumarin-DPA-Cu(II) complexes

Two new coumarin derivatives displayed highly selective "Off-On" fluorescence changes with pyrophosphate between various anions including ATP, ADP, AMP and inorganic phosphate in 100% aqueous solution.

Polydiacetylene-based colorimetric self-assembled vesicular receptors for biological phosphate ion recognition

Self-assembled vesicular polydiacetylene (PDA) particles with embedded metal complex receptor sites have been prepared. The particles respond to the presence of ATP and PPi (pyrophosphate) in buffered aqueous solution by visible changes of their color and emission properties. Blue PDA vesicles of uniform size of about 200 nm were obtained upon UV irradiation from mono- and dinuclear zinc(II)-cyclen and iminodiacetato copper [Cu(II)-IDA] modified diacetylenes, embedded in amphiphilic diacetylene monomers. Addition of ATP and PPi to the PDA vesicle solution induces a color change from blue to red observable by the naked eye. The binding of ATP and PPi changes the emission intensity. Other anions such as ADP, AMP, H2PO4-, CH3COO-, F-, Cl-, Br- and I-, failed to induce any spectral changes. The zinc(II)-cyclen nanoparticles are useful for the facile detection of PPi and ATP in millimolar concentrations in neutral aqueous solutions, while Cu(II)-IDA modified vesicular PDA receptors are able to selectively discriminate between ATP and PPi.

An "Off-On" type UTP/UDP selective fluorescent probe and its application to monitor glycosylation process

A New fluorescent sensor based on a perylene-dpa-Zn platform was synthesized. Selective "Off-On" type fluorescence changes were observed upon the addition of UTP and UDP, which was also applied to monitor glycosylation processes.

9-Chloro-2,4-dimethoxyacridinium trifluoromethanesulfonate

In the mol­ecular structure of the title compound, C₁₅H₁₃ClNO₂⁺·CF₃SO₃⁻, the meth­oxy groups are nearly coplanar with the acridine ring system, making dihedral angles of 0.4 (2) and 5.1 (2)°. Multidirectional π–π contacts between acridine units are observed in the crystal structure. N—H⋯O and C—H⋯O hydrogen bonds link cations and anions, forming a layer structure.

Chemosensors for pyrophosphate

The selective detection of the anion pyrophosphate (PPi) is a major research focus. PPi is a biologically important target because it is the product of ATP hydrolysis under cellular conditions, and because it is involved in DNA replication catalyzed by DNA polymerase, its detection is being investigated as a real-time DNA sequencing method. In addition, within the past decade, the ability to detect PPi has become important in cancer research. In general, the sensing of anions in aqueous solution requires a strong affinity for anions in water as well as the ability to convert anion recognition into a fluorescent or colorimetric signal. Among the variety of methods for detecting PPi, fluorescent chemosensors and colorimetric sensors for PPi have attracted considerable attention during the past 10 years. Compared with the recognition of metal ions, it is much more challenging to selectively recognize anions in an aqueous system due to the strong hydration effects of anions. Consequently, the design of PPi sensors requires the following: an understanding of the molecular recognition between PPi and the binding sites, the desired solubility in aqueous solutions, the communicating and signaling mechanism, and most importantly, selectivity for PPi over other anions such as AMP and ADP, and particularly phosphate and ATP. This Account classifies chemosensors for PPi according to topological and structural characteristics. Types of chemosensors investigated and reported in this study include those that contain metal ion complexes, metal complexes combined with excimers, those that function with a displacement approach, and those based on hydrogen-bonding interaction. Thus far, the utilization of a metal ion complex as a binding site for PPi has been the most successful strategy. The strong binding affinity between metal ions and PPi allows the detection of PPi in a 100% aqueous solution. We have demonstrated that carefully designed receptors can distinguish between PPi and ATP based on their different total anionic charge densities. We have also demonstrated that a PPi metal ion complex sensor has a bioanalytical application. This sensor can be used in a simple and quick, one-step, homogeneous phase detection method in order to confirm DNA amplification after polymerase chain reaction (PCR).

Turn-on fluorescence sensing of nucleoside polyphosphates using a xanthene-based Zn(II) complex chemosensor

Fluorescence sensing with small molecular chemosensors is a versatile technique for elucidation of function of various biological substances. We now report a new fluorescent chemosensor for nucleoside polyphosphates such as ATP using metal-anion coordination chemistry. The chemosensor 1-2Zn(II) is comprised of the two sites of 2,2'-dipicolylamine (Dpa)-Zn(II) as the binding motifs and xanthene as a fluorescent sensing unit for nucleoside polyphosphates. The chemosensor 1-2Zn(II) selectively senses nucleoside polyphosphates with a large fluorescence enhancement (F/F(o) > 15) and strong binding affinity (K(app) approximately = 1 x 10(6) M(-1)), whereas no detectable fluorescence change was induced by monophosphate species and various other anions. The 'turn-on,' fluorescence of 1-2Zn(II) is based on a new mechanism, which involves the binding-induced recovery of the conjugated form of the xanthene ring from its nonfluorescent deconjugated state which was formed by an unprecedented nucleophilic attack of zinc-bound water. The selective and highly sensitive ability of 1-2Zn(II) to detect nucleoside polyphosphates enables its bioanalytical applications in fluorescence visualization of ATP particulate stores in living cells, demonstrating the potential utility of 1-2Zn(II).

Luminescent lanthanide complexes as probes for the determination of enzyme activities

The determination of enzyme activities and the screening of enzyme regulators is a major task in clinical chemistry and the development of new drugs. A broad variety of enzymatic reactions is associated with the consumption or formation of small molecules like H(2)O(2), ATP, pyrophosphate, or phosphate. Luminescent lanthanide complexes can be applied to monitor these enzymatic conversions and therefore can serve as probes for the determination of enzyme activities. The utility of this concept will be demonstrated by means of some selected examples including europium and terbium complexes. Accordingly, this new approach could be already implemented for the determination of glucose oxidase, catalase, and peroxidase activity. In particular, enzymes that catalyze phosphorylation or dephosphorylation reactions came to the fore of interest because of their high relevance as drug targets. These include (protein) kinases, adenylyl cyclases, phosphodiesterases, phosphatases, and ATPases. The development and design of fluorescent lanthanide complexes should lead to probes with optimized selectivity and response times that can be applied for high-throughput screening of enzyme inhibitors and for real-time monitoring of enzyme kinetics. In contrast to other assays for enzyme activity determination, this method does not require the use of radioactively labelled substrates or the accomplishment of rather complex and expensive immunoassays.

Colorimetric sensor for triphosphates and their application as a viable staining agent for prokaryotes and eukaryotes

The chromogenic complex 1 x Zn (where 1 is (E)-4-(4-dimethylamino-phenylazo)-N,N-bispyridin-2-ylmethyl-benzenesulfonamide) showed high affinity toward the phosphate ion in tetrabutylammonium phosphate in acetonitrile solution and could preferentially bind to adenosine triphosphate (ATP) in aqueous solution at physiological pH. This binding caused a visual change in color, whereas no such change was noticed with other related anions (adenosine monophosphate, adenosine diphosphate, pyrophosphate, and phosphate) of biological significance. Thus, 1 x Zn could be used as a staining agent for different biological cells through binding to the ATP, generated in situ by the mitochondria (in eukaryotes). For prokaryotes (bacteria) the cell membrane takes care of the cells' energy conversion, since they lack mitochondria. ATP is produced in their unique cell structure on the cell membrane, which is not found in any eukaryotes. These stained cells could be viewed with normal light microscopy. This reagent could even be used for distinguishing the gram-positive and the gram-negative bacteria (prokaryotes). This dye was found to be nonlipophilic in nature and nontoxic to living microbes (eukaryotes and prokaryotes). Further, stained cells were found to grow in their respective media, and this confirmed the maintenance of viability of the microbes even after staining, unlike with many other dyes available commercially.

A cholic acid-based fluorescent chemosenor for the detection of ATP

A novel ditopic cholic acid-based fluorescent chemosensor for ATP, 1a, was designed and synthesized. Its interactions with phosphates, AMP, ADP, ATP, CTP, GTP, and TTP have been investigated. When ATP was added to a 1:1 aqueous CH3CN solution of the sensor at pH 7.4, a significant decrease in fluorescence of 1a was observed, whereas other guest molecules showed a much smaller effect. The complex between 1a and ATP was confirmed through combined UV, 1H, 13C and 31P NMR spectroscopic methods. The uniqueness of the new sensor is that it binds with ATP 33-124 times more selectively than other nucleotides, as evidenced from the respective binding constants. 1a is a highly sensitive sensing probe; as little as 30 nM ATP can cause 15% fluorescence quenching of the sensor.

Colorimetric sensor for ATP in aqueous solution

A new chromogenic complex 1.Zn has been synthesized, and its interactions with different biologically important phosphates have been investigated in aqueous solution (pH approximately 7.2). A visual color change can be detected on binding of ATP to 1.Zn, whereas no such change is observed when other biologically related anions (AMP, ADP, PPi, or Phosphate) are used. Complex 1.Zn can also be used as a staining agent for yeast cells allowing detection under normal light microscopy.