A highly selective pyrophosphate sensor based on ESIPT turn-on in water

Pyrophosphate (PPi) is a biologically important target. A binuclear system 3?2Zn is found to selectively recognize PPi, leading to a ratiometric fluorescent sensor at pH 7.4 in water. The binding event triggered a large fluorescence response (～100 nm bathochromic shift) by turning on the excited state intramolecular proton transfer (ESIPT). Detection of PPi released from a PCR experiment indicated that this new probe could be a useful tool in bioanalytical applications.     

Fluorescence Sensor with A New ON1–OFF–ON2 Switching Mechanism Using the Excited State Intermolecular Proton Transfer Reaction of An Anthracene‐diurea Compound

A new photoreaction mechanism of “Three‐state molecular switch” fluorescence sensor based on ON¹‐OFF‐ON² sequence was achieved by anthracene‐diurea compound, which was designed using two phenylurea groups and one anthracene, 9,10BtDSPUA. Photochemical properties of 9,10BtDSPUA and interaction between 9,10BtDSPUA and anion were investigated in detail by absorption, ¹H NMR, fluorescence, and fluorescence decay measurements. While the fluorescence of 9,10BtDSPUA in DMSO (ON¹) was quenched in the presence of low concentration of acetate anion (OFF), fluorescence enhancement occurred by the addition of high concentration of acetate anion (ON²). This compound forms complex with acetate anion through hydrogen bonding interaction in the ground state resulted in tautomer formation by excited state intermolecular proton transfer (ESIPT) on irradiation. Whereas single coordination of acetate anion to anthracene‐diurea compound may cause fluorescence quenching, full coordination may cause fluorescence enhancement due to suppressing ESIPT. This suppressing ESIPT was occurred by electron‐donating resonance effect between two urea moieties. This study is the first example of ON¹‐OFF‐ON² fluorescence sensor for concentration detection of acetate anion.     

A highly selective and sensitive fluorescence sensing system for distinction between diphosphate and nucleoside triphosphates

Among the numerous chemosensors available for diphosphate (P(2)O(7)(4-), PPi) and nucleoside triphosphates (NTPs), only a few can distinguish between PPi and NTPs. Hence, very few bioanalytical applications based on such selective chemosensors have been realized. We have developed a new fluorescence sensing system for distinction between PPi and NTPs based on the combination of two sensors, a binuclear Zn(II) complex (1·2Zn) and boronic acid (BA), in which one chemosensor (1·2Zn) shows signal changes depending on the PPi (or NTP) concentration, and the other (BA) blocks the signal change caused by NTPs; this system enables the distinction of PPi from NTPs and is sensitive to nanomolar concentrations of PPi. The new sensing system has been successfully used for the direct quantification of RNA polymerase activity.     

Pyrophosphate-selective fluorescent chemosensor based on 1,8-naphthalimide-DPA-Zn(II) complex and its application for cell imaging

A new zinc(II) complex with a two-dipicolylamine-substituted 1,8-naphthalimide for recognition of pyrophosphate with ratiometrical fluorescence changes in aqueous solution has been synthesized and characterized. Its biological application to monitor the intracellular pyrophosphate (PPi) was successfully demonstrated by the observation that the fluorescence of 1 was enhanced by the presence of the Zn(2+) ion and was quenched by addition of PPi.     

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) complex of terpyridine for the highly selective fluorescent recognition of pyrophosphate

Pyrophosphate ion (PPi) is crucial in varieties of biological processes and industrial applications, and thus it is very important how to recognize it with high selectivity. In this contribution, one terpyridine (tpy)-based fluorescent molecule, 4-(methylphenyl)-2,2':6',2'-terpyridine (mptpy), has been reported to display a highly selective recognition for PPi in the presence of Zn(II). After exposure toward the Zn(II) ion, the characteristic emission of mptpy at 376 nm red-shifted to 406 nm with a strong enhancement upon an excitation at 280 nm, and then blue-shifted to 388 nm with the further addition of PPi. Absorption and fluorescence measurements showed that other phosphates including phosphate (Pi) as well as nucleotide triphosphates could not induce the spectral changes similar to PPi, demonstrating the unique binding effect between mptpy-Zn(II) and PPi. This process could also discriminate PPi from other inorganic anions. Therefore, a tpy-based fluorescence method for the highly selective recognition of PPi could be developed.     

The steric effect of aromatic pendant groups and electrical bistability in π-stacked polymers for memory devices

In order to investigate the steric effect of aromatic pendant groups and the electrical bistability in nonconjugated polymers potentially for memory device applications, two π-stacked polymers with different steric structures are synthesized and characterized. They exhibit two conductivity states and can be switched from an initial low-conductivity (OFF) state to a high-conductivity (ON) state. Additionally, they demonstrate nonvolatile write-once-read-many-times (WORM) memory behavior with an ON/OFF current ratio up to 10(4), and flash memory behavior with an ON/OFF current ratio of approximately 10(5). Both steady-state and time-resolved fluorescence spectroscopies are used to examine the conformational change of the polymers responding to an applied external electrical voltage. The results provide useful information on different steric effects of pendant groups in polymer chains, resulting in various electrical behaviors. The possibility in realizing an "erasable" behavior through breaking π-stacked structures of pendant groups by a reversal of the electric field was also discussed on the basis of temperature-dependent fluorescence spectroscopy investigation. These results may thus offer a guideline for the design of practical polymer memory devices via tuning steric structure of π-stacked polymers.     

基于碳点的荧光纳米开关灵敏检测Cu(Ⅱ)离子和焦磷酸盐

利用羟基与氨基在高温条件下反应,不断聚合生成碳点（CDs）,该碳点可发射不依赖激发波长的明亮的红色荧光.将CDs作为目标敏感荧光团时,发现Cu²⁺可特异性猝灭碳点的荧光,而焦磷酸盐（PPi）可在一定程度上恢复上述体系的荧光.其中,Cu²⁺对CDs的荧光猝灭是由于Cu²⁺与CDs发生络合反应,从而发生静态猝灭过程;而加入PPi之后,由于它与CDs的结合能力更强,因此Cu²⁺离开CDs的表面,体系的荧光得以恢复.在此基础上构建了一种高选择性、高灵敏度的off-on荧光纳米开关传感体系,分别用于Cu²⁺和PPi的定量检测,检出限分别达2.14 μmol/L和1.85 μmol/L.该传感体系可应用于实际样品检测,拓宽了荧光CDs的传感应用,为其在生物体内目标分子的检测提供了可能性.     

Hydrogen-Bonded Complexes of Fluorophenylacetylenes: To Fluoresce or Not?

The hydrogen-bonded complexes of fluorophenylacetylenesexhibit unusual and interesting fluorescence turn ON/OFF behaviour following excitation to ¹ππ* (S₁) state. The fluorescence switching behaviour can be realized by (i) “change in the intermolecular structure, (ii) change in the position of fluorine substitution and (iii) change in the hydrogen bonding partner or a combination thereof. Experiments indicate that the ≡C−H⋅⋅⋅X (X=O, N) hydrogen bonding with the acetylenic group plays a pivotal role in this switching behaviour. Intriguingly, weaker ≡C−H⋅⋅⋅X hydrogen bonding leads to fluorescence OFF state, which is turned ON by stronger hydrogen bonding. The observed fluorescence this switching behaviour is rationalized on the basis of a phenomenological model which suggests a coupling between the initially excited S₁ state and a dark S_n state in the Franck-Condon region with limited window controlled by the ≡C−H⋅⋅⋅X hydrogen bonding as a crucial parameter. Such fluorescence switching behaviour in hydrogen-bonded complexes is unprecedented and these intriguing results hopefully will stimulate theoreticians to test ′state of the art′ theories to explain these observations in a consistent manner.     

A self-assembled conjugated micelle with improved sensitivity for monitoring alkaline phosphatase activity

An amphiphilic coumarin derivative which forms a π-extended micelle conformation 1 was designed and developed. The exciton efficiently migrates throughout the coumarin aggregates of 1, showing amplified fluorescence quenching in the presence of Cu²⁺ ions. The 1-Cu²⁺ complex displays a highly sensitive response to pyrophosphate (PPi), leading to 80% fluorescence recovery. The activity of alkaline phosphatase (ALP) was monitored by a real-time assay where a solution containing 1, Cu²⁺, and PPi in aqueous solution exhibits a sensitive turn-off fluorescence response to ALP.     

A Metalloregulated Four‐State Nanoswitch Controls Two‐Step Sequential Catalysis in an Eleven‐Component System

The nanomechanical switch 1 with its three orthogonal binding motifs—the zinc(II) porphyrin, azaterpyridine, and shielded phenanthroline binding station—is quantitatively and reversibly toggled back and forth between four different switching states by means of addition and removal of appropriate metal‐ion inputs. Two of the four switching stages are able to initiate catalytic transformations (ON1, ON2), while the two others shut down any reaction (OFF1, OFF2). Thus, in a cyclic four‐state switching process the sequential transformation A + B + C → AB + C → ABC can be controlled, which proceeds stepwise along the switching states OFF1→ON1 (click reaction: A + B → AB )→OFF2→ON2 (Michael addition: AB + C → ABC )→OFF1. Two consecutive cycles of the sequential catalysis were realized without loss in activity in a reaction system with eleven different components.     

A Fluorescence Sensor Array Based on Zinc(II)-Carboxyamidoquinolines: Toward Quantitative Detection of ATP**

The newly prepared fluorescent carboxyamidoquinolines ( 1 – 3 ) and their Zn(II) complexes ( Zn@1-Zn@3 ) were used to bind and sense various phosphate anions utilizing a relay mechanism, in which the Zn(II) ion migrates from the Zn@1-Zn@3 complexes to the phosphate, namely adenosine 5’-triphosphate (ATP) and pyrophosphate (PPi), a process accompanied by a dramatic change in fluorescence. Zn@1-Zn@3 assemblies interact with adenine nucleotide phosphates while displaying an analyte-specific response. This process was investigated using UV-vis, fluorescence, and NMR spectroscopy. It is shown that the different binding selectivity and the corresponding fluorescence response enable differentiation of adenosine 5’-triphosphate (ATP), adenosine 5’-diphosphate (ADP), pyrophosphate (PPi), and phosphate (Pi). The cross-reactive nature of the carboxyamidoquinolines-Zn(II) sensors in conjunction with linear discriminant analysis (LDA) was utilized in a simple fluorescence chemosensor array that allows for the identification of ATP, ADP, PPi, and Pi from 8 other anions including adenosine 5’-monophosphate (AMP) with 100 % correct classification. Furthermore, the support vector machine algorithm, a machine learning method, allowed for highly accurate quantitation of ATP in the range of 5–100 μM concentration in unknown samples with error <2.5 %.     

A Pyrene‐functionalized Polynorbornene for Ratiometric Fluorescence Sensing of Pyrophosphate

A novel pyrene‐functionalized polynorbornene ( P1 ) bearing sulfonamide NH and triazolium donors has been synthesized for ratiometric fluorescence sensing of PPi in aqueous solution. In addition, P1 is also used to monitor intracellular PPi and to detect PPi released during polymerase chain reaction.     

Residual and exploitable fluorescence in micellar self-assembled ON-OFF sensors for copper(II)

A set of new ligands, L2H(2)-L5H(2), containing the 1,4,8,11-tetraaza-5,7-dione framework has been prepared, The ligands feature lipophilic substituents either on the carbon atom in the 6 position or on the amino groups, or on both. The solution behaviour of the ligands when included in TritonX-100 micelles has been investigated by means of potentiometric titrations and protonation and complexation constants for the Cu(2+) cation have been determined in micellar medium. Micellar assemblies containing the ligands and pyrene have been prepared, and coupled pH-metric and fluorimetric titrations allowed the determination of the response of the systems as ON-OFF fluorescent sensors for Cu(2+). A correlation between the effective lipophilicity of the ligand and the residual fluorescence (i.e. the fluorescence of the OFF state) was observed, and with the more lipophilic ligand, L3H(2), we obtained a residual fluorescence as low as 8%, with a significant improvement with respect to other published systems. On the other hand, introduction of functionalities on the amino groups of 1,4,8,11-tetraaza-5,7-dione brings the drawback of a small but significant decrease of the exploitable fluorescence, i.e. the fluorescence of the system in the absence of added Cu(2+), at the pH value suitable for full metal complexation.     

On-off-on luminescent pyrophosphate probe based on the use of Mn-doped ZnS quantum dots and using Eu(III) as a mediator

A selective phosphorescent on-off-on probe with long decay lifetime has been designed for the detection of pyrophosphate ions (PPi). The detection scheme is based on the use of europium(III)-modulated Mn(II)-doped ZnS quantum dots capped with N-acetyl-L-cysteine. Both the aggregation of quantum dots and electron transfer induced by Eu(III) ions cause phosphorescence to be quenched (“off” state). Phosphorescence is, however, restored on addition of PPi to the system (“on” state). The effect is attributed to the removal of Eu(III) from the carboxy groups on the surface of the quantum dots owing to the stronger interaction between PPi and Eu(III). A linear relationship exists between phosphorescence intensity (best measured at excitation/emission wavelengths of 316/594 nm) and PPi concentration in the 400 nM to 6000 nM with a detection limit of 145 nM. An additional attractive feature is provided by the long-lived phosphorescence (1920 μs) of the quantum dots. It can be used to eliminate interference by short-lived fluorescence in biological samples by performing time resolved measurements. The probe was applied to the determination of PPi in spiked in urine samples and gave recoveries in the range from 98 to 105% with RSDs of <2.0%.

Open image in new window

Graphical abstract Schematic of a long-lived phosphorescent on-off-on probe for the sensitive and selective detection of pyrophosphate ions (PPi). It is based on the use of Eu(III)-modulated Mn(II)-doped ZnS quantum dots (QDs). Phosphorescence is quenched of QDs after the addition of Eu³⁺but restored after the addition of PPi.

     

A Toggle Nanoswitch Alternately Controlling Two Catalytic Reactions

Reversible switching between two states of the triangular nanoswitch [Cu( 1 )]⁺ was accomplished by alternate addition of 2‐ferrocenyl‐1,10‐phenanthroline ( 2 ) and copper(I) ions. The two switching states regulate the binding and release of two distinct catalysts, piperidine and [Cu( 2 )]⁺, in a fully interference‐free manner and allow alternating on/off switching of two orthogonal catalytic processes. In switching state I, piperidine is released from the nanoswitch and catalyzes a Knoevenagel addition between 4‐nitrobenzaldehyde and diethyl malonate (ON‐1 and OFF‐2), while in state II the released [Cu( 2 )]⁺ catalyzes a click reaction between 4‐nitrophenylacetylene and benzylazide (OFF‐1 and ON‐2). Upon addition of one equivalent of 2 to the (OFF‐1 and ON‐2)‐state, both catalytically active processes are shut down (OFF‐1 and OFF‐2).     

Strong Emission Enhancement in pH-Responsive 2:2 Cucurbit[8]uril Complexes

Organic fluorophores, particularly stimuli-responsive molecules, are very interesting for biological and material sciences applications, but frequently limited by aggregation- and rotation-caused photoluminescence quenching. A series of easily accessible bipyridinium fluorophores, whose emission is quenched by a twisted intramolecular charge-transfer (TICT) mechanism, is reported. Encapsulation in a cucurbit[7]uril host gave a 1:1 complex exhibiting a moderate emission increase due to destabilization of the TICT state inside the apolar cucurbituril cavity. A much stronger fluorescence enhancement is observed in 2:2 complexes with the larger cucurbit[8]uril, which is caused by additional conformational restriction of rotations around the aryl/aryl bonds. Because the cucurbituril complexes are pH switchable, this system represents an efficient supramolecular ON/OFF fluorescence switch.     

Colorimetric and orange light-emitting fluorescent probe for pyrophosphate in water

A dual-mode probe based on a benzothiazolium hemicyanine chromophore was designed and synthesized for the detection of pyrophosphate (PPi) in water. The use of a fluorescent probe for colorimetric and long-wavelength fluorescence detection of PPi could be suitable for both rapid in-field and bioimaging experiments.     

In Situ Synthesis and Nonvolatile Rewritable‐Memory Effect of Polyaniline‐Functionalized Graphene Oxide

A new polyaniline (PANI)‐functionalized graphene oxide (GO‐PANI) was prepared by using an in situ oxidative graft polymerization of aniline on the surface of GO. Its highest occupied molecular orbital (HOMO), lowest unoccupied molecular orbital (LUMO), ionization potential (IP), and electron affinity (EA) values experimentally estimated by the onset of the redox potentials were ?5.33, ?3.57, 5.59, and 3.83 eV, respectively. A bistable electrical‐switching effect was observed in electronic device with the GO‐PANI film sandwiched between the indium tin oxide (ITO) and Al electrodes. This device exhibited two accessible conductivity states, that is, the low‐conductivity (OFF) state and the high‐conductivity (ON) state, and can be switched to the ON state under a negative electrical sweep, and can also be reset to the initial OFF state by a reverse (positive) electrical sweep. The ON state is nonvolatile and can withstand a constant voltage stress of ?1 V for 3 h and 10⁸ read cycles at ?1 V under ambient conditions. The nonvolatile nature of the ON state and the ability to write, read, and erase the electrical states, fulfill the functionality of a rewritable memory. An ON/OFF current ratio of more than 10⁴ at ?1 V achieved in this memory device is high enough to promise a low misreading rate through the precise control of the ON and OFF states. The mechanism associated with the memory effects was elucidated from molecular simulation results.     

A new fluorescent sensor for the detection of pyrophosphate based on a tetraphenylethylene moiety

We have developed a new fluorescent sensor 1-2Zn based on a tetraphenylethylene (TPE) moiety for the detection of PPi. This TPE-based chemosensor showed ‘turn-on’ fluorescence emission according to the concentration of PPi. The fluorescence enhancement upon binding of PPi to 1-2Zn resulted from the restriction of intramolecular rotation of phenyl rings in 1-2Zn.