Development of an Organic Dye-Conjugated β-Diketonate-Europium Complex Luminescence Probe for Discrimination and Detection of Intracellular Biothiols

Small molecular biothiols, cysteine (Cys), homocysteine (Hcy) and glutathione (GSH), play important roles in organisms, and their concentration levels are indicative of some human diseases. Herein we report an organic dye-conjugated β-diketonate-Eu³⁺ complex, [Eu(NBD-keto)₃(DPBT)] (NBD-keto: 7-nitro-2,1,3-benzoxadiazole (NBD)-conjugated to 1,1,1,2,2-pentafluoro-5-phenyl-3,5-pentanedionate through a “O” ether bond; DPBT: 2-(N,N-diethylanilin-4-yl)-4,6-bis(3,5-dimethylpyrazol-1-yl)-1,3,5-triazine), which acts as a unique luminescent probe for detecting and discriminating biothiols. [Eu(NBD-keto)₃(DPBT)] itself is not luminescent due to intramolecular interactions between NBD and β-diketonate-Eu³⁺ moieties. Upon reaction with biothiols, the β-diketonate-Eu³⁺ complex [Eu(keto)₃(DPBT)] is generated, which emits long-lived red emission at 610 nm. Meanwhile, three biothiol-substituted NBD derivatives that exhibit different luminescence behaviors, green emissive (short-lived) NBD-NR (R=Cys or Hcy) at 540 nm and non-luminescent NBD-SR (R=GSH), are also generated. These luminescence response behaviors allow time-gated and steady-state luminescence modes to be combined for detecting total biothiols and discriminating GSH and Cys/Hcy. Using this probe, the quantitative detection and discrimination of GSH and Cys/Hcy in lysis solutions of HeLa cells were realized, which revealed the potential of the probe for biomedical applications.     

A red-emitting water-soluble fluorescent probe for biothiol detection with a large Stokes shift

A highly water soluble fluorescent probe was developed for sensitive and selective detection of biothiols with a red emission and a large Stokes shift. The probe was successfully applied to detect biothiols both in aqueous solution and in living cells.     

Novel Phosphorescent Hydrogels Based on an IrIII Metal Complex

Novel phosphorescent hydrogels have been explored by immobilizing an Ir^III metal complex into the matrices of hydrogels. FTIR spectra demonstrate that the Ir^III–PNaAMPS hydrogel is achieved by irreversible incorporation of positively charged [Ir(ppy)₂(dmbpy)]Cl (ppy = 2‐phenylpyrine, dmbpy = 4,4′‐dimethyl‐2,2′‐bipyridine) into negatively charged poly(2‐acrylamido‐2‐methylpropane sulfonic acid sodium) (PNaAMPS) hydrogel via electrostatic interaction. The photoluminescent spectra indicate that the Ir^III–PNaAMPS hydrogel exhibits stable phosphorescence. In vitro cultivation of human retinal pigment epithelial cells demonstrates the cytocompatibility of the Ir^III–PNaAMPS hydrogel. This work herein represents a facile pathway for fabrication of phosphorescent hydrogels.     

Synthesis,Crystal Structure and Biothiols Detection Capability of a New “off-on” Fluoresent Probe

Biothiols such as cysteine(Cys), homocysteine(Hcy) and glutathione(GSH) act as critical roles in maintaining biological redox homeostasis, which is crucial for a plenty of physiological and pathological processes. Therefore, the detection of biothiols is very important and beneficial for many applications. Herein, we have designed and developed a new crystal dimethyl 4-(2,4-dinitrophenylsulfonyloxy)pyridine-2,6-dicarboxylate(P) with 2,4-dinitrobenzene-1-sulfonyl(DNBS) pendant for light-up and detection of biothiols(Cys was selected as the analyte model). The fluorescence "off-on" switch is triggered by the cleavage of DNBS unit by the interaction with biothiols via nucleophilic aromatic substitution reaction. The turn-on fluorescent probe exhibited excellent selectivity and sensitivity toward biothiols.     

Cyclometalated Mono‐ and Dinuclear IrIII Complexes with “Click”‐Derived Triazoles and Mesoionic Carbenes

Orthometalation at Ir^III centers is usually facile, and such orthometalated complexes often display intriguing electronic and catalytic properties. By using a central phenyl ring as C?H activation sites, we present here mono‐ and dinuclear Ir^III complexes with “click”‐derived 1,2,3‐triazole and 1,2,3‐triazol‐5‐ylidene ligands, in which the wingtip phenyl groups in the aforementioned ligands are additionally orthometalated and bind as carbanionic donors to the Ir^III centers. Structural characterization of the complexes reveal a piano stool‐type of coordination around the metal centers with the “click”‐derived ligands bound either with C^N or C^C donor sets to the Ir^III centers. Furthermore, whereas bond localization is observed within the 1,2,3‐triazole ligands, a more delocalized situation is found in their 1,2,3‐triazol‐5‐ylidene counterparts. All complexes were subjected to catalytic tests for the transfer hydrogenation of benzaldehyde and acetophenone. The dinuclear complexes turned out to be more active than their mononuclear counterparts. We present here the first examples of stable, isomer‐pure, dinuclear cyclometalated Ir^III complexes with poly‐mesoionic‐carbene ligands.     

Protein Labelling with Versatile Phosphorescent Metal Complexes for Live Cell Luminescence Imaging

To take advantage of the luminescent properties of d⁶ transition metal complexes to label proteins, versatile bifunctional ligands were prepared. Ligands that contain a 1,2,3‐triazole heterocycle were synthesised using Cu^I catalysed azide–alkyne cycloaddition “click” chemistry and were used to form phosphorescent Ir^III and Ru^II complexes. Their emission properties were readily tuned, by changing either the metal ion or the co‐ligands. The complexes were tethered to the metalloprotein transferrin using several conjugation strategies. The Ir^III/Ru^II–protein conjugates could be visualised in cancer cells using live cell imaging for extended periods without significant photobleaching. These versatile phosphorescent protein‐labelling agents could be widely applied to other proteins and biomolecules and are useful alternatives to conventional organic fluorophores for several applications.     

A Multi‐signal Fluorescent Probe with Multiple Binding Sites for Simultaneous Sensing of Cysteine,Homocysteine, and Glutathione

A novel fluorescent probe was developed by integrating chlorinated coumarin and benzothiazolylacetonitrile and exploited for simultaneous detection of cysteine (Cys), homocysteine (Hcy), and glutathione (GSH). Featuring four binding sites and different reaction mechanisms for different biothiols, this probe exhibited rapid fluorescence turn‐on for distinguishing Cys, Hcy, and GSH with 108‐, 128‐, 30‐fold fluorescence increases at 457, 559, 529 nm, respectively, across different excitation wavelengths. Furthermore, the probe was successfully applied to the fluorescence imaging of endogenous Cys and GSH and exogenous Cys, Hcy, and GSH in living cells.     

A Multi‐signal Fluorescent Probe with Multiple Binding Sites for Simultaneous Sensing of Cysteine,Homocysteine, and Glutathione

A novel fluorescent probe was developed by integrating chlorinated coumarin and benzothiazolylacetonitrile and exploited for simultaneous detection of cysteine (Cys), homocysteine (Hcy), and glutathione (GSH). Featuring four binding sites and different reaction mechanisms for different biothiols, this probe exhibited rapid fluorescence turn‐on for distinguishing Cys, Hcy, and GSH with 108‐, 128‐, 30‐fold fluorescence increases at 457, 559, 529 nm, respectively, across different excitation wavelengths. Furthermore, the probe was successfully applied to the fluorescence imaging of endogenous Cys and GSH and exogenous Cys, Hcy, and GSH in living cells.     

A Novel Fluorescent Probe Based on Perylene Derivative for Hg2+ Ions and Biological Thiols and its Application in Live Cell Imaging and Theoretical Calculations

The selective and sensitive detection of biothiols; cysteine (Cys), homocysteine (Hcy) and glutathione (GSH) in aqueous solutions is of considerable importance because of their pivotal roles in maintaining the reducing environment in the cells. This study describes a strategy for the determination of biothiols based on the PDI/Met‐Hg²⁺complex platform. We designed and fabricated methionine modified perylene diimide molecule as a selective sensing probe for Hg²⁺ ions in aqueous solutions ( PDI/Met‐Hg ²⁺). The complex between perylene bisimide derivative ( PDI/Met) and Hg²⁺ was investigated and it demonstrated turn‐on fluorescence response for the detection of the biological thiols. Besides, PDI/Met displayed fluorescence quenching response in the presence of mercury ions and the emission intensity of PDI/Met‐Hg²⁺ was recovered after transferring biothiols (Cys, Hcy, and GSH). Thus, PDI/Met could be utilized as a fluorescent chemosensor for the sequential recognition of mercury ions and biological thiols.     

Rational Design of an Ultrasensitive and Highly Selective Chemodosimeter by a Dual Quenching Mechanism for Cysteine Based on a Facile Michael‐Transcyclization Cascade Reaction

Differentiation of biologically important thiols, such as cysteine (Cys), homocysteine (Hcy), and glutathione (GSH) is still a challenging task. Herein, we present a novel fluorescent chemodosimeter capable of selectively detecting Cys over other biothiols including Hcy and GSH and other amino acids by a facile thiol‐Michael addition/transcyclization rearrangement cascade click process. The unique transcyclization step is critical for the selectivity as a result of the kinetically favorable formation of a six‐membered ring with the Cys Michael adduct. Moreover, the probe adopts a distinctive dual quenching mechanism—photoinduced electron transfer (PET) and photoinduced intramolecular charge transfer (ICT) to deliver a drastic turn‐on fluorescence response only at the Cys‐selective transcylization step. The judicious selection of strong electron‐withdrawing naphthalimide fluorophore with maleimide group enhances the electrophilicity and thus reactivity for the cascade process leading to fast detection and ultrasensitivity with a detection limit of 2.0 nm (S/N=3). The probe has demonstrated its practical utility potential in Cys imaging in live cells.     

Smart Poly(N‐isopropylacrylamide) Containing Iridium(III) Complexes as Water‐Soluble Phosphorescent Probe for Sensing and Bioimaging of Homocysteine and Cysteine

Homocysteine (Hcy) and cysteine (Cys) are two important kinds of amino acids in human bodies. Herein, we synthesized an iridium(III) complex‐functionalized poly(N‐isopropylacrylamide) and its hydrogel, which could be used as the excellent phosphorescent bioprobe for sensing Hcy and Cys. Their detection can be realized in aqueous system through the variations in absorption and photoluminescence spectra. Furthermore, living cell imaging experiments demonstrate that the phosphorescent bioprobe is membrane permeable and can monitor the changes of Hcy and Cys within living cells. In addition, the probe is also thermoresponsive, and its photoluminescence intensified with increasing temperature. These results suggests that this bioprobe has promising application in biomedical fields.     

A Phenothiazine-HPQ Based Fluorescent Probe with a Large Stokes Shift for Sensing Biothiols in Living Systems

Due to the redox properties closely related to numerous physiological and pathological processes, biothiols, including cysteine (Cys), homocysteine (Hcy) and glutathione (GSH), have received considerable attention in biological science. On account of the important physiological roles of these biothiols, it is of profound significance to develop sensitive and selective detection of biothiols to understand their biological profiles. In this work, we reported an efficient fluorescent probe, PHPQ-SH, for detecting biothiols in vitro and vivo, based on the phenothiazine-HPQ skeleton, with DNBS (2,4-dinitrobenzenesulfonate) as the response unit. Probe PHPQ-SH exhibited brilliant sensing performances toward thiols, including a large Stokes shift (138 nm), excellent sensitivity (for GSH, LOD = 18.3 nM), remarkable fluorescence enhancement (163-fold), low cytotoxicity, rapid response (8 min), and extraordinary selectivity. Finally, the probe PHPQ-SH illustrated herein was capable of responding and visualizing biothiols in MCF-7 cells and zebrafish.     

Two chemodosimeters for fluorescence recognition of biothiols in aqueous solution and their bioimaging application

Two fluorescein derivatives containing 2,4-dinitrobenzenesulfonyl group have been developed as fluorescent probes to detect the biothiols (Cys, Hcy and GSH) in aqueous solution. Probes 1 and 2 can distinguish these biothiols in the presence of other amino acids. While probe 1 can recognize the biothiols in PBS/DMSO (v:v = 95:5, pH = 7.40) solution, notably probe 2 could be used in PBS buffer solution (pH = 7.40). The detection limit of Cys for probe 2 reached at 0.021 μM in aqueous solution, which was lower than the intracellular concentration of Cys. In the recognition process, a reaction between the probes and the biothiols occurred, in which the S–O bond was cleaved to remove 2, 4-dinitrobenzenesulfonyl group. The data of ¹H NMR, MS and DFT/TD-DFT calculation further confirmed the detection mechanism. Moreover, two probes were successfully applied to the HeLa cell imaging.     

A Solution‐Processable Donor–Acceptor Compound Containing Boron(III) Centers for Small‐Molecule‐Based High‐Performance Ternary Electronic Memory Devices

A novel small‐molecule boron(III)‐containing donor–acceptor compound has been synthesized and employed in the fabrication of solution‐processable electronic resistive memory devices. High ternary memory performances with low turn‐on (V_Th1=2.0 V) and distinct threshold voltages (V_Th2=3.3 V), small reading bias (1.0 V), and long retention time (>10⁴ seconds) with a large ON/OFF ratio of each state (current ratio of “OFF”, “ON1”, and “ON2”=1:10³:10⁶) have been demonstrated, suggestive of its potential application in high‐density data storage. The present design strategy provides new insight in the future design of memory devices with multi‐level transition states.     

Are Triphenylamine‐Functionalized or Carbazole‐Functionalized Iridium Complexes the More Effective Phosphorescent Materials? A Theoretical Perspective

The ground and excited states, charge injection/transport, and phosphorescence properties of eleven carbazole‐ and triphenylamine‐functionalized Ir^III complexes were investigated by using the DFT method. By analyzing the spin–orbit coupling (SOC) matrix elements, radiative decay rate constants k_r, and the electronic structures and energies at the ${{\rm{S}}_{\rm{0}}^{{\rm{opt}}} }$ and ${{\rm{T}}_{\rm{1}}^{{\rm{opt}}} }$ states, it was possible to rationalize the order of the experimental phosphorescence quantum yields of a series of Ir^III complexes and to predict that [Ir(Nph‐2‐Cz‐tz)₃] has a higher phosphorescence quantum yield than [Ir(TPA‐tz)₃] (TPA=triphenylamine, tz=thiazolyl, Cz=carbazole, Nph=N‐phenyl). Carbazole‐functionalized Ir^III complexes were shown to be efficient phosphorescent materials that have not only fast but also balanced electron/hole‐transport performance as well as high phosphorescence quantum yields. The phosphorescence emission spectra can be modulated by modifying or replacing a pyridyl substituent.     

Benzothiazole‐Pyimidine‐Based BF2 Complex for Selective Detection of Cysteine

Due to the similar structure and reactivity of cysteine (Cys), homocysteine (Hcy) and glutathione (GSH), the simultaneous discrimination of Cys over Hcy and GSH by a single fluorescent sensor is still a great challenge. In this work, a benzothiazole‐pyimidine‐based boron difluoride complex ( BPB ) was developed as a new fluorescent sensor for Cys. The sensor exhibits a highly selective “turn‐on” response to cysteine over Hcy, GSH and other amino acids in aqueous solution at physiological pH. The observed pseudo‐first‐order rate constant for the reaction of BPB with Cys was calculated to be about 0.062 min⁻¹. The detection limit of this sensor for Cys was determined to be 332 nm, and bioimaging of exogenous Cys by this sensor was successfully applied in living cells, thus indicating that this sensor holds great potential for biological applications.     

meso‐(2‐Pyridyl)‐boron(III)‐subporphyrin: Perimeter Iridium(III) Coordination

Peripherally metalated porphyrinoids are promising functional π‐systems displaying characteristic optical, electronic, and catalytic properties. In this work, 5‐(2‐pyridyl)‐ and 5,10,15‐tri(2‐pyridyl)‐B^III‐subporphyrins were prepared and used to produce cyclometalated subporphyrins by reactions with [Cp*IrCl₂]₂, which proceeded through an efficient C?H activation to give the corresponding mono‐ and tri‐Ir^III complexes, respectively. While the mono‐Ir^III complex was obtained as a diastereomeric mixture, a C₃‐symmetric tri‐Ir^III complex with the three Cp*‐units all at the concave side was predominantly obtained in a high yield of 90 %, which displays weak NIR phosphorescence even at room temperature in degassed CH₂Cl₂, differently from the mono‐Ir^III complexes.     

A special o-dialdehyde fluorescent probe simultaneously sensing Hcy,GSH and its application in living cells and zebrafish imaging

The development of fluorescent probes enabling to distinguish Cys, Hcy and GSH has always been a considerable challenge, in particular the distinction of Hcy and other two biothiols, because Hcy has a very similar structure with Cys and a relatively lower concentration in living organisms. In this work, a special o-dialdehyde fluorescent probe, quinoline-2,3-dicarboxaldehyde (QDA), has been synthesized and demonstrated superior performance in differentiating detection of Hcy and GSH, which is different from the previous reported o-dialdehyde probes specifically detecting GSH. Furthermore, the probe can selectively distinguish Hcy and GSH from different signal channels in living cells and zebrafish, meaning it has great potential in biological applications. This finding will provide a novel idea for the design of fluorescent probes to distinguish biothiols.     

A CuII-Salicylidene Glycinato Complex for the Selective Fluorometric Detection of Homocysteine over 20 Proteinogenic Amino Acids

Homocysteine (Hcy) is a sulfur-containing α-amino acid that differs by one methylene (CH₂) subunit from homologous cysteine (Cys). Elevated levels of Hcy are diagnostic markers of cardiovascular disease and other medical conditions. We present a new Cu^II-salicylidene glycinato complex 1 for the selective fluorometric detection of Hcy in water. In the presence of this analyte, the non-fluorescent copper-complex demetallates and disassembles into its building blocks. This process liberates a 3-chloro-5-sulfosalicylaldehyde signaling unit and is accompanied by a 51-fold turn-on fluorescence at 485 nm (λ_ex=350 nm). Out of twenty proteinogenic amino acids, only histidine (12-fold turn-on fluorescence) and Cys (8-fold turn-on fluorescence) trigger some disassembly of probe 1 . In comparison with important pioneering work on the detection of biothiols, this study strikingly demonstrates that structural modifications of chelate core structures steer substrate selectivity of metal-based probes. Importantly, probe 1 has proven suitable for the detection of Hcy in artificial urine.     

Molecular Logic Gates and Switches Based on 1,3,4‐Oxadiazoles Triggered by Metal Ions

Organic molecular devices for information processing applications are highly useful building blocks for constructing molecular‐level machines. The development of “intelligent” molecules capable of performing logic operations would enable molecular‐level devices and machines to be created. We designed a series of 2,5‐diaryl‐1,3,4‐oxadiazoles bearing a 2‐(para‐substituted)phenyl and a 5‐(o‐pyridyl) group (substituent X=NMe₂, OEt, Me, H, and Cl; 1 a – e ) that form a bidentate chelating environment for metal ions. These compounds showed fluorescence response profiles varying in both emission intensity and wavelength toward the tested metal ions Ni²⁺, Cu²⁺, Zn²⁺, Cd²⁺, Hg²⁺, and Pb²⁺ and the responses were dependent on the substituent X, with those of 1 d being the most substantial. The 1,3,4‐oxadiazole O or N atom and pyridine N atom were identified as metal‐chelating sites. The fluorescence responses of 1 d upon metal chelation were employed for developing truth tables for OR, NOR, INHIBIT, and EnNOR logic gates as well as “ON‐OFF‐ON” and “OFF‐ON‐OFF” fluorescent switches in a single 1,3,4‐oxadiazole molecular system.