Fluorescent Complex Research Articles

A carbon quantum dot and rhodamine-based ratiometric fluorescent complex for the recognition of histidine in aqueous systems

A simple and effective ratiometric fluorescent complex has been developed for the selective sensing of histidine in aqueous systems.

Strong Fluorescent Lanthanide Salen Complexes: Photophysical Properties, Excited-State Dynamics, and Bioimaging.

The synthesis, excited-state dynamics, and biological application of luminescent lanthanide salen complexes (Ln = Lu, Gd, Eu, Yb, salen = N, N'-bis(salicylidene)ethylenediamine-based ligands) with sandwich structures are described. Among them, Lu(III) complexes show unusually strong ligand-centered fluorescence with quantum yields up to 62%, although the metal center is close to a chromophore ligand. The excited-state dynamic studies including ultrafast spectroscopy for Ln-salen complexes revealed that their excited states are solely dependent on the salen ligands and the ISC rates are slow (108-109 s-1). Importantly, time-dependent density functional theory calculations attribute the low energy transfer efficiency to the weak spin-orbital coupling (SOC) between the singlet and triplet excited states. More importantly, Lu-salen has been applied as a molecular platform to construct fluorescence probes with organelle specificity in living cell imaging, which demonstrates the advantages of the sandwich structures as being capable of preventing intramolecular metal-ligand interactions and behaviors different from those of the previously reported Zn-salens. Most importantly, the preliminary study for in vivo imaging using a mouse model demonstrated the potential application of Ln coordination complexes in therapeutic and diagnostic bioimaging beyond living cells or in vitro.

Watching an Engineered Calcium Biosensor Glow: Altered Reaction Pathways before Emission.

Biosensors have become an indispensable tool set in life sciences. Among them, fluorescent protein-based biosensors have great biocompatibility and tunable emission properties but their development is largely on trial and error. To facilitate a rational design, we implement tunable femtosecond stimulated Raman spectroscopy, aided by transient absorption and quantum calculations, to elucidate the working mechanisms of a single-site Pro377Arg mutant of an emission ratiometric Ca2+ biosensor based on a green fluorescent protein-calmodulin complex. Comparisons with the parent protein and the Ca2+-free/bound states unveil more structural inhomogeneity yet an overall faster excited-state proton-transfer (ESPT) reaction inside the Ca2+-bound biosensor. The correlated photoreactant and photoproduct vibrational modes in the excited state reveal more chromophore twisting and trapping in the Ca2+-bound state during ESPT and the largely conserved chromophore dynamics in the Ca2+-free state from parent protein. The uncovered structural dynamics insights throughout an ESPT reaction inside a calcium biosensor provide important design principles in maintaining a hydrophilic, less compact, and more homogeneous environment with directional H-bonding (from the chromophore to surrounding protein residues) via bioengineering methods to improve the ESPT efficiency and quantum yield while maintaining photostability.

Paramagnetism and Fluorescence of Zinc(II) Tripyrrindione: A Luminescent Radical Based on a Redox-Active Biopyrrin.

The ability of bilins and other biopyrrins to form fluorescent zinc complexes has been known for more than a century; however, the exact identity of the emissive species remains uncertain in many cases. Herein, we characterize the hitherto elusive zinc complex of tripyrrin-1,14-dione, an analogue of several orange urinary pigments. As previously observed for its Pd(II), Cu(II), and Ni(II) complexes, tripyrrindione binds Zn(II) as a dianionic radical and forms a paramagnetic complex carrying an unpaired electron on the ligand π-system. This species is stable at room temperature and undergoes quasi-reversible ligand-based redox chemistry. Although the complex is isolated as a coordination dimer in the solid state, optical absorption and electron paramagnetic resonance spectroscopic studies indicate that the monomer is prevalent in a tetrahydrofuran solution. The paramagnetic Zn(II) tripyrrindione complex is brightly fluorescent (λabs = 599 nm, λem = 644 nm, ΦF = 0.23 in THF), and its study provides a molecular basis for the observation, made over several decades since the 1930s, of fluorescent behavior of tripyrrindione pigments in the presence of zinc salts. The zinc-bound tripyrrindione radical is thus a new addition to the limited number of stable radicals that are fluorescent at room temperature.

Self-Assembly of Europium-Containing Polyoxometalates/Tetra-n-alkyl Ammonium with Enhanced Emission for Cu2+ Detection.

Lanthanide-containing polyoxometalates (POMs) can be used to detect various materials, but their luminescence in water has suffered enormous limitations due to the strong fluorescence quenching. Herein, to resolve this problem, three-dimensional nanoparticles built by mixed Weakley-type europium-containing POMs (Na9[EuW10O36]·32H2O, abbreviated to EuW10) and tetra-n-alkyl ammonium (TA) with enhanced fluorescent properties have been designed in aqueous solution using an ionic self-assembly (ISA) technique, which is mainly driven by the electrostatic interaction between EuW10 and TA. The morphology and fluorescent properties of the system as well as some influencing factors (alkyl chain length, amino group, and inorganic salt concentration) were systematically investigated. The results indicated that the fluorescent intensity of EuW10/tetramethylammonium bromide (TMAB) composite increased about 14 times, whereas the extent of increase of fluorescence for EuW10/tetraethylammonium bromide (TEAB) and EuW10/tetrabutylammonium bromide (TMAB) composites gradually decrease due to the bulkier steric hindrance of the longer alkyl chain. Besides, the luminescence of EuW10/TMAB nanoparticles is pH responsive, and the reversibility of their structures and luminescence can be realized upon the addition of NaOH/HCl. Moreover, the EuW10/TMAB system also shows great fluorescence-sensing behavior, which could detect Cu2+ with a detection limit of 0.15 μM. Our work provides a facile construction strategy for a functional fluorescent complex via POMs-based supramolecular self-assembly in aqueous solution, which will be further used in biomarkers and sensors.

Rapid, sensitive and highly specific label-free fluorescence biosensor for microRNA by branched rolling circle amplification

A simple fluorescence biosensor for rapid and sensitive target microRNA (miRNA) quantification by branched rolling circle amplification (BRCA) is developed in this work. Target miRNA functions as primer to recognize and hybridize with a circle DNA template, initiating rolling circle amplification (RCA) by Phi29 DNA polymerase. The introduction of reverse primers complementary to the RCA products enables isothermal BRCA, in which a large amount of deoxynucleotide (dNTP) were consumed and same number of pyrophosphates (PPi) were produced. In this study, a simple and non-expensively synthesized terpyridine-based Zn(II) complex is utilized as fluorescent probe for selective detection of pyrophosphate (PPi) over dNTP. The PPi generated in this isothermal amplification process efficiently chelates to this terpyridine-Zn(II) complex, forming a highly fluorescent complex, terpyridine-Zn(II)-PPi, whose fluorescence intensity is closely related with the initial target miRNA concentration. The utilization of the isothermal BRCA amplification and direct monitoring of the DNA polymerization by-product, i.e. PPi, for non-label fluorescence detection of miRNA greatly simplify this sensor procedure. This sensor shows a linear response between the fluorescence intensity and the target miRNA concentration from 50 to 500 fM with a detection limit of 25 fM. This much-simplified sensor offers a sensitive and easy-to-use platform for miRNA quantification, and hence may significantly enhance the utilisation of miRNAs as biomarkers in drug discovery, clinical diagnosis and life science research.

In vivo bio-imaging of sodium meta-arsenite and hydrogen phosphate in zebrafish embryos using red fluorescent zinc complex

The photophysical behaviours of quinoline based red fluorescent zinc complex (QAZn) in the presence of the highly toxic AsO2− and biologically active H2PO4− ions have been explored in aqueous DMSO solution. The sequential detection of both the anions was examined using absorption and fluorescence techniques. As the zinc complex (QAZn) could form strong adducts with AsO2− and H2PO4− ions, it could be easier to recognize the ions. Moreover, successive addition of H2PO4 to QAZn-AsO2 solution caused the dissociation of Zn2+ from parent zinc complex (QAZn) and the liberated free ligand restored its original green fluorescence. Since the probe showed lowest mortality, it has been further exploited for live cell studies in zebrafish embryos. Moreover, the spectroscopic data of probe QAZn were utilized to construct the molecular logic circuits with AND and NOT gates.

Which Amino Acids are Capable of Nucleating Fluorescent Silver Clusters in Proteins?

In this experimental and theoretical joint study, we used single amino acids as model systems for studying protein–cluster interactions. We probed 12 natural amino acids with different functional groups as potential templates of fluorescent silver (Ag) nanoclusters obtained by sodium borohydride reduction of Ag ions. We also calculated the Gibbs free energies of the complexes formed between Ag+ ions, Ag atoms, and two-atom Ag clusters with the amino acids’ various functional groups. Only cysteine and tyrosine could form fluorescent complexes with Ag clusters. This agrees with the calculated Gibbs free energies for the Ag cluster–amino acid complexes. We also show that the tyrosine-based fluorescent Ag cluster could be obtained using a green synthetic method in which tyrosine, at alkali pH, acts as a reducing agent. The optimized structure of a complex of Ag3+ cluster with three semiquinone tyrosine rings is proposed. These results can be used in designing and synthesizing new peptide-templated biolabels.

Improved spectrofluorimetric determination of mebendazole, a benzimidazole anthelmintic drug, through complex formation with lanthanum (III); Application to pharmaceutical preparations and human plasma

A, rapid and specific spectrofluorimetric procedure was developed and validated for determination of mebendazole. The reaction of mebendazole with lanthanum (III) ions in aqueous buffered solution (pH 5.5) produced a highly fluorescent stable complex which exhibited an emission at 340 nm (λex 295 nm). Different types of surfactant were examined to enhance the fluorescence of the complex but none of them was effective. Other reaction parameters that affect the formation and stability of the resulting complex were studied and adjusted. The linearity range for the relationship between the fluorescence intensity and the drug concentration was 0.07–0.8 μg mL−1 with a correlation coefficient (r) of 0.9997. The quantitation and detection limits were 0.068 and 0.022 μg mL−1, respectively. The metal was found to react with the drug in the ratio of 2:1 drug to metal with a binding constant of 1.67 × 105. The change in Gibb's free energy for the reaction was −29.8 KJ mol−1, which indicates the high feasibility of the reaction. Some dosage forms and spiked human plasma were analyzed successfully with the developed method with high recovery. The main percentage recovery was in the range of 100.32–100.52% for dosage forms and 94.74–97.31% for spiked plasma. The results of both the reported and proposed methods were statistical compared and the comparison revealed good accuracy and precision of the proposed method.

In Vivo Selectivity and Localization of Reactive Oxygen Species (ROS) Induction by Osmium Anticancer Complexes That Circumvent Platinum Resistance.

Platinum drugs are widely used for cancer treatment. Other precious metals are promising, but their clinical progress depends on achieving different mechanisms of action to overcome Pt-resistance. Here, we evaluate 13 organo-Os complexes: 16-electron sulfonyl-diamine catalysts [(η6-arene)Os(N,N′)], and 18-electron phenylazopyridine complexes [(η6-arene)Os(N,N’)Cl/I]+ (arene = p-cymene, biphenyl, or terphenyl). Their antiproliferative activity does not depend on p21 or p53 status, unlike cisplatin, and their selective potency toward cancer cells involves the generation of reactive oxygen species. Evidence of such a mechanism of action has been found both in vitro and in vivo. This work appears to provide the first study of osmium complexes in the zebrafish model, which has been shown to closely model toxicity in humans. A fluorescent osmium complex, derived from a lead compound, was employed to confirm internalization of the complex, visualize in vivo distribution, and confirm colocalization with reactive oxygen species generated in zebrafish.

A facile surface modification strategy for fabrication of fluorescent silica nanoparticles with the aggregation-induced emission dye through surface-initiated cationic ring opening polymerization

Fluorescent silica nanoparticles (FSNPs) have attracted great interest for potential applications in biological and biomedical fields because they possess higher fluorescence quantum yield and better fluorescence stability as comparison with small organic fluorescent molecules. The encapsulation of covalent linkage with fluorescent organic dyes or fluorescent metal complexes has demonstrated to be the commonly adopted strategies for fabrication of FSNPs previously. However, it is still challengeable to obtain FSNPs based polymer composites with intensive fluorescence and good water dispersibility through a one-pot surface modification strategy. In this paper, we developed a facile method to fabricate novel FSNPs based polymer composites (PhE@MSNs-PEtOx) through introducing the aggregation-induced emission (AIE) dye (PhE-OH) and poly(2-ethyl-2-oxazoline) (PEtOx) onto mesoporous silica nanoparticles (MSNs) based on cationic ring opening polymerization (CROP). The resulting PhE@MSNs-PEtOx composites possess strong fluorescence emission, excellent hydrophilicity and biocompatibility. These features make the final FSNPs based polymer composites great potential for biomedical applications. Taken together, we have developed for the first time that FSNPs based polymer composites can be facilely prepared through the one-pot introduction of AIE dyes and hydrophilic PEtOx on MSNs. Moreover, the novel FSNPs based composites could also be utilized for other biomedical applications considered their properties.

Tracking yeast pheromone receptor Ste2 endocytosis using fluorogen-activating protein tagging

To observe internalization of the yeast pheromone receptor Ste2 by fluorescence microscopy in live cells in real time, we visualized only those molecules present at the cell surface at the time of agonist engagement (rather than the total cellular pool) by tagging this receptor at its N-terminus with an exocellular fluorogen-activating protein (FAP). A FAP is a single-chain antibody engineered to bind tightly a nonfluorescent, cell-impermeable dye (fluorogen), thereby generating a fluorescent complex. The utility of FAP tagging to study trafficking of integral membrane proteins in yeast, which possesses a cell wall, had not been examined previously. A diverse set of signal peptides and propeptide sequences were explored to maximize expression. Maintenance of the optimal FAP-Ste2 chimera intact required deletion of two, paralogous, glycosylphosphatidylinositol (GPI)-anchored extracellular aspartyl proteases (Yps1 and Mkc7). FAP-Ste2 exhibited a much brighter and distinct plasma membrane signal than Ste2-GFP or Ste2-mCherry yet behaved quite similarly. Using FAP-Ste2, new information was obtained about the mechanism of its internalization, including novel insights about the roles of the cargo-selective endocytic adaptors Ldb19/Art1, Rod1/Art4, and Rog3/Art7.

Improved Chemical-Genetic Fluorescent Markers for Live Cell Microscopy.

Inducible chemical-genetic fluorescent markers are promising tools for live cell imaging requiring high spatiotemporal resolution and low background fluorescence. The fluorescence-activating and absorption shifting tag (FAST) was recently developed to form fluorescent molecular complexes with a family of small, synthetic fluorogenic chromophores (so-called fluorogens). Here, we use rational design to modify the binding pocket of the protein and screen for improved fluorescence performances with four different fluorogens. The introduction of a single mutation results in improvements in both quantum yield and dissociation constant with nearly all fluorogens tested. Our improved FAST (iFAST) allowed the generation of a tandem iFAST (td-iFAST) that forms green and red fluorescent reporters 1.6-fold and 2-fold brighter than EGFP and mCherry, respectively, while having a comparable size.

Effects of compression on orientation of ligands in fluorescent complexes between hydroxyapatite with amino acids and their optical properties

This study aims to reveal the effects of pressure during cold isostatic pressing (CIP) on the microstructure and optical properties of fluorescent HAp complexes. Although the microsturucture-dependent properties of fluorescent HAp complexes have been reported to improve the antibacterial properties of photocatalyst coating layers, the mechanism behind the changes in the fluorescence properties of highly compressed HAp complexes has not yet been unveiled. CIP was successfully used to fabricate fluorescent HAp – amino acid complexes, and their fluorescence intensities increased with increasing fabrication pressure. Peak wavelength of fluorescence emitted by the HAp – amino acid complexes exhibited yellow to red shift. Although the thickness of the amino acid layer was saturated in higher pressure cases, the concentration of amino acids increased proportionally with pressure, which suggests changes in the packing structures of the ligands in the HAp– amino acid complexes. Polarized Raman spectroscopy measurements clearly detected ligands normally arranged to the HAp layer under high pressure fabrication conditions, which can provide the tightly packed ligand structure in the HAp– amino acid complexes. These tightly packed ligand structure in the HAp– amino acid complexes could emit stronger fluorescence owing to the increased density of complexations. This newly found pressure dependency in the optical properties of HAp–amino acid complexes is beneficial for developing biocompatible fluorescence materials or enhancement agents for antibacterial coating layers.

Roger Yonchien Tsien. 1 February 1952—24 August 2016

Roger Yonchien Tsien displayed precocious childhood talents in chemistry. After graduating from Harvard University in chemistry and physics in 1972, he pursued a PhD programme in the Physiological Laboratory, Cambridge, under the supervison of Professor Richard Adrian (FRS 1977) with Marshal Scholarship support. His thesis ‘The design and use of organic chemical tools in cellular physiology’ won the Gedge Prize and a Comyns Berkeley Research Fellowship by Gonville and Caius College, supporting his postdoctoral work developing Ca 2+ -sensitive electrodes and fluorescent probes measuring cellular [Ca 2+ ]. His novel tetracarboxylate quin-2 readily accessed cells as its subsequently cleavable acetomethoxy ester and signalled in the physiological [Ca 2+ ] range. At Berkeley, further improved ratiometric and strongly fluorescent probes included the Ca 2+ -sensing indo-1, fura-2 and fluo-3 sensors for other strategic ions and molecules that could photolytically uncage key intracellular regulators. At San Diego, design of fluorescent protein complexes built from the cAMP-binding phosphokinase A was followed by Nobel prizewinning work expressing green-fluorescent protein (GFP) and developing spectral GFP variants forming fluorescent resonance energy transfer (FRET) pairs. Their conjugation with further proteins specifically binding particular ions or molecules under study permitted measurement of these by optical methods. Further detector protein complexes such as DsRed, fluorescent at longer wavelengths, were to complement GFP. These interests culminated in the development of chemical tools with potential diagnostic and therapeutic clinical applications through their optical and magnetic resonance signals. His scientific work bequeathed a lasting wealth of chemical tools invaluable for physiological investigation with both current and future applicability.

Fluorescent ternary complexes of some biogenic amines and their metabolites with europium and oxytetracycline for applications in the chemical analysis

New ternary complexes of europium with oxytetracycline possessing the intense fluorescence have been obtained for prospective applications in the high-sensitive detection of biogenic amines and their metabolites in biological fluids. Their stability constants have been determined using the Foster–Hammick–Wardley method based on the fluorescent spectroscopy data. The dependence between structure differences, stability constants of ternary complexes of europium–oxytetracycline with biogenic amines, and their metabolites, and sensitivity of their determination has been established.

Label-free and sensitive detection assay for terminal deoxynucleotidyl transferase via polyadenosine-coralyne fluorescence enhancement strategy

Terminal deoxynucleotidyl transferase (TdT) is a unique template-free polymerase that randomly adds multiple deoxyribonucleoside triphosphates (dNTPs) to the 3′-OH terminus of ssDNA. This characteristic makes TdT a versatile enzymatic tool in many fields. Moreover, aberrant TdT expression is a well-recognized biomarker of several leukemic diseases and is related to carcinogenesis. In this study, we developed a facile, rapid, label-free, and convenient assay for TdT detection. TdT-generated poly A tails formed a fluorescent enhancement complex in the presence of coralyne. To achieve a better signal-to-noise ratio, we used potassium thiocyanate (KSCN), instead of other halogen anions (KCl, KBr, KI, NaI) as the quenching agent of dissociate coralyne. Our results demonstrate that this assay is extremely facile, rapid, and label-free; at levels as low as 0.025 U/mL, TdT was distinctly detected within 55 min. And the determination of TdT activity in RBL-2H3 and Reh cells lysates exhibited a good sensing performance, demonstrating its potential applications in biochemical research and clinical diagnosis.

Fluorescent meso-benzyl curcuminoid boron complex: Synthesis, photophysics, DFT and NLO study

Curcumin based fluorescent NLOphore was synthesized. Solvent polarizability (SP) was found to be responsible for the solvatochromic nature of dye as confirmed from the multilinear regression analysis. DFT computations using global hybrid (B3LYP and BHHLYP) and range-separated hybrid (CAM-B3LYP) functionals with the basis set 6-31 + G(d,p) were performed to determine the linear as well as NLO properties. NLO response was measured using Z scan technique. The computed NLO values (βo = 426.64 × 10−30 esu) were found to be superior to that of urea (βo = 0.371 × 10−30 esu). The value of nonlinear absorption coefficient (β) and third-order nonlinear susceptibility (χ)3 were found to be 2.19 × 10−12 (m/W) and is 2.09 × 10−13 (e.s.u) respectively. The result of present work might be useful for the designing of curcumin based NLOphores for industrial applications.

Nonconjugated Fluorescent Molecular Cages of Trinuclear Fluoroborate Complexes with Salicylaldehyde-Based Schiff Base Ligands.

Fluorescent organic materials are commonly π-conjugated planar molecules. In the present work, however, we report a novel class of nonconjugated fluorescent molecular cages of trinuclear fluoroborate complexes (nine samples) with salicylaldehyde-based Schiff base ligands. Owing to the stress from lone pair electrons of N atom in the triethylamine bridge, these B(III) complexes exhibit unusual enantiomers with a tripodlike side-single-opening structure. They emit blue, green, and red emission with large Stokes shifts (up to 159 nm) and high fluorescence quantum yields in both solution (up to 0.24) and solid state (up to 0.25), which might contribute to their strong intramolecular hydrogen bonds and weak intermolecular and intramolecular π–π interactions. Combining their advantages of nonconjugation and biocompatibility, these flexible complexes have potential applications in living cell imaging and anion hosts. We have examined the inherent relationships between their chemical structures and emission properties and afforded a new stage for the design of nonconjugated fluorescent fluoroborate complexes.

Synthesis of a Novel Fluorescent Ruthenium Complex with an Appended Ac₄GlcNAc Moiety by Click Reaction.

The O-linked β-N-acetylglucosamine (O-GlcNAc) modification is an abundant post-translational modification in eukaryotic cells, which plays a fundamental role in the activity of many cells and is associated with pathologies like type II diabetes, Alzheimer’s disease or some cancers. However, the precise connexion between O-GlcNAc-modified proteins and their function in cells is largely undefined for most cases. Confocal microscopy is a powerful and effective tool for in-cell elucidation of the function of biological molecules. Chemical labeling of non-ultraviolet or non-fluorescent carbohydrates with fluorescent tag is an essential step that makes intra-cellular microscopic inspection possible. Here we report a strategy based on the 1,3-dipolar cycloaddition, called click chemistry, between unnatural N-acetylglucosamine (GlcNAc) analogues Ac4GlcNAc (substituted with an azido group) and the corresponding fluorescent tag Ru(bpy)2(Phen-alkyne)Cl2 (4) to synthesize the fluorescent dye Ru(bpy)2(Phen-Ac4GlcNAc)Cl2 (5) under mild and neutral reaction conditions. Moreover, 5 showed good stability, desirable fluorescence characteristics, and exhibited rather low levels of cytotoxicity against sensitive MCF-7 cells. Additionally, we have achieved successful fluorescent imaging of 5 transported in living MCF-7 cells. Cell images displayed that proteins are potentially labelled with 5 in the cytoplasm.