Molecular Design of an Environmentally Sensitive Fluorescent Nucleoside, 3‐Deaza‐2′‐Deoxyadenosine Derivative: Distinguishing Thymine by Probing the DNA Minor Groove

An environmentally sensitive fluorescent nucleoside containing a 3‐deazaadenine skeleton has been developed, and its photophysical properties were investigated. Newly developed C3‐naphthylethynylated 3‐deaza‐2′‐deoxyadenosine (^3nzA, 1 ) exhibited dual fluorescence emission from an intramolecular charge‐transfer state and a locally excited state, depending upon molecular coplanarity. DNA probes containing 1 clearly discriminated a perfectly matched thymine base on the complementary strand by a distinct change in emission wavelength.     

New fluorene-based alternating copolymers with pendent N,N-diethylaniline group: Highly sensitive and selective detection for Hg with “Turn-on” fluorescence response

Two fluorene-based alternating copolymers P1 and P2 with the N,N-diethylaniline pendent group in different contents on the polymer backbone were synthesized through Suzuki Coupling Reaction, and were fully characterized by ¹H NMR, elemental analysis, and gel-permeation chromatography (GPC). Photophysical studies show that changes of the contents of the N,N-diethylaniline groups have little effect on the ground state electronic structure, but take a significant effect on the excited state. The intensities of green emission band in these polymers changes with the different content of diethylaniline groups, and are supposed to be originated from an intramolecular charge transfer process. Both of the P1 and P2 show remarkable fluorescence emission “turn-on” responses exclusively to Hg²⁺. Moreover, fluorescent titration experiments indicate that the two copolymers have high sensitivity for Hg²⁺. The coordination between metal ions and N atoms could greatly weaken the electron-donating ability of N atoms, consequently inhibit the intramolecular charge transfer process, leading to fluorescence emission enhancement. As far as we know, this is the first report for detection of Hg²⁺ with “turn-on” output signals based on polyfluorenes.     

Effect of Dimer Structure and Inhomogeneous Broadening of Energy Levels on the Action of Flavomononucleotide in Rigid Polyvinyl Alcohol Films

The results of time-resolved fluorescence measurements of flavin mononucleotide (FMN) in rigid polyvinyl alcohol films (PVA) demonstrate that fluorescence intensity decays are strongly accelerated in the presence of fluorescent dimers and nonradiative energy transfer processes. The fluorescence decay originating both from H and J dimer states of FMN was experimentally observed for the first time. The mean fluorescence lifetimes for FMN dimers were obtained: τfl = 2.66 ns (at λ_exc = 445 nm) and τfl = 2.02 (at λ_exc = 487 nm) at λ_obs = 600 nm and T = 253 K from H and J state of dimers, respectively. We show that inhomogeneous orientational broadening of energy levels (IOBEL) affects the shape of the fluorescence decay and leads to the dependence of the average monomer fluorescence lifetime on excitation wavelength. IOBEL affected the nonradiative energy transfer and indicated that different flavin positioning in the protein pocket could (1) change the spectroscopic properties of flavins due to the existence of “blue” and “red” fluorescence centers, and (2) diminish the effectiveness of energy transfer between FMN molecules.     

A Multifunctional and Fast-Response Lysosome-Targetable Fluorescent Probe for Monitoring pH and Isoxaflutole

A new chemosensor, namely N-(2-morpholinoethyl)acetamide-4-morpholine-1,8-naphthimide (MMN), was designed and synthesized through an amidation reaction. MMN was fabricated as a multifunctional fluorescent probe for monitoring pH and isoxaflutole. MMN exhibited excellent stability in MeCN/H₂O (v/v, 9/1), with an obvious “off–on” fluorescence response toward pH changes due to intramolecular charge transfer (ICT), where the linear response ranges of MMN in the weakly acidic system were from 4.2 to 5.0 and from 5.0 to 6.0 with apparent pK_a = 4.62 ± 0.02 and 5.43 ± 0.02. Based on morpholine as the lysosome targetable unit, MMN could selectively locate lysosomes in live cells. MMN also successfully detected the presence of H⁺ in test papers. Finally, MMN could specifically recognize isoxaflutole at a detection limit of 0.88 μM. A possible sensing mechanism was identified based on density function theory calculations. These results indicate that MMN could be a superior potential chemosensor for detecting pH and isoxaflutole selectively and sensitively and could be used in real sample detection.     

The design and synthesis of a novel 1,8-naphthalimide PAMAM light-harvesting dendron with fluorescence “off-on” switching core

A novel polyamidoamine dendron core, peripherally functionalized with 1,8-naphthalimide fluorophores, was configured as a light harvesting antenna in which the system surface was labelled with blue emitting 4-allyloxy-1,8-naphthalimide “donor” dyes capable of both absorbing light and efficiently (96%) transferring the energy to a single, yellow-green emitting 4-N-methylpiperazinyl-1,8-naphthalimide “acceptor” dye. The 1,8-naphthalimide core was designed on the “fluorophore-spacer-receptor” format and was able to function as a fluorescence photoinduced electron transfer sensor. Two different photoinduced electron transfer effects were observed in the new antenna namely that from the receptor to the core fluorophore and that from the polyamidoamine backbone to the peripheral 1,8-naphthalimides. Althogh the core emission intensity of the system was enhanced > four times by reducing the pH from 10 to 2, the fluorescence enhancement of the system in acidic medium, excited within the periphery (λ_ex = 360 nm), was approximately twice that of the core fluorescence enhancement after direct excitation of the focal 1,8-naphthalimide (λ_ex = 420 nm), because of more efficient energy transfer. The observed “off-on” switching of the core fluorescence over a wid pH scale indicates that the novel light harvesting antenna would be able to act as a highly efficient fluorescent sensor.     

Nile red probing for sphere-to-rod-to-wormlike micelle transition in aqueous surfactant solution

Nile red (phenoxazone-9) was used as a fluorescence probe to detect the sphere-to-rod-to-wormlike micellar transition in the aqueous mixtures of cetyltrimethylammonium bromide and sodium salicylate or potassium bromide, and also in the aqueous solution of a Gemini surfactant, ethanediyl-α,ω-bis(dimethyl dodecyl ammonium bromide). The results showed the I_a/I_b of Nile red (the fluorescence intensity ratio of the twisted intramolecular charge transfer band to the planar locally excited band) was a more sensitive index than the I_a (the fluorescence intensity of the twisted intramolecular charge transfer band) to represent the micellar transition. This was attributed to the special molecular structure of Nile red that has a large conjugated ring and the can form hydrogen bond with water molecules at the electron acceptor group. This led to sensitive response of the twisted intramolecular charge transfer state of Nile red to the change of microenvironment.     

New fluorescent elastomeric materials based on synthetic and natural epoxidized rubbers

New fluorescent elastomeric materials were successfully prepared by reaction of an excited state intramolecular proton transfer-exhibiting silyl-functionalized benzothiazole dye with synthetic and natural epoxidized rubbers. The fluorescence emission and excitation spectra were obtained from the dye and the elastomeric materials to characterize its photophysical behavior. The benzothiazole derivative is fluorescent in the yellow region and presents a Stokes shift of 188 nm (solution) and 198 nm (solid state). After purification, the obtained materials from epoxidized rubbers presented excitation and emission maxima located at 358 nm and 550 nm, respectively, with a Stokes shift of 192 nm. The fluorescent dye could not be extracted from these films by solubilization–precipitation procedure, indicating the presence of covalent bonding between the dye and the matrix. On the other hand, the dye could be readily washed out of films that had been prepared using the corresponding nonepoxidized rubbers. © 2008 Wiley Periodicals, Inc. J Appl Polym Sci, 2008     

Fluorescence Recognition of Anions Using a Heteroditopic Receptor: Homogenous and Two-Phase Sensing

In contrast to monotopic receptor 3, the anthracene functionalized squaramide dual-host receptor 1 is capable of selectively extracting sulfate salts, as was evidenced unambiguously by DOSY, mass spectrometry, fluorescent and ion chromatography measurements. The receptors were investigated in terms of anion and ion pair binding using the UV–vis and ¹H NMR titrations method in acetonitrile. The reference anion receptor 3, lacking a crown ether unit, was found to lose the enhancement in anion binding induced by the presence of cations. Besides the ability to bind anions in an enhanced manner exhibited by ion pair receptors 2 and 4, changing the 1-aminoanthracene substituent resulted in their exhibiting a lower anion affinity than receptor 1. By using receptor 1 and adjusting the water content in organic phase it was possible to selectively detect sulfates both by “turn-off” and “turn-on” fluorescence, and to do so homogenously and under interfacial conditions. Such properties of receptor 1 have allowed the development of a new type of sensor capable of recognizing and extracting potassium sulfate from the aqueous medium across a phase boundary, resulting in an appropriate fluorescent response in the organic solution.     

The Role of Non-Specific Interactions in Canonical and ALT-Associated PML-Bodies Formation and Dynamics

In this work, we put forward a hypothesis about the decisive role of multivalent nonspecific interactions in the early stages of PML body formation. Our analysis of the PML isoform sequences showed that some of the PML isoforms, primarily PML-II, are prone to phase separation due to their polyampholytic properties and the disordered structure of their C-terminal domains. The similarity of the charge properties of the C-terminal domains of PML-II and PML-VI isoforms made it possible for the first time to detect migration of PML-VI from PML bodies to the periphery of the cell nucleus, similar to the migration of PML-II isoforms. We found a population of “small” (area less than 1 µm²) spherical PML bodies with high dynamics of PML isoforms exchange with nucleoplasm and a low fraction of immobilized proteins, which indicates their liquid state properties. Such structures can act as “seeds” of functionally active PML bodies, providing the necessary concentration of PML isoforms for the formation of intermolecular disulfide bonds between PML monomers. FRAP analysis of larger bodies of toroidal topology showed the existence of an insoluble scaffold in their structure. The hypothesis about the role of nonspecific multiple weak interactions in the formation of PML bodies is further supported by the change in the composition of the scaffold proteins of PML bodies, but not their solidification, under conditions of induction of dimerization of PML isoforms under oxidative stress. Using the colocalization of ALT-associated PML bodies (APBs) with TRF1, we identified APBs and showed the difference in the dynamic properties of APBs and canonical PML bodies.     

Complementary Effects of Carbamylated and Citrullinated LL37 in Autoimmunity and Inflammation in Systemic Lupus Erythematosus

LL37 acts as T-cell/B-cell autoantigen in Systemic lupus erythematosus (SLE) and psoriatic disease. Moreover, when bound to “self” nucleic acids, LL37 acts as “danger signal,” leading to type I interferon (IFN-I)/pro-inflammatory factors production. T-cell epitopes derived from citrullinated-LL37 act as better antigens than unmodified LL37 epitopes in SLE, at least in selected HLA-backgrounds, included the SLE-associated HLA-DRB1*1501/HLA-DRB5*0101 backgrounds. Remarkably, while “fully-citrullinated” LL37 acts as better T-cell-stimulator, it loses DNA-binding ability and the associated “adjuvant-like” properties. Since LL37 undergoes a further irreversible post-translational modification, carbamylation and antibodies to carbamylated self-proteins other than LL37 are present in SLE, here we addressed the involvement of carbamylated-LL37 in autoimmunity and inflammation in SLE. We detected carbamylated-LL37 in SLE-affected tissues. Most importantly, carbamylated-LL37-specific antibodies and CD4 T-cells circulate in SLE and both correlate with disease activity. In contrast to “fully citrullinated-LL37,” “fully carbamylated-LL37” maintains both innate and adaptive immune-cells’ stimulatory abilities: in complex with DNA, carbamylated-LL37 stimulates plasmacytoid dendritic cell IFN-α production and B-cell maturation into plasma cells. Thus, we report a further example of how different post-translational modifications of a self-antigen exert complementary effects that sustain autoimmunity and inflammation, respectively. These data also show that T/B-cell responses to carbamylated-LL37 represent novel SLE disease biomarkers.     

A turn-off fluorescence sensor for cyanide detection which in turn inhibit 2-way ESIPT investigated by experimental and theoretical study

A ligand based on 3-((quinoline-7-yl) methyeleneamino) phenazine-2-ol) (HAPQA) has been designed and synthesized for the selective detection of cyanide ions. The ligand HAPQA exhibits excited-state intramolecular proton transfer (ESIPT) with a long wavelength emission fluorescent (575 nm) which gradually quenches with the addition of cyanide ions. The photophysical properties of the probe as well as its selectivity towards CN⁻ ions are explored using UV–visible, emission spectroscopy and time-resolved fluorescence spectroscopic studies. The ligand exhibits strong H-bonding-mediated inhibition of 2-way excited-state intramolecular proton transfer (ESIPT) in HAPQA selectively with cyanide ions over all other ions. The deep orange colour fluorescence of the ligand in acetonirile turns into bright green coloured solution in presence of cyanide ions with a detection limit of 0.60 μM. DFT calculations has been done to study the ground and excited state energy optimized structure and proposed mechanism which is in harmony with the experimental findings and the ESIPT process observed in ligand HAPQA. Thus, the receptor can be used as a Colorimetric and fluorescent sensor for the determination of CN⁻ ion.     

树枝形聚合物修饰双8-羟基喹啉衍生物的合成及稳态光物理性质研究

设计合成了1—3代芳醚骨架树枝形聚合物修饰的双8-羟基喹啉衍生物．对这些化合物在不同溶剂中的荧光光谱研究表明，随着代数的增加，目标树枝形聚合物的荧光量子产率增大，树枝形聚合物对核心发色团具有一定的隔离作用，并且目标分子内可以发生从骨架向核心发色团的能量传递．     

Novel ESIPT fluorescent benzazolyl-4-quinolones: Synthesis, spectroscopic characterization and photophysical properties

Two, novel, benzazolyl-quinolone heterocycles, fluorescent by virtue of intramolecular proton transfer mechanism in the excited state (ESIPT), were obtained using the Gould-Jacobs reaction. The intramolecular cyclization step in the preparation of the anilinomethylene malonate derivatives was carried out using polyphosphoric acid, heat transfer fluids (Dowtherm A Fluid, mineral oil and diphenyl ether) as well as tandem methodology, at temperatures ranging from 180 °C to 250 °C. Tandem methodology provided better yields and lower by-product formation. The synthesized quinolones were characterized using elemental analysis, IR, ¹³C and ¹H NMR spectroscopy. Photophysical behaviour was studied using UV–Vis and steady-state fluorescence, both in solution and in solid state. The quinolones were fluorescent in solution in the orange-red region (500–800 nm), under UV radiation, and displayed a large Stokes shift (165–194 nm).     

Synthesis and luminescent properties of perylene bisimide-cored dendrimers with carbazole surface groups

A group of perylene bisimide (PBI) cored dendrimers were designed and synthesized. The polyphenylene dendrons containing carbazole functional groups at periphery were attached to the PBI core with expectation to control the intermolecular interaction and to tune the charge transporting ability of dendrimers. Their photophysical, electrochemical and thermal properties were investigated. The spectral data showed that energy transfer and photoinduced charge transfer coexist between the carbazole peripheries and the PBI core, competing to influence the luminescent properties of these dendrimers. The red OLEDs were fabricated with these dendrimers as non-doped emitting layer by solution method. The dendrimers bearing carbazoles exhibited improved EL performance than those model compounds. The improved charge balance state caused by these carbazole units is suggested to be responsible for the EL performance.     

Cyanine Dyes for Photo-Thermal Therapy: A Comparison of Synthetic Liposomes and Natural Erythrocyte-Based Carriers

Cyanine fluorescent dyes are attractive diagnostic or therapeutic agents due to their excellent optical properties. However, in free form, their use in biological applications is limited due to the short circulation time, instability, and toxicity. Therefore, their encapsulation into nano-carriers might help overcome the above-mentioned issues. In addition to indocyanine green (ICG), which is clinically approved and therefore the most widely used fluorescent dye, we tested the structurally similar and cheaper alternative called IR-820. Both dyes were encapsulated into liposomes. However, due to the synthetic origin of liposomes, they can induce an immunogenic response. To address this challenge, we proposed to use erythrocyte membrane vesicles (EMVs) as “new era” nano-carriers for cyanine dyes. The optical properties of both dyes were investigated in different biological relevant media. Then, the temperature stability and photo-stability of dyes in free form and encapsulated into liposomes and EMVs were evaluated. Nano-carriers efficiently protected dyes from thermal degradation, as well as from photo-induced degradation. Finally, a hemotoxicity study revealed that EMVs seem less hemotoxic dye carriers than clinically approved liposomes. Herein, we showed that EMVs exhibit great potential as nano-carriers for dyes with improved stability and hemocompatibility without losing excellent optical properties.     

Proposal of a New Method for Measuring F?rster Resonance Energy Transfer (FRET) Rapidly,Quantitatively and Non-Destructively

The process of radiationless energy transfer from a chromophore in an excited electronic state (the “donor”) to another chromophore (an “acceptor”), in which the energy released by the donor effects an electronic transition, is known as “Förster Resonance Energy Transfer” (FRET). The rate of energy transfer is dependent on the sixth power of the distance between donor and acceptor. Determining FRET efficiencies is tantamount to measuring distances between molecules. A new method is proposed for determining FRET efficiencies rapidly, quantitatively, and non-destructively on ensembles containing donor acceptor pairs: at wavelengths suitable for mutually exclusive excitations of donors and acceptors, two laser beams are intensity-modulated in rectangular patterns at duty cycle ½ and frequencies f₁ and f₂ by electro-optic modulators. In an ensemble exposed to these laser beams, the donor excitation is modulated at f₁, and the acceptor excitation, and therefore the degree of saturation of the excited electronic state of the acceptors, is modulated at f₂. Since the ensemble contains donor acceptor pairs engaged in FRET, the released donor fluorescence is modulated not only at f₁ but also at the beat frequency Δf: = |f₁ − f₂|. The depth of the latter modulation, detectable via a lock-in amplifier, quantitatively indicates the FRET efficiency.     

Reconstructing a Flavodoxin Oxidoreductase with Early Amino Acids

Primitive proteins are proposed to have utilized organic cofactors more frequently than transition metals in redox reactions. Thus, an experimental validation on whether a protein constituted solely by early amino acids and an organic cofactor can perform electron transfer activity is an urgent challenge. In this paper, by substituting “late amino acids (C, F, M, T, W, and Y)” with “early amino acids (A, L, and V)” in a flavodoxin, we constructed a flavodoxin mutant and evaluated its characteristic properties. The major results showed that: (1) The flavodoxin mutant has structural characteristics similar to wild-type protein; (2) Although the semiquinone and hydroquinone flavodoxin mutants possess lower stability than the corresponding form of wild-type flavodoxin, the redox potential of double electron reduction E_m,7 (fld) reached −360 mV, indicating that the flavodoxin mutant constituted solely by early amino acids can exert effective electron transfer activity.     

Effect of different electron donating groups on the performance of dye-sensitized solar cells

A series of organic sensitizers containing identical π-spacers and electron acceptors but different, aromatic amine electron-donating groups, were used in dye-sensitized solar cells to study the effect of the electron donating groups on device performance. The derived photophysical and photovoltaic properties, as well as density functional theory calculations, revealed that the tetrahydroquinoline dye was prone to aggregate upon the surface of titanium dioxide owing to the dye's planar structure. A 45% improvement in efficiency of a tetrahydroquinoline dye based cell was achieved when chenodeoxycholic acid was employed as co-adsorbent. However, the airscrew type of triphenylamine unit and Y type structure of the substituted phenothiazine framework suppressed dye aggregation on titanium dioxide. The efficiency of a phenothiazine dye-based cell fabricated using saturated co-adsorbent in dichloromethane was only 15% greater than that achieved in the absence of co-adsorbent. Electrochemical Impedance Spectroscopy was used to determine the interfacial charge transfer process occurring in solar cells that employed different dyes in both the absence and presence of chenodeoxycholic acid as co-adsorbent.     

Synthesis,Properties and Bioimaging Applications of Silver-Based Quantum Dots

Ag-based quantum dots (QDs) are semiconductor nanomaterials with exclusive electrooptical properties ideally adaptable for various biotechnological, chemical, and medical applications. Silver-based semiconductor nanocrystals have developed rapidly over the past decades. They have become a promising luminescent functional material for in vivo and in vitro fluorescent studies due to their ability to emit at the near-infrared (NIR) wavelength. In this review, we discuss the basic features of Ag-based QDs, the current status of classic (chemical) and novel methods (“green” synthesis) used to produce these QDs. Additionally, the advantages of using such organisms as bacteria, actinomycetes, fungi, algae, and plants for silver-based QDs biosynthesis have been discussed. The application of silver-based QDs as fluorophores for bioimaging application due to their fluorescence intensity, high quantum yield, fluorescent stability, and resistance to photobleaching has also been reviewed.