Construction of Fluorescent Probes Via Protection/Deprotection of Functional Groups: A Ratiometric Fluorescent Probe for Cu2+

Herein a ratiometric fluorescent Cu²⁺ probe was rationally constructed in a straightforward manner with the concept of aldehyde group protection/deprotection. The probe showed a ratiometric fluorescent response to Cu²⁺ with a large emission wavelength shift (>100 nm) and displayed high selectivity for Cu²⁺ over other metal ions due to distinct deprotection conditions. In addition, a Cu²⁺‐promoted dethioacetalization mechanism was proposed.     

基于香豆素的比率型次氯酸荧光探针

次氯酸(HCl O)是生物体内重要的活性氧(ROS)之一,在人类免疫功能系统中扮演着重要的角色,有助于对入侵细菌和病原体进行破坏。本文设计并合成了基于香豆素为母体单元的比率型次氯酸荧光探针。研究结果表明,该探针对次氯酸识别显示出较高的选择性,检测线低至12 mol/L,荧光响应可在5 s内迅速完成,并伴随着溶液颜色由无色转变为黄绿色。其它常见的阴离子及氧化型物质对次氯酸检测均无干扰。此外,高分辨率质谱、荧光光谱和紫外可见光谱变化共同证实了该探针对次氯酸的检测机制为次氯酸对探针氧化水解。     

Assembly of Water-soluble AIE-active Fluorescent Organic Nanoparticles for Ratiometric Detection of Hypochlorite in Living Cells

Hypochlorous acid (HOCl) plays a crucial role in many physiological processes and is widely used as bleach, deodorant and fungicide. In this work, we designed an amphiphilic hydrazone fluorescent molecule THG-1 containing hydrophilic sugar units and hydrophobic tetraphenylethylene unit for ratiometric detection of HOCl with high sensitivity and excellent selectivity based on HOCl-triggered hydrolyzation reaction and aggregation-induced emission (AIE) effect. The detection mechanism was verified by liquid chromatograph mass spectrometry experiments and scanning electron microscope (SEM) tests. Contrast experiments revealed that the numbers of lactose unit and hydrazone linker were essential for assembly of THG-1 and detection of HOCl. In addition, THG-1 was successfully used for imaging of exogenous and endogenous HOCl in living cells.     

An ESIPT-Based Ratiometric Fluorescent Probe for Highly Sensitive and Rapid Detection of Sulfite in Living Cells

The novel ratiometric fluorescent probe HPQRB with an ESIPT effect based on Michael addition for highly sensitive and fast detection of sulfite in living HepG2 cells is reported. HPQRB can be easily synthesized by a two-step condensation reaction. HPQRB has a large emission shift (Δλ=116 nm), which is beneficial for fluorescence imaging research, and its sulfite-responsive site is based on a rhodamine-like structure with the emission peak at 566 nm, which decreases with increasing sulfite concentration. and its HPQ structure always has an ESIPT effect throughout the reaction process, keeping the emission peak at 450 nm as a self-reference. In particular, HPQRB has high selectivity for sulfite and responds quickly (within 30 s) with a low detection limit (44 nM). Furthermore, HPQRB has been successfully used for fluorescence imaging of sulfite in HepG2 cells, demonstrating the superior ability to detect sulfite under physiological conditions.     

基于分子内电荷转移的阴离子比率荧光分子探针

设计合成了一种基于4-甲基-1-羟基二苯甲酮对硝基苯腙的比色和比率荧光阴离子受体1。此类受体以羟基和腙单元为识别位点,以硝基苯基为信号报告基团。向受体1的DMSO溶液中加入AcO-、H2PO4-、F-后,溶液颜色由黄色变为紫红色,而加入所研究的其它阴离子则无变化,从而实现对AcO-、H2PO4-、F-这三种离子的裸眼识别。利用紫外-可见吸收光谱、荧光光谱考察了其与AcO-,H2PO4-,F-,Cl-,Br-,I-等阴离子的识别作用。1H NMR滴定为受体分子与阴离子之间氢键作用本质提供了有力证据。     

Na+ Selective Fluorescent Tools Based on Fluorescence Intensity Enhancements,Lifetime Changes,and on a Ratiometric Response

Over the years, we developed highly selective fluorescent probes for K⁺ in water, which show K⁺-induced fluorescence intensity enhancements, lifetime changes, or a ratiometric behavior at two emission wavelengths (cf. Scheme 1, K1 – K4 ). In this paper, we introduce selective fluorescent probes for Na⁺ in water, which also show Na⁺ induced signal changes, which are analyzed by diverse fluorescence techniques. Initially, we synthesized the fluorescent probes 2 , 4 , 5 , 6 and 10 for a fluorescence analysis by intensity enhancements at one wavelength by varying the Na⁺ responsive ionophore unit and the fluorophore moiety to adjust different K_d values for an intra- or extracellular Na⁺ analysis. Thus, we found that 2 , 4 and 5 are Na⁺ selective fluorescent tools, which are able to measure physiologically important Na⁺ levels at wavelengths higher than 500 nm. Secondly, we developed the fluorescent probes 7 and 8 to analyze precise Na⁺ levels by fluorescence lifetime changes. Herein, only 8 (K_d=106 mm ) is a capable fluorescent tool to measure Na⁺ levels in blood samples by lifetime changes. Finally, the fluorescent probe 9 was designed to show a Na⁺ induced ratiometric fluorescence behavior at two emission wavelengths. As desired, 9 (K_d=78 mm ) showed a ratiometric fluorescence response towards Na⁺ ions and is a suitable tool to measure physiologically relevant Na⁺ levels by the intensity change of two emission wavelengths at 404 nm and 492 nm.     

A Ratiometric Fluorescent Probe for Gold and Mercury Ions

A fluorescent probe that displays a ratiometric fluorescence response towards gold and mercury ions has been devised. Emitting at a relatively longer wavelength, the conjugated form of the fluorescent dye transforms in the presence of the gold or mercury ions into a new dye, the molecular structure of which lacks the conjugation and consequently emits at a distinctly shorter wavelength.     

一种基于喹唑啉酮衍生物的荧光探针对次氯酸根离子的识别

次氯酸根(ClO~-)在人体免疫系统中发挥着重要的作用,其识别与检测备受关注。本文设计合成了一种含有喹唑啉酮骨架的腙型荧光探针(HEMQ),并通过~1H NMR、~(13)C NMR、高分辨质谱(HRMS)表征了其结构。探针HEMQ在V(乙醇)∶V(水)=1∶1(c(PBS)=0.02 mol/L,pH=8.7)溶液中对ClO~-具有良好的选择性且响应快速,荧光发生显著猝灭。探针HEMQ对ClO~-具有较高的灵敏度,检测限为1.0×10-4mol/L。此外,ClO~-可引起探针溶液由黄色到无色的颜色变化,因此HEMQ可作为比色、荧光双通道响应的ClO~-探针。     

A Sensitive and Selective Fluorescent Thiol Probe in Water Based on the Conjugate 1,4‐Addition of Thiols to α,β‐Unsaturated Ketones

Shedding light on thiol detection : A compound (see scheme) was developed as a novel, highly sensitive and selective fluorescent thiol probe, which also features suitable water solubility, functions rapidly under neutral conditions, and has excitation and emission in the visible region. Thus, it may be useful for potential biological applications.

     

一种基于菲并咪唑的新型次氯酸荧光探针及细胞成像研究

该文设计并合成了一种基于菲并咪唑的新型次氯酸荧光探针,该探针由商用试剂9,10-菲醌和4-(甲基巯基)苯甲醛通过一步反应生成,只需简单后处理(过滤和水洗)即可得到大量纯品(产率达85%)。由于硫的重原子效应,探针荧光较弱。但在次氯酸存在下,探针分子内的硫原子被氧化成亚砜,重原子效应减弱,同时分子内电荷转移效应(ICT)加强,导致荧光增强。借助高分辨质谱,证明了探针与次氯酸盐的反应机理。在PBS缓冲溶液中(DMF∶H₂O=2∶8,体积比,pH 7.4),探针MPI可定量检测0～100μmol/L范围内的HClO,检出限为0.26μmol/L。该探针对次氯酸具有较高的灵敏性和选择性。更重要的是,MPI具有良好生物相容性和细胞渗透性,可用于活细胞内次氯酸的可视化成像。探针MPI有望为机体内次氯酸的检测与追踪提供一种可靠、有效的方法。     

Rational Design of a Solvatochromic Fluorescent Uracil Analogue with a Dual‐Band Ratiometric Response Based on 3‐Hydroxychromone

Fluorescent nucleoside analogues with strong and informative responses to their local environment are in urgent need for DNA research. In this work, the design, synthesis and investigation of a new solvatochromic ratiometric fluorophore compiled from 3‐hydroxychromones (3HCs) and uracil fragments are reported. 3HC dyes are a class of multi‐parametric, environment‐sensitive fluorophores providing a ratiometric response due to the presence of two well‐resolved bands in their emission spectra. The synthesized conjugate demonstrates not only the preservation but also the improvement of these properties. The absorption and fluorescence spectra are shifted to longer wavelengths together with an increase of brightness. Moreover, the two fluorescence bands are better resolved and provide ratiometric responses across a broader range of solvent polarities. To understand the photophysical properties of this new fluorophore, a series of model compounds were synthesized and comparatively investigated. The obtained data indicate that uracil and 3HC fragments of this derivative are coupled into an electronic conjugated system, which on excitation attains strong charge‐transfer character. The developed fluorophore is a prospective label for nucleic acids. Abstract in Ukrainian: .     

基于对二烷基氨基苯甲酰苯胺分子内电荷转移的单糖比值法荧光受体

Two dual fluorescent receptors (1 and 2) for monosaccharides based on 4-dialky(alkyl=methyl and n-butyl) containing boronic acid group at the amido aniline were synthesized and their spectral properties were investigated. These receptors exhibited dual fluorescence with the long-wavelength band displaying strong solvent-polarity dependence, indicating the occurrence of the excited-state intramolecular charge transfer （ICT).With increasing pH value in aqueous solutions, the hybridization of the boron atom changed from sp^2 to sp^3, inducing a decrease in the total fluorescence quantum yield. The experimental results indicated that the anionic form of the boronate group acted as an electron donor and the benzanilide-like charge transfer was promoted upon hybridization change. In the presence of monosaccharides, the boronic acid in 1 and 2 changed from neutral to anionic form. The intensity of the locally excited (LE) state emission decreased in the presence of sugars while a slight increase in the intensity at the charge transfer (CT) emission occurred. Based on the change in the CT to LE intensity ratios of 1 and 2 due to sugar binding, ratiometric fluorescent assays for monosaccharide sensing were established.     

Reaction‐Based Fluorescent Probe for Detection of Endogenous Cyanide in Real Biological Samples

Herein, two compounds ( 1 a and 1 b ) were rationally constructed as novel reaction‐based fluorescent probes for CN^? by making use of the electron‐withdrawing ability of the cyano group that was formed from the sensing reaction. Notably, this design strategy was first employed for the development of fluorescent CN^? probes. The experimental details showed that probe 1 a exhibited a fluorescence turn‐on response to CN^?, whereas other anions, biological thiols, and hydrogen sulfide gave almost no interference. The detection limit of probe 1 a for CN^? was found to be 0.12 μM . The sensing reaction product of 1 a with CN^? was characterized by NMR spectroscopy and mass spectrometry. TD‐DFT calculations demonstrated that the formed cyano group drives the intramolecular charge transfer (ICT) process from coumarin dye to the cyano group and thus the original strong ICT from the coumarin dye to the 3‐position pyridyl vinyl ketone substituent is weakened, which results in recovery of coumarin fluorescence. The practical utility of 1 a was also examined. By fabricating paper strips, probe 1 a can be used as a simple tool to detect CN^? in field measurements. Moreover, probe 1 a has been successfully applied for quantitative detection of endogenous CN^? from cassava root.     

A New Ratiometric Fluorescent Probe Based on BODIPY for Highly Selective Detection of Hydrogen Sulfide

Hydrogen sulfide (H₂S) as small molecular signal messenger plays key functions in numerous biological processes. The imaging detection of intracellular hydrogen sulfide is of great significance. In this work, a ratiometric fluorescent probe BH based on an asymmetric BODIPY dye for detection of H₂S was designed and synthesized. After the interaction with hydrogen sulfide, probe display colorimetric and ratiometric fluorescence response, with its maximum emission fluorescence wavelength red-shifted from 542 nm to 594 nm, which is attributed to the sequential nucleophilic reaction of H₂S leading to enhanced molecular conjugation after ring formation of the BODIPY skeleton. A special response mechanism has been fully investigated by NMR titration and MS, so that the probe has excellent detection selectivity. Furthermore, probe BH has low cytotoxicity and fluorescence imaging experiments indicate that it can be used to monitor hydrogen sulfide in living cells.     

Colorimetric and Fluorescent Bimodal Ratiometric Probes for pH Sensing of Living Cells

pH measurement is widely used in many fields. Ratiometric pH sensing is an important way to improve the detection accuracy. Herein, five water‐soluble cationic porphyrin derivatives were synthesized and their optical property changes with pH value were investigated. Their pH‐dependent assembly/disassembly behaviors caused significant changes in both absorption and fluorescence spectra, thus making them promising bimodal ratiometric probes for both colorimetric and fluorescent pH sensing. Different substituent identity and position confer these probes with different sensitive pH‐sensing ranges, and the substituent position gives a larger effect. By selecting different porphyrins, different signal intensity ratios and different fluorescence excitation wavelengths, sensitive pH sensing can be achieved in the range of 2.1–8.0. Having demonstrated the excellent reversibility, good accuracy and low cytotoxicity of the probes, they were successfully applied in pH sensing inside living cells.     

Ratiometric Fluorescent pH Probes Based on Glycopolymers

Effectively detecting pH changes plays a critical role in exploring cellular functions and determining physiological and pathological processes. A novel ratiometric pH probe based on a glycopolymer, armored with properties of serum‐stability, tumor‐targeting, and pH monitoring, is designed. Random copolymers of 2‐(methacrylamido) glucopyranose and fluorescein O‐methacrylate are first synthesized by reversible addition fragmentation chain transfer polymerization. Acryloxyethyl thiocarbamoyl rhodamine B is then attached to the polymer chain to prepare ratiometric fluorescent pH probes via a thiol‐ene reaction. The synthesized polymeric probes are characterized by NMR, gel permeation chromatography, UV–vis spectroscopy, and transmission electron microscopy, and the fluorescence responses are examined in phosphate buffer at different pHs. The cytotoxicity and confocal imaging experiments of the probes are detected using HeLa cells, demonstrating a low toxicity and superior biocompatibility for detecting pH changes in bioapplications.

     

A Highly Chemically Stable Metal–Organic Framework as a Luminescent Probe for the Regenerable Ratiometric Sensing of pH

A heteroatom‐rich 3D noninterpenetrating metal–organic framework (MOF) Cd‐EDDA constructed from an ethylene glycol ether bridging tetracarboxylate ligand H₄EDDA (5,5′‐(ethane‐1,2‐diylbis(oxy))diisophthalic acid) shows good chemical resistance to both acidic and alkaline solutions with a pH ranging from 2.0 to 12.2. There is a corresponding ratiometric luminescence response to pH from 2.0 to 11.5, and the sensing mechanism is also discussed through ion chromatography and molecular force field‐based calculations. Importantly, the probe can easily be regenerated simply by modulating the pH of the solution, thus being the first example of a regenerable MOF‐based ratiometric luminescent probe for pH.