Fluorescent Small Molecule Research Articles

Small molecule-mediated induction of endoplasmic reticulum stress in cancer cells.

The endoplasmic reticulum (ER) is one of the crucial sub-cellular organelles controlling myriads of functions including protein biosynthesis, folding, misfolding and unfolding. As a result, dysregulation of these pathways in the ER is implicated in cancer development and progression. Subsequently, targeting the ER in cancer cells emerged as an interesting unorthodox strategy in next-generation anticancer therapy. However, development of small molecules to selectively target the ER for cancer therapy remained elusive and unexplored. To address this, herein, we have developed a novel small molecule library of sulfonylhydrazide-hydrazones through a short and concise chemical synthetic strategy. We identified a fluorescent small molecule that localized into the endoplasmic reticulum (ER) of HeLa cells, induced ER stress followed by triggering autophagy which was subsequently inhibited by chloroquine (autophagy inhibitor) to initiate apoptosis. This small molecule showed remarkable cancer cell killing efficacy in different cancer cells as mono and combination therapy with chloroquine, thus opening a new direction to illuminate ER-biology towards the development of novel anticancer therapeutics.

New small molecule fluorescent probes for G protein-coupled receptors: valuable tools for drug discovery.

G protein-coupled receptors (GPCRs) are essential signaling proteins and tractable therapeutic targets. To develop new drug candidates, GPCR drug discovery programs require versatile, sensitive pharmacological tools for ligand binding and compound screening. With the availability of new imaging modalities and proximity-based ligand binding technologies, fluorescent ligands offer many advantages and are increasingly being used, yet labeling small molecules remains considerably more challenging relative to peptides. Focusing on recent fluorescent small molecule studies for family A GPCRs, this review addresses some of the key challenges, synthesis approaches and structure-activity relationship considerations, and discussesadvantages of using high-resolution GPCR structures to inform conjugation strategies. While no single approach guarantees successful labeling without loss of affinity or selectivity, the choice of fluorophore, linker type and site of attachment have proved to be critical factors that can significantly affect their utility in drug discovery programs, and as discussed, can sometimes lead to very unexpected results.

A simple organic multi-analyte fluorescent prober: One molecule realizes the detection to DNT, TATP and Sarin substitute gas

The detections of explosives and chemical warfare agents (CWAs) are always important for global security. In this study, a simple donor (D)- acceptor (A) type small organic fluorescent triazole-based molecule (T1) is reported. T1 is composed of a central 4H-1, 2, 4-triazole (TAZ) “core” and three external triphenylamine (TPA) groups. Its spin-coating films can realize the multi-analyte fluorescent prober to detect DNT (2, 4-dinitrotoluene), hydrogen peroxide (H2O2, the substitute for triacetone triperoxide (TATP)) and diethylchlorophosphate (DCP, the substitute for Sarin) vapors. Additionally, the combination of the triple sensing mechanism in the different channels affords three distinct sets of output-signal responses, these three hazardous compounds could be identified rapidly with high sensitivity and selectivity: fluorescence turn-off response to DNT, fluorescence turn-on response to H2O2 and fluorometric-colorimetric dual-channel response to DCP. T1 fluorescent probe is highly advantageous for concurrently monitoring various hazardous target substances and simultaneously possessing the desirable sensitivity and selectivity, excellent reusability. Hereby, this study provides a prototype method to build novel multifunctional fluorescent probes to explosives and CWAs.

Photocaged Hoechst Enables Subnuclear Visualization and Cell Selective Staining of DNA in vivo.

Selective targeting of DNA by means of fluorescent labeling has become a mainstay in the life sciences. While genetic engineering serves as a powerful technique and allows the visualization of nucleic acid by using DNA‐targeting fluorescent fusion proteins in a cell‐type‐ and subcellular‐specific manner, it relies on the introduction of foreign genes. On the other hand, DNA‐binding small fluorescent molecules can be used without genetic engineering, but they are not spatially restricted. Herein, we report a photocaged version of the DNA dye Hoechst33342 (pcHoechst), which can be uncaged by using UV to blue light for the selective staining of chromosomal DNA in subnuclear regions of live cells. Expanding its application to a vertebrate model organism, we demonstrate uncaging in epithelial cells and short‐term cell tracking in vivo in zebrafish. We envision pcHoechst as a valuable tool for targeting and interrogating DNA with precise spatiotemporal resolution in living cells and wild‐type organisms.

Synthesis of small molecule dye additive for efficient and DIO-free ternary organic solar cells

A promising technique to enhance absorption of light in organic solar cells, “ternary approach” represents an important function in improving the device performance. We combined one small molecule dye (5,8-di(benzofuran-2-yl)-2,3-diphenylquinoxaline) (DB-Qx) with [6, 6]-phenyl C71 butyric acid methyl ester (PC71BM) (as the electron acceptor) and poly[4,8-bis(5-(2-ethylhexyl)thiophen-2-yl)benzo[1,2-b:4,5-b′]dithiopheneco-3-fluorothieno[3,4-b]thiophene-2-carboxylate] (PTB7-Th)(as the electron donor polymer) to form ternary solar cells. The morphology of the active layer of the ternary blend and hole mobility was potentially enhanced by the addition of a molecular donor. The complementary absorption of the two donors and matching photo-luminesce overlapping of DB-Qx with PTB7-Th contributed to improving the device performance. This means that the molecular donor in the ternary blend has an active function in the morphology. The devices produced PCE of 8.64% in the ternary blend system relative to 5.98% in the binary blend system. And, since the emission of DB-Qx partially overlaps with the absorption of PTB7Th, the transfer of energy from DB-Qx to PTB7-TH can improve the exciton utilization efficiency and achieve enhanced overall power conversion efficiency in this ternary solar cell. In this study, we synthesized a small fluorescent molecule material and constructed efficient ternary blend PSCs. Remarkably, the inverted device DIO-free ternary solar cells boost PCE from 5.98 to 8.64% and also exhibit the combined improvement in JSC and the morphology compared to those of DIO-processed films.

A Rapid Synthesis of Nuclear-Staining Small Fluorescent Molecules for Brain Imaging

Summary Fluorescent probes are important tools in cellular imaging. However, many readily available small-molecule imaging probes are either cytotoxic or easily photobleached and thus not compatible with lengthy live cell or tissue-imaging experiments. One particularly limited field of application is neuroscience, in which small-molecule probes for live cell imaging at the brain tissue level are highly scarce. Here, we describe a rapid synthetic route to generate a series of nuclear stains that enable experiments with live brain cells (i.e., water solubility, cell permeability, high quantum yield, high photostability, and most important, negligible cytotoxicity). As a proof of principle, we demonstrate that these probes are compatible with ex vivo and in vivo nuclear labeling experiments, including retrograde transport to monitor and map certain brain regions of the mouse model. The structural versatility and superior non-cytotoxic properties of these probes may suggest their potential use in labeling and tracing of neuronal populations.

Custom G4 Microarrays Reveal Selective G-Quadruplex Recognition of Small Molecule BMVC: A Large-Scale Assessment of Ligand Binding Selectivity.

G-quadruplexes (G4) are considered new drug targets for human diseases such as cancer. More than 10,000 G4s have been discovered in human chromatin, posing challenges for assessing the selectivity of a G4-interactive ligand. 3,6-bis(1-Methyl-4-vinylpyridinium) carbazole diiodide (BMVC) is the first fluorescent small molecule for G4 detection in vivo. Our previous structural study shows that BMVC binds to the MYC promoter G4 (MycG4) with high specificity. Here, we utilize high-throughput, large-scale custom DNA G4 microarrays to analyze the G4-binding selectivity of BMVC. BMVC preferentially binds to the parallel MycG4 and selectively recognizes flanking sequences of parallel G4s, especially the 3′-flanking thymine. Importantly, the microarray results are confirmed by orthogonal NMR and fluorescence binding analyses. Our study demonstrates the potential of custom G4 microarrays as a platform to broadly and unbiasedly assess the binding selectivity of G4-interactive ligands, and to help understand the properties that govern molecular recognition.

Efficient deep-blue fluorescent emitters from imidazole functionalized anthracenes for simple structure deep-blue electroluminescent devices

Abstract Deep-blue organic light emitting diodes (OLEDs) with high color purity are highly desired for high efficiency performing devices. Herein, we report four deep-blue fluorescent small molecules based on anthracene and imidazole moieties, namely mPA-PPPI, mNA-PPPI, mPA-PTPI and mNA-PTPI. These four molecules are composed of either phenyl anthracene (mPA) or naphthyl anthracene (mNA) core, and phenylene-3,5-bis(1-phenylphenanthro imidazole) (PPPI) and phenylene-3,5-bis(1,4,5-triphenyl imidazole) (PTPI) substituents. Their optical, electrochemical, photophysical, and thermal properties have been investigated and their device performances were evaluated. All compounds exhibited deep-blue emission color with excellent thermal and electrochemical stabilities. In particular, the simple structure device based on mPA-PPPI emitted a strong deep-blue color with CIE coordinates of x = 0.15, y = 0.06, low turn on voltage of 3.0 V, high color purity (full width at half maximum of 55 nm) and external quantum efficiency as high as 3.90%.

Synthesis and characterization of two novel red-shifted isothiocyanate BODIPYs and their application in protein conjugation

Fluorescent organic small molecules are very important tools for researchers in the fields of biochemistry and biotechnology, and boron-dipyrromethene (BODIPY) class of organic fluorophores gained much attention in recent years due to their remarkable photophysical properties and chemical versatility. Their application often involves conjugation with biomolecules, which can be accomplished by inserting a reactive functionality to the fluorescent dye. In this paper we present the preparation and characterization of two unpublished BODIPYs bearing the electrophilic isothiocyanate group, widely used for conjugation with proteins and biological amines. These dyes were prepared by inserting a nitrobenzene group to the BODIPY core via direct arylation, which was later converted to the isothiocyanate functionality. The arylated BODIPYs retained their fluorescence and showed red-shifted absorption and fluorescence spectra, when compared to previously published isothiocyanate-BODIPYs. Their application in bioconjugation was tested with bovine serum albumin (BSA) and was confirmed from spectroscopic and electrophoretic analysis.

Screening of Drug-Induced Steatosis and Phospholipidosis Using Lipid Droplet-Selective Two-Photon Probes.

Lipid droplets (LDs) are organelles that play a major role in regulating the storage of neutral lipids. Dysregulation of LDs is associated with metabolic disorders, such as fatty liver diseases, obesity, diabetes, and atherosclerosis. We have developed LD-selective small-molecule fluorescence probes (probes 3 and 4) that are available for both one- and two-photon microscopy, employing live or fixed cells. We found that probes 3 and 4 sensitively detect the increased LDs in response to oleic acid or endoplasmic reticulum stress, both in cells and tissues of the liver. The narrow absorption and emission bands of probes 3 and 4 allow multicolor imaging for the study of the role of LDs in pathophysiology and LD-associated signaling by the coapplication of the probes for different organelles or antibodies against specific proteins. In addition, we show here, for the first time, that two-photon microscopy imaging using our LD-selective probes with LysoTracker provides a novel method for screening drugs to potentially induce steatosis and/or phospholipidosis.

Ring-Degenerate Rearrangement Resulting from the Azo Coupling Reaction of a 3-Aryl-1,3a,6a-triazapentalene.

The 3-(4-(methoxycarbonyl)phenyl)triazapentalene is a highly fluorescent small molecule which is readily accessible via a two-step synthesis. In the search for postfunctionalization methods, a radical CH-arylation with diazonium salts was attempted. However, azo coupling resulted in a ring-degenerate rearrangement toward a 2-aryl-4-azotriazapentalene, which was confirmed via crystallographic analysis. A mechanism involving the generation of a nitrilimine is proposed. In addition, reduction of the azo group led to cleavage of the triazapentalene core. The present results further demonstrate the sensitivity of the triazapentalene fluorophore.

Multicolored Cathodically Coloring Electrochromism and Electrofluorochromism in Regioisomeric Star-Shaped Carbazole Dibenzofurans

In this work, a series of fluorescent cathodically coloring electrochromic (EC) small molecules o-, m-, and p-DBFDCz with 3,5-di(9H-carbazol-9-yl)benzene (DCz) linked to dibenzofuran (DBF) at different substitutional positions were synthesized and fully characterized. These compounds are electroactive and undergo quasi-reversible two-step single-electron reduction generating radical anions and dianions. The absorptions of o-, m-, and p-DBFDCz in the neutral states lie in the UV region (λonset ≈ 350 nm), showing high transparency, while the absorption of their reduced states can be largely tuned across the visible region through driving voltage and substitutional positions. Initially generated spectroelectrochemically radical anions show absorption in the short-wavelength region of ∼380-500 nm with weak broad absorptions at longer wavelengths. On further reduction, these bands disappear on the cost of growing intense bands from dianions at longer wavelengths of 500-700 nm with some tail absorptions in the shorter-wavelength region. This renders the colors of the EC devices based on these materials, which are changed from green to red, yellow to magenta, and light to deep blue for o-, m-, and p-DBFDCz, respectively, covering four legs of the L*a*b* color space. Besides excellent optical contrast (>90%) and high coloration efficiency (up to 504 cm2 C-1), the fluorescence observed in solution of neutral o-, m-, and p-DBFDCz can be modulated between the fluorescence and quenched states by direct electrochemical redox reactions. Both EC and electrofluorochromic (EFC) processes are reversible on cycling. This research demonstrates the feasibility of developing multifunctional EC/EFC materials with multicolored electrochromism through exploiting electrochemical properties of traditional fluorescent small molecules.

In Vivo Nerve-Specificity of Rhodamines and Si-rhodamines.

Accidental nerve damage or transection of vital nerve structures remains an unfortunate reality that is often associated with surgery. Despite the existence of nerve-sparing techniques, the success of such procedures is not only complicated by anatomical variance across patients but is also highly dependent on a surgeon's first-hand experience that is acquired over numerous procedures through trial and error, often with highly variable success rates. Fluorescent small molecules, such as rhodamines and fluoresceins have proven incredibly useful for biological imaging in the life sciences, and they appeared to have potential in illuminating vital nerve structures during surgical procedures. In order to make use of the current clinically relevant imaging systems and to provide surgeons with fluorescent contrast largely free from the interference of hemoglobin and water, it was first necessary to spectrally tune known fluorescent scaffolds towards near infrared (NIR) wavelengths. To determine whether the well-documented Si-substitution strategy could be applied towards developing a NIR fluorophore that retained nerve-specific properties of candidate molecules, an in vivo comparison was made between two compounds previously shown to highlight nervous structures - TMR and Rhodamine B - and their Si-substituted derivatives.

A new sensitive and subunit-selective molecular tool for investigating protein kinase A in the brain.

Despite cellular complexity, a limited number of small molecules act as intracellular second messengers. Protein kinase A (PKA) is the main transducer of the information carried by cyclic adenosine monophosphate (cAMP). Recently, cellular imaging has achievedmajor technical advancements, although the search for more specific and sensitive low-molecular-weight probes to explore subcellular events involving second messengers is still in progress. The convergent synthesis of a novel, fluorescent small molecule comprising the cAMP structure and a rhodamine-based fluorescent residue, connected through a flexible linker, is described here. The interaction motif of this compound with PKA was investigated in silico using a blind docking approach, comparing its theoretical binding energy with the one calculated for cAMP. Moreover, the predicted pharmacokinetic properties were also computed and discussed. The new probe was tested on three areas of the mouse central nervous system (parietal cerebral cortex, hippocampus, and cerebellar cortex) with different fixation methods demonstrating remarkable selectivity towards the PKA RIα subunit. The probe showed overall better performances when compared to other commercially available fluorescent cAMP analogues, acting at lower concentrations, and providing stable labeling.

Lasing‐Encoded Microsensor Driven by Interfacial Cavity Resonance Energy Transfer

AbstractMicrolasers are emerging tools for biomedical applications. In particular, whispering‐gallery‐mode (WGM) microlasers are promising candidates for sensing at the biointerface owing to their high quality‐factor and potential in molecular assays, and intracellular and extracellular detection. However, lasing particles with sensing functionality remain challenging since the overlap between the WGM optical mode and external gain medium is much lower compared to internal gain inside the cavity. To overcome this problem, the concept of Förster resonant energy transfer (FRET) is exploited on WGM droplet microlaser by separating donor and acceptor molecules at the cavity–surface interface. It is first discovered that the interfacial FRET laser not only originates from conventional FRET but utilizes coherent radiative energy transfer (CRET) to excite acceptor molecules by inducing light‐harvesting effect near the cavity interface. Simulations and experiments have revealed that the absorption spectrum of individual analyte plays a crucial role in interfacial FRET laser. Distinct lasing spectra can therefore distinguish molecules of different absorption properties upon binding. Finally, detection of small fluorescent molecules and photosynthetic protein is performed. The results presented here not only demonstrate the wide‐ranging potential of microlaser external cavity implementation in molecular sensing applications, but also provide comprehensive insights into cavity energy transfer in laser physics.

Strategies Targeting Soluble β-Amyloid Oligomers and their Application to Early Diagnosis of Alzheimer's Disease.

Alzheimer's Disease (AD) is the most common neurodegenerative disorder, and it is still incurable. Early diagnosis and intervention are crucial for delaying the onset and progression of the disease. Mounting evidence indicates that the neurotoxic effects might be attributed to Soluble β-Amyloid Oligomers (SAβO). The SAβO are believed to be neurotoxic peptides more predominant than Aβ plaques in the early stage, and their key role in AD is self-evident. Unfortunately, identification of SAβO proves to be difficult due to their heterogeneous and transient nature. In spite of many obstacles, multiple techniques have recently been developed to target SAβO effectively. This review focuses on the recent progress in the approaches towards SAβO detection in order to shed some light on the future development of SAβO assays. Literatures were obtained from the following libraries: Web of Science, PubMed, EPO, SIPO, USPTO. Articles were critically reviewed based on their titles, abstracts, and contents. A total of 85 papers are referenced in the review. Results are divided into three categories based on the types of detection methods: small molecule fluorescence probes, oligomer-specific antibodies and electrochemical biosensors. Finally, the improvements and challenges of these approaches applied in the early diagnosis of AD were discussed. This review article covers three kinds of strategies that could be translated into clinic practice and lead to earlier diagnosis and therapeutic interventions of AD.

Small molecule-induced DNA hydrogel with encapsulation and release properties.

Hydrogels are networks of polymers that can be used for packaging different payload types. They are proven to be versatile materials for various biomedical applications. Implanted hydrogels with encapsulated drugs have been shown to release the therapeutic payloads at disease sites. Hydrogels are usually made through chemical polymerization reactions. Whereas, DNA is a naturally occurring biopolymer which can assemble into highly ordered structures through noncovalent interactions. Here, we have employed a small molecule, cyanuric acid (CA), to assemble polyA-tailed DNA motif into a hydrogel. Encapsulation of a small molecule chemotherapeutic drug, a fluorescent molecule, two proteins and several nanoparticle formulations has been studied. Release of doxorubicin, small fluorescent molecule and fluorescently-labeled antibodies has been demonstrated.

Rational design of small molecule fluorescent probes for biological applications.

Fluorescent small molecules are powerful tools for visualizing biological events, embodying an essential facet of chemical biology. Since the discovery of the first organic fluorophore, quinine, in 1845, both synthetic and theoretical efforts have endeavored to "modulate" fluorescent compounds. An advantage of synthetic dyes is the ability to employ modern organic chemistry strategies to tailor chemical structures and thereby rationally tune photophysical properties and functionality of the fluorophore. This review explores general factors affecting fluorophore excitation and emission spectra, molar absorption, Stokes shift, and quantum efficiency; and provides guidelines for chemist to create novel probes. Structure-property relationships concerning the substituents are discussed in detail with examples for several dye families. We also present a survey of functional probes based on PeT, FRET, and environmental or photo-sensitivity, focusing on representative recent work in each category. We believe that a full understanding of dyes with diverse chemical moieties enables the rational design of probes for the precise interrogation of biochemical and biological phenomena.

A strategy to construct fluorescent non-aromatic small-molecules: hydrogen bonds contributing to the unexpected fluorescence.

Propanedioyl dihydrazide (PDH), traditionally believed to be non-fluorescent, was first discovered to emit substantial fluorescence in both the solid state and solvents. Then, significantly, a novel strategy is provided: fluorescent non-aromatic small molecules with rigid molecular structures could be constructed by forming hydrogen bonds.

Quinoline-based fluorescent small molecules for live cell imaging.

Small molecule probes are essential tools for biomedical applications, with utility as cellular stains, labels for biomolecules, environmental indicators, and biosensors. However, a fluorophore's characteristics are difficult to predict solely through calculations or rational design, making the development of a core scaffold that is amenable to late stage functionalization particularly desirable. In this chapter, we describe the synthesis and application of a tunable quinoline scaffold that can be readily functionalized and optimized for a variety of imaging applications. We present a facile synthesis that results in three functional domains that influence the compound's photophysical properties, structural diversity, and polarization. We demonstrate a method with which to study the scaffold's tunable photophysical properties as a result of its structure and environment, and finally exhibit its utility in pH sensitive, live-cell imaging.