Glycosylation enhances the aqueous sensitivity and lowers the cytotoxicity of a naphthalimide zinc ion fluorescence probe

Carbohydrate-Functionalized Anthracene Carboximides as Multivalent Ligands and Bio-Imaging Agents

Anthracene carboximides (ACIs) conjugated with gluco-, galacto- and mannopyranosides are synthesized, by glycosylation of N-hydroxyethylanthracene carboximide acceptor with glycosyl donors. Glycoconjugation of anthracene carboximide increases the aq. solubility by more than 3-fold. The glycoconjugates display red-shifted absorption and emission, as compared to anthracene. Large Stokes shift (λabs/λem=445/525 nm) and high fluorescence quantum yields (Φ) of 0.86 and 0.5 occur in THF and water, respectively. The ACI-glycosides undergo facile photodimerization in aqueous solutions, leading to the formation of the head-to-tail dimer, as a mixture of syn and anti-isomers. Solution phase and solid-state characterizations by dynamic light scattering (DLS), microscopic imaging by atomic force (AFM) and transmission electron (TEM) microscopies reveal self-assembled vesicle structures of ACI glycosides. These self-assembled structures act as multivalent glycoclusters for ligand-specific lectin binding, as evidenced by the binding of Man-ACI to Con A, by fluorescence and turbidity assays. The conjugates do not show cellular cytotoxicity (IC50) till concentrations of 50 μM with HeLa and HepG2 cell lines and are cell-permeable, showing strong fluorescence inside the cells. These properties enable the glycoconjugates to be used in cell imaging. The non-selective cellular uptake of the glycoconjugates suggests a passive diffusion through the membrane.

De Novo Access to BODIPY C-Glycosides as Linker-Free Nonsymmetrical BODIPY-Carbohydrate Conjugates

Recent years have witnessed an increasing interest in the synthesis and study of BODIPY-glycoconjugates. Most of the described synthetic methods toward these derivatives involve postfunctional modifications of the BODIPY core followed by the covalent attachment of the fluorophore and the carbohydrate through a "connector". Conversely, few de novo synthetic approaches to linker-free carbohydrate-BODIPY hybrids have been described. We have developed a reliable modular, de novo, synthetic strategy to linker-free BODIPY-sugar derivatives using the condensation of pyrrole C-glycosides with a pyrrole-carbaldehyde derivative mediated by POCl3. This methodology allows labeling of carbohydrate biomolecules with fluorescent-enough BODIPYs within the biological window, stable in aqueous media, and able to display singlet oxygen generation.

Synthesis of carbohydrate–BODIPY hybrids

Owing to the relevance of fluorescently labeled carbohydrates in the study of biological processes, we have investigated several routes for the preparation of saccharides covalently linked to borondipyrromethene (BODIPY) fluorophores. We have shown that BODIPY dyes can be used as aglycons through synthetic saccharide protocols. In particular, a per-alkylated 8-(2-hydroxy-methylphenyl)-4,4′-dicyano-BODIPY derivative, which withstands glycosylation and protection/deprotection reaction conditions without decomposition, has been used in the stepwise synthesis of two fluorescently labeled trisaccharides. These saccharides displayed high water solubility and a low tendency to (H-)aggregation, a phenomenon that causes loss of photophysical efficiency in BODIPYs. Two additional synthetic strategies toward glyco-BODIPYs have also been described. The first method relies on a Ferrier-type C-glycosylation of the BODIPY core, leading to linker-free carbohydrate–BODIPY hybrids. Secondly, the application of the Nicholas propargylation reaction to 1,3,5,7-tetramethyl BODIPYs provides access to 2,6-dipropargylated BODIPYs that readily undergo CuAAC reactions with azido-containing sugars. From a photophysical standpoint, the BODIPY-labeled saccharides could be used as stable and fluorescent water-soluble chromophores, thereby addressing one of the current challenges in molecular imaging.

Selective synthesis of α- and β-glycosides of N-acetyl galactosamine using rare earth metal triflates

Structures containing galactose and GalNAc residues are specifically recognized by asialoglycoprotein receptors, allowing them to selectively internalize by hepatocytes for drug-targeting delivery. However, methods for direct synthesis of GalNAc glycosides are still challenging due to the poor participating group of 2-acetamido. Here, we develop a facile strategy to synthesize various GalNAc glycosides by employing a series of rare earth metal triflates, and the results demonstrate that both α-glycosides and β-glycosides of GalNAc can be obtained by conducting with Hf(OTf)4 and Sc(OTf)3, respectively. These applicable results indicate that any interested GalNAc-containing substrates could be prepared by this simple strategy.

A GLUTs/GSH cascade targeting-responsive bioprobe for the detection of circulating tumor cells

A GLUTs/GSH cascade targeting-responsive bioprobe, GluCC, was rationally designed and synthesized for the first time via the coordination of copper ions with a glucose-modified coumarin derivative ligand (GluC). GluCC can specifically detect circulating tumor cells (CTCs) in lung metastatic mice models by targeting the Warburg effect and responding to overexpressed glutathione in the tumor microenvironment. This bioprobe with a simple detection procedure has significant advantages for CTC detection.

Recent research progress in galactose-based fluorescent probes for detection of biomarkers of liver diseases

This highlight illustrates the challenges and latest progress in galactose-based fluorescent probes for early diagnosis of liver diseases.

A ratiometric fluorescent probe based on quinoline for monitoring and imaging of Leucine aminopeptidase in liver tumor cells

Leucine aminopeptidase (LAP) is known as an important potential biomarker for liver malignancy and it is urgent to develop an intuitive and effective method to monitor the activity of LAP in liver cancer. Although, numerous LAP fluorescent probes had been developed, it is still a challenge to detect LAP activity in liver cancer. Herein, combained with the DFT, we reported a novel galactose-appended hepatoma-specific ratiometric fluorescent probe (Gal-QL-Leu) based on quinoline group for imaging and tracing LAP in liver tumor cells. Probe Gal-QL-Leu demonstrated a obvious ratiometric characteristics, better selectivity, good biocompatibility and high sensitivity. Moreover, the selective imaging of LAP in HepG2, HCT116, A549 and HeLa cells had been achieved with probe Gal-QL-Leu, demonstrating good application prospect in the detection of LAP activity in liver tumor cells.

Supramolecular Assembly of TPE-Based Glycoclusters with Dicyanomethylene-4H-pyran (DM) Fluorescent Probes Improve Their Properties for Peroxynitrite Sensing and Cell Imaging

Two red-emitting dicyanomethylene-4H-pyran (DM) based fluorescent probes were designed and used for peroxynitrite (ONOO^- ) detection. Nevertheless, the aggregation-caused quenching effect diminished the fluorescence and restricted their further applications. To overcome this problem, tetraphenylethylene (TPE) based glycoclusters were used to self-assemble with these DM probes to obtain supramolecular water-soluble glyco-dots. This self-assembly strategy enhanced the fluorescence intensity, leading to an enhanced selectivity and activity of the resulting glyco-dot comparing to DM probes alone in PBS buffer. The glyco-dots also exhibited better results during fluorescence sensing of intracellular ONOO^- than the probes alone, thereby offering scope for the development of other similar supramolecular glyco-systems for chemical biological studies.

A Novel Donor-Acceptor Fluorescent Sensor for Zn2+ with High Selectivity and its Application in Test Paper

A novel donor-acceptor fluorescent sensor was designed and synthesized. The sensor exhibited high selectivity and sensitivity to Zn²⁺ in acetonitrile solution. When 3.0 equiv. of Zn²⁺ was added gradually, the emission intensity at 500 nm increased 54-fold, accompanied by the fluorescent color of the solution changed from dark to green. Job's plot and ESI-MS were carried out to verify a 1:1 stoichiometric complex was formed between the sensor and Zn²⁺. The limit of detection (LOD) to Zn²⁺ was measured to be 2.81 × 10^-9 mol L^-1. Moreover, the sensor not only could be used to detect Zn²⁺ in practical water samples with high accuracy, but also could be made into test paper for the qualitative detection for Zn²⁺.

BODIPYs as Chemically Stable Fluorescent Tags for Synthetic Glycosylation Strategies towards Fluorescently Labeled Saccharides

A series of fluorescent boron-dipyrromethene (BODIPY, 4,4-difluoro-4-bora-3a,4a-diaza-s-indacene) dyes have been designed to participate, as aglycons, in synthetic oligosaccharide protocols. As such, they served a dual purpose: first, by being incorporated at the beginning of the process (at the reducing-end of the growing saccharide moiety), they can function as fluorescent glycosyl tags, facilitating the detection and purification of the desired glycosidic intermediates, and secondly, the presence of these chromophores on the ensuing compounds grants access to fluorescently labeled saccharides. In this context, a sought-after feature of the fluorescent dyes has been their chemical robustness. Accordingly, some BODIPY derivatives described in this work can withstand the reaction conditions commonly employed in the chemical synthesis of saccharides; namely, glycosylation and protecting-group manipulations. Regarding their photophysical properties, the BODIPY-labeled saccharides obtained in this work display remarkable fluorescence efficiency in water, reaching quantum yield values up to 82 %, as well as notable lasing efficiencies and photostabilities.

Design, synthesis and evaluation of a novel fluorescent probe to accurately detect H2S in hepatocytes and natural waters

Design and synthesis of fluorescent probe with fast response, excellent water solubility and good hepatocyte-targeting capacity to detect hydrogen sulfide (H₂S) in hepatocytes and water samples is of great significance. Here, a novel fluorescent probe QL-Gal-N₃ for detection of H₂S was designed and synthesized based on H₂S-mediated azide reduction strategy. This sensor demonstrated low toxicity, fast response (within 1 min), high selectivity and low detection limit (as low as 126 nM in water) for the detection of H₂S. HeLa, A549 and HepG-2 cells were chosen to investigate the hepatocyte-targeting ability of QL-Gal-N₃ respectively. The results indicated that the specific recognition of ASGPR over-expressed in hepatocytes by galactose group was an important reason for the good targeting ability of probe QL-Gal-N₃. Furthermore, due to the introduction of glycosyl moiety, the water solubility of fluorescent probe was enhanced obviously. It was successfully applied for the detection of H₂S in environmental water samples including river water, tap water, lake water and waste water.

Fluorescent glycoconjugates and their applications

Fluorescent glycoconjugates are discussed for their applications in biology in vitro, in cell assays and in animal models. Advantages and limitations are presented for each design using a fluorescent core conjugated with glycosides, or vice versa.

Fluorescent supramolecular hierarchical self-assemblies from glycosylated 4-amino- and 4-bromo-1,8-naphthalimides

The investigation into the self-assembly formation of the glycan based 4-amino- and 4-bromo-1,8-naphthalimide (Nap) structures1–3is presented.

A Malonyl-Based Scaffold for Conjugatable Multivalent Carbohydrate-BODIPY Presentations

A concise synthetic route from methylmalonate to a tetravalent aliphatic scaffold has been developed. The ensuing tetra-tethered derivative is equipped with two hydroxyl groups, as well as orthogonal alkene and alkyne functionalities. The usefulness of the scaffold has been demonstrated with the preparation of two representative multivalent derivatives: (i) a tetravalent compound containing two D-mannose units, one fluorescent boron-dipyrromethene (BODIPY) dye and a suitably functionalized amino acid and (ii) by way of dimerization and saponification, a water-soluble tetramannan derivative containing two fluorescent BODIPY units. Additionally, photophysical measurements conducted on these derivatives support the viability of the herein designed single and double BODIPY-labeled carbohydrate-based clusters as fluorescent markers.

A highly sensitive fluorescent sensor for Zn2+ based on diarylethene with an imidazole unit

A new sensitive sensor for Zn²⁺ based on diarylethene with an imidazole unit has been synthesized. Its photochromic and fluorescent behaviors have been systematically investigated by the stimulation of UV/vis lights and Zn²⁺ ion in THF solution. It displayed a dual-mode with a "turn on" fluorescence and color response to Zn²⁺. With the addition of Zn²⁺, the emission intensity enhanced 26-fold, accompanied by the fluorescent color changed from dark red to bright yellow. The 1:1 stoichiometry between the sensor and Zn²⁺ was verified by Job's plot and MS. The LOD for Zn²⁺ was determined to be 6.12 × 10^-9 mol L^-1. Furthermore, a logic circuit was designed by using the fluorescence at 578 nm as output and the combinational stimuli of UV/vis and Zn²⁺/EDTA as inputs.

A novel jointly colorimetric and fluorescent sensor for Cu2+ recognition and its complex for sensing S2- by a Cu2+ displacement approach in aqueous media

In this work, a simple and easily synthesized Schiff-based derivative colorimetric and fluorescent sensor (1), 4-dimethylamino-benzoic acid (2-imidazole formaldehyde)-hydrazide, was obtained for the detection of Cu²⁺ and S^2-. The compound 1 exhibited dual spectral responses to Cu²⁺, that is, vivid color change and fluorescence enhancement in the presence of Cu²⁺. The detection limits were valued as 0.46 μM and 15 nM according to absorption and fluorescent response, respectively. Both of them are below the World Health Organization (WHO) guidelines for drinking water (31.5 μM). In addition, the ensemble (1-Cu²⁺) selectively and sensitively detected a low concentration of S^2-. As the addition of S^2- instantly removed Cu²⁺ from the ensemble (1-Cu²⁺) resulting in a color change from yellow to colorless and a "turn-off" fluorescent response. The detection limit for S^2- was estimated as 0.12 μM (from fluorescent method) and 0.68 μM (from absorption method), respectively, each of which was also lower than the maximum allowable level of S^2- (15 μM) in drinking water defined by the WHO. The binding process was confirmed via UV-vis absorption, fluorescence measurements, ¹H NMR, mass spectroscopy and density functional theory calculation. What's more, successful practical application of test paper is used to inspect the S^2- which means the convenient and rapid assay in real samples can be achieved.

Supramolecular glyco-poly-cyclodextrin functionalized thin-layer manganese dioxide for targeted stimulus-responsive bioimaging

We have developed a supramoleuclar imaging probe based on thin-layer manganese dioxide functionalized with a fluorescent, multivalent glyco-poly-cycolodextrin for the targeted, stimulus-responsive bioimaging of cancer cells.

A supramolecular pyrenyl glycoside-coated 2D MoS2 composite electrode for selective cell capture

Here we demonstrate the simple construction and characterization of a pyrenyl glycoside-coated 2D MoS₂ material composite capable of selectively capturing proteins and live cells on an electrode, as determined by differential pulse voltammetry.

Lighting-up protein–ligand interactions with fluorescent PET (photoinduced electron transfer) sensor designs

Extending the versatile fluorescent PET sensing/switching system causes ‘off–on’ signalling when a ligand binds to its appropriate protein.

Taking Orders from Light: Photo-Switchable Working/Inactive Smart Surfaces for Protein and Cell Adhesion

Photoresponsive smart surfaces are promising candidates for a variety of applications in optoelectronics and sensing devices. The use of light as an order signal provides advantages of remote and noninvasive control with high temporal and spatial resolutions. Modification of the photoswitches with target biomacromolecules, such as peptides, DNA, and small molecules including folic acid derivatives and sugars, has recently become a popular strategy to empower the smart surfaces with an improved detection efficiency and specificity. Herein, we report the construction of photoswitchable self-assembled monolayers (SAMs) based on sugar (galactose/mannose)-decorated azobenzene derivatives and determine their photoswitchable, selective protein/cell adhesion performances via electrochemistry. Under alternate UV/vis irradiation, interconvertible high/low recognition and binding affinity toward selective lectins (proteins that recognize sugars) and cells that highly express sugar receptors are achieved. Furthermore, the cis-SAMs with a low binding affinity toward selective proteins and cells also exhibit minimal response toward unselective protein and cell samples, which offers the possibility in avoiding unwanted contamination and consumption of probes prior to functioning for practical applications. Besides, the electrochemical technique used facilitates the development of portable devices based on the smart surfaces for on-demand disease diagnosis.

Synthesis, G-quadruplex binding properties and cytotoxicity of naphthalimide–thiourea conjugates

The hydrogen bonding between a thiourea moiety and a G-quadruplex plays a crucial role in the sequence-specific DNA binding of naphthalimide–thiourea conjugates.

Supramolecular core–glycoshell polythiophene nanodots for targeted imaging and photodynamic therapy

We show that supramolecular core–glycoshell nanodots are capable of targeted imaging and photodynamic therapy of liver and triple-negative breast cancer cells.

A glycosylation strategy to develop a low toxic naphthalimide fluorescent probe for the detection of Fe3+in aqueous medium

A glycosylation strategy based on click chemistry was employed to develop a naphthalimide-based Fe³⁺fluorescent probe with low cytotoxicity and good water-solubility.

Fluorescent glycoprobes: a sweet addition for improved sensing

We highlight recent progress from our labs for the development of fluorescent glycoprobes for sensing ions/lectins and targeted detection of intracellular species, including the construction of their 2D material composites for targeted fluorescence imaging and theranostics.

Triazole-Linked Quinoline Conjugate of Glucopyranose: Selectivity Comparison among Zn2+, Cd2+, and Hg2+ Based on Spectroscopy, Thermodynamics, and Microscopy, and Reversible Sensing of Zn2+ and the Structure of the Complex Using DFT

A water-soluble triazole-linked quinoline conjugate of glucopyranose (L) has been synthesized and characterized, and its single-crystal X-ray diffraction (XRD) structure has been established. Binding of L toward different biologically relevant metal ions has been studied using fluorescence and absorption spectroscopy in HEPES buffer at pH 7.4. The conjugate L detects Zn2+ and Cd2+ with 30 ± 2 and 14 ± 1-fold fluorescence enhancement, respectively, but in the case of Hg2+, only a fluorescence quench was observed. The stoichiometry of the complex is 1:2 metal ion to the ligand in the case of Zn2+ and Cd2+ resulting in [Zn(L)2] and [Cd(L)2], and it is 1:1 in the case of Hg2+, as confirmed from their electrospray ionization mass spectrometry (ESIMS) spectra. Zn2+ shows greater exothermicity over Cd2+, whereas Hg2+ shows endothermicity , which supports the differences in their binding strength and the nature of the corresponding complex. L exhibits rod-shaped particles and upon complexation with Zn2+, it exhibits sphere-like morphological features in scanning electron microscopy (SEM) images. However, clustered aggregates are observed in Cd2+, whereas the [HgL] complex exhibits small fused spherical structures, and therefore the signature of these ions is seen in microscopy images. The computational studies revealed that the syn-[Zn(L)2] complex is stabilized by 9.7 kcal mol-1 more than that in the case of anti-[Zn(L)2] owing to the formation of hydrogen bonds between the two glucosyl moieties within the syn-complex. Among the anions studied, [Zn(L)2] is sensitive and selective toward the phosphate ion (H2PO4 -) with a minimum detection limit of 16 ± 2 ppb. Similarly, the [HgL] can act as a secondary sensor for CN- while also exhibiting reversibility. Based on the input-output characteristics, INHIBIT logic gate was built in the case of Zn2+ vs H2PO4 - and IMPLICATION logic gate was built in the case of Hg2+ vs CN-.

Glycosidase activated release of fluorescent 1,8-naphthalimide probes for tumor cell imaging from glycosylated 'pro-probes'

Glycosylated 4-amino-1,8-naphthalimide derivatives possess a native glycosidic linkage that can be selectively hydrolysed in situ by glycosidase enzymes to release the naphthalimide as a fluorescent imaging or therapeutic agent. In vitro studies using a variety of cancer cell lines demonstrated that the naphthalimides only get taken up into cells upon enzymatic cleavage from the glycan unit; a mechanism that offers a novel approach for the targeted delivery of probes/drugs.

Self and directed assembly: people and molecules

Self-assembly and directed-assembly are two very important aspects of supramolecular chemistry. As a young postgraduate student working in Canada with Tom Fyles my introduction to Supramolecular Chemistry was through the self-assembly of phospholipid membranes to form vesicles for which we were developing unimolecular and self-assembling transporter molecules. The next stage of my development as a scientist was in Japan with Seiji Shinkai where in a “Eureka” moment, the boronic acid templating unit (directed-assembly) of Wulff was combined with photoinduced electron transfer systems pioneered by De Silva. The result was a turn-on fluorescence sensor for saccharides; this simple result has continued to fuel my research to the present day. Throughout my career as well as assembling molecules, I have enjoyed bringing together researchers in order to develop collaborative networks. This is where molecules meet people resulting in assemblies worth more than the individual “molecule” or “researcher”. My role in developing networks with Japan was rewarded by the award of a Daiwa-Adrian Prize in 2013 and I was recently rewarded for developing networks with China with an Inaugural CASE Prize in 2015.

Nanomolar pyrophosphate detection and nucleus staining in living cells with simple terpyridine-Zn(II) complexes

Great efforts have been made to develop fluorescent probes for pyrophosphate (PPi) detection. Nucleus staining with fluorescence microscopy has been also widely investigated. But fluorescent probes for PPi detection with high sensitivity in water medium and nucleus staining with low-cost non-precious metal complexes in living cells are still challenging. Herein, we report simple terpyridine-Zn(II) complexes for selective nanomolar PPi detection over ATP and ADP in water based on aggregation induced emission (AIE) and intramolecular charge transfer (ICT). In addition, these terpyridine-Zn(II) complexes were successfully employed for nucleus staining in living cells. These results demonstrated simply obtained terpyridine-Zn(II) complexes are powerful tool for PPi detection and the development of PPi-related studies.

Interlocked supramolecular glycoconjugated polymers for receptor-targeting theranostics

We report an interlocked supramolecular ensemble formed between a conjugated polymer (CP) and a fluorescent glycoprobe for receptor-targeting cancer cell theranostics.

N-Oxyamide-linked glycoglycerolipid coated AuNPs for receptor-targeting imaging and drug delivery

We report the construction of gold glyconanoparticles coated by N-oxyamide-linked glycoglycerolipids for receptor-targeting imaging and drug delivery.

A long lifetime switch-on iridium(iii) chemosensor for the visualization of cysteine in live zebrafish

A long lifetime iridium(iii) complex chemosensor1for cysteine detection has been synthesized.

A long lifetime luminescent iridium(iii) complex chemosensor for the selective switch-on detection of Al3+ ions

A novel luminescent cyclometalated iridium(iii) complex 1 was synthesized and employed as a chemosensor for the detection of Al³⁺ ions. 1 displays a long lifetime luminescence that allow 1 to detect Al³⁺ ions in strong fluorescence media.

Targeted fluorescence imaging enhanced by 2D materials: a comparison between 2D MoS2 and graphene oxide

2D MoS₂ enhances the receptor-targeting cell and tissue imaging ability of a fluorophore-labeled ligand in a concentration-dependent manner.