Fluorescent probe for monosaccharides based on a functionalized boron-dipyrromethene with a boronic acid group

Bis-arylidene oxindoles for colorectal cancer nanotherapy

Oxindoles are potent anti-cancer agents and are also used against microbial and fungal infections and for treating neurodegenerative diseases. These oxindoles are earlier established as estrogen receptor (ER)-targeted agents for killing ER (+) cancer cells. Our previously developed bis-arylidene oxindole, Oxifen (OXF) exhibits effective targeting towards ER (+) cancer cells which has a structural resemblance with tamoxifen. Herein, we have designed and synthesized few structural analogues of OXF such as BPYOX, ACPOX and ACPOXF to examine its cytotoxicity in different cancer as well as non-cancer cell lines and its potential to form self- aggregates in aqueous solution. Among these series of molecules, ACPOXF showed maximum toxicity in colorectal cancer cell line which are ER (-) but it also kills non-cancer cell line HEK-293, thereby reducing its cancer cell selectivity. Incidentally, ACPOXF exhibits self-aggregation, without the help of a co-lipid with nanometric size in aqueous solution. ACPOXF self-aggregate was co-formulated with glucocorticoid receptor (GR) synthetic ligand, dexamethasone (Dex) (called, ACPOXF-Dex aggregate) which could selectively kill ER (-) colorectal cancer cells and also could increase survivability of colon-tumour bearing mice. ACPOXF-Dex induced ROS up-regulation followed by apoptosis through expression of caspase-3. Further, we observed upregulation of antiproliferative factor, p53 and epithelial-to-mesenchymal (EMT) reversal marker E-cadherin in tumour mass. In conclusion, a typical structural modification in ER-targeting Oxifen moiety resulted in its self-aggregation that enabled it to carry a GR-ligand, thus broadening its selective antitumor property especially as colon cancer therapeutics.

Fluorescent half-sandwich iridium picolinamidate complexes for in-cell visualization

In this work, we report on the development of fluorescent half-sandwich iridium complexes using a fluorophore attachment strategy. These constructs consist of pentamethylcyclopentadienyl (Cp*) iridium units ligated by picolinamidate donors conjugated to green-emitting boron-dipyrromethene (bodipy) dyes. Reaction studies in H₂O/THF mixtures showed that the fluorescent Ir complexes were active as catalysts for transfer hydrogenation, with activities similar to that of their non-fluorescent counterparts. The iridium complexes were taken up by NIH-3T3 mouse fibroblast cells, with 50% inhibition concentrations ranging from ~20-70 μM after exposure for 3 h. Visualization of the bodipy-functionalized Ir complexes in cells using fluorescence microscopy revealed that they were localized in the mitochondria and lysosome but not the nucleus. These results indicate that our fluorescent iridium complexes could be useful for future biological studies requiring intracellular catalyst tracking.

A selective hybrid fluorescent sensor for fructose detection based on a phenylboronic acid and BODIPY-based hydrophobicity probe

Fructose is widely used in the food industry. However, it may be involved in diseases by generating harmful advanced glycation end-products. We have designed and synthesized a novel fluorescent probe for fructose detection by combining a phenylboronic acid group with a BODIPY-based hydrophobicity probe. This probe showed a linear fluorescence response to d-fructose concentration in the range of 100-1000 μM, with a detection limit of 32 μM, which is advantageous for the simple and sensitive determination of fructose.

O-BODIPYs as fluorescent labels for sugars: glucose, xylose and ribose

Fluorescent 1 : 1, 1 : 2 and 1 : 3 sugar-O-BODIPY conjugates of glucose, xylose and ribose were characterised by 1H–11B HMBC and 11B NMR to discriminate between boron bound to 1,2-, 1,3- or 1,4-diol sites and furanose/pyranose sugar forms.

A straightforward synthesis of phenyl boronic acid (PBA) containing BODIPY dyes: new functional and modular fluorescent tools for the tethering of the glycan domain of antibodies

We report here on the efficient and straightforward synthesis of a series of modular and functional PBA-BODIPY dyes 1–4. They are an outstanding example of the efficient merge of the versatility of the 3,5-dichloro-BODIPY derivatives and the receptor-like ability of the PBA moiety. The potential bioanalytical applicability of these tools was assessed by measuring the binding to glycan chains of antibodies by a Quartz Crystal Microbalance (QCM).

PBA-BODIPY dyes as functional and modular fluorescent probes for the tethering of the glycan domain of mAbs.

Fructose recognition using new “Off–On” fluorescent chemical probes based on boronate-tagged 1,8-naphthalimide

A fluorescent probe with a planar structure was designed based on a PET mechanism to detect fructose with lower LOD than analytical methods.

Performance enhancement of BODIPY dimer-based small-molecule solar cells using a visible-photon-capturing diketopyrrolopyrrole π-bridge

Utilization of the visible-photon-capturing DPP instead of the BDT π-bridge leads to a 70% increase in the photocurrent.

Recent advances in fluorescent arylboronic acids for glucose sensing

Continuous glucose monitoring (CGM) is crucial in order to avoid complications caused by change in blood glucose for patients suffering from diabetes mellitus. The long-term consequences of high blood glucose levels include damage to the heart, eyes, kidneys, nerves and other organs, among others, caused by malign glycation of vital protein structures. Fluorescent monitors based on arylboronic acids are promising candidates for optical CGM, since arylboronic acids are capable of forming arylboronate esters with 1,2-cis-diols or 1,3-diols fast and reversibly, even in aqueous solution. These properties enable arylboronic acid dyes to provide immediate information of glucose concentrations. Thus, the replacement of the commonly applied semi-invasive and non-invasive techniques relying on glucose binding proteins, such as concanavalin A, or enzymes, such as glucose oxidase, glucose dehydrogenase and hexokinases/glucokinases, might be possible. The recent progress in the development of fluorescent arylboronic acid dyes will be emphasized in this review.

Fluorescent indicators based on BODIPY

This critical review covers the advances made using the 4-bora-3a,4a-diaza-s-indacene (BODIPY) scaffold as a fluorophore in the design, synthesis and application of fluorescent indicators for pH, metal ions, anions, biomolecules, reactive oxygen species, reactive nitrogen species, redox potential, chemical reactions and various physical phenomena. The sections of the review describing the criteria for rational design of fluorescent indicators and the mathematical expressions for analyzing spectrophotometric and fluorometric titrations are applicable to all fluorescent probes (206 references).

Carbohydrate recognition by boronolectins, small molecules, and lectins

Carbohydrates are known to mediate a large number of biological and pathological events. Small and macromolecules capable of carbohydrate recognition have great potentials as research tools, diagnostics, vectors for targeted delivery of therapeutic and imaging agents, and therapeutic agents. However, this potential is far from being realized. One key issue is the difficulty in the development of "binders" capable of specific recognition of carbohydrates of biological relevance. This review discusses systematically the general approaches that are available in developing carbohydrate sensors and "binders/receptors," and their applications. The focus is on discoveries during the last 5 years.

Carboxyl BODIPY dyes from bicarboxylic anhydrides: one-pot preparation, spectral properties, photostability, and biolabeling

New fluorescent dyes based on 4,4-difluoro-4-bora-3a,4a-diaza-s-indacene (BODIPY) and functionalized with a free carboxyl group have been conveniently synthesized from pyrroles and dicarboxylic anhydrides in one-pot reactions. Their spectral properties in different solvents showed little effect of solvatochromism (<10 nm). The methyl groups on the BODIPY skeleton benefit the fluorescence quantum yields (Phi(f) up to 0.80 in water) but affect the photostability of the dyes. Photooxidation and photodegradation experiments suggest that dyes 1a and 2a exhibit excellent photostability, especially in water, and several factors were taken into account to elucidate the experimental phenomena. Dyes 1c and 2c, derived from 1a and 2a via the esterification of NHS (N-hydroxysuccinimidyl ester), can be easily acquired in high yields (>90%). Single crystal X-ray structures of dyes 2c and 3a are also obtained and discussed. The fluorescence labeling of BSA and followed prestaining method for gel electrophoresis of BSA demonstrate that the protein can be directly observed by naked eyes at as low as 2 ng level under a normal UV fluorescence electrophorogram gel image system.

Synthesis, evaluation, and computational studies of naphthalimide-based long-wavelength fluorescent boronic Acid reporters

Boronic acids that change fluorescence properties upon sugar binding are very useful for the synthesis of carbohydrate sensors. Along this line, boronic acids that fluoresce beyond 500 nm are especially useful. A series of boronic acid fluorescent reporter compounds based on the 4-amino-1,8-naphthalimide structure have been synthesized (1a-d) and evaluated under near physiological conditions. These compounds showed good water solubility and significant changes in fluorescence properties after binding with sugars, with the emission wavelength being at around 570 nm. Analogues in this series with different substitutions showed similar properties. We have also examined the mechanism of the observed fluorescence changes for these compounds.

The chemistry of fluorescent bodipy dyes: versatility unsurpassed

The world of organic luminophores has been confined for a long time to fairly standard biological labeling applications and to certain analytical tests. Recently, however, the field has undergone a major change of direction, driven by the dual needs to develop novel organic electronic materials and to fuel the rapidly emerging nanotechnologies. Among the many diverse fluorescent molecules, the Bodipy family, first developed as luminescent tags and laser dyes, has become a cornerstone for these new applications. The near future looks extremely bright for "porphyrin's little sister".

Substituent Effects on Monoboronic Acid Sensors for Saccharides Based on N-Phenyl-1,8-naphthalenedicarboximides

In the course of our investigations on new monoboronic acid saccharide sensors with C(0) spacers, a series of probes 1-6 based on 1,8-naphthalenedicarboximide were synthesized. Sensor 1 displays features typical of PET monoboronic acid sensors and shows high selectivity to fructose. Sensor 2 exhibits a novel dual emission and remarkable sensitivity for glucose relative to fructose and galactose through subtle changes in pH. Sensor 3 displays significantly enhanced fluorescence in the presence of galactose at low pH. Although probes 4-6 exhibit unique properties such as high quantum yield (Phi(F) = 0.407) and excellent solubility in water, they did not show significant change in fluorescence intensity in the presence of monosaccharides. The effects of substituent on all six probes lend support to the proposed photoelectrochemical model.

The Design of Boronic Acid Spectroscopic Reporter Compounds by Taking Advantage of the pKa-Lowering Effect of Diol Binding: Nitrophenol-Based Color Reporters for Diols

The complex that forms between a boronic acid and a diol is often much more acidic than the starting boronic acid. In conditions where the solution pH is between the two pK(a) values, the boron atom will convert from a neutral trigonal form to an anionic tetrahedral form upon complexation. Such a change is likely to dramatically alter the electron density of neighboring groups. Utilizing this effect, we have designed and synthesized two nitrophenol-based boronic acid reporter compounds that change ionization states and therefore spectroscopic properties upon diol binding. Both compounds show significant UV changes upon addition of saccharides. For example, a blue shift of the absorption max from 373 to 332 nm was observed with the addition of D-fructose to 2-hydroxy-5-nitrophenylboronic acid at neutral pH. Such a reporter compound can be used as a recognition and signaling unit for the construction of polyboronic acid sensors for the selective and specific recognitions of saccharides of biological significance.

Synthesis, Chiroptical Properties, and Solid-State Structure Determination of Two New Chiral Dipyrrin Difluoroboryl Chelates

Two new types of optically active BODIPY fluorophores bearing chiral phenyl substituents either at the meso-position or at both external alpha-positions have been synthesized. Their chiroptical properties are strongly dependent both on the position of the chiral group and on the protonation of the chromophore. The solid-state structures of one of the difluoroboryl chelates bearing the chiral phenyl substituent at the meso-position (9a) as well as of the corresponding ligand (8a) and its perchlorate have been determined by X-ray diffraction analysis. These are, to the best of our knowledge, the first crystal structures of a dipyrrin free base and of a dipyrrin salt which have been obtained by X-ray diffraction analysis. Hence, for the first time, the helical structure of a protonated dipyrrin chromophore has been proved experimentally.

Voltammetric Response of Phenylboronic Acid Monolayer-modified Gold Electrode to Sugars

The surface of a gold (Au) disk electrode was modified with a self-assembled monolayer consisting of phenylboronic acid moiety to fabricate a voltammetric sensor sensitive to sugars. The modified Au electrode exhibited a voltammetric response to sugars in the presence of Fe(CN)6(3-) ion in the sample solution at neutral pH. The peak current of the cyclic voltammograms decreased depending on the type and concentration of sugars. The dynamic range of the electrode is 3 - 100 mM for glucose and mannose and 1 - 30 mM for fructose. The sugar sensor can be used repeatedly after rinsing in 10 mM acetate buffer (pH 4.5).

New Hg2+-Selective Chromo- and Fluoroionophore Based upon 8-Hydroxyquinoline

A new 8-hydroxyquinoline derivative having an appended boron-dipyrromethene function has been prepared, and its metal ion sensing properties were investigated. The designed compound exhibited pronounced Hg(2+)-selective on-off-type fluoroionophoric properties among the representative transition- and heavy-metal ions in aqueous dioxane solution. The fluorescence was efficiently quenched more than 98% with 5 equiv of Hg(2+) ions, and the detection limit was found to be 5 x 10(-)(6) M in a dioxane-water (1:3, v/v) solvent system. The ionophore also showed a selective chromogenic behavior toward Hg(2+) ions by changing the color of the solution from light amber to red, which can be detected with the naked eye.

A novel type of fluorescent boronic acid that shows large fluorescence intensity changes upon binding with a carbohydrate in aqueous solution at physiological pH

In this paper we report 8-quinolineboronic acid as a novel type of fluorescent probe for carbohydrates. This boronic acid responds to the binding of a carbohydrate with over 40-fold increases in fluorescence intensity and shows optimal fluorescence change at physiological pH in aqueous solution.