Advancing Glucose Sensing Through Auto-Fluorescent Polymer Brushes: From Surface Design to Nano-Arrays.

Designing smart (bio)interfaces with the capability to sense and react to changes in local environments offers intriguing possibilities for new surface-based sensing devices and technologies. Polymer brushes make ideal materials to design such adaptive and responsive interfaces given their large variety of functional and structural possibilities as well as their outstanding abilities to respond to physical, chemical, and biological stimuli. Herein, a practical sensory interface for glucose detection based on auto-fluorescent polymer brushes decorated with phenylboronic acid (PBA) receptors is presented. The glucose-responsive luminescent surfaces, which are capable of translating conformational transitions triggered by pH variations and binding events into fluorescent readouts without the need for fluorescent dyes, are grown from both nanopatterned and non-patterned substrates. Two-photon laser scanning confocal microscopy and atomic force microscopy (AFM) analyses reveal the relationship between the brush conformation and glucose concentration and confirm that the phenylboronic acid functionalized brushes can bind glucose over a range of physiologically relevant concentrations in a reversible manner. The combination of auto-fluorescent polymer brushes with synthetic receptors presents a promising avenue for designing innovative and robust sensing systems, which are essential for various biomedical applications, among other uses.

Capturing Sialyl-glycan on Live Cancer Cells by Tailored Boronopeptide.

Boronic acid-containing molecules are substantially popularized in chemical biology and medicinal chemistry due to the broad spectrum of covalent conjugations as well as interaction modules offered by the versatile boron atom. Apparently, the WGA peptide (wheat germ agglutinin, 62-73), which shows a considerably low binding affinity to sialic acid, turned into a selective and >5 folds potent binder with the aid of a suitable boronic acid probe installed chemoselectively. In silico studies prompted us to install BA probes on the cysteine residue, supposedly located in close proximity to the bound sialic acid. In vitro studies revealed that the tailored boronopeptides show enhanced binding ability due to the synergistic recognition governed by selective non-covalent interactions and cis-diol boronic acid conjugation. The intense binding is observed even in 10 % serum, thus enabling profiling of sialyl-glycan on cancer cells, as compared with the widely used lectin, Sambucus nigra. The synergistic binding mode between the best boronopeptide (P3) binder and sialic acid was analyzed via 1 H and 11 B NMR.

Tuning the Stability and Kinetics of Dioxazaborocanes.

We investigated the equilibrium reaction of boronic acid (BA), diethanolamines (DEA), and 1,3,6,2-dioxazaborocanes (DOAB) in aqueous solutions, both theoretically and experimentally. Our findings show that the association constant can be adjusted by substituting BA and DEA derivatives, ranging from 100 to 103 M-1, exhibiting a bell-shaped pH dependency. The highest stability was achieved when the pKa values of DEA and BA were closely matched. This approach enabled the preparation of a highly stable DOAB under physiological conditions. Furthermore, the hydrolysis kinetics of DOABs were controllable over a range of five orders of magnitude based on the substituent's steric effect. In the slowest case, this resulted in quasi-static stability with only 1% cleavage in the first hour, followed by a week-long cleavage period to reach equilibrium. These insights could establish a unique chemistry platform for designing scheduled cleavability on a day-to-week timescale, relevant to protein engineering, immunotherapy, and other smart drug delivery applications.

Solid-State Synthesis of B←N Adducts by the Amine-Facilitated Trimerization of the Phenylboronic Acid.

Stable boroxine-amine adducts comprising dative B←N bond(s) were prepared by mechanochemically-induced reactions of phenylboronic acid (PBA) and amines (pyridine, DMAP, 1H-pyrazole, piperidine, DABCO, hexamethylenetetramine, or 4,4'-bipyridine). In-situ Raman monitoring, ex-situ PXRD and DFT calculations were used for product identification. Stoichiometry of the product (3 : 1, 3 : 2 or 6 : 1 adduct) was controlled by the amine structure and the molar ratio of the reactants. The 1 : 2 H-bonded assembly of PBA and 4,4'-bipyridine (bpy) was confirmed as an intermediate in the adduct formation for bpy. Competitive binding experiments indicated that the exchange of the amines in the 3 : 1 adducts follows the computed adduct stabilities that increase with the amine basicity. Following the DFT prediction, the first adduct with two different amines, DMAP and pip, bound to one boroxine moiety was isolated and structurally characterized. Results show that calculations can be used to predict possible and preferred product(s) and their spectral characteristics.

Thermochromic Afterglow from Benzene-1,4-Diboronic Acid-Doped Co-crystals.

The accurate thermosensing requires a minimum impact of autofluorescence and light scattering from the samples. In this study, we discovered that commercially available benzene-1,4-diboronic acid (BDBA) doped co-crystals with trimethylolpropane (TMP) exhibit excellent thermochromic dual phosphorescence properties over a wide temperature range from -132 to 40 °C, despite its simple structure that does not have any donor-acceptor linkage. The dual phosphorescence was consisted of monomeric benzene-1,4-diboronate (BDBA ester) and aggregation-stabilized species. With an increase in temperature, the emission intensity from the monomeric state significantly decreased, whereas that originating from the aggregated state remained almost constant owing to the difference in their thermal stabilities. Further investigation revealed that molecular distortions in singlet excited states enable efficient intersystem crossing, causing efficient phosphorescence from the monomeric state of BDBA ester.

Rational Design of Highly Selective Sialyllactose-Imprinted Nanogels.

We describe a facile method to prepare water-compatible molecularly imprinted polymer nanogels (MIP NGs) as synthetic antibodies against target glycans. Three different phenylboronic acid (PBA) derivatives were explored as monomers for the synthesis of MIP NGs targeting either α2,6- or α2,3-sialyllactose, taken as oversimplified models of cancer-related sT and sTn antigens. Starting from commercially available 3-acrylamidophenylboronic acid, also its 2-substituted isomer and the 5-acrylamido-2-hydroxymethyl cyclic PBA monoester derivative were initially evaluated by NMR studies. Then, a small library of MIP NGs imprinted with the α2,6-linked template was synthesized and tested by mobility shift Affinity Capillary Electrophoresis (msACE), to rapidly assess an affinity ranking. Finally, the best monomer 2-acrylamido PBA was selected for the synthesis of polymers targeting both sialyllactoses. The resulting MIP NGs display an affinity constant≈106 M-1 and selectivity towards imprinted glycans. This general procedure could be applied to any non-modified carbohydrate template possessing a reducing end.

Preparation of Biomimetic Selenium-Baicalein Nanoparticles and Their Targeted Therapeutic Application in Nonsmall Cell Lung Cancer.

In this study, we prepared bionic selenium-baicalein nanoparticles (ACM-SSe-BE) for the targeted treatment of nonsmall cell lung cancer. Due to the coating of the A549 membrane, the system has homologous targeting capabilities, allowing for the preparation of target tumor cells. The borate ester bond between selenium nanoparticles (SSe) and baicalein (BE) is pH-sensitive and can break under acidic conditions in the tumor microenvironment to achieve the targeted release of BE at the tumor site. Moreover, SSe further enhances the antitumor effect of BE by increasing the production of ROS in tumor cells. Transmission electron microscopy (TEM) images and dynamic light scattering (DLS) showed that the ACM-SSe-BE had a particle size of approximately 155 ± 2 nm. FTIR verified the successful coupling of SSe and BE. In vitro release experiments indicated that the cumulative release of ACM-SSe-BE at pH 5.5 after 24 h was 69.39 ± 1.07%, which was less than the 20% release at pH 7.4, confirming the pH-sensitive release of BE in ACM-SSe-BE. Cell uptake experiments and in vivo imaging showed that ACM-SSe-BE had good targeting ability. The results of MTT, flow cytometry, Western blot, and cell immunofluorescence staining demonstrated that ACM-SSe-BE promoted A549 cell apoptosis and inhibited cell proliferation. The in vivo antitumor results were consistent with those of the cell experiments. These results clearly suggested that ACM-SSe-BE will be a promising bionic nanosystem for the treatment of nonsmall cell lung cancer.

Ratiometric fluorescence detection of dopamine based on copper nanoclusters and carbon dots.

Nanoclusters for fluorescence detection are generally comprised of rare and expensive noble metals, and the nanoclusters based on more affordable transition metal have attracted increasing attention. This study designed a ratiometric fluorescent probe to detect dopamine (DA), an important neurotransmitter. With carbon dots encapsulated within silica (CDs@SiO2) as the reference, the emitted reference signal was almost unchanged due to the protection of inert silicon shell. Meanwhile, copper nanoclusters modified with 3-aminophenyl boronic acid (APBA-GSH-CuNCs) provided the sensing signal, in which the phenylboric acid could specifically recognize the cis-diol structure of DA, and caused the fluorescence quenching by photoinduced electron transfer. This dual emission ratiometric fluorescent probe exhibited high sensitivity and anti-interference, and was able to selectively responded to DA with a linear range of 0-1.4 mM, the detection limit of 5.6 nM, and the sensitivity of 815 mM-1. Furthermore, the probe successfully detected DA in human serum samples, yielding recoveries ranging from 92.5% to 102.7%. Overall, this study highlights the promising potential of this ratiometric probe for detecting DA.

Boron-containing carbonic anhydrases inhibitors.

Over the last decades, the medicinal chemistry of boron-based compounds has been extensively explored, designing valuable small molecule drugs to tackle diseases and conditions, such as cancer, infections, inflammatory and neurological disorders. Notably, boron has proven to also be a valuable element for the development of inhibitors of the metalloenzymes carbonic anhydrases (CAs), a class of drug targets with significant potential in medicinal chemistry. Incorporating boron into carbonic anhydrase inhibitors (CAIs) can modulate the ligand ability to recognize the target and/or influence selectivity towards different CA isoforms, using the tail approach and boron-based tails. The electron-deficient nature of boron and its associated properties have also led to the discovery of novel zinc-binding CAIs, such as boronic acids and the benzoxaboroles, capable of inhibiting the CAs upon a Lewis acid-base mechanism of action. The present manuscript reviews the state-of-the-art of boron-based CAIs. As research in the applications of boron compounds in medicinal chemistry continues, it is anticipated that new boron-based CAIs will soon expand the current array of such compounds. However, further research is imperative to fully unlock the potential of boron-based CAIs and to advance them towards clinical applications.

Peptidic boronic acids are potent cell-permeable inhibitors of the malaria parasite egress serine protease SUB1.

Malaria is a devastating infectious disease, which causes over 400,000 deaths per annum and impacts the lives of nearly half the world's population. The causative agent, a protozoan parasite, replicates within red blood cells (RBCs), eventually destroying the cells in a lytic process called egress to release a new generation of parasites. These invade fresh RBCs to repeat the cycle. Egress is regulated by an essential parasite subtilisin-like serine protease called SUB1. Here, we describe the development and optimization of substrate-based peptidic boronic acids that inhibit Plasmodium falciparum SUB1 with low nanomolar potency. Structural optimization generated membrane-permeable, slow off-rate inhibitors that prevent Pfalciparum egress through direct inhibition of SUB1 activity and block parasite replication in vitro at submicromolar concentrations. Our results validate SUB1 as a potential target for a new class of antimalarial drugs designed to prevent parasite replication and disease progression.

Boronic acid with high oxidative stability and utility in biological contexts.

Despite their desirable attributes, boronic acids have had a minimal impact in biological contexts. A significant problem has been their oxidative instability. At physiological pH, phenylboronic acid and its boronate esters are oxidized by reactive oxygen species at rates comparable to those of thiols. After considering the mechanism and kinetics of the oxidation reaction, we reasoned that diminishing electron density on boron could enhance oxidative stability. We found that a boralactone, in which a carboxyl group serves as an intramolecular ligand for the boron, increases stability by 104-fold. Computational analyses revealed that the resistance to oxidation arises from diminished stabilization of the p orbital of boron that develops in the rate-limiting transition state of the oxidation reaction. Like simple boronic acids and boronate esters, a boralactone binds covalently and reversibly to 1,2-diols such as those in saccharides. The kinetic stability of its complexes is, however, at least 20-fold greater. A boralactone also binds covalently to a serine side chain in a protein. These attributes confer unprecedented utility upon boralactones in the realms of chemical biology and medicinal chemistry.

Functionalization of Siloxanes with Arynes Generated from o-Triazenylarylboronic Acids.

Herein, we report the functionalization of polyhedral oligosilsesquioxanes (POSS) and related siloxanes with arynes. Using o-triazenylarylboronic acids as aryne precursors and silica gel as the activator, the transformation of siloxane bearing various arynophilic moieties on the side chains was achieved with high yields without touching the siloxane core. This method was applied to the conjugation of POSS and pharmaceutical cores using an aryne derived from the synthetic intermediate of cabozantinib. Furthermore, orthogonal dual functionalization of POSS was realized by combining the aryne reaction with Huisgen cyclization.

Bi-functionality of glyoxal caged nucleic acid coupled with CRISPR/Cas12a system for Hg2+ determination.

A highly sensitive and selective fluorescence method has been conducted for the detection of Hg2+ based on aminophenylboronic acid-modified carboxyl magnetic beads (CMB@APBA) and CRISPR/Cas12a system mediated by glyoxal caged nucleic acid (gcDNA). As a bi-functional DNA linker, gcDNA offers advantages of simultaneous recognition by boronic acid and complementary DNA/RNA. Under acidic condition, gcDNA can be immobilized on CMB@APBA through the formation of borate ester bond. The formed boric acid-esterified gcDNA can further bind with complementary CRISPR RNA through A-T base pairing to activate Cas12a with kcat/Km ratio of 3.4 × 107 s-1 M-1, allowing for amplified signal. Hg2+ can specifically combine with CMB@APBA, resulting in the release of gcDNA from CMB@APBA and the following inhibition on the activation of CRISPR/Cas12a system around magnetic bead. Under optimal conditions, the method exhibits a linear range from 20 to 250 nM, with a detection limit of 2.72 nM. The proposed method can detect Hg2+ in milk and tea beverages, providing a great significance for on-site monitoring of Hg2+ contamination in food.

Multi-walled carbon nanotubes functionalized with a new Schiff base containing phenylboronic acid residues: application to the development of a bienzymatic glucose biosensor using a response surface methodology approach.

An innovative supramolecular architecture is reported for bienzymatic glucose biosensing based on the use of a nanohybrid made of multi-walled carbon nanotubes (MWCNTs) non-covalently functionalized with a Schiff base modified with two phenylboronic acid residues (SB-dBA) as platform for the site-specific immobilization of the glycoproteins glucose oxidase (GOx) and horseradish peroxidase (HRP). The analytical signal was obtained from amperometric experiments at - 0.050 V in the presence of 5.0 × 10-4 M hydroquinone as redox mediator. The concentration of GOx and HRP and the interaction time between the enzymes and the nanohybrid MWCNT-SB-dBA deposited at glassy carbon electrodes (GCEs) were optimized through a central composite design (CCD)/response surface methodology (RSM). The optimal concentrations of GOx and HRP were 3.0 mg mL-1 and 1.50 mg mL-1, respectively, while the optimum interaction time was 3.0 min. The bienzymatic biosensor presented a sensitivity of (24 ± 2) × 102 µA dL mg-1 ((44 ± 4) × 102 µA M-1), a linear range between 0.06 mg dL-1 and 21.6 mg dL-1 (3.1 µM-1.2 mM) (R2 = 0.9991), and detection and quantification limits of 0.02 mg dL-1 (1.0 µM) and 0.06 mg dL-1 (3.1 µM), respectively. The reproducibility for five sensors prepared with the same MWCNT-SB-dBA nanohybrid was 6.3%, while the reproducibility for sensors prepared with five different nanohybrids and five electrodes each was 7.9%. The GCE/MWCNT-SB-dBA/GOx-HRP was successfully used for the quantification of glucose in artificial human urine and commercial human serum samples.

Simple Binding and Dissociation of a Sialoglycoprotein Using Boronic Acid-Modified Functional Interfaces on Microparticles.

An overexpression of sialic acid is an indicator of metastatic cancer, and selective detection of sialic acid shows potential for cancer diagnosis. Boronic acid is a promising candidate for this purpose because of its ability to specifically bind to sialic acid under acidic conditions. Notably, the binding strength can be easily modulated by adjusting the pH, which allows for a simple dissociation of the bound sialic acid. In this study, we developed 5-boronopicolinic acid (5-BPA)-modified magnetic particles (BMPs) to selectively capture sialic acid biomolecules. We successfully captured fetuin, a well-known sialoglycoprotein, on BMPs at >104 molecules/particle using an acetate buffer (pH 5.0). Facile dissociation then occurred when the system was changed to a pH 7.6 phosphate buffer. This capture-and-release process could be repeated at least five times. Moreover, this system could enrich fetuin by more than 20 times. In summary, BMPs are functional particles for facile purification and concentration through the selective capture of sialic acid proteins and can improve detection sensitivity compared with conventional methods. This technology shows potential for the detection of sialic acid overexpression by biological particles.

Colorimetric Immunoassays with Boronic Acid-Decorated, Peroxidase-like Metal-Organic Frameworks as the Carriers of Antibodies and Enzymes.

The sensitivity of immunoassays is generally limited by the low signal reporter/recognition element ratio. Nanomaterials serving as the carriers can enhance the loading number of signal reporters, thus improving the detection sensitivity. However, the general immobilization strategies, including direct physical adsorption and covalent coupling, may cause the random orientation and conformational change in proteins, partially or completely suppressing the enzymatic activity and the molecular recognition ability. In this work, we proposed a strategy to load recognition elements of antibodies and enzyme labels using boronic acid-modified metal-organic frameworks (MOFs) as the nanocarriers for signal amplification. The conjugation strategy was proposed based on the boronate ester interactions between the carbohydrate moieties in antibodies and enzymes and the boronic acid moieties on MOFs. Both enzymes and MOFs could catalyze the oxidation of 3,3',5,5'-tetramethylbenzidine (TMB) by H2O2, therefore achieving dual signal amplification. To indicate the feasibility and sensitivity of the strategy, colorimetric immunoassays of prostate specific antigen (PSA) were performed with boronic acid-modified Cu-MOFs as peroxidase mimics to catalyze TMB oxidation and nanocarriers to load antibody and enzyme (horseradish peroxidase, HRP). According to the change in the absorbance intensity of the oxidized TMB (oxTMB), PSA at the concentration range of 1~250 pg/mL could be readily determined. In addition, this work presented a site-specific and oriented conjugation strategy for the modification of nanolabels with recognition elements and signal reporters, which should be valuable for the design of novel biosensors with high sensitivity and selectivity.

Acidity Constants of Boronic Acids as Simply as Possible: Experimental, Correlations, and Prediction.

The wide use of boronic compounds, especially boronic acids and benzoxaboroles, in virtually all fields of chemistry is related to their specific properties. The most important of them are the ability to form cyclic esters with diols and the complexation of anions. In both cases, the equilibrium of the reaction depends mainly on the acidity of the compounds, although other factors must also be taken into account. Quantification of the acidity (pKa value) is a fundamental factor considered when designing new compounds of practical importance. The aim of the current work was to collect available values of the acidity constants of monosubstituted phenylboronic acids, critically evaluate these data, and supplement the database with data for missing compounds. Measurements were made using various methods, as a result of which a fast and reliable method for determining the pKa of boronic compounds was selected. For an extensive database of monosubstituted phenylboronic acids, their correlation with their Brønsted analogues-namely carboxylic acids-was examined. Compounds with ortho substituents do not show any correlation, which is due to the different natures of both types of acids. Nonetheless, both meta- and para-substituted compounds show excellent correlation. From a practical point of view, acidity constants are best determined from the Hammett equation. Computational approaches for determining acidity constants were also analyzed. In general, the reported calculated values are not compatible with experimental ones, providing comparable results only for selected groups of compounds.

Arylboronic Acid Pinacol Esters as Stable Boron Sources for Dihydrodibenzoborepin Derivatives and a Dibenzoborole.

The general synthesis of boron-containing cyclic compounds (boracycles) necessitates toxic organotin precursors or highly reactive boron halides. Here, we report the synthesis of seven- and five-membered boracycles utilizing arylboronic acid pinacol esters (ArBpins) as stable boron sources. Grignard reagents generated from 2,2'-dibromodibenzyl or 2,2'-dibromobiphenyl reacted with ArBpins, where Ar = 9-anthryl (Anth), 2,4,6-trimethylphenyl (Mes), or 2,4,6-triisopropylphenyl (Tip), to give 10,11-dihydro-5H-dibenzo[b,f]borepins or dibenzoborole derivatives. This Bpin-based method was successfully applied to a one-shot double boracycle formation, providing a dihydrodibenzoborepin-anthracene-dihydrodibenzoborepin triad molecule in a good yield. The dihydrodibenzoborepin bearing the Anth group was directly converted to the unsaturated borepin by NBS/AIBN. All products were characterized by NMR, HRMS, and in some cases, single-crystal X-ray diffraction analysis. Additionally, the photophysical properties of the products are also reported.

Synthesis of Boronate Affinity-Based Oriented Dummy Template-Imprinted Magnetic Nanomaterials for Rapid and Efficient Solid-Phase Extraction of Ellagic Acid from Food.

Ellagic acid (EA) is a natural polyphenol and possesses excellent in vivo bioactivity and antioxidant behaviors, which play an important role in the treatment of oxidative stress-related diseases, such as cancer. Additionally, EA is also known as a skin-whitening ingredient. The content of EA would determine its efficacy. Therefore, the accurate analysis of EA content can provide more information for the scientific consumption of EA-rich foods and cosmetics. Nevertheless, the analysis of EA in these samples is challenging due to the low concentration level and the presence of interfering components with high abundance. Molecularly imprinted polymers are highly efficient pretreatment materials in achieving specific recognition of target molecules. However, the traditional template molecule (EA) could not be absolutely removed. Hence, template leakage continues to occur during the sample preparation process, leading to a lack of accuracy in the quantification of EA in actual samples, particularly for trace analytes. In addition, another drawback of EA as an imprinting template is that EA possesses poor solubility and a high price. Gallic acid (GA), called dummy templates, was employed for the synthesis of MIPs as a solution to these challenges. The approach used in this study was boronate affinity-based oriented surface imprinting. The prepared dummy-imprinted nanoparticles exhibited several significant advantages, such as good specificity, high binding affinity ((4.89 ± 0.46) × 10-5 M), high binding capacity (6.56 ± 0.35 mg/g), fast kinetics (6 min), and low binding pH (pH 5.0) toward EA. The reproducibility of the dummy-imprinted nanoparticles was satisfactory. The dummy-imprinted nanoparticles could still be reused even after six adsorption-desorption cycles. In addition, the recoveries of the proposed method for EA at three spiked levels of analysis in strawberry and pineapple were 91.0-106.8% and 93.8-104.0%, respectively, which indicated the successful application to real samples.

Targeted pH-responsive delivery of rosmarinic acid via phenylboronic acid functionalized mesoporous silica nanoparticles for liver and lung cancer therapy.

Currently, chemotherapy is one of the most practiced approaches for the treatment of cancers. However, existing chemotherapeutic drugs have poor aqueous solubility, poor selectivity, higher systematic toxicity, and poor target accumulation. In this study, we designed and synthesized a boronic acid/ester-based pH-responsive nano-valve that specifically targets the microenvironment in cancer cells. The nano-valve comprises phenylboronic acid-coated mesoporous silica nanoparticles (B-MSN) loaded with polyphenolic compound Rosmarinic acid (ROS-B-MSN). The nano-valve was further coated with lignin (LIG) to achieve our desired LIG-ROS-BMSN nano-valve for targeted chemotherapy against Hep-G2 and NCI-H460 cell lines. The structure and properties of NPs were characterized by Fourier-transformed infrared spectroscopy (FTIR), Scanning Electron Microscopy (SEM) in combination with EDX, and Dynamic light scattering (DLS). The outcomes revealed that the designed LIG-ROS-BMSN were in the nanorange (144.1 ± 0.70 nm), had negative Zeta potential (-15.7 ± 0.46 mV) and had a nearly spherical morphology. In vitro, drug release investigations showed a controlled pH-dependent release profile under mild acidic conditions that could enhance the targeted chemotherapeutic response against cancer in mild acidic environments. The obtained LIG-ROS-BMSN nano valve achieved significantly lower IC50 values of (1.70 ± 0.01 µg/mL and 3.25 ± 0.14 µg/mL) against Hep-G2 and NCI-H460 cell lines as compared to ROS alone, which was (14.0 ± 0.7 µg/mL and 29.10 ± 0.25 µg/mL), respectively. The cellular morphology before and after treatment was further confirmed via inverted microscopy. The outcomes of the current study imply that our designed LIG-ROS-BMSN nanovalve is a potential carrier for cancer chemotherapeutics.