Boronic Acid Moiety Research Articles

Aminophenylboronic acid polymer nanoparticles for quantitation of glucose and for insulin release.

We have developed a simple route for the preparation of aminophenylboronic acid polymer nanoparticles (APB PNs) from 3-aminophenylboronic acid and formaldehyde under alkaline conditions according to an extended Stӧber method. Insulin and R6G have been selected to prepare functional insulin-APB PNs and R6G-APB PNs, respectively. During the formation of APB PNs, the representative molecules are embedded inside the APB PNs. Through specific binding of glucose with boronic acid moieties on the R6G-APB PNs and insulin-APB PNs, glucose induces expansion of the APB PNs, leading to release of R6G and insulin molecules, respectively. As a result of release of R6G molecules, the fluorescence intensity of R6G-APB PN solution increases, allowing quantitation of glucose in PBS solutions (10 mM, pH 7.4) with a linear range over 0-10 mM. Release of insulin from insulin-APB PNs is significant and rapid when the glucose concentration is higher than 7 mM. Having advantages of low cost, simple preparation, biocompatibility, and continuous response to glucose, the insulin-APB PNs hold great potential as an alternative for treating diabetic patients. Graphical Abstract Quantitation of glucose and release of insulin by glucose responsive 3-aminophenylboronic acid polymer nanoparticles.

Boronic acid-containing optically active microspheres: Preparation, chiral adsorption and chirally controlled release towards drug DOPA

A judicious combination of chiral structure with other functionalities in one entity may provide novel materials. For this purpose, boronic acid functional group was integrated with optically active helical substituted polyacetylene microspheres. To prepare the designed functional microspheres, two substituted acetylene monomers, i.e. chiral monomer M1 and achiral monomer M2 which was prepared from a boronic acid derivative, were synthesized and copolymerized through suspension polymerization for constructing polymeric microspheres. SEM images demonstrated the successful formation of the microspheres. X-ray photoelectron spectroscopy was measured to determine boronic acid content on the surface of the as-prepared microspheres. Circular dichroism spectra showed that one-handed helices were formed in the copolymer chains constructing the microspheres, which enabled the microspheres to exhibit enantio-differentiating adsorption capacity towards 3,4-dihydroxy-l-phenylalanine (l-DOPA), whereas 3,4-dihydroxy-d-phenylalanine (d-DOPA) was preferentially released. Amazing synergistic effects occurred in the helical polymer chains and the pendant boronic acid moieties. Desorption capacity and recyclability of the microspheres were also clearly verified. The unprecedented optically active microspheres hold practical applications for developing materials used for chiral adsorption, enantiomeric drug controlled release, etc.

RNase H-Assisted Imaging of Peroxynitrite in Living Cells with 5′-Boronic Acid Modified DNA

RNase H is a ubiquitous intracellular enzyme able to selectively hydrolyze the RNA strand of an RNA/DNA hybrid duplex. In the present study, we demonstrate that 5′-boronic acid-modified oligonucleotides could inhibit RNase H activity; actvity which could subsequently be restored upon oxidation of the boronic acid moiety. This unprecedented dual property was exploited to engineer a new stimuli-responsive system for the chemoselective imaging of endogenous and exogenous peroxynitrite in RAW264.7 cells.

The N-B Interaction through a Water Bridge: Understanding the Chemoselectivity of a Fluorescent Protein Based Probe for Peroxynitrite.

Boronic acid and esters have been extensively utilized for molecular recognition and chemical sensing. We recently reported a genetically encoded peroxynitrite (ONOO(-))-specific fluorescent sensor, pnGFP, based on the incorporation of a boronic acid moiety into a circularly permuted green fluorescent protein (cpGFP) followed by directed protein evolution. Different from typical arylboronic acids and esters, the chromophore of pnGFP is unreactive to millimolar concentrations of hydrogen peroxide (H2O2). The focus of this study is to explore the mechanism for the observed unusual chemoselectivity of pnGFP toward peroxynitrite over hydrogen peroxide by using site-directed mutagenesis, X-ray crystallography, (11)B NMR, and computational analysis. Our data collectively support that a His residue on the protein scaffold polarizes a water molecule to induce the formation of an sp(3)-hybridized boron in the chromophore, thereby tuning the reactivity of pnGFP with various reactive oxygen and nitrogen species (ROS/RNS). Our study demonstrates the first example of tunable boron chemistry in a folded nonnative protein, which offers wide implications in designing selective chemical probes.

Alternating Intramolecular and Intermolecular Catalyst-Transfer Suzuki-Miyaura Condensation Polymerization: Synthesis of Boronate-Terminated π-Conjugated Polymers Using Excess Dibromo Monomers.

The Suzuki-Miyaura coupling polymerization of dibromoarene 1 and arylenediboronic acid (ester) 2 with a Pd catalyst having a high propensity for intramolecular catalyst transfer is reported. The polymerization of excess 1 with 2 affords high-molecular-weight π-conjugated polymer having boronic acid (ester) moieties at both ends, contrary to Flory's principle. This unstoichiometric polycondensation behavior is accounted for by intramolecular transfer of the Pd catalyst on 1. In the polymerization of 1 and 2 having different aryl residues, high-molecular-weight polymer is obtained when the stronger donor aromatic is used as the dibromo monomer and the weaker donor or acceptor aromatic is used as diboronic acid (ester) monomer. The pinacol boronate moieties at both ends of the obtained poly(p-phenylene) (PPP) can be converted to benzoic acid ester, hydroxyl group, and bromine. Furthermore, the reaction of the pinacol boronate-terminated PPP with poly(3-hexylthiophene) (P3HT) having bromine at one end yields a triblock copolymer of P3HT-b-PPP-b-P3HT.

Conversion of a Benzofuran Ester to an Amide through an Enamine Lactone Pathway: Synthesis of HCV Polymerase Inhibitor GSK852A.

HCV NS5B polymerase inhibitor GSK852A (1) was synthesized in only five steps from ethyl 4-fluorobenzoylacetate (3) in 46% overall yield. Key to the efficient route was the synthesis of the highly functionalized benzofuran core 15 from the β-keto ester in one pot and the efficient conversion of ester 6 to amide 19 via enamine lactone 22. Serendipitous events led to identification of the isolable enamine lactone intermediate 22. Single crystal X-ray diffraction and NMR studies supported the intramolecular hydrogen bond shown in enamine lactone 22. The hydrogen bond was considered an enabler in the proposed pathway from ester 6 to enamine lactone 22 and its rearrangement to amide 19. GSK852A (1) was obtained after reductive amination and mesylation with conditions amenable to the presence of the boronic acid moiety which was considered important for the desirable pharmacokinetics of 1. The overall yield of 46% in five steps was a significant improvement to the previous synthesis from the same β-keto ester in 5% yield over 13 steps.

Boronic acid modified fiber optic SPR sensor and its application in saccharide detection

To extend the application of fiber-optic surface plasmon resonance (SPR) sensing technology, the chemical molecular, 2-(((6-aminohexyl)(benzyl)amino)methyl) phenyl boronic acid (ABA-PBA), is prepared as the recognition monolayer and immobilized on the fiber-optic SPR probe. The boronic acid moiety in ABA-PBA monolayer can covalently bond with 1, 2- or 1, 3- diols moiety of sugar. A monolayer of ABA-PBA is assembled on the SPR sensing region and confirmed by surface enhanced Raman scattering (SERS) technique. Spectrophotometric method is used to determine the pKa of ABA-PBA. The interaction between ABA-PBA monolayer and saccharide can induce the shift of resonance wavelength. By using the miniature fiber-optic SPR sensor, saccharide concentration can be monitored in real time. It shows good selectivity to fructose at low concentrations (10–50mM).

Tumor vascular targeted liposomal-bortezomib minimizes side effects and increases therapeutic activity in human neuroblastoma

Neuroblastoma is a childhood cancer with poor long-term prognosis in advanced stages. A major aim in neuroblastoma therapy is to develop targeted drug delivery systems to ameliorate drug therapeutic index and efficacy. In this study, a novel bortezomib (BTZ) liposomal formulation was set-up and characterized. Since BTZ is freely permeable across the lipidic bilayer, an amino-lactose (LM) was synthesized as complexing agent to entrap BTZ inside the internal aqueous compartment of stealth liposomes. High encapsulation efficiency was achieved by a loading method based on the formation of boronic esters between the boronic acid moiety of BTZ and the hydroxyl groups of LM. Next, NGR peptides were linked to the liposome surface as a targeting-ligand for the tumor endothelial cell marker, aminopeptidase N. Liposomes were characterized for size, Z-potential, polydispersity index, drug content, and release. Lyophilization in the presence of cryoprotectants (trehalose, sucrose) was also examined in terms of particle size changes and drug leakage.BTZ was successfully loaded into non-targeted (SL[LM-BTZ]) and targeted (NGR-SL[LM-BTZ]) liposomes with an entrapment efficiency of about 68% and 57%, respectively. These nanoparticles were suitable for intravenous administration, presenting an average diameter of 170nm and narrow polydispersity. Therefore, orthotopic NB-bearing mice were treated with 1.0 or 1.5mg/kg of BTZ, either in free form or encapsulated into liposomes. BTZ loaded liposomes showed a significant reduction of drug systemic adverse effects with respect to free drug, even at the highest dose tested. Moreover, mice treated with 1.5mg/kg of NGR-SL[LM-BTZ] lived statistically longer than untreated mice (P=0.0018) and SL[LM-BTZ]-treated mice (P=0.0256). Our results demonstrate that the novel vascular targeted BTZ formulation is endowed with high therapeutic index and low toxicity, providing a new tool for future applications in neuroblastoma clinical studies.

Design and synthesis of a hydrogen peroxide-responsive amino acid that induces peptide bond cleavage after exposure to hydrogen peroxide

Oxidative stress-responsive compounds are attracting significant attention in the field of medicinal chemistry and chemical biology. Here, we disclose the development of a hydrogen peroxide (H2O2)-responsive amino acid that induces peptide bond cleavage in the presence of H2O2 that closely relates to oxidative stress. The H2O2-responsive amino acid possessing a boronate or boronic acid moiety was incorporated into a peptide using Fmoc-based solid-phase peptide synthesis or that with minor modifications, respectively, and the peptide bond cleavage of the obtained peptide was successfully triggered by the addition of H2O2.

Bioreversible Protein Labeling For Cellular Delivery

A growing number of potential chemotherapeutic agents are proteins. A major challenge to the use of proteins as intracellular drugs is their traversal of the negatively charged glycocalyx and cell membrane. Many methods have been developed over the past several decades to try to overcome this obstacle, including liposome carriers, various polymers, cell‐penetrating peptides, and changes to the protein itself. All of these methods have downsides, including cytotoxicity, low delivery yields, and irreversible changes to the proteins. Here, we present two complementary methods of bioreversible protein modification that endow cell permeability, and we demonstrate their efficacy using the green fluorescent protein (GFP). The first method labels lysine residues with a module that combines the trimethyl lock scaffold to enable bioreversibility in the presence of cellular esterases, and a boronic acid moiety to promote cellular entry by increasing contact with the glycocalyx. This modification enables cellular uptake of GFP through endocytosis. The second method uses a fluorenyl diazo compound to label carboxylic acids of the target protein, forming ester bonds that are labile to cellular esterases. The pendant fluorenyl groups endow GFP with high levels of cytosolic delivery. Both strategies enhance delivery of a native protein into a cell, which is critical for clinical utility.

A carbon nanofiber-based label free immunosensor for high sensitive detection of recombinant bovine somatotropin.

A carbon nanofiber-based label free electrochemical immunosensor for sensitive detection of recombinant bovine somatotropin (rbST) was developed. In this immunosensor design, a mild site-directed antibody immobilization via interaction of boronic acid and oligosaccharide moiety found on Fc region of an antibody was performed to preserve the biological activity of antibody and improve the sensor's sensitivity. Electrochemical characterization of the immunosensor fabrication was carried out by differential pulse voltammetry (DPV) in Fe(CN)6(3-)/Fe(CN)6(4-) probe. A comparison study between different transducer platforms showed carbon nanofiber gave higher current signal response than single-walled carbon nanotube. In this work, calibration curve was obtained from the decrease of DPV peak current of Fe(CN)6(3-)/Fe(CN)6(4-) after immunocomplexed was formed. A linear relationship between DPV current change signal response and rbST concentrations from 1 pg/mL to 10 ng/mL (correlation coefficient of 0.9721) was achieved with detection limit of 1 pg/mL. Our developed immunosensor demonstrated high selectivity in cross-reactivity studies and a good percentage recovery in spiked bovine serum sample.

A high boronate avidity monolithic capillary for the selective enrichment of trace glycoproteins

Boronate affinity materials, as effective sample enrichment sorbents for glycoproteomic analysis, have attracted increasing attention in recent years. However, most of boronate affinity materials suffer from an apparent limitation, limited binding strength. As a result, extraction of glycoproteins of trace concentration is rather difficult or impossible. In this study, we present a high boronate avidity monolithic capillary. Branched polyethyleneimine (PEI) was used as a scaffold to amplify the number of boronic acid moieties. While 2,4-difluoro-3-formyl-phenylboronic acid (DFFPBA), which exhibited ultrahigh affinity toward cis-diol-containing compounds, was employed as an affinity ligand. Due to the PEI-assisted synergistic multivalent binding, the monolithic column exhibited high boronate avidity toward glycoproteins, with binding constants of 10−6–10−7M. Such binding strength was the highest among already reported boronic acid-functionalized materials that can be used for glycoproteomic analysis. Besides, the boronate avidity monolithic column exhibited one additional beneficial feature, lowered binding pH (≥6.5). These features greatly favored the selective enrichment of trace glycoproteins from real samples. The feasibility for practical applications was demonstrated with the selective enrichment of trace glycoproteins in human saliva. As compared with other boronate avidity/affinity materials, the boronate avidity monolithic capillary exhibited the best performance.

Molecular design of boronic acid-functionalized squarylium cyanine dyes for multiple discriminant analysis of sialic acid in biological samples: selectivity toward monosaccharides controlled by different alkyl side chain lengths.

We designed a new series of boronic acid-functionalized squarylium cyanine dyes (SQ-BA) with different lengths of alkyl chain residues, suitable for multiple discriminant analysis (MDA) of sialic acid (Neu5Ac) in biological samples. The SQ-BA dyes form aggregates based on hydrophobic interactions, which result in quenched fluorescence in aqueous solutions. When the boronic acid binds with saccharides, the fluorescence intensity increases as a result of dissociation to the emissive monomeric complex. We inferred that different dye aggregate structures (H-aggregates and J-aggregates) were induced depending on the alkyl chain length, so that monosaccharides would be recognized in different ways (especially, multipoint interaction with J-aggregates). A distinctive emission enhancement of SQ-BA dyes with shorter-alkyl-chains in the presence of Neu5Ac was observed (2.4-fold fluorescence enhancement; with formation constant 10(1.7) M(-1)), with no such enhancement for SQ-BA dyes with longer-alkyl-chain. In addition, various enhancement factors for other monosaccharides were observed depending on the alkyl chain length. Detailed thermodynamic and NMR studies of the SQ-BA complexes revealed the unique recognition mechanism: the dye aggregate with a shorter-alkyl-chain causes the slipped parallel structure and forms a stable 2:1 complex with Neu5Ac, as distinct from longer-alkyl-chain dyes, which form a 1:1 monomeric complex. MDA using the four SQ-BA dyes was performed for human urine samples, resulting in the successful discrimination between normal and abnormal Neu5Ac levels characteristic of disease. Thus, we successfully controlled various responses to similar monosaccharides with a novel approach that chemically modified not the boronic acid moiety itself but the length of the alkyl chain residue attached to the dye in order to generate specificity.

High-efficiency immunoassay platforms with controllable surface roughness and oriented antibody immobilization.

High-efficiency immunoassay platforms with controlled surface roughness (single- and dual-scale structured surface) were prepared by combining a facile layer-by-layer particle deposition approach with oriented immobilization of antibodies through boronic acid moieties. The as-prepared surfaces showed significantly enhanced antibody loading capacity and antigen recognition, as proved by fluorescence images.

Improved Lithium-Storage Capability and Cyclability of Tin Dioxide Confined in Highly Crosslinked Graphene Framework

The dimensional stability of SnO2 nanoparticles during Li+ insertion/de-insertion was improved by confining them within a highly crosslinked graphene framework. The composite was synthesized by reacting an optimal amount of bezene-1,4-diboronic acid (BDBA) with SnO2-anchored graphene oxide (SG) that had a high density of oxygen functionalities. The latter was prepared by irradiating ozone on as-synthesized SG. The resultant composite (SGF) possessed a high boron/carbon ratio and a low fraction of unreacted boronic acid moieties, indicating the production of a highly crosslinked framework. The SGF showed excellent stability with a high capacity when cycled between 0.1 and 3.0 V vs. Li/Li+. A decrease of the low-end potential limit induced instability of the boronic ester linkage, which led to a relatively fast capacity fading. The SGF delivered capacities greater than 940 mAh·g−1 after 150 cycles at 200 mA·g−1, with a fading rate of 1.3 mAh·g−1·cycle−1 (from 2nd to 150th cycles). This was contrasted with 10.4 mAh·g−1·cycle−1 for SGF prepared without ozone-treatment and cycled between 0.01 and 3.0 V vs. Li/Li+. The rate capabilities of SGF were also comparable to or better than those reported previously for SnO2/graphene composites, implying that the highly crosslinked framework does not hamper the electroactivity of SnO2 nanoparticles.

Sugar response of layer-by-layer films composed of poly(vinyl alcohol) and poly(amidoamine) dendrimer bearing 4-carboxyphenylboronic acid

Multilayered thin films composed of poly(vinyl alcohol) (PVA) and 4-carboxyphenylboronic acid-modified poly(amidoamine) dendrimer (4-PBA-PAMAM) were prepared by a layer-by-layer (LbL) deposition of PVA and 4-PBA-PAMAM on the surface of a quartz plate to study the response of the multilayered films to sugars. PVA/4-PBA-PAMAM films were constructed successfully at pH 7.0–9.0 through the formation of boronate ester bonds between the boronic acid moiety in 4-PBA-PAMAM and 1,3-diol units in PVA, while the film deposition was unsuccessful at pH 6.0 probably owing to weaker affinity between 4-PBA-PAMAM and PVA in the weakly acidic medium. The films were stable in aqueous solutions at pH 7.5 or higher whereas the films decomposed in neutral and acidic solutions, which can be ascribed to lower affinity of neutral trigonal PBA derivatives than that of negatively charged tetragonal PBAs. PVA/4-PBA-PAMAM films decomposed in response to glucose and fructose depending on the concentration as a result of competitive binding of the sugars to 4-PBA-PAMAM in the film. The degree of glucose-induced decomposition of the film was 20–25 % in the presence of 30 mM at pH 7.4 and 9.0. On the other hand, in 10 mM fructose solution, the degree of film decomposition was 90 and 60 % at pH 9.0 and 7.4, respectively. A possible application of the LbL films to sugar-sensitive delivery systems was discussed.

Abstract 4571: Antitumor effects of an antibody (cetuximab)-targeted nanoparticle containing siRNA against EGFR

Abstract Objective: Effective therapies for lung cancer that have mutated EGFR remain elusive. Because of the success of antibody-drug-conjugates, we are exploring the use of antibody targeted nanoparticles (NP) containing siRNA to produce multifunctional therapeutics. Here, we investigate the use of cetuximab (CTX) (commercial antibody to EGFR) targeted NPs containing siRNA against EGFR (sequence is for a region of the mRNA conserved in all types of mutations) in H1975 NSCLC xenografts. Methods: We synthesized a cationic mucic acid polymer by polymerizing a derivative of mucic acid, mucic acid ethylenediamine, with dimethyl suberimidate. This polycation can self-assemble with siRNA to form the NP. A methoxy polyethylene glycol (PEG) was modified to have a 5-nitrophenyl boronic acid (5-nPBA) moiety at one end to attach to diol groups on mucic acid and stabilize the NP. 5-nPBA-PEG with a carboxylic acid end group was conjugated to CTX to target the NP to EGFR receptors on the surface of cancer cells. These polymers were mixed with siRNA to form NPs, characterized by dynamic light scattering and cryo-transmission electron microscopy for size, and zeta potential measurements for surface charge. The NP was tested in vivo against tumors grown with H1975 NSCLC cells that contain the L858R and T790M mutations. NPs dosed iv (tail vein) at 9.3 mg/kg CTX targeting agent and 5 mg/kg siEGFR were injected twice a week for two weeks into nude mice with H1975 NSCLC xenografts and the anti-tumor effects compared to 9.3 mg/kg CTX (dosed iv tail vein) alone. Results: The CTX-targeted cMAP-siRNA NPs are ca. 40 nm in diameter as determined by both dynamic light scattering and cryo-TEM. The NPs' surface charge is slightly negative at -3.5 mV in 10 mM phosphate buffered at pH 7.4 (surrogate for extracellular conditions in vivo). When the NPs are in 1 mM KCl at pH 5.5 (surrogate for intracellular, endocytosis localization), the NP zeta potential is +1 mV indicating detachment of 5-nPBA-PEG from the NP at acidic pH. Thus, the NP is stabilized and targeted until it is endocytosed, where it disassembles to release the siRNA payload. We confirmed delivery of siEGFR to the tumor following two NP doses via a real-time PCR assay. In contrast to CTX treated mice that showed tumor growth delay but ultimately had tumors that grew to over 1000 mm3, NP treated mice had tumors that remained below 200 mm3 53 days following completion of 4 doses. Conclusions: NPs containing full antibodies as targeting agents and siRNA payloads can be formulated into well defined, stable experimental therapeutics. The NP system used here has a pH-tunable 5-nPBA that allows for targeting and stabilizing the NP at a physiologic pH of 7.4. The targeting agent and PEG coating is able to detach from the NP at acidic pH like those found in endosomes, enabling the siRNA payload to escape and reach its site of action within the cell. These NPs produce significant tumor regression in vivo that is superior to CTX alone. Citation Format: Dorothy W. Pan, Mark E. Davis. Antitumor effects of an antibody (cetuximab)-targeted nanoparticle containing siRNA against EGFR. [abstract]. In: Proceedings of the 105th Annual Meeting of the American Association for Cancer Research; 2014 Apr 5-9; San Diego, CA. Philadelphia (PA): AACR; Cancer Res 2014;74(19 Suppl):Abstract nr 4571. doi:10.1158/1538-7445.AM2014-4571

B and H-NMR Evaluation of Chemical Interactions between Two Polyphenols; Epigallocatechingallate and Quercetin with Bortezomib

Bortezomib (Velcade) is a boronic acid dipeptide, proteasome inhibitor drug that its antimyeloma activity in treatment of patients with multiple myeloma (MM) has been approved by FDA. Studies show that consumption of daily diet rich in polyphenols affect Bortezomib’s bioavailability and reduce its antitumor activity. In the present study we made an attempt to investigate the interactions between Bortezomib and some common polyphenols to examine whether these polyphenols interact with the drug. For this purpose, interactions between four dietary polyphenols including: Emodin, Rhein, Epigallocatechingallate (EGCG) and Quercetin with methyl boronic acid, Bortezomib’s substitute, were studied using 1H and 11B- NMR spectroscopy. The results suggest that the vicinal diols in the structure of the two polyphenols (EGCG and Quercetin) interact with the boronic acid moiety of Bortezomib and convert the active triangular boronic acid to an inactive tetrahedral boronate through direct chemical interaction, and this conversion abolishes the antimyeloma activity of Bortezomib. In conclusion, our study suggests that the consumption of dietary sources enriched in EGCG and Quecetin during treatment with Bortezomib in MM patients should be considered.

Boronic Acids as Probes for Investigation of Allosteric Modulation of the Chemokine Receptor CXCR3

The chemokine receptor CXCR3 is a G protein-coupled receptor, which conveys extracellular signals into cells by changing its conformation upon agonist binding. To facilitate the mechanistic understanding of allosteric modulation of CXCR3, we combined computational modeling with the synthesis of novel chemical tools containing boronic acid moiety, site-directed mutagenesis, and detailed functional characterization. The design of boronic acid derivatives was based on the predictions from homology modeling and docking. The choice of the boronic acid moiety was dictated by its unique ability to interact with proteins in a reversible covalent way, thereby influencing conformational dynamics of target biomolecules. During the synthesis of the library we have developed a novel approach for the purification of drug-like boronic acids. To validate the predicted binding mode and to identify amino acid residues responsible for the transduction of signal through CXCR3, we conducted a site-directed mutagenesis study. With the use of allosteric radioligand RAMX3 we were able to establish the existence of a second allosteric binding pocket in CXCR3, which enables different binding modes of structurally closely related allosteric modulators of CXCR3. We have also identified residues Trp109(2.60) and Lys300(7.35) inside the transmembrane bundle of the receptor as crucial for the regulation of the G protein activation. Furthermore, we report the boronic acid 14 as the first biased negative allosteric modulator of the receptor. Overall, our data demonstrate that boronic acid derivatives represent an outstanding tool for determination of key receptor-ligand interactions and induction of ligand-biased signaling.

Synthesis of Water-Dispersed Ferrecene/Phenylboronic Acid-Modified Bifunctional Gold Nanoparticles and the Application in Biosensing.

Phenylboronic acids can form tight covalent bonds with diol-containing biomolecules. In this work, water-dispersed bifunctional gold nanoparticles (AuNPs) modified with ferrecene (Fc)-derivatized peptides and 4-mercaptophenylboronic acids (MBA) (denoted as Fc–MBA–AuNPs) were synthesized and characterized by UV/vis spectrometry and transmission electron microscopy. To demonstrate the application and the analytical merits of the nanoparticles in biosensing, glycoprotein avidin was tested as a model analyte. Specifically, avidin was captured by the biotin-covered gold electrode via the strong biotin-avidin interaction. Then, Fc–MBA–AuNPs were attached by the captured avidin through the formation of tight covalent bonds between the boronic acid moieties of Fc–MBA–AuNPs and the oligosaccharides of avidin. As a result, a detection limit of 0.2 pM was achieved. We believe that the bifunctional nanoparticles would found many applications in amplified detection of diol-containing species by rational design of the surface chemistry of electrode.