A new thermosensitive fluorescent probe for diol sensing: Poly(N-isopropylacrylamide-co-vinylphenylboronic acid)-alizarin red S complex

A label-free fluorescent peptide probe for sensitive and selective determination of copper and sulfide ions in aqueous systems

A label free fluorescent peptide probe (HDSGWEVHH) was used for Cu2+ and S2- determination in aqueous solution. Our results demonstrated that HDSGWEVHH is highly selective and sensitive for monitoring free Cu2+ concentration via quenching of the probe fluorescence upon Cu2+ binding. The mechanism of the complexation is investigated with Cyclic Voltammetry (CV), 1H nuclear magnetic resonance (NMR), electron paramagnetic resonance (EPR) spectroscopy and computational techniques. Theoretical calculation results indicated the binding ratio of the probe to Cu2+ is 2 : 1 and the binding constant was obtained as 1.72 × 10 8 M-1. Cu2+ concentration can be detected with the detection limit of 16 nM. Free Cu2+ concentration released from the metallothionein-Cu complex at different pH values was detected. Cu2+ concentration in real water and tea samples was also detected, and the results were consistent with the ones monitored by atomic absorption spectrometer. Because of the exceedingly small K sp value of CuS (1.27 × 10-36), S2- can sequester Cu2+ from HDSGWEVHH to restore the tryptophan (W) fluorescence. Thus the HDSGWEVHH-Cu2+ complex can also be used for S2- detection. The S2- concentrations can be monitored with a detection limit of 19 nM. The assay is also amenable to measurement of S2- concentration in pure water samples. Thus the probe designed herein is sensitive, label free, low cost, and environmentally friendly for Cu2+ and S2- determination in aqueous solutions.

Recent trends in sorbents for bioaffinity chromatography

Isolation or enrichment of biological molecules from complex biological samples is mostly a prerequisite in proteomics, genomics, and glycomics. Different techniques have been used to advance the efficiency of the purification of biological molecules. Bioaffinity chromatography is one of the most powerful technique that plays an important role in the isolation of target biological molecules by the specific interactions with ligands that are immobilized on different support materials. This review examines the recent developments in bioaffinity chromatography particularly over the past 5 years in the literature. Also properties of supports, immobilization techniques, types of binding agents, and methods used in bioaffinity chromatography applications are summarized.

Phenylboronic Acid-polymers for Biomedical Applications

Background:

Phenylboronic acid-polymers (PBA-polymers) have attracted tremendous attention as potential stimuli-responsive materials with applications in drug-delivery depots, scaffolds for tissue engineering, HIV barriers, and biomolecule-detecting/sensing platforms. The unique aspect of PBA-polymers is their interactions with diols, which result in reversible, covalent bond formation. This very nature of reversible bonding between boronic acids and diols has been fundamental to their applications in the biomedical area.

Methods:

We have searched peer-reviewed articles including reviews from Scopus, PubMed, and Google Scholar with a focus on the 1) chemistry of PBA, 2) synthesis of PBA-polymers, and 3) their biomedical applications.

Results:

We have summarized approximately 179 papers in this review. Most of the applications described in this review are focused on the unique ability of PBA molecules to interact with diol molecules and the dynamic nature of the resulting boronate esters. The strong sensitivity of boronate ester groups towards the surrounding pH also makes these molecules stimuli-responsive. In addition, we also discuss how the re-arrangement of the dynamic boronate ester bonds renders PBA-based materials with other unique features such as self-healing and shear thinning.

Conclusion:

The presence of PBA in the polymer chain can render it with diverse functions/ relativities without changing their intrinsic properties. In this review, we discuss the development of PBA polymers with diverse functions and their biomedical applications with a specific focus on the dynamic nature of boronate ester groups.

Molecularly imprinted polymeric shell coated monodisperse-porous silica microspheres as a stationary phase for microfluidic boronate affinity chromatography

Molecular imprinting of cis-diol functionalized agents via boronate affinity interaction has been usually performed using nanoparticles as a support which cannot be utilized as a stationary phase in continuous microcolumn applications. In this study, monodisperse-porous, spherical silica particles in the micron-size range, with bimodal pore diameter distribution were selected as a new support for the synthesis of a molecularly imprinted boronate affinity sorbent, using a cis-diol functionalized agent as the template. A specific surface area of 158 m² /g was achieved with the imprinted sorbent by using monodisperse-porous silica microspheres containing both mesoporous and macroporous compartments as the support. High porosity originating from the macroporous compartment and sufficiently high particle size provided good column permeability to the imprinted sorbent in microcolumn applications. The mesoporous compartment provided a large surface area for the parking of imprinted molecules while the macroporous compartment facilitated the intraparticular diffusion of imprinted target within the microsphere interior. A microfluidic boronate affinity system was first constructed by using molecularly imprinted polymeric shell coated monodisperse-porous silica microspheres as a stationary phase. The synthetic route for the imprinting process, the reversible adsorption/ desorption behavior of selected target and the selectivity of imprinted sorbent in both batch and microfluidic boronate affinity chromatography systems are reported.

Application of high-performance magnetic nanobeads to biological sensing devices

Nanomaterials have extensive applications in the life sciences and in clinical diagnosis. We have developed magnetic nanoparticles with high dispersibility and extremely low nonspecific binding to biomolecules and have demonstrated their application in chemical biology (e.g., for the screening of drug receptor proteins). Recently, the excellent properties of nanobeads have made possible the development of novel rapid immunoassay systems and high-precision technologies for exosome detection. For immunoassays, we developed a technology to encapsulate a fluorescent substance in magnetic nanobeads. The fluorescent nanobeads allow the rapid detection of a specific antigen in solution or in tissue specimens. Exosomes, which are released into the blood, are expected to become markers for several diseases, including cancer, but techniques for measuring the absolute quantity of exosomes in biological fluids are lacking. By integrating magnetic nanobead technology with an optical disc system, we developed a novel method for precisely quantifying exosomes in human serum with high sensitivity and high linearity without requiring enrichment procedures. This review focuses on the properties of our magnetic nanobeads, the development of novel biosensors using these nanobeads, and their broad practical applications.

Structure-Reactivity Relationships in Boronic Acid-Diol Complexation

Boronic acids have found widespread use in the field of biomaterials, primarily through their ability to bind with biologically relevant 1,2- and 1,3-diols, including saccharides and peptidoglycans, or with polyols to prepare hydrogels with dynamic covalent or responsive behavior. Despite a wide range of boronic acid architectures that have been previously considered, there is a need for greater understanding of the structure-reactivity relationships that govern binding affinity to diols. In this study, various boronic acids and other organoboron compounds were investigated to determine their pK a and their binding constants with the biologically relevant diols including sorbitol, fructose, and glucose. Boronic acid pK a values were determined through spectroscopic titration, whereas binding constants were determined by fluorescence spectroscopy during competitive binding studies. Key structure-reactivity relationships clearly indicated that both boronic acid structure and solution pH must be carefully considered. By considering a variety of boronic acids with systematically varied electronics and sterics, these results provide guidance during selection of organoboron compounds in sensing, delivery, and materials chemistry.

Responsive Boronic Acid-Decorated (Co)polymers: From Glucose Sensors to Autonomous Drug Delivery

Boronic acid-containing (co)polymers have fascinated researchers for decades, garnering attention for their unique responsiveness toward 1,2- and 1,3-diols, including saccharides and nucleotides. The applications of materials that exert this property are manifold including sensing, but also self-regulated drug delivery systems through responsive membranes or micelles. In this review, some of the main applications of boronic acid containing (co)polymers are discussed focusing on the role of the boronic acid group in the response mechanism. We hope that this summary, which highlights the importance and potential of boronic acid-decorated polymeric materials, will inspire further research within this interesting field of responsive polymers and polymeric materials.

Synthesis and polymerization of boronic acid containing monomers

This mini-review summarizes the most commonly used methods for the synthesis of phenylboronic acid-(co)polymers ranging from simple straightforward polymerization to complex post-polymerization modification.

Boronate affinity materials for separation and molecular recognition: structure, properties and applications

Boronate affinity materials, as unique sorbents, have emerged as important media for the selective separation and molecular recognition of cis-diol-containing compounds. With the introduction of boronic acid functionality, boronate affinity materials exhibit several significant advantages, including broad-spectrum selectivity, reversible covalent binding, pH-controlled capture/release, fast association/desorption kinetics, and good compatibility with mass spectrometry. Because cis-diol-containing biomolecules, including nucleosides, saccharides, glycans, glycoproteins and so on, are the important targets in current research frontiers such as metabolomics, glycomics and proteomics, boronate affinity materials have gained rapid development and found increasing applications in the last decade. In this review, we critically survey recent advances in boronate affinity materials. We focus on fundamental considerations as well as important progress and new boronate affinity materials reported in the last decade. We particularly discuss on the effects of the structure of boronate ligands and supporting materials on the properties of boronate affinity materials, such as binding pH, affinity, selectivity, binding capacity, tolerance for interference and so on. A variety of promising applications, including affinity separation, proteomics, metabolomics, disease diagnostics and aptamer selection, are introduced with main emphasis on how boronate affinity materials can solve the issues in the applications and what merits boronate affinity materials can provide.

Magnetic vinylphenyl boronic acid microparticles for Cr(VI) adsorption: kinetic, isotherm and thermodynamic studies

Magnetic vinylphenyl boronic acid microparticles, poly(ethylene glycol dimethacrylate(EG)-vinylphenyl boronic acid(VPBA)) [m-poly(EG-VPBA)], produced by suspension polymerization and characterized, was found to be an efficient solid polymer for Cr(VI) adsorption. The m-poly(EG-VPBA) microparticles were prepared by copolymerizing of ethylene glycol dimethylacrylate (EG) with 4-vinyl phenyl boronic acid (VPBA). The m-poly(EG-VPBA) microparticles were characterized by N2 adsorption/desorption isotherms, electron spin resonance (ESR), X-ray diffraction (XRD), fourier transform infrared spectroscopy (FTIR), thermal gravimetric analysis (TGA), elemental analysis, scanning electron microscope (SEM) and swelling studies. The m-poly(EG-VPBA) microparticles were used at adsorbent/Cr(VI) ion ratios. The influence of pH, Cr(VI) initial concentration, temperature of the removal process was investigated. The maximum removal of Cr(VI) was observed at pH 2. Langmuir isotherm and Dubinin-Radushkvich isotherm were found to better fit the experiment data rather than Fruendlich isotherm. The kinetics of the adsorption process of Cr(VI) on the m-poly(EG-VPBA) microparticles were investigated using the pseudo first-order, pseudo-second-order, Ritch-second-order and intraparticle diffusion models, results showed that the pseudo-second order equation model provided the best correlation with the experimental results. The thermodynamic parameters (free energy change, ΔG(0) enthalpy change, ΔH(0); and entropy change, ΔS(0)) for the adsorption have been evaluated.

Solvatochromic study of highly fluorescent alkylated isocyanonaphthalenes, their π-stacking, hydrogen-bonding complexation, and quenching with pyridine

Mono- and dialkylated derivatives of 1-amino-5-isocyanonaphthalene (ICAN) were studied as new members of a multifunctional, easy-to-prepare fluorophore family, which showed excellent solvatochromic properties. The monoallyl derivative and the starting ICAN exhibited strong fluorescence quenching in the presence of small amounts of pyridine. The formation of a hydrogen-bonded ground-state pyridine complex was detected; however, analysis of quantum chemical calculations suggested the presence of an additional π-stacked pyridine complex. The Stern-Volmer plot of the quenching process exhibited a downward curvature and after reaching a minimum the fluorescence intensity increased back to a significant level at high pyridine concentrations. Significant fluorescence was observed even in pure pyridine. A new mechanism and a simple mathematical equation were derived to explain the downward curvature and the remaining fluorescence by the formation of a fluorescent π-stacked complex.

Synthesis of end-functionalized boronic acid containing copolymers and their bioconjugates with rod-like viruses for multiple responsive hydrogels

End-functionalized boronic acid containing copolymers are grafted to a rod-like M13 virus. The resultant virus polymer can reversibly form hydrogels, which can be regulated by temperature, pH and glucose.

Multi-stimuli responsive polymers – the all-in-one talents

The integration of several responsive moieties within one polymer yields smart polymers exhibiting a multifaceted responsive behaviour.

Characterization of chemically defined poly-N-isopropylacrylamide based copolymeric adjuvants

PNiPAAm is a thermo-responsive polymer with an adjuvant activity. To identify the minimal chemical structure present within PNiPAAm responsible for its adjuvant property, three different constituent polymers with specific functional groups were synthesized through free radical reaction and tested their adjuvant potential along with PNiPAAm. Among them, polymer with isopropyl attached to an amide showed maximal adjuvant activity in rodents followed by polymer with amide or ketone functional groups. However, secondary amine containing polymer did not show any adjuvant activity. In addition, to improve the adjuvant properties of PNiPAAm, we incorporated an affinity ligand, boronate. At first, we synthesized and characterized the dual responsive copolymers PNiPAAm-co-VPBA and PNiPAAm-co-VPBA-co-DMAEMA. Biocompatibility of these copolymers was confirmed both in vitro and in vivo. Mice injected with these copolymers mixed with collagen (CII) developed significant levels of anti-CII antibodies comprising of all the major IgG subclasses and an increased T cell activation. At the injection site, massive infiltration of immune cells was observed. However, only PNiPAAm-co-VPBA-co-DMAEMA-CII induced arthritis in mice after injection of 0.5M fructose confirming the importance of effective release of CII from the polymer for its adjuvant activity. Thus, a fine balance of hydrophobicity and hydrophilicity promotes adjuvant properties and continuous release of antigen, in this case CII, from polymer is essential for its adjuvant activity.

The development of boronic acids as sensors and separation tools

Synthetic receptors for diols that incorporate boronic acid motifs have been developed as new sensors and separation tools. Utilizing the reversible interactions of diols with boronic acids to form boronic esters under new binding regimes has provided new hydrogel constructs that have found use as dye-displacement sensors and electrophoretic separation tools; similarly, molecular boronic-acid-containing chemosensors were constructed that offer applications in the sensing of diols. This review provides a somewhat-personal perspective of developments in boronic-acid-mediated sensing and separation, placed in the context of the seminal works of others in the area, as well as offering a concise summary of the contributions of the co-authors in the area.

Aqueous polymeric sensors based on temperature-induced polymer phase transitions and solvatochromic dyes

This feature article provides, for the first time, an overview of the research that guided the way from fundamental studies of the thermo-responsive phase separation of aqueous polymer solutions to polymeric sensor systems. The incorporation of solvatochromic dyes into thermoresponsive polymers as well as the concepts of polymeric sensors are presented and discussed in detail.

Controlling deposition and release of polyol-stabilized latex on boronic acid-derivatized cellulose

Poly(glycerol monomethacrylate)-stabilized polystyrene (PGMA-PS) latex particles undergo specific, pH-dependent adsorption onto regenerated cellulose film bearing surface phenylboronic acid groups (cellulose-PBA). Deposition occurs at pH 10 and is driven by the boronate ester formation with the polyol latex surface coating. In contrast, no deposition occurs at pH 4, and previously deposited particles can be readily desorbed at this lower pH. In control experiments, conventional anionic sulfate-stabilized polystyrene latex did not deposit onto the hydrophilic cellulose surface. The distribution of boronate groups in the cellulose was determined by exposure to Alizarin Red S dye, which forms a fluorescent complex with phenylboronic acid; confocal microscopy was used to determine a surface density of 3 nm(2) per boronic acid group on the cellulose surface. Although the boronic acid binding constant with PGMA is relatively low (5.4 L/mol), the cooperative interactions between multiple PBA surface sites and the many PGMA chains per latex particle are sufficient to induce specific latex adsorption, providing a convenient new tool for controlling nanoparticle deposition on surfaces.

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.