Boronic acid-based chemical sensors for saccharides

Molecular two-point recognition of fructosyl valine and fructosyl glycyl histidine in water by fluorescent Zn(II)-terpyridine complexes bearing boronic acids

Selective recognition of fructosyl amino acids in water by arylboronic acid-based receptors is a central field of modern supramolecular chemistry that impacts biological and medicinal chemistry. Fructosyl valine (FV) and fructosyl glycyl histidine (FGH) occur as N-terminal moieties of human glycated hemoglobin; therefore, the molecular design of biomimetic receptors is an attractive, but very challenging goal. Herein, we report three novel cationic Zn-terpyridine complexes bearing a fluorescent N-quinolinium nucleus covalently linked to three different isomers of strongly acidified phenylboronic acids (ortho-, 2Zn; meta-, 3Zn and para-, 4Zn) for the optical recognition of FV, FGH and comparative analytes (D-fructose, Gly, Val and His) in pure water at physiological pH. The complexes were designed to act as fluorescent receptors using a cooperative action of boric acid and a metal chelate. Complex 3Zn was found to display the most acidic -B(OH)2 group (pKa = 6.98) and exceptionally tight affinity for FV (K = 1.43 × 105 M-1) with a strong quenching analytical response in the micromolar concentration range. The addition of fructose and the other amino acids only induced moderate optical changes. On the basis of several spectroscopic tools (1H, 11B NMR, UV-Vis, and fluorescence titrations), ESI mass spectrometry, X-ray crystal structure, and DFT calculations, the interaction mode between 3Zn and FV is proposed in a 1 : 1 model through a cooperative two-point recognition involving a sp3 boronate-diol esterification with simultaneous coordination bonding of the carboxylate group of Val to the Zn atom. Fluorescence quenching is attributed to a static complexation photoinduced electron transfer mechanism as evidenced by lifetime experiments. The addition of FGH to 3Zn notably enhanced its emission intensity with micromolar affinity, but with a lower apparent binding constant than that observed for FV. FGH interacts with 3Zn through boronate-diol complexation and coordination of the imidazole ring of His. DFT-optimized structures of complexes 3Zn-FV and 3Zn-FGH show a picture of binding which shows that the Zn-complex has a suitable (B⋯Zn) distance to the two-point recognition with these analytes. Molecular recognition of fructosyl amino acids by transition-metal-based receptors has not been explored until now.

A multilocus-dendritic boronic acid functionalized magnetic nanoparticle for capturing circulating tumor cells in the peripheral blood of mice with metastatic breast cancer

BACKGROUND

Dynamic fluctuation of circulating tumor cells (CTCs) can serve as an indicator of tumor progression. However, the sensitive isolation of CTCs remains extremely challenging due to their rarity and heterogeneity. Against this dilemma, dendritic boronic acid-modified magnetic nanoparticles (MNPs) were prepared in this study, and polyethyleneimine (PEI) was utilized as a scaffold to significantly increase the number of boronic acid moieties. Then the novel developed material was applied to monitor the number of CTCs in mice with metastatic breast cancer to evaluate the therapeutic effects of matrine (Mat), doxorubicin (Dox), and Mat in combination with Dox.

RESULTS

Compared to the low binding capacity of a single boronic acid ligand, dendritic boronic acid shows enhanced sensitivity in binding to sialic acid (SA), which is overexpressed in CTCs. The results showed that the capture efficiency of this modified material could achieve 94.7% and successfully captured CTCs in blood samples from mice with metastatic breast cancer. The CTC counts were consistent with the results of the pathologic examination, demonstrating the reliability and utility of the method.

SIGNIFICANCE

The dendritic boronic acid nanomaterials prepared in this study showed high specificity, sensitivity, and accuracy for cancer cell capture. The approach is expected to provide new insights into cancer diagnosis, personalized therapy, and optimization of treatment regimens.

Stimuli-Responsive Boronate Formation to Control Nucleic Acid-Based Functional Architectures

Boronate esters, formed by the reaction of an oligonucleotide bearing a 5'-boronic acid moiety with the 3'-terminal cis-diol of another oligonucleotide, support the assembly of functional nucleic acid architectures. Reversible formation of boronate esters occurs in templated fashion and has been shown to restore the activity of split DNA and RNA enzymes as well as a split fluorescent light-up aptamer. Apart from their suitability for the design and application of split nucleic acid enzymes and aptamers in the field of biosensing, boronate esters may have played an important role in early life as surrogates of the natural phosphodiester bond. Their formation is reversible and thus fulfills an important requirement for biological self-assembly. Here we discuss the general concept of stimuli-dependent boronate formation and its application in biomolecules with implications for future research.

Water-soluble fluorescent chemosensor for sorbitol based on a dicationic diboronic receptor. Crystal structure and spectroscopic studies

Selective recognition of saccharides by phenylboronic dyes capable of functioning in aqueous conditions is a central topic of modern supramolecular chemistry that impacts analytical sciences and biological chemistry. Herein, a new dicationic diboronic acid structure 11 was synthesized, structurally described by single-crystal X-ray diffraction, and studied in-depth as fluorescent receptor for six saccharides in pure water at pH = 7.4. This dicationic receptor 11 has been designed particularly to respond to sorbitol and involves two convergent and strongly acidified phenyl boronic acids, with a pKa of 6.6, that operate as binding sites. The addition of sorbitol in the micromolar concentration range to receptor 11 induces strong fluorescence change, but in the presence of fructose, mannitol, glucose, lactose and sucrose, only moderate optical changes are observed. This change in emission is attributed to a static complexation photoinduced electron transfer mechanism as evidenced by lifetime experiments and different spectroscopic tools. The diboronic receptor has a high affinity/selectivity to sorbitol (K = 31 800 M-1) over other saccharides including common interfering species such as mannitol and fructose. The results based on 1H, 11B NMR spectroscopy, high-resolution mass spectrometry and density functional theory calculations, support that sorbitol is efficiently bound to 11 in a 1 : 1 mode involving a chelating diboronate-sorbitol complexation. Since the experimental B⋯B distance (5.3 Å) in 11 is very close to the calculated distance from the DFT-optimized complex with sorbitol, the efficient binding is attributed to strong acidification and preorganization of boronic acids. These results highlight the usefulness of a new diboronic acid receptor with a strong ability for fluorescent recognition of sorbitol in physiological conditions.

Two-dimensional isomer differentiation using liquid chromatography-tandem mass spectrometry with in-source, droplet-based derivatization

Saccharides are increasingly used as biomarkers and for therapeutic purposes. Their characterization is challenging due to their low ionization efficiencies and inherent structural heterogeneity. Here, we illustrate how the coupling of online droplet-based reaction, in a form of contained electrospray (ES) ion source, with liquid chromatography (LC) tandem mass spectrometry (MS/MS) allows the comprehensive characterization of sucrose isomers. We used the reaction between phenylboronic acid and cis-diols for on-the-fly derivatization of saccharides eluting from the LC column followed by in situ MS/MS analysis, which afforded diagnostic fragment ions that enabled differentiation of species indistinguishable by chromatography or mass spectrometry alone. For example, chromatograms differing only by 2% in retention times were flagged to be different based on incompatible MS/MS fragmentation patterns. This orthogonal LC-contained-ES-MS/MS method was applied to confirm the presence of turanose, palatinose, maltulose, and maltose, which are structural isomers of sucrose, in three different honey samples. The reported workflow does not require modification to existing mass spectrometers, and the contained-ES platform itself acts both as the ion source and the reactor, all promising widespread application.

Fluorescence Sensing of Monosaccharides by Bis-boronic Acids Derived from Quinolinium Dicarboxamides: Structural and Spectroscopic Studies

Three new diboronic acid-substituted bisquinolinium salts were synthesized, structurally described by single-crystal X-ray diffraction, and studied in-depth as fluorescent receptors for six monosaccharides and two open-chain polyols in water at physiological pH. The dicationic pyridine-2,6-dicarboxamide-based receptors contain two N-quinolinium rings as the fluorescent units covalently linked to three different isomers of phenylboronic acid (ortho, 2; meta, 3; and para, 4) as chelating binding sites for polyols. Additions of glucose/fructose in the micromolar concentration range to receptors 2 and 3 induce significant fluorescence changes, but in the presence of arabinose, galactose, mannose, and xylose, only modest optical changes are observed. This optical change is attributed to a static photoinduced electron transfer mechanism. The meta-diboronic receptor 3 exhibited a high affinity/selectivity toward glucose (K = 3800 M^-1) over other monosaccharides including common interfering species such as fructose and mannitol. Based on multiple spectroscopic tools, electrospray ionization high-resolution mass spectrometry, crystal structures, and density functional theory calculations, the binding mode between 3 and glucose is proposed as a 1:1 complex with the glucofuranose form involving a cooperative chelating diboronate binding. These results demonstrate the usefulness of a new set of cationic fluorescent diboronic acid receptors with a strong ability for optical recognition of glucose in the sub-millimolar concentration range.

Torrefaction characteristics of cellulose loaded with boric acid

To explore the catalytic effect of boric acid on biomass, cellulose loaded with boric acid was roasted by a tubular furnace. The gaseous products were adsorbed by activated carbon and then analyzed by GC-MS. Boric acid was shown to improve the selectivity of the product levoglucosenone (LGO). The effects of the parameters such as boric acid loading, nitrogen flow, and temperature on the torrefaction behavior of cellulose were investigated. In the studied temperature range of 240-420 °C, the yield of LGO first increases and then decreases. In addition, its yield increases directly with increasing nitrogen flow rate. The results show that the highest LGO yield of 6.64% (analytical value) can be obtained under 10% (w/w) boric acid loading, 380 °C and nitrogen flow rate of 65 ml/min conditions.

Carbon-based glyco-nanoplatforms: towards the next generation of glycan-based multivalent probes

Cell surface carbohydrates mediate a wide range of carbohydrate-protein interactions key to healthy and disease mechanisms. Many of such interactions are multivalent in nature and in order to study these processes at a molecular level, many glycan-presenting platforms have been developed over the years. Among those, carbon nanoforms such as graphene and their derivatives, carbon nanotubes, carbon dots and fullerenes, have become very attractive as biocompatible platforms that can mimic the multivalent presentation of biologically relevant glycosides. The most recent examples of carbon-based nanoplatforms and their applications developed over the last few years to study carbohydrate-mediate interactions in the context of cancer, bacterial and viral infections, among others, are highlighted in this review.

Liquid Chromatography-Tandem Mass Spectrometry with Online, In-Source Droplet-Based Phenylboronic Acid Derivatization for Sensitive Analysis of Saccharides

The ability to identify abnormalities in the body's saccharide profile is a promising means for early disease detection but requires analytical tools capable of detecting saccharides at low concentrations and/or for volume-limited samples. The preferred analysis approach for these compounds, liquid chromatography-electrospray ionization-mass spectrometry (LC-ESI-MS), often lacks sensitivity due to poor ionization efficiency. In this work, we employ a modified electrospray interface-termed contained-electrospray (contained-ESI) to couple accelerated droplet chemistry to conventional LC-MS for the online and automated separation, derivatization, and detection of saccharides. The chromatographic component enables complex sample and mixtures analysis with low sample volume requirements, while the enhanced reaction kinetics afforded by electrosprayed microdroplets facilitates rapid, on-the-fly derivatization to boost sensitivity. Derivatization occurs during ion formation as analytes elute from the column, eliminating the need for superfluous post-column derivatization hardware or complicated benchtop protocols. A grounded coupler was incorporated to shield the LC from the high-voltage ion source, and method conditions were optimized to accommodate the low flow rates preferred for microdroplet reactions. The new LC-contained-ESI-MS/MS platform was demonstrated for the analysis of several mono-, di-, and oligosaccharides using in-source droplet-based phenylboronic acid derivatization. Femtomole limits of detection were achieved for a 1 μL injection, representing sensitivity enhancement of 1-2 orders of magnitude over conventional LC-ESI-MS/MS without derivatization. In addition, isobaric saccharides that are difficult to differentiate by MS alone were easily distinguished. Method precision, accuracy, and linearity were established, and the ability to detect oligosaccharides at trace levels in human urine and plasma was demonstrated.

MIL-53 and its OH-bonded variants for bio-polyol adsorption from aqueous solution

The adsorption of bio-polyols from dilute aqueous solution is important but faces challenges in the sustainable bio-refinery process. One solution to increase adsorption efficiency is to leverage host–guest interactions between the polyols and materials to grant a preference for polyols. In this study, we synthesized MIL-53 and diverse OH-bonded variants, and studied their adsorption properties towards ethanediol, 1,3-propanediol and glycerol in water. Among the four materials, OH–MIL-53 exhibited fast adsorption kinetics and high capacity, and could be completely regenerated through ethanol elution. Hydrophobic interactions between the alkyl chains of the polyols and the organic linkers of OH–MIL-53 and hydrogen bonding interactions between their OH groups were identified. The synergistic effect of the host–guest interactions is responsible for the unique adsorption performances of OH–MIL-53 towards polyols, and particularly for 1,3-propanediol.

Delicate host–guest interaction drives OH-bonded MOF to capture bio-polyols from diluted aqueous solution, with high capacity, fast kinetics and recyclability.

Leveraging Arylboronic Acid - Cellulose Binding as a Versatile and Scalable Approach to Hydrophobic Patterning

Paper-based analytical devices, or μPADs, have proven to be valuable bioanalytical tools for a broad range of applications. New methods for μPAD fabrication are needed, however, to facilitate their mass production at a competitive cost. To address this need, we report the use of a boronic acid-containing siloxane polymer (BorSilOx) for patterning hydrophobic barriers for μPADs. This material functions by covalently binding to hydroxyl groups in the paper substrate. It is compatible with inkjet printing or roll-to-roll (stamping) processes, as demonstrated here using three different deposition methods. BorSilOx is able to render a broad range of cellulosic materials (from paper towels to wood) hydrophobic, with contact angle measurements demonstrating superhydrophobicity in many cases. We further demonstrate the utility of the polymer in μPADs via assays for pH and glucose.

Applications of the Reversible Boronic Acids/Boronate Switch to Nucleic Acids

Over the last decades, boron and nucleic acids chemistries have gained a lot of attention for biological, medicinal and analytical applications. Our laboratory has a long-standing interest in both chemistries and owing to the ability of boronic acids to react with cis-diol function in aqueous media we developed over the years a variety of applications ranging from molecular recognition and sensing to the development of reversible dynamic systems in which the natural phosphodiester linkage was replaced by a boronate. In this account, we summarize research results from our group from our preliminary studies on molecular recognition of ribonucleosides to the dynamic assembly of functional DNAzymes. In particular, the various parameters influencing the dynamic nature of these reversible covalent bonds able to respond to external stimuli are discussed. Finally, current challenges and opportunities for boron-based nucleic acids are also addressed.

Mechanism of Self-Healing Hydrogels and Application in Tissue Engineering

Self-healing hydrogels and traditional hydrogels both have three-dimensional polymeric networks that are capable of absorbing and retaining a large amount of water. Self-healing hydrogels can heal and restore damage automatically, and they can avoid premature failure of hydrogels caused by mechanical damage after implantation. The formation mechanism of self-healing hydrogels and the factors that hydrogels can load are various. Researchers can design hydrogels to meet the needs of different tissues through the diversity of hydrogels Therefore, it is necessary to summarize different self-healing mechanisms and different factors to achieve different functions. Here, we briefly reviewed the hydrogels designed by researchers in recent years according to the self-healing mechanism of water coagulation. Then, the factors for different functions of self-healing hydrogels in different tissues were statistically analyzed. We hope our work can provide effective support for researchers in the design process of self-healing hydrogel.

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.

In-Source Microdroplet Derivatization Using Coaxial Contained-Electrospray Mass Spectrometry for Enhanced Sensitivity in Saccharide Analysis

Online, droplet-based in-source chemical derivatization is accomplished using a coaxial-flow contained-electrospray ionization (contained-ESI) source to enhance sensitivity for the mass spectrometric analysis of saccharides. Derivatization is completed in microseconds by exploiting the reaction rate acceleration afforded by electrospray microdroplets. Significant improvements in method sensitivity are realized with minimal sample preparation and few resources when compared to traditional benchtop derivatizations. For this work, the formation of easily ionizable phenylboronate ester derivatives of several mono-, di-, and oligosaccharides is achieved. Various reaction parameters including concentration and pH were evaluated, and a Design of Experiments approach was used to optimize ion source parameters. Signal enhancements of greater than two orders of magnitude were observed for many mono- and disaccharides using in-source phenylboronic acid derivatization, resulting in parts-per-trillion (picomolar) limits of detection. In addition, amino sugars such as glucosamine, which do not ionize in negative mode, were detected at low parts-per-billion concentrations, and isobaric sugars such as lactose and sucrose were easily distinguished. The new in-source derivatization approach can be employed to expand the utility of ESI-MS analysis for compounds that historically experience limited sensitivity and detectability, while avoiding resource-intensive, bulk-phase derivatization procedures.

Lessons in Organic Fluorescent Probe Discovery

Fluorescent probes have gained profound use in biotechnology, drug discovery, medical diagnostics, molecular and cell biology. The development of methods for the translation of fluorophores into fluorescent probes continues to be a robust field for medicinal chemists and chemical biologists, alike. Access to new experimental designs has enabled molecular diversification and led to the identification of new approaches to probe discovery. This review provides a synopsis of the recent lessons in modern fluorescent probe discovery.

Progress in the pretreatment and analysis of carbohydrates in food: An update since 2013

Carbohydrates in foods and other matrices plays vital roles in their diverse biological functions. Carbohydrates serve not only as functional substances but also as structural materials, such as components of membranes, and participate in cellular recognition. The fact that carbohydrates are indispensable has contributed to the need for pretreatment and analytical methods to be developed for their characterization. The aim of this review is to provide a comprehensive overview of carbohydrate pretreatment and determination methods in various matrices. The pretreatment methods include simple and more developed approaches (e.g., solid phase extraction, supercritical fluid extraction, and different microextraction methods, among others). The analytical methods include those by liquid chromatography (including high-performance anion-exchange chromatography), capillary electrophoresis, gas chromatography and supercritical fluid chromatography, and others. Different pretreatment methods and determination approaches are updated, compared, and discussed. Moreover, we discuss and compare the strengths and weaknesses of different methods and suggest their future prospects.

Detection of ligand binding to glycopolymers using saturation transfer difference NMR

We report the use of saturation transfer difference (STD) NMR spectroscopy to observe the interaction of various phenylboronic acids (PBAs) with synthetic glycopolymers presenting galactose and glucose. After optimizing experimental parameters to maximize spin diffusion within the glycopolymers, STD NMR experiments were successfully used to detect binding of PBAs to the polymers. Amplification factor build-up curves in conjunction with differential epitope mapping experiments were used to generate an epitope map for the bound boronic acids. STD NMR was also used to detect the interaction between indole and a galactosylated glycopolymer, providing an indole-based view of this CH-π interaction, a common binding motif in carbohydrate recognition.

A Vibration-Induced-Emission-Based Fluorescent Chemosensor for the Selective and Visual Recognition of Glucose

The development of chemosensors to detect analytes in biologically relevant solutions is a challenging task. We report the synthesis of a fluorescent receptor that combines vibration-induced emission (VIE) and dynamic covalent chemistry for the detection of glucose in aqueous media. We show that the bis-2-(N-methylaminomethyl)phenylboronic acid-decorated N,N'-diphenyl-dihydrodibenzo[a,c]phenazine (DPAC) receptor 1 can detect glucose and discriminate between closely related monosaccharides including those commonly found in blood. Preliminary studies suggest monosaccharides bind to the DPAC-receptor with a 1:1 stoichiometry to produce pseudomacrocyclic complexes, which in turn leads to distinct optical changes in the fluorescent emission of the receptor for each host. Moreover, the complexation-induced change in emission can be detected visually and quantified in a ratiometric way. Our results highlight the potential of VIE-type receptors for the quantitative determination of saccharides in biological samples.

Boronic Acid Pairs for Sequential Bioconjugation

Boronic acids can play diverse roles when applied in biological environments, and employing boronic acid structures in tandem could provide new tools for multifunctional probes. This Letter describes a pair of boronic acid functional groups, 2-nitro-arylboronic acid (NAB) and (E)-alkenylboronic acid (EAB), that enable sequential cross-coupling through stepwise nickel- and copper-catalyzed processes. The selective coupling of NAB groups enables the preparation of stapled peptides, protein-protein conjugates, and other bioconjugates.

Recent advances in multivalent carbon nanoform-based glycoconjugates

Multivalent carbohydrate-mediated interactions are fundamental to many biological processes, including disease mechanisms. To study these significant glycan-mediated interactions at a molecular level, carbon nanoforms such as fullerenes, carbon nanotubes, or graphene and their derivatives have been identified as promising biocompatible scaffolds that can mimic the multivalent presentation of biologically relevant glycans. In this minireview, we will summarize the most relevant examples of the last few years in the context of their applications.

Non-isotope enriched phenylboronic acid-decorated dual-functional nano-assembles for an actively targeting BNCT drug

The feasibility of boron neutron capture therapy (BNCT) greatly depends on the selective accumulation of ¹⁰B in tumors. The p-boronophenylalanine-fructose (BPA-f) complex has been established as a conventional BNCT agent due to its preferential uptake into tumors, which is driven by amino acid transporters. However, the retention of BPA-f in tumors is highly limited because of an antiport mechanism, which is regulated by a gradient of amino acid concentration across the cancer cell membrane. Thus, to preserve a high ¹⁰B concentration in tumors, patients are inevitably subjected to a constant intravenous infusion. To this end, we employed a phenylboronic acid (PBA)-decorated polymeric nanoparticle (Nano^PBA) as a sialic acid-targeting BNCT agent. In this manner, the PBA can exhibit dual functionalities, i.e., exhibiting a neutron capture capacity and hypersialyated cancer cell targeting effect. Our developed Nano^PBA possesses a supramolecular structure composed of a core and shell comprised of poly(lactic acid) (PLA) and poly(ethylene glycol) (PEG) segments, respectively. The PBA moiety is installed at the PEG end, providing an unusually strong targeting effect, supposedly via multivalent binding onto the cancer cell membrane. As in BNCT, we verified the feasibility of Nano^PBA against a B16 melanoma-bearing mouse model. By virtue of efficient tumor targeting, even at a 100-fold lower dose than BPA-f, the Nano^PBA achieved a potent antitumor effect.

Investigation of interaction between boronic acids and sugar: effect of structural change of sugars on binding affinity using steady state and time resolved fluorescence spectroscopy and molecular docking

Binding interactions of boronic acid derivatives viz. 2-Methylphenylboronic acid (B1) and 3-Methoxyphenylboronic acid (B2) with mono saccharides (arabinose, fructose and galactose) and disaccharides (sucrose, lactose and maltose) in aqueous condition at pH 7.4 by means of fluorescence spectroscopy is reported in the present investigation. Sugar sensing as well as continuous glucose monitoring (CGM) plays a significant role in diabetes regulation. Sugar sensors mediated through enzymes have their own drawbacks, which led to encouragement to search for designing new sensors through alternate approaches. Among many, fluorescence-based sensors are drawing more attention. Boronic acid-based fluorescence sensors have the capacity to bind reversibly with diols, which makes their demand high in applications. Addition of sugar reduces fluorescence intensities. Change in intensities is associated to cleavage of intermolecular hydrogen bonding which leads in reduced stability of boronate ester. Lineweaver-Burk and Benesi-Hildebrand equation is used for analysing data. Mono sugars are estimated to have higher binding constants. Mutarotation leads to structural changes in saccharides which play a key role in binding interactions. Sugars in furanose form are found to be highly favoured for binding. Molecular docking of B1 and B2 with proteins with PDB ID: 2IPL and 2IPM being periplasmic was done with the help of Schrodinger Maestro 11.2 version. GLIDE scores terms are used for expressing binding affinity.

Adsorption behaviors on trace Pb2+ from water of biochar adsorbents from konjac starch

Biochar adsorbents used to treat different heavy metals in water are efficient and low-cost. Appropriate raw materials, excellent selectivity and detailed adsorption mechanism are of important for research on biochar adsorbents. In this work, konjac starch was dispersed in polyvinylpyrrolidone (PVP) solution to prepare different sizes hydrophilic carbon spheres (HCSs) by hydrothermal synthesis method. Adsorption kinetics of the HCSs towards Pb2+ is described perfectly by the pseudo-second-order equation. With the temperature increasing, adsorption thermodynamics are more consistent with the Freundlich model. The calculated ΔG, ΔH and ΔS shows the adsorption of the HCSs towards Pb2+ is a spontaneous, endothermic and entropy increase process. In addition, HCSs have excellent selectivity for the adsorption of Pb2+ and Cu2+. HCSs prepared from konjac starch make full use of natural biomass resources, they can be used as a potential adsorbent material in treatment on heavy metal ion from water field.

Understanding the binding interaction between phenyl boronic acid P1 and sugars: determination of association and dissociation constants using S-V plots, steady-state spectroscopic methods and molecular docking

Continuous monitoring of glucose and sugar sensing plays a vital role in diabetes control. The drawbacks of the present enzyme-based sugar sensors have encouraged the investigation into alternate approaches to design new sensors. The popularity of fluorescence sensors is due to their ability to bind reversibly to compounds containing diol. In this study we investigated the binding ability of phenyl boronic acid P1 for monosaccharides and disaccharides (sugars) in aqueous medium at physiological pH 7.4 using steady-state fluorescence and absorbance. P1 fluorescence was quenched due to formation of esters with sugars. Absorbance and fluorescence measurements led to results that indicated that the sugars studied could be ordered in terms of their affinity to P1, as stated: sucrose > lactose > galactose > xylose > ribose > arabinose. In each case, the slope of modified Stern-Volmer plots was nearly 1, indicating the presence of only a single binding site in boronic acids for sugars. Docking studies were carried out using Schrodinger Maestro v.11.2 software. The binding affinity of phenyl boronic acid P1 with periplasmic protein (PDB ID 2IPM and 2IPL) was estimated using GlideScore.

A colorimetric sensor array based on natural pigments for the discrimination of saccharides

A colorimetric sensor array based on natural pigments was developed to discriminate between various saccharides. Anthocyanins, pH-sensitive natural pigments, were extracted from fruits and flowers and used as components of the sensor array. Variation in pH, due to the reaction between saccharides and boronic acids, caused obvious colour changes in the natural pigments. Only by observing the difference map with the naked eye could 11 common saccharides be divided into independent individuals. In conjunction with pattern recognition, the sensor array clearly differentiated between sugar and sugar alcohol with highly accuracy and allowed rapid quantification of different concentrations of maltitol and fructose. This sensor array for saccharides is expected to become a promising alternative tool for food monitoring. The link between anthocyanin and saccharide detection opened a new guiding direction for the application of anthocyanins in foods.

Boronic acid sensors with double recognition sites: a review

Boronic acids reversibly and covalently bind to Lewis bases and polyols, which facilitated the development of a large number of chemical sensors to recognize carbohydrates, catecholamines, ions, hydrogen peroxide, and so on. However, as the binding mechanism of boronic acids and analytes is not very clear, it is still a challenge to discover sensors with high affinity and selectivity. In this review, boronic acid sensors with two recognition sites, including diboronic acid sensors, and monoboronic acid sensors having another group or binding moiety, are summarized. Owing to double recognition sites working synergistically, the binding affinity and selectivity of sensors can be improved significantly. This review may help researchers to sort out the binding rules and develop ideal boronic acid-based sensors.

Benzoxaboroles as dynamic covalent receptors for bioconjugation and transport of nucleosides and related drugs: Proof of action in HeLa cells

In this work we describe not previously explored binding studies on the reversible interaction of benzoxaborole with ligands of medical and pharmaceutical interest such as nucleosidic drugs gemcitabine and capecitabine, as well as the hydrophobic chemotherapeutic doxorubicin. We include functional derivatives of benzoxaborole such as a near infrared fluorescent boronolectine, Cy-Bx, The dynamic covalent interaction in physiological conditions was assessed by spectroscopic techniques yielding moderate to high binding affinities. The cytotoxic activity of the drugs upon conjugation to the boronolectins was evaluated revealing significant influence of the bioconjugation status on the cellular viability. The availability of the conjugate for cellular uptake and localization in the model cancer cell line HeLa was assessed by fluorescence imaging. Benzoxaborole and the fluorescent boronolectin Cy-Bx, proved to be versatile conjugation tools for 1,2 and 1,3-diol containing pharmacophores as well as bioisosteric forms such as 1,2-hydroxyamino, envisioning these small boronolectins as components in systems for drug release with tracking capability.

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.

Aqueous dynamic covalent assembly of molecular ladders and grids bearing boronate ester rungs

Mimicking the self-assembly of nucleic acid sequences into double-stranded molecular ladders that incorporate hydrogen bond-based rungs, dynamic covalent interactions enable the fabrication of molecular ladder and grid structures with covalent bond-based rungs.

Ground-State Charge-Density Distribution in a Crystal of the Luminescent ortho-Phenylenediboronic Acid Complex with 8-Hydroxyquinoline

This contribution is devoted to the first electron density studies of a luminescent oxyquinolinato boron complex in the solid state. ortho-Phenylenediboronic acid mixed with 8-hydroxyquinoline in dioxane forms high-quality single crystals via slow solvent evaporation, which allows successful high resolution data collection (sin θ/λ = 1.2 Å^-1) and charge density distribution modeling. Particular attention has been paid to the boron-oxygen fragment connecting the two parts of the complex, and to the solvent species exhibiting anharmonic thermal motion. The experiment and theory compared rather well in terms of atomic charges and volumes, except for the boron centers. Boron atoms, as expected, constitute the most electron-deficient species in the complex molecule, whereas the neighboring oxygen and carbon atoms are the most significantly negatively charged ones. This part of the molecule appears to be very much involved in the charge transfer occurring between the acid fragment and oxyquinoline moiety leading to the observed fluorescence, as supported by the time-dependent density functional theory (TDDFT) results and the generated transition density maps. TDDFT calculations indicated that p-type atomic orbitals contributing to the HOMO-1, HOMO, and LUMO play the major role in the lowest energy transitions, and enabled further comparison with the charge density features, which is discussed in details. Furthermore, the results confirmed the known fact the Q ligand character is most important for the spectroscopic properties of this class of complexes.