Interactions between boric acid derivatives and saccharides in aqueous media: Structures and stabilities of resulting esters

Phenylboronic acid functionalized dextran loading curcumin as nano-therapeutics for promoting the bacteria-infected diabetic wound healing

Chronic bacterial infections, excessive inflammation, and oxidative stress significantly hinder diabetic wound healing by prolonging the inflammatory phase and complicating the healing process. In this study, phenylboronic acid functionalized dextran (PODP) was developed to encapsulate curcumin, referred to as PODP@Cur. Experimental results indicate that PODP significantly improves the water solubility of curcumin and exhibits synergistic biological activity both in vitro and in vivo. PODP@Cur is capable of accelerating drug release under the pathological microenvironment with ROS accumulation. Furthermore, phenylboronic acid (PBA) has demonstrated potential for targeted bacterial drug delivery, enhancing antibacterial efficacy and trapping free LPS/PGN from dead bacteria to reduce undesirable inflammation. In a diabetic mouse model, PODP@Cur exhibits an excellent antibacterial, anti-inflammatory and antioxidant activities to ultimately promote the efficient and safe wound healing. Due to the specific interaction between PBA and LPS, PODP@Cur could enhance antibacterial activity against bacteria, reduce toxic side effects on normal cells, and alleviate the LPS-mediated pro-inflammatory pathological microenvironment. Therefore, PODP@Cur is capable of being exploited as an efficient and safe candidate for promoting the bacteria-infected diabetic wound healing.

Comprehensive O-Glycan Analysis by Porous Graphitized Carbon Nanoliquid Chromatography-Mass Spectrometry

The diverse and unpredictable structures of O-GalNAc-type protein glycosylation present a challenge for its structural and functional characterization in a biological system. Porous graphitized carbon (PGC) liquid chromatography (LC) coupled to mass spectrometry (MS) has become one of the most powerful methods for the global analysis of glycans in complex biological samples, mainly due to the extensive chromatographic separation of (isomeric) glycan structures and the information delivered by collision induced fragmentation in negative mode MS for structural elucidation. However, current PGC-based methodologies fail to detect the smaller glycan species consisting of one or two monosaccharides, such as the Tn (single GalNAc) antigen, which is broadly implicated in cancer biology. This limitation is caused by the loss of small saccharides during sample preparation and LC. Here, we improved the conventional PGC nano-LC-MS/MS-based strategy for O-glycan analysis, enabling the detection of truncated O-glycan species and improving isomer separation. This was achieved by the implementation of 2.7 μm PGC particles in both the trap and analytical LC columns, which provided an enhanced binding capacity and isomer separation for O-glycans. Furthermore, a novel mixed-mode PGC-boronic acid-solid phase extraction during sample preparation was established to purify a broad range of glycans in an unbiased manner, including the previously missed mono- and disaccharides. Taken together, the optimized PGC nano-LC-MS/MS platform presents a powerful component of the toolbox for comprehensive O-glycan characterization.

Reactive Microneedle Patches with Antibacterial and Dead Bacteria-Trapping Abilities for Skin Infection Treatment

Bacterial skin infections are highly prevalent and pose a significant public health threat. Current strategies are primarily focused on the inhibition of bacterial activation while disregarding the excessive inflammation induced by dead bacteria remaining in the body and the effect of the acidic microenvironment during therapy. In this study, a novel dual-functional MgB2 microparticles integrated microneedle (MgB2 MN) patch is presented to kill bacteria and eliminate dead bacteria for skin infection management. The MgB2 microparticles not only can produce a local alkaline microenvironment to promote the proliferation and migration of fibroblasts and keratinocytes, but also achieve >5 log bacterial inactivation. Besides, the MgB2 microparticles effectively mitigate dead bacteria-induced inflammation through interaction with lipopolysaccharide (LPS). With the incorporation of these MgB2 microparticles, the resultant MgB2 MN patches effectively kill bacteria and capture dead bacteria, thereby mitigating these bacteria-induced inflammation. Therefore, the MgB2 MN patches show good therapeutic efficacy in managing animal bacterial skin infections, including abscesses and wounds. These results indicate that reactive metal borides-integrated microneedle patches hold great promise for the treatment of clinical skin infections.

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.

Quantitative determination of chondroitin sulfate with various molecular weights in raw materials by pre-column derivatization with 6-aminoquinolyl-N-hydroxysuccinimidyl carbamate

A simple and reliable HPLC method was developed for quantification of chondroitin sulfate (CS). The procedure is based on precolumn hydrolysis of CS to liberate galactosamine and subsequent derivatization with 6-aminoquinolyl-N-hydroxysuccinimidyl carbamate. Hydrolysis and derivatization conditions were optimized. A linear correlation coefficient of 0.9999 was calculated within the range of 10-1500 μg/mL from the standard curve. The method produces good precision and good accuracy (100.75 % recovery). An advantage over other common methods is its ability to quantify CS of all molecular weights and structures, as evidenced by the determination of CS fractions with narrow molecular weight distributions obtained through depolymerization by different methods, while enzymatic HPLC was proven to be infeasible. Extraction recoveries of CS from monosaccharide mixed samples were > 93 %. The reliability was also validated by a small difference (-1.95 % to 4.12 %) relative to enzymatic HPLC results in analysing representative CS samples of different animal origins and suppliers.

Separation of carbohydrates using dynamically adsorbed borate stationary phase for hydrophilic interaction liquid chromatography

In this work, a chromatographic method for the separation of carbohydrates was proposed. Tris-(hydroxymethyl)-amine (TRIS) functionalized silica-based hydrophilic interaction liquid chromatography (HILIC) stationary was synthesized. The dynamically absorbed borate layer is generated by using borate buffer as a polar modifier due to the complexation of borate with TRIS ligand in the stationary phase. The chromatographic systems were analyzed by the linear solvation energy relationship model. The calculated system constants revealed the enhancement of anionic exchange by the addition of borate in the mobile phase system. In addition, ligand exchange is critical for the retention and elution order of sugars and sugar alcohols. Carbohydrates displayed prolonged retention with different selectivity profiles relating to their complexation coefficients with borate. Experiment results showed that the effect of borate in this chromatographic system was stable within the range of pH 3-7 and borate concentration of 5-15 mM. This work provides a complementary solution for the separation of carbohydrates. It can also be extended to the separation of glycosides.

Recent advances in nanopore-based analysis for carbohydrates and glycoconjugates

Saccharides are not only the basic constituents and nutrients of living organisms, but also participate in various life activities, and play important roles in cell recognition, immune regulation, development, cancer, etc. The analysis of carbohydrates and glycoconjugates is a necessary means to study their transformations and physiological roles in living organisms. Existing detection techniques can hardly meet the requirements for the analysis of carbohydrates and glycoconjugates in complex matrices as they are expensive, involve complex derivatization, and are time-consuming. Nanopore sensing technology, which is amplification-free and label-free, and is a high-throughput process, provides a new solution for the identification and sequencing of carbohydrates and glycoconjugates. This review highlights recent advances in novel nanopore-based single-molecule sensing technologies for the detection of carbohydrates and glycoconjugates and discusses the advantages and challenges of nanopore sensing technologies. Finally, current issues and future perspectives are discussed with the aim of improving the performance of nanopores in complex media diagnostic applications, as well as providing a new direction for the quantification of glycan chains and the study of glycan chain properties and functions.

Production of high-purity lactulose via an integrated one-pot boronate affinity adsorbent based adsorption-assisted isomerization and simultaneous purification

High-purity lactulose is mandatory for its medical uses and food applications. This work developed an efficient lab-scale strategy for the synthesis of high-purity lactulose by combining lactose-to-lactulose isomerization with simultaneous recovery of lactulose, which was conducted concurrently and semi-continuously in a boronate affinity adsorbent-packed column. The first step covers the boronate affinity adsorbent-based adsorption-assisted lactose-to-lactulose isomerization. Under optimized conditions, in situ selectively binding of the newly formed lactulose onto the boronate affinity adsorbent enables a much-enhanced lactulose yield up to 80.20% with the lowest byproducts yield of 6.30%. Afterward, over 90% of the adsorbed lactulose can be recovered through sequential desorption with purity >98%. The net outcome of the applied strategy was the yield of high-purity lactulose up to 72.31%, the highest value ever reported. Moreover, the packed column displayed excellent operational stability. The encouraging results validate the high potential of this approach in the sustainable production of high-purity lactulose.

Duckweed pectic-arabinogalactan-proteins can crosslink through borate diester bonds

Material containing pectin and arabinogalactan-protein (AGP) was released and purified from Spirodela alcohol insoluble residues. Results of carbohydrate analyses and two-dimensional NMR spectroscopy suggest that this material is composed of apiogalacturonan and rhamnogalacturonan-I covalently attached to AGPs. 11B NMR spectroscopy indicated that some of the glycoses in this complex exist as their boric acid monoesters. Borate diesters were formed when the pectic-AGPs were allowed to react at pH above 6.2 with the boron-depleted pectic-AGPs, suggesting that in vitro two pectic-AGP molecules can crosslink to one another through borate. Borate diesters also formed when the pectic-AGPs were incubated with monomeric rhamnogalacturonan-II in the presence of Pb2+ ion at pH 9.2. This data presents evidence of the first wall polymer after rhamnogalacturonan-II to crosslink through borate diesters. We suggest that the formation of these borate-crosslinks may help Spirodela respond to high-pH condition.

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.

Borophosphate glasses as active agents for antimicrobial hydrogels

Herein we report the synthesis of transition-metal-free potassium borophosphate glasses and their application as bactericidal and bacteriostatic material. The antimicrobial activity was achieved through a simple change in the molar ratio of boron and phosphorus atoms, making borophosphate glass soluble in water. The glasses were analyzed by X-ray powder diffraction, Raman spectroscopy, laser-induced breakdown spectroscopy, and water absorption. The addition of a boron compound is required to obtain potassium-based phosphate glasses. Moreover, the change in the phosphorus and boron molar ratio (P/B), 2, 1 or 0.5 affects the glass solubilization in water, which increases with the phosphorus content. The glass materials were submitted to tests of biological activity against the bacteria Staphylococcus aureus, Escherichia coli, and Pseudomonas aeruginosa. These water-soluble borophosphate glasses were employed in the development of hydrogel formulations using Carbopol®. Phosphorous-rich samples at a concentration of 15 % (w/w) in hydrogel showed better antimicrobial activity against S. aureus and E. coli, when compared to other samples, including commercial alcohol hand sanitizer gel, with an average size of the inhibition halo of 24.02±1.43 and 19.24±1.63mm, respectively.

Advances in Gelatin Bioinks to Optimize Bioprinted Cell Functions

Gelatin is a widely utilized bioprinting biomaterial due to its cell-adhesive and enzymatically cleavable properties, which improve cell adhesion and growth. Gelatin is often covalently cross-linked to stabilize bioprinted structures, yet the covalently cross-linked matrix is unable to recapitulate the dynamic microenvironment of the natural extracellular matrix (ECM), thereby limiting the functions of bioprinted cells. To some extent, a double network bioink can provide a more ECM-mimetic, bioprinted niche for cell growth. More recently, gelatin matrices are being designed using reversible cross-linking methods that can emulate the dynamic mechanical properties of the ECM. This review analyzes the progress in developing gelatin bioink formulations for 3D cell culture, and critically analyzes the bioprinting and cross-linking techniques, with a focus on strategies to optimize the functions of bioprinted cells. This review discusses new cross-linking chemistries that recapitulate the viscoelastic, stress-relaxing microenvironment of the ECM, and enable advanced cell functions, yet are less explored in engineering the gelatin bioink. Finally, this work presents the perspective on the areas of future research and argues that the next generation of gelatin bioinks should be designed by considering cell-matrix interactions, and bioprinted constructs should be validated against currently established 3D cell culture standards to achieve improved therapeutic outcomes.

Analysis of tri-benzeneboronic esters of monosaccharides formed in aqueous solution by MALDI-TOF MS and DFT calculations

The affinity interactions between boronic acids and sugars have been successfully exploited in many fields, such as the sensing of saccharides, selective enrichment of glycoconjugates, and drug delivery. However, despite multiple techniques having been adopted to investigate the reaction of boronate affinity, the pathway of boronate esters formation under aqueous conditions remains controversial. We report a MALDI-MS approach to investigate the interactions between phenylboronic acid and monosaccharides in neutral aqueous solution by using polylevodopa as an innovative substrate instead of conventional matrix. A series of unusual tri-benzeneboronic esters were then revealed. The mass spectrometry data indicate that they bear a dibenzenepyroboronate cyclic ester moiety with seven-membered ring or eight-membered ring. With the aid of theoretical computations, their most likely geometrical structures are elucidated, and these tri-benzeneboronic esters are proposed to be formed via a boroxine binding monosaccharide pathway. This work provides more insight into the mechanism of boronate affinity interaction between boronic acid and sugars and proves the developed MALDI-MS approach is promising for studying interactions between small molecules.

Boron Adsorption Kinetics of Microcrystalline Cellulose and Polymer Resin

Tailoring boron-polysaccharide interactions is an important strategy for developing functional soft materials such as hydrogels, fire retardants, and sorbents for environmental remediation, for example, using lignocellulosic biomass. For such applications to be realized, it is paramount to understand the adsorption kinetics of borate anions on cellulose and their local structures. Here, the kinetic aspects of boron adsorption by microcrystalline cellulose, lignin, and polymeric resin are investigated and compared. Borate anions interact with the vicinal diols in the glucopyranoside moieties of cellulose to yield chemisorbed boron chelate complexes. In contrast to cellulose, technical lignin contains fewer cis-vicinal diols, and it does not have a tendency to form such chelate complexes upon treatment with the aqueous boric acid solution. The formation kinetics and stability of these chelate complexes strongly depend on nanoscale structures, as well as reaction conditions such as pH and concentration of the sorbate and sorbent. Specifically, insights into the distinct boron adsorption sites were obtained by solid-state one-dimensional (1D) ¹¹B magic-angle spinning NMR and the local structures and intermolecular interactions in the vicinities of boron chelate complexes are elucidated by analyzing two-dimensional (2D) ¹H-¹³C and ¹¹B-¹H heteronuclear correlation NMR spectra. The total boron adsorption capacity of cellulose is estimated to be in the 1.3-3.0 mg range per gram of sorbent, which is lower than the boron adsorption capacity of a polystyrene-based resin, ∼17.2 mg of boron per gram of Amberlite IRA 743. Our study demonstrates that the local backbone and side chain flexibility as well as the structures of polyol groups play a significant role in determining the kinetic and thermodynamic stability of chelate complexes, yielding to different boron adsorption capabilities of lignocellulosic polymers.

A new boronate ester-based crosslinking strategy allows the design of nonswelling and long-term stable dynamic covalent hydrogels

Dynamic hydrogels are viscoelastic materials that can be designed to be self-healing, malleable, and injectable, making them particularly interesting for a variety of biomedical applications. To design dynamic hydrogels, dynamic covalent crosslinking reactions are attracting increasing attention. However, dynamic covalent hydrogels tend to swell, and often lack stability. Boronate ester-based hydrogels, which result from the dynamic covalent reaction between a phenylboronic acid (PBA) derivative and a diol, are based on stable precursors, and can therefore address these limitations. Yet, boronate ester formation hardly occurs at physiological pH. To produce dynamic covalent hydrogels at physiological pH, we performed a molecular screening of PBA derivatives in association with a variety of diols, using hyaluronic acid as a polymer of interest. The combination of Wulff-type PBA (wPBA) and glucamine stood out as a unique couple to obtain the desired hydrogels. We showed that optimized wPBA/glucamine hydrogels are minimally- to non-swelling, stable long term (over months), tunable in terms of mechanical properties, and cytocompatible. We further characterized their viscoelastic and self-healing properties, highlighting their potential for biomedical applications.

Structural optimization of BODIPY photosensitizers for enhanced photodynamic antibacterial activities

Enhancing the interactions between photosensitizers and bacteria is key to developing effective photodynamic antibacterial agents. However, the influence of different structures on the therapeutic effects has not been systematically investigated. Herein, 4 BODIPYs with distinct functional groups, including the phenylboronic acid (PBA) group and pyridine (Py) cations, were designed to explore their photodynamic antibacterial activities. The BODIPY with the PBA group (IBDPPe-PBA) exhibits potent activity against planktonic Staphylococcus aureus (S. aureus) upon illumination, while the BODIPY with Py cations (IBDPPy-Ph) or both the PBA group and Py cations (IBDPPy-PBA) can significantly minimize the growth of both S. aureus and Escherichia coli (E. coli). In particular, IBDPPy-Ph can not only eliminate the mature S. aureus biofilm and E. coli biofilm in vitro, but also promote the healing of the infected wound. Our work provides an alternative for reasonable design of photodynamic antibacterial materials.

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.

Mannitol as an Excipient for Lyophilized Injectable Formulations

The review summarizes the current state of knowledge of mannitol as an excipient in lyophilized injectable small and large molecule formulations. When compared with glycine, the physicochemical properties of mannitol make it a desirable and preferred bulking agent. Though mannitol is a popular bulking agent in freeze-dried formulations, its use may pose certain challenges such as vial breakage or its existence as a metastable crystalline hemihydrate in the final cake, necessitating appropriate mitigation strategies. The understanding of the phase behavior of mannitol in aqueous systems, during the various stages of freeze-drying, can be critical for the optimization of freeze-drying cycle parameters in multi-component formulations. Finally, using a decision tree as a guiding tool, we demonstrate the use of orthogonal techniques for attaining a stable and cost-effective lyophilized drug product containing mannitol.

Molecular Level Sucrose Quantification: A Critical Review

Sucrose is a primary metabolite in plants, a source of energy, a source of carbon atoms for growth and development, and a regulator of biochemical processes. Most of the traditional analytical chemistry methods for sucrose quantification in plants require sample treatment (with consequent tissue destruction) and complex facilities, that do not allow real-time sucrose quantification at ultra-low concentrations (nM to pM range) under in vivo conditions, limiting our understanding of sucrose roles in plant physiology across different plant tissues and cellular compartments. Some of the above-mentioned problems may be circumvented with the use of bio-compatible ligands for molecular recognition of sucrose. Nevertheless, problems such as the signal-noise ratio, stability, and selectivity are some of the main challenges limiting the use of molecular recognition methods for the in vivo quantification of sucrose. In this review, we provide a critical analysis of the existing analytical chemistry tools, biosensors, and synthetic ligands, for sucrose quantification and discuss the most promising paths to improve upon its limits of detection. Our goal is to highlight the criteria design need for real-time, in vivo, highly sensitive and selective sucrose sensing capabilities to enable further our understanding of living organisms, the development of new plant breeding strategies for increased crop productivity and sustainability, and ultimately to contribute to the overarching need for food security.

Reactive metal boride nanoparticles trap lipopolysaccharide and peptidoglycan for bacteria-infected wound healing

Bacteria and excessive inflammation are two main factors causing non-healing wounds. However, current studies have mainly focused on the inhibition of bacteria survival for wound healing while ignoring the excessive inflammation induced by dead bacteria-released lipopolysaccharide (LPS) or peptidoglycan (PGN). Herein, a boron-trapping strategy has been proposed to prevent both infection and excessive inflammation by synthesizing a class of reactive metal boride nanoparticles (MB NPs). Our results show that the MB NPs are gradually hydrolyzed to generate boron dihydroxy groups and metal cations while generating a local alkaline microenvironment. This microenvironment greatly enhances boron dihydroxy groups to trap LPS or PGN through an esterification reaction, which not only enhances metal cation-induced bacterial death but also inhibits dead bacteria-induced excessive inflammation both in vitro and in vivo, finally accelerating wound healing. Taken together, this boron-trapping strategy provides an approach to the treatment of bacterial infection and the accompanying inflammation.

MRI Contrast Agents in Glycobiology

Molecular recognition involving glycoprotein-mediated interactions is ubiquitous in both normal and pathological natural processes. Therefore, visualization of these interactions and the extent of expression of the sugars is a challenge in medical diagnosis, monitoring of therapy, and drug design. Here, we review the literature on the development and validation of probes for magnetic resonance imaging using carbohydrates either as targeting vectors or as a target. Lectins are important targeting vectors for carbohydrate end groups, whereas selectins, the asialoglycoprotein receptor, sialic acid end groups, hyaluronic acid, and glycated serum and hemoglobin are interesting carbohydrate targets.

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.

Boronic Acid: A Novel Pharmacophore Targeting Src Homology 2 (SH2) Domain of STAT3

SH2 domains have been recognized as promising targets for various human diseases. However, targeting SH2 domains with phosphopeptides or small-molecule inhibitors derived from bioisosteres of the phosphate group is still challenging. Identifying novel bioisosteres of the phosphate group to achieve favorable in vivo potency is urgently needed. Here, we report the feasibility of targeting the STAT3-SH2 domain with a boronic acid group and the identification of a highly potent inhibitor compound 7 by replacing the carboxylic acid of compound 4 with a boronic acid. Compound 7 shows higher binding affinity, better cellular potency, more favorable PK profiles, and higher in vivo antitumor activity than 4. The stronger anticancer effect of 7 partially stems from its covalent binding mode with the SH2 domain, verified by the washout experiments. The relatively high level of sequence conservation among SH2 domains makes the results presented here of general significance.

Evaluation of the effect of background electrolyte composition and independence of parameters in determining binding constants of betulin derivatives to β- and dimethyl-β-cyclodextrins by affinity capillary electrophoresis

The values of the apparent binding constants for β-cyclodextrin complexes of betulin derivatives determined by mobility shift affinity capillary electrophoresis were found to be independent of the composition of the two background electrolytes used (tetraborate buffer, pH 9.18, and phosphate buffer, pH 8.00, both of them with 20 mM ionic strength). It has been found that, if there is not a constant plateau on the binding curve, then four independent parameters can be determined: binding constants (also referred to as stability, association or formation constants) and ionic mobilities of 1:1 and 1:2 complexes. However, at least 10-12 data points in the binding curve should be used to reliably estimate the parameters. For the first time, the apparent binding constants for complexes of ester betulin derivatives with dimethyl-β-cyclodextrin have been determined by mobility shift affinity capillary electrophoresis. The logarithms of the constants for 1:1 and 1:2 complexes at 25°C for betulin 3,28-diphthalate with a 95 % confidence interval are 4.98 (4.95-5.01) and 7.52 (7.26-7.68); for betulin 3,28-disulfate, the values are 4.97 (4.89-5.03) and 8.24 (6.82 - 8.52). It has been found that betulin 3,28-disuccinate forms only a 1:1 complex and the binding constant logarithm is 5.25 ± 0.02. This article is protected by copyright. All rights reserved.

Nanopore Identification of Alditol Epimers and Their Application in Rapid Analysis of Alditol-Containing Drinks and Healthcare Products

Alditols, which have a sweet taste but produce much lower calories than natural sugars, are widely used as artificial sweeteners. Alditols are the reduced forms of monosaccharide aldoses, and different alditols are diastereomers or epimers of each other and direct and rapid identification by conventional methods is difficult. Nanopores, which are emerging single-molecule sensors with exceptional resolution when engineered appropriately, are useful for the recognition of diastereomers and epimers. In this work, direct distinguishing of alditols corresponding to all 15 monosaccharide aldoses was achieved by a boronic acid-appended hetero-octameric Mycobacterium smegmatis porin A (MspA) nanopore (MspA-PBA). Thirteen alditols including glycerol, erythritol, threitol, adonitol, arabitol, xylitol, mannitol, sorbitol, allitol, dulcitol, iditol, talitol, and gulitol (l-sorbitol) could be fully distinguished, and their sensing features constitute a complete nanopore alditol database. To automate event classification, a custom machine-learning algorithm was developed and delivered a 99.9% validation accuracy. This strategy was also used to identify alditol components in commercially available "zero-sugar" drinks and healthcare products, suggesting their use in rapid and sensitive quality control for the food and medical industry.

One, two, many: Strategies to alter the number of carbohydrate binding sites of lectins

Carbohydrates are more than an energy-storage. They are ubiquitously found on cells and most proteins, where they encode biological information. Lectins bind these carbohydrates and are essential for translating the encoded information into biological functions and processes. Hundreds of lectins are known, and they are found in all domains of life. For half a century, researchers have been preparing variants of lectins in which the binding sites are varied. In this way, the traits of the lectins such as the affinity, avidity and specificity towards their ligands as well as their biological efficacy were changed. These efforts helped to unravel the biological importance of lectins and resulted in improved variants for biotechnological exploitation and potential medical applications. This review gives an overview on the methods for the preparation of artificial lectins and complexes thereof and how reducing or increasing the number of binding sites affects their function.

Polymeric nanoparticles surface-complexed with boric acid actively target solid tumors overexpressing sialic acid

Sialic acid is a fundamental component of the tumor microenvironment, modulates cell-cell and cell-extracellular matrix interactions and is associated with bad prognosis and clinical outcomes in different cancers. Capitalizing on the ability of boric acid to form cyclic esters with diols, in this work, we design self-assembled multi-micellar colloidal systems of an amphiphilic poly(vinyl alcohol)-g-poly(methyl methacrylate) copolymer surface-modified with boric acid for the active targeting of solid tumors that overexpress sialic acid. Nanoparticles display sizes in the 100-200 nm range and a spherical morphology, as determined by dynamic light scattering and high resolution-scanning electron microscopy, respectively. The uptake and anti-proliferative activity are assessed in 2D and 3D models of rhabdomyosarcoma in vitro. Surface boration increases the nanoparticle permeability and uptake, especially in rhabdomyosarcoma spheroids that overexpress sialic acid to a greater extent than 2D cultures. The biodistribution of non-borated and borated nanoparticles upon intravenous injection to a subcutaneous rhabdomyosarcoma murine xenograft model confirm a statistically significant increase in the intertumoral accumulation of the modified nanocarriers with respect to the unmodified counterparts and a sharp decrease in major clearance organs such as the liver. Overall, our results highlight the promise of these borated nanomaterials to actively target hypersialylated solid tumors.

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.

Multimodal Applications of Zinc Gallate-Based Persistent Luminescent Nanoparticles in Cancer Treatment: Tumor Margining, Diagnosis, and Boron Neutron Capture Therapy

On the basis of the boron neutron capture therapy (BNCT) modality, we have designed and synthesized a zinc gallate (ZnGa₂O₄)-based nanoformulation for developing an innovative theranostic approach for cancer treatment. Initially, the (ZnGa_1.995Cr_0.005O₄ or ZnGa₂O₄:(0.5%)Cr persistent luminescence nanoparticles (PLNPs) embedded on silica matrix were synthesized. Their surface functionalization was performed using organic synthesis strategies to attach the amine functional moieties which were further coupled with poly(vicinal diol). These diols were helpful for conjugation with ¹⁰B(OH)₃, which subsequently served to couple with an in-house-synthesized variant of pH-(low)-insertion peptide (pHLIP) finally giving a tumor-targeting nanoformulation. Most importantly, the polymeric diols helped in conjugation of a substantial number of ¹⁰B to provide the therapeutic dose required for effective BNCT. This nanoformulation internalized substantially (∼80%) to WEHI-164 cancer cells within 6 h. Tumor homing studies indicated that the accumulation of this formulation at the acidic tumor site was within 2 h. The in vitro evaluation of the formulation against WEHI-164 cancer cells followed by neutron irradiation revealed its potent cytotoxicity with IC₅₀ ∼ 25 μM. In the case of studies on animal models, the melanoma-induced C57BL/6 and fibrosarcoma-induced BALB/c mice were treated with formulations through intratumoral and intravenous injections, respectively, followed by neutron irradiation, leading to a significant killing of the cancer cells, which was evidenced by a reduction in tumor volume (75-80%) as compared with a control tumor. Furthermore, the histopathological studies confirmed a damaging effect only on tumor cells, while there was no sign of damage to the vital organs in treated mice as well as in controls.

A Nanopore-Based Saccharide Sensor

Saccharides play critical roles in many forms of cellular activities. Saccharide structures are however complicated and similar, setting a technical hurdle for direct identification. Nanopores, which are emerging single molecule tools sensitive to minor structural differences between analytes, can be engineered to identity saccharides. A hetero-octameric Mycobacterium smegmatis porin A nanopore containing a phenylboronic acid was prepared, and was able to clearly identify nine monosaccharide types, including D-fructose, D-galactose, D-mannose, D-glucose, L-sorbose, D-ribose, D-xylose, L-rhamnose and N-acetyl-D-galactosamine. Minor structural differences between saccharide epimers can also be distinguished. To assist automatic event classification, a machine learning algorithm was developed, with which a general accuracy score of 0.96 was achieved. This sensing strategy is generally suitable for other saccharide types and may bring new insights to nanopore saccharide sequencing.

Anion Recognition by Benzoxaborole

The binding types (H-bonding or coordinate) and stability constants for complexes of 11 mono- and di-anions with benzoxaborole (1) were determined by ¹H and ¹¹B NMR titrations in DMSO or MeCN. Compared to phenylboronic acid (PBA), 1 is a stronger Lewis acid and a poorer H-bond donor with only one B-OH group, which is expected therefore to recognize anions mostly through the coordinate bonding. This is the case however only with F^-, HPO₄^2-, and PhPO₃^2- anions, which are coordinately bonded to 1, and partially with SO₄^2-, which forms only the H-bonded complex with PBA, but both H-bonded and coordinate complexes with 1. The majority of tested anions (AcO^-, PhPO₃H^-, (PhO)₂PO₂^-, Cl^-, and Br^-) form H-bonded complexes with both 1 and PBA, whereas H₂PO₄^- changes the binding mode from coordinate for PBA to H-bonded for 1. The preferable binding type for each anion is confirmed by calculations of DFT-optimized structures of the anion complexes of 1. The preferable binding type can be rationalized considering the effects of the steric hindrance, more significant for the coordinate bonding, and of increased anion basicity, which is favorable for both binding types, but enhances the strength of coordinate bonding more significantly than the strength of H-bonding.

Differential Response of Candida Species Morphologies and Isolates to Fluconazole and Boric Acid

Candida albicans is the most prevalent cause of vulvovaginal candidiasis ("yeast infection" or VVC) and recurrent vulvovaginal candidiasis (RVVC), although the incidence of non-albicans yeast species is increasing. The azole fluconazole is the primary antifungal drug used to treat RVVC, yet isolates from some species have intrinsic resistance to fluconazole, and recurrent infection can occur even with fluconazole-susceptible populations. The second-line broad-spectrum antimicrobial drug, boric acid, is an alternative treatment that has been found to successfully treat complicated VVC infections. Far less is known about how boric acid inhibits growth of yeast isolates in different morphologies compared to fluconazole. We found significant differences in drug resistance and drug tolerance (the ability of a subpopulation to grow slowly in high levels of drug) between C. albicans, Candida glabrata, and Candida parapsilosis isolates, with the specific relationships dependent on both drug and phenotype. Population-level variation for both susceptibility and tolerance was broader for fluconazole than boric acid in all species. Unlike fluconazole, which neither prevented hyphal formation nor disrupted mature biofilms, boric acid inhibited C. albicans hyphal formation and reduced mature biofilm biomass and metabolic activity in all isolates in a dose-dependent manner. Variation in planktonic response did not generally predict biofilm phenotypes for either drug. Overall, our findings illustrate that boric acid is broadly effective at inhibiting growth across many isolates and morphologies, which could explain why it is an effective treatment for RVVC.

Ratiometric fluorescence sensing of d-allulose using an inclusion complex of γ-cyclodextrin with a benzoxaborole-based probe

Because d-allulose has been attracting attention as a zero-calorie sugar, the selective sensing of d-allulose is desired to investigate its health benefits. We report herein a novel fluorescence chemosensor that is based on an inclusion complex of γ-cyclodextrin (γ-CyD) with a benzoxaborole-based probe. Two inclusion complexes, 1/γCyD and 2/γCyD, were prepared by mixing γ-CyD with their corresponding probes in a water-rich solvent, where γ-CyD encapsulates two molecules of the probes inside its cavity to form a pyrene dimer. Both 1/γCyD and 2/γCyD exhibit monomeric and dimeric fluorescence from the pyrene moieties. By the reaction of 1/γCyD with saccharides, the intensities of monomeric and dimeric fluorescence remained unchanged and decreased, respectively. We have demonstrated that 1/γCyD has much higher affinity for d-allulose than for the other saccharides (d-fructose, d-glucose, and d-galactose). The conditional equilibrium constants for the reaction systems were determined to be 498 ± 35 M^-1 for d-fructose, 48.4 ± 25.3 M^-1 for d-glucose, 15.0 ± 3.3 M^-1 for d-galactose, and (8.05 ± 0.59) × 10³ M^-1 for d-allulose. These features of 1/γCyD enable ratiometric fluorescence sensing with high sensitivity and selectivity for d-allulose. The limits of detection and quantification of 1/γCyD for d-allulose at pH 8.0 were determined to be 6.9 and 21 μM, respectively. Induced circular dichroism spectral study has shown that the reaction of 1/γCyD with d-allulose causes the monomerisation of the dimer of probe 1 that is encapsulated by γ-CyD, which leads to the diminishment of the dimeric fluorescence.

New Horizons: Next-Generation Insulin Analogues: Structural Principles and Clinical Goals

Design of "first-generation" insulin analogues over the past 3 decades has provided pharmaceutical formulations with tailored pharmacokinetic (PK) and pharmacodynamic (PD) properties. Application of a molecular tool kit-integrating protein sequence, chemical modification, and formulation-has thus led to improved prandial and basal formulations for the treatment of diabetes mellitus. Although PK/PD changes were modest in relation to prior formulations of human and animal insulins, significant clinical advantages in efficacy (mean glycemia) and safety (rates of hypoglycemia) were obtained. Continuing innovation is providing further improvements to achieve ultrarapid and ultrabasal analogue formulations in an effort to reduce glycemic variability and optimize time in range. Beyond such PK/PD metrics, next-generation insulin analogues seek to exploit therapeutic mechanisms: glucose-responsive ("smart") analogues, pathway-specific ("biased") analogues, and organ-targeted analogues. Smart insulin analogues and delivery systems promise to mitigate hypoglycemic risk, a critical barrier to glycemic control, whereas biased and organ-targeted insulin analogues may better recapitulate physiologic hormonal regulation. In each therapeutic class considerations of cost and stability will affect use and global distribution. This review highlights structural principles underlying next-generation design efforts, their respective biological rationale, and potential clinical applications.

Internal and External Catalysis in Boronic Ester Networks

In dynamic materials, the reversible condensation between boronic acids and diols provides adaptability, self-healing ability, and responsiveness to small molecules and pH. The thermodynamics and kinetics of bond exchange determine the mechanical properties of dynamic polymer networks. Here, we investigate the effects of diol structure and salt additives on the rate of boronic acid-diol bond exchange, binding affinity, and the mechanical properties of the corresponding polymer networks. We find that proximal amides used to conjugate diols to polymers and buffering anions induce significant rate acceleration, consistent with an internal and external catalysis, respectively. This rate acceleration is reflected in the stress relaxation of the gels. These findings contribute to the fundamental understanding of the boronic ester dynamic bond and offer molecular strategies to tune the macromolecular properties of dynamic materials.

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.

Functional Phenylboronate Polymers for the Recovery of Diols, Sugar Alcohols, and Saccharides from Aqueous Solution

The ongoing transition from fossil to renewable feedstocks demands new efficient processes for an economically viable production of biomass-derived commodities and fine chemicals. Novel energy- and material-efficient product purification and separation will play a crucial role due to altered product and feed composition. The present study comprises the synthesis and tests of cross-linked p-vinylphenylboronate polymers for the separation of 18 diols, sugar alcohols, and saccharides, which can be obtained during biomass processing. The separation was based on molecular recognition, that is, esterification of the phenylboronate with vicinal diols. A correlation of the molecular complexation constant, the polymer swelling, and the maximum adsorption capacity was found. The adsorption curves over time were recorded. Preliminary results on competitive adsorption of binary mixtures showed a high potential for the separation of substrates with significantly different complexation constants. Desorption tests implied easier desorption of substrates that only adsorb on the outer polymer shell.

Structural principles of insulin formulation and analog design: A century of innovation

BACKGROUND

The discovery of insulin in 1921 and its near-immediate clinical use initiated a century of innovation. Advances extended across a broad front, from the stabilization of animal insulin formulations to the frontiers of synthetic peptide chemistry, and in turn, from the advent of recombinant DNA manufacturing to structure-based protein analog design. In each case, a creative interplay was observed between pharmaceutical applications and then-emerging principles of protein science; indeed, translational objectives contributed to a growing molecular understanding of protein structure, aggregation and misfolding.

SCOPE OF REVIEW

Pioneering crystallographic analyses-beginning with Hodgkin's solving of the 2-Zn insulin hexamer-elucidated general features of protein self-assembly, including zinc coordination and the allosteric transmission of conformational change. Crystallization of insulin was exploited both as a step in manufacturing and as a means of obtaining protracted action. Forty years ago, the confluence of recombinant human insulin with techniques for site-directed mutagenesis initiated the present era of insulin analogs. Variant or modified insulins were developed that exhibit improved prandial or basal pharmacokinetic (PK) properties. Encouraged by clinical trials demonstrating the long-term importance of glycemic control, regimens based on such analogs sought to resemble daily patterns of endogenous β-cell secretion more closely, ideally with reduced risk of hypoglycemia.

MAJOR CONCLUSIONS

Next-generation insulin analog design seeks to explore new frontiers, including glucose-responsive insulins, organ-selective analogs and biased agonists tailored to address yet-unmet clinical needs. In the coming decade, we envision ever more powerful scientific synergies at the interface of structural biology, molecular physiology and therapeutics.

Boronic Acid Ligands Can Target Multiple Subpopulations of Pancreatic Cancer Stem Cells via pH-Dependent Glycan-Terminal Sialic Acid Recognition

Eradication of cancer stem cells (CSCs) is an ultimate goal in cancer chemotherapy. Although a ligand-assisted targeting approach seems rational, the existence of subpopulations of CSCs and their discrimination from those present on healthy sites makes it a severe challenge. Some boronic acid (BA) derivatives are known for the ability to bind with glycan-terminal sialic acid (SA), in a manner dependent on the acidification found in hypoxic tumoral microenvironment. Taking advantage of this feature, here we show that the BA-ligand fluorescence conjugate can effectively target multiple CSC subpopulations in parallel, which otherwise must be independently aimed when using antibody--ligands.

Protodeboronation of (Hetero)Arylboronic Esters: Direct versus Prehydrolytic Pathways and Self-/Auto-Catalysis

The kinetics and mechanism of the base-catalyzed hydrolysis (ArB(OR)₂ → ArB(OH)₂) and protodeboronation (ArB(OR)₂ → ArH) of a series of boronic esters, encompassing eight different polyols and 10 polyfluoroaryl and heteroaryl moieties, have been investigated by in situ and stopped-flow NMR spectroscopy (¹⁹F, ¹H, and ¹¹B), pH-rate dependence, isotope entrainment, ²H KIEs, and KS-DFT computations. The study reveals the phenomenological stability of boronic esters under basic aqueous-organic conditions to be highly nuanced. In contrast to common assumption, esterification does not necessarily impart greater stability compared to the corresponding boronic acid. Moreover, hydrolysis of the ester to the boronic acid can be a dominant component of the overall protodeboronation process, augmented by self-, auto-, and oxidative (phenolic) catalysis when the pH is close to the pK_a of the boronic acid/ester.

A molecularly imprinted nanoreactor with spatially confined effect fabricated with nano-caged cascaded enzymatic system for specific detection of monosaccharides

Glucose oxidase (GOx), traditionally regarded as an oxidoreductase with high β-D-glucose specificity, has been widely applied as sensing probe for β-D-glucose detection. However, it is found that the specificity of GOx is not absolute and GOx cannot decern β-D-glucose among its isomers such as xylose, mannose and galactose. The existence of the other monosaccharides in sensing system could compromise the sensitivity for β-D-glucose, therefore, it is of great urgency to achieve the highly specific catalytic performance of GOx. Herein, porous metal-organic frameworks (MOF) are prepared as the host matrix for immobilization of both GOx and bovine hemoglobin (BHb), obtained a cascaded catalytic system (MOF@GOx@BHb) with both enhanced GOx activity and peroxidase-like activity owing to the spatially confined effect. Then, using β-D-glucose as both template molecules and substances, hydroxyl radicals are produced continuously and applied for initiating the polymerization of molecular imprinting polymers (MIPs) on the surface of MOF@GOx@BHb. Impressively, the obtaining molecularly imprinted GOx (noted as MOF@GOx@BHb-MIPs) achieves the highly sensitive and specific detection of β-D-glucose in the concentration range of 0.5-20 μM with the LOD = 0.4 μM (S/N = 3) by colorimetry. Similarly, MOF@GOx@BHb-MIPs are subsequently obtained using mannose, xylose and galactose as template molecules, respectively, and also show satisfied specific catalytic activity towards corresponding templates, indicating the effectiveness of the proposed strategy to achieve highly specific catalytic performance of GOx.