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

N-Terminal Modification of Gly-His-Tagged Proteins with Azidogluconolactone

Site-specific protein modifications are vital for biopharmaceutical drug development. Gluconoylation is a non-enzymatic, post-translational modification of N-terminal HisTags. We report high-yield, site-selective in vitro α-aminoacylation of peptides, glycoproteins, antibodies, and virus-like particles (VLPs) with azidogluconolactone at pH 7.5 in 1 h. Conjugates slowly hydrolyse, but diol-masking with borate esters inhibits reversibility. In an example, we multimerise azidogluconoylated SARS-CoV-2 receptor-binding domain (RBD) onto VLPs via click-chemistry, to give a COVID-19 vaccine. Compared to yeast antigen, HEK-derived RBD was immunologically superior, likely due to observed differences in glycosylation. We show the benefits of ordered over randomly oriented multimeric antigen display, by demonstrating single-shot seroconversion and best virus-neutralizing antibodies. Azidogluconoylation is simple, fast and robust chemistry, and should accelerate research and development.

Insertion of a synthetic switch into insulin provides metabolite-dependent regulation of hormone-receptor activation

Insulin-signaling requires conformational change: whereas the free hormone and its receptor each adopt autoinhibited conformations, their binding leads to structural reorganization. To test the functional coupling between insulin's "hinge opening" and receptor activation, we inserted an artificial ligand-dependent switch into the insulin molecule. Ligand-binding disrupts an internal tether designed to stabilize the hormone's native closed and inactive conformation, thereby enabling productive receptor engagement. This scheme exploited a diol sensor (meta-fluoro-phenylboronic acid at GlyA1) and internal diol (3,4-dihydroxybenzoate at LysB28). The sensor recognizes monosaccharides (fructose > glucose). Studies of insulin-signaling in human hepatoma-derived cells (HepG2) demonstrated fructose-dependent receptor autophosphorylation leading to appropriate downstream signaling events, including a specific kinase cascade and metabolic gene regulation (gluconeogenesis and lipogenesis). Addition of glucose (an isomeric ligand with negligible sensor affinity) did not activate the hormone. Similarly, metabolite-regulated signaling was not observed in control studies of 1) an unmodified insulin analog or 2) an analog containing a diol sensor without internal tethering. Although secondary structure (as probed by circular dichroism) was unaffected by ligand-binding, heteronuclear NMR studies revealed subtle local and nonlocal monosaccharide-dependent changes in structure. Insertion of a synthetic switch into insulin has thus demonstrated coupling between hinge-opening and allosteric holoreceptor signaling. In addition to this foundational finding, our results provide proof of principle for design of a mechanism-based metabolite-responsive insulin. In particular, replacement of the present fructose sensor by an analogous glucose sensor may enable translational development of a "smart" insulin analog to mitigate hypoglycemic risk in diabetes therapy.

Boronic acid complexes with amino phenolic N,O-ligands and their use for non-covalent protein fluorescence labeling

Phenylboronic acid (PBA) forms neutral tetrahedral N,O-coordinated 6-membered cyclic complexes with stability constants reaching the values as large as 1.3 × 10⁴ M^-1 at pH 7.4 in water with amino phenolic compounds including 2-(2'-hydroxyphenyl)-1H-benzimidazole (HPBI) often used for protein probing and labeling. The crystal structures of isolated complexes demonstrate unusually high for boronate adducts degree of the tetrahedral character of the boron atom with short B-N bonds in agreement with their high solution stability. The complexation of PBA with HPBI, causes a strong enhancement of the fluorescence of the "enol" form of the ligand, increases the affinity of the dye to a protein (bovine serum albumin) and makes more pronounced the shift in emission maximum induced by the protein binding. Similar, but larger effects are observed with an amino HPBI derivative and with a stronger boronic acid benzoxaborole. Thus, the binding constant to the protein about 2 × 10⁴ M^-1 for free HPBI increases to 1.2 × 10⁶ M^-1 for the complex of 5-amino-HPBI with benzoxaborole making it suitable for an efficient non-covalent protein labeling or bioconjugation.

'Smart' insulin-delivery technologies and intrinsic glucose-responsive insulin analogues

Insulin replacement therapy for diabetes mellitus seeks to minimise excursions in blood glucose concentration above or below the therapeutic range (hyper- or hypoglycaemia). To mitigate acute and chronic risks of such excursions, glucose-responsive insulin-delivery technologies have long been sought for clinical application in type 1 and long-standing type 2 diabetes mellitus. Such 'smart' systems or insulin analogues seek to provide hormonal activity proportional to blood glucose levels without external monitoring. This review highlights three broad strategies to co-optimise mean glycaemic control and time in range: (1) coupling of continuous glucose monitoring (CGM) to delivery devices (algorithm-based 'closed-loop' systems); (2) glucose-responsive polymer encapsulation of insulin; and (3) mechanism-based hormone modifications. Innovations span control algorithms for CGM-based insulin-delivery systems, glucose-responsive polymer matrices, bio-inspired design based on insulin's conformational switch mechanism upon insulin receptor engagement, and glucose-responsive modifications of new insulin analogues. In each case, innovations in insulin chemistry and formulation may enhance clinical outcomes. Prospects are discussed for intrinsic glucose-responsive insulin analogues containing a reversible switch (regulating bioavailability or conformation) that can be activated by glucose at high concentrations.

Potentiometric Determination of Circulating Glycoproteins by Boronic Acid End-Functionalized Poly(ethylene glycol)-Modified Electrode

Despite tremendous complexity in glycan structure, sialic acid (SA) provides an analytically accessible index for glycosylation, owing to its uniquely anionic nature and glycan-chain terminal occupation. Taking advantage of boronic acid (BA) based SA-recognition chemistry, we here demonstrate a label-free, no enzymatic, potentiometric determination of fetuin, a blood-circulating glycoprotein implicated in physiological and various pathological states. A phenylboronic acid (PBA) ω-end-functionalized poly(ethylene glycol) (PEG) with an α-tethering unit bearing pendent alkyne groups was "grafted-to" a gold electrode modified with 11-azide-undecathiol by a copper-catalyzed azide-alkyne cycloaddition reaction. Using the electrode, fetuin was potentiometrically detectable with a μM-order-sensitivity that is comparable to what is found in blood-collected specimen. Our finding may have implications for developing a remarkably economic hemodiagnostic technology with ease of downsizing and mass production.

Anion recognition by anthracene appended ortho-aminomethylphenylboronic acid: a new PET-based sensing mechanism

Carboxylate, phosphate and sulphate anions form hydrogen bonded complexes with the B(OH)2 group of the receptor 1 producing a turn-off fluorescence response, while the malonate monoanion induces the opposite turn-on effect.

Chemosensing of neurotransmitters with selectivity and naked eye detection of l-DOPA based on fluorescent Zn(ii)-terpyridine bearing boronic acid complexes

A new range of fluorescent Zn(ii)-terpyridine complexes are described and studied in-depth as chemosensors for catecholamine-based neurotransmitters in pure water.

Conversion of lignocellulose into biochar and furfural through boron complexation and esterification reactions

The aim of this work was to study the conversion of lignocellulose into biochar and furfural through boron complexation and esterification reaction. Boric acid was used to modify lignocellulose to obtain a high biochar yield boron-lignocellulosic material through complexation and esterification reactions. Furthermore, clean furfural was obtained as the gas products of boron-lignocellulosic materials pyrolysis. The structures of the boron-lignocellulosic materials were characterized, and their compound principle was revealed. Boric acid treatments increased the initial thermal degradation temperature of lignocellulose and promoted the formation of biochar and furfural. The biochar yield rate increased by 135.7% from 18.6 to 42.9% at 600 ℃ after 5% boric acid solution treatment. Compared with pure lignocellulose, cleaner and higher quantities of furfural were obtained from boron-lignocellulose pyrolysis. Finally, the possible chemical decomposition pathways of boron-lignocellulosic materials were identified. This study provides a new perspective on the thermochemical conversion of lignocellulose to furfural and biochar.

Linking Molecular Behavior to Macroscopic Properties in Ideal Dynamic Covalent Networks

Dynamic covalent networks (DCvNs) are increasingly used in advanced materials design with applications ranging from recyclable thermosets to self-healing hydrogels. However, the relationship between the underlying chemistry at the junctions of DCvNs and their macroscopic properties is still not fully understood. In this work, we constructed a robust framework to predict how complex network behavior in DCvNs emerges from the chemical landscape of the dynamic chemistry at the junction. Ideal dynamic covalent boronic ester-based hydrogels were used as model DCvNs. We developed physical models that describe how viscoelastic properties, as measured by shear rheometry, are linked to the molecular behavior of the dynamic junction, quantified via fluorescence and NMR spectroscopy and DFT calculations. Additionally, shear rheometry was combined with Transition State Theory to quantify the kinetics and thermodynamics of network rearrangements, enabling a mechanistic understanding including preferred reaction pathways for dynamic covalent chemistries. We applied this approach to corroborate the "loose-bolt" postulate for the reaction mechanism in Wulff-type boronic acids. These findings, grounded in molecular principles, advance our understanding and rational design of dynamic polymer networks, improving our ability to predict, design, and leverage their unique properties for future applications.

Electrochemical Immunosensing Platform for the Determination of the 20S Proteasome Using an Aminophenylboronic/Poly-indole-6-carboxylic Acid-Modified Electrode

The first electrochemical immunosensor for the determination of the 20S proteasome (P20S) was developed, entailing the immobilization of an antibody on an aminophenylboronic/poly-indole-6-carboxylic acid-modified electrode. The proposed electrochemical bioplatform is a simple and feasible analytical tool applicable for the determination of P20S in human plasma, considering its high clinical and biological relevance. Cyclic voltammetry, electrochemical impedance spectroscopy, and square wave voltammetry (SWV) were used to determine the optimal step-by-step process to obtain the electrochemical immunosensor. The interaction of P20S with the recognition layer of the immobilized antibody on the nanostructured surface took place by incubating the electrode in a P20S solution at 20 °C for 2 h. Using SWV as an electro-analytical technique, this immunosensor can quantify P20S. The current was linear with the P20S concentration within two dynamic concentration ranges from 20.0 to 80.0 and 80.0 to 200.0 ng·mL^-1 (r² = 0.992 and 0.98, respectively) with a limit of detection and quantification of 6 and 18 ng·mL^-1, respectively. Moreover, the immunosensor showed considerable repeatability and reproducibility, when the determination was done in human serum, which confirms that it is a promising alternative for direct detection of P20S in biological fluids with minimal interference.

Direct Observation of Cell Surface Sialylation by Atomic Force Microscopy Employing Boronic Acid-Sialic Acid Reversible Interaction

Tracing cell surface sialylation dynamics at a scale of the glycolipoprotein microdomain (lipid rafts) formations remains an intriguing challenge of cellular biology. Here, we demonstrate that this goal is accessible, taking advantage of a boronic acid (BA)-based reversible molecular recognition chemistry. A BA-end-functionalized poly(ethylene glycol) was decorated onto an atomic force microscopy (AFM) cantilever, which provided a dynamic and sialic acid (SA)-specific imaging mode. Using this technique, we were able to heat map the SA expression levels not only on protein-decorated substrates but also directly on the cell surfaces, with a submicrometer scale resolution that may be relevant to that of the lipid rafts formation. The SA specificity and the binding reversibility of the probe were confirmed from its pH-dependent characteristics and an inhibition assay using free state SA. This finding may provide a noninvasive means for assessing a variety of SA-involved glycosylation dynamics spanning from physiology to pathology.

Monosaccharides Dehydration Assisted by Formation of Borate Esters of α-Hydroxyacids in Choline Chloride-Based Low Melting Mixtures

The synthesis of 5-hydroxymethylfurfural (5-HMF) and 2-furfural (2-F) by hexoses and pentoses dehydration is considered as a promising path to produce materials from renewable resources. Low-transition-temperature mixtures (LTTMs) enable selective (>80%) dehydration of ketoses to furanic derivatives at moderate temperature (<100°C). However, aldoses dehydration generally requires higher temperatures and an isomerization catalyst. Chromium trichloride has been reported as one of the most efficient catalyst but its kinetic inertness could limit its performances below 100°C. Consequently, we investigate herein boric acid catalysis of aldoses dehydration in LTTMs based on choline halides and organic acids at 90°C. The limited activity of boric acid regarding furanic compounds synthesis (e.g., 5% 5-HMF yield and 23% glucose conversion after 1 h at 90°C with maleic acid) can be enhanced through tetrahydroxyborate esters (THBE) formation with α-hydroxyacids (e.g., 19% 5-HMF yield and 61% glucose conversion after 1 h at 90°C). THBE formation is however associated with H₃O⁺ generation favoring the appearance of side products (humins). We demonstrate that boric acid catalysis is not straightforward and that the use of THBE under moderate acidity should be further investigated to limit humins formation and promote furanic derivatives synthesis.

Mechanistic aspects of saccharide dehydration to furan derivatives for reaction media design

The conversion of abundant hexoses (e.g. glucose, mannose and galactose) and pentoses (e.g. xylose and arabinose) to 5-hydroxymethylfurfural (5-HMF) and 2-furfural (2-F) is subject to intensive research in the hope of achieving competitive production of diverse materials from renewable resources. However, the abundance of literature on this topic as well as the limited number of studies systematically comparing numerous monosaccharides hinder progress tracking. Herein, we compare and rationalize reactivities of different ketoses and aldoses. Dehydration mechanisms of both monosaccharide types are reviewed regarding the existing experimental evidence. Ketose transformation to furan derivatives likely proceeds through cyclic intermediates and is hindered by side-reactions such as isomerization, retro-aldol reactions and polymerization. Different strategies can improve furan derivative synthesis from ketoses: limiting the presence of water, improving the dehydration rate, protecting 5-HMF and 2-F reactive moieties with derivatization or solvent interactions and extracting 5-HMF and 2-F from the reaction medium. In contrast to ketoses, aldose conversion to furan derivatives is not favored compared to polymerization reactions because it involves their isomerization or a ring contraction. Enhancing aldose isomerization is possible with metal catalysts (e.g. CrCl3) promoting a hydride shift mechanism or with boric/boronic acids promoting an enediol mechanism. This catalysis is however far more challenging than ketose dehydration because catalyst activity depends on numerous factors: Brønsted acidity of the medium, catalyst ligands, catalyst affinity for monosaccharides and their accessibility to several chemical species simultaneously. Those aspects are methodically addressed to support the design of new monosaccharide dehydration systems.

Boronic acid and diol-containing polymers: how to choose the correct couple to form "strong" hydrogels at physiological pH

Dynamic covalent hydrogels crosslinked by boronate ester bonds are promising materials for biomedical applications. However, little is known about the impact of the crosslink structure on the mechanical behaviour of the resulting network. Herein, we provide a mechanistic study on boronate ester crosslinking upon mixing hyaluronic acid (HA) backbones modified, on the one hand, with two different arylboronic acids, and on the other hand, with three different saccharide units. Combining rheology, NMR and computational analysis, we demonstrate that carefully selecting the arylboronic-polyol couple allows for tuning the thermodynamics and molecular exchange kinetics of the boronate ester bond, thereby controlling the rheological properties of the gel. In particular, we report the formation of "strong" gels (i.e. featuring slow relaxation dynamics) through the formation of original complex structures (tridentate or bidentate complexes). These findings offer new prospects for the rational design of hydrogel scaffolds with tailored mechanical response.

Examination of pinanediol-boronic acid ester formation in aqueous media: relevance to the relative stability of trigonal and tetrahedral boronate esters

The interaction of pinanediol with 2-fluorophenylboronic acid and several other substituted phenylboronic acids was studied in 40% vol. aqueous acetonitrile by 1H and 11B NMR, potentiometric and spectrophotometric titrations at variable pH values. The experimental results reveal the formation of a very stable trigonal ester (Ktrig ≈ 2 × 104 M-1) and a significantly less stable tetrahedral hydroxocomplex (Ktet ≈ 5 × 103 M-1) in contrast to the traditionally observed inverted order of stabilities Ktrig < Ktet. Comparison of the crystal structure of the trigonal ester isolated from aqueous acetonitrile with the DFT simulated structure of the respective hydroxocomplex shows that an unusual order of stabilities Ktrig > Ktet is observed in spite of the existence of the usual strain release effect in the O-B-O angle considered responsible for the typically observed increased stability of the tetrahedral hydroxocomplex. A complementary study of the stability of the six-membered cyclic boronate esters of chromotropic acid demonstrated the order Ktrig ≪ Ktet although the strain was absent in these esters. The results for m-, p-substituted phenylboronic acids show that the stability of both five- and six-membered trigonal esters formed with pinanediol and chromotropic acid, respectively, is insensitive to electronic effects but the electron accepting substituents stabilize the hydroxocomplexes. It follows from the whole set of results that Ktet can be much larger than Ktrig in the absence of the strain, but with a sufficiently acidic diol, and that the presence of the strain does not necessarily make Ktet larger than Ktrig for a less acidic diol with a purely saturated hydrocarbon backbone. Thus, the electronic effects manifested in the acidity of the diol appear to be more significant than the strain release effect in determining the Ktet/Ktrig ratio.

Doubly Dynamic Hydrogel Formed by Combining Boronate Ester and Acylhydrazone Bonds

The incorporation of double dynamic bonds into hydrogels provides an effective strategy to engineer their performance on demand. Herein, novel hydrogels were PREPARED by combining two kinetically distinct dynamic covalent bonds, boronate ester and acylhydrazone bonds, and the synergistic properties of the hydrogels were studied comprehensively. The functional diblock copolymers P(N-isopropyl acrylamide-co-N-acryloyl-3-aminophenylboronic acid)-b-(N-isopropyl acrylamide-co-diacetone acrylamide) (PAD) were prepared via reversible addition-fragmentation chain transfer (RAFT) polymerization. The hydrogel was constructed by exploiting dynamic reaction of phenyboronic acid moieties with polyvinyl alcohol (PVA) and ketone moieties with adipic dihydrazide (ADH) without any catalyst. The active boronate ester linkage endows the hydrogel with fast gelation kinetics and self-healing ability, and the stable acylhydrazone linkage can enhance the mechanical property of the hydrogel. The difference in kinetics endows that the contribution of each linkage to mechanical strength of the hydrogel can be accurately estimated. Moreover, the mechanical property of the hydrogel can be readily engineered by changing the composition and solid content, as well as by controlling the formation or dissociation of the dynamic linkages. Thus, we provide a promising strategy to design and prepare multi-responsive hydrogels with tunable properties.

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.

Self-crosslinking smart hydrogels through direct complexation between benzoxaborole derivatives and diols from hyaluronic acid

By tailoring the structure of benzoxaborole (BOR), self-crosslinking hydrogels based on hyaluronic acid (HA) modified with BOR derivatives are obtained for the first time through the direct BOR-HA diol complexation at physiological pH.

Adaptable boronate ester hydrogels with tunable viscoelastic spectra to probe timescale dependent mechanotransduction

Cells are capable of sensing the differences in elastic and viscous properties (i.e., the 'viscoelasticity') of their tissue microenvironment and responding accordingly by changing their transcriptional activity and modifying their behaviors. When designing viscoelastic materials to mimic the mechanical properties of native tissue niches, it is important to consider the timescales over which cells probe their microenvironment, as the response of a viscoelastic material to an imposed stress or strain is timescale dependent. Although the timescale of cellular mechano-sensing is currently unknown, hydrogel substrates with tunable viscoelastic spectra can allow one to probe the cellular response to timescale dependent mechanical properties. Here, we report on a cytocompatible and viscoelastic hydrogel culture system with reversible boronate ester cross-links, formed from pendant boronic acid and vicinal diol moieties, where the equilibrium kinetics of esterification were leveraged to tune the viscoelastic spectrum. We found that viscoelasticity increased as a function of the boronic acid and vicinal diol concentration, and also increased with decreasing cross-linker concentration, where the maximal loss tangent achieved with this system was 0.55 at 0.1 rad s-1. Additionally, we found that the cis-vicinal diols configuration altered the viscoelastic spectra, where a tan δ peak occurred at ~1 rad s-1 for hydrogels functionalized with boronic acid, while an additional peak formed at ≥10 rad s-1 for hydrogels functionalized with both boronic acid and cis-vic-diols. In experiments with NIH-3T3 fibroblasts cultured on these hydrogels, the projected cell area and nuclear area, focal adhesion tension, and subcellular localization of YAP/TAZ were all found to be lower for cells cultured on the viscoelastic hydrogels compared to elastic hydrogels with a similar storage modulus. Despite these differences, there was not a statistically significant relationship between the frequency dependent viscoelastic material properties characterized in this study and cellular morphologies, focal adhesion tension, or the subcellular localization of YAP. While these results demonstrate that mechanotransduction pathways are affected by viscoelasticity, they also suggest that these mechanotransduction pathways are not particularly sensitive to the frequency dependent viscoelastic material properties from 0.1 to 10 rad s-1.

Improving cellular uptake of therapeutic entities through interaction with components of cell membrane

Efficient cellular delivery of biologically active molecules is one of the key factors that affect the discovery and development of novel drugs. The plasma membrane is the first barrier that prevents direct translocation of chemic entities, and thus obstructs their efficient intracellular delivery. Generally, hydrophilic small molecule drugs are poor permeability that reduce bioavailability and thus limit the clinic application. The cellular uptake of macromolecules and drug carriers is very inefficient without external assistance. Therefore, it is desirable to develop potent delivery systems for achieving effective intracellular delivery of chemic entities. Apart from of the types of delivery strategies, the composition of the cell membrane is critical for delivery efficiency due to the fact that cellular uptake is affected by the interaction between the chemical entity and the plasma membrane. In this review, we aimed to develop a profound understanding of the interactions between delivery systems and components of the plasma membrane. For the purpose, we attempt to present a broad overview of what delivery systems can be used to enhance the intracellular delivery of poorly permeable chemic entities, and how various delivery strategies are applied according to the components of plasma membrane.

A Tetrahedral Boronic Acid Diester Formed by an Unnatural Amino Acid in the Ligand Pocket of an Engineered Lipocalin

Boronic acids have long been known to form cyclic diesters with cis‐diol compounds, including many carbohydrates. This phenomenon was previously exploited to create an artificial lectin by incorporating p‐borono‐l‐phenylalanine (Bpa) into the ligand pocket of an engineered lipocalin, resulting in a so‐called Borocalin. Here we describe the X‐ray analysis of its covalent complex with 4‐nitrocatechol as a high‐affinity model ligand. As expected, the crystal structure reveals the formation of a cyclic diester between the biosynthetic boronate side chain and the two ortho‐hydroxy substituents of the benzene ring. Interestingly, the boron also has a hydroxide ion associated, despite an only moderately basic pH 8.5 in the crystallization buffer. The complex is stabilized by a polar contact to the side chain of Asn134 within the ligand pocket, thus validating the functional design of the Borocalin as an artificial sugar‐binding protein. Our structural analysis demonstrates how a boronate can form a thermodynamically stable diester with a vicinal diol in a tetrahedral configuration in aqueous solution near physiological pH. Moreover, our data provide a basis for the further engineering of the Borocalin with the goal of specific recognition of biologically relevant glycans.

Hypochlorite fluorescence sensing by phenylboronic acid-alizarin adduct based carbon dots

The selective fluorescence sensing of hypochlorite (ClO^-) was achieved at pH 7.4 by a simple analytical procedure through the fluorescence quenching of autoclave synthesized carbon dots (CDs), which used as precursor an adduct formed between 3-aminophenylboronic acid (APBA) and alizarin red S (ARS). The use of this adduct allowed the preparation of CDs with a red shifted emission (560 nm) and excitation in the visible range (490 nm). Quantification of hypochlorite was achieved at physiological pH (pH 7.4) in aqueous solutions by fluorescence quenching with a linearity range of 0-200 μM (limit of detection of 4.47 μM, and limit of quantification of 13.41 μM). The selectivity of hypochlorite sensing was confirmed by comparison with other potential analytes, such as glucose, fructose and hydrogen peroxide. Finally, the validity of the proposed assay was further demonstrated by performing recovery assays in different matrices. Thus, this CDs allows the fluorescent sensing of ClO^- with spectral properties more suitable for in vitro/in vivo applications.

Mobile-Phase Modulators as Salt Tolerance Enhancers in Phenylboronate Chromatography: Thermodynamic Evaluation of the Mechanisms Underlying the Adsorption of Monoclonal Antibodies

Phenylboronate chromatography has been employed for bioseparation applications though details concerning the mechanisms of interaction between the ligand and macromolecules remain widely unknown. Here, the phenomena underlying the adsorption of an anti-human interleukin-8 (anti-IL8) monoclonal antibody (mAb) onto an m-aminophenylboronic acid (m-APBA) ligand in the presence of different mobile-phase modulators (NaF/MgCl ₂ /(NH ₄ ) ₂ SO ₄ ) and under different pH values (7.5/8.5/9.0) is investigated. Flow microcalorimetry (FMC) is applied to measure instantaneous heat energy transfer, providing insights about the role of specific and nonspecific interactions involved in the adsorptive process. Results show that the adsorption of anti-IL8 mAb to m-APBA is enthalpically driven, corroborating the presence of the reversible esterification reaction between boronic acid or boronates and cis-diol-containing molecules. Nevertheless, for all mobile-phase modulators studied, changes in thermogram profiles are observed as well as reductions in the net heat of adsorption when increasing the pH. Overall, FMC and parallel chromatographic experiments data suggest that ligand salt tolerance could be enhanced using mobile-phase modulators, with all salts studied promoting the specific cis-diol interactions and reducing nonspecific interactions. The last feature is more noticeable at pH values above ligand's pK _a , mainly due to the ability of NaF and (NH ₄ ) ₂ SO ₄ to diminish electrostatic interactions when compared to the commonly used NaCl.

Constant Potential Amperometric Flow-Injection Analysis of Ions and Neutral Molecules Transduced by Electroactive (Conductive) Polymers

We first report on constant potential (dc) amperometric flow-injection analysis (FIA) transduced by electroactive (conductive) polymers. Amperometric response is caused by the polymer recharging in order to maintain the electrode potential at a constant level when (i) ions are crossing the film|solution interface and polarizing electrode|film interface or (ii) ions or neutral molecules are specifically interacting with the polymer recharging it. The response under constant solution flow is a current peak and in flow-injection mode is a couple of current peaks directed opposite of the first sharp, analytically valuable peak. In both constant flow and flow-injection regimes, the peak current is dependent on analyte concentrations; obviously, the FIA mode provides more advantageous analytical characteristics. Constant potential amperometric flow-injection analysis is shown for boronate- and sulfate-functionalized polyanilines as well as for Prussian Blue, a member of the inorganic polymer family. As a proof of concept, the successful dc amperometric detection of lactate in human sweat with boronate-functionalized polyaniline has been shown. The proposed approach would revolutionize the field of conductive/electroactive polymer-supported ion sensing with the introduction of reliable and robust amperometry as a valuable alternative to existing potentiometry.

Dopamine/2-Phenylethylamine Sensitivity of Ion-Selective Electrodes Based on Bifunctional-Symmetrical Boron Receptors

Piperazine-based compounds bearing two phenylboronic acid or two benzoxaborole groups (PBPA and PBBB) were applied as dopamine receptors in polymeric membranes (PVC/DOS) of ion-selective electrodes. The potentiometric sensitivity and selectivity of the sensors towards dopamine were evaluated and compared with the results obtained for 2-phenylethylamine. Since the developed electrodes displayed strong interference from 2-phenylethylamine, single-molecule geometry optimizations were performed using the density functional theory (DFT) method in order to investigate the origin of dopamine/2-phenylethylamine selectivity. The results indicated that phenylboronic acid and benzoxaborole receptors bind dopamine mainly through the dative B⁻N bond (like 2-phenylethylamine) and the potentiometric selectivity is mainly governed by the higher lipophilicity of 2-phenylethylamine.

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.

Synthesis, Purification, and Mass Spectrometric Characterization of Stable Isotope-Labeled Amadori-Glycated Phospholipids

Nonenzymatic glycation of lipids plays an important role in several physiological and pathological processes, such as normal aging and complications of diabetes mellitus. To develop liquid chromatography coupled with mass spectrometric (LC-MS) methods for accurate analysis of Amadori compound-glycated lipids from biological samples, it is essential to obtain isotope-labeled Amadori-lipid standards. Herein, we report optimized methods for the preparation of six stable isotope-labeled Amadori-glycated lipid standards covering four types of lipids, including [¹³C₆]Amadori-phosphatidyl ethanolamine (PE), -phosphatidyl serine (PS), -LysoPE, and -LysoPS. Optimal conditions for the synthesis and purification of these four types of Amadori-glycated lipids were detailed in this study. LC-MS and LC-UV analyses showed that destination products were highly purified (>95%). Accurate mass and MS/MS fragmentation in both positive- and negative-ion modes further validated the identification of these six synthetic [¹³C₆]Amadori-glycated lipid standards. Successful preparation of these highly purified isotope-labeled standards makes it possible to develop targeted LC-MS/MS methods for accurate analysis of Amadori-glycated phospholipids from biological samples.

Several effects of boron are induced by uncoupling steroid hormones from their transporters in blood

Boron is increasingly added to food supplements due to multiple effects that have been reported in mammals after boric acid administration. Among these effects are inflammatory process control, bone and muscle strength enhancement, protein expression regulation, and a decreased risk of developing some pathologies in which these processes are key, such as osteoporosis, dermatological inflammatory non-infectious maladies and diseases affecting the central nervous system. Experimental data have suggested that steroid hormone levels in plasma change after boric acid administration, but a clear mechanism behind these variations has not been established. We analyzed possibilities for these changes and hypothesized that boric acid disrupts the interactions between steroid hormones and several carriers in plasma. In particular, we proposed that there is an uncoupling of the interactions between sex hormone binding globulin (SHBG) and estrogens and testosterone and that there are alterations in the binding of hydrophobic ligands by other carrier proteins in plasma. Further experimental and computational studies are required to support the hypothesis that boric acid and probably other boron-containing compounds can displace steroid hormones from their plasma carriers. If such phenomena are confirmed, boron administration with a clear mechanism could be employed as a therapeutic agent in several diseases or physiological events that require modulation of steroid hormone levels in plasma.

Diazaborines as New Inhibitors of Human Neutrophil Elastase

Boronic acids (BAs) are a prominent functionality extensively used to design biologically active compounds and functional biomaterials. Boronic acids open shell can lead to unspecific reactivity of BAs with endogenous nucleophiles and to undesired off-target effects. Here, diazaborines are presented as a new class of boron-based warheads for serine proteases inhibition, in which the boron function is stabilized in the form of an aromatic boron-based heterocycle. In this study, diazaborines were readily synthesized in a single step in yields up to 96%, without any chromatographic operation and were shown to reversibly inhibit human neutrophil elastase (HNE) serine protease with IC₅₀ values in the low μM range. Diazaborines were also selective toward HNE, as no inhibition was observed against a panel of five closely related serine proteases. Synthetic and theoretical studies performed on this system suggest that, similar to BAs, the reaction mechanism involves the formation of a reversible covalent bond between the diazaborine boron center and the catalytic serine oxygen. Finally, different from BAs, diazaborines were shown to be very stable in pH 7.4 phosphate buffer and human plasma.

Recent advances in electrochemical non-enzymatic glucose sensors - A review

This review encompasses the mechanisms of electrochemical glucose detection and recent advances in non-enzymatic glucose sensors based on a variety of materials ranging from platinum, gold, metal alloys/adatom, non-precious transition metal/metal oxides to glucose-specific organic materials. It shows that the discovery of new materials based on unique nanostructures have not only provided the detailed insight into non-enzymatic glucose oxidation, but also demonstrated the possibility of direct detection in whole blood or interstitial fluids. We critically evaluate various aspects of non-enzymatic electrochemical glucose sensors in terms of significance as well as performance. Beyond laboratory tests, the prospect of commercialization of non-enzymatic glucose sensors is discussed.