Synthesis and Evaluation of Dual Wavelength Fluorescent Benzo[b]thiophene Boronic Acid Derivatives for Sugar Sensing

Exploring the Potential of Linear π-Bridge Structures in a D-π-A Organic Photosensitizer for Improved Open-Circuit Voltage

We present the design, synthesis, and evaluation of novel metal-free photosensitizers based on D-π-A structures featuring tri-arylamine as an electron donor, cyanoacrylic acid as an anchoring group, and substituted derivative π-bridges including 9,9-dimethyl-9H-fluorene, benzo[b]thiophene, or naphtho [1,2-b:4,3-b']dithiophene. The aim of the current research is to unravel the relationship between chemical structure and photovoltaic performance in solar cell applications by investigating the properties of these organic sensitizers. The newly developed photosensitizers displayed variations in HOMO-LUMO energy gaps and photovoltaic performances due to their distinct π-bridge structures and exhibited diverse spectral responses ranging from 343 to 490 nm. The t-shaped and short linear photosensitizers demonstrated interesting behaviors in dye-sensitized solar cells, such as the effect of the molecular size in electron recombination. The study showed that a t-shaped photosensitizer with a bulky structure reduced electron recombination, while short linear photosensitizers with a smaller molecular size resulted in a higher open-circuit voltage value and enhanced photovoltaic performance. Impedance analysis further supported the findings, highlighting the influence of dye loading and I3- ion surface passivation on the overall performance of solar cells. The molecular design methodology proposed in this study enables promising photovoltaic performance in solar cells, addressing the demand for highly efficient, metal-free organic photosensitizers.

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.

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.

Boronic Acid Appended Naphthyl-Pyridinium Receptors as Chemosensors for Sugars

There remains a need in clinics and research to have simple and sensitive detection systems that allow the detection and quantification of sugar markers of biomedical relevance such as sugars lactulose and mannitol for noninvasive gut permeability assessment. We have prepared a new class of boronic acid-appended naphthyl-pyridinium receptor compounds as chemosensors. These were studied for their ability to act as modular internal charge transfer (ICT) fluorescent probes or donor/acceptor pair ensembles where the receptor compound can act as a quencher for an anionic dye. As an ICT sensor, fluorescence intensity increased upon diol recognition, which stems from the neutralization of the pyridinium nitrogen that is perturbing the chromophoric properties. We found these ICT probes provide good sensitivity for disaccharide lactulose with low micromolar detection and quantification limits. In addition, their ability to form a non-fluorescent ground state complex with anionic reporter dyes, such as HPTS or TSPP, was examined as probes for various sugars. We have identified three receptor/quencher compounds with high quenching efficiency for anionic dyes. Subsequently, a range of sugars and sugar derivatives were tested for chemosenstivity of our probes. This study illustrates an approach for designing boronic acid-based chemoreceptors for the recognition and quantification of sugars and sugar derivatives.

Water-soluble diboronic acid-based fluorescent sensors recognizing d-sorbitol

Water-soluble diboronic acid sensor 15c exhibited higher selectivity for d-sorbitol than monoboronic acid sensor 1 and hydroxy derivative 2. And it could be applied for d-sorbitol sensing and analysis in real samples.

A General Synthetic Route to Polycyclic Aromatic Dicarboximides by Palladium-Catalyzed Annulation Reaction

Here we report a general method for the synthesis of polycyclic aromatic dicarboximides (PADIs) by palladium-catalyzed annulation of naphthalene dicarboximide to different types of aromatic substrates. Reaction conditions were optimized by systematic variation of ligand, solvent, and additive. It was shown that solvent has a decisive effect on the yield of the reaction products, and thus 1-chloronaphthalene as solvent afforded the highest yield. By applying the optimized reaction conditions, a broad series of planar carbo- and heterocycle containing PADIs were synthesized in up to 97% yield. Moreover, this approach could be applied to curved aromatic scaffold to achieve the respective bowl-shaped PADI. Two-fold annulation was accomplished by employing arene diboronic esters, affording polycyclic aromatic bis(dicarboximides). The optical and electrochemical properties of this broad series of PADIs were explored as well.

A new selective fluorene-based fluorescent internal charge transfer (ICT) sensor for sugar alcohols in aqueous solution

Sugar alcohols, such as sorbitol, are commonly used as a replacement for sucrose in the food industry, applied as starting material for vitamin C synthesis, and involved as one of the causative factors in diabetic complications. Therefore, their detection and quantification in aqueous solution are necessary. The reversible covalent interactions between boronic acids and diols are the basis of efficient methods for the detection of saccharides. Herein, we report a new internal charge transfer (ICT) fluorene-based fluorescent boronic acid sensor (1) 2-[(9,9-dimethyl-9H-fluoren-2-yl-amino)methyl] phenyl boronic acid that shows significant fluorescence changes upon addition of saccharides. The boronic acid has high affinity (K a = 1107.9 M(-1)) and selectivity for sorbitol at pH = 8.31. It showed a linear response toward sorbitol in the concentration range from 1.0 × 10(-5) to 6.0 × 10(-4) mol L(-1) with the detection limit of 7.04 × 10(-6) mol L(-1). Sensor 1 was used to detect sorbitol in real samples with good recovery.

Naphthalimide-based fluorescent photoinduced electron transfer sensors for saccharides

A fluorescent probe based on PET mechanism exhibited significant fluorescence enhancement toward saccharides and was used to detect fructose in beverages with good recovery.

Improved activity of immobilized antibody by paratope orientation controller: probing paratope orientation by electrochemical strategy and surface plasmon resonance spectroscopy

Electrochemical method and surface plasmon resonance (SPR) spectroscopic analysis are utilized herein to investigate antibody immobilization without and with orientation control for site-positioning paratopes (antigen binding site) of the antibody molecules. Biotin and its antibody were selected in current study as model. Such an approach employed thiophene-3-boronic acid (T3BA) as paratope orientation controller, (i) enabled site orientation of the antibody molecules reducing the hiding of paratopes, and (ii) maintained the activity of the captured antibodies, as confirmed by electrochemical and SPR analysis. Anti-biotin antibody (a glycoprotein) was covalently bound to a self-assembled monolayer of T3BA modified on a nanogold-electrodeposited screen-printed electrode through boronic acid-saccharide interactions, with the boronic acid units specifically binding to the glycosylation sites of the antibody molecules. The immunosensor functioned based on competition between the analyte biotin and biotin-tagged, potassium hexacyanoferrate(II)-encapsulated liposomes. The current signal produced by the released liposomal Fe(CN)6(4-), measured using square wave voltammetry, yielded a sigmoidally shaped dose-response curve that was linear over eight orders of magnitude (from 10(-11) to 10(-3)M). Furthermore this biosensing system fabricated based on T3BA approach was found to possess significantly improved sensitivity, and the limit of detection toward biotin was calculated as 0.102 ng mL(-1) (equivalent to 6 μL of 4.19 × 10(-10)M biotin).

Binding sugars: from natural lectins to synthetic receptors and engineered neolectins

The large diversity and complexity of glycan structures together with their crucial role in many biological or pathological processes require the development of new high-throughput techniques for analyses. Lectins are classically used for characterising, imaging or targeting glycoconjugates and, when printed on microarrays, they are very useful tools for profiling glycomes. Development of recombinant lectins gives access to reliable and reproducible material, while engineering of new binding sites on existing scaffolds allows tuning of specificity. From the accumulated knowledge on protein-carbohydrate interactions, it is now possible to use nucleotide and peptide (bio)synthesis for producing new carbohydrate-binding molecules. Such a biomimetic approach can also be addressed by boron chemistry and supra-molecular chemistry for the design of fully artificial glycosensors.

A new class of fluorescent boronic acids that have extraordinarily high affinities for diols in aqueous solution at physiological pH

The boronic acid group is an important recognition moiety for sensor design. Herein, we report a series of isoquinolinylboronic acids that have extraordinarily high affinities for diol-containing compounds at physiological pH. In addition, 5- and 8-isoquinolinylboronic acids also showed fairly high binding affinities towards D-glucose (K(a)=42 and 46 M(-1), respectively). For the first time, weak but encouraging binding of cis-cyclohexanediol was found for these boronic acids. Such binding was coupled with significant fluorescence changes. Furthermore, 4- and 6-isoquinolinylboronic acids also showed the ability to complex methyl α-D-glucopyranose (K(a)=3 and 2 M(-1), respectively).

Carbohydrate recognition by boronolectins, small molecules, and lectins

Carbohydrates are known to mediate a large number of biological and pathological events. Small and macromolecules capable of carbohydrate recognition have great potentials as research tools, diagnostics, vectors for targeted delivery of therapeutic and imaging agents, and therapeutic agents. However, this potential is far from being realized. One key issue is the difficulty in the development of "binders" capable of specific recognition of carbohydrates of biological relevance. This review discusses systematically the general approaches that are available in developing carbohydrate sensors and "binders/receptors," and their applications. The focus is on discoveries during the last 5 years.

Carbohydrate biomarkers for future disease detection and treatment

Carbohydrates are considered as one of the most important classes of biomarkers for cell types, disease states, protein functions, and developmental states. Carbohydrate "binders" that can specifically recognize a carbohydrate biomarker can be used for developing novel types of site specific delivery methods and imaging agents. In this review, we present selected examples of important carbohydrate biomarkers and how they can be targeted for the development of therapeutic and diagnostic agents. Examples are arranged based on disease categories including (1) infectious diseases, (2) cancer, (3) inflammation and immune responses, (4) signal transduction, (5) stem cell transformation, (6) embryo development, and (7) cardiovascular diseases, though some issues cross therapeutic boundaries.

Synthesis, evaluation, and computational studies of naphthalimide-based long-wavelength fluorescent boronic Acid reporters

Boronic acids that change fluorescence properties upon sugar binding are very useful for the synthesis of carbohydrate sensors. Along this line, boronic acids that fluoresce beyond 500 nm are especially useful. A series of boronic acid fluorescent reporter compounds based on the 4-amino-1,8-naphthalimide structure have been synthesized (1a-d) and evaluated under near physiological conditions. These compounds showed good water solubility and significant changes in fluorescence properties after binding with sugars, with the emission wavelength being at around 570 nm. Analogues in this series with different substitutions showed similar properties. We have also examined the mechanism of the observed fluorescence changes for these compounds.

Modeling the excitation wavelengths (lambda(ex)) of boronic acids

The quantitative structure-property relationship (QSPR) method was used to model the fluorescence excitation wavelengths (lambda(ex)) of 42 boronic acid-based fluorescent biosensors (30 in the training set and 12 in the test set). In this QSPR study, unsupervised forward selection (UFS), stepwise multiple linear regression (SMLR), partial least squares regression (PLS) and associative neural networks (ASNN) were employed to simulate linear and nonlinear models. All models were validated by a test set and Tropsha's validation model. The resulting ASNN nonlinear model demonstrates significant improvement on the predictive ability of the neural network compared to the SMLR and PLS linear models. The descriptors used in the models are discussed in detail. These QSPR models are useful tools for the prediction of fluorescence excitation wavelengths of arylboronic acids.