Fluorinated Boronic Acid-Appended Bipyridinium Salts for Diol Recognition and Discrimination via 19F NMR Barcodes

19F NMR Probes: Molecular Logic Material Implications for the Anion Discrimination and Chemodosimetric Approach for Selective Detection of H2O2

Detection and discrimination of similar solvation energies of bioanalytes are vital in medical and practical applications. Currently, various advanced techniques are equipped to recognize these crucial bioanalytes. Each strategy has its own benefits and limitations. One-dimensional response, lack of discrimination power for anions, and reactive oxygen species (ROS) generally limit the utilized fluorescent probe. Therefore, a cutting-edge, refined method is expected to conquer these limitations. The use of 19F NMR spectroscopy for detecting and discriminating essential analytes in practical applications is an emerging technique. As an alternative strategy, we report two fluorinated boronic acid-appended pyridinium salts 5-F-o-BBBpy (1) and 5-CF3-o-BBBpy (2). Probe (1) acts as a chemosensor for identifying and discriminating inorganic anions with similar solvation energies with strong bidirectional 19F shifts in the lower ppm range. Probe (2) turns as a chemo dosimeter for the selective detection and precise quantification of hydrogen peroxide (H2O2) among other competing ROS. To demonstrate real-life applicability, we successfully quantified H2O2 via probe (2) in different pharmaceutical, dental, and cosmetic samples. We found that tuning the -F/-CF3 moiety to the arene boronic acid enables the π-conjugation, a crucial prerequisite for the discrimination of anions and H2O2. Characteristic 19F NMR fingerprints in the presence of anions revealed a complementary implication (IMP)/not implication (NIMP) logic function. Finally, the 16 distinct binary Boolean operations on two logic values are defined for "functional completeness" using the special property of the IMP gate. Boolean logic's ability to handle information by utilizing characteristic 19F NMR fingerprints has not been seen previously in a single chemical platform for detecting and differentiating such anions.

Quantifying CO-release from a photo-CORM using 19F NMR: An investigation into light-induced CO delivery

Carbon monoxide (CO) is an innate signaling molecule that can regulate immune responses and interact with crucial elements of the circadian clock. Moreover, pharmacologically, CO has been substantiated for its therapeutic advantages in animal models of diverse pathological conditions. Given that an excessive level of CO can be toxic, it is imperative to quantify the necessary amount for therapeutic use accurately. However, estimating gaseous CO is notably challenging. Therefore, novel techniques are essential to quantify CO in therapeutic applications and overcome this obstacle precisely. The classical Myoglobin (Mb) assay technique has been extensively used to determine the amount of CO-release from CO-releasing molecules (CORMs) within therapeutic contexts. Nevertheless, specific challenges arise when applying the Mb assay to evaluate CORMs featuring innovative molecular architectures. Here, we report a fluorinated photo-CORM (CORM-FBS) for the photo-induced CO-release. We employed the 19F NMR spectroscopy approach to monitor the release of CO as well as quantitative evaluation of CO release. This new 19F NMR approach opens immense opportunities for researchers to develop reliable techniques for identifying molecular structures, quantitative studies of drug metabolism, and monitoring the reaction process.

Glucose sandwich assay based on surface-enhanced Raman spectroscopy

A facile and sensitive glucose sandwich assay using surface-enhanced Raman scattering (SERS) has been developed. Glucose was captured by 3-aminopheyonyl boronic acid (APBA) modified Ag nanoparticles decorated onto a polyamide surface. Then, Ag nanoparticles modified with 3-amino-6-ethynylpicolinonitrile (AEPO) and APBA were used as SERS tags. APBA forms specific cis-diol compounds with glucose molecules avoiding interference by other saccharides and biomolecules in urine enabling its selective detection. As the actual Raman reporter, AEPO exhibited a distinctive SERS peak in the Raman silent region, thus increasing the sensitivity of the glucose detection to 10-11 M. Additionally, the developed SERS assay was reusable, and its applicability in artificial urine samples demonstrated future clinical utility confirming the potential of this innovative technology as a diagnostic tool for glucose sensing.

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.

Stereospecific recognition of a chiral centre over multiple flexible covalent bonds by 19F-NMR

High performance in chiral recognition by a reactive ¹⁹F-tag was demonstrated for a variety of enantiomers. The analytes with up to five flexible covalent bonds from the chiral center can be discriminated by a sensitive chiral reporter manifested in the ¹⁹F-NMR spectrum. Simultaneous identification of chiral amines in a mixture and high accuracy ee determination were achieved.

Ratiometric Strategy Based on Intramolecular Internal Standard for Reproducible and Simultaneous Fingerprint Recognition of Diols via 19F NMR Spectroscopy

¹⁹F NMR spectroscopy has been widely used as a convenient and noninvasive analytical technique for understanding complex natural phenomena at the atomic level. However, current NMR referencing techniques are most optimized for ¹H NMR, which causes some limitations while referencing heteronuclear NMR. Despite its promising advantages, ¹⁹F NMR spectroscopy often exhibits large variations in experimental results and lacks consistency compared with ¹H NMR. Herein, we propose a new strategy to improve the consistency of ¹⁹F NMR referencing using an internal standard method. As a proof-of-concept, BA-Py-TFP was applied as a sensor for diols via ¹⁹F NMR spectroscopy. This strategy proved to be a robust and reproducible referencing method with acceptable deviation (Δδ_F = 43-58 ppb) across diverse NMR spectrometers at different institutions. In particular, this new strategy allows reliable fingerprint recognition for analytes and enables qualitative and quantitative analyses of mixtures of multiple analytes simultaneously. The high recovery rates for d-glucose in the human serum matrix suggest its potential suitability for a diverse range of applications, such as in diabetes-related diagnostics.

Rapid and Selective 19F NMR-Based Sensors for Fingerprint Identification of Ribose

Ribose plays an important role in the process of life. Excessive ribose in the human cerebrospinal fluid or urine can be used as an early diagnostic marker of leukoencephalopathy. Fluorinated phenylboronic acid combined with ¹⁹F NMR spectroscopy was a powerful method for molecular recognition. However, phenylboronic acid-based sensors for selective detection of ribose are rarely reported in the literature. In this study, the rapid and highly selective recognition of ribose was studied by ¹⁹F NMR and 2-fluorophenylboric acid. It was found that 2-fluoro-phenylboric acid was an appropriate ¹⁹F NMR-based sensor molecule for the determination of ribose under physiological conditions with high selectivity and robust anti-interference ability. When 2-fluorophenylboric acid was used for the detection of ribose in human urine without any sample pretreatment, a limit of detection of 78 μM was obtained at room temperature under given ¹⁹F NMR experimental conditions (400 MHz, 512 scans, ca. 12 min), which can well meet the needs of practical application.

Recognition-Enabled Automated Analyte Identification via 19F NMR

Nuclear magnetic resonance (NMR) is an indispensable tool for structural elucidation and noninvasive analysis. Automated identification of analytes with NMR is highly pursued in metabolism research and disease diagnosis; however, this process is often complicated by the signal overlap and the sample matrix. We herein report a detection scheme based on ¹⁹F NMR spectroscopy and dynamic recognition, which effectively simplifies the detection signal and mitigates the influence of the matrix on the detection. It is demonstrated that this approach can not only detect and differentiate capsaicin and dihydrocapsaicin in complex real-world samples but also quantify the ibuprofen content in sustained-release capsules. Based on the ¹⁹F signals obtained in the detection using a set of three ¹⁹F probes, automated analyte identification is achieved, effectively reducing the odds of misrecognition caused by structural similarity.

Merging Electron Deficient Boronic Centers with Electron-Withdrawing Fluorine Substituents Results in Unique Properties of Fluorinated Phenylboronic Compounds

Fluorinated boron species are a very important group of organoboron compounds used first of all as receptors of important bioanalytes, as well as biologically active substances, including Tavaborole as an antifungal drug. The presence of substituents containing fluorine atoms increases the acidity of boronic compounds, which is crucial from the point of view of their interactions with analytes or certain pathogen's enzymes. The review discusses the electron acceptor properties of fluorinated boronic species using both the acidity constant (pK_a) and acceptor number (AN) in connection with their structural parameters. The NMR spectroscopic data are also presented, with particular emphasis on ¹⁹F resonance due to the wide range of information that can be obtained from this technique. Equilibria in solutions, such as the dehydration of boronic acid to form boroxines and their esterification or cyclization with the formation of 3-hydroxyl benzoxaboroles, are discussed. The results of the latest research on the biological activity of boronic compounds by experimental in vitro methods and theoretical calculations using docking studies are also discussed.

Photo- and Electrochemical Dual-Responsive Iridium Probe for Saccharide Detection

Dual detection systems are of interest for rapid, accurate data collection in sensing systems and in vitro testing. We introduce an Ir^III complex with a boronic acid receptor site attached to the 2‐phenylpyridine ligand as an ideal probe with photo‐ and electrochemical signals that is sensitive to monosaccharide binding in aqueous solution. The complex displays orange luminescence at 618 nm, which is reduced by 70 and 40 % upon binding of fructose and glucose, respectively. The electro‐chemiluminescent signal of the complex also shows a direct response to monosaccharide binding. The Ir^III complex shows the same response upon incorporation into hydrogel matrices as in solution, thus demonstrating the potential of its integration into a device, as a nontoxic, simple‐to‐use tool to observe sugar binding over physiologically relevant pH ranges and saccharide concentrations. Moreover, the complex's luminescence is responsive to monosaccharide presence in cancer cells.

A Bisboronic Acid Sensor for Ultra-High Selective Glucose Assay by 19F NMR Spectroscopy

Glucose is a significant analyte both in biology and biomedical science, it is of great importance to selectively detect glucose both in body fluids and complex mixture. In this study, a simple ¹⁹F NMR based sensor was synthesized easily, which exhibited a high selectivity and robust anti-interference ability toward glucose detection both in a mixture containing up to 10 saccharides and human urine samples without any pretreatment. Combined with this sensor system, glucose could be well detected in human urine samples and the limit of detection was 0.41 mM by using a 400 MHz NMR spectrometer with 128 scans (ca. 4 min). This method had a potential for specific detection of glucose in complex mixture and diagnosis of diabetes mellitus related diseases in body fluid.

Molecular Boronic Acid-Based Saccharide Sensors

Boronic acids can reversibly bind diols, a molecular feature that is ubiquitous within saccharides, leading to their use in the design and implementation of sensors for numerous saccharide species. There is a growing understanding of the importance of saccharides in many biological processes and systems; while saccharide or carbohydrate sensing in medicine is most often associated with detection of glucose in diabetes patients, saccharides have proven to be relevant in a range of disease states. Herein the relevance of carbohydrate sensing for biomedical applications is explored, and this review seeks to outline how the complexity of saccharides presents a challenge for the development of selective sensors and describes efforts that have been made to understand the underpinning fluorescence and binding mechanisms of these systems, before outlining examples of how researchers have used this knowledge to develop ever more selective receptors.

Multinuclear NMR Study on the Formation and Polyol-Induced Deformation Mechanisms of Wormlike Micelles Composed of Cetyltrimethylammonium Bromide and 3-Fluorophenylboronic Acid

We had previously confirmed a glucose-responsive decrease in the viscosity of cetyltrimethylammonium bromide (CTAB) and phenylboronic acid (PBA) wormlike micelle (WLM) systems. However, the mechanisms of the formation of WLMs and the decrease in viscosity with glucose addition have not been determined. In this study, we elucidated the mechanisms using 3-fluorophenylboronic acid (3FPBA) based on ¹¹B NMR and ¹⁹F NMR analyses. The system in 60 mM CTAB/60 mM 3FPBA at pH 7.4 demonstrated high viscoelasticity, and the formation of WLMs in the system was confirmed by rheological characteristics. The ¹¹B NMR spectrum at pH 7.4 revealed that 3FPBA existed in a neutral form with sp²-hybridized boron; however, the ¹¹B signal disappeared in the presence of CTAB. In contrast, ¹⁹F NMR studies indicated that the quaternary ammonium ion of CTAB interacts with the phenyl group of 3FPBA in the sp² form via cation-π interactions. PBA derivatives react with various polyols; thus, we investigated the change in the viscous system after the addition of sugar and sugar alcohols. The viscosity of the WLMs decreased with increased polyol concentration, especially those of fructose and mannitol, in which the decrease was apparent at 40-160 mM polyols. The ¹⁹F NMR spectra revealed that polyol addition induced decrease in the sp² form of 3FPBA and increase in the sp³ form of 3FPBA. Based on the results, we propose the following mechanism of the polyol response: (1) The WLMs are stabilized by CTAB and 3FPBA in the sp² form using cation-π interactions as the driving force. (2) When polyol is added to the system, the sp² form of 3FPBA decreases and its sp³ form increases. (3) This change means that the structural component of WLMs decreases, which induces the disruption of WLMs, and the viscosity decreases. The formation and deformation mechanisms of the WLMs determined in this study are notable because 3FPBA interacts as a neutral compound, whereas CTAB often interacts with anionic aromatic compounds to form WLMs. Without ¹⁹F NMR measurements, these mechanisms would not have been discovered.

Simultaneous detection of small molecule thiols with a simple 19F NMR platform

Thiols play critical roles in regulating biological functions and have wide applications in pharmaceutical and biomedical industries. However, we still lack a general approach for the simultaneous detection of various thiols, especially in complex systems. Herein, we establish a ¹⁹F NMR platform where thiols are selectively fused into a novelly designed fluorinated receptor that has two sets of environmentally different ¹⁹F atoms with fast kinetics (k ₂ = 0.73 mM^-1 min^-1), allowing us to generate unique two-dimensional codes for about 20 thiols. We demonstrate the feasibility of the approach by reliably quantifying thiol drug content in tablets, discriminating thiols in living cells, and for the first time monitoring the thiol related metabolism pathway at the atomic level. Moreover, the method can be easily extended to detect the activity of thiol related enzymes such as γ-glutamyl transpeptidase. We envision that the versatile platform will be a useful tool for detecting thiols and elucidating thiol-related processes in complex systems.

Rapid chiral analysis based on liquid-phase cyclic chemiluminescence

Rapid chiral analysis has become one of the important aspects of academic and industrial research. Here we describe a new strategy based on liquid-phase cyclic chemiluminescence (CCL) for rapid resolution of enantiomers and determination of enantiomeric excess (ee). A single CCL measurement can acquire multistage signals that provide a unique way to examine the intermolecular interactions between chiral hosts and chiral guests, because the lifetime (τ) of the multistage signals is a concentration-independent and distinguishable constant for a given chiral host-guest system. According to the τ values, CCL allows discrimination between a wide range of enantiomeric pairs including chiral alcohols, amines and acids by using only one chiral host. Even the chiral systems hardly distinguished by nuclear magnetic resonance and fluorescence methods can be distinguished easily by CCL. Additionally, the τ value of a mixture of two enantiomers is equal to the weighted average of each enantiomer, which can be used for the direct determination of ee without the need to separate the chiral mixture and create calibration curves. This is extremely crucial for the cases without readily available enantiomerically pure samples. This strategy was successfully applied to monitoring of the Walden inversion reaction and analysis of chiral drugs. The results were in good agreement with those obtained by high-performance liquid chromatography, indicating the utility of CCL for routine quick ee analysis. Mechanism study revealed that the τ value is possibly related to the activity of the chiral substance to catalyze a luminol-H2O2 reaction. Our research provides an unprecedented and general protocol for chirality differentiation and ee determination, which is anticipated to be a useful technology that will find wide application in chirality-related fields, particularly in asymmetric synthesis and the pharmaceutical industry.

Direct Chiral 19F NMR Analysis of Fluorine-Containing Analytes and Its Application to Simultaneous Chiral Analysis

We have demonstrated the efficient chiral analysis of fluorine-containing compounds by ¹⁹F NMR spectroscopy. The highly sensitive fluorine nucleus allowed chiral analysis of complex mixtures and even asymmetric reaction mixtures of multisubstrates. A single ¹⁹F NMR experiment was sufficient to determine the enantiomeric excesses and yields of the five products simultaneously.

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.

1 H NMR Chemosensing of Potassium Ions Enabled by Guest-Induced Selectivity Switch of a Gold Nanoparticle/Crown Ether Nanoreceptor

A sensing protocol to detect potassium ions in water by ¹ H NMR spectroscopy is described. The method exploits the K⁺ -modulated affinity of 18-crown-6 functionalized gold nanoparticles towards organic ions, combined with NOE magnetization transfer. Binding of K⁺ to the crown ether moieties switches the nanoreceptor preference (and its ability to transfer magnetization) from organic cations (tyramine) to organic anions (phloretate). In this way, a ratiometric NMR signal is produced with a detection limit of 0.6 mM. Detection can be performed in 20 min with standard instruments and with little interference from other alkali and alkaline earth metal ions present in the sample.

A chiral sensor for recognition of varied amines based on 19F NMR signals of newly designed rhodium complexes

A novel chiral octahedral rhodium complex containing fluorine has been developed to be an excellent chiral sensor for a variety of amines including diamines, monoamines, amino alcohols and amino acids, showing well distinguishable 19F NMR signals and an accurate measurement of enantiomeric determination.

Barcoded point-of-care bioassays

Barcoded bioassays are ready to promote bioanalysis and biomedicine toward the point of care.

Detection and identification of designer drugs by nanoparticle-based NMR chemosensing

Properly designed monolayer-protected nanoparticles (2 nm core diameter) can be used as nanoreceptors for selective detection and identification of phenethylamine derivatives (designer drugs) in water. The molecular recognition mechanism is driven by the combination of electrostatic and hydrophobic interactions within the coating monolayer. Each nanoparticle can bind up to 30-40 analyte molecules. The affinity constants range from 105 to 106 M-1 and are modulated by the hydrophobicity of the aromatic moiety in the substrate. Detection of drug candidates (such as amphetamines and methamphetamines) is performed by using magnetization (NOE) or saturation (STD) transfer NMR experiments. In this way, the NMR spectrum of the drug is isolated from that of the mixture, allowing broad-class multianalyte detection and even identification of unknowns. The introduction of a dimethylsilane moiety in the coating monolayer allows performing STD experiments in complex mixtures. In this way, a detection limit of 30 μM is reached with standard instruments.

A multinuclear NMR perspective on the complexation between bisboronic acids and bisbenzoxaboroles with cis-diols

A new way of using solution NMR (especially ¹⁹F NMR) to study organoboron molecule/cis-diol equilibria is presented.

Influence of fluorine substituents on the properties of phenylboronic compounds

Rapid development of research on the chemistry of boronic acids is connected with their applications in organic synthesis, analytical chemistry, materials’ chemistry, biology and medicine. In many applications Lewis acidity of boron atoms plays an important role. Special group of arylboronic acids are fluoro-substituted compounds, in which the electron withdrawing character of fluorine atoms influences their properties. The present paper deals with fluoro-substituted boronic acids and their derivatives: esters, benzoxaboroles and boroxines. Properties of these compounds, i.e. acidity, hydrolytic stability, structures in crystals and in solution as well as spectroscopic properties are discussed. In the next part examples of important applications are given.

Fluorinated Boronic Acid-Appended Pyridinium Salts and 19F NMR Spectroscopy for Diol Sensing

The identification and discrimination of diols is of fundamental importance in medical diagnostics, such as measuring the contents of glucose in the urine of diabetes patients. Diol sensors are often based on fluorophore-appended boronic acids, but these severely lack discriminatory power and their response is one-dimensional. As an alternative strategy, we present the use of fluorinated boronic acid-appended pyridinium salts in combination with ¹⁹F NMR spectroscopy. A pool of 59 (bio)analytes was screened, containing monosaccharides, phosphorylated and N-acetylated sugars, polyols, carboxylic acids, nucleotides, and amines. The majority of analytes could be clearly detected and discriminated. In addition, glucose and fructose could be distinguished up to 1:9 molar ratio in mixtures. Crucially, the receptors feature high sensitivity and selectivity and are water-soluble, and their ¹⁹F-NMR analyte fingerprint is pH-robust, thereby making them particularly well-suited for medical application. Finally, to demonstrate this applicability, glucose could be detected in synthetic urine samples down to 1 mM using merely a 188 MHz NMR spectrometer.

Convergent Approach to Boronic Acid Functionalized Polycarbonates: Accessing New Dynamic Material Platforms

Polycarbonates are routinely utilized for diverse medicinal applications and are highly efficacious scaffolds for drug delivery and antimicrobial treatments. In order to provide for robust, dynamic platforms for biomedical applications, we have developed new routes for the incorporation of boronic acids into the polycarbonate backbone. These routes take advantage of straightforward postsynthesis modification of established polycarbonate backbones, enabling the preparation of a diverse array of boronic acid functionalized polycarbonates from readily accessible polycarbonates. In particular, this approach circumvents the need for de novo monomer synthesis, functional group incompatibilities, and deprotection steps that often limit other methods. This strategy has been demonstrated using a broad array of unprotected boronic acids to produce both neutral and cationic boronic acid functionalized polycarbonates.

Recent Advances in Multinuclear NMR Spectroscopy for Chiral Recognition of Organic Compounds

Nuclear magnetic resonance (NMR) is a powerful tool for the elucidation of chemical structure and chiral recognition. In the last decade, the number of probes, media, and experiments to analyze chiral environments has rapidly increased. The evaluation of chiral molecules and systems has become a routine task in almost all NMR laboratories, allowing for the determination of molecular connectivities and the construction of spatial relationships. Among the features that improve the chiral recognition abilities by NMR is the application of different nuclei. The simplicity of the multinuclear NMR spectra relative to ¹H, the minimal influence of the experimental conditions, and the larger shift dispersion make these nuclei especially suitable for NMR analysis. Herein, the recent advances in multinuclear (¹⁹F, ³¹P, ¹³C, and ⁷⁷Se) NMR spectroscopy for chiral recognition of organic compounds are presented. The review describes new chiral derivatizing agents and chiral solvating agents used for stereodiscrimination and the assignment of the absolute configuration of small organic compounds.

Recent advances in boronic acid-based optical chemosensors

This minireview highlights the developments in optical chemosensors from 2014 to 2016 that utilise the boronic acid interaction with polyols or Lewis bases.