John S. Fossey

A water-soluble boronate-based fluorescent probe for the selective detection of peroxynitrite and imaging in living cells

A water-soluble boronate-based fluorescent probe was evaluated for the detection of peroxynitrite (ONOO−) in the presence of a monosaccharide. The enhanced fluorescence of the probe when bound with D-fructose was switched off in the presence of peroxynitrite. In contrast, other reactive oxygen/nitrogen species (ROS/RNS) led to only slight fluorescence decreases due to protection by an internal N–B interaction. The interaction of the probe with D-fructose not only strengthens the fluorescence signal, but also protects the boronic acid from oxidation by other ROS/RNS. Therefore, under conditions generating various ROS/RNS, the boronate-based saccharide complex preferentially reacts with peroxynitrite. The probe was used in cell imaging experiments for the detection of endogenous and exogenous peroxynitrite. The sensor displays good “on–off” responses towards peroxynitrite, both in RAW 264.7 cells and HeLa cells.

Facile On-Site Detection of Substituted Aromatic Pollutants in Water Using Thin Layer Chromatography Combined with Surface-Enhanced Raman Spectroscopy

A novel facile method for on-site detection of substituted aromatic pollutants in water using thin layer chromatography (TLC) combined with surface-enhanced Raman spectroscopy (SERS) was explored. Various substituted aromatics in polluted water were separated by a convenient TLC protocol and then detected using a portable Raman spectrometer with the prepared silver colloids serving as SERS-active substrates. The effects of operating conditions on detection efficacy were evaluated, and the application of TLC-SERS to on-site detection of artificial and real-life samples of aromatics/polluted water was systematically investigated. It was shown that commercially available Si 60-F(254) TLC plates were suitable for separation and displayed low SERS background and good separation efficiency, 2 mM silver colloids, 20 mM NaCl (working as aggregating agent), 40 mW laser power, and 50 s intergration time were appropriate for the detection regime. Furthermore, qualitative and quantitative detection of most of substituted aromatic pollutants was found to be readily accomplished using the developed TLC-SERS technique, which compared well with GC-MS in terms of identification ability and detection accuracy, and a limit of detection (LOD) less than 0.2 ppm (even at ppb level for some analytes) could be achieved under optimal conditions. The results reveal that the presented convenient method could be used for the effective separation and detection of the substituted aromatic pollutants of water on site, thus reducing possible influences of sample transportation and contamination while shortening the overall analysis time for emergency and routine monitoring of the substituted aromatics/polluted water.

Simple protocols for NMR analysis of the enantiomeric purity of chiral diols

A three-component chiral derivatization protocol for determining the enantiopurity of chiral diols by 1H NMR spectroscopic analysis is described here. The present approach involves the derivatization of 1,2- 1,3- and 1,4-diols with 2-formylphenylboronic acid and enantiopure α-methylbenzylamine. This method affords a mixture of diastereoisomeric iminoboronate esters whose ratio can be determined by integration of well-resolved diastereotopic resonances in their 1H NMR spectra, thus enabling the determination of the enantiopurity of the parent diol. The protocol as described takes less than 90 min to complete.

Portable Surface-Enhanced Raman Scattering Sensor for Rapid Detection of Aniline and Phenol Derivatives by On-Site Electrostatic Preconcentration

A portable surface-enhanced Raman scattering (SERS) sensor is developed and applied to simultaneous detection of aniline and phenol derivatives in a label-free way with an electrostatic preconcentration technique to amplify the signals. A SERS-active substrate, silver-electrodeposited screen-printed electrodes (Ag-SPEs), is used for qualification and quantification of polar organic pollutants. Observation of SERS spectra at different potentials indicates that polar pollutants are selectively adsorbed on the Ag-SPEs at a given potential, suggesting that Ag-SPEs could selectively attract polar pollutants to an oppositely charged electrode at different potentials. Optimum SERS-active substrate was obtained when a potential of -0.15 V vs Ag/AgCl was applied on the SPEs in 0.1 M AgNO(3) solution for 10 min. Moreover, the effects of experimental variables such as the electrodeposition time and potential of Ag and preconcentration time of polar molecules on the SERS signals are presented. Under optimum conditions and with a 785 nm laser, the method is effective over a wide range of concentration (1 nM to 1 μM) for aniline and phenol derivatives. The novel method described herein presents a new detection regime for environmental pollutant analysis and also demonstrates simultaneous multiplexed detection of polar organic pollutants using convenient Ag-SPEs.

Simple protocols for NMR analysis of the enantiomeric purity of chiral primary amines

A simple three-component chiral derivatization protocol for determining the enantiopurity of chiral primary amines by 1H NMR spectroscopic analysis is described here. The method involves condensation of the amines with 2-formylphenylboronic acid and enantiopure 1,1′-bi-2-naphthol. This approach affords a mixture of diastereoisomeric iminoboronate esters whose ratio can be determined by the integration of well-resolved diastereotopic resonances in their 1H NMR spectra, thus enabling the enantiopurity of the parent amine to be determined easily. The protocol, as described, takes less than 90 min to complete.

Nitrogen cation–π interactions in asymmetric organocatalytic synthesis

Cation-π interactions have been widely exploited and utilised in the structural biology arena, their fundamental importance in supramolecular chemistry and the pivotal role they play in host guest chemistry has rapidly expanded. In terms of organic synthesis π-π, CH-π and cation-π interactions are often invoked providing hypotheses for observed selectivities and reaction outcomes although fundamental studies of these interactions are less well reported, especially in the organic synthesis arena. This article considers cation-π interactions in the field of asymmetric organocatalysis and provides a summary of cases where such interactions may play an important role. Importantly this article sets out to highlight where such interactions could be operating in order to highlight the potential wealth of investigations to be had in this area rather than categorically claiming such interactions are in operation. For asymmetric catalysis this is particularly important as the geometry of a transition state dictates the stereochemical outcome of the reaction, this article provides a perspective on such phenomena.

A simple visual sensor with the potential for determining the concentration of fluoride in water at environmentally significant levels

We have developed a simple and robust fluorescence based boronic-acid molecular sensor for determining the concentration of fluoride in water at environmentally significant levels. The simplicity of the method and the ability to measure fluoride in water between 0.1 and 1.5 ppm is particularly noteworthy given the WHO requirements for detecting levels of fluoride in drinking water below 1.5 ppm.

Recent advances in the use of chiral metal complexes with achiral ligands for application in asymmetric catalysis

This perspective describes recent progress in asymmetric catalysis with chiral only-at-metal complexes displaying Λ/Δ enantiomorphs in the absence of central chirality within the ligands, with an emphasis on Ir(III) and Rh(III) systems. The good selectivity achieved when using these complexes in asymmetric catalysis has been demonstrated in asymmetric transformations through various mechanisms, including hydrogen-bond donor–acceptor, secondary amine or Bronsted base hydrogen-bond donor bifunctional catalysis, Lewis acid and photoredox catalysis under mild reaction conditions. This perspective highlights the widening field of chiral-at-metal catalysis and presents a selection of asymmetric transformations which have been successfully carried out using them.

Analysis of protein glycation using phenylboronate acrylamide gel electrophoresis

The incorporation of the specialized carbohydrate affinity ligand methacrylamido phenylboronic acid in polyacrylamide gels for SDS‐PAGE analysis has been successful for the separation of carbohydrates and has here been adapted for the analysis of post‐translationally modified proteins. While conventional SDS‐PAGE analysis cannot distinguish between glycated and unglycated proteins, methacrylamido phenylboronate acrylamide gel electrophoresis (mP‐AGE) in low loading shows dramatic retention of δ‐gluconolactone modified proteins, while the mobility of the unmodified proteins remains unchanged. With gels containing 1% methacrylamido phenylboronate, mP‐AGE analysis of gluconoylated recombinant protein Sbi results in the retention of the modified protein at a position expected for a protein that has quadrupled its expected molecular size. Subsequently, mP‐AGE was tested on HSA, a protein that is known to undergo glycation under physiological conditions. mP‐AGE could distinguish between various carbohydrate‐protein adducts, using in vitro glycated HSA, and discriminate early from late glycation states of the protein. Enzymatically glycosylated proteins show no altered retention in the phenylboronate‐incorporated gels, rendering this method highly selective for glycated proteins. We reveal that a trident interaction between phenylboronate and the Amadori cis 1,2 diol and amine group provides the molecular basis of this specificity. These results epitomize mP‐AGE as an important new proteomics tool for the detection, separation, visualization and identification of protein glycation. This method will aid the design of inhibitors of unwanted carbohydrate modifications in recombinant protein production, ageing, diabetes, cardiovascular diseases and Alzheimers disease.

The Development of Boronic Acids as Sensors and Separation Tools

Synthetic receptors for diols that incorporate boronic acid motifs have been developed as new sensors and separation tools. Utilizing the reversible interactions of diols with boronic acids to form boronic esters under new binding regimes has provided new hydrogel constructs that have found use as dye-displacement sensors and electrophoretic separation tools; similarly, molecular boronic-acid-containing chemosensors were constructed that offer applications in the sensing of diols. This review provides a somewhat-personal perspective of developments in boronic-acid-mediated sensing and separation, placed in the context of the seminal works of others in the area, as well as offering a concise summary of the contributions of the co-authors in the area.