Novel glutathione conjugates of phenyl isocyanate identified by ultra‐performance liquid chromatography/electrospray ionization mass spectrometry and nuclear magnetic resonance

Phenyl isocyanate is a highly reactive compound that is used as a reagent in organic synthesis and in the production of polyurethanes. The potential for extensive occupational exposure to this compound makes it important to elucidate its reactivity towards different nucleophiles and potential targets in the body. In vitro reactions between glutathione and phenyl isocyanate were studied. Three adducts of glutathione with phenyl isocyanate were identified using ultra‐performance liquid chromatography/electrospray ionization mass spectrometry and nuclear magnetic resonance (NMR). Mass spectrometric data for these adducts have not previously been reported. Nucleophilic attack on phenyl isocyanate occurred via either the cysteinyl thiol group or the glutamic acid α‐amino group of glutathione. In addition, a double adduct was formed by the reaction of both these moieties. NMR analysis confirmed the proposed structure of the double adduct, which has not previously been described. These results suggest that phenyl isocyanate may react with free cysteines, the α‐amino group and also with lysine residues whose side chain contains a primary amine. Copyright © 2014 John Wiley & Sons, Ltd.     

Dimensional stability of sparse network microstructures formed by photopolymerization‐induced phase separation

The morphology of sparse filament networks formed during photopolymerization‐induced phase separation of mixtures of NOA81 (a UV‐curable thiol‐ene adhesive) in mixed cosolvents consisting of water, diglyme, and polyethers of varying molecular weight was investigated as a function of the molecular weight and relative amount of the polyethers used. During photopolymerization (50 mW/cm^?2 of 365 nm radiation for 60 s) of solutions containing 5 wt % NOA81 and a total oligo‐ether or polyether to water ratio of 8:1 by weight, viscoelastic phase separation produced a sparse network of interconnected NOA81 filaments. During the subsequent evaporation and/or solidification of the solvents, the network compacted significantly via a collapse process that was curtailed by increasing both the weight fraction and molecular weight of the nonvolatile polyether. The influence of mass and momentum transport processes on the collapse of the phase‐separated network and the resultant final morphology was determined with the aid of dimensional analysis, leading to the identification of sedimentation and compaction driven by the motion of the interface as key factors. The networks exhibiting the least collapse combine a high level of interconnectivity and specific surface area with a low occupied volume fraction while being fabricated via a simple, template‐free process. © 2010 Wiley Periodicals, Inc. J Polym Sci Part B: Polym Phys 48: 396–410, 2010     

Facile synthesis of dendrimers combining aza‐Michael addition with Thiol‐yne click chemistry

We report a highly efficient approach to prepare dendrimers by taking advantage of the orthogonal characteristic of aza‐Michael addition and thiol‐yne reactions. A fifth generation dendrimer was synthesized within five steps without protection/activation procedures. The reactions proceed under benign conditions without byproducts, and the target products can be easily purified via extraction or precipitation without chromatography. The structure of each generation dendrimer was characterized using NMR spectroscopy, size exclusion chromatography, and mass spectrometry. The obtained dendrimers can have peripheral amine or alkyne groups. We demonstrated that these groups can be used for selective and specific conjugation with various functional groups. © 2012 Wiley Periodicals, Inc. J Polym Sci Part A: Polym Chem, 2013     

Ratiometric Fluorescent pH Probes Based on Glycopolymers

Effectively detecting pH changes plays a critical role in exploring cellular functions and determining physiological and pathological processes. A novel ratiometric pH probe based on a glycopolymer, armored with properties of serum‐stability, tumor‐targeting, and pH monitoring, is designed. Random copolymers of 2‐(methacrylamido) glucopyranose and fluorescein O‐methacrylate are first synthesized by reversible addition fragmentation chain transfer polymerization. Acryloxyethyl thiocarbamoyl rhodamine B is then attached to the polymer chain to prepare ratiometric fluorescent pH probes via a thiol‐ene reaction. The synthesized polymeric probes are characterized by NMR, gel permeation chromatography, UV–vis spectroscopy, and transmission electron microscopy, and the fluorescence responses are examined in phosphate buffer at different pHs. The cytotoxicity and confocal imaging experiments of the probes are detected using HeLa cells, demonstrating a low toxicity and superior biocompatibility for detecting pH changes in bioapplications.

     

High‐Tg Thiol‐Click Thermoset Networks via the Thiol‐Maleimide Michael Addition

Thiol‐click reactions lead to polymeric materials with a wide range of interesting mechanical, electrical, and optical properties. However, this reaction mechanism typically results in bulk materials with a low glass transition temperature (T_g) due to rotational flexibility around the thioether linkages found in networks such as thiol‐ene, thiol‐epoxy, and thiol‐acrylate systems. This report explores the thiol‐maleimide reaction utilized for the first time as a solvent‐free reaction system to synthesize high‐T_g thermosetting networks. Through thermomechanical characterization via dynamic mechanical analysis, the homogeneity and T_gs of thiol‐maleimide networks are compared to similarly structured thiol‐ene and thiol‐epoxy networks. While preliminary data show more heterogeneous networks for thiol‐maleimide systems, bulk materials exhibit T_gs 80 °C higher than other thiol‐click systems explored herein. Finally, hollow tubes are synthesized using each thiol‐click reaction mechanism and employed in low‐ and high‐temperature environments, demonstrating the ability to withstand a compressive radial 100 N deformation at 100 °C wherein other thiol‐click systems fail mechanically.

     

The power of thiol‐ene chemistry

As a tribute to Professor Charlie Hoyle, we take the opportunity to review the impact of thiol‐ene chemistry on polymer and materials science over the past 5 years. During this time, a renaissance in thiol‐ene chemistry has occurred with recent progress demonstrating its unique advantages when compared with traditional coupling and functionalization strategies. Additionally, the robust nature of thiol‐ene chemistry allows for the preparation of well‐defined materials with few structural limitations and synthetic requirements. To illustrate these features, the utility of thiol‐ene reactions for network formation, polymer functionalization, dendrimer synthesis, and the decoration of three‐dimensional objects is discussed. Also, the development of the closely related thiol‐yne chemistry is described. © 2010 Wiley Periodicals, Inc. J Polym Sci Part A: Polym Chem 48: 743–750, 2010     

Amperometric Detection of Sulfide: An Electrocatalytic Reaction with Ferrocene Carboxylate

The electrocatalytic oxidation of sulfide and sulfhydryl thiol species by ferrocene carboxylate at both glassy carbon and boron doped diamond electrodes is examined. The enhancement in the oxidative current recorded in the presence of sulfide, allowed linear ranges up to 1 mM for sulfide detection to be achieved. In the absence of the mediator, no defined oxidation wave was observed for the direct oxidation of sulfide. Furthermore, the use of hydrodynamic voltammetry produced a limit of detection of 2 μM. The procedure was applied to the recovery of a sulfide spike in river water, with a recovery of 104% obtained.     

Effect of short-chain alcohols on the oil-in-water microemulsion polymerization of styrene

The influence of short-chain alcohols, 1-butanol (C₄OH), 2-pentanol (C₅OH) and 1-hexanol (C₆OH), on the formation of oil-in-water styrene microemulsions and the subsequent free-radical polymerization was studied. Sodium dodecyl sulfate was used as the surfactant. The overall performance of C₄OH as the cosurfactant is quite different from C₅OH and C₆OH. The range of the microemulsion region in decreasing order is C₄OH > C₅OH > C₆OH. The primary parameters selected for the microemulsion polymerization study were the concentrations of cosurfactant and styrene. Only a small fraction of microemulsion droplets initially present in the reaction system can be successfully transformed into latex particles and the remaining droplets serve as a reservoir to supply the growing particles with monomer. Limited flocculation of latex particles also occurs during polymerization and the degree of flocculation is most significant for the C₄OH system. Received: 24 August 1999/Accepted in revised form: 22 October 1999