Hydroxyl Radicals Attack Metallic Gold

Reduced Glutathione-Modified Electrode for the Detection of Hydroxyl Free Radicals

Hydroxyl radicals (•OH) are known as essential chemicals for cells to maintain their normal functions and defensive responses. However, a high concentration of •OH may cause oxidative stress-related diseases, such as cancer, inflammation, and cardiovascular disorders. Therefore, •OH can be used as a biomarker to detect the onset of these disorders at an early stage. Reduced glutathione (GSH), a well-known tripeptide for its antioxidant capacity against reactive oxygen species (ROS), was immobilized on a screen-printed carbon electrode (SPCE) to develop a real-time detection sensor with a high selectivity towards •OH. The signals produced by the interaction of the GSH-modified sensor and •OH were characterized using cyclic voltammetry (CV) and electrochemical impedance spectroscopy (EIS). The CV curve of the GSH-modified sensor in the Fenton reagent exhibited a pair of well-defined peaks, demonstrating the redox reaction of the electrochemical sensor and •OH. The sensor showed a linear relationship between the redox response and the concentration of •OH with a limit of detection (LOD) of 49 µM. Furthermore, using EIS studies, the proposed sensor demonstrated the capability of differentiating •OH from hydrogen peroxide (H2O2), a similar oxidizing chemical. After being immersed in the Fenton solution for 1 hr, redox peaks in the CV curve of the GSH-modified electrode disappeared, revealing that the immobilized GSH on the electrode was oxidized and turned to glutathione disulfide (GSSG). However, it was demonstrated that the oxidized GSH surface could be reversed back to the reduced state by reacting with a solution of glutathione reductase (GR) and nicotinamide adenine dinucleotide phosphate (NADPH), and possibly reused for •OH detection.

Reactive Oxygen Species Responsive Cleavable Hierarchical Metallic Supra-Nanostructure

A reactive oxygen species (ROS) responsive cleavable hierarchical metallic supra-nanostructure (HMSN) is reported. HMSN structured with thin branches composed of primary gold (Au) nanocrystals and silver (Ag) nano-linkers is synthesized by a one-pot aqueous synthesis with a selected ratio of Au/Ag/cholate. ROS responsive degradability of HMSN is tested in the presence of endogenous and exogeneous ROS. Significant ROS-responsive structural deformation of HMSN is observed in the ROS exposure with hydrogen peroxide (H2 O2 ) solution. The ROS responsiveness of HMSN is significantly comparable with negligible structural changes of conventional spherical gold nanoparticles. The demonstrated ROS responsive degradation of HMSN is further confirmed in various in vitro ROS conditions of each cellular endogenous ROS and exogeneous ROS generated by photodynamic therapy (PDT) or X-ray radiation. Then, in vivo ROS responsive degradability of HMSN is further evaluated with intratumoral injection of HMSN and exogeneous ROS generation via PDT in a mouse tumor model. Additional in vivo biodistribution and toxicity of intravenously administrated HMSN at 30-day post-injection are investigated for potential in vivo applications. The observed ROS responsive degradability of HMSN will provide a promising option for a type of ROS responsive-multifunctional nanocarriers in cancer treatment and various biomedical applications.

Accelerated degradation of pharmaceuticals by ferrous ion/chlorine process: Roles of Fe(IV) and reactive chlorine species

In this study, we determined the mechanisms and kinetics of the degradations of ibuprofen (IBP) and sulfamethoxazole (SMX), and identified the active species contributions in ferrous ion (Fe(II))/free chlorine (FC) system. Reactive chlorine species (RCS) were the major contributor to the degradations of IBP (73.0%) and SMX (59.3%), respectively, at pH 3. Due to the low reaction rates between Fe(IV) and target pollutants (k_{Fe(IV), IBP} = (1.5 ± 0.03) × 10³ M^-1 s^-1 and k_{Fe(IV), SMX} = (4.8 ± 0.2) × 10³ M^-1 s^-1) and the low [Fe(IV)]_ss ((5.0 ± 0.6) × 10^-8 M), Fe(IV) was not the main contributor and only contributed 0.17% and 0.86% to the degradation of IBP and SMX, respectively, at pH 3. The degradations of pharmaceuticals were facilitated by acidic conditions. Chloride (Cl^-) accelerated the degradation of SMX and had a weak effect on the degradation of IBP. Natural organic matter limited the degradation of IBP and SMX. Overall, we demonstrated that multiple active oxidants (Fe(IV) and RCS) are produced by Fe(II)/FC and elucidated the mechanism of active oxidants degradation of pollutants.

Facile Strategy for Mass Production of Pt Catalysts for Polymer Electrolyte Membrane Fuel Cells Using Low-Energy Electron Beam

There are so many variables affecting the large-scale chemical synthesis of nanoparticles that mass production remains a challenge. Here, using a high-efficiency compact electron beam generator irradiating a low-energy electron beam, we fabricate carbon-supported Pt nanoparticles (Pt/C) in an open chamber to present the applicability of an electron beam to the mass production of metal nanocatalysts for polymer electrolyte membrane fuel cells (PEMFCs). The amount of dispersants (glycerol) and radical scavengers (isopropyl alcohol, IPA), the most important factors in the electron beam-induced fabrication process, is systematically controlled to find the conditions for the synthesis of the particle structure suitable for PEMFC applications. Furthermore, the effects of the structural changes on the electrochemical properties of the catalysts are thoroughly investigated. Through in-depth studies, it is clearly revealed that while dispersants control the nucleation step of monomers affecting the degree of dispersion of nanoparticles, radical scavengers with strong oxidizing power have an effect on the particle growth rate. Therefore, this study is expected to present the applicability of low-energy electron beam to the mass production of metal nanocatalysts for PEMFCs, and to provide insights into the fabrication of nanoparticles using low-energy electron beams.

Rational Design of Ultrathin Gas Barrier Layer via Reconstruction of Hexagonal Boron Nitride Nanoflakes to Enhance the Chemical Stability of Proton Exchange Membrane Fuel Cells

Hexagonal boron nitride (hBN) has great potential as a promising gas barrier layer in proton exchange membrane fuel cells (PEMFCs) as it shows high proton conductivity as well as excellent gas-blocking capability. However, structural defects and mechanical damage during the transfer of the hBN layer and membrane swelling have limited the application of hBN sheets to PEMFCs. Here, an ultrathin gas barrier layer is successfully fabricated on a proton exchange membrane via reconstruction of mechanically exfoliated hBN nanoflakes using a direct spin-coating process. The hBN-coated layer effectively suppresses the gas crossover and inhibits the formation of reactive oxygen radicals in the electrodes without reducing the proton conductivity of the membrane. It is also demonstrated that the structural advantages of hBN-coated gas barrier layers promise high performance of a unit cell even after a open-circuit voltage (OCV) hold test for 100 h. Furthermore, through in-depth postmortem analyses, a time-dependent degradation mechanism of membrane electrode assembly under the OCV condition is rationally proposed.