Electrically Detected Paramagnetic Resonance in Ag-Paint-Coated Polycrystalline DPPH

Abstract

We describe a simple experimental method to detect electron paramagnetic resonance (EPR) in polycrystalline 2,2-diphenyl-1-picrylhydrazyl (DPPH) sample, the standard g-marker for EPR spectroscopy, without using a cavity resonator or a prefabricated waveguide. It is shown that microwave (MW) current injected into a layer of silver paint coated on an insulating DPPH sample is able to excite the paramagnetic resonance in DPPH. As the applied dc magnetic field H is swept, the high-frequency resistance of the Ag-paint layer, measured at room temperature with a single port impedance analyzer in the MW frequency range f = 1–2.85 GHz, exhibits a sharp peak at a critical value of the dc field (H = H r) while the reactance exhibits a dispersion-like behavior around the same field value for a given f. H r increases linearly with f. We interpret the observed features in the impedance to EPR in DPPH driven by the Oersted magnetic field arising from the MW current in the Ag-paint layer. We also confirm the occurrence of EPR in DPPH independently using a coplanar-waveguide-based broadband technique in the frequency range of 2–4 GHz.

Carbon Materials Containing Single-Atom Co–N4 Sites Enable Near-Infrared Photooxidation

“…Since the spin state, especially the high spin state, could influence the intersystem crossing (ISC) process via energy transfer, the EPR technique was used to analyze the oxidation states of transition metals and spin states of the catalyst. As calibrated using 2,2-diphenyl-1-picrylhydrazyl (DPPH) with a reference g -value of 2.0036, − a Co 2+ signal peak with a g -value of 3.57 was obtained (Figure S12), which is closest to the high spin signal peak of Co 2+ ( g = 4). , During in situ XPS measurements of Co–N–C-600 under illumination (Figure d), compared to dark conditions, the peaks of Co 3+ and Co 2+ shifted negatively, and the Co 2+ /Co 3+ ratio significantly increased. This suggests that under photoexcitation, electron transfer occurs from the surrounding ligand to the Co metal center, leading to the partial reduction of Co 3+ to Co 2+ (active centers) and an enhancement of the instantaneous magnetic effects. , It can couple with electron spin, thereby altering the spin direction and significantly increasing the intersystem crossing efficiency, consequently enhancing the 1 O 2 generation. , …”

Evaluation and comparison of antioxidant abilities of five bioactive molecules with C–H and O–H bonds in thermodynamics and kinetics

“…2,2-diphenyl-1-picrylhydrazyl (DPPH ˙ ) is a relatively stable neutral radical and is frequently used as reactive oxygen species (ROS) model to evaluate the radical-scavenging activity of antioxidants. 22 It was chosen as the hydrogen atom acceptor, and the second-order rate constants k H (M −1 s −1 ) of the competitive HAT reactions BNAH/DPPH ˙ , (+)-catechin/DPPH ˙ , F420H/DPPH ˙ , and caffeic acid/DPPH ˙ were researched using the stopped-flow technique by monitoring the absorbance decay of DPPH ˙ at 518 nm using pseudo-first-order kinetic model. The kinetic absorbance decay curves of these four HAT reactions are shown in ESI †.…”

New Insights into the Actual H-Abstraction Activities of Important Oxygen and Nitrogen Free Radicals: Thermodynamics and Kinetics in Acetonitrile

“…The nitrogen-centered radical 2,2-diphenyl-1-picrylhydrazyl (DPPH • ) is a relatively stable neutral radical and is frequently used as a reactive oxygen species (ROS) model to evaluate the radical-scavenging activity of an antioxidant. 14 It has been extensively employed in kinetic studies of H-abstraction from a lot of antioxidants. 15 , 16 H-abstraction reactions ( eq 1 ) are one of the most important reactions of these radicals, and a lot of studies have been devoted to the mechanistic investigations of these processes.…”

“…Hydrogen atom transfers (HATs) from C–H and O–H bonds have been the object of extensive investigation. − 2,2′,6,6′-Tetramethylpiperidine 1-oxyl (TEMPO • ) and its derivatives are popular in radical reactions and academic research studies. , Alkoxy radicals such as the cumyloxyl radical (CumO • ) and tert -butoxyl radical ( t BuO • ), alkyl peroxy radicals (ROO • ) such as CumOO • and t BuOO • , and phenol radicals (ArO • ) are all important oxygen-centered radicals that are involved in a variety of chemical and biological processes. The nitrogen-centered radical 2,2-diphenyl-1-picrylhydrazyl (DPPH • ) is a relatively stable neutral radical and is frequently used as a reactive oxygen species (ROS) model to evaluate the radical-scavenging activity of an antioxidant . It has been extensively employed in kinetic studies of H-abstraction from a lot of antioxidants. , H-abstraction reactions (eq ) are one of the most important reactions of these radicals, and a lot of studies have been devoted to the mechanistic investigations of these processes. …”