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Antioxidants
Published in Leslie R. Rudnick, Lubricant Additives, 2017
Robert G. Rowland, Jun Dong, Cyril A. Migdal
It has recently been proposed that this first step actually proceeds by a proton-coupled electron transfer (PCET) mechanism. In this mechanism, a proton is transferred in a σ-bond fashion between heteroatoms (from one oxygen to another in this case), while an electron is simultaneously transferred from an orthogonal orbital on the phenol (generally perpendicular to the aromatic ring, allowing for 2p-π overlap) to a singly occupied molecular orbital (SOMO) on the radical [144]. The steric hindrance provided by the two butyl moieties on the ortho-positions effectively prevents the phenol radical from attacking other hydrocarbons [215]. The phenol radical can react with a second alkyl peroxyl radical to form a peroxycyclohexadienone, which is stable at temperatures up to about 100°C–120°C [216,217]. Since each phenol molecule is capable of reacting with two radicals, the stoichiometric factor n = 2 [144,216].
Nanoconfinement in advanced oxidation processes
Published in Critical Reviews in Environmental Science and Technology, 2023
Bo-Tao Zhang, Zihan Yan, Yuchun Liu, Zhuo Chen, Yikai Zhang, Maohong Fan
A catalyst with dual catalytic sites by confining single iron atoms in 2D MoS2 nanosheets has demonstrated synergistic catalysis as highly reactive and stable catalysts for efficient catalytic oxidation via PDS activation (Huang et al., 2020). The high catalytic activity was attributed to the strong metal-support interactions and the low formal oxidation state of Fe by density functional theory (DFT) calculations. The vacancy-rich N@FexOy@MoS2 catalyst has a density of catalytic sites, dispersibility and conductivity for fast mass and electron transport for efficient PMS activation (Ye et al., 2022). The co-catalyst MoS2 accelerates the Fe redox cycle in a synergistic adsorption-driven oxidation process. The single Fe atoms are anchored at the edge Mo vacancies of MoS2 and Fe(II) could be rapidly regenerated through the Mo-S2-Fe-S2-Mo edge configuration due to the electron transfer bridge function of the adjacent S atoms (Zhou et al., 2022). FeS2@2D Mo2C can activate PMS for dye removal by proton-coupled electron transfer under the nanoconfinement effect (Nie et al., 2022).
A simplified Bixon–Jortner–Plotnikov method for fast calculation of radiationless transfer rates in symmetric molecules
Published in Molecular Physics, 2023
A. I. Martynov, A. S. Belov, V. K. Nevolin
Many works are aimed at developing a method for calculating rate constants of radiationless energy transfer, a class of processes of great importance and interest. The dark transfer mediates phenomena such as charge transfer in DNA [1–3] and proton-coupled electron transfer in enzymatic processes [4]. Transfer between excited states plays an important role in OLEDs [5–7] and solar cells [8]. To create such devices, one needs to know the rates of fluorescence (Rad), internal conversion (IC), and intersystem conversion (ISC). The Rad rate can be found easily since it requires only the transition energy and oscillator strength. However, the IC and ISC rates require taking into account electronic-vibrational interactions and the density of states. The existing methods often have a high computational cost because of the need of an exhaustive search over vibrational states. Analytic expressions usually work in a limited range of model parameters. It would be helpful to devise a method that can compute the transfer rate in an acceptable time with a small loss of precision.
A cobalt adduct of an N-hydroxy-piperidinium cation
Published in Journal of Coordination Chemistry, 2022
Sophie W. Anferov, John S. Anderson
In this study, we have synthesized a Co complex of an interesting oxidation and protonation state of TEMPO, a commonly utilized aminoxyl radical. This complex can be characterized and verified via IR spectroscopy and SXRD analysis. DFT studies were used to assess the formation of this complex and suggest it occurs through a multi-site proton coupled electron transfer. This species was also found to be thermally unstable, and we propose that its decomposition occurs through N − O cleavage of the bound TEMPOH2+ fragment to form an oxidized hydroxide complex and neutral 2,2,6,6-tetramethylpiperidine. These results demonstrate the utility of redox-active ligands in stabilizing novel complexes and support the inclusion of other oxidation states of TEMPO in mechanistic proposals.