Capture of Hydroxyl Radicals by Hydronium Cations in Water Microdroplets

Dong, Xiao; Meng, Yifan; Xu, Yuan; Jin, Shuihui; Song, Xiaowei; Zare, Richard N.; Zhang, Xinxing

doi:10.1002/ange.202207587

Cited by 12 publications

(10 citation statements)

References 39 publications

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“…It is postulated that there is a high electric field (∼10 9 V/m) at the microdroplets’ surface due to either the formation of electric double layers or the alignment of the free O–H bonds of water molecules. − This high field can even pull electrons out of hydroxide ions, − resulting in an electron and a hydroxyl radical. The electron is responsible for the above-mentioned reduction reactions, − and the hydroxyl radical can cause oxidation reactions or combine with others to form H 2 O 2 . − In some cases, reduction by the electron and oxidation by OH were observed simultaneously for the same substrate molecules . It was also observed that, on the aerial surface of air bubbles in water, the oxidation potentials of OH – to OH occurred 0.7 V below redox tabled values as measured by electrochemical methods, so it should be easier for OH – to give up the electron at the air–water interface compared to the bulk.…”

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confidence: 99%

Spontaneous Reduction of Transition Metal Ions by One Electron in Water Microdroplets and the Atmospheric Implications

Zhang

Liang

et al. 2023

J. Am. Chem. Soc.

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Freshman chemistry teaches that Fe 3+ and Cu 2+ ions are stable in water solutions, but their reduced forms, Fe 2+ and Cu + , cannot exist in water as the major oxidation state due to the fast oxidation by O 2 and/or disproportionation. Contrary to these well-known facts, significant fractions of dissolved Fe and Cu species exist in their reduced oxidation states in atmospheric water such as deliquesced aerosols, clouds, and fog droplets. Current knowledge attributes these phenomena to the stabilization of the lower oxidation states by the complexation of ligands and the various photochemical or thermal pathways that can reduce the higher oxidation states. In this study, by spraying the water solutions of transition metal ions into microdroplets, we show the results of the spontaneous reduction of ligated Fe(III) and Cu(II) species into Fe(II) and Cu(I) species, presenting a previously unknown source of reduced transition metal ions in atmospheric water. It is the spontaneously generated electrons in water microdroplets that are responsible for the reduction. Control experiments in the atmosphere and in a glove box filled with precisely controlled gaseous contents reveal that O 2 , CO 2 , and NO 2 are the major competitors for the electrons, forming O 2 − , HCO 2 − , and NO 2 − , respectively. Taking these findings together, we opine that microdroplet chemistry might play significant but previously underestimated roles in atmospheric redox chemistry.

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confidence: 99%

Spontaneous Reduction of Transition Metal Ions by One Electron in Water Microdroplets and the Atmospheric Implications

Zhang

Liang

et al. 2023

J. Am. Chem. Soc.

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“…In the case to oxidize aromatic rings, it showed characteristic of adding •OH radicals onto the compounds, reacting with a compound by H abstraction or addition. (37,38) 6…”

Section: Resultsmentioning

confidence: 99%

Silica particles convert thiol-containing molecules to disulfides

Kołasiński

Zare

2023

Preprint

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Synthetic amorphous silica is a common food additive and a popular cosmetic ingredient. Mesoporous silica nanoparticles are also widely studied for their potential use in drug delivery and imaging applications because of their unique properties, such as tunable pore sizes, large surfaces areas, and assumed biocompatibility. Such a nanomaterial, when consisting of pure silicon dioxide, is generally considered to be inert, but in this study, we showed that oxidation yields for different compounds were facilitated by simply incubating aqueous solutions with pure silica particles in the dark. Three thiol-containing molecules, L-cysteine, glutathione, and D-penicillamine, were studied separately, and it was found that more than 95% of oxidation happened after incubating any of these compounds with mesoporous silica nanoparticles in the dark for a day at room temperature. Oxidation increased over incubation time and more oxidation was found for particles having larger surface areas. For nonporous silica nanoparticles, yields of oxidation were different based on structures of molecules, correlating with steric hindrance while accessing surfaces. We propose that the silyloxy radical on silica surfaces is what facilitates oxidation. Density functional theory calculations were conducted for total energy changes for reactions between different aqueous species and silicon dioxide surfaces. These calculations identified two most plausible pathways of lowest energy to generate SiO• radicals from water radical cations and •OH radicals, previously known to exist at water interfaces.

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“…On the other hand, the strong electric eld established by the microdroplet electrical double layer (also reported to be in the order of 1 V nm −1 ) was recently postulated by Zare and others to generate hydroxyl radicals in the liquid phase which contributed to the observed spontaneous formation of hydrogen peroxide. 25,34 Isotope labeling method was used to determine the origin of the oxygen atom. The analyte was L-phosphatidylcholine (PC 18 : 1/18 : 1) with two double bonds (one at each fatty acid chain).…”

Section: Source Of Oxygen Atomsmentioning

confidence: 99%