Water Charge Transfer Accelerates Criegee Intermediate Reaction with H₂O^– Radical Anion at the Aqueous Interface

Abstract

Criegee intermediates (CIs) are important carbonyl oxides that may react with atmospheric trace chemicals and impact the global climate. The CI reaction with water has been widely studied and is a main channel for trapping CIs in the troposphere. Previous experimental and computational reports have largely focused on reaction kinetic processes in various CI−water reactions. The molecular-level origin of CI's interfacial reactivity at the water microdroplet surface (e.g., as found in aerosols and clouds) is unclear. In this study, by employing the quantum mechanical/molecular mechanical (QM/MM) Born−Oppenheimer molecular dynamics with the local second-order Møller− Plesset perturbation theory, our computational results reveal a substantial water charge transfer up to ∼20% per water, which creates the surface H 2 O + /H 2 O − radical pairs to enhance the CH 2 OO and anti-CH 3 CHOO reactivity with water: the resulting strong CI−H 2 O − electrostatic attraction at the microdroplet surface facilitates the nucleophilic attack to the CI carbonyl by water, which may counteract the apolar hindrance of the substituent to accelerate the CI−water reaction. Our statistical analysis of the molecular dynamics trajectories further resolves a relatively long-lived bound CI(H 2 O − ) intermediate state at the air/water interface, which has not been observed in gaseous CI reactions. This work provides insights into what may alter the oxidizing power of the troposphere by the next larger CIs than simple CH 2 OO and implicates a new perspective on the role of interfacial water charge transfer in accelerating molecular reactions at aqueous interfaces.

Kinetics of the Simplest Criegee Intermediate Reaction with Water Vapor: Revisit and Isotope Effect

“…The corresponding reaction pathways have been computed with high-level quantum chemistry methods − and confirmed by further experiments. , Smith et al found that this reaction is faster at a lower temperature and shows a highly negative temperature dependence . We note that a recent theoretical study has mentioned the importance of charge separation on water surfaces promoting reaction between CIs and H 2 O – radical anion …”

High Electric Fields on Water Microdroplets Catalyze Spontaneous and Fast Reactions in Halogen-Bond Complexes

“…The air–water interface is another type of water–hydrophobic interface. In the recent years, water microdroplet chemistry has drawn tremendous attention for its abilities to accelerate chemical reactions by several orders of magnitude compared with the same reactions in bulk water, and to trigger spontaneous reactions that cannot occur in bulk water. − It has been shown in many studies that there is a spontaneous high electric field (as high as 1.4 V/nm) at the air–water interface of microdroplets. − Several studies have reported that the field originates from the formation of electric double layers, or the alignment of the free O–H bonds of the interfacial water molecules, or the partial charge transfer that resulted in the interfacial H 2 O + --H 2 O – pairs. − A plethora of redox reactions can be triggered by the electric field at the air–water interface of water microdroplets, − and more importantly, scalability by microdroplet chemistry becomes practical …”

Water Microdroplets-Initiated Methane Oxidation

“…One way is the direct transfer of single electron from the hydroxyl anion (OH – ) to generate the hydroxyl radical (OH – → OH· + e) facilitated by the strong electric field across the AWI (10 7 V/cm). − Another way involves single-electron transfer from the OH – to H + (H + + OH – → H· + OH·), which is reported as a thermodynamically favorable process in the AWI region (Δ H = −375 kJ mol –1 ) . Many spontaneous redox reactions across the AWI have been successfully observed during this process. − Furthermore, the charge transfer during contact electrification between the water–solid and water–gas interfaces also contribute to the abundant presence of OH·. , With aid of the generated OH· across the AWI, organic syntheses have been readily achieved by the radical-initiated C­(sp 3 )–H activation of toluene in the water microdroplets such its C–N coupling with amines and its C–C coupling with carbon dioxide. , …”