Mechanism and kinetics of the reaction of the Criegee intermediate CH2OO with acetic acid studied using a step-scan Fourier-transform IR spectrometer

SERS-Based Hydrogen Bonding Induction Strategy for Gaseous Acetic Acid Capture and Detection

Surface-enhanced Raman scattering (SERS) can overcome the existing technological limitations, such as complex processes and harsh conditions in gaseous small-molecule detection, and advance the development of real-time gas sensing at room temperature. In this study, a SERS-based hydrogen bonding induction strategy for capturing and sensing gaseous acetic acid is proposed for the detection demands of gaseous acetic acid. This addresses the challenges of low adsorption of gaseous small molecules on SERS substrates and small Raman scattering cross sections and enables the first SERS-based detection of gaseous acetic acid by a portable Raman spectrometer. To provide abundant hydrogen bond donors and acceptors, 4-mercaptobenzoic acid (4-MBA) was used as a ligand molecule modified on the SERS substrate. Furthermore, a sensing chip with a low relative standard deviation (RSD) of 4.15% was constructed, ensuring highly sensitive and reliable detection. The hydrogen bond-induced acetic acid trapping was confirmed by experimental spectroscopy and density functional theory (DFT). In addition, to achieve superior accuracy compared to conventional methods, an innovative analytical method based on direct response hydrogen bond formation (IO-H/Iref) was proposed, enabling the detection of gaseous acetic acid at concentrations as low as 60 ppb. The strategy demonstrated a superior anti-interference capability in simulated breath and wine detection systems. Moreover, the high reusability of the chip highlights the significant potential for real-time sensing of gaseous acetic acid.

Detailed mechanism and kinetics of reactions of anti- and syn-CH3CHOO with HC(O)OH: infrared spectra of conformers of hydroperoxyethyl formate

The reaction of CH3CHOO with HC(O)OH has a large rate coefficient so that it might play a significant role in the formation of secondary organic aerosols (SOA) in the atmosphere. We investigated the detailed mechanism and kinetics of the reactions of Criegee intermediate anti- and syn-CH3CHOO with HC(O)OH with a step-scan Fourier-transform infrared spectrometer by recording time-resolved absorption spectra of transient species and end products produced upon irradiation at 308 nm of a flowing mixture of CH3CHI2/O2/HC(O)OH at 298 K and 60 Torr. Thirteen bands of hydroperoxyethyl formate [HC(O)OCH(CH3)OOH, HPEF], the hydrogen-transferred adduct of CH3CHOO and HC(O)OH, were observed. Careful analysis deconvoluted these bands into absorption of three conformers of HPEF: a transient HPEF (P2*/P3*), a more stable open-form HPEF (mainly P2), and a stable intramolecularly hydrogen-bonded HPEF (mainly P1). At a later period, the end-product formic acetic anhydride [CH3C(O)OC(O)H, FAA], a dehydrated product of HPEF, was observed; this end-product is the same as that observed in CH2OO + CH3C(O)OH. Theoretical calculations on the reaction pathway scheme were performed to elucidate these reaction paths. Syn-CH3CHOO + HC(O)OH produced conformers P2*/P3* initially, followed by conversion to conformers P2, whereas anti-CH3CHOO + HC(O)OH produced conformers P2 and P1 directly. We derived a rate coefficient for the reaction CH3CHOO + HC(O)OH to be k = (2.1 ± 0.7) × 10-10 cm3 molecule-1 s-1 at 298 K and 40-80 Torr; the rate coefficient appeared to show insignificant conformation-specificity. We also found that FAA was produced mainly from the dehydration of the open-form HPEF (P2) with a rate coefficient k = (1420 ± 70) s-1; the intramolecularly hydrogen-bonded HPEF (P1) is stable.

Organic Peroxides in Aerosol: Key Reactive Intermediates for Multiphase Processes in the Atmosphere

Organic peroxides (POs) are organic molecules with one or more peroxide (-O-O-) functional groups. POs are commonly regarded as chemically labile termination products from gas-phase radical chemistry and therefore serve as temporary reservoirs for oxidative radicals (HOx and ROx) in the atmosphere. Owing to their ubiquity, active gas-particle partitioning behavior, and reactivity, POs are key reactive intermediates in atmospheric multiphase processes determining the life cycle (formation, growth, and aging), climate, and health impacts of aerosol. However, there remain substantial gaps in the origin, molecular diversity, and fate of POs due to their complex nature and dynamic behavior. Here, we summarize the current understanding on atmospheric POs, with a focus on their identification and quantification, state-of-the-art analytical developments, molecular-level formation mechanisms, multiphase chemical transformation pathways, as well as environmental and health impacts. We find that interactions with SO2 and transition metal ions are generally the fast PO transformation pathways in atmospheric liquid water, with lifetimes estimated to be minutes to hours, while hydrolysis is particularly important for α-substituted hydroperoxides. Meanwhile, photolysis and thermolysis are likely minor sinks for POs. These multiphase PO transformation pathways are distinctly different from their gas-phase fates, such as photolysis and reaction with OH radicals, which highlights the need to understand the multiphase partitioning of POs. By summarizing the current advances and remaining challenges for the investigation of POs, we propose future research priorities regarding their origin, fate, and impacts in the atmosphere.

Reaction Kinetics of Criegee Intermediates with Nitric Acid

This work investigated the reaction kinetics of HNO₃ with four Criegee intermediates (CIs): CH₂OO, (CH₃)₂COO, methyl vinyl ketone oxide (MVKO), and methacrolein oxide (MACRO). Our results show that these reactions are extremely fast with rate coefficients of (1.51 ± 0.45) × 10^-10, (3.54 ± 1.06) × 10^-10, (3.93 ± 1.18) × 10^-10, and (3.0 ± 1.0) × 10^-10 cm³ s^-1 for reactions of HNO₃ with CH₂OO, (CH₃)₂COO, syn-MVKO, and anti-MACRO, respectively. This is consistent with previous results for the reactions between CIs and carboxylic acids, but the rate coefficient of CH₂OO + HNO₃ in the literature [Foreman Angew. Chem. 2016, 128, 10575] was found to be overestimated by a factor of 3.6. In addition, we did not observe any significant pressure dependence in the HNO₃ reactions with CH₂OO and (CH₃)₂COO under 100-400 Torr. Our results indicate that in a dry area with severe NO_x pollution, the reactions of CIs with HNO₃ and their products may be worthy of attention, but these reactions may be insignificant under high-humidity conditions. However, CI reactions with HNO₃ may not play an important role in the atmospheric removal processes of HNO₃ because of the low concentrations of CIs.