Abstract:Acidity
changes the physical properties of atmospheric aerosol
particles and the mechanisms of reactions that occur therein and on
the surface. Here, we used surface-sensitive pneumatic ionization
mass spectrometry to investigate the effects of pH on the heterogeneous
reactions of aqueous α-terpineol (C10H17OH), a representative monoterpene alcohol, with gaseous ozone. Rapid
(≤10 μs) ozonolysis of α-terpineol produced Criegee
intermediates (CIs, zwitterionic/diradical carbonyl oxides) on the
surface of water m… Show more
“…13 More detailed assignments have been published elsewhere. 13,15,36 In secondary organic aerosol or in highly acidic water (pH < 4), 7,15 some α-HHs may form cyclic peroxyhemiacetals via intramolecular rearrangement, but this was not the case under the present experimental conditions (pH ≥ 4.5). Also, we previously confirmed that the contribution of the backward reaction between H 2 O 2 and the functionalized aldehyde to regenerate the α-terpineol α-HHs was negligible.…”
Section: ■ Materials and Methodsmentioning
confidence: 59%
“…Then, the Criegee intermediates rapidly isomerize 24,34−36 or react with water to produce the corresponding α-HHs, which are detected as the Cl − adducts, α-HH-Cl − (m/z 255/257). 13,14,36 In bulk water ([H 2 O] = 55.6 M), the hydration of the Criegee intermediates to produce the α-HHs is expected to be the dominant pathway. 15,33 We recently reported that α-HHs decompose in bulk water to form H 2 O 2 and the corresponding functionalized aldehyde, which then undergoes hydration to form a functionalized geminal diol (Scheme 1).…”
Ozonolysis of unsaturated organic species with water produces α-hydroxyalkylhydroperoxides (α-HHs), which are reactive intermediates that lead to the formation of H 2 O 2 and multifunctionalized species in atmospheric condensed phases. Here, we report temperaturedependent rate coefficients (k) for the aqueous-phase decomposition of α-terpineol α-HHs at 283−318 K and terpinen-4-ol α-HHs at 313−328 K. The temporal profiles of α-HH signals, detected as chloride adducts by negative-ion electrospray mass spectrometry, showed singleexponential decay, and the derived first-order k for α-HH decomposition increased as temperature increased, e.g., k(2882) × 10 −3 s −1 for α-terpineol α-HHs at pH 6.1. Arrhenius plot analysis yielded activation energies of 17.9 ± 0.7 (pH 6.1) and 17.1 ± 0.2 kcal mol −1 (pH 6.2) for the decomposition of α-terpineol and terpinen-4-ol α-HHs, respectively. Activation energies of 18.6 ± 0.2 and 19.2 ± 0.5 kcal mol −1 were also obtained for the decomposition of α-terpineol α-HHs in acidified water at pH 5.3 and 4.5, respectively. Theoretical kinetic and thermodynamic calculations confirmed that both water-catalyzed and proton-catalyzed mechanisms play important roles in the decomposition of these α-HHs. The relatively strong temperature dependence of k suggests that the lifetime of these α-HHs in aqueous phases (e.g., aqueous aerosols, fog, cloud droplets, wet films) is controlled not only by the water content and pH but also by the temperature of these media.
“…13 More detailed assignments have been published elsewhere. 13,15,36 In secondary organic aerosol or in highly acidic water (pH < 4), 7,15 some α-HHs may form cyclic peroxyhemiacetals via intramolecular rearrangement, but this was not the case under the present experimental conditions (pH ≥ 4.5). Also, we previously confirmed that the contribution of the backward reaction between H 2 O 2 and the functionalized aldehyde to regenerate the α-terpineol α-HHs was negligible.…”
Section: ■ Materials and Methodsmentioning
confidence: 59%
“…Then, the Criegee intermediates rapidly isomerize 24,34−36 or react with water to produce the corresponding α-HHs, which are detected as the Cl − adducts, α-HH-Cl − (m/z 255/257). 13,14,36 In bulk water ([H 2 O] = 55.6 M), the hydration of the Criegee intermediates to produce the α-HHs is expected to be the dominant pathway. 15,33 We recently reported that α-HHs decompose in bulk water to form H 2 O 2 and the corresponding functionalized aldehyde, which then undergoes hydration to form a functionalized geminal diol (Scheme 1).…”
Ozonolysis of unsaturated organic species with water produces α-hydroxyalkylhydroperoxides (α-HHs), which are reactive intermediates that lead to the formation of H 2 O 2 and multifunctionalized species in atmospheric condensed phases. Here, we report temperaturedependent rate coefficients (k) for the aqueous-phase decomposition of α-terpineol α-HHs at 283−318 K and terpinen-4-ol α-HHs at 313−328 K. The temporal profiles of α-HH signals, detected as chloride adducts by negative-ion electrospray mass spectrometry, showed singleexponential decay, and the derived first-order k for α-HH decomposition increased as temperature increased, e.g., k(2882) × 10 −3 s −1 for α-terpineol α-HHs at pH 6.1. Arrhenius plot analysis yielded activation energies of 17.9 ± 0.7 (pH 6.1) and 17.1 ± 0.2 kcal mol −1 (pH 6.2) for the decomposition of α-terpineol and terpinen-4-ol α-HHs, respectively. Activation energies of 18.6 ± 0.2 and 19.2 ± 0.5 kcal mol −1 were also obtained for the decomposition of α-terpineol α-HHs in acidified water at pH 5.3 and 4.5, respectively. Theoretical kinetic and thermodynamic calculations confirmed that both water-catalyzed and proton-catalyzed mechanisms play important roles in the decomposition of these α-HHs. The relatively strong temperature dependence of k suggests that the lifetime of these α-HHs in aqueous phases (e.g., aqueous aerosols, fog, cloud droplets, wet films) is controlled not only by the water content and pH but also by the temperature of these media.
“…The reaction rate acceleration can stem from an increase in reactant concentration (molecular crowding) or the stabilization of a transition state (or a combination of both); however, a full understanding of this mechanism remains lacking. The enhancement of redox reactions has been broadly studied in this context, with prominent examples including H-abstraction by OH, ozonolysis − and ozonations, Fenton and Fenton-like reactions, Dakin and Baeyer–Villiger oxidations, halide anion oxidation by OH and O 3 , and the spontaneous formation of hydrogen peroxide and spontaneous reduction of organic molecules at the neat water surface.…”
Chemistry on water is a fascinating area of research. The surface of water and the interfaces between water and air or hydrophobic media represent asymmetric environments with unique properties that lead to unexpected solvation effects on chemical and photochemical processes. Indeed, the features of interfacial reactions differ, often drastically, from those of bulk-phase reactions. In this Perspective, we focus on photoinduced oxidation reactions, which have attracted enormous interest in recent years because of their implications in many areas of chemistry, including atmospheric and environmental chemistry, biology, electrochemistry, and solar energy conversion. We have chosen a few representative examples of photoinduced oxidation reactions to focus on in this Perspective. Although most of these examples are taken from the field of atmospheric chemistry, they were selected because of their broad relevance to other areas. First, we outline a series of processes whose photochemistry generates hydroxyl radicals. These OH precursors include reactive oxygen species, reactive nitrogen species, and sulfur dioxide. Second, we discuss processes involving the photooxidation of organic species, either directly or via photosensitization. The photochemistry of pyruvic acid and fatty acid, two examples that demonstrate the complexity and versatility of this kind of chemistry, is described. Finally, we discuss the physicochemical factors that can be invoked to explain the kinetics and thermodynamics of photoinduced oxidation reactions at aqueous interfaces and analyze a number of challenges that need to be addressed in future studies.
“…These results indicated that α-TOH shows interfacial-activity, in agreement with previous interfacial properties reported for other flavors and essential oils by Turina, Nolan, Zygadlo, Perillo (2006) and Arneodo, Baszkin, Benoit, Fellous, Thies (1988) 24 , 25 . α-TOH (C 10 H 18 O; M w : 154.25 g mol −1 ) is sparingly soluble in water, exhibiting a partition coefficient (log K ow ) and water solubility 26 estimated as 2.6 and 2.4 g L −1 , respectively. This value is 82 times higher than the water solubility of limonene (C 10 H 16 ; M w : 136.24 g mol −1 ) 27 , its non-hydroxylated counterpart.…”
Section: Resultsmentioning
confidence: 99%
“…In turn, its ring structure is a non-polar region. Therefore, like for other oxygenated monoterpenoids 26 , α-TOH presents an amphiphilic character, impacting directly in its ability to lower the IFT between two immiscible liquids. Fig.…”
In this study, the interfacial ability of α-terpineol (α-TOH) was reported, followed by its trapping into oil-in-water (O/W) nanoemulsion as active-ingredient and the long-term observation of this nanosystem influenced by the storage-time (410-days) and temperature (5, 25, 50 °C). The results indicated that the α-TOH can reduce the interfacial tension on the liquid-liquid interface (ΔG°m = −1.81 KJ mol−1; surface density = 8.19 × 10−6 mol m−2; polar head group area = 20.29 Å2), in the absence or presence of surfactant. The O/W nanoemulsion loaded with a high amount of α-TOH (90 mg mL−1; 9α-TOH-NE) into the oil phase was successfully formulated. Among the physical parameters, the mean droplet diameter (MDD) showed a great thermal dependence influenced by the storage-temperature, where the Ostwald ripening (OR) was identified as the main destabilizing phenomena that was taking place on 9α-TOH-NE at 5 and 25 °C along with time. Despite of the physical instability, the integrity of both nanoemulsion at 5 °C and 25 °C was fully preserved up to 410th day, displaying a homogeneous and comparable appearance by visual observation. On contrary, a non-thermal dependence was found for chemical stability, where over 88% of the initial amount of the α-TOH nanoemulsified remained in both 9α-TOH-NE at 5 and 25 °C, up to 410th day. Beyond the key data reported for α-TOH, the importance of this research relies on the long-term tracking of a nanostructured system which can be useful for scientific community as a model for a robust evaluation of nanoemulsion loaded with flavor oils.
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