TY - JOUR
T1 - Reactivity of Ketyl and Acetyl Radicals from Direct Solar Actinic Photolysis of Aqueous Pyruvic Acid
AU - Eugene, Alexis J.
AU - Guzman, Marcelo I.
N1 - Publisher Copyright:
© 2017 American Chemical Society.
PY - 2017/4/20
Y1 - 2017/4/20
N2 - The variable composition of secondary organic aerosols (SOA) contributes to the large uncertainty for predicting radiative forcing. A better understanding of the reaction mechanisms leading to aerosol formation such as for the photochemical reaction of aqueous pyruvic acid (PA) at λ ≥ 305 nm can contribute to constrain these uncertainties. Herein, the photochemistry of aqueous PA (5-300 mM) continuously sparged with air is re-examined in the laboratory under comparable irradiance at 38° N at noon on a summer day. Several analytical methods are employed to monitor the time series of the reaction, including (1) the derivatization of carbonyl (C=O) functional groups with 2,4-dinitrophenylhydrazine (DNPH), (2) the separation of photoproducts by ultrahigh pressure liquid chromatography (UHPLC) and ion chromatography (IC) coupled to mass spectrometry (MS), (3) high resolution MS, (4) the assignment of 1H NMR and 13C gCOSY spectroscopic features, and (5) quantitative 1H NMR. The primary photoproducts are 2,3-dimethyltartaric acid and unstable 2-(1-carboxy-1-hydroxyethoxy)-2-methyl-3-oxobutanoic acid, a polyfunctional β-ketocarboxylic acid with eight carbons (C8) that quickly decarboxylates into 2-hydroxy-2-((3-oxobutan-2-yl)oxy)propanoic acid. Kinetic isotope effect studies performed for the first time for this system reveal the existence of tunneling during the initial loss of PA. Thus, the KIEs support a mechanism initiated by photoinduced proton coupled electron transfer (PCET). Measured reaction rates at variable initial [PA]0 were used to calculate the sum of the quantum yields for the products, which displays a hyperbolic dependence: -Φproduct = 1.99 [PA]0/(113.2 + [PA]0). The fast photochemical loss of aqueous PA with an estimated lifetime of 21.7 min is interpreted as a significant atmospheric sink for this species. The complexity of these aqueous phase pathways indicates that the solar photochemistry of an abundant α-ketocarboxylic acid can activate chemical processes for SOA formation.
AB - The variable composition of secondary organic aerosols (SOA) contributes to the large uncertainty for predicting radiative forcing. A better understanding of the reaction mechanisms leading to aerosol formation such as for the photochemical reaction of aqueous pyruvic acid (PA) at λ ≥ 305 nm can contribute to constrain these uncertainties. Herein, the photochemistry of aqueous PA (5-300 mM) continuously sparged with air is re-examined in the laboratory under comparable irradiance at 38° N at noon on a summer day. Several analytical methods are employed to monitor the time series of the reaction, including (1) the derivatization of carbonyl (C=O) functional groups with 2,4-dinitrophenylhydrazine (DNPH), (2) the separation of photoproducts by ultrahigh pressure liquid chromatography (UHPLC) and ion chromatography (IC) coupled to mass spectrometry (MS), (3) high resolution MS, (4) the assignment of 1H NMR and 13C gCOSY spectroscopic features, and (5) quantitative 1H NMR. The primary photoproducts are 2,3-dimethyltartaric acid and unstable 2-(1-carboxy-1-hydroxyethoxy)-2-methyl-3-oxobutanoic acid, a polyfunctional β-ketocarboxylic acid with eight carbons (C8) that quickly decarboxylates into 2-hydroxy-2-((3-oxobutan-2-yl)oxy)propanoic acid. Kinetic isotope effect studies performed for the first time for this system reveal the existence of tunneling during the initial loss of PA. Thus, the KIEs support a mechanism initiated by photoinduced proton coupled electron transfer (PCET). Measured reaction rates at variable initial [PA]0 were used to calculate the sum of the quantum yields for the products, which displays a hyperbolic dependence: -Φproduct = 1.99 [PA]0/(113.2 + [PA]0). The fast photochemical loss of aqueous PA with an estimated lifetime of 21.7 min is interpreted as a significant atmospheric sink for this species. The complexity of these aqueous phase pathways indicates that the solar photochemistry of an abundant α-ketocarboxylic acid can activate chemical processes for SOA formation.
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U2 - 10.1021/acs.jpca.6b11916
DO - 10.1021/acs.jpca.6b11916
M3 - Article
C2 - 28362101
AN - SCOPUS:85019906679
SN - 1089-5639
VL - 121
SP - 2924
EP - 2935
JO - Journal of Physical Chemistry A
JF - Journal of Physical Chemistry A
IS - 15
ER -