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Photochemistry of pyruvic acid in water and ice

Citation

Guzman, Marcelo Ioel (2007) Photochemistry of pyruvic acid in water and ice. Dissertation (Ph.D.), California Institute of Technology. http://resolver.caltech.edu/CaltechETD:etd-11292006-181629

Abstract

The 321 nm band photodecarboxylation of aqueous pyruvic acid, PA, solutions was studied in the range 5 <= [PA] <= 100 mM. Prompt and delayed CO2 production stages are detected using TEMPO as a scavenger. These two processes are resolved in the photolysis of frozen solutions: after simultaneous evolution during illumination, additional CO2 is quantified in the dark (Ea ~ 22 kJ mol^-1, T < 268 K). Photodecarboxylation rates of deareated aqueous PA solutions drop a two-fold in the frozen state at 253 K relative to the fluid at 293 K. Benzoylformic acid frozen solutions decarboxylate with no post-illumination CO2 emissions.

^1H-NMR studies of the hydration of aqueous PA between the carbonyl and its hydrated gem-diol species in the frozen state indicate that the fraction of the carbonyl-form of PA, approaches ~ 20% at temperatures below 263 K, regardless of the initial PA concentration in the range 0.1 M >= [PA] <= 4.6 M. PA is cooperatively hydrated while dissolved in increasingly viscous aqueous microfluids often called quasi liquid layers (QLL) down to vitrification.

Electron magnetic resonance signals found in frozen aqueous PA solutions UV-irradiated at 77 K correspond to distant triplet radical pairs separated by ~ 0.9 nm. They originate by photoinduced electron transfer between a triplet excited state PA and ground state PA to produce ^3[PA^+. PA^-.]. The subsequent deprotonation of PA^+. into an acylcarbonyloxyl radical that undergoes ultrafast decarboxylation accounts for the unquenchable source of CO2, even at cryogenic temperatures. Liquid chromatography with UV and ESI-MS detection in combination with ^13C-isotope labeling experiments were used for products identification. The fate of the radical anion PA^-. after protonation into a ketyl-radical is recombination into 2,3-dimethyltartaric acid or addition to a second PA molecule. The later process leads to an unstable 2-oxodicarboxylic acid that eliminates CO2 to produce 2-(3-oxobutan-2-yloxy)-2-hydroxypropanoic.

In conclusion, the possibility of photolysis in ice core records due to penetrating Cerenkov radiation derived from cosmic rays is explored. Potential impacts of the photolysis of organic matter trapped in ice with the subsequent release of CO and CO2 over the last two millennia is analyzed.

Item Type:Thesis (Dissertation (Ph.D.))
Subject Keywords:2-oxopropanoic acid; dicarbonyl; gem-diol; hydration equilibrium; ice; ice core; ketocarboxylic acid; organic aerosol; photochemistry; photodecarboxylation; photoinduced electron transfer; pyruvic acid; quasi liquid layer; reaction mechanism; snow
Degree Grantor:California Institute of Technology
Division:Engineering and Applied Science
Major Option:Environmental Science and Engineering
Thesis Availability:Public (worldwide access)
Research Advisor(s):
  • Hoffmann, Michael R.
Thesis Committee:
  • Hoffmann, Michael R. (chair)
  • Seinfeld, John H.
  • Wennberg, Paul O.
  • Flagan, Richard C.
Defense Date:12 October 2006
Record Number:CaltechETD:etd-11292006-181629
Persistent URL:http://resolver.caltech.edu/CaltechETD:etd-11292006-181629
Default Usage Policy:No commercial reproduction, distribution, display or performance rights in this work are provided.
ID Code:4688
Collection:CaltechTHESIS
Deposited By: Imported from ETD-db
Deposited On:11 Dec 2006
Last Modified:26 Dec 2012 03:11

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PDF (Chapter_1_Introduction.pdf) - Final Version
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PDF (Chapter_2_Background.pdf) - Final Version
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PDF (Chapter_3_Hydration_in_Ice.pdf) - Final Version
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PDF (Chapter_4_Photolysis_in_Water.pdf) - Final Version
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PDF (Chapter_5_EMR_in_Ice.pdf) - Final Version
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PDF (Chapter_6_Photolysis_Ice.pdf) - Final Version
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PDF (Chapter_7_CO_and_CO2_Production_in_Ice_Core_Records.pdf) - Final Version
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