Document Type

Dissertation

Degree

Doctor of Philosophy (PhD)

Major/Program

Chemistry

First Advisor's Name

Kevin O'Shea

First Advisor's Committee Title

Committee Chair

Second Advisor's Name

Jeffrey A. Joens

Second Advisor's Committee Title

Committee Member

Third Advisor's Name

Shekhar Bhansali

Third Advisor's Committee Title

Committee Member

Fourth Advisor's Name

Christopher J. Dares

Fourth Advisor's Committee Title

Committee Member

Fifth Advisor's Name

Stanislaw Wnuk

Fifth Advisor's Committee Title

Committee Member

Keywords

Environmental Chemistry

Date of Defense

11-12-2020

Abstract

Singlet oxygen, 1O2, can be easily generated by a sensitizer, solar radiation, and molecular oxygen. 1O2 is very important in a range of biological and environmental systems. The products and mechanisms of the 1O2 reactions are well studied in organic solvents, and despite well-established solvent effects, studies on the reactions of the singlet oxygen in aqueous media are limited. Herein, 1O2 reactions with biologically and environmentally relevant conjugated π systems in aqueous solutions are presented. Water-soluble isomeric 1, 3-hexadienes are simple mechanistic probes for the 1O2 reactions since concerted and non-concerted pathways produce distinct products. The isomerization of sorbic acid and sorbic alcohol is commonly used as triplet dissolved organic matter (3DOM*) quenchers. However, contributions from the singlet oxygenation of sorbic acid or alcohol during 3DOM* quantification has been neglected. The major reaction of 1O2 with Sorbic Acid, SCOOH, and sorbic alcohol, SOH, was the [4+2] pathway vii to produce the endoperoxide. The singlet oxygenation of SCOOH and SOH in D2O produced minor products from the [2+2] reaction pathways not observed in methanol-d4 or chloroform-d3. Domoic acid (DA), a potent marine toxin, was readily oxidized upon reaction with 1O2. The [2+2] cycloaddition and ene reactions at the Z double bond were the major singlet oxygenation reaction pathways observed in aqueous media. The bimolecular rate constant for the DA reaction with 1O2 was 5.1 x 105 M-1 s-1. The 1O2 reaction product mixture of DA did not exhibit significant biological activity indicating that singlet oxygenation could be an essential natural detoxification process. Melanin, a pyrrole containing photoprotective pigment in the skin, is subject to irreversible damage by photooxidation. The reactions of singlet oxygen with the model pyrroles produced hydroxypyrrolones (HPOnes) as the major products. The singlet oxygenation of several pyrroles despite varying substitution at the α-carbon yielded identical major products. The bimolecular rate constants of singlet oxygen reactions with the studied pyrroles were from 1.2 to 18.9 x 108 M−1s−1. 1H-pyrrole-2,3,4-tricarboxylic acid (TCOOH-Py), a maker to assess melanin photoaging, reacted with 1O2 at rates near diffusion control, k(1O2+TCOOH-Py)=18.9±0.05 x 108 M−1s−1. TCOOH-Py concentrations may underestimate skin damage.

Identifier

FIDC009232

Previously Published In

Jaramillo, M.; Joens, J. A.; O’Shea, K. E. Fundamental Studies of the Singlet Oxygen Reactions with the Potent Marine Toxin Domoic Acid. Environ. Sci. Technol. 2020, 54 (10), 6073–6081.

Available for download on Wednesday, October 27, 2021

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