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Substituent Effects in Chain-Breaking Aryltellurophenol Antioxidants
Uppsala University, Disciplinary Domain of Science and Technology, Chemistry, Department of Chemistry - BMC, Organic Chemistry. (Lars Engman)
Uppsala University, Disciplinary Domain of Science and Technology, Chemistry, Department of Chemistry - BMC, Organic Chemistry. (Lars Engman)ORCID iD: 0000-0003-0689-3180
Uppsala University, Disciplinary Domain of Science and Technology, Chemistry, Department of Chemistry - Ångström, Inorganic Chemistry. (Henrik Ottosson)
Uppsala University, Disciplinary Domain of Science and Technology, Chemistry, Department of Chemistry - Ångström, Inorganic Chemistry. (Henrik Ottosson)
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(English)Manuscript (preprint) (Other academic)
Abstract [en]

2-Aryltellurophenols substituted in the aryltelluro or phenolic part of the molecule were prepared by lithiation of the corresponding O-THP-protected 2-bromophenol, followed by reaction with a suitable diaryl ditelluride and deprotection. In a two-phase system containing N-acetylcysteine as a co-antioxidant in the aqueous phase, all compounds quenched lipid peroxyl radicals more efficiently than α-tocopherol with 3 to 5-fold longer inhibition times. Compounds carrying electron donating para-substituents in the phenolic or aryltelluro part of the molecule showed the best results. The mechanism for quenching of peroxyl radicals was discussed in the light of calculated OH bond dissociation energies, deuterium labeling experiments and studies of thiol-consumption in the aqueous phase. 

National Category
Organic Chemistry
Research subject
Chemistry with specialization in Organic Chemistry
Identifiers
URN: urn:nbn:se:uu:diva-329202OAI: oai:DiVA.org:uu-329202DiVA: diva2:1139908
Note

Poon, J. and Yan, J. are equally contributing.

Available from: 2017-09-10 Created: 2017-09-10 Last updated: 2017-09-16
In thesis
1. Regenerable Organochalcogen Antioxidants: An Explorative Study
Open this publication in new window or tab >>Regenerable Organochalcogen Antioxidants: An Explorative Study
2017 (English)Doctoral thesis, comprehensive summary (Other academic)
Abstract [en]

Antioxidants are widely used to protect organic materials from damages caused by autoxidation, an oxidation process that occurs under normal aerobic conditions. In this thesis, novel multifunctional organoselenium and organotellurium antioxidants were designed, synthesized, and evaluated in search for compounds with better radical-trapping capacity, regenerability, and hydroperoxide-decomposing ability.

Selenium was incorporated into ebselenols and hydroxy-2,3-dihydrobenzo[b]selenophenes and tellurium into diaryl disulfides and aryltellurophenols. All newly developed antioxidants were evaluated in a chlorobenzene/water two-phase lipid peroxidation system containing suitable co-antioxidants in the aqueous phase. Ebselenol carrying a hydroxyl group (OH) ortho to selenium showed a two-fold longer inhibition time than the reference α-tocopherol in the presence of aqueous-phase ascorbic acid. 2,3-Dihydrobenzo[b]selenophenes carrying a 5- or 7-OH outperformed α-tocopherol both when it comes to radical-trapping capacity and regenerability. Alkyltellurothiophenols, in situ formed from their corresponding disulfides by tris(2-carboxyethyl)phosphine, were also efficient regenerable radical-trapping antioxidants. The consumption of N-acetylcysteine in the water phase was followed and found to be limiting for the duration of the inhibition. The hydroperoxide-decomposing ability of all organoselenium antioxidants was evaluated. Ebselenols were often better glutathione peroxidase mimics than the parent.

In an effort to find out more about antioxidant mechanisms, aryltellurophenols carrying electron donating and electron withdrawing groups in the phenolic or aryltelluro parts were synthesized and OH bond dissociation enthalpies, BDEO-Hs, were calculated. Compounds carrying electron donating groups in the phenolic or aryltelluro part of the molecule showed the best radical-trapping capacity. Deuterium labelling experiments suggested that hydrogen atom transfer could be the rate-limiting step in the antioxidant mechanism.  

Place, publisher, year, edition, pages
Uppsala: Acta Universitatis Upsaliensis, 2017. 70 p.
Series
Digital Comprehensive Summaries of Uppsala Dissertations from the Faculty of Science and Technology, ISSN 1651-6214 ; 1556
Keyword
autoxidation, antioxidant, selenium, tellurium, regenerable, multifunctional, radical-trapping, hydroperoxide-decomposing, co-antioxidant
National Category
Organic Chemistry
Research subject
Chemistry with specialization in Organic Chemistry
Identifiers
urn:nbn:se:uu:diva-329217 (URN)978-91-513-0068-9 (ISBN)
Public defence
2017-10-27, B7:101a, BMC, Husargatan 3, 751 23, Uppsala, 09:30 (English)
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Supervisors
Available from: 2017-10-05 Created: 2017-09-10 Last updated: 2017-10-18

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