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| Author(s): |
Adriana Correia de Velosa
Total Authors: 1
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| Document type: | Master's Dissertation |
| Press: | São Paulo. |
| Institution: | Universidade de São Paulo (USP). Conjunto das Químicas (IQ e FCF) (CQ/DBDCQ) |
| Defense date: | 2003-12-22 |
| Examining board members: |
Etelvino Jose Henriques Bechara;
Paolo Di Mascio;
Iseli Lourenço Nantes
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| Advisor: | Etelvino Jose Henriques Bechara |
| Field of knowledge: | Physical Sciences and Mathematics - Chemistry |
| Indexed in: | Banco de Dados Bibliográficos da USP-DEDALUS |
| Location: | Universidade de São Paulo. Biblioteca do Conjunto das Químicas; CQ T/574.19121; V443e |
| Abstract | |
Triplet carbonyls can be named reactive oxygen species once they behave chemically as alkyloxyl radicals and therefore can potentially drive beneficial and deleterious processes in biological systems. In the case of lipid peroxidation, these species have been found not only to be reaction products but also to amplify the radical chain by hydrogen abstraction of polyunsatured lipid molecules. With the aim of finding efficient and reliable chemical probes for triplet carbonyls, we studied here the quenching properties of conjugated dienes, namely 2,4-hexadienoate and 2,4- pentadienoate anions and corresponding alkyl esters, upon triplet acetone generated either chemically (thermolysis of tetramethyl-1 ,2-dioxetane) or enzymically (aerobic oxidation of isobutanal/horseradish peroxidase). As expected, the quenching rate constants were found to be diffusion controlled, although those for the pentadienoate derivatives were 3-fold lower than those measured for the hexadienoates. Therefore, independently of the presence of allylic hydrogens in the diene probe, the triplet acetone quenching occurred by a physical process followed by cis,trans-isomerization, without hydrogen abstraction from the quencher. The reactivity of the studied dienes towards oxygen reactive species known to be formed during lipid peroxidation, such as singlet oxygen, and peroxyl, hydroxyl and superoxide radicals, was also investigated to assure they would not interfere with the radical lipoperoxidation chain. Indeed, none of the dienes showed antioxidant activity on classical model systems. Preliminary experiments with model systems widely used to study lipid peroxidation showed that the trans, trans-ethyl sorbate can inhibit the mitochondrial swelling induced by enzymically formed triplet benzophenone and to quench the chemiluminescence of microsome preparations challenged with iron/ascorbate. This is in agreement with reported work showing that the lipid peroxidation chain associated with mitochondria permeabilization and polyunsaturated fatty acid peroxidation is amplified by intermediate triplet carbonyl products. Altogether our data indicate that conjugated dienes can be used as specific quenchers of triplet carbonyls formed in biological systems without reacting with other reactive intermediates. (AU) | |