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Gewählte Publikation:

Bamonti, L; Hosoya, T; Pirker, KF; Bohmdorfer, S; Mazzini, F; Galli, F; Netscher, T; Rosenau, T; Gille, L.
(2013): Tocopheramines and tocotrienamines as antioxidants: ESR spectroscopy, rapid kinetics and DFT calculations
BIOORGAN MED CHEM. 2013; 21(17): 5039-5046. FullText FullText_BOKU

Abstract:
Tocopheramines (TNH2) and tocotrienamines (T3NH2) are analogues of tocopherols (TOH) and tocotrienols in which phenolic OH is replaced by NH2. It was shown in previous studies that TNH2 and T3NH2 act as potent antioxidants. In this study we compared the one-electron oxidation of TNH2/T3NH2 by diphenyl picryl hydrazyl (DPPH.) and galvinoxyl (GOX.) radicals with the one of alpha-TOH as a reference compound using ESR spectroscopy, stopped flow spectrophotometry and density functional theory (DFT) calculations. ESR spectroscopy revealed the presence of tocopheramine radicals during electrochemical oxidation of alpha-TNH2. Kinetic measurements demonstrated that in apolar n-hexane TNH2/T3NH2 derivatives reacted two to three orders of magnitude slower than alpha-TOH with the model radicals. DFT calculations indicated that this correlates well with the higher bond dissociation energy (BDE) for N-H in TNH2 than for O-H in alpha-TOH in pure H-atom transfer (HAT). In the more polar medium ethanol TNH2/T3NH2 derivatives partially reacted faster than alpha-TOH depending on the reaction partner. DFT calculations suggest that this is due to reaction mechanisms alternative to HAT. According to thermochemistry data sequential proton loss and electron transfer (SPLET) is more favored for alpha-TOH in ethanol than for TNH2. Therefore, for TNH2 a contribution of the alternative mechanism of sequential electron transfer-proton transfer (SET-PT) could be a possible explanation. These data show that the antioxidant reactivity strongly depends on the structure, reaction partners and environment. Accoriling to these findings TNH2/T3NH2 should be superior as antioxidants over alpha-TOH in polar head group regions of membranes but not in the apolar core of lipid bilayers. (C) 2013 Elsevier Ltd. All rights reserved.
Autor*innen der BOKU Wien:
Böhmdorfer Stefan
Hosoya Takashi
Pirker Katharina
Rosenau Thomas

Find related publications in this database (Keywords)
Tocopheramines
Radicals
Stopped flow spectrophotometry
ESR spectroscopy
DFT calculations


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