2D NMR of the Metabolic Antioxidant Dihydrolipoic Acid and its Derivatives
作者:
SchepkinVictor,
KawabataTeruyuki,
TritschlerHans J.,
PackerLester,
期刊:
Free Radical Research
(Taylor Available online 1996)
卷期:
Volume 25,
issue 3
页码: 195-205
ISSN:1071-5762
年代: 1996
DOI:10.3109/10715769609149045
出版商: Taylor&Francis
关键词: Dihydrolipoic acid;lipoic acid;bisnor dihydrolipoic acid;tetranor dihydrolipoic acid;NMR assignment
数据来源: Taylor
摘要:
Dihydroplipoate and lipoate are physiological thiols which in addition to their coenzyme functions exhibit antioxidant activity. For NMR investigations of their protective mechanism in biological and model systems it is very important to know the full assignment of proton and carbon spectra of these molecules in water (D2O). An unambiguous assignment of proton and carbon NMR spectra has been made for dihydrolipoate and its short chain derivatives bisnor-and tetranor-lipoic acid in D2O and CDCl3solutions using 2D NMR methods.Oxidation of dihydrolipoic acid produces substantial electron density deshielding of the carbons nearest to the SH groups with the largest shift found at the inner SH group (17.79 ppm in D2O, 16.93 in CDCl3) and almost no changes in the tail portion of the molecule. However, bisnor-dihydrolipoic acid and especially tetranor-dihydrolipoic acid have more carbon deshielding near the outer SH group of the molecule which correlates with their known diminished ion chelating activity.Moreover, the proton triplet at position 2 of lipoic acid has strong pH dependence (pK = 4.58) due to the close proximity to the carboxylic group and this feature may be used for monitoring pH.
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