Enhanced Antioxidant Activity under Biomimetic Settings of Ascorbic Acid Included in Halloysite Nanotubes

Antioxidant activity of native vitamin C (ascorbic acid, AH<sub>2</sub>) is hampered by instability in solution. Selective loading of AH<sub>2</sub> into the inner lumen of natural halloysite nanotubes (HNT) yields a composite nanoantioxidant (HNT/AH<sub>2</sub>),...

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Main Authors: Andrea Baschieri (Author), Riccardo Amorati (Author), Tiziana Benelli (Author), Laura Mazzocchetti (Author), Emanuele D'Angelo (Author), Luca Valgimigli (Author)
Format: Book
Published: MDPI AG, 2019-01-01T00:00:00Z.
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Summary:Antioxidant activity of native vitamin C (ascorbic acid, AH<sub>2</sub>) is hampered by instability in solution. Selective loading of AH<sub>2</sub> into the inner lumen of natural halloysite nanotubes (HNT) yields a composite nanoantioxidant (HNT/AH<sub>2</sub>), which was characterized and investigated for its reactivity with the persistent 1,1-diphenyl-2-picrylhydrazyl (DPPH&#8226;) radical and with transient peroxyl radicals in the inhibited autoxidation of organic substrates, both in organic solution (acetonitrile) and in buffered (pH 7.4) water in comparison with native AH<sub>2</sub>. HNT/AH<sub>2</sub> showed excellent antioxidant performance being more effective than native ascorbic acid by 131% in acetonitrile and 290% (three-fold) in aqueous solution, under identical settings. Reaction with peroxyl radicals has a rate constant of 1.4 &#215; 10<sup>6</sup> M<sup>&#8722;1</sup> s<sup>&#8722;1</sup> and 5.1 &#215; 10<sup>4</sup> M<sup>&#8722;1</sup> s<sup>&#8722;1</sup>, respectively, in buffered water (pH 7.4) and acetonitrile, at 30 &#176;C. Results offer physical understanding of the factors governing HNT/AH<sub>2</sub> reactivity. Improved performance of HNT/AH<sub>2</sub> is unprecedented among forms of stabilized ascorbic acid and its relevance is discussed on kinetic grounds.
Item Description:2076-3921
10.3390/antiox8020030