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

1
Department of Chemistry “G. Ciamician”, University of Bologna, Via S. Giacomo 11, I-40126 Bologna, Italy
2
Department of Industrial Chemistry “Toso Montanari”, University of Bologna, Viale Risorgimento 4, I-40136 Bologna, Italy
*
Author to whom correspondence should be addressed.
Antioxidants 2019, 8(2), 30; https://doi.org/10.3390/antiox8020030
Received: 31 December 2018 / Revised: 21 January 2019 / Accepted: 24 January 2019 / Published: 27 January 2019
(This article belongs to the Special Issue The Chemistry of Antioxidant Activity)
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Abstract

Antioxidant activity of native vitamin C (ascorbic acid, AH2) is hampered by instability in solution. Selective loading of AH2 into the inner lumen of natural halloysite nanotubes (HNT) yields a composite nanoantioxidant (HNT/AH2), which was characterized and investigated for its reactivity with the persistent 1,1-diphenyl-2-picrylhydrazyl (DPPH•) 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 AH2. HNT/AH2 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 × 106 M−1 s−1 and 5.1 × 104 M−1 s−1, respectively, in buffered water (pH 7.4) and acetonitrile, at 30 °C. Results offer physical understanding of the factors governing HNT/AH2 reactivity. Improved performance of HNT/AH2 is unprecedented among forms of stabilized ascorbic acid and its relevance is discussed on kinetic grounds. View Full-Text
Keywords: halloysite; nanotube; nanoantioxidant; ascorbic acid; vitamin C; stability; antioxidant; peroxyl radicals; rate constant; biomimetic halloysite; nanotube; nanoantioxidant; ascorbic acid; vitamin C; stability; antioxidant; peroxyl radicals; rate constant; biomimetic
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This is an open access article distributed under the Creative Commons Attribution License which permits unrestricted use, distribution, and reproduction in any medium, provided the original work is properly cited (CC BY 4.0).

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Baschieri, A.; Amorati, R.; Benelli, T.; Mazzocchetti, L.; D’Angelo, E.; Valgimigli, L. Enhanced Antioxidant Activity under Biomimetic Settings of Ascorbic Acid Included in Halloysite Nanotubes. Antioxidants 2019, 8, 30.

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