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Molecules 2013, 18(6), 6128-6141; doi:10.3390/molecules18066128
Article

Superoxide Scavenging Effects of Some Novel Bis-Ligands and Their Solvated Metal Complexes Prepared by the Reaction of Ligands with Aluminum, Copper and Lanthanum Ions

*  and
Division of Analytical Chemistry of Medicines, Showa Pharmaceutical University, 3-3165 Higashitamagawagakuen, Machida, Tokyo 194-8543, Japan
* Author to whom correspondence should be addressed.
Received: 4 March 2013 / Revised: 20 May 2013 / Accepted: 20 May 2013 / Published: 23 May 2013
(This article belongs to the Special Issue Antioxidants 2012)
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Abstract

Novel antioxidants have been synthesized and characterized by their chemical properties as antioxidants with high superoxide scavenging activity. (2R,3R)-diphenylethylenediamine is a spacer in antioxidants, and we synthesized targets 11a and 11b by conjugation with o-hydroquinone and p-hydroquinone at the two N-termini, respectively. Superoxide scavenging activities of the plant flavonoid-like 11a and 11b were compared with those of known antioxidants, and shown to increase in the following order: curcumin << ascorbic acid < Trolox < ()-epicatechin < 11a < quercetin ≤ 11b . Compound 11a also formed a solvated 11a–metal complex with metal ions. The 11a–Cu2+ complex was shown to have higher superoxide scavenging activity than that of 11a, 11b, Cu2+, and the 11a–Al3+ and 11a–La3+ complexes, whereas the 11a–Al3+ complex increased rather than decreased superoxide levels. The 11a–Al3+ complex did not abstract one electron from the SOMO of O2−. since the HOMO and LUMO phases of Al3+ do not exist in the center of the 11a–Al3+ complex. However, the SOMO of the 11a–Cu2+ complex distributed in the center of Cu2+ may abstract one electron from the SOMO of O2−.. These results suggest that 11a and 11b are powerful antioxidants.
Keywords: superoxide; catechol; p-hydroquinone; antioxidants; density functional theory; aluminum; copper; lanthanum; solvated metal complexes superoxide; catechol; p-hydroquinone; antioxidants; density functional theory; aluminum; copper; lanthanum; solvated metal complexes
This is an open access article distributed under the Creative Commons Attribution License (CC BY 3.0).
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Kobayashi, S.; Kanai, S. Superoxide Scavenging Effects of Some Novel Bis-Ligands and Their Solvated Metal Complexes Prepared by the Reaction of Ligands with Aluminum, Copper and Lanthanum Ions. Molecules 2013, 18, 6128-6141.

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