Melanins are stable and non-toxic biomaterials with a great potential as chemopreventive agents for diseases connected with oxidative stress, but the mechanism of their antioxidant action is unclear. Herein, we show that polydopamine (PDA), a well-known synthetic melanin, becomes an excellent trap for alkylperoxyl radicals (ROOC, typically formed during autoxidation of lipid substrates) in the presence of hydroperoxyl radicals (HOOC). The key reaction explaining this peculiar antioxidant activity is the reduction of the orthoquinone moieties present in PDA by the reaction with HOOC. This reaction occurs via a H-atom transfer mechanism, as demonstrated by the large kinetic solvent effect of the reaction of a model quinone (3,5-di-tert-butyl-1,2-benzoquinone) with HOOC (k = 1.5 10 7 and 1.1 10 5 M À1 s À1 in PhCl and MeCN). The chemistry disclosed herein is an important step to rationalize the redox-mediated bioactivity of melanins and of quinones.

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The autoxidation kinetics of stripped sunflower oil (SSO), squalene (SQ), and p-cymene (p-C) initiated by 2,2′-azobis­(isobutyronitrile) at 303 K were investigated under controlled conditions by differential oximetry in order to build reference model systems that are representative of the natural variability of oxidizable materials, for quantitative antioxidant testing. Rate constants for oxidative chain propagation (k p) and chain termination (2k t) and the oxidizability (k p/√2k t) were measured using 2,6-di-tert-butyl-4-methoxyphenol, 2,2,5,7,8-pentamethyl-6-chromanol, BHT, and 4-methoxyphenol as reference antioxidants. Measured values of k p (M–1 s–1)/2k t (M–1 s–1)/oxidizability (M–1/2 s–1/2) at 303 K in chlorobenzene were 66.9/3.45 × 106/3.6 × 10–2, 68.0/7.40 × 106/2.5 × 10–2, and 0.83/2.87 × 106/4.9 × 10–4, respectively, for SSO, SQ, and p-C. Quercetin, magnolol, caffeic acid phenethyl ester, and 2,4,6-trimethylphenol were investigated to validate calibrations. The distinctive usefulness of the three substrates in testing antioxidants is discussed.

species of helicenes 1-9 have been measured and calculated to afford a complete rationalization of the redox behaviour of these appealing chiral compounds.

Many studies suggest that there are distinct regulatory processes controlling compound leaf development in different clades of legumes. Loss of function of the LEAFY (LFY) orthologs results in a reduction of leaf complexity to different degrees in inverted repeat-lacking clade (IRLC) and non-IRLC species. To further understand the role of LFY orthologs and the molecular mechanism in compound leaf development in non-IRLC plants, we studied leaf development in unifoliate leaf (un) mutant, a classical mutant of mungbean (Vigna radiata L.), which showed a complete conversion of compound leaves into simple leaves. Our analysis revealed that UN encoded the mungbean LFY ortholog (VrLFY) and played a significant role in leaf development. In situ RNA hybridization results showed that STM-like KNOXI genes were expressed in compound leaf primordia in mungbean. Furthermore, increased leaflet number in heptafoliate leaflets1 (hel1) mutants was demonstrated to depend on the function of VrLFY and KNOXI genes in mungbean. Our results suggested that HEL1 is a key factor coordinating distinct processes in the control of compound leaf development in mungbean and its related non-IRLC legumes.