Donator acceptor map for carotenoids, melatonin and vitamins
ABSTRACT Bright yellow and red colors in animals and plants are assumed to be caused by carotenoids (CAR). In animals, these pigments are deposited in scales, skin and feathers. Together with other naturally occurring and colorless substances such as melatonin and vitamins, they are considered antioxidants due to their free-radical-scavenging properties. However, it would be better to refer to them as "antiradicals", an action that can take place either donating or accepting electrons. In this work we present quantum chemical calculations for several CAR and some colorless antioxidants, such as melatonin and vitamins A, C and E. The antiradical capacity of these substances is determined using vertical ionization energy (I), electron affinity (A), the electrodonating power (omega(-)) and the electroaccepting power (omega(+)). Using fluor and sodium as references, electron acceptance (R(a)) and electron donation (R(d)) indexes are defined. A plot of R(d) vs R(a) provides a donator acceptor map (DAM) useful to classify any substance regarding its electron donating-accepting capability. Using this DAM, a qualitative comparison among all the studied compounds is presented. According to R(d) values, vitamin E is the most effective antiradical in terms of its electron donor capacity, while the most effective antiradical in terms of its electron acceptor capacity, R(a), is astaxanthin, the reddest CAR. These results may be helpful for understanding the role played by naturally occurring pigments, acting as radical scavengers either donating or accepting electrons.
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ABSTRACT: Sexual selection promotes the evolution of signals, many of which can reliably indicate condition, health or good genes of individuals. In order to be evolutionarily stable, indicator signals must be costly to produce. Carotenoid colouration evolved in many species by sexual selection. Carotenoids besides acting as pigments have been implicated in immune defence and antioxidation which makes them likely candidates for honest signalling. A trade-off for carotenoid availability was proposed as the basis for signal honesty. Alternatively, it was suggested that carotenoid colouration is not advertising the presence of the pigment per se, but the quality of antioxidant resources which then affect carotenoid concentration. One possibility is that carotenoid-based colouration could signal colourless antioxidant mechanisms, which are partially regulated by vitamins. β-Carotene is one of the most common precursors of vitamin A and, although present in bird diet, is not available for feather colouration. If an indirect association exists between carotenoid signal and condition, then manipulation of β-carotene concentration could reveal that this link is indirect. We tested this by conditioning the availability of β-carotene in the diet of a cardueline finch with yellow carotenoid colouration during moult. β-Carotene-supplemented males had higher plasma carotenoid concentration and higher response to a cellular immunity challenge (phytohaemagglutinin (PHA)) than control males. β-Carotene-supplemented males also had more saturated plumage colouration and were preferred by females in a mate choice test. Our results support the possibility of an indirect role for yellow carotenoid colouration.Behavioral Ecology and Sociobiology 01/2015; 69(3). DOI:10.1007/s00265-014-1860-2 · 3.05 Impact Factor
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ABSTRACT: Abstract Astaxanthin when esterified with ferulic acid is better singlet-oxygen quencher with k2 = (1.58 ± 0.1) 10(10) L mol(-1)s(-1) in ethanol at 25°C compared to astaxanthin with k2 = (1.12 ± 0.01) 10(9) L mol(-1)s(-1). The ferulate moiety is in the astaxanthin diester a better radical scavenger than free ferulic acid as seen from the rate constant of scavenging of 1-hydroxyethyl radicals in ethanol at 25°C with a second-order rate constant of (1.68 ± 0.1) 10(8) L mol(-1)s(-1) compared to (1.60 ± 0.03) 10(7) L mol(-1)s(-1) for the astaxanthin:ferulic acid mixture, 1:2 equivalents. The mutual enhancement of antioxidant activity for the newly synthetized astaxanthin diferulate becoming a bifunctional antioxidant is rationalized according to a two-dimensional classification plot for electron donation and electron acceptance capability.Free Radical Research 11/2014; DOI:10.3109/10715762.2014.982112 · 2.99 Impact Factor
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ABSTRACT: The calculations of local reactivity descriptors, the electron donor Fukui function f -(r), the average local ionization energy Ī(r), the Fukui function dual descriptor f ((2))(r), and the electron acceptor Fukui function f (+)(r) for α-tocopherol, the main biologically active form of vitamin E for antioxidant reactions in phospholipid membranes, is presented. The calculations are performed at B3LYP/6-311++G** level of theory in the gas-phase. The obtained results indicate that the most preferred sites for donating electron in a reaction with radical or oxidizing molecule are associated mostly with π electrons above and below the aromatic part of the α-tocopherol chromanol ring. The most reactive sites for accepting electrons are associated with the leaving H(9) atom in the extension of the phenolic OH bond on the α-tocopherol chromanol ring plane, in the place where the formation of H-bond of the precursor complex between approaching reactive oxygen radical and phenolic OH group of α-tocopherol could be expected. The separated reactive sites in α-tocopherol suggest that the proton and electron, along with the hydrogen atom transfer (HAT) process, could also be transferred to different proton and electron acceptors as in bidirectional proton coupled electron transfer (PCET) reactions. The results presented in this paper suggest that large charge redistribution and significant π-π interactions may be expected in antioxidant reactions of α-tocopherol.Journal of Molecular Modeling 04/2015; 21(4):2644. DOI:10.1007/s00894-015-2644-y · 1.87 Impact Factor