Antiradical capacity of ommochromes

Abstract

Ommochromes are colored substances that apparently function as biological signals among arthropods and insects. These substances may prevent oxidative stress by scavenging free radicals. Two principal mechanisms exist for scavenging free radicals: the electron transfer and hydrogen atom transfer. In this investigation, a theoretical study of the antiradical capacity of five ommochromes was performed within the density functional theory framework. Vertical ionization energy and vertical electron affinity were used to study the electron transfer mechanism between ommochromes and four free radicals: CH3O•, NO2•, HO•, and HOO•. For the hydrogen transfer mechanism, dissociation energy (D0) and Gibbs free energy were calculated, taking into account hydrogen atoms at different positions in the ommochromes. Both mechanisms are thermodynamically possible. The best antiradical is ommatin D. The UV/VIS spectra for ommochromes were obtained with ommatin D registering as the ommochrome with the greatest λmax value. In summary, ommatin D is the best antiradical and also the redder molecule. These results are important and may help to elucidate the function of these molecules in the animal kingdom. Graphical abstract Ommochromes are red and yellow substances present in arthropods and insects. According with computational chemistry, these substances present the capacity of prevent oxidative stress since they scavenge free radicals. These results may help to elucidate the function of these molecules in the animal Kingdom.

Ommochromes in invertebrates: biochemistry and cell biology

“…This result is consistent with in silico measurements of hydrogen‐donor capacities of ommochromes (Fig. C) (Romero & Martínez, ; Zhuravlev et al, ). For xanthommatin, the three best H‐donor sites localise to the aspartyl chain while the two best ones of ommatin D are within the pyrido[a]phenoxazone system (Fig.…”

“…It occurs because the electronic delocalisation of the phenoxazine chromophore is increased in H 2 ‐xanthommatin, leading to greater stabilisation by resonance of the oxonium ion (O + ) (Schäfer & Geyer, ). Recent studies suggested that these redox and related antiradical behaviours allow phenoxazine‐based compounds to buffer oxidative stress (Romero & Martínez, ; Farmer et al, ; Shah, Margison & Pratt, ). The theoretical basis of this putative biological role was modelled using computational and quantum chemistry, as well as in biological assays.…”

“…C). To assess whether ommochromes could act as antiradical compounds in vivo , free energies of reactions involving ommochromes and four relevant radicals were calculated in silico (Romero & Martínez, ). Ommatin D could react spontaneously and liberate more energy with the four different radicals compared to xanthommatin (Fig.…”

“…Ommatin D could react spontaneously and liberate more energy with the four different radicals compared to xanthommatin (Fig. C) (Romero & Martínez, ). These results are in agreement with the differences in H‐donor capacities of these two ommochromes.…”

“…The chemical properties of chromophores often make them suitable for transporting electrons or reacting with oxidants, reducers and free radicals, as well as functioning in vision (Needham, ). All these functions have been proposed to be fulfilled by ommochromes in nature (Needham, ; Stavenga, ; Insausti, Le Gall & Lazzari, ; Romero & Martínez, ), often without direct proof. Furthermore, protostomes generally lack the glutarate and nicotinamide biosynthesis pathway that catabolises the amino acid tryptophan (Linzen, ).…”