Insight into Antioxidant and Photoprotective Properties of Natural Compounds from Marine Fungus

Abstract

This computational and experimental work aims to elucidate physicochemical and photophysical natures of free radical scavenging and ultraviolet radiation (UVR) filtering activities of five terpenoids available in the extract of marine fungus. The antioxidant activities of ochraceopone F (C1), aspertetranone D (C2), cycloechinulin (C3), wasabidienone E (C4), and mactanamide (C5) are evaluated by using density functional theory (DFT) at the M05-2X/6-311++G(d,p) level of theory in the gas phase, water, and pentyl ethanoate (PEA). Double antioxidant mechanisms allowing the second (H + /e − ) donation such as double hydrogen atom transfer (dHAT), double single electron transfer-proton transfer (dSET-PT), and double sequential proton loss-electron transfer (dSPL-ET) are considered. Reaction enthalpies (Δ r H 0 ), standard Gibbs free energies (Δ r G 0 ) and potential energy surfaces of reactions toward HOO • radical are then established to evaluate the hydrogen transfer (HT) and radical adduct formation (RAF) mechanisms. The computational results are supported by DPPH • and ABTS •+ antioxidant essays. Results show that all compounds C1−C5 are able to scavenge two free radicals via dHAT, dSET-PT, and dSPL-ET mechanisms. Among the compounds, C3 and C4 represent the most potential antioxidants, especially via HAT and RAF mechanisms in all the reaction media. Their rate constants for both HAT and RAF reactions are remarkably higher than that of Trolox and ascorbic acid. The kinetic calculations on activation Gibbs free energies (ΔG ⧧ ) and rate constants (k TST ) based on conventional transition state theory (TST) reveal that HAT and RAF processes are in competition in solvents. Photophysical processes occurring during UVR exposure are investigated using the time dependent density functional theory (TD-DFT) combined with UV−vis experiments. The obtained results highlight the promising activities of C1−C5 in UVR absorption in the ranges of UVA and UVB. Among them, C3 and C4 also show better UV absorption properties with the easiest excitations (band gaps equal to 4.06 and 3.65 eV). This study suggests the natural candidates possibly used in organic sunscreen.

In Silico Evaluation of the Radical Scavenging Mechanism of Mactanamide

“…Therefore, omitting this state in the evaluation of the antioxidant activity in polar solvents leads to inaccurate results, explaining the discrepancy between experimental and computational data in the above-described study. 2 In a comparison with the reference antioxidant Trolox, 3 the HOO • radical scavenging of MA is slightly lower in the lipid medium; however, in polar solvent it is about 18 times higher. Thus, MA is a promising antioxidant in physiological environments, in particular in aqueous media.…”

“…Thus, the H-abstraction occurs at the O11–H bond and not the C3–H bond, as suggested in the former study. 2 This may explain that H abstraction at the O11–H occurs via proton coupled electron transfer mechanism, while abstraction at the C3–H bond occurs via hydrogen atom-transfer pathway. 16 The HOO • radical scavenging of MA in the gas phase is lower than that of Trolox ( k Eck = 1.87 × 10 7 M –1 s –1 ).…”

“…However, computational results reported in the same study suggested that MA is a weaker radical scavenger than the other natural products (the overall rate constants k overall = 1.11 × 10 –3 and 2.39 × 10 –1 M –1 s –1 in pentyl ethanoate and water solvents, respectively, for MA vs k overall = 1.16–2.60 × 10 4 M –1 s –1 for the other compounds). 2 While the calculations were performed for HOO • scavenging that was not assessed experimentally, based on the results of DPPH and ABST assays that are good predictors of overall antioxidant activity, it is expected that MA is a better radical scavenger, and therefore, there is a conflict between the reported experimental data and the calculated results.…”

Antioxidant and UV-radiation absorption activity of aaptamine derivatives – Potential application for natural organic sunscreens

“…30 Details of this calculation can be found in our previous work. 23…”

“…22 Recently, we reported the antioxidant and photo-protective properties of different natural compounds in which the cycloechinulin and wasabidienone extracted from marine fungus showed the most potential antioxidant and photo-protective properties. 23 To the best of our knowledge, there have not been any studies that consider both the radical scavenging and photo-protective properties of the aaptamine derivatives. In this study, the antioxidant properties through free radical scavenging activity and the UV filter properties of three different aaptamine derivatives including piperidine [3,2-b] 1) were elucidated using density functional theory (DFT).…”