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- Title
Effect of pH on elementary steps of dopachrome conversion from first-principles calculation.
- Authors
Kishida, Ryo; Ushijima, Yohei; Saputro, Adhitya G.; Kasai, Hideaki
- Abstract
Dopachrome conversion, in which dopachrome is converted into 5,6-dihydroxyindole ( DHI) or 5,6-dihydroxyindole-2-carboxylic acid ( DHICA) upstream of eumelanogenesis, is a key step in determining the DHI/ DHICA monomer ratio in eumelanin, which affects the antioxidant activity. Although the ratio of DHI/ DHICA formed and the conversion rate can be regulated depending on p H, the mechanism is still unclear. To clarify the mechanism, we carried out first-principles calculations. The results showed the kinetic preference of proton rearrangement to form quinone methide intermediate via β-deprotonation. We also identified possible pathways to DHI/ DHICA from the quinone methide. The DHI formation can be achieved by spontaneous decarboxylation after proton rearrangement from carboxyl group to 6-oxygen. α-Deprotonation, which leads to DHICA formation, can also proceed with a significantly reduced activation barrier compared with that of the initial dopachrome. Considering the rate of the proton rearrangements in a given p H, we conclude that the conversion is suppressed at acidic p H.
- Subjects
DOPACHROME tautomerase; PROTON transfer reactions; REARRANGEMENTS (Chemistry); MELANINS; DECARBOXYLATION
- Publication
Pigment Cell & Melanoma Research, 2014, Vol 27, Issue 5, p734
- ISSN
1755-1471
- Publication type
Article
- DOI
10.1111/pcmr.12256