New Pathways of Betanidin and Betanin Enzymatic Oxidation

Abstract

Betanidin is a basic betacyanin with a 5,6-dihydroxyl moiety which causes its high antioxidant activity. For the purpose of structural study, the enzymatic oxidation of betanidin and betanin (5-O-glucosylated betanidin), followed by chromatographic separation of the oxidation products with spectrophotometric and mass spectrometric detection (LC-DAD-MS/MS) was performed. Within the pH 4-8 range, two main oxidation peaks of betanidin were observed, betanidin quinonoid (possibly betanidin o-quinone) and 2-decarboxy-2,3-dehydrobetanidin, whereas at pH 3 only dehydrogenated and decarboxylated derivatives were detected, suggesting different stabilities of the products at different pH values. The presence of two prominent oxidation products, 2-decarboxy-2,3-dehydrobetanidin and 2,17-bidecarboxy-2,3-dehydrobetanidin, at pH 3 indicates their generation via two possible reaction routes with two different quinonoid intermediates: dopachrome derivative and quinone methide. Both reaction paths lead to the decarboxylative dehydrogenation of betanidin. Subsequent oxidation and rearrangement of the conjugated chromophoric system results in the formation of 14,15-dehydrogenated derivatives. Betanin is oxidized with generation of a quinone methide intermediate, which rearranges to 2,3-dehydro- or neoderivatives. The products of enzymatic oxidation of betacyanins thus formed are derivatives of 5,6-dihydroxyindole and related structures known as the key intermediates in melanogenesis.

Dynamics of Interfacial Electron Transfer from Betanin to Nanocrystalline TiO2: The Pursuit of Two-Electron Injection

“…18 The electrochemical oxidation of Bd was found to proceed by a two-electron, one-proton process in the pH range of 3−5 and by a two-electron, two-proton process in the pH range of 6−8. Enzymatic oxidation of Bt 19 was observed to lead to the two-electron oxidation product 2-decarboxy-2,3-dehydrobetanin (dhBt, VI of Figure 1), presumably through rearrangement of the quinone methide intermediate (QM, V of Figure 1). dhBt, for which λ max = 445 nm, was observed to undergo further oxidation and decarboxylation.…”

Two-electron photo-oxidation of betanin on titanium dioxide and potential for improved dye-sensitized solar energy conversion

“…9 Wybraniec et al 10,11,12 have studied the oxidation of betanin (Bt) and its aglycone betanidin (Bd). They report that in the pH range 3 to 5, electrochemical oxidation of Bd is a reversible two-electron, one-proton process, while at somewhat higher pH this changes to a twoelectron, two-proton process.…”

Green biosynthesis of gold nanoparticles using Chenopodium formosanum shell extract and analysis of the particles' antibacterial properties

“…(c). Previous studies have reported that the betanin was oxidized to 2‐decarboxy‐2,3‐dehydrobetanin mainly . It was reported that the principal reason of stability on the surface of Au NPs was the electrostatic repulsion force of negatively charged betanin .…”

“…Previous studies have reported that the betanin was oxidized to 2-decarboxy-2,3-dehydrobetanin mainly. 32,33 It was reported that the principal reason of stability on the surface of Au NPs was the electrostatic repulsion force of negatively charged betanin. 31 Furthermore, the ionization of the surface functional groups (carboxylic and amino) was able to stabilize the formed Au NPs and prevent their agglomeration.…”