Studies on Nonenzymatic Oxidation Mechanisms in Neobetanin, Betanin, and Decarboxylated Betanins

Abstract

A comprehensive nonenzymatic oxidation mechanism in betanin plant pigment as well as its derivatives, 2-decarboxybetanin, 17-decarboxybetanin, 2,17-bidecarboxybetanin, and neobetanin, in the presence of ABTS cation radicals was investigated by LC-DAD-ESI-MS/MS. The main compounds formed during the first step of betanin and 2-decarboxybetanin oxidation are 2-decarboxy-2,3-dehydrobetanin and 2-decarboxyneobetanin, respectively. In contrast to betanin, the reaction mechanism for 2-decarboxybetanin includes more oxidation pathways. Parallel transformation of 2-decarboxybetanin quinone methide produces neoderivatives according to an alternative reaction that omits the presumably more stabile intermediate 2-decarboxy-2,3-dehydrobetanin. The main oxidation product after the first reaction step for both 17-decarboxybetanin and 2,17-bidecarboxybetanin is 2,17-decarboxy-2,3-dehydrobetanin. This product is formed through irreversible decarboxylation of the 17-decarboxybetanin quinone methide or by oxidation of 2,17-bidecarboxybetanin. Oxidation of neobetanin results primarily in a formation of 2-decarboxy-2,3-dehydroneobetanin by a decarboxylative transformation of the formed neobetanin quinone methide. The elucidated reaction scheme will be useful in interpretation of redox activities of betalains in biological tissues and food preparations.

Formulation of Titration Curves for Some Redox Systems

“…Approach II offers also special advantages when referred to redox systems, where organic species of great complexity, e.g. plant pigments participating redox reactions [35]- [40], are considered.…”

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.…”