Pathways to betalains stabilization and its consequences

Author(s)

Amanda Capistrano Pinheiro

• Document type: Doctoral Thesis
• Press: São Paulo.
• Institution: Universidade de São Paulo (USP). Conjunto das Químicas (IQ e FCF) (CQ/DBDCQ)
• Defense date: 2022-07-26

Examining board members

Erick Leite Bastos; Wilhelm Josef Baader; Carla Cristina Schmitt Cavalheiro; Fabiano Severo Rodembusch

• Advisor: Erick Leite Bastos

Abstract

Betalains are antioxidant natural pigments found in a restricted number of plants and fungi. The most striking structural feature of these metabolites is the presence of a 1,7-diazaheptamethynium system in which an imine or iminium group is conjugated to an enamine. The use of betalains as a raw material for the development of chemical inputs is partially limited by their sensitivity to hydrolysis. In this Doctoral Thesis, different strategies were proposed for the stabilization of betalains, whose consequences include the development of functional pseudonatural products and responsive chiral materials obtained by self-assembly. During the studies of intramolecular stabilization, OxiBeet, the first betalain-nitrone, was created. This new betalain is more stable in neutral or alkaline aqueous media than its imine analogue, has a high in vitro antioxidant capacity and its one electron oxidation product is a persistent nitroxide radical stabilized by resonance. In an attempt to promote stabilization by encapsulation, betalain@cucurbit[7]uril inclusion complexes were synthesized. The kinetic stabilization promoted by the macrocycle is accompanied by an increase in the fluorescence quantum yield of betalain derived from p-phenylenediamine of up to two orders of magnitude depending on the viscosity of the medium and pH. Ultrafast spectroscopy studies support the formation of a low-emissive charge transfer state for this betalain when the para-amino moiety is deprotonated. When the synthesis of this betalain is carried out using the amine as a limiting reagent, a blue solid is obtained. Analysis by transmission electron microscopy and electronic circular dichroism spectroscopy revealed the formation of chiral helical nanowires. Thus, new approaches for stabilizing betalains were explored and resulted in pseudo-natural products with properties that are not found in natural products of this class and that have potential for technological application. (AU)

• FAPESP's process: 15/18474-4 - Functionalization of polysaccharides with photoresponsive betalains
• Grantee: Amanda Capistrano Pinheiro
• Support Opportunities: Scholarships in Brazil - Doctorate (Direct)