BeetBlue: semi-synthesis and spectroscopic properties of a bioinspired chiral polimethyne dye

Betalains are nitrogen-containing pigments of red-violet or yellow color found in a restricted number of species of plants and fungi. This Doctoral Thesis presents the development of a betalain derivative with an extended π system called BeetBlue, the characterization of its structural, redox and spectroscopic properties and the study of its behavior in the presence of other chemical species. This dye was semi-synthesized from the coupling of 2,4-dimethylpyrrole and betalamic acid extracted from hydrolyzed beet juice. Although the diazapolimethyne system with nine methylene groups of BeetBlue is analogous to that of indocyanine green, a fluorescent dye of great interest, BeetBlue is blue-violet and poorly fluorescent in solutions of molecular solvents. The decrease in polarity or increase in the viscosity of the medium increases its fluorescence quantum yield by up to three orders of magnitude, and the complexation with lanthanides in aqueous medium changes its color from blue to orange. BeetBlue is sensitive to basecatalyzed hydrolysis and oxidation, which offers new opportunities for its use in the development of analytical methods. This dye is non-cytotoxic to retinal epithelial cells and did not affect the development of zebrafish embryos and larvae. BeetBlue is the prototype of a new class of water-soluble chiral polymethynic pigments, the quasibetalains, which present great potential for application as safe dyes for the environment and animal health. (AU)