Polysaccharide-mediated formation of pigments from serotonin
As a continuation of the research on the pigment formation from catecholamines, we studied the polysaccharide-mediated oxidation of serotonin and other 5-hydroxy indoles into pigmented substances. As for catecholamines, we observed that many polysaccharides promote the oxidation of such compounds, particularly in the presence of Cu (II). The same polysaccharides, e.g., carrageenan or fucoidan, which strongly promoted the oxidation of catecholamines, strongly promoted the oxidation of serotonin, leading to the formation of darkly colored pigments. The reactions were evaluated using RP-HPLC and size exclusion chromatography (SEC) as the main analytical techniques. SEC proved particularly informative as these analyses allowed us to monitor (1) the decline in the substrate, (2) the formation of low-molecular mass oxidation products, (3) the formation of polysaccharide-associated pigments, and (4) the formation of potential pigment-based nanoparticles. We observed that increased amounts of polysaccharide or Cu (II) increased the amount of pigment generated. However, other cations like Co(II), Ni(II), Mn(II), or Fe(II) had no or very little effect on the reactivity. Apart from serotonin, 5-hydroxy indole could serve as a substrate to generate polysaccharide-associated pigments. However, reactions with the related substrate, 5-hydroxy indole-3-acetic acid yielded a low molecular mass chromophore, but not any polysaccharide-associated pigments. Large-scale reactions were set up in an attempt to isolate and characterize any pigments that were generated. The reaction mixtures could readily be dialyzed and lyophilized to obtain polysaccharide-associated pigments. Pigments were evaluated using UV-Vis spectroscopy, SEC analysis, FT_IR spectroscopy, and atomic absorption spectroscopy to evaluate the amount of Cu remaining in the materials.
Noor Abdulrahman S Alattas,
"Polysaccharide-mediated formation of pigments from serotonin"
ETD Collection for Tennessee State University.