Synthesis of L-DOPA Based Melanins with Reproducible Physic-Chemical Properties

2018-12-17T17:58:39Z (GMT) by Koen Vercruysse Jayla Moore
This report expands our ongoing research efforts into the non-enzymatic synthesis of melanins. We have explored four different methods for the synthesis of L-DOPA based melanins and evaluated the reproducibility of some of their physic-chemical properties. The melanins were synthesized through the addition of NaOH, tyrosinate or Fe<sup>2+</sup>/H<sub>2</sub>O<sub>2</sub>. Two different approaches for the reactions involving Fe<sup>2+</sup> and H<sub>2</sub>O<sub>2</sub> were tested: a) addition of H<sub>2</sub>O<sub>2</sub> spread out over multiple days or b) addition of H<sub>2</sub>O<sub>2</sub> in one fraction at the start of the reaction. The physic-chemical properties of the melanins explored involved: 1) retention on size exclusion chromatography column, 2) FT-IR spectroscopy, 3) UV-Vis spectroscopy and 4) the capacity to reduce a redox dye, dichlorophenolindophenol. Overall the results obtained indicated that 1) the various synthesis methods lead to melanins with reproducible physic-chemical properties, 2) that the melanins synthesized in the presence of Fe<sup>2+</sup>/H<sub>2</sub>O<sub>2</sub> are distinctly different from the melanins synthesized in the presence of NaOH or tyrosinate and 3) that no distinctly different melanins were generated when comparing the two different synthesis approaches involving Fe<sup>2+</sup>/H<sub>2</sub>O<sub>2</sub>. Only the melanins synthesized in the presence of Fe<sup>2+</sup>/H<sub>2</sub>O<sub>2</sub> appeared to possess the capacity to reduce dichlorophenolindophenol.