The effect of Cu(II) ions on dopachrome has been studied by means of UV-Vis spectra in buffer solution at pH 6.5. Cu(II) ions markedly accelerated the rate of bleaching of dopachrome (DC) at 475 nm and simultaneously exhibited general absorption in the range of 300-800 nm in the system with oxygen removed by bubble nitrogen gas. The experimental results revealed that Cu(II) ions catalyzed not only the rearrangement of DC to yield mainly 5 ,6-dihydroxyindole-2-carboxylic acid (DHICA) on first-order kinetics with respect to DC in the first part of the reaction, but also the reaction of 5,6-dihydroxyindole (DHI) and DHICA to form indole-5, 6-quinone (IQ) and indole-5,6-quinone-2-carboxylic acid (IQCA), which would immediately polymerize to yield melanin.
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