The Interaction of L-DOPA Melanin with p-tert-Butylcatechol

The interaction between the skin depigmenter 4-tert-butylcatechol (tBC) and L-DOPA melanin was qualitatively studied by means of spectroscopically monitoring the binding of tBC melanin as well as the oxidation of tBC in the presence and absence of melanin. Additionally, we assessed the quantitative effect of tBC on melanin's chemical reactivity by using the reduction of potassium ferricyanide as a redox marker. The kinetics of ferricyanide reduction in the ternary (melanin/tBC/ferricyanide) system are essentially different from those in each of the binary components (i.e., melanin/ferricyanide and tBC/ferricyanide). The experiments indicate that tBC can bind to melanin (KB = 3.8 × 103 M−1) and that melanin can act as a “catalyst-like” electron transfer agent which couples ferricyanide reduction with tBC oxidation (k' = 1.4 × 10−6 mole min−1). These kinetic and thermodynamic parameters may provide a means of quantitatively comparing melanins obtained from different biological and pathological situations, and they may make possible an understanding of cutaneous depigmentation processes on the molecular level.