Melanin-Based Coatings as Lead-Binding Agents

Table 3

Binding parameters of synthetic-eumelanin-coated discs with different metal ions.

	𝐾𝐿 (M^−1)^a	Capacity; μg/disc^a	Capacity; nmol/disc^a	Highest % bound; (initial [M^2+])^b
Pb^2+c	1.83(±0.02)⋅10^4	130.3 (±5.5)	629 (±27)	>95% (15.1–30.2 μM)
Cu^2+	1.41(±0.33)⋅10^4	49.0 (±3.2)	771 (±51)	92.3% (21.5 μM)
Cd^2+	9.70(±0.74)⋅10^3	49.8 (±5.0)	443 (±45)	68.9% (16.2 μM)
Zn^2+	6.44(±0.19)⋅10^3	25.0 (±3.2)	383 (±49)	47.9% (33.6 μM)

^aTitrations in 50 mM NaNO₃, initial pH 4.75, binding isotherms are shown in Figures 2(c) and 3. Values calculated from linearized Langmuir isotherms (𝑅²≥0.99) from at least three independent titrations with different discs; standard deviations shown.
^bFor each metal ion, the highest observed percentage bound at equilibrium is listed, with the initial concentration where this occurs shown in parentheses. ^cValues for Pb²⁺ are repeated from Tables 1 and 2.