Model compounds for microbial iron-transport compounds. Part V. Substituent effects in the catechol/FeCl3 system

Surface-Initiated, Catechol-Containing Polymer Films for Effective Chelation of Aluminum Ions

We present a new route for obtaining surface-tethered polymer films containing pendant catechol functional groups via surface-initiated activators regenerated by electron-transfer atom-transfer radical polymerization (SI-ARGET ATRP) of glycidyl methacrylate (GMA) and post-polymerization modification of the resulting poly(glycidyl methacrylate) (pGMA) films with dopamine. This method enables a high degree of functionalization of pGMA films with catechol groups at a controlled level, depending on the duration of the post-polymerization modification reaction. The dopamine-pGMA films readily absorbs Al³⁺ and Zn²⁺ ions, as verified by quartz crystal microbalance with dissipation (QCM-D) under continuous flow conditions, and demonstrates a four-fold molar selectivity to Al³⁺ over Zn²⁺. The ions desorb from the films upon rinsing with pure deionized (DI) water, which regenerates the catechol sites in the dopamine-pGMA film. Subsequent exposure to metal ions after rinsing steps yields reproducible levels of loading.

Fe(III)-Coordination Properties of Neuromelanin Components: 5,6-Dihydroxyindole and 5,6-Dihydroxyindole-2-carboxylic Acid

The Fe(III)-coordination chemistry of neuromelanin building-block compounds, 5,6-dihydroxyindole (DHI), 5,6-dihydroxyindole-2-carboxylic acid (DHICA), and 5,6-dihydroxy-N-methyl-indole (Me-DHI), and the neurotransmitter dopamine were explored in aqueous solution by anaerobic pH-dependent spectrophotometric titrations. The Fe(III)-binding constants and pH-dependent speciation parallel those of catechol in that mono, bis, and tris FeLx species are present at concentrations dependent on the pH. The bis FeL2 dihydroxyindole species are favorable for L = DHI and DHICA under neutral to mildly acidic conditions. DHI and DHICA are stronger Fe(III) chelates than catechol, dopamine, and Me-DHI at pH values from 3 to 10. Oxidation studies reveal that iron accelerates the air oxidation of DHI and DHICA.