(a) Structure of the siderophores desferrioxamine-B (DFOB) and desferrioxamine-D (DFOD). The terminating group R of DFOB is an amine group with a pKa of 8.4. The three hydroxyl groups have pKa values of 8.73, 8.99, and 10.1, respectively . The terminating group R of DFOD is acetylated and has no charge. The stability constant for Fe-DFOB and Fe-DFOD are 1030.7 and 1030.76, respectively (I=0.1M) . (b) Structure of EDTA with pKa values of 2, 2.69, 6.13, and 9.52 . The dominant species under the experimental conditions is doubly negatively charged. (c) Structure of the sodium salt of the anionic surfactant dodecyl sulfate (SDS) with a pKa of 2.3 .