Fig. 2

Structural diagrams and properties of organic dyes at pH = 9. a Tartrazine (TZ) anion, 465.39 g mol⁻¹. b Allura Red (AR) anion, 450.44 g mol⁻¹. c Brilliant Blue FCF (BB) zwitterion, 746.87 g mol⁻¹. d Bromophenol Blue (BPB) anion, 667.95 g mol⁻¹. e Bromocresol Green (BCG) anion, 698.02 g mol⁻¹. f Cyanocobalamin FCF (B12) zwitterion, 1,355.39 g mol⁻¹. g Rhodamine B (RB) zwitterion, 442.56 g mol⁻¹. h Malachite Green (MAL) cation, 329.47 g mol⁻¹. i Methylene Blue (MB) cation, 284.40 g mol⁻¹. j Methyl Green (MG) cation, 387.57 g mol⁻¹. Values in parentheses at the upper left of each panel provide predicted nearest integer charge q (e); translational hydrodynamic radius a (in nm); and measured electrophoretic mobility μ_e,meas (in 10⁻⁸ m² V⁻¹ s⁻¹). Below this, we list reported pK_a value(s) or range(s) from literature sources (see Supplementary Methods). Charges are approximate, and have been rounded to the nearest integer (see Supplementary Methods). Estimates of equivalent hydrodynamic sphere radii are made using WinHydroPro and HyperChem (see the Methods section). Corresponding minimized molecular models from HyperChem are shown in Supplementary Fig. 1