Fig. 5. (a) Schematic illustration of the oxidation process of dopamine impacted by pH and oxidants. (b) Adhesion of dopamine after 1 h in situ polymerization at different pH values. (c) Molecular structure change of DHI moieties after adding Na₂S₂O₈. (d) Electron density of DHI moieties before and after adding Na₂S₂O₈. The electrostatic potentials are mapped onto the electron density surfaces with an isovalue of 0.001 electrons per bohr³. The color scale ranges from −12.55 (red) to 12.55 kcal mol⁻¹ (blue). (e) Representative force–distance curves of dopamine in the presence of Na₂S₂O₈. (f) Schematic illustration of a competition process to affect the cyclization of dopamine by introducing DETA. (g) Representative force–distance curves of dopamine and DETA at pH 8.5. (h) Energy barrier of Michael addition: intramolecular cyclization of dopamine (blue line), and the oxidized dopamine and DETA (yellow line). The inset images show the transition state of intramolecular cyclization of dopamine and the reaction of oxidized dopamine and DETA.