Extended Data Figure 3 ∣. Structural characterization and metal-binding analysis of M^II-(AB)₂ complexes under competitive conditions with Cu^II.

a, Crystal structures (ribbon models) of (AB)₂ formed under Co^II//Cu^II (PDB:7RRB), Cu^II//Co^II (PDB:7RRR), Ni^II//Cu^II (PDB:7LR5), and Cu^II//Ni^II (PDB:7LRA) conditions. Root mean square deviation (RMSD) values were determined in comparison with the crystal structures of 2Co^II-(AB)₂ and 2Ni^II-(AB)₂ (grey cartoon models). b, Experimental SAXS profile of (AB)₂ (0.8 mM) in Co^II//Cu^II, Cu^II//Co^II, Ni^II//Cu^II, and Cu^II//Ni^II conditions ([M^II] = 1.6 mM) compared with the theoretical SAXS profile of 1Cu^II-(AB)₂. c, ESI-MS spectrum of (AB)₂ (5 μM) without metal ions. d, ESI-MS spectrum of (AB)₂ (5 μM) with sub-stoichiometric amounts of Cu^II (5 μM) and Co^II or Ni^II (5 μM). Circles in ESI-MS spectra represent the number of Co^II (magenta), Ni^II (green), and Cu^II (cyan) ions bound to (AB)₂. e, Competitive metal-binding titration of (AB)₂ with Co^II (magenta), Ni^II (green), and Cu^II (cyan) in 20 mM NH₄HCO₃ (pH 7.8). Mag-Fura-2 (5 μM) was used for competitive Co^II and Ni^II titration, and Newport green DCF (5 μM) was used for competitive Cu^II titration. Experimental data points and error bars are presented as mean and standard deviation of three independent measurements. Log-scale plots (left) of Fig. 2c to compare experimental scattering profiles of f, Co^II//Cu^II and Cu^II//Co^II, and g, Ni^II//Cu^II and Cu^II//Ni^II with theoretical scattering profiles. Right panels present expanded low q-ranges of the scattering plots (left).