Fig. 4: Electrospray ionization mass spectrometry (ESI-MS) of SD/Ag51b before and after adding bipy.

Positive-ion ESI-MS of SD/Ag51b dissolved in CH3OH before (a) and after adding bipy (b); Δ = PW9O349−. The charge states for all labeled species in (a) and (b) are +2 and +3, respectively. Inset: The expanded experimental (green line) and simulated (red line) isotope-distribution patterns of 1a–1g. The expanded experimental (green line) and simulated (red line) isotope-distribution patterns of 2a–2j (c) and 2k–2q (d).