P1 SAXS data with Gd-HPDO3A. (a) SAXS curves (linear scale) at various Gd-HPDO3A concentrations. Insets: the square root of the scattering intensity at zero angle, I(0)1/2, and linear fit for determination of the CMP; chemical formula of Gd-HPDO3A. (b) CRYSOL fits with a hexameric P1 model (PDB entry 7qo8; see supporting information), logarithmic scale. For reasons of legibility, the different SAXS curves were shifted. (c) Guinier fits used to determine the Rg and I(0) values.