SAXS data for free iohexol. (a) SAXS curves at variable iohexol concentrations. No scaling was applied. Inset: Guinier fits and extracted Rg using PRIMUS. (b) Iohexol SAXS curve at the lowest measured concentration (13 mM). Left bottom inset: iohexol molecule (PubChem) and the distance between two distal O atoms (PyMOL). The continuous fit to the SAXS data was carried out with CRYSOL from the atomic model. Top right inset: pair distance distribution function p(r) (arbitrary units), extracted with GNOM.