Where order blurs: structural journeys across the fluid–solid continuum of sodium deoxycholate

Sodium deoxycholate (NaDC) displays a rich landscape of concentrated phases whose organization remains only partially understood. In this ongoing study, we want to combine small-angle X-ray scattering (SAXS) with controlled slow dehydration or other controllable experimental variables to track the structural evolution of NaDC as it transitions from highly hydrated aggregates toward increasingly ordered states. The resulting scattering patterns reveal a sequence of mesophase-like arrangements that echo those recently reported when NaDC associates with cationic and block-cationic polymers, suggesting common structural motifs emerging under crowding or charge-compensated conditions. Our current goal is to establish a structural bridge between four key organizational states of NaDC: the recently resolved crystal structure, the fiber-like assemblies observed in gels and those observed in dehydrated gel samples, and the putative hexagonal phase proposed in concentrated solutions. Preliminary comparisons indicate partial correspondence between the packing features of the solid state and those inferred from SAXS profiles of the dense phases, though significant discrepancies remain. By placing concentrated NaDC phases, polymer–NaDC coassemblies, and solid-state data on the same structural map, this work aims to clarify how hydration, ionic environment, and confinement shape bile salt ordering. The results presented here represent an evolving effort to connect mesoscopic scattering signatures with molecular-level organization across the NaDC phase diagram.