The Self-Recognition and Self-Assembly of Folic Acid Salts in Isotropic Water Solution

The self‐assembly of alkaline folates in isotropic water solutions, with or without added salts, has been investigated by small‐angle neutron‐scattering, circular‐dichroism, and NMR techniques. The assembled species are chiral, cylindrical aggregates of finite length, composed of stacked tetramers; each tetramer is formed by Hoogsteen‐bonded folate residues. The assembly process is more efficient in the presence of an excess of NaI ions, leading to longer aggregates with stronger tetramer‐tetramer‐tetramer interaction. In pure water, the rods are shorter and the tetramer‐tetramer interaction weaker. Association between folates can be detected by circular‐dichroism spectroscopy starting from a concentration of 6· 10−4 mol l−1, well below the critical concentration for the formation of the cholesteric mesophase (ca. 0.5 mol l−1).