Unique phase behaviour and self-assembly of a lysine derivative, Fmoc-homoarginine, in water-DMSO mixtures

Ternary solutions of an amino acid derivative, Fmoc-homoarginine (Fmoc-hArg), dimethylsulfoxide (DMSO), and water exhibit unique phase behaviour. Fmoc-hArg is dissolved in DMSO to provide a clear solution, but the solution becomes turbid after aging (turn-over phase separation). The turbid DMSO solution of Fmoc-hArg becomes clear by addition of water at a volume fraction of water in the DMSO-water mixture from 0.2 to 0.4, and turbid again at . Concentrated-phase droplets in the turbid solutions at act as centers of spherulite and needle-like crystal formation. This unique phase behaviour is explained theoretically on the basis of the competition between the micellization and phase separation and the Flory-Huggins theory.