Liquid-liquid phase separation and self-assembly of a lysine derivative Fmoc-L-lysine in water-DMSO mixtures

The self-assembly process of a lysine derivative (9-fluorenylmethyloxycarbonyl-L-lysine; Fmoc-Lys) in water-DMSO mixtures was investigated by time-resolved static and dynamic light scattering (SLS and DLS), small-angle X-ray scattering (SAXS), optical microscopy (OM), and scanning electron microscopy (SEM). SLS, DLS, and SAXS indicated liquid-liquid phase separation caused by the addition of water to the DMSO solution of Fmoc-Lys and the formation of spherical droplets of the phase-separating concentrated phase with concentrations as high as 0.6 g/cm3. However, in the colloidal phaseseparating solution, the concentrated phase droplets did not grow through the Ostwald ripening process, but OM and SEM implied that a crystal phase of Fmoc-Lys appeared after a long lag phase in the phase-separating solution. This crystallization process for Fmoc-Lys after liquid-liquid phase separation in DMSO-water mixtures has been reproduced semiquantitatively by lattice theory.

Automated summary

The self-assembly process of Fmoc-Lys in water-DMSO mixtures was studied, revealing liquid-liquid phase separation and the formation of concentrated phase droplets and crystal phase. However, the droplets did not grow through Ostwald ripening process.