title: Gelation of Fmoc-diphenylalanine is a first order phase transition.
abstract: We explore the gel transition of the aromatic dipeptide derivative molecule fluorenylmethoxycarbonyl-diphenylalanine (Fmoc-FF). The addition of water to a solution of Fmoc-FF in dimethyl sulfoxide (DMSO) results in increased attractions leading to self-assembly of Fmoc-FF molecules into a space-filling fibrous network. We provide evidence that gel formation is associated with a first order phase transition resulting in nucleation and growth of strongly anisotropic crystals with high aspect ratios. The strength of attraction between Fmoc-FF molecules as a function of water concentration is estimated from long-time self-diffusion measurements using (1)H NMR diffusion-ordered spectroscopy (DOSY). The resulting phase behavior follows that observed for a wide range of other crystallizing nanoparticles and small molecules - a result consistent with the short-range nature of the intermolecular attractions. Furthermore, we use NMR to measure the rate of increase in the fraction of bound Fmoc-FF molecules after water is suddenly mixed into the system. We observe a lag time in the formation of the new phase indicative of the existence of a free energy barrier to the formation of a crystal nucleus of critical size. The application of classical nucleation theory for a cylindrical nucleus indicates that one-dimensional crystal growth is driven by an imbalance of the surface energies of the ends and sides of the fiber.
authors: Department of Chemical and Biomolecular Engineering, University of Illinois at Urbana-Champaign, Urbana, IL 61801, USA. dudukov1@illinois.edu.
authors: Nikola A
authors: NA
authors: Dudukovic
authors: Charles F
authors: CF
authors: Zukoski
mesh_terms: D003460:Crystallization; D004121:Dimethyl Sulfoxide / Q000737:chemistry; D004151:Dipeptides; D005449:Fluorenes / Q000737:chemistry*; D005782:Gels / Q000737:chemistry*; D009682:Magnetic Resonance Spectroscopy; D044367:Phase Transition; D010649:Phenylalanine / Q000031:analogs & derivatives* / Q000737:chemistry; D014867:Water / Q000737:chemistry
chemical_list: C496789:9-fluorenylmethoxycarbonyl; D004151:Dipeptides; D005449:Fluorenes; D005782:Gels; D014867:Water; C026650:phenylalanylphenylalanine; D010649:Phenylalanine; D004121:Dimethyl Sulfoxide