Gelation of Fmoc-diphenylalanine is a first order phase transition.
Soft Matter
; 11(38): 7663-73, 2015 Oct 14.
Article
em En
| MEDLINE
| ID: mdl-26295906
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.
Texto completo:
1
Base de dados:
MEDLINE
Assunto principal:
Fenilalanina
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Transição de Fase
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Fluorenos
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Géis
Idioma:
En
Ano de publicação:
2015
Tipo de documento:
Article