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Issue 38, 2015
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Gelation of Fmoc-diphenylalanine is a first order phase transition

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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 1H 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.

Graphical abstract: Gelation of Fmoc-diphenylalanine is a first order phase transition

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The article was received on 07 Jun 2015, accepted on 17 Aug 2015 and first published on 17 Aug 2015

Article type: Paper
DOI: 10.1039/C5SM01399B
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Soft Matter, 2015,11, 7663-7673

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    Gelation of Fmoc-diphenylalanine is a first order phase transition

    N. A. Dudukovic and C. F. Zukoski, Soft Matter, 2015, 11, 7663
    DOI: 10.1039/C5SM01399B

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