Micro- and nano-sized peptidic assemblies prepared via solid-vapor approach: Morphological and spectroscopic aspects

The short aromatic dipeptide L-diphenylalanine (FF) was used to build supramolecular assemblies from amorphous films that were deposited onto Si substrates using an adapted form of the solid-vapor method [Adv. Mater. 20 (2008) 3754-3758]. The morphological and spectroscopic behaviors of the resulting micro- and nano-sized 1-D arrays were investigated. The formation of the structures was examined under different preparation conditions: specifically, the nature of the solvent (water or aniline), the concentration of peptides in the precursor solution and the incubation time were varied. Our results indicate that changes in preparation have dramatic consequences on the final morphology of the assemblies. Particularly, our data suggest that the solvent vapor pressure and a reduction of the hydrophobic capabilities of the substrate play a relevant role on structuration since they presumably increase heat and mass transport, respectively. Spectroscopic data reveal that the use of different vapors promotes the emergence of new vibrational modes, which is interpreted as a change in the symmetry of the molecular arrangement that is accompanied by an increase in the number of degrees of freedom. These findings strongly indicate that different symmetries-presumably orthorhombic and hexagonal symmetries-can be obtained depending on the type of solvent used during the preparation. To assess the interaction between our structures and a functionalizing agent, aniline was polymerized onto the structured films and then their morphological and spectroscopic behaviors were also investigated. (C) 2012 Elsevier B.V. All rights reserved.