Peptide amphiphile molecules (PAs) developed in our laboratory self‐assemble from aqueous media into three‐dimensional networks of bioactive nanofibers. Multiple non‐covalent interactions promote assembly of the supramolecular nanofibers and ultimately determine the bulk physical properties of the macroscopic gels. In this study, we use oscillatory rheology, Fourier‐transform infrared spectroscopy, and circular‐dichroism spectroscopy to better understand the assembly mechanism of a typical PA molecule known as PA‐1. Self‐assembly of PA‐1 is triggered by counterion screening and stabilized by van der Waals and hydrophobic forces, ionic bridging, and coordination and hydrogen bonding. The concentration, electronic structure, and hydration of counterions significantly influence self‐assembly and gel mechanical properties.

Self-assembled peptide amphiphile nanofibers have been investigated for their potential use as in vivo scaffolds for tissue engineering and drug delivery applications. We report here the synthesis of magnetic resonance (MR) active peptide amphiphile molecules that self-assemble into spherical and fiber-like nanostructures, enhancing T(1) relaxation time. This new class of MR contrast agents can potentially be used to combine high-resolution three-dimensional MR fate mapping of tissue-engineered scaffolds with targeting of specific cellular receptors.

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Catalytic particles based on supramolecular systems have demonstrated significant improvement in the field of catalysis. In this work, histidine-functionalized self-assembling peptide amphiphiles (PAs) were synthesized in order to form self-assembly high-aspect-ratio nanofibers with internal order that can present imidazolyl groups capable of ester hydrolysis. Self-assembly of the molecules making up the catalytic particle was studied by transmission electron microscopy and circular dichroism. The reactive sites were designed with histidine residues to catalyze the hydrolysis of 2,4-dinitrophenyl acetate (DNPA). Enzymatic hydrolysis of DNPA was observed in the presence of the nanofibers by UV−vis spectroscopy and the Michaelis−Menten enzyme kinetics model. Significantly faster hydrolysis rate was observed in the presence of self-assembled nanofibers relative to spherical aggregates expected to have less order as well as single molecule catalysts.

The self-assembly of peptide amphiphiles (PAs) into nanofibers and their bioactivity as well as physical properties have been investigated by our laboratory over the past few years. We report here on the use of transmission infrared spectroscopy (IR) and polarization modulation-infrared reflection-absorption spectroscopy (PM-IRRAS) to characterize the internal structure of the nanofibers. Depositing nanofibers flat on surfaces, and using the surface selection rules in PM-IRRAS, we demonstrate that peptide amphiphiles form b-sheets oriented parallel to the longaxis of nanofibers that pack radially from the nanofiber core. We show also that the extent of internal order depends on the molecular architecture and peptide sequence of PAs, with branched PAs yielding nanofibers with the lowest degree of internal order. Measurements of intensity and spectral position of the alkyl bands suggest that the hydrophobic core of these nanofibers can have internal order to an extent that correlates with order in their peptidic domains. We expect that bioactivity and physical properties will be controlled by the degree of internal order in these self-assembling nanostructures.