Characterization, Spectroscopic and Kinetic Analyses of the Unexpected Gel Formed by Glycyl-Alanyl-Glycine (GAG) in an Ethanol/Water Mixture

The introduction of a co-solvent system (55 mol% ethanol/45 mol% water) promoted the aggregation, fibrilization and subsequent gelation of the cationic tripeptide glycylanalylglycine (GAG). This is surprising because, unlike known gelators throughout the literature, GAG lacks hydrophobicity, extended chain length, alternating charges, and/or aromaticity. This tertiary system was extensively studied through the use of vibrational spectroscopies (FTIR, VCD), nuclear magnetic resonance spectroscopy (NMR), electronic spectroscopies (UVCD), microscope imaging (bright-field, AFM) and rheology. Conformational resampling from pPII to β-strand was observed with the addition of ethanol co-solvent, the result of ethanol penetrating into the hydration shell of the peptide. Significant enhancement of the amide I′ in the VCD spectrum with an increase in peptide concentration was attributed to the formation of helically twisted fibrils, which extended into a gel network. Bright-field and atomic force microscopy of the fibrils revealed dimensions of approximately 500 μm in length, 500 nm in height, and 7 μm in cross-section, dimensions characteristic of enormous size compared with those of other small peptide hydrogel fibrils, which exhibit on a sub-micrometer scale. The gelation of cationic GAG in 55 mol% ethanol/45 mol% water was broken down into a set of distinguishable kinetic processes which proceeded in the following order: aggregation into tapes and ribbons (10-1 min-1), fibrilization as a cooperative process (10-2 min-1), initial gelation (10-2 min-1), and subsequent further adjustments of the gelation process (10-4 min-1). Understanding the kinetics of these processes has significant application for drug delivery and the synthesis of new biomaterials.M.S., Chemistry -- Drexel University, 201