Sequence-dependent gelation kinetics of β-hairpin peptide hydrogels.

The gelation kinetics of four β-hairpin oligopeptides that have been designed to exhibit responsive behavior to changes in environmental conditions, such as pH, ionic strength and temperature, are characterized using multiple particle tracking microrheology and circular dichroism (CD) spectroscopy. The peptides, predominantly an alternating sequence of valine and lysine residues, differ by a point substitution of a single amino acid near a type II'β-turn sequence. The rate of gelation becomes faster for point substitutions which reduce the total charge of the peptide. Similarly, increasing the ionic strength reduces or screens intra- and inter-molecular electrostatic repulsions, again leading to faster gelation kinetics. CD measurements show that the concentration of folded peptide at the gel point decreases as the gelation kinetics become slower, possibly indicating a relationship between the assembly rate and the resulting gel microstructure. Finally, a model is developed based on the electrostatic barrier to peptide folding and association which agrees semi-quantitatively with the microrheology results. This represents a first step towards understanding the role of peptide charge and physico-chemical conditions in the self-assembly of these peptide hydrogelators.