Structure and properties of Gly-His-Gly hydrogels and their potential as biomaterials with applications in drug delivery Reinhard Schweitzer-Stenner 1 , Nichole O’Neill 1 , Thamires Lima 2 , Fabio Furlan Ferreira 3 , Nicolas Alvarez 2 1 Chemistry, Drexel University, Philadelphia, PA, USA, 2 Chemical and Biological Engineering, Drexel University, Philadelphia, PA, USA, 3 Centro de Ciências Naturais e Humanas, Universidade Federal do ABC, Santo André, São Paulo, Brazil Our group has identified a novel class of peptides with the general motif GXG (X being a variable residue) that can act as ultra-low molecular weight gelators [1] . A subset of these peptides that are currently of high interest are those which contain a central aromatic residue (GX Ar G) [2] . These peptides can self-assemble into exceedingly long fibrils that form highly dense sample spanning networks that underly very strong hydrogels. Most recently our group has taken interest in using GHG supramolecular assemblies in biomedical applications. Its capability to form a fibril phase within a narrow neutral pH range and participate in ππ-interactions makes it an ideal candidate for hydrophobic drug delivery [3] . The tunability of the GHG system’s chemical and bulk properties have been investigated using different salts where either the cations (NH 4 + , Na + , Mg 2+ ) or the anions (HPO 4 2- , Cl - , NO 2 - ) varied along the Hofmeister series. The kinetics of gelation probed by rheology suggest that cations with a higher salting out capability accelerate gelation in line with the Hofmeister series, whereas the reverse is observed for the anionic series. Interestingly, melting of GHG gels and fibrils probed by rheology and UV circular dichroism experiments revealed that salts at different ends of the cationic series reduce the thermal stability of the peptide fibrils to a similar extent. We also observed that the physical properties of the hydrogels appear to form a network of fibrils that possibly “cross-link” or produce a stable interaction between adjacent fibrils which allows the material to remain intact under extensional stress, an observation not seen in systems prepared in the absence of salt. The systems prepared without salts form a material that resemble a colloidal paste. Extensional rheology experiments are underway on these salt systems to confirm this observation. References 1. R. Schweitzer-Stenner and N.J. Alvarez. Short Peptides as Tunable, Switchable and Strong Gelators. J. Phys. Chem. B 125, 6760-6775, 2021. 2. L. J. Thursch, T.A. Lima, N. O'Neill, F. F. Ferreira, R. Schweitzer-Stenner and N.J. Alvarez. Influence of central side chain on self-assembly of glycine -x-glycine peptides. Soft Matter 19, 394-409, 2023. 3. M. Hesser, L.J. Thursch, T.R. Lewis, T.A. Lima, N.J. Alvarez and R. Schweitzer-Stenner. Concentration Dependence of a Hydrogel Phase Formed by the Deprotonation of the Imidazole Side Chain of Glycylhistidylglycine. Langmuir, 37, 6935- 6946, 2021.
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