Infrared and vibrational circular dichroism spectroscopy: a powerful toolset for probing GXG hydrogels and determining the main fibril axis Nichole O'Neill 1 , Thamires Lima 2 , Fabio Furlan Ferreira 3 , Nicolas Alvarez 2 , Reinhard Schweitzer-Stenner 1 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 Peptides can self-assemble into supramolecular structures, such as ribbons, nanotubes, and monolayers which can be used as scaffolds for biomaterials. Controlled morphology and tuning of the physical and chemical properties of peptide materials are achieved through the modulation of the biopolymer’s primary sequence and saline content. Our group has identified a novel class of peptides with the motif Gly-X-Gly (X being a variable residue) that can act as ultra-low molecular weight gelators[1]. Particularly of interest are Gly-His-Gly and Gly- Phe-Gly. Their gel phase in which these peptides adopt non-canonical structures both exhibit unusual properties. These peptides have been shown to self-assemble into a highly dense network of exceedingly long fibrils which contribute to its strong gel phase (G’ > 10 6 Pa) [2-3]. Refined crystal structures were obtained for the crystalline fibrils of each system using powder x-ray diffraction (PXRD). Gly-Phe-Gly adopts an unusual inverse pPII conformation that occupy the “forbidden” region of the Ramachandran plot which we recently reported is stabilized by a plethora of intermolecular interactions facilitated by the large number of different functional groups of the unblocked tripeptide[3]. The crystalline structures are corroborated by simulations of infrared and vibrational circular dichroism (VCD) amide I′ profiles that are compared with the respective experimental spectra. The underlying theoretical model utilizes excitonic coupling between amide I modes. Moreover, we determined the main fibril axis by utilizing the experimental set-up of our IR/VCD spectrometer. Determining the main fibril axis of this system can provide insight into the drug-fibril interactions and mechanism for time-controlled drug release. References 1. Milorey, B.; Farrell, S.; Toal, S. E.; Schweitzer-Stenner, R. Chem. Commun. 2015, 51 (92), 16498– 16501. 2. Hesser, M.; Thursch, L.; Lewis, T.; DiGuiseppi, D.; Alvarez, N. J.; Schweitzer-Stenner, R. Soft Matter 2020, 16 (17), 4110–4114. 3. O’Neill, N, Lima, T.; Ferreira, F.; Alvarez, N.; Schweitzer-Stenner, R. J Phys Chem B. 2022,126 (40), 8080-8093.
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