In Silicon Deciphering Atomic-Scale Structural Units in Peptide Glass.

Peptide glasses are an emerging class of biofunctional amorphous materials, but their atomic-level structure has remained elusive. Here, we resolve the three-dimensional (3D) organization of peptide glasses using a cyclic dipeptide model, combining molecular dynamics simulations with 2D solid-state NMR fingerprinting. Our analysis quantifies three defining hallmarks of the glassy state: (i) pronounced conformational heterogeneity that distinguishes it from the crystalline state; (ii) reorganization of diverse H-bonding types producing annealing-rate-dependent spectral fingerprints; and (iii) dominance of non-hydrogen-bonded contacts that generate annealing - temperature-dependent spectroscopic signatures. These features give rise to molecular clusters with a branched H-bonding topology that quantitatively reproduce bulk spectroscopic properties, establishing a representative structural unit analogous to the crystalline unit cell. This framework enables the identification of structural organization in amorphous peptide glasses with different thermal histories, paving the way for rational design of functional small-molecule glassy materials.