Tunable\nand Cooperative Thermomechanical Properties\nof Protein–Metal–Organic Frameworks

Abstract

We recently introduced\nprotein–metal–organic frameworks\n(protein-MOFs) as chemically designed protein crystals, composed of\nferritin nodes that predictably assemble into 3D lattices upon coordination\nof various metal ions and ditopic, hydroxamate-based linkers. Owing\nto their unique tripartite construction, protein-MOFs possess extremely\nsparse lattice connectivity, suggesting that they might display unusual\nthermomechanical properties. Leveraging the synthetic modularity of\nferritin-MOFs, we investigated the temperature-dependent structural\ndynamics of six distinct frameworks. Our results show that the thermostabilities\nof ferritin-MOFs can be tuned through the metal component or the presence\nof crowding agents. Our studies also reveal a framework that undergoes\na reversible and isotropic first-order phase transition near-room\ntemperature, corresponding to a 4% volumetric change within 1 °C\nand a hysteresis window of ∼10 °C. This highly cooperative\ncrystal-to-crystal transformation, which stems from the soft crystallinity\nof ferritin-MOFs, illustrates the advantage of modular construction\nstrategies in discovering tunableand unpredictablematerial\nproperties.