First-time applications of solid-state exchange 13C NMR techniques to the study of the reorientation dynamics of hydrocarbon molecules adsorbed on zeolites have enabled the geometry and time scales of molecular hopping processes between adjacent adsorption sites to be characterized directly and model free. Two-dimensional exchange 13C NMR on static samples establishes the geometry of the site-hopping dynamics, while one-dimensional magic-angle spinning (MAS) exchange-induced-sidebands (EIS) 13C NMR permits motional correlation times on the order of milliseconds to seconds to be extracted directly from the experimental data. Variable-temperature experiments performed on Ca-LSX zeolite samples with average bulk loadings of 0.5, 1, and 2 benzene molecules per supercage yield apparent Arrhenius activation energies of about 66 ± 6 kJ mol-1 for the discrete, localized reorientation dynamics of benzene molecules among different Ca2+ cation adsorption sites (∼0.5 nm apart). Arrhenius preexponential factors were established to be on the order of 1 × 1012 s-1, consistent with elementary hopping processes. Motional correlation times exhibit only minor variations upon changes in benzene loading over the range studied.

The proteinaceous byssal plaque-thread structures created by marine mussels exhibit extraordinary load-bearing capability. Although the nanoscopic protein interactions that support interfacial adhesion are increasingly understood, major mechanistic questions about how mussel plaques maintain toughness on supramolecular scales remain unanswered. This study explores the mechanical properties of whole mussel plaques subjected to repetitive loading cycles, with varied recovery times. Mechanical measurements were complemented with scanning electron microscopy to investigate strain-induced structural changes after yield. Multicyclic loading of plaques decreases their low-strain stiffness and introduces irreversible, strain-dependent plastic damage within the plaque microstructure. However, strain history does not compromise critical strength or maximum extension compared with plaques monotonically loaded to failure. These results suggest that a multiplicity of force transfer mechanisms between the thread and plaque-substrate interface allow the plaque-thread structure to accommodate a wide range of extensions as it continues to bear load. This improved understanding of the mussel system at micron-to-millimeter lengthscales offers strategies for including similar fail-safe mechanisms in the design of soft, tough and resilient synthetic structures.