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Grafting metal cations to missing linker defect sites in zirconium-based metal-organic frameworks, such as UiO-66, produces a uniquely well-defined and homotopic catalytically active site. We present here the synthesis and characterization of a group of UiO-66-supported metal catalysts, M-UiO-66 (M = Ni, Co, Cu, and Cr), for the catalytic dimerization of alkenes. The hydrogen-deuterium exchange via deuterium oxide adsorption followed by infrared spectroscopy showed that the last molecular water ligand desorbs from the sites after evacuation at 300 °C leading to M(OH)-UiO-66 structures. Adsorption of 1-butene is studied using calorimetry and density functional theory techniques to characterize the interactions of the alkene with metal cation sites that are found active for alkene oligomerization. For the most active Ni-UiO-66, the removal of molecular water from the active site significantly increases the 1-butene adsorption enthalpy and almost doubles the catalytic activity for 1-butene dimerization in comparison to the presence of water ligands. Other M-UiO-66 (M = Co, Cu, and Cr) exhibit 1-3 orders of magnitude lower catalytic activities compared to Ni-UiO-66. The catalytic activities correlate linearly with the Gibbs free energy of 1-butene adsorption. Density functional theory calculations probing the Cossee-Arlman mechanism for all metals support the differences in activity, providing a molecular level understanding of the metal site as the active center for 1-butene dimerization.

Nickel-functionalized UiO-66 metal organic frameworks (MOFs) oligomerize ethylene in the absence of cocatalysts or initiators after undergoing ethylene-pressure-dependent transients and maintain stable oligomerization rates for >15 days on stream. Higher ethylene pressures shorten induction periods and engender more active sites for ethylene oligomerization; these sites exhibit invariant selectivity-conversion characteristics to justify that only one type of catalytic center is relevant for oligomerization. The number of active sites is estimated using in situ NO titration to disambiguate the effect of increased reaction rates upon exposure to increasing ethylene pressures. After accounting for augmented site densities with increasing ethylene pressures, ethylene oligomerization is first order in ethylene pressure from 100 to 1800 kPa with an activation energy of 81 kJ mol-1 at temperatures from 443-503 K on Ni/UiO-66. A representative Ni/UiO-66 cluster model that mimics high ethylene pressure process conditions is validated with ab initio thermodynamic analysis, and the Cossee-Arlman mechanism is posited based on comparisons between experimental and computed activation enthalpies from density functional theory calculations on these cluster models of Ni/UiO-66. The insights gained from experiment and theory help rationalize evolution in structure and stability for ethylene oligomerization Ni/UiO-66 MOF catalysts.

Transendothelial migration is a crucial step during metastasis. Before circulating tumor cells enter the endothelium, they face the glycocalyx. While invasive migration of cancer cells is well studied, few investigations exist regarding their interaction with the glycocalyx. Here, the interaction of three breast cell lines with an endothelial glycocalyx is studied. Benign MCF-10A, noninvasive malign MCF-7, and invasive MDA-MB-231 cells penetrate the glycocalyx, just adhere to it or approach without even attaching to it. Remarkable fluctuations in these interaction modes are detected by time-resolved interaction profiles. Adhesion, migration, and invasion characteristics as well as combinations of interaction modes, cell shapes, and cell extensions are studied. The motility and penetration depth into the glycocalyx are analyzed. The invasive cells are the most flexible, penetrating the glycocalyx mostly with a round shape and feet-like membrane extensions. Noninvasive cancer cells penetrate the glycocalyx the deepest over time and benign cells integrate more likely into the endothelial cell layer underneath the glycocalyx.