EPR study of ceria–silica and ceria–alumina catalysts: Localization of superoxide radical anions

Oxygen adsorption experiments were performed on evacuated and prereduced CeO₂/SiO₂ and CeO₂/Al₂O₃ catalysts with and without platinum. Considerable amounts of the superoxide radical ions were stabilized on all the samples. Signal parameters suggest Ce⁴⁺–O₂⁻ positioning for all detectable superoxide species. Physisorbed oxygen broadens O₂⁻ signal beyond detection for all the alumina-based samples, while the same procedure for all the silica-based samples did not change signal shape of O₂⁻ species. Detectable O₂⁻ species are localized in the bulk of ceria and the nature of support (silica or alumina) determines the number of oxygen vacancies and the rate of electron transfer. XRD data suggest that for alumina-based samples small and/or thin islands of ceria dominate, while comparatively large ceria particles are stabilized on the surface of silica-based samples with the same ceria content. Average size of ceria crystallites is still not determining factor and cannot account for the observed differences. Higher concentrations of paramagnetic species may be stabilized on alumina-based samples and thus, sensor-like behavior towards gaseous oxygen at room temperature was detected for them—oxygen admission reversibly changes superoxide lineshape. For silica samples, only minor changes of O₂⁻ lineshapes were typical upon the change of the partial pressure of oxygen at ambient and low temperatures. Addition of platinum has little effect on parameters of the O₂⁻ signal, except an enhancement of the superoxide decay in the reducing media. Possible site for O₂⁻ stabilization inside the lattice of CeO₂ was proposed and relevance of the observed effects to the redox catalysis discussed.     

Reprogramming the chemical reactivity of iron in cancer stem cells

Cancer stem cells (CSCs) have been shown to be refractory to conventional therapeutic agents, can promote metastasis, and have been linked to cancer relapse. Salinomycin can selectively kill CSCs. We have shown that salinomycin derivatives accumulate in lysosomes and sequester iron in this organelle. As a result, accumulation of iron leads to the production of reactive oxygen species and lysosomal membrane permeabilization, which in turn promotes cell death by ferroptosis. These findings have revealed the prevalence of iron homeostasis in CSCs and paved the way toward the development of next-generation therapeutics.     

hcp‐Co Nanowires Grown on Metallic Foams as Catalysts for Fischer–Tropsch Synthesis

The Fischer–Tropsch synthesis (FTS) is a structure‐sensitive exothermic reaction that enables catalytic transformation of syngas to high quality liquid fuels. Now, monolithic cobalt‐based heterogeneous catalysts were elaborated through a wet chemistry approach that allows control over nanocrystal shape and crystallographic phase, while at the same time enables heat management. Copper and nickel foams have been employed as supports for the epitaxial growth of hcp‐Co nanowires directly from a solution containing a coordination compound of cobalt and stabilizing ligands. The Co/Cu_foam catalyst was tested for Fischer–Tropsch synthesis in a fixed‐bed reactor, showing stability and significantly superior activity and selectivity towards C5+ compared to a Co/SiO₂‐Al₂O₃ reference catalyst under the same conditions.     

Positive block matrices and numerical ranges

Any positive matrix M partitioned in four n-by-n blocks satisfies the unitarily invariant norm inequality $6M6\le 6M_{1,1}+M_{2,2}+\omega I6$, where ω is the width of the numerical range of $M_{1,2}$. Some related inequalities and a reverse Lidskii majorization are given.     

Reachability analysis of linear systems using support functions

This work is concerned with the algorithmic reachability analysis of continuous-time linear systems with constrained initial states and inputs. We propose an approach for computing an over-approximation of the set of states reachable on a bounded time interval. The main contribution over previous works is that it allows us to consider systems whose sets of initial states and inputs are given by arbitrary compact convex sets represented by their support functions. We actually compute two over-approximations of the reachable set. The first one is given by the union of convex sets with computable support functions. As the representation of convex sets by their support function is not suitable for some tasks, we derive from this first over-approximation a second one given by the union of polyhedrons. The overall computational complexity of our approach is comparable to the complexity of the most competitive available specialized algorithms for reachability analysis of linear systems using zonotopes or ellipsoids. The effectiveness of our approach is demonstrated on several examples.     

A construction of commutative nilsemigroups

All commutative nilsemigroups are constructed from congruences on free commutative semigroups.