#dimers

Taming defective porous materials for robust and selective heterogeneous catalysis

The production of 1-butene via ethylene dimerization is one of the few industrial processes that employs homogeneous catalysis due to its high selectivity, despite the massive amounts of activators and solvents required. Now, a new paper by the University of the Basque Country (UPV/EHU), in collaboration with the López group at the Institute of Chemical Research of Catalonia (ICIQ) and RTI International, shows a more sustainable alternative via metal-organic frameworks (MOFs), a family of porous materials formed by metallic nodes connected through organic ligands.

The scientists demonstrate that tailored MOFs under condensation regimes catalyze the ethylene dimerization to 1-butene with high selectivity and stability in the absence of activators and solvent. The research, published in Nature Communications, opens new avenues to develop robust heterogeneous catalysts for a wide variety of gas-phase reactions.

The researchers engineered defects in the MOF (Ru)HKUST-1 without compromising the framework structure via two strategies: a conventional ligand exchange approach during MOF synthesis, and a pioneering post-synthetic thermal approach. The researchers then characterized the defects, which have been shown to be catalytically active for ethylene dimerization.

Reactive optical matter: Light-induced motion

Newton's third law dictates that forces between interacting particles are equal and opposite for closed systems. In a non-equilibrium environment, the third law can be defied, giving rise to "nonreciprocal" forces. Theoretically, this was shown when dissimilar, optically trapped particles were mediated by an external field. In a recent study, Yuval Yifat and colleagues measured the net nonreciprocal forces in electrodynamically interacting, asymmetric nanoparticle dimers and nanoparticle aggregates. In the experiments, the nanoparticle structures were confined to pseudo one-dimensional geometries and illuminated by plane waves. The observed motion was due to the conservation of total momentum for particles and fields with broken mirror symmetry (represented by a changed direction of motion). The results are now published on Light: Science & Applications.

The ability to convert light energy into self-directed motion with light-driven nanomotors or micromachines has already attracted great interest. A variety of methods in optics can produce rotational motion or give rise to translational motion with photoreactive materials. The promise to engineer light-driven nanomotors arose from recent theoretical work, which predicted that dissimilar particles illuminated by an electromagnetic plane wave, will experience a nonreciprocal net force.

The predicted nonreciprocal forces were demonstrated with simulations to vary very little with interparticle separation. However, straightforward experimental evidence on the phenomenon was not presented thus far. Exploring the reactive optical effects can open new possibilities of self-assembling, light-driven micromachines to herald a new field in optics and photonics.

The Scientific research Notes Of S. Sunkavally (years: 2002-2011).

Cell's skeleton is never still

New computer models that show how microtubules age are the first to match experimental results and help explain the dynamic processes behind an essential component of every living cell, according to Rice University scientists.

The results could help scientists fine-tune medications that manipulate microtubules to treat cancer and other diseases. Rice theoretical biophysicist Anatoly Kolomeisky and postdoctoral researcher Xin Li reported their results in the Journal of Physical Chemistry B.

Microtubules are cylinders made of 13 protein strands and are one of several components of a cell's cytoskeleton. Motor proteins walk along these bundles to deliver cargoes to various parts of a cell and to discard trash. Microtubules also play a part in cell division, movement and signaling. Cells constantly build, destroy and rebuild these cylinders and reuse the molecular blocks.

"One of the most interesting phenomena associated with microtubules is this dynamic instability," Kolomeisky said. "When you look at them in cells or in vitro, they grow and grow, and suddenly start to shrink without any change in the external conditions. Then suddenly, they start to grow again."

This instability is essential to cellular processes. "If the cell stabilizes, it dies," said Kolomeisky, a professor of chemistry and of chemical and biomolecular engineering at Rice. In fact, he said, the goal of many drugs that target microtubules aim to stabilize growth so a cell stops functioning before it can reproduce. That's important in the fight against cancer, he said.