Making Monodisperse Macromolecules through Self-Interruption
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Ph.D.)
Living polymerization is a method for creating polymers with a predictable molecular weight and narrow, but not perfect, distribution. This stands in contrast with biological macromolecules, such as nucleic acids and proteins, which are perfectly monodisperse. Currently, monodisperse natural and synthetic macromolecules can only be obtained in low quantities with tedious, multi-step methods. In an effort to change that, Virgil Percec and co-workers developed a living polymerization method—involving ring-opening metathesis polymerization (ROMP)—that relies on a process of self-interruption to yield monodisperse macromolecules by chain reactions (DOI:
10.1021/jacs.0c07912).
The self-interruption process takes place after a certain degree of polymerization, at which point the reactive chains get encapsulated by the spherical macromolecule that has formed, bringing chain growth to a halt. The research team took a method that had been demonstrated previously for the iterative synthesis of dendrimers and adapted it in this new context to generate monodisperse macromolecules. The authors say they expect the self-interrupted living polymerization methodology may be extended to additional classes of molecules and lead to the development of new techniques for creating monodisperse synthetic macromolecules.
Organic Linkers Shape MOF Formation
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Ph.D.)
The chemistry of metal–organic frameworks (MOFs) continues to evolve and grow as the structures are tapped for powerful storage and adsorption applications. The diversity in MOF structures is partly due to a building block strategy for their synthesis, which involves both organic linker and inorganic metal clusters as well-defined blocks. The organic linker is not a rigid building block, however, as it often adjusts its geometry through bending and torsion during a reaction in order accommodate the overall supramolecule’s structure. Now a group of chemists led by Pantelis N. Trikalitis has developed a sulfone-functionalized ligand that directs the formation of a new and fascinating MOF with considerable CO
2 uptake (DOI:
10.1021/jacs.0c07081).
The new sulfone-functionalized ligand serves as a desymmetrized building block for MOFs when combined with zirconium/hafnium cations and rare earth metal cations. In one example, the Zr-based MOF has large pores in the mesoporous range and a high BET surface area. Due to the combination of this high pore volume with polar −SO2 groups, the Zr-MOF displays strong enhancement and selectivity of CO2 uptake, reaching 76.6% at 273 K. This approach represents a general strategy for the synthesis and discovery of more complex and novel MOFs.
Better Together: Enabling Mitochondrial Aggregation via Supramolecular Interactions
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Ph.D.)
Mitochondrial fusion is critical in regulating cellular metabolism and homeostasis. By the process of fusion, mitochondria can interact with each other and overcome defects to preserve essential functionality. The inability of mitochondria to aggregate and fuse has been associated with neurodegenerative disorders such as Parkinson’s and Huntington’s diseases, and different strategies to induce aggregation by controlling protein expression have been explored over the past decade. To date, these approaches have had limited success as clinically relevant therapies.
As an alternative to protein-regulation-based methods, Ruibing Wang and co-workers have developed an elegant solution by using supramolecular assembly to induce mitochondrial aggregation and fusion (DOI:
10.1021/jacs.0c06783). Using host–guest interactions between two molecules respectively grafted onto the surface of mitochondria and a large polysaccharide (hyaluronic acid), namely adamantane and cucurbit[7]uril, mitochondrial aggregation driven by non-covalent interactions is demonstrated. The study goes on to successfully induce mitochondrial aggregation and fusion in stressed neutrons and a zebrafish model for Parkinson’s disease. The approach detailed in this paper paves the way for therapeutic strategies that can be used to combat mitochondrial dysfunction in oxidative stress-related diseases, such as neurodegenerative diseases, diabetes, and cardiovascular disorders.
New BCM Method Enables Easy Formation of Actinide Chalcogenides
The actinides are one of the least understood series within the periodic table due to their radioactivity. However, owing to the unique properties of actinide 5f orbitals, scientists are keen to discern their potency in fields such as cancer therapy, magnetism, and small-molecule catalysis. One approach to studying the electronic nature of actinides is to form an actinide chalcogenide, which contains elements from Group 16 such as sulfur, selenium, or tellurium. But, obtaining phase-pure actinide chalcogenides has been problematic due to the high affinity of the actinides for oxygen and contamination from the starting materials in established synthetic routes.
Using the new boron–chalcogen mixture (BCM) method, Logan Breton, Vladislav Klepov, and Hans-Conrad zur Loye have synthesized a variety of phase-pure actinide chalcogenides (DOI:
10.1021/jacs.0c06483). Starting with the relevant actinide oxide, the authors impressively demonstrate the formation of binary uranium and thorium sulfides, i.e., uranium perovskites, via solid-state reactions, and rare-earth uranium sulfides by flux crystal growth. The boron–chalcogen mixture used in their method exploits boron’s activity as an “oxygen sponge” to remove all traces of oxygen. With the advent of this facile and convenient synthetic route to actinide chalcogenides, the researchers hope to promote research into the properties and applications of these unique and promising materials.
This article is cited by 1 publications.
- Virgil Percec, Qi Xiao, Gerard Lligadas, Michael J. Monteiro. Perfecting self-organization of covalent and supramolecular mega macromolecules via sequence-defined and monodisperse components. Polymer 2020, 211 , 123252. https://doi.org/10.1016/j.polymer.2020.123252
