Biological membranes play key roles in the body. They determine, for example, how molecules enter and exit cells, and the architecture of their lipid bilayer allows them to host enzymes and enhance their catalytic performance under natural conditions.
To clarify the mechanisms that govern these processes, a team of chemists in Japan has generated in water tiny, catalytically active, free-standing membrane pockets, called vesicles, using a self-assembly method based on a small palladium complex. The team was led by Yasuhiro Uozumi from the RIKEN Advanced Science Institute in Wako and the Institute for Molecular Science in Okazaki.
Many researchers have already used ultra-small self-assembled pockets to perform reactions in solution while protecting the reagents from their potentially destructive surroundings. However, unlike Uozumi’s vesicles, few of these reaction vessels were ‘architecture-based’ catalysts; that is, structures that exhibit activity only when self-assembled.
The team’s palladium complex is a rigid, planar, pincer-like structure with hydrophilic ‘arms’ and hydrophobic ‘legs’. The different affinity for water and orientation of these functional groups directs vesicle assembly in water. Furthermore, these properties allow the complex to gain unique catalytic activity for specific chemical reactions. “This, conceivably, would approach an artificial enzymatic system,” notes Uozumi.
“The vesicle, which bears a hydrophobic inner region, was self-constructed in water, and this inner region served as a reservoir for the substrate,” says Uozumi. He explains that the entire reaction system—including the medium, molecular structure of the palladium complex, and substrate—cooperatively governs a ‘self-concentration’ process. During this process, substrate molecules penetrate the hydrophilic outer shell and accumulate in the hydrophobic reservoir where the reaction takes place (Fig. 1). After a quick catalytic transformation, the product exits the vesicle.
The researchers conducted a series of carbon–carbon bond-forming reactions, which are central to chemical synthesis, in the presence of the vesicles. They found that the vesicles stimulated the transformations in high yields at room temperature in water. The palladium complex was also recoverable in its original, disassembled form after the reaction. When they ran the same experiment in hydrophobic organic solvents, which hinder vesicle formation, no catalysis occurred—proof that water-mediated self-assembly is crucial for the catalytic activity of the complex.
The team is currently developing new catalysts by changing the hydrophilic and hydrophobic groups and substituting palladium for other metal species. It is also applying these catalysts to other organic reactions. These water-enabled transformations will lead to greener and safer approaches to organic chemistry, Uozumi concludes.
The corresponding author for this highlight is based at the Green Nanocatalysis Research Team, RIKEN Advance Science Institute
 Hamasaka, G., Muto, T. & Uozumi, Y. Molecular-architecture-based administration of catalysis in water: self-assembly of an amphiphilic palladium pincer complex. Angewandte Chemie, International Edition 50, 4876–4878 (2011).
Complementing conventional antibiotics
24.05.2018 | Goethe-Universität Frankfurt am Main
Building a brain, cell by cell: Researchers make a mini neuron network (of two)
23.05.2018 | Institute of Industrial Science, The University of Tokyo
A research team led by physicists at the Technical University of Munich (TUM) has developed molecular nanoswitches that can be toggled between two structurally different states using an applied voltage. They can serve as the basis for a pioneering class of devices that could replace silicon-based components with organic molecules.
The development of new electronic technologies drives the incessant reduction of functional component sizes. In the context of an international collaborative...
At the LASYS 2018, from June 5th to 7th, the Laser Zentrum Hannover e.V. (LZH) will be showcasing processes for the laser material processing of tomorrow in hall 4 at stand 4E75. With blown bomb shells the LZH will present first results of a research project on civil security.
At this year's LASYS, the LZH will exhibit light-based processes such as cutting, welding, ablation and structuring as well as additive manufacturing for...
There are videos on the internet that can make one marvel at technology. For example, a smartphone is casually bent around the arm or a thin-film display is rolled in all directions and with almost every diameter. From the user's point of view, this looks fantastic. From a professional point of view, however, the question arises: Is that already possible?
At Display Week 2018, scientists from the Fraunhofer Institute for Applied Polymer Research IAP will be demonstrating today’s technological possibilities and...
So-called quantum many-body scars allow quantum systems to stay out of equilibrium much longer, explaining experiment | Study published in Nature Physics
Recently, researchers from Harvard and MIT succeeded in trapping a record 53 atoms and individually controlling their quantum state, realizing what is called a...
The historic first detection of gravitational waves from colliding black holes far outside our galaxy opened a new window to understanding the universe. A...
02.05.2018 | Event News
13.04.2018 | Event News
12.04.2018 | Event News
24.05.2018 | Ecology, The Environment and Conservation
24.05.2018 | Medical Engineering
24.05.2018 | Physics and Astronomy