Nav: Home

Self-sorting through molecular geometries

January 09, 2019

Supramolecular assemblies are nanostructures resulting from molecules binding together, through intermolecular interactions, into larger units. One approach for controlling supramolecular assembly involves self-sorting: molecules recognizing copies of themselves, and binding with them. Now, the findings of an interdisciplinary collaboration between the Supramolecular group (Tomoki Ogoshi and coworkers) Atomic Force Microscopy (AFM) group (Hitoshi Asakawa, Takeshi Fukuma, and coworkers) of the Nano Life Science Institute (WPI-NanoLSI) Kanazawa University showed that self-sorting behavior can arise from the principle of geometrical complementarity by shape: in a mixture of specific pentagonal and hexagonal molecular building blocks, pentagons bind to pentagons and hexagons to hexagons, and no mixing occurs.

Asakawa and members of the AFM group conducted experiments with molecules called pillar[n]arenes, with n = 5 and n = 6, corresponding to pentagonal and hexagonal shapes, respectively. Both molecules come in two 'flavors': positively (cationic) or negatively charged (anionic). The polygonal molecules are essentially rings of 5 or 6 identical organic units, each featuring a benzene ring, but the composition of the units is different for the cationic and the anionic variants.

Ogoshi and his colleagues of the Supramolecular group let cationic pillar[5]arenes (P[5]+ in shorthand notation) adsorb on a quartz substrate. From this structure, they were able to grow P[5]+/P[5]-/P[5]+/... multilayers by immersing it alternatingly in anionic and cationic pillar[5]arene solutions. The addition of a layer was verified each time by ultraviolet-visible spectroscopy measurements. The resulting overall structure is a 'nanomat' of tubular structures with pentagonal pores. Similar results were obtained for the pillar[6]arenes: stacks of alternating cationic and anionic layers of the hexagonal molecules could be easily fabricated. The arrangement of pillar[n]arenes on a surface was investigated by collaboration with Prof. Takanori Fukushima, Prof. Tomofumi Tada and co-workers from Tokyo Institute of Technology.

What the scientists found surprising was that it was not possible to stack pentagonal and hexagonal building blocks when trying to build an anionic layer on a cationic one (and vice versa). This is a manifestation of self-sorting: only like polygons can self-assemble, even if ionic interactions drive the formation of cation-anion layered structures.

The researchers also examined the structure of the first layer of P[5]+ or P[6]+ molecules on the quartz substrate. For the hexagonal molecules, the two-dimensional packing structure did no exhibit long-range structural order, whereas for the pentagonal molecules, it did. This is partly attributed to a lower density for the latter. For the multilayer 'nanomats', the same trend was observed: long-range order for the pentagonal stacks. The ring shape-dependent packing structures were simulated by a Monte Carlo simulation by collaboration with Prof. Tomonori Dotera from Kindai University.

The self-sorting effect discovered by Ogoshi and colleagues has promising potential applications. Quoting the scientists: "The ultimate challenge will be to propagate cavity-shape information on the surface to provide shape-recognisable adsorption and adhesive materials."
-end-
[Background]

Pillar[n]arenes


Pillar[n]arenes, collectively named pillararenes (and sometimes pillarenes), are cyclic organic molecules consisting of n so-called hydroquinone units, which can be substituted. Hydroquinone, also known as quinol, has the chemical formula C6H4(OH)2. It consists of a benzene ring with two hydroxyl (OH) groups bound to it at opposite sides of the benzene hexagon.

The first pillararene was synthesized in 2008 by Tomoki Ogoshi and colleagues from Kanazawa University. The name pillararene was chosen since the molecules are cylindrical (pillar-like) in shape and composed of aromatic moieties (arenes).

Furthermore, Ogoshi and colleagues have shown that n = 5 and n = 6 pillararenes exhibit self-sorting capabilities. Cationic and anion versions of the molecules form tubular structures preserving the original pentagonal or hexagonal geometry of the pillararene cavity.

Kanazawa University

Related Molecules Articles:

Discovery of periodic tables for molecules
Scientists at Tokyo Institute of Technology (Tokyo Tech) develop tables similar to the periodic table of elements but for molecules.
New method for imaging biological molecules
Researchers at Karolinska Institutet in Sweden have, together with colleagues from Aalto University in Finland, developed a new method for creating images of molecules in cells or tissue samples.
How two water molecules dance together
Researchers have gained new insights into how water molecules interact.
Hand-knitted molecules
Molecules are usually formed in reaction vessels or laboratory flasks.
How molecules teeter in a laser field
When molecules interact with the oscillating field of a laser, an instantaneous, time-dependent dipole is induced.
Data storage using individual molecules
Researchers from the University of Basel have reported a new method that allows the physical state of just a few atoms or molecules within a network to be controlled.
Small molecules come into focus
Many biologically important small molecules, like hormones and amino acids, are too small to be measured by conventional detection methods.
We now know how RNA molecules are organized in cells
With their new finding, Canadian scientists urge revision of decades-old dogma on protein synthesis
A new way to create molecules for drug development
Chemists at The Ohio State University have developed a new and improved way to generate molecules that can enable the design of new types of synthetic drugs.
How ions gather water molecules around them
Charged particles in aqueous solutions are always surrounded by a shell of water molecules.
More Molecules News and Molecules Current Events

Best Science Podcasts 2019

We have hand picked the best science podcasts for 2019. Sit back and enjoy new science podcasts updated daily from your favorite science news services and scientists.
Now Playing: TED Radio Hour

Rethinking Anger
Anger is universal and complex: it can be quiet, festering, justified, vengeful, and destructive. This hour, TED speakers explore the many sides of anger, why we need it, and who's allowed to feel it. Guests include psychologists Ryan Martin and Russell Kolts, writer Soraya Chemaly, former talk radio host Lisa Fritsch, and business professor Dan Moshavi.
Now Playing: Science for the People

#538 Nobels and Astrophysics
This week we start with this year's physics Nobel Prize awarded to Jim Peebles, Michel Mayor, and Didier Queloz and finish with a discussion of the Nobel Prizes as a way to award and highlight important science. Are they still relevant? When science breakthroughs are built on the backs of hundreds -- and sometimes thousands -- of people's hard work, how do you pick just three to highlight? Join host Rachelle Saunders and astrophysicist, author, and science communicator Ethan Siegel for their chat about astrophysics and Nobel Prizes.