Coming round to stable self-assembly

May 28, 2013
The team used linear and cyclic block copolymers to create flower-shaped micelles. The cyclic-based micelles withstood considerably higher temperatures and salinity levels, and could have numerous applications in industry and green chemistry.

Nanostructures that assemble themselves from polymer molecules could prove to be useful tools in chemistry and industry. However, it is difficult to develop structurally robust self-assembling materials because they are often adversely affected by their surroundings.

Many have evolved to protect themselves in hostile environments. For example, types of archaea - single-cell microorganisms living in hot springs - have cyclic molecules in their cell membranes that form shields to preserve the cell under .

Inspired by nature's use of cyclic structures, Takuya Yamamoto and co-workers at the Department of Organic and , Tokyo Institute of Technology, have dramatically enhanced both the thermal and salt stability of self-assembling polymeric structures, simply by changing the shape of the founding polymers from linear to cyclic.

The team designed new block copolymers - structures comprising several polymers connected by covalent bonding - which self-assembled into shapes called micelles (Fig.1). Micelles have a hydrophilic (water-attracting) , and a hydrophobic (water-repelling) core.

"We designed a cyclic amphiphilic block copolymer by mimicking fat molecules in the of archaea," explains Yamamoto. "Both linear and cyclic copolymers were then used to create identical self-assembling flower-shaped micelles." The team discovered that although the , concentration and dimensions of micelles built from the two differently shaped block copolymers remained the same, the cyclic-based micelles were able to withstand higher temperatures.

"The micelle from cyclic withstood temperatures up to 40°C higher than the linear-based micelles," explains Yamamoto. The researchers found that the tail ends of the linear copolymers were more likely to break loose from the flower-shaped structure during heating, allowing for bridging between micelles to occur. This meant that the micelles join together in an agglomerate blob at a relatively low temperature. The micelles created by the cyclical copolymers, on the other hand, had no 'loose ends' to form bridges, meaning the structures remained stable up to far higher temperatures.

The same structural differences allow for a greater tolerance of salt concentrations in the cyclic-based micelles. The loose tails in linear-based micelles allowed rapid dehydration to occur in highly saline environments, whereas the closed cyclic structures are structurally stronger, making them more resilient to salt.

"The combination of higher salting-out concentrations and thermal resistance means these micelles have numerous potential applications," explains Yamamoto. "Possibilities include drug delivery systems, where heating is not possible and salt provides an alternative method for controlling how a micelle responds in order to release a drug." The team also hope that their micelles could provide the basis for many new materials in the field of green chemistry, because their structural robustness is based purely on their shape rather than on complex chemical reactions.

Explore further: Nanoscale packaging could aid delivery of cancer-fighting drugs

More information: Honda, S. et al. Topology-directed control on thermal stability: micelles formed from linear and cyclized amphiphilic block copolymers. JACS Communications, published online July 2010.
Honda, S. et al. Tuneable enhancement of the salt and thermal stability of polymeric micelles by cyclized amphiphiles. Nature Communications 4, Mar 2013.

Related Stories

Chemists design molecule that responds to stimuli

November 23, 2010

(PhysOrg.com) -- The venus flytrap plant captures its prey when it senses the presence of an insect on the tips of its leaves. An amphiphilic molecule designed by chemists at The City College of New York acts in a similar ...

Self-healing dynamic membrane

June 28, 2012

The market for membranes, porous materials used mainly to filter liquids, is booming. However, their design leaves room for improvement. Taking their inspiration from cellular membranes, French researchers from the Institut ...

Recommended for you

Electrical circuit made of gel can repair itself

August 25, 2015

(Phys.org)—Scientists have fabricated a flexible electrical circuit that, when cut into two pieces, can repair itself and fully restore its original conductivity. The circuit is made of a new gel that possesses a combination ...

Scientists grow high-quality graphene from tea tree extract

August 21, 2015

(Phys.org)—Graphene has been grown from materials as diverse as plastic, cockroaches, Girl Scout cookies, and dog feces, and can theoretically be grown from any carbon source. However, scientists are still looking for a ...

0 comments

Please sign in to add a comment. Registration is free, and takes less than a minute. Read more

Click here to reset your password.
Sign in to get notified via email when new comments are made.