Featured Research

from universities, journals, and other organizations

Self-assembly Used To Make Molecule-sized Particles With Patches Of Charge

Date:
October 21, 2009
Source:
University of Pennsylvania
Summary:
Physicists, chemists and engineers have demonstrated a novel method for the controlled formation of patchy particles, using charged, self-assembling molecules that may one day serve as drug-delivery vehicles to combat disease and perhaps be used in small batteries that store and release charge.

Physicists, chemists and engineers at the University of Pennsylvania have demonstrated a novel method for the controlled formation of patchy particles, using charged, self-assembling molecules that may one day serve as drug-delivery vehicles to combat disease and perhaps be used in small batteries that store and release charge.

Researchers demonstrated that the positive electrical charges of calcium ions -- just like the calcium in teeth and bone -- can form bridges between negatively charged polymers that would normally repel each other. The polymers, similar to the lipids that make the membranes surrounding living cells, have both a water-loving part linked to a water-repelling part. On the surfaces of these cell-sized polymer sacks, the calcium ions create calcium-rich islands or patches on top of negatively-charged polymer. Copper ions also work, and the patches can be made to coalesce and cover half of the particle. This polarized structure is the basic arrangement needed to set up, for example, the two electrodes of a microscopic battery. They could also one day be functionalized into docking sites to enhance targeted delivery of drug-laden particles to cells.

While the concept seems simple, that opposite charges attract, the creation and control of patches on one small particle has been a challenge. Scientists like Dennis E. Discher, principal investigator of the study and a professor of chemical and biomolecular engineering at Penn, are designing materials at the nanoscale because future technologies will increasingly rely on structures with distinct and controlled surfaces. Physicians, for example, will improve medical therapies by wrapping drugs within the bioengineered polymer sacks, or by creating tiny biomedical sensors. Green energy production and storage will also require structures with scales no longer measured by inches, but by micrometers and nanometers.

The collaboration involved faculty from Penn's School of Engineering and Applied Science, the School of Medicine and the School of Arts and Sciences, and demonstrated, more specifically, the selective binding of multivalent cationic ligands within a mixture of both polyanionic and non-ionic amphiphiles that all co-assemble into either patchy sacks called vesicles or molecular cylinders called worm-like micelles. Similar principles have been explored with lipids in the field of membrane biophysics because calcium is key to many cellular signaling processes. The trick is that the energy of attraction of opposite charges must be adjusted to find a balance with the large entropic price for localization into spots. If the attractions are too large, the ions precipitate, just like adding too much sugar to tea or coffee.

Using a little bit of acid or a little of base, the patchy polymer vesicles and cylinders can be made with tunable sizes, shapes and spacings. Assemblies with single large patches are called Janus assemblies, named after the double-faced Roman god, and the assemblies generally last for years because these are polymer-based structures.

"The key advance we present in this study is the restricted range of conditions that are required for self assembly in these solutions," Discher said. "We show that, in addition to polymers, negatively-charged cell lipids which are involved in all sorts of cell-signaling processes like cell motion and cancer mechanics, can also make domains or islands with calcium."

The work is representative of national research into soft matter, materials constructed from organic molecules like lipids, peptides and nucleic acids. A properly designed molecular system can produce a wide array of nanostructures and microstructures, emulating and extending what is found in nature.

The study, published as the cover article in the journal Nature Materials, was conducted by members of Penn's Laboratory for Research on the Structure of Matter, including David A. Christian, Aiwei Tian and Karthikan Rajagopal of the Department of Chemical and Biomolecular Engineering; Wouter G. Ellenbroek and Andrea J. Liu of the Department of Physics and Astronomy; Ilya Levental of the Bioengineering Graduate Group; Paul A. Janmey of the Department of Physiology; Tobias Baumgart of the Department of Chemistry; and Discher.


Story Source:

The above story is based on materials provided by University of Pennsylvania. Note: Materials may be edited for content and length.


Journal Reference:

  1. Christian et al. Spotted vesicles, striped micelles and Janus assemblies induced by ligand binding. Nature Materials, 2009; 8 (10): 843 DOI: 10.1038/nmat2512

Cite This Page:

University of Pennsylvania. "Self-assembly Used To Make Molecule-sized Particles With Patches Of Charge." ScienceDaily. ScienceDaily, 21 October 2009. <www.sciencedaily.com/releases/2009/10/091020181303.htm>.
University of Pennsylvania. (2009, October 21). Self-assembly Used To Make Molecule-sized Particles With Patches Of Charge. ScienceDaily. Retrieved July 22, 2014 from www.sciencedaily.com/releases/2009/10/091020181303.htm
University of Pennsylvania. "Self-assembly Used To Make Molecule-sized Particles With Patches Of Charge." ScienceDaily. www.sciencedaily.com/releases/2009/10/091020181303.htm (accessed July 22, 2014).

Share This




More Matter & Energy News

Tuesday, July 22, 2014

Featured Research

from universities, journals, and other organizations


Featured Videos

from AP, Reuters, AFP, and other news services

Government Approves East Coast Oil Exploration

Government Approves East Coast Oil Exploration

AP (July 18, 2014) The Obama administration approved the use of sonic cannons to discover deposits under the ocean floor by shooting sound waves 100 times louder than a jet engine through waters shared by endangered whales and turtles. (July 18) Video provided by AP
Powered by NewsLook.com
Sunken German U-Boat Clearly Visible For First Time

Sunken German U-Boat Clearly Visible For First Time

Newsy (July 18, 2014) The wreckage of the German submarine U-166 has become clearly visible for the first time since it was discovered in 2001. Video provided by Newsy
Powered by NewsLook.com
Obama: U.S. Must Have "smartest Airports, Best Power Grid"

Obama: U.S. Must Have "smartest Airports, Best Power Grid"

Reuters - US Online Video (July 17, 2014) President Barak Obama stopped by at a lunch counter in Delaware before making remarks about boosting the nation's infrastructure. Mana Rabiee reports. Video provided by Reuters
Powered by NewsLook.com
Crude Oil Prices Bounce Back After Falling Below $100 a Barrel

Crude Oil Prices Bounce Back After Falling Below $100 a Barrel

TheStreet (July 16, 2014) Oil Futures are bouncing back after tumbling below $100 a barrel for the first time since May yesterday. Jeff Grossman is the president of BRG Brokerage and trades at the NYMEX. Grossman tells TheStreet the Middle East is always a concern for oil traders. Oil prices were pushed down in recent weeks on Libya increasing its production. Supply disruptions in Iraq fading also contributed to prices falling. News from China's economic front showing a growth for the second quarter also calmed fears on its slowdown. Jeff Grossman talks to TheStreet's Susannah Lee on this and more on the Energy Department's Energy Information Administration (EIA) report. Video provided by TheStreet
Powered by NewsLook.com

Search ScienceDaily

Number of stories in archives: 140,361

Find with keyword(s):
Enter a keyword or phrase to search ScienceDaily for related topics and research stories.

Save/Print:
Share:

Breaking News:
from the past week

In Other News

... from NewsDaily.com

Science News

Health News

Environment News

Technology News



Save/Print:
Share:

Free Subscriptions


Get the latest science news with ScienceDaily's free email newsletters, updated daily and weekly. Or view hourly updated newsfeeds in your RSS reader:

Get Social & Mobile


Keep up to date with the latest news from ScienceDaily via social networks and mobile apps:

Have Feedback?


Tell us what you think of ScienceDaily -- we welcome both positive and negative comments. Have any problems using the site? Questions?
Mobile: iPhone Android Web
Follow: Facebook Twitter Google+
Subscribe: RSS Feeds Email Newsletters
Latest Headlines Health & Medicine Mind & Brain Space & Time Matter & Energy Computers & Math Plants & Animals Earth & Climate Fossils & Ruins