Uncharged organic molecule can bind negatively charged ions

February 26, 2008

Indiana University Bloomington chemists have designed an organic molecule that binds negatively charged ions, a feat they hope will lead to the development of a whole new molecular toolbox for biologists, chemists and medical researchers who want to remove chlorine, fluorine and other negatively charged ions from their solutions.

"What we've done is create an efficient synthesis that gives us access to a whole new family of binding agents," said Amar Flood, who reports the discovery with postdoctoral scholar Yongjun Li in Angewandte Chemie this week. "The synthesis is extremely modular, as well, so we imagine these molecules can be easily modified to bind a wide variety of negative ions with great specificity."

Uncharged organic molecule can bind negatively charged ions
This complex organic molecule is capable of binding a negatively charged ion (chloride). The versatile, easy-to-make molecule may represent a new family of binding agents for use in biology and medicine. Credit: Amar Flood

Chelating agents are small molecules that grab atoms (or, sometimes, even smaller molecules) out of a solution and hold onto them. Chelators play a valuable role in both nature and laboratory settings. For example, the human protein calmodulin not only grabs positively charged calcium ions out of the solution surrounding it, it also influences cell processes according to how many calcium ions it has grabbed. In labs, EDTA (ethylenediaminetetraacetic acid) is frequently used to remove calcium and magnesium ions so that chemical reactions go faster or more efficiently.

Many organic molecules exist that can bind positively charged ions, or cations, and this has much to do with the fact that it is easy to synthesize organic molecules with negatively charged parts. It is those negatively charged parts that interact with positive ions, or cations, grabbing them out of solution and holding onto them so the cations cannot react or interfere with other processes.

Attempts at manufacturing organic binding agents with positively charged parts is not hard, but designing them in such a way that they don't attract the attention of solvent molecules has been a major challenge for chemists.

Flood and Li's solution was to create a donut-shaped organic molecule whose center would serve as the binding spot. A halide ion might fit snugly inside the hole, but the arrangement of atoms surrounding the hole would exclude any solutions.

Flood also wanted the synthesis of such a molecule to be cheap, easy and flexible, so he looked to the "click chemistry" devised by Scripps Research Institute chemist K. Barry Sharpless. Click chemistry is an efficient method of joining molecules together to form larger molecules. Flood's particular application of click chemistry results in an eight-member macrocycle with a 3.7 angstrom hole in the middle.

The more-or-less symmetrical molecule that Flood and Li built contains four triazole rings sporting three nitrogen atoms each. It is presumed the nitrogens withdraw electron density from the carbon and hydrogen atoms closest to the molecule's hole, thereby creating an alluring binding spot for fluorine or chlorine ions. This binding is made all the more orderly because the macrocycle is preorganized to host its anionic guest.

"This thing is so easy to make," Flood said. "The triazole moiety has got more character to it than meets the eye. It's not just a byproduct of the click chemistry. We see lots of potential in it."

The other four members of Flood and Li's eight-member ring are entirely substitutable. Modifying these may give the chelator different binding affinities for a given anion.

The work Flood and Li describe in their Angewandte Chemie paper was funded by Indiana University.

Source: Indiana University

Explore further: Origins of life: New model may explain emergence of self-replication on early Earth

Related Stories

Where is solar power headed?

July 22, 2015

Most experts agree that to have a shot at curbing the worst impacts of climate change, we need to extricate our society from fossil fuels and ramp up our use of renewable energy.

Solving mysteries of conductivity in polymers

July 15, 2015

Materials known as conjugated polymers have been seen as very promising candidates for electronics applications, including capacitors, photodiodes, sensors, organic light-emitting diodes, and thermoelectric devices. But they've ...

Old astronomic riddle on the way to be solved

July 15, 2015

Scientists at the University of Basel were able to identify for the first time a molecule responsible for the absorption of starlight in space: the positively charged buckminsterfullerene. Their results have been published ...

An elusive molecule—finally revealed

July 13, 2015

Scientists at the University of Arizona have discovered a mysterious molecule with a structure simple enough to make it into high school textbooks, yet so elusive that chemists have argued for more than a century over whether ...

Recommended for you

Researchers design first artificial ribosome

July 29, 2015

Researchers at the University of Illinois at Chicago and Northwestern University have engineered a tethered ribosome that works nearly as well as the authentic cellular component, or organelle, that produces all the proteins ...

Meet the high-performance single-molecule diode

July 29, 2015

A team of researchers from Berkeley Lab and Columbia University has passed a major milestone in molecular electronics with the creation of the world's highest-performance single-molecule diode. Working at Berkeley Lab's Molecular ...

Researchers build bacteria's photosynthetic engine

July 29, 2015

Nearly all life on Earth depends on photosynthesis, the conversion of light energy into chemical energy. Oxygen-producing plants and cyanobacteria perfected this process 2.7 billion years ago. But the first photosynthetic ...

2 comments

Adjust slider to filter visible comments by rank

Display comments: newest first

zevkirsh
3 / 5 (1) Feb 26, 2008
i wonder if it would be possible to line all these rings up into a wierd polymer
NeilFarbstein
1 / 5 (1) Feb 26, 2008
triazole has been incorporated into polymers that transport hydrogen ions through fuel cell membranes at higher temperatures and greater efficency.

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.