Ions—charged atoms or molecules—play an important role in nature, in our bodies as well as for science and technology. It is often necessary to trap, remove, mask, stabilize, or transport ions, whether in the body or the lab. With positively charged metal ions, this goal is often achieved with chelate ligands, organic molecules that tightly grab hold of the ions.
However, it is difficult to develop suitable chelators for negatively charged anions such as chloride and fluoride. Amar Flood and Yongjun Li at Indiana University (Bloomington, USA) have now synthesized a donut-shaped molecule that tightly and selectively takes chloride ions up into its center. As they report in the journal Angewandte Chemie , bridging hydrogen bonds are responsible for holding the chloride ion in place.
Chelators (from the Greek word for pincer) are small organic molecules that grab onto atoms or other small molecules, holding them by means of multiple binding sites. Chelate therapy is used to absorb and remove heavy metals in cases of poisoning, for example. It is a breeze to bind cations in this way. The development of organic molecules whose positively charged “arms” are arranged so as to tightly and selectively bind anions has not been successful to date.
Flood and Li found their new anion chelator more or less by coincidence when they were producing various macrocycles by means of an inexpensive, flexible synthetic technique known as “click chemistry”, which is a simple and efficient way to put molecules together into large entities. The researchers “clicked” four small rings together to form a large ring. This process also generates four more rings, made of three nitrogen atoms and two carbon atoms (triazole rings). These are not only by-products of the click chemistry, they are essential for binding the chloride ion, which can comfortably nestle into the empty center of the large donut-shaped ring. The triazoles hold on to the chloride ion by means of bridging hydrogen bonds, which is amazing because it was previously assumed that hydrogen bonds were not strong enough to form a sufficiently stable bond between a halogen ion and a chelate complex. It is probably vital that the binding sites in the structurally stable macrocycle are preorganized into the correct configuration so that the chelator does not have to rearrange itself around the ion before binding can occur, as is the case for open-chain chelators.
The four other nonbinding rings of the macrocycle can be varied almost as desired, so the researchers hope to generate a whole family of new chelators that are able to bind a spectrum of other anions with high specificity.
Author: Amar H. Flood, Indiana University, Bloomington (USA), http://flood.chem.indiana.edu/
Title: Pure C-H Hydrogen Bonding to Chloride Ions: A Preorganized and Rigid Macrocyclic Receptor
Angewandte Chemie International Edition 2008, 47, No. 14, 2649–2652, doi: 10.1002/anie.200704717
Researchers identify potentially druggable mutant p53 proteins that promote cancer growth
09.12.2016 | Cold Spring Harbor Laboratory
Plant-based substance boosts eyelash growth
09.12.2016 | Fraunhofer-Institut für Angewandte Polymerforschung IAP
Physicists of the University of Würzburg have made an astonishing discovery in a specific type of topological insulators. The effect is due to the structure of the materials used. The researchers have now published their work in the journal Science.
Topological insulators are currently the hot topic in physics according to the newspaper Neue Zürcher Zeitung. Only a few weeks ago, their importance was...
In recent years, lasers with ultrashort pulses (USP) down to the femtosecond range have become established on an industrial scale. They could advance some applications with the much-lauded “cold ablation” – if that meant they would then achieve more throughput. A new generation of process engineering that will address this issue in particular will be discussed at the “4th UKP Workshop – Ultrafast Laser Technology” in April 2017.
Even back in the 1990s, scientists were comparing materials processing with nanosecond, picosecond and femtosesecond pulses. The result was surprising:...
Have you ever wondered how you see the world? Vision is about photons of light, which are packets of energy, interacting with the atoms or molecules in what...
A multi-institutional research collaboration has created a novel approach for fabricating three-dimensional micro-optics through the shape-defined formation of porous silicon (PSi), with broad impacts in integrated optoelectronics, imaging, and photovoltaics.
Working with colleagues at Stanford and The Dow Chemical Company, researchers at the University of Illinois at Urbana-Champaign fabricated 3-D birefringent...
In experiments with magnetic atoms conducted at extremely low temperatures, scientists have demonstrated a unique phase of matter: The atoms form a new type of quantum liquid or quantum droplet state. These so called quantum droplets may preserve their form in absence of external confinement because of quantum effects. The joint team of experimental physicists from Innsbruck and theoretical physicists from Hannover report on their findings in the journal Physical Review X.
“Our Quantum droplets are in the gas phase but they still drop like a rock,” explains experimental physicist Francesca Ferlaino when talking about the...
16.11.2016 | Event News
01.11.2016 | Event News
14.10.2016 | Event News
09.12.2016 | Life Sciences
09.12.2016 | Ecology, The Environment and Conservation
09.12.2016 | Health and Medicine