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
How brains surrender to sleep
23.06.2017 | IMP - Forschungsinstitut für Molekulare Pathologie GmbH
A new technique isolates neuronal activity during memory consolidation
22.06.2017 | Spanish National Research Council (CSIC)
An international team of scientists has proposed a new multi-disciplinary approach in which an array of new technologies will allow us to map biodiversity and the risks that wildlife is facing at the scale of whole landscapes. The findings are published in Nature Ecology and Evolution. This international research is led by the Kunming Institute of Zoology from China, University of East Anglia, University of Leicester and the Leibniz Institute for Zoo and Wildlife Research.
Using a combination of satellite and ground data, the team proposes that it is now possible to map biodiversity with an accuracy that has not been previously...
Heatwaves in the Arctic, longer periods of vegetation in Europe, severe floods in West Africa – starting in 2021, scientists want to explore the emissions of the greenhouse gas methane with the German-French satellite MERLIN. This is made possible by a new robust laser system of the Fraunhofer Institute for Laser Technology ILT in Aachen, which achieves unprecedented measurement accuracy.
Methane is primarily the result of the decomposition of organic matter. The gas has a 25 times greater warming potential than carbon dioxide, but is not as...
Hydrogen is regarded as the energy source of the future: It is produced with solar power and can be used to generate heat and electricity in fuel cells. Empa researchers have now succeeded in decoding the movement of hydrogen ions in crystals – a key step towards more efficient energy conversion in the hydrogen industry of tomorrow.
As charge carriers, electrons and ions play the leading role in electrochemical energy storage devices and converters such as batteries and fuel cells. Proton...
Scientists from the Excellence Cluster Universe at the Ludwig-Maximilians-Universität Munich have establised "Cosmowebportal", a unique data centre for cosmological simulations located at the Leibniz Supercomputing Centre (LRZ) of the Bavarian Academy of Sciences. The complete results of a series of large hydrodynamical cosmological simulations are available, with data volumes typically exceeding several hundred terabytes. Scientists worldwide can interactively explore these complex simulations via a web interface and directly access the results.
With current telescopes, scientists can observe our Universe’s galaxies and galaxy clusters and their distribution along an invisible cosmic web. From the...
Temperature measurements possible even on the smallest scale / Molecular ruby for use in material sciences, biology, and medicine
Chemists at Johannes Gutenberg University Mainz (JGU) in cooperation with researchers of the German Federal Institute for Materials Research and Testing (BAM)...
19.06.2017 | Event News
13.06.2017 | Event News
13.06.2017 | Event News
23.06.2017 | Physics and Astronomy
23.06.2017 | Physics and Astronomy
23.06.2017 | Information Technology