How you get the chameleon of the molecules to settle on a particular “look” has been discovered by RUB chemists led by Professor Dominik Marx. The molecule CH5+ is normally not to be described by a single rigid structure, but is dynamically flexible.
Giving the “chameleon” molecule structure: Depending on how many H2 solvent molecules (blue) attach to the CH5+ molecule, the area in which the hydrogen atoms of the CH5+ molecule move changes (red). Its structure is thus partially “frozen”. The areas represent quantum mechanical probability densities at a temperature of 20 Kelvin.
Image: A. Witt, S. Ivanov, D. Marx
By means of computer simulations, the team from the Centre for Theoretical Chemistry showed that CH5+ takes on a particular structure once you attach hydrogen molecules. “In this way, we have taken an important step towards understanding experimental vibrational spectra in the future”, says Dominik Marx. The researchers report in the journal “Physical Review Letters”.
In the CH5+ molecule, the hydrogen atoms are permanently on the move
The superacid CH5+, also called protonated methane, occurs in outer space - where new stars are formed. Researchers already discovered the molecule in the 1950s, but many of its features are still unknown. Unlike conventional molecules in which all the atoms have a fixed position, the five hydrogen atoms in CH5+ are constantly moving around the carbon centre. Scientists speak of “hydrogen scrambling”.
This dynamically flexible structure has been explained by the research groups led by Dominik Marx and Stefan Schlemmer of the University of Cologne as part of a long-term collaboration (we reported in July 2005 and March 2010: http://www.pm.ruhr-uni-bochum.de/pm2005/msg00209.htm, http://aktuell.rub.de/pm2010/msg00066.htm).
Marx‘s team now wanted to know if the structure can be “frozen” under certain conditions by attaching solvent molecules – a process called microsolvation.
Microsolvatation: addition of hydrogen molecules to CH5+ one by one
To this end, the chemists surrounded the CH5+ molecule in the virtual lab with a few hydrogen molecules (H2). Here, the result is the same as when dissolving normal ions in water: a relatively tightly bound shell of water molecules attaches to each ion in order to then transfer individual ions with several solvent molecules bound to them to the gas phase. To describe the CH5+ hydrogen complexes, classical ab initio molecular dynamics simulations are not sufficient. The reason is that “hydrogen scrambling” is based on quantum effects. Therefore Marx’s group used a fully quantum mechanical method which they developed in house, known as ab initio path integral simulation. With this, the essential quantum effects can be taken into account dependent on the temperature.
Hydrogen molecules give the CH5+ molecule “structure”
The chemists carried out the simulations at a temperature of 20 Kelvin, which corresponds to -253 degrees Celsius. In the non-microsolvated form, the five hydrogen atoms in the CH5+ molecule are permanently changing positions even at such low temperatures - and entirely due to quantum mechanical effects. If CH5+ is surrounded by hydrogen molecules, this “hydrogen scrambling” is, however, significantly effected and may even completely come to a halt: the molecule assumes a rudimentary structure. How this looks exactly depends on how many hydrogen molecules are attached to the CH5+ molecule. “What especially interests me is if superfluid helium - like the hydrogen molecules here – can also stop hydrogen scrambling in CH5+” says Marx.
Experimental researchers use superfluid helium to measure high-resolution spectra of molecules embedded in such droplets. For CH5+ this has so far not been possible. In the superfluid phase, the helium atoms are, however, indistinguishable due to quantum statistical effects. To be able to describe this fact, the theoretical chemists at the RUB spent many years developing a new, even more complex path-integral-based simulation method that has recently also been applied to real problems.
Researchers at the RUB explore the influences of microsolvation on small molecules in the gas phase and in helium droplets in the Excellence Cluster “Ruhr Explores Solvation” RESOLV (EXC 1069), which was approved by the German Research Foundation in June 2012.
A. Witt, S. Ivanov, D. Marx (2013): Microsolvation-Induced Quantum Localization in Protonated Methane, Physical Review Letters, doi: 10.1103/PhysRevLett.110.083003
Prof. Dr. Dominik Marx, Centre for Theoretical Chemistry, Department of Chemistry and Biochemistry at the Ruhr-Universität, 44780 Bochum, Germany, Tel. +49/234/32-28083, E-Mail: email@example.com
Click for moreAnimations and background information on pure CH5+
Dr. Josef König | idw
Nanoparticle Exposure Can Awaken Dormant Viruses in the Lungs
16.01.2017 | Helmholtz Zentrum München - Deutsches Forschungszentrum für Gesundheit und Umwelt
Cholera bacteria infect more effectively with a simple twist of shape
13.01.2017 | Princeton University
Laser-driving of semimetals allows creating novel quasiparticle states within condensed matter systems and switching between different states on ultrafast time scales
Studying properties of fundamental particles in condensed matter systems is a promising approach to quantum field theory. Quasiparticles offer the opportunity...
Among the general public, solar thermal energy is currently associated with dark blue, rectangular collectors on building roofs. Technologies are needed for aesthetically high quality architecture which offer the architect more room for manoeuvre when it comes to low- and plus-energy buildings. With the “ArKol” project, researchers at Fraunhofer ISE together with partners are currently developing two façade collectors for solar thermal energy generation, which permit a high degree of design flexibility: a strip collector for opaque façade sections and a solar thermal blind for transparent sections. The current state of the two developments will be presented at the BAU 2017 trade fair.
As part of the “ArKol – development of architecturally highly integrated façade collectors with heat pipes” project, Fraunhofer ISE together with its partners...
At TU Wien, an alternative for resource intensive formwork for the construction of concrete domes was developed. It is now used in a test dome for the Austrian Federal Railways Infrastructure (ÖBB Infrastruktur).
Concrete shells are efficient structures, but not very resource efficient. The formwork for the construction of concrete domes alone requires a high amount of...
Many pathogens use certain sugar compounds from their host to help conceal themselves against the immune system. Scientists at the University of Bonn have now, in cooperation with researchers at the University of York in the United Kingdom, analyzed the dynamics of a bacterial molecule that is involved in this process. They demonstrate that the protein grabs onto the sugar molecule with a Pac Man-like chewing motion and holds it until it can be used. Their results could help design therapeutics that could make the protein poorer at grabbing and holding and hence compromise the pathogen in the host. The study has now been published in “Biophysical Journal”.
The cells of the mouth, nose and intestinal mucosa produce large quantities of a chemical called sialic acid. Many bacteria possess a special transport system...
UMD, NOAA collaboration demonstrates suitability of in-orbit datasets for weather satellite calibration
"Traffic and weather, together on the hour!" blasts your local radio station, while your smartphone knows the weather halfway across the world. A network of...
10.01.2017 | Event News
09.01.2017 | Event News
05.01.2017 | Event News
17.01.2017 | Earth Sciences
17.01.2017 | Machine Engineering
17.01.2017 | Physics and Astronomy