26 June 2009

Super fast film recording makes ultra precise chemistry possible


A Danish research group are the first to film the formation of a new molecule out of two separate chemical substances. It is an achievement that could allow for energy-efficient chemical production and more effective chemical and enzyme processes in everything from waste-water treatment plants to catalytic converters in cars. 

It a typical experiment the researchers take between 40.000
and 60.000 images. To the naked eye the many individual
images are virtually identical. But by letting the computer
analyse the tiny little differences they get a graphic curve,
which describes precisely what happens when the molecules
fuse together.

Exactly what happens when two molecules fuse together and form a completely new chemical compound has always been something of a mystery. The size scale is a millionth of a millimetre. The time scale is less than a billionth of a second. The reaction is also too little to see and too quick to measure.

But a research group from the Danish National Research Foundation's ”Centre for Molecular Movies” under the Department of Chemistry and the Niels Bohr Institute at the University of Copenhagen have been able to make what, in technical terms, is called structural tracking of time-resolved using X-ray scattering. They have in other words made a film of the molecules' dance, where the the individual images in the film represent less than a millionth of a millisecond.

First film of the birth of chemicals
Filming the formation of molecules sounds like something chemists and physicists would do everyday before breakfast. But according to PhD student Morten Christensen, who has stood "behind the camera", the group's work is setting new standards for the field.

”Our article is really front page material. We are the first to have followed a fundamental chemical reaction of this type. In the context of chemistry and physics it is really strong,” explains the young researcher. 

It is only relatively recently that it has become possible to create such short and intense X-ray flashes, which the group has used. And it is even more unusual to be using the method to film the formation of a new molecule during a controlled chemical reaction. 

Together with physicist Kristoffer Haldrup, Morten Christensen has filmed a reaction they controlled. Other research groups have broken up molecules and observed how the remnants recombined.

Follow the process live
The group from the Centre for Molecular Movies created a photoactive platinum molecule in the laboratory at the Department of Chemistry in Copenhagen. By activating the platinum molecule with laser light it is able to bind ions of the metal thallium and when these two substances meet in a liquid solution they form a completely new molecule. After a few microseconds the new molecule breaks up into two parts which are then ready to react again. According to Morten Christensen, it is completely new, being able to control a reaction that can go both ways and being able to follow the structural changes in the process live at the same time.

The film recordings are made at the kilometres long European Synchroton Radiation Facility (ESRF) in Grenoble, which is one of the three places in the world where you can make the most powerful X-ray beams.

With over 3500 visiting researchers a year, the synchroton facility is a popular instrument. Each research team is typically allotted three or four days with the synchroton, so that when they are there they work around the clock. On the other hand the results of the laborious stay make it completely worth it. 

”When we have finished developing this method we will be able to follow precisely how and in what sequence the atoms move around when changes are introduced in the structure of the molecules,” explains Morten Christensen proudly.

Read the article in Angewandte Chemie:
Structural tracking of bimolecular reaction by time-resolved X-ray scattering >>