"It's an extremely common situation to have a mixture say a blood sample, or something from a complex chemical process - that contains a left-handed version of some compounds and a right handed version others for example, left handed alanine along with right handed citric acid. Optical polarimetery really struggles with such a situation if there's more than about 3 compounds, it's pretty hopeless. We hope our technique will provide a tool which can produce a complete analysis of such a mixture".
In contrast, the method developed by Patterson, Doyle and Schnell, by comparison, relies on what is called the electric dipole moment of each molecule, or the way each interacts with an external electric field. As a consequence of their mirror-image construction, molecules rotate in opposite directions when certain microwave fields are applied and this results in a signature which tells if the molecules are left or right handed.
To measure the dipole moment of molecules, the team used microwaves.
Researchers fed a gaseous sample into a chamber, then cooled it to -226 degrees Celsius. As the cold gas interacted with a precisely-tuned microwave fieldwhich caused the molecules to spin and give off their own microwave radiation. By monitoring those emissions, researchers are able to tell whether the molecules are right- or left-handed.
The researchers tested their method using the organic compound 1,2-propanediol, and were able to reliably differentiate between the two variants, but also determine the ratio of variants in a mixture by finely-tuning the microwave frequency.
"We can soon measure mixtures of different compounds and determine the enantiomer ratios of each," explains Schnell. In a next step the researchers plan to apply the technique in a broadband spectrometer at CFEL that could then measure the ratios in other mixtures of substances.
In the longer run,
|Contact: Peter Reuell|