X-ray prism reveals chemical changes
12 Dec 2012 by qmcqmmjcbp.d qmcqmmjcbp.d
Ultrashort, ultrabright X-ray laser pulses can reveal details of chemically important molecules at room temperature suggest researchers at SLAC National Accelerator Laboratory. This method could shed light on the chemistry behind processes such as photosynthesis or aid studies of industrial catalysts. The team used X-ray emission spectroscopy to learn about the chemical makeup of samples and whether this would change over time.
A very simple spectrometer is a prism that separates sunlight into a rainbow of colours.
“The spectrometer used in the LCLS experiments works in a similar fashion with an array of 16 specialised crystals that select the different ‘colours’ of emitted X-rays,” explained Roberto Alonso-Mori, a research associate at SLAC who built the new spectrometer.
The team focuses on complexes containing manganese, an important element in the water-splitting stage of photosynthesis. Similar compounds to manganese can be found in industrial catalysts.
The researchers found that manganese compounds remain intact for long enough to obtain detailed information about their chemical environment before the compounds were destroyed in the X-ray pulses.
“Previous experiments at LCLS have shown that the intact overall atomic structure of biological samples can be probed at room temperature before they are destroyed. This study goes one step further, showing that even the local chemistry at the metal site can be probed,” said Uwe Bergmann, deputy director for the LCLS and study leader.
The method can also be used in conjunction with X-ray diffraction to reveal the overall structure of proteins and other molecules based on patterns produced when X-ray light strikes the crystalized samples.
Previous research has involved diffraction at LCLS to study the structure of Photosystem ii, an important protein complex in photosynthesis. Future research will use the X-ray emission spectroscopy to study this molecule.
The team say that spectroscopy is the key to revealing chemical changes over time in sensitive samples studied at LCLS.
“The atomic structure is important, but for a complete understanding of complex processes, like photosynthesis, the chemistry is what’s really important,” said Bergman.
The research is published in Proceedings of the National Academy of Sciences.
