Observation of laser power changes in ultrafast protein dynamics

When researchers at the Max Planck Institute of Medicine conducted their first ultrafast X-ray crystallographic experiment on myoglobin in 2015, they were not aware that they had conducted the wrong experiment. By increasing the power of X-ray free electron lasers to ensure usable diffraction patterns, lead researcher Ilme Schlichting said that they "suddenly entered the wrong [excited] state without noticing.".

The laser did not observe a single photon excitation pathway that reflects the natural dynamics of myoglobin, but instead violently collided to induce multiphoton absorption. This raises a question, is the oscillation they see in protein artifacts this more energetic excitation? Now, Schlichting and her team have conducted experiments again at lower power for inspection.

The result surprised Schlichting. "We anticipate slight changes in the dynamics, but what we see is a significant change in carbon monoxide," she said. Unlike the instant photolysis they observed at high laser power, this reaction took hundreds of femtoseconds at low power. She said that the group modeled their observations and attributed their results to two different reaction pathways, the latter of which may better represent real reactions.

However, myoglobin only differs slightly at low power. This reassures Richard Neutz, a biochemistry professor at the University of Gothenburg. Although unrelated to the group, he did review the work before publication and wrote corresponding opinions on the impact of the results. "This work is very important because it indicates that we were not completely wrong before," he said. Essentially, past high-power experiments were not perfect, but still provided valuable insights into protein dynamics. "On the other hand," Neutze said, "the author also suggests that if you are really interested in ultrafast chemistry, it is important to conduct experiments correctly because there are subtle differences in the mechanisms that are important.".

In the end, Schlichting said that researchers only need to remain transparent about the systems they are engaged in. These experiments themselves are challenging. "Sometimes you either go home without any data or do it in a multiphoton state," she said, "but you should be honest with it.".

Source: Laser Net