Irradiating ammonia– which is made up of one nitrogen and 3 hydrogens– with ultraviolet light causes one hydrogen to dissociate from the ammonia. SLAC researchers utilized an ultrafast “electron video camera” to see exactly what that hydrogen was doing as it dissociated.
Proving the method works puts scientists one action closer to deciphering the secrets of hydrogen transfers.
Scientists have actually captured fast-moving hydrogen atoms– the keys to many biological and chemical reactions– in action.
A group led by scientists at the Department of Energys SLAC National Accelerator Laboratory and Stanford University utilized ultrafast electron diffraction (UED) to record the movement of hydrogen atoms within ammonia molecules. Others had thought they might track hydrogen atoms with electron diffraction, but up until now no one had actually done the experiment effectively.
Irradiating ammonia– which is made up of one nitrogen and 3 hydrogens– with ultraviolet light causes one hydrogen to dissociate from the ammonia. SLAC scientists used an ultrafast “electron camera” to view exactly what that hydrogen was doing as it dissociated. In the future, researchers might use the strategy to study hydrogen transfers– vital chemical responses that drive many biological processes. They used gas-phase ammonia, which has 3 hydrogen atoms connected to a nitrogen atom. The team struck ammonia with ultraviolet light, dissociating, or breaking, one of the hydrogen-nitrogen bonds, then fired a beam of electrons through it and recorded the diffracted electrons.
The Potential of High-Energy Electrons
The results, released on October 5 in the journal Physical Review Letters, leverage the strengths of high-energy Megaelectronvolt (MeV) electrons for studying hydrogen atoms and proton transfers, in which the particular proton that makes up the nucleus of a hydrogen atom moves from one molecule to another.
Proton transfers drive numerous responses in biology and chemistry– believe enzymes, which assist catalyze biochemical reactions, and proton pumps, which are vital to mitochondria, the powerhouses of cells– so it would be practical to understand exactly how its structure develops during those reactions. But proton transfers occur super-fast– within a few femtoseconds, one-millionth of one billionth of one second. Its challenging to catch them in action.
Obstacles in Observation Techniques.
One possibility is to shoot X-rays at a particle, and then use the spread X-rays to find out about the particles structure as it develops. Unfortunately, X-rays only communicate with electrons– not atomic nuclei– so its not the most delicate approach.
To get to the responses they were looking for, a team led by SLAC scientist Thomas Wolf, put MeV-UED, SLACs ultrafast electron diffraction video camera to work. They utilized gas-phase ammonia, which has three hydrogen atoms connected to a nitrogen atom. The team struck ammonia with ultraviolet light, dissociating, or breaking, one of the hydrogen-nitrogen bonds, then fired a beam of electrons through it and caught the diffracted electrons.
Achievements and Implications.
In this procedure, the group successfully detected signals from the hydrogen atom separating from the nitrogen nucleus and noted the subsequent molecular structural modification. Additionally, the deflected electrons shot off at various angles, enabling differentiation in between the two signals.
” Having something thats delicate to the electrons and something thats delicate to the nuclei in the same experiment is very beneficial,” Wolf said. “If we can see what takes place first when an atom dissociates– whether the nuclei or the electrons make the very first transfer to separate– we can address concerns about how dissociation reactions occur.”.
With that info, scientists could surround the elusive system of proton transfer, which could assist to address myriad questions in chemistry and biology. Knowing what protons are doing might have important implications in structural biology, where traditional methods like X-ray crystallography and cryo-electron microscopy have difficulty “seeing” protons.
Future Directions.
In the future the group will do the exact same experiment utilizing X-rays at SLACs X-ray laser, the Linac Coherent Light Source (LCLS), to see just how various the outcomes are. They also hope to up the intensity of the electron beam and improve the time resolution of the experiment so that they can really fix private steps of proton dissociation gradually.
Reference: “Femtosecond Electronic and Hydrogen Structural Dynamics in Ammonia Imaged with Ultrafast Electron Diffraction” by Elio G. Champenois, Nanna H. List, Matthew Ware, Mathew Britton, Philip H. Bucksbaum, Xinxin Cheng, Martin Centurion, James P. Cryan, Ruaridh Forbes, Ian Gabalski, Kareem Hegazy, Matthias C. Hoffmann, Andrew J. Howard, Fuhao Ji, Ming-Fu Lin, J. Pedro F. Nunes, Xiaozhe Shen, Jie Yang, Xijie Wang, Todd J. Martinez and Thomas J. A. Wolf, 5 October 2023, Physical Review Letters.DOI: 10.1103/ PhysRevLett.131.143001.
The research was funded in part by the DOE Office of Science. MeV-UED is an instrument of SLACs LCLS X-ray laser facility. LCLS is a DOE Office of Science user center.
