Splitting water based on nuclear spin

Separation of water based on the nuclear spin of individual molecules has been made possible thanks to what scientists are dubbing an electric prism. Water exists in two nuclear spin states depending on the orientation of the spin of the hydrogen atoms. They can be either ortho – symmetric with both spins in the same direction, or para –asymmetric with the opposite spins. In theory, water should not be able to switch between the two, but often do as they collide with each other and surfaces around them. “It is very challenging to separate them and produce water that is not a mixture of both,” said Jochen Küpper from Deutsches Elektronen-Synchrotron (DESY) DESY scientists developed a means to isolate ortho or para water from a mixture. They placed a drop of water into a compartment pressurised with neon or argon, which was then released into a vacuum through a pulsed valve. “Due to the large pressure difference, the gas expands quickly into the vacuum when the valve is opened, dragging along water molecules, and at the same time, cooling them down,” said Daniel Horke, first author of the study published in Angewandt Chemie International Edition. This expansion results in a narrow beam of ultracold water molecules which propagate at supersonic speed. Because they are so dilute, individual molecules no longer collide. A strong electric field deflects the molecules from their original path, acting like a prism for nuclear spin states. “Para and ortho water interact with the electric field differently,” said Horke. “Thus they also get deflected differently, allowing us to separate them in space and obtain pure para and ortho samples.” Spectroscopy showed the purity of para and ortho water was 74% and 97% respectively. The work may have important implications for other studies; it could improve NMR to help determine the structure of proteins, for example. “Para hydrogen has successfully been used to enhance the sensitivity of the NMR method,” said Horke. “Enriching para water in a protein’s water shell could become an interesting approach to improve NMR spectroscopy of these biological systems due to an almost natural environment.” In astrophysics it is assumed that the relative amounts of each species can be linked to the temperature of interstellar ice. This theory is based on the temperature dependence of hydrogen’s ortho-to-para ration, approximately three to one at room temperature, dropping as temperature drops. Separating para and ortho water