SPring-8, the large synchrotron radiation facility

JASRI, in collaboration with the University of Houston, the University of Michigan, and the University of Tennessee in the United States, has discovered the anomalous electronic state of water confined in nanodomains^*1, such as those in biological cells, which is distinctly different from that of bulk water, for example, water contained in a cup. This was achieved using the high-brilliance and high-energy synchrotron radiation X-rays at SPring-8^*2.

Water molecules consist of a negatively charged oxygen atom and two positively charged hydrogen atoms. Water molecules are considered to be weakly bound to each other by the electrostatic force between oxygen and hydrogen atoms, forming a network structure. This model has also been applied to water confined in small spaces of a few nanometers in scale, namely, nanodomains, and used for the simulation to predict the behavior of water in electrolyte membranes of fuel cells or of biological cells. However, because water confined in nanodomains exhibits a different behavior from bulk water, for example, it does not freeze even at -20 °C, whether this water model can be applied to water confined in nanodomains without modification has remained an unresolved issue.

In order to resolve this issue, the research group precisely measured the momentum distribution of electrons in water molecules confined in nanodomains of two different kinds of nafion (proton exchange membrane) by the “Compton scattering^*3” technique using the high-brilliance and high-energy synchrotron radiation X-rays at SPring-8. As a result, they found that the momentum distribution of electrons in water molecules confined in nanodomains increases and that the amount of increase in the momentum distribution of electrons in such water molecules was 17-fold that estimated using the conventional model for bulk water. These results cannot be explained by the conventional model of water molecules being bonded to each other by a weak electrostatic force to form a network structure. The results strongly suggest the necessity of a new model of water molecules confined in nanodomains, whereby individual water molecules are more strongly bonded to each other. The achievements of this study will provide new insight into the chemistry of water in nanodomains, which has been attracting attention with respect to fuel cells and biological reactions. In addition, the development of simulation methods for predicting the behavior of water molecules on the basis of the water model obtained in this study will promote the development of electrolyte membranes of fuel cells and the understanding of the behavior of water in biological cells. Therefore, it is expected that the achievements will lead to the development of its application in next-generation energy storage systems and to advances in medicine.

The results were achieved by an international joint research team consisting of Masayoshi Ito (associate senior scientist) and Yoshiharu Sakurai (associate chief scientist) of JASRI, George Reiter (Professor) of the University of Houston, Aniruddha Deb (Assistant Professor) of the University of Michigan, and Stephen Padission (Professor) of the University of Tennessee in the United States. Their achievements were published online in the American scientific journal, Physical Review Letters.

Publication:
"Anomalous Ground State of the Electrons in Nanoconfined Water"
G. F. Reiter, Aniruddha Deb, Y. Sakurai, M. Itou, V. G. Krishnam and S. J. Paddison
Physical Review Letters, 111 036803 (2013)