Structural Study of Trehalose Dihydrate by Neutron and X-ray Diffraction Experiments

The structure of α,α-trehalose dihydrate was studied by neutron and X-ray diffraction experiments to understand the relation between its superior biological protective function and the role of the hydrogen bond connecting the trehalose molecules. By direct observation of hydrogen using the neutron diffraction method, the nuclear positions and anisotropic thermal parameters of hydrogen atoms are determined accurately. The nuclear positions show clear discrepancies from the centers of the electron cloud of hydrogen determined from the X-ray data. The result is interpreted in terms of a local electric dipole moment in the hydrogen atoms. The magnitude of the dipole moment is markedly large for the hydrogen atoms participating in the hydrogen bond. The detailed electron density distribution has been determined by using X-ray data obtained at 150 K. It clearly shows the electron cloud of hydrogen spreading over the chain of hydrogen bonds. It was found that there is a part where the electron density is very lo...