Accurate determination of electron density distribution of orbital ordered state using large-angle CBED patterns

Evaluation of accuracy in the determination of crystal structure factors using large-angle convergent-beam electron diffraction patterns

Microscopy ◽

10.1093/jmicro/dfaa041 ◽

2020 ◽

Author(s):

Daisuke Morikawa ◽

Kenji Tsuda

Keyword(s):

Electron Diffraction ◽

Density Distribution ◽

Electron Density ◽

Electron Density Distribution ◽

Large Angle ◽

Convergent Beam Electron Diffraction ◽

Beam Electron ◽

Diffraction Patterns ◽

Convergent Beam ◽

Ordered State

Abstract The accuracy of electron density distribution analysis using large-angle convergent-beam electron diffraction (LACBED) patterns is evaluated for different convergence angles. An orbital ordered state of FeCr2O4 is used as an example of the analysis. Ideal orbital-ordered and non-ordered states are simulated by using orbital scattering factors. LACBED patterns calculated for the orbital-ordered state were used as hypothetical experimental data sets. Electron density distribution of the Fe 3d orbitals has been successfully reconstructed with a higher accuracy from LACBED patterns with convergence angles larger than 15.2 mrad, which is 4 times as large as that for conventional convergent-beam electron diffraction patterns. Excitation of particular Bloch waves with the aid of LACBED patterns has a key role in the accurate analysis of electron density distributions.

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High-resolution neutron and X-ray diffraction room-temperature studies of an H-FABP–oleic acid complex: study of the internal water cluster and ligand binding by a transferred multipolar electron-density distribution

IUCrJ ◽

10.1107/s2052252515024161 ◽

2016 ◽

Vol 3 (2) ◽

pp. 115-126 ◽

Cited By ~ 22

Author(s):

E. I. Howard ◽

B. Guillot ◽

M. P. Blakeley ◽

M. Haertlein ◽

M. Moulin ◽

...

Keyword(s):

Oleic Acid ◽

Fatty Acid ◽

High Resolution ◽

Density Distribution ◽

Electron Density ◽

Electron Density Distribution ◽

Room Temperature ◽

Water Molecules ◽

X Ray

Crystal diffraction data of heart fatty acid binding protein (H-FABP) in complex with oleic acid were measured at room temperature with high-resolution X-ray and neutron protein crystallography (0.98 and 1.90 Å resolution, respectively). These data provided very detailed information about the cluster of water molecules and the bound oleic acid in the H-FABP large internal cavity. The jointly refined X-ray/neutron structure of H-FABP was complemented by a transferred multipolar electron-density distribution using the parameters of the ELMAMII library. The resulting electron density allowed a precise determination of the electrostatic potential in the fatty acid (FA) binding pocket. Bader's quantum theory of atoms in molecules was then used to study interactions involving the internal water molecules, the FA and the protein. This approach showed H...H contacts of the FA with highly conserved hydrophobic residues known to play a role in the stabilization of long-chain FAs in the binding cavity. The determination of water hydrogen (deuterium) positions allowed the analysis of the orientation and electrostatic properties of the water molecules in the very ordered cluster. As a result, a significant alignment of the permanent dipoles of the water molecules with the protein electrostatic field was observed. This can be related to the dielectric properties of hydration layers around proteins, where the shielding of electrostatic interactions depends directly on the rotational degrees of freedom of the water molecules in the interface.

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