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An X-ray diffraction pattern of a crystallized enzyme. The pattern of spots (reflections) and the relative strength of each spot (intensities) can be used to determine the structure of the enzyme. The relative intensities of the reflections provides information to determine the arrangement of molecules within the crystal in atomic detail.
A regular array of scatterers produces a regular array of spherical waves. Although these waves cancel one another out in most directions through destructive interference, they add constructively in a few specific directions. [21] [22] [23] An intuitive understanding of X-ray diffraction can be obtained from the Bragg model of diffraction. In ...
"Phase determination by multiple-wavelength X-ray diffraction: crystal structure of a basic blue copper protein from cucumbers". Science 241, 806–811. B. Vijayakumar and D. Velmurugan (2013). "Use of europium ions for SAD phasing of lysozyme at the Cu Kα wavelength" Acta Crystallogr. F69, 20–24.
The Scherrer equation, in X-ray diffraction and crystallography, is a formula that relates the size of sub-micrometre crystallites in a solid to the broadening of a peak in a diffraction pattern. It is often referred to, incorrectly, as a formula for particle size measurement or analysis.
The measurement of the angles can be used to determine crystal structure, see x-ray crystallography for more details. [ 5 ] [ 13 ] As a simple example, Bragg's law, as stated above, can be used to obtain the lattice spacing of a particular cubic system through the following relation:
The units of the structure-factor amplitude depend on the incident radiation. For X-ray crystallography they are multiples of the unit of scattering by a single electron (2.82 m); for neutron scattering by atomic nuclei the unit of scattering length of m is commonly used.
The most common powder X-ray diffraction (XRD) refinement technique used today is based on the method proposed in the 1960s by Hugo Rietveld. [2] The Rietveld method fits a calculated profile (including all structural and instrumental parameters) to experimental data.
In physics, the phase problem is the problem of loss of information concerning the phase that can occur when making a physical measurement. The name comes from the field of X-ray crystallography, where the phase problem has to be solved for the determination of a structure from diffraction data. [1]