In X-ray crystallography, anomalous scattering refers to a change in a diffracting X-ray’s phase that is unique from the rest of the atoms in a crystal due to strong X-ray absorbance . The amount of energy that individual atoms absorb depends on their atomic number. The relatively light atoms found in proteins such as carbon, nitrogen, and oxygen do not contribute to anomalous scattering at normal X-ray wavelengths used for X-ray crystallography . Thus, in order to observe anomalous scattering, a heavy atom must be native to the protein or a heavy atom derivative should be made. In addition, the X-ray’s wavelength should be close to the heavy atom’s absorption edge.

Anomalous Dispersion

• Multi-wavelength anomalous dispersion
  Multi-wavelength anomalous dispersion
  Multi-wavelength anomalous diffraction is a technique used in X-ray crystallography that facilitates the determination of the three-dimensional structure of biological macromolecules via solution of the phase problem...
  
   (MAD)
• Single wavelength anomalous dispersion
  Single wavelength anomalous dispersion
  Single-wavelength anomalous dispersion is a technique used in X-ray crystallography that facilitates the determination of the structure of proteins or other biological macromolecules by allowing the solution of the phase problem. In contrast to multi-wavelength anomalous dispersion, SAD uses a...
  
  (SAD)