Multi-wavelength anomalous diffraction (sometimes Multi-wavelength anomalous dispersion; abbreviated MAD) is a technique used in
X-ray crystallography
X-ray crystallography is the experimental science of determining the atomic and molecular structure of a crystal, in which the crystalline structure causes a beam of incident X-rays to Diffraction, diffract in specific directions. By measuring th ...
that facilitates the determination of the three-dimensional structure of biological macromolecules (e.g. DNA, drug receptors) via solution of the
phase problem
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 de ...
.
MAD was developed by
Wayne Hendrickson while working as a
postdoctoral research
A postdoctoral fellow, postdoctoral researcher, or simply postdoc, is a person professionally conducting research after the completion of their doctoral studies (typically a PhD). Postdocs most commonly, but not always, have a temporary acade ...
er under
Jerome Karle
Jerome Karle (born Jerome Karfunkle; June 18, 1918 – June 6, 2013) was an American physical chemist. Jointly with Herbert A. Hauptman, he was awarded the Nobel Prize in Chemistry in 1985, for the direct analysis of crystal structures using X-ra ...
at the
United States Naval Research Laboratory
The United States Naval Research Laboratory (NRL) is the corporate research laboratory for the United States Navy and the United States Marine Corps. Located in Washington, DC, it was founded in 1923 and conducts basic scientific research, appl ...
.
The mathematics upon which MAD (and progenitor
Single-wavelength anomalous diffraction Single-wavelength anomalous diffraction (SAD) 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 ...
) was based were developed by
Jerome Karle
Jerome Karle (born Jerome Karfunkle; June 18, 1918 – June 6, 2013) was an American physical chemist. Jointly with Herbert A. Hauptman, he was awarded the Nobel Prize in Chemistry in 1985, for the direct analysis of crystal structures using X-ra ...
, work for which he was awarded the 1985
Nobel Prize in Chemistry
The Nobel Prize in Chemistry () is awarded annually by the Royal Swedish Academy of Sciences to scientists in the various fields of chemistry. It is one of the five Nobel Prizes established by the will of Alfred Nobel in 1895, awarded for outst ...
(along with
Herbert Hauptman).
Compared to the predecessor SAD, MAD has greatly elevated phasing power from using multiple wavelengths close to the edge. However, because it requires a synchrotron beamline, a longer exposure (risking radiation damage), and only allows a limited choice of heavy atoms (those with edges reachable by a synchrotron), MAD has declined in popularity relative to SAD.
See also
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Single wavelength anomalous dispersion (SAD)
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Multiple isomorphous replacement (MIR)
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Anomalous scattering
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Anomalous X-ray scattering Anomalous X-ray scattering (AXRS or XRAS) is a non-destructive determination technique within X-ray diffraction that makes use of the anomalous dispersion that occurs when a wavelength is selected that is in the vicinity of an absorption edge of on ...
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Patterson map
References
Further reading
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External links
MAD phasing— an in depth tutorial with examples, illustrations, and references.
NRL Recognition of Nobel Prize
Computer programs
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''Shake-and-Bake''
(''SnB'') —
SHELX
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Tutorials and examples
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{{Crystallography
Crystallography