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X-ray crystallography of biological molecules took off with Dorothy Crowfoot Hodgkin, who solved the structures of cholesterol (1937), penicillin (1946) and vitamin B 12 (1956), for which she was awarded the Nobel Prize in Chemistry in 1964. In 1969, she succeeded in solving the structure of insulin, on which she worked for over thirty years.
The contact goniometer was the first instrument used to measure the interfacial angles of crystals. The International Union of Crystallography (IUCr) gives the following definition: "The law of the constancy of interfacial angles (or 'first law of crystallography') states that the angles between the crystal faces of a given species are constant, whatever the lateral extension of these faces ...
This means that X-rays are seemingly "reflected" off parallel crystal lattice planes perpendicular at the same angle as their angle of approach to the crystal with respect to the lattice planes; in the elastic light (typically X-ray)-crystal scattering, parallel crystal lattice planes perpendicular to a reciprocal lattice vector for the crystal ...
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:
Since a measured scattering vector in X-ray crystallography, = with as the outgoing (scattered from a crystal lattice) X-ray wavevector and as the incoming (toward the crystal lattice) X-ray wavevector, is equal to a reciprocal lattice vector as stated by the Laue equations, the measured scattered X-ray peak at each measured scattering vector ...
Molecular replacement (MR) [1] is a method of solving the phase problem in X-ray crystallography.MR relies upon the existence of a previously solved protein structure which is similar to our unknown structure from which the diffraction data is derived.
Inelastically scattered X-rays have intermediate phases and so in principle are not useful for X-ray crystallography. In practice X-rays with small energy transfers are included with the diffraction spots due to elastic scattering, and X-rays with large energy transfers contribute to the background noise in the diffraction pattern.
The discovery of X-rays and electrons in the last decade of the 19th century enabled the determination of crystal structures on the atomic scale, which brought about the modern era of crystallography. The first X-ray diffraction experiment was conducted in 1912 by Max von Laue, [7] while electron diffraction was first realized in 1927 in the ...