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X-ray Crystallography

X-ray crystallography

X-ray crystallography was first developed as a means of determining the nature of X-rays themselves. It was not intended to be a research tool. In crystallography X-rays are used to probe the structures of crystals. The pattern of diffracted X-rays is similar to an atomic "shadow." By examining where the X-rays are blocked by the crystal's atoms, scientists can define the structure of those atoms.

Medical Uses for Crystallography

Perhaps the most important application of X-ray crystallography is its use in synthesizing (blending) substances. Many of the medicinal chemicals that have been discovered by scientists are very difficult to produce naturally in large amounts. When this happens, it becomes necessary to create the chemicals in the laboratory through synthesis. Before a chemist can synthesize a substance, a map of its atomic structure must be obtained. This map can only be drawn by using X-ray crystallography.

Few scientists have been more successful at this than British chemist Dorothy Hodgkin (1910-). During World War II (1939-1945), Hodgkin and her colleagues determined the structure of penicillin. The synthesis of this drug was necessary for mass wartime production. Since then Hodgkin's team has worked on the mapping of vitamin B12, the vitamin prescribed to prevent pernicious anemia (a chronic blood disorder characterized by weakness and pallor). The team also worked on mapping insulin. Insulin is used in the treatment of diabetes (another blood disorder).

Other researchers have used X-ray technologies to record the structures of proteins, hemoglobin, and the double-helix of DNA structure (deoxyribonucleic acid).

Creating a New Science

The development of X-ray crystallography also created the science of mineralogy. Once the inner structures of many minerals were determined, mineralogists were able to define the major mineral groups. The understanding that stems from crystallography has also allowed scientists to construct the man-made minerals used in industry.

[See also Barium ; Bragg, William Henry and William Lawrence ; Coolidge, William ; Radiotherapy ]

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X-ray crystallography

X-ray crystallography, the study of crystal structures through X-ray diffraction techniques. When an X-ray beam bombards a crystalline lattice in a given orientation, the beam is scattered in a definite manner characterized by the atomic structure of the lattice. This phenomenon, known as X-ray diffraction, occurs when the wavelength of X-rays and the interatomic distances in the lattice have the same order of magnitude. In 1912, the German scientist Max von Laue predicted that crystals exhibit diffraction qualities. Concurrently, W. Friedrich and P. Knipping created the first photographic diffraction patterns. A year later Lawrence Bragg successfully analyzed the crystalline structures of potassium chloride and sodium chloride using X-ray crystallography, and developed a rudimentary treatment for X-ray/crystal interaction (Bragg's Law). Bragg's research provided a method to determine a number of simple crystal structures for the next 50 years. In the 1960s, the capabilities of X-ray crystallography were greatly improved by the incorporation of computer technology. Modern X-ray crystallography provides the most powerful and accurate method for determining single-crystal structures. Structures containing 100–200 atoms now can be analyzed on the order of 1–2 days, whereas before the 1960s a 20-atom structure required 1–2 years for analysis. Through X-ray crystallography the chemical structure of thousands of organic, inorganic, organometallic, and biological compounds are determined every year.

See M. Buerger, X-Ray Crystallography (1980).

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X-ray crystallography

X-ray crystallography The use of X-ray diffraction to determine the structure of crystals or molecules, such as nucleic acids. The technique involves directing a beam of X-rays at a crystalline sample and recording the diffracted X-rays on a photographic plate. The diffraction pattern consists of a pattern of spots on the plate, and the crystal structure can be worked out from the positions and intensities of the diffraction spots. X-rays are diffracted by the electrons in the molecules and if molecular crystals of a compound are used, the electron density distribution in the molecule can be determined.

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X-ray diffraction crystallography

X-ray diffraction crystallography A method of analysis in which an X-ray beam of known wavelength is directed at a crystal, and the beam is diffracted by reflections off planes of atoms in the crystal. By recording the angular positions of diffracted beams, the spacing between atomic planes can be determined according to the Bragg equation, nλ = 2d sinθ (see BRAGG'S LAW). The procedure is repeated for various directions in the crystal and a model of its internal structure established. In geology, the technique is used to identify minerals.

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X-ray crystallography

X-ray crystallography Use of X-rays to discover the molecular structure of crystals. It uses the phenomenon of X-ray diffraction, the scattering of an X-ray beam by the atomic structure of a crystal, and has been used to show that DNA can produce crystals.

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