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Structural Elucidation of Substances by X-ray Crystallography

Structural Elucidation of Substances by X-ray Crystallography

X-ray crystallography is a tool used for determining the atomic and molecular structure of a crystal. X-ray crystallography is still one of the best methods for the structural analysis of many substances. It is a powerful, simple, and reliable technique that is used by laboratories.

This technique was developed in 1912 by William Henry Bragg and William Lawrence Bragg (a father and son team who won the 1915 Nobel Prize in Physics for their work in the field), who built upon earlier work by Max von Laue. X-ray crystallography uses electromagnetic radiation (specifically, X-rays) to determine the molecular and atomic structure of a crystal A three-dimensional picture of the electron densities can then be produced. Information such as the mean position of atoms within the structure, covalent bonding between them, and their crystallographic disorder can then be determined, which represents the three-dimensional structure of a molecule.

The technique of single crystal X-ray crystallography has three basic steps.

First and usually most difficult step is to produce an adequate crystal of the studied material. The crystal should be sufficiently large with all dimensions larger than 0.1 mm, pure in composition and regular in structure, and have no significant internal imperfections such as cracks or twinning. The crystal is subsequently placed in an intense beam of X-rays, usually of a single wavelength, to produce regular reflection pattern. The angles and intensities of diffracted X-rays are measured with each compound having a unique diffraction pattern. Previous reflections disappear and new ones appear along with the gradual rotation of the crystal, and the intensity of every spot is recorded at every orientation of the crystal. Multiple data sets may have to be collected since each set covers slightly more than half a full rotation of the crystal and typically contains tens of thousands of reflections. Ultimately, these collected data are combined computationally with complementary chemical information to obtain and refine a model from the arrangement of atoms within the crystal. The final refined model of the atomic arrangement is called a crystal structure and usually stored in a public database.

Since many diverse types of structure can form crystals, X-ray crystallography can have many research applications. The substances that can be analyzed by this method include salts, minerals, metals, semiconductors as well as biological compounds including proteins, nucleic acids, and vitamins. it is now often used to identify the structure of various biological materials, vitamins, pharmaceutical drugs, thin-film materials, and multi-layered materials. It has become one of the standard ways of analyzing a material if the structure is unknown across the geological, environmental, chemical, material science and pharmaceutical sectors (plus many others) due to its non-destructive nature and its high accuracy and precision. It has become particularly useful across the proteomics and pharmaceutical sectors. Some of the specific areas that can now be probed with X-ray crystallography include measuring the thickness of films, identifying specific crystal phases and orientations that can help to determine the catalytic activity of materials, determining the purity of a sample, determining how a drug might interact with specific proteins and how the drug can be improved, analysing how proteins interact with other proteins, for investigating microstructures, and for analysing what amino acids are present in a protein which can help to determine efficacy of enzyme. These are just a few specific examples of use of X-ray crystallography.  Some macromolecules, especially those with a high atomic weight such as membrane proteins, can be difficult to crystallize. Many different fields of study including biology, chemistry, and geology have found uses of this X-ray crystallography technique.

 

Teacher’s Name: Dr. Madhu Rani Sinha

Designation: Associate Professor

Department: Chemistry

Email id: madhu.che@patnawomenscollege.in