Jerome Karle – pioneer in X-Ray diffraction studies

Jerome Karle – pioneer in X-Ray diffraction studies

Article on Jerome Karle

Biography & contributions

Jerome Karle is an American physical chemist and Nobel laureate born on June 18, 1918 – died on June 06, 2013. Karle was the co developer of mathematical methods for deducing the molecular structure of chemical compounds from the patterns formed when x-rays are diffracted by their crystals.

Karle and other eminent chemist Herbert A. Hauptman together shared the Nobel Prize in Chemistry in 1985 for their work in using X-ray scattering techniques to determine the structure of crystals and biological, chemical, metallurgical and physical characteristics. They were able to employ the Sayre equation in centrosymmetric structure, developing the so-called direct methods.

In this direct method through isolating the position of the atoms in a crystal, the molecular structure of the material being studied can be determined, allowing processes to be designed to duplicate the molecules being studied. This technique, after over a period of time became crucial for the development of new pharmaceutical products and other synthesized materials.

Facts about x-ray scattering techniques

X-ray scattering techniques are a family of non-destructive analytical techniques which reveal information about the crystal structure, chemical composition, and physical properties of materials and thin films. These techniques are based on observing the scattered intensity of an X-ray beam hitting a sample as a function of incident and scattered angle, polarization, and wavelength or energy.

Crystal Structure

The structure of all crystals can be described in terms of a lattice, with a group of atoms attached to every lattice point. The group of atoms is called the basis; when repeated in space it forms the crystal structure. The basis consists of a primitive cell, containing one single lattice point. Arranging one cell at each lattice point will fill up the entire crystal.

A crystal structure describes a highly ordered structure, occurring due to the intrinsic nature of molecules to form symmetric patterns. A crystal structure can be thought of as an infinitely repeating array of 3D 'boxes', known as unit-cells.

The unit cell is calculated from the simplest possible representation of molecules, known as the asymmetric unit. The asymmetric unit is translated to the unit cell through symmetry operations, and the resultant crystal lattice is constructed through repetition of the unit cell infinitely in 3-dimensions.

A crystal's structure and symmetry play a role in determining many of its physical properties, such as cleavage, electronic band structure, and optical transparency.

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