Celebrating 100 years of X-ray Crystallography
D. Indumathi, The Institute of Mathematical Sciences, Chennai

We know that atoms and molecules in crystals are arranged in ordered structures. They also have many symmetries or periodicities in their arrangement and this gives them different properties. This is why diamond shines while your lead (graphite) pencil does not, although both are made of carbon! (See back inside cover of JM for their structures.) 
Gemstones, snowflakes or grains of salt— all are crystals occurring in nature. Throughout history, people have been fascinated by their beauty and mystery. Two thousand years ago, the process of crystallizing sugar and salt was already known to the ancient Indian and Chinese civilizations. Since then, the study of crystals’ inner structure and properties has known steady progress.
Snowflakes
400 years ago, Kepler observed the symmetrical form of ice crystals (in 1611), thus beginning the wider study of the role of symmetry in matter. Snowflakes are collections of one or more ice crystals  (see cover photo of JM). Their hexagonal (6-sided) symmetry visible in the picture results from the way in which water molecules are bound to each other. 
X-rays and crystal structure
In the early 20th century, it was discovered that X-rays could be used to ‘see’ the structure of matter in a non-intrusive manner, thus beginning the dawn of modern crystallography — the science that examines the arrangement of atoms in solids. When you shine X-rays on crystals, they bounce off in specific directions in a process called diffraction. These rays fall on photographic film and leave complex patterns on it. By studying these patterns it is possible to deduce (guess, in a reasoned fashion) the structure of the crystal. In particular, it also tells us how different atoms in a crystal are bound to each other. Crystallographers now apply this knowledge to modify a structure and thus change its properties and behavior. 
Since this discovery, crystallography has become the very core of structural science, revealing the structure of DNA, allowing us to understand and fabricate computer memories, showing us how proteins are created in cells and helping scientists to design powerful new materials and drugs. Thus crystallography has many applications. It permeates our daily lives and forms the backbone of industries which are increasingly reliant on knowledge generation to develop new products.
International Year of Crystallography
2014 marks the centennial of the birth of X-ray crystallography, thanks to the work of William Henry Bragg and William Lawrence Bragg (father and son) and Max von Laue —the latter was awarded the 1914 Nobel Prize in Physics for his discovery of the diffraction of X-rays by crystals.
A century later, the International Year of Crystallography 2014 highlights the continuing importance of crystallography and its role in widely diverse fields that include agro-food, aeronautics, automobiles, cosmetics and computers as well as the electro-mechanical, pharmaceutical and mining industries.
Biomolecules 
This year also commemorates the 50th anniversary of another Nobel Prize, awarded to Dorothy Hodgkin for her work on vitamin B12 and penicillin.
— See http://www.iycr2014.org/ for more information on the International Year of Crystallography.
Bio Crystals
Dorothy Crowfoot Hodgkin was a British chemist, who was one of the
pioneers of the field of protein crystallography. She is particularly noted for discovering three-dimensional biomolecular structures.

Some biological molecules, such as DNA, can form crystals if treated in
certain ways.  Then these can be studied through X-ray diffraction.

X-ray crystallography of biological molecules was pioneered by Dorothy
Crowfoot Hodgkin. She solved the structures of cholesterol (1937),
penicillin (1946) and vitamin B12 (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.

Cholesterol is an important component of cell membranes. Penicillin is
one of the first antibiotics discovered while Vitamin B12 (or cobalamin),
is crucial for the normal functioning of the brain and nervous system,
and for the formation of blood. Finally, insulin plays an important role
in regulating the matabolism of carbohydrate and fat in the human body.
So you can see that Hodgkin worked on molecules that were important to
life and health.

The picture shows a high-resolution model of six insulin molecules
assembled in a hexamer, highlighting the threefold symmetry. The central
sphere is a zinc ion that holds it together, with the "basketball hoops"
from the zinc being histidine residues involved in zinc binding. Inactive
insulin is stored in the body as a hexamer, while the active form is
the monomer. Hodgkin determined the three-dimensional structure of
insulin.