The three-dimensional shape of a molecule relates to how the molecule will work - in a chemical reaction in the laboratory, or in a cell in your body. Once the relationship between the structure and properties is understood, it is often possible to design new materials, such as plastic, drugs, alloys, and superconductors, which have specific desired properties. For instance, crystallographers found that, in its crystal form, coenzyme B12 has a very long chemical bond (on a molecular scale) between the central cobalt and the carbon atom. This located a weak, reactive part of the molecule, where a free radical reaction is initiated when the bond breaks.2 With this knowledge, other scientists may be able to develop new catalysts to speed up the chemical reaction.

A precise fit between two molecules is often the requirement for a reaction. Crystallographers have recently discovered how proteins recognize the shape of DNA to turn genes on and off.3 With information like this, other scientists may design drugs to control blood pressure, inhibit the growth of the AIDS virus, or cure the common cold.

Crystal structure of a protein which regulates DNA. Two gray helical ribbons represent the DNA; cylinders outline the protein ÿ-helices; the dark lines show bonds between atoms in an important part of the protein which makes specific contacts to the DNA.

Liquid crystals are sometimes described as the "fourth state of matter." The molecules in liquid crystals are arranged in an orderly, periodic way, but these materials are fluid, like a liquid. Using diffraction techniques, polarizing microscopy and/or nuclear magnetic resonance (NMR), crystallographers can determine the approximate arrangement of molecules in liquid crystals. They have also studied transitions between liquid crystalline phases in real time using synchrotron x-ray sources. There is still a great deal that we do not understand about these novel materials.

A schematic cartoon showing one possible arrangement of molecules in a liquid crystal. Ovals represent the polar head group and "tails" the hydrocarbon chain.4

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