What do diamonds, ice, sand, and table salt have in common? Like most solids, they have crystalline structures: they are made up of atoms or molecules arranged in a regular, repeating order. A century ago, scientists developed a technique called x-ray crystallography that made it possible to analyze the structure of crystalline solids. Since that time crystallography has become a key tool in many scientific fields, including mineralogy, medicine, archaeology, and food science. Twenty-three Nobel Prizes have been awarded for discoveries that relied on crystallography.
The United Nations and the International Union of Crystallography have proclaimed 2014 the International Year of Crystallography to educate people about this versatile technique, which is still relatively unknown to the general public. Since crystallography is widely used in many different scientific fields, this event offers a teaching hook for chemistry, physics, and biology classes.
Annenberg’s new chemistry course, Chemistry: Challenges and Solutions, unit 13, describes the chemical bonds that hold crystalline substances together, and the insight that launched the field of crystallography. British physicist William Henry Bragg and his son William Lawrence Bragg recognized that when a beam of X-rays was aimed at a crystal, planes of atoms within the crystal would diffract (scatter) the rays in patterns that could be used to map the crystal’s internal structure. The Braggs shared a Nobel Prize in 1915 for their work.
Physical Science, session 5, “Density and Pressure,” explains X-ray diffraction and how scientists can use it to reconstruct the size and shape of particles that are too small to be seen with the naked eye. X-rays make this kind of visualization possible because their wavelengths are short enough to interact with individual atoms of molecules.
Crystallography generated key insights in early medical research. Dorothy Crowfoot Hodgkin, a British chemist, used it to map the structures of insulin, penicillin, and vitamin B-12. In 1964 Hodgkin became the third woman to receive the Nobel Prize in chemistry, following Marie Curie and Irène Joliot-Curie. Another key advance occurred when researchers found ways to crystallize biological materials, such as proteins and DNA. In Annenberg’s Rediscovering Biology course, unit 2, “Proteins and Proteomics,” Ned David describes the rapid evolution of techniques for crystallizing proteins. Drug designers use crystallography to visualize the three-dimensional structure of a protein so that they can find the best place for a drug to bind snugly to the protein.
The invention of synchrotrons (large particle accelerators that generate intense light and x-rays) has furthered the growth of crystallography. For examples of crystallography’s diverse applications, see the web page for x-ray scattering research at Lawrence Berkeley Laboratory’s Advanced Light Source. The International Year of Crystallography’s learning page has images, video and audio clips, and links to other online resources about crystallography.
How will you be teaching about crystallography in 2014?