SCIENCE MUSEUM LONDONMolecular model of penicillin, whose structure was discovered by Dorothy Hodgkin in 1945SCIENCE MUSEUM LONDON
The double helix representing DNA is one of the most recognizable images produced by 20th century science. The discovery of its molecular structure occurred in 1953, thanks largely to the work of British biophysicist Rosalind Franklin, who used the technique known as X-ray diffraction to obtain the image. The story is well known: Francis Crick and James Watson used Franklin’s data—without her knowledge and approval—and wrote the seminal article in 1953, which was published in the journal Nature. The DNA “photo” taken by Franklin is one of the superstar images of crystallography, whose experimental and theoretical methods began to be developed in 1895 with the discovery of X-rays by the German scientist Wilhelm Röntgen. UNESCO recognized the importance of this basic science and has designated 2014 as the International Year of Crystallography.
“Crystallography has been the method most often employed by Nobel Prize winners to date, a total of 29,” says Iris Torriani, a researcher at the Physics Institute of the University of Campinas (Unicamp-IFGW). In September, the National Synchrotron Light Laboratory (LNLS), based in Campinas, will host an international conference on “Biological crystallography and its complementary methods,” and Torriani is one of the coordinators. Originally from Argentina but now living in Brazil, she has been working with crystallography at UNICAMP since 1974. Some of her most significant research is related to the study of biological macromolecules using X-ray scattering at low angles with instrumentation developed under her direction at LNLS.
SCIENCE MUSEUM LONDONThe Braggs: father William Henry (right) and his son Lawrence. Above, the original diffractometerSCIENCE MUSEUM LONDON
After Wilhelm Röntgen’s discovery, physicists plunged into the study of X-ray properties and their applications. In 1912, the German scientist Max von Laue conducted an experiment using diffraction, which showed that X-rays behave like electromagnetic waves. He radiated a crystal and recorded the X-rays transmitted on a radiographic plate. The result was a plate with several points arranged symmetrically, the diffractogram (XRD pattern), which proved the existence of a diffraction network formed by the regular arrangement of atoms in the crystal. By applying mathematical calculations using data observed in the diffractogram (XRD pattern), such as angles, distances between points and their intensity, it was possible to establish the regular arrangement of atoms in a crystal. That is, the atomic structure of the irradiated material was revealed. “X-rays and some mathematical concepts are tools that tell us where each atom is located in the molecules we study,” says Torriani.
In 1913, two scientists, the Englishman William Henry Bragg and his son William Lawrence, made a huge advance in the science of crystallography. Based on experiments by Lawrence, the senior Bragg built the first ray diffractometer. The instrument allowed the X-rays to be directed toward the crystal face at any angle, and recorded the intensity of the diffracted beams using a radiation detector, which went on to become the most accurate and easy-to-use method. The analyzed material could be organic or inorganic in origin. Some materials are obviously not crystalline, and often it is necessary to use complicated techniques to crystallize the object of the study, such as a protein, for example.
KING'S COLLEGE LONDONRosalind Franklin, creator of the seminal image of DNA by X-ray diffraction, which inspired Watson and CrickKING'S COLLEGE LONDON
After developing the diffractometer, the Braggs used it to determine the structure of the diamond in 1913. This work marked the beginning of X-ray crystallography. In subsequent years many other physicists and chemists did the same with many different materials. One of the best examples is that of British chemist Dorothy Hodgkin, who determined the structure of penicillin in 1945, Vitamin B12 in 1957 and insulin in 1969. More recently, in 2009, Ada Yonath, Thomas Steitz and V. Ramakrishnan described the structure of ribosomes, which are responsible for protein synthesis. All won Nobel Prizes in Physics, Chemistry or Physiology and Medicine; to date Lawrence Bragg is the youngest to have been awarded the prize—at age 25, in 1915. The exception was Rosalind Franklin, who had already died by the time Crick, Watson and Wilkins were awarded the prize in 1962.
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