Symposium on Teaching Crystallography
Introduction Mlrlam Rosa Vassar College. Poughkeepsie, NY 12601 Helen M. b n n a n President, American Crystallographic Association Fox Chase Cancer Center, 7701 Burholme Avenue, Philadelphia, PA 19111
As a technique, X-ray diffraction has been responsible for results leading to fundamental and important structural concepts in rimarkably varied areas since the first X-ray photograph was taken in 1912. I t remains the single most general method for the determination of the -.-~ - - exnerimental ~ structure of molecules, large and small. Modern chemistry, withits emphasis on the nature of the chemical bond, as well as the newer field of molecular biology owe their beginnings to structural results derived from X-ray diffraction. Most of the early X-ray analyses focused on structures of known structural formulas, for example, the verification of the flat ring structure of benzene in 1928 by Kathleen Lonsdale. Other oroblems of chemical significance have been studied for which the relevant molecul& structures were not known; sometimes these crystallographic results have gone against the proposed molecular structures obtained from conventional cbemical methods. For example, the correct steroid skeleton structure, the structures of penicillin andvitamin BIZ,all of which eluded chemists for quite some time, were determined by Dorothy Hodgkin and her co-workers. Likewise, the work on boron hydrides by William Lipscomb led to a revision in the ideas about chemical valency and a newfound appreciation for the intricacies of boron chemistry. Similarly, the description of the double helical structure of DNA by Watson and Crick in 1952 from an interpretation of the X-ray photographs of Rosalind Franklin has been legendary in its impact on the scientific world. Crrstallomaphy bridges the cbemical, biological, physical, and material sciences. I t s importance can be seen in a perusal of the number of Nobel Prizes (see table) in the areas of chemistry, physics, and medicine and physiology that have been awarded throughout the years for work in this area. In fact. the verv first Nobel Prize ever awarded in Phvsics (1901) was to Roentgen for his discovery of X-rays. ~Gbseouent awards recoenize the develooment of the theory of Xray diffraction, themethods used ior structure solut
