Presentation Speech by Professor Ingvar Lindqvist of the Royal Academy of Sciences

Translation from the Swedish text

Your Majesties, Your Royal Highnesses, Ladies and Gentlemen,

The youth of to-day find it quite natural that there are such things as atoms and molecules. They have often seen molecular models in school and experienced the molecule as something obviously existing. There have been people over thousands of years who have come to the conclusion – instinctively, emotionally, or logically – that molecules should exist. These people have also had ideas about the shape and properties of the molecules.

These efforts reached their climax at the end of the 19th century in three extraordinary theories: the idea by van ‘t Hoff about the significance of the tetrahedral carbon atom, the revelation by Kekult of the structure of benzene and the description by Werner of many metal complexes as having octahedral, tetrahedral or planar square structures. The geniality of these ideas has been strongly confirmed in our century to an extent which proves how epoch-making these achievements were.

It is not, however, until the 20th century that the scientists have created methods which admit a complete determination of the structures of molecules. In this context structure means the geometrical arrangement of atoms as well as the bonding distances between atoms. The most important of these methods is X-ray crystallography.

In such investigations the X-rays are arranged to strike a crystal. The radiation is then scattered in certain directions and the light intensity is measured for each such scattered X-ray. Such an experiment was first made by Max von Laue who obtained the Nobel Prize for physics in 1914 for his discovery. The Braggs, father and son, made the first structure determinations of simple chemical compounds and were awarded the Nobel Prize for physics in 1915.

It was not, however, possible to determine crystal structures without some assumptions or guesses, because the phase differences between the different scattered X-rays were not known. The crystallographers had to use a trial and error method.

Several methodological improvements have since taken place, but it has for a long time been considered a great scientific achievement to determine the molecular structures of organic molecules as large as penicillin or vitamin B₁₂. As late as 1964 Dorothy Hodgkins was awarded the Nobel Prize in chemistry for such structure determinations.

It therefore was met with great interest and much opposition and discussion when Herbert Hauptman and Jerome Karle during the years 1950-56 published a series of papers in which they claimed to have found a general method, a “direct” method for solving the phase problem, thus opening the possibility to determine the structure directly from the experimental results without any further assumptions. Hauptman and Karle built their method on two established facts. One was that the electron density in a molecule can never be negative – there are electrons or there are not. The other fact was that the number of experimental results is large enough to permit application of statistical methods. Recent developments have shown that they were right and the production of modern computers has strongly contributed to the rapidity and efficiency of their methods. These methods are now so efficient that structure determinations for which the Nobel Prize was awarded in 1964 can today be made by a clever beginner.

At the same time it has been more and more important for the chemists to know the exact structures of molecules which take part in important chemical and biochemical reactions. One could without exaggeration say that it is only in the last ten years that chemistry has developed into a truly molecular era. Molecules with desired structures and properties can be produced and the molecular mechanism is known for increasingly more reactions.

It is this importance to chemistry which has motivated a Nobel Prize in chemistry to the mathematician Herbert Hauptman and the physicist Jerome Karle. Another way to express it is, that the imagination and ingenuity of the laureates have made it unnecessary to exercise these qualities in normal structure determinations. On the other hand they have increased the possibilities for the chemists to use their imagination and their ingenuity.

Herbert Hauptman and Jerome Karle,

Your basic development of the direct methods for X-ray crystallographic structure determination has given the chemists an efficient tool for faster and more detailed studies of the structures of molecules and therefore also for the study of chemical reactions. On behalf of the Academy I wish to convey to you our warmest congratulations and I now ask you to receive your prizes from the hands of His Majesty the King.