Election to Sigma Xi has been an early milestone in many distinguished careers, the first professional honor many young scientists receive in recognition of their potential to make meaningful contributions to research. Many Sigma Xi members have gone on to win major awards. In the Society's history, more than 175 members have received the Nobel Prize. Four members joined this illustrious group in 1998.

1998 Nobel Prize in Physiology or Medicine

Robert F. Furchgott and Louis J. Ignarro

For their discoveries concerning nitric oxide as a signaling molecule in the cardiovascular system.

Robert F. Furchgott, a pharmacologist at the State University of New York Health Science Center in Brooklyn, studied the effect of drugs on blood vessels but often achieved contradictory results. The same drug sometimes caused a contraction and at other times, a dilatation. Furchgott wondered if the variation could depend on whether the surface cells (the endothelium) inside the blood vessels were intact or damaged. In 1980, he demonstrated in an ingenious experiment that acetylcholine dilated blood vessels only if the endothelium was intact. He concluded that blood vessels are dilated because the endothelial cells produce an unknown signal molecule that makes vascular smooth muscle cells relax. He called this signal molecule EDRF, the endothelium-derived relaxing factor, and his findings led to a quest to identify the factor. He was elected to membership in Sigma Xi by the Northwestern University Chapter in 1939.

Louis J. Ignarro, a pharmacologist at the University of California at Los Angeles, participated in the quest for EDRF's chemical nature. He performed a brilliant series of analyses and concluded in 1986, together with and independently of Robert Furchgott, that EDRF was identical to nitric oxide. The problem was solved and Furchgott's endothelial factor identified. He was elected to membership in Sigma Xi by the University of Minnesota Chapter in 1966.

They shared the 1998 Nobel Prize in Physiology or Medicine with Ferid Murad, a pharmacologist at the University of Texas at Houston.

1998 Nobel Prize in Chemistry

Walter Kohn and John Pople

To Walter Kohn for his development of the density-functional theory and to John Pople of his development of computational methods in quantum chemistry.

Researchers have long sought methods for understanding how bonds between the atoms in molecules function. The growth of quantum mechanics in physics at the beginning of the 1900s opened new possibilities, but applications within chemistry were long in coming. It was not until the advent of the computer that it became possible to handle the complicated mathematical relations of quantum mechanics for such complex systems as molecules. Computer-based calculations are now used generally to supplement experimental techniques.

Walter Kohn, a research physicist at the University of California at Santa Barbara, developed theoretical work that formed the basis for simplifying the mathematics in descriptions of the bonding of atoms. Conventional calculation of the properties of molecules is based on a description of the motion of individual electrons. For this reason, such methods are mathematically very complicated. Kohn showed that it is not necessary to consider the motion of each individual electron: it suffices to know the average number of electrons located at any one point in space. This has led to a computationally simpler method, the "density-functional theory." Today, for example, calculations can be used to explain how enzymatic reactions occur. Kohn was elected to membership in Sigma Xi by the Harvard University Chapter in 1949.

John Pople, a chemist at Northwestern University, developed computational methods making possible the theoretical study of molecules, their properties and how they act together in chemical reactions. These methods are based on the fundamental laws of quantum mechanics as defined by, among others, the physicist E. Schršdinger. A computer is fed with particulars of a molecule or a chemical reaction and the output is a description of the properties of that molecule or how a chemical reaction may take place. The result is often used to illustrate or explain the results of different kinds of experiments. Pople made his computational techniques easily accessible to researchers by designing the GAUSSIAN computer program. The first version was published in 1970. The program has since been developed and is now used by thousands of chemists in universities and commercial companies the world over. Pople was elected to membership in Sigma Xi by the Carnegie Institute of Technology Chapter in 1965.