Linus Pauling

Linus Pauling (1901-1994), American theoretical chemist and biologist, whose achievements rank among the most important of any in 20th-century science. His main contributions were to the understanding of molecular structure and chemical bonding (see Molecule; Chemical Reactions). Pauling is one of the few people to have been awarded two Nobel Prizes: He received the 1954 Nobel Prize in chemistry for his work on forces between molecules, and the 1962 Nobel Peace Prize for his work on ending the testing of nuclear weapons. Throughout his career, Pauling demonstrated intuition, inspiration, and a phenomenal memory. He often applied principles from one field of science to another.

Linus Carl Pauling was born in Portland, Oregon. He began his scientific studies at Oregon Agricultural College in Corvallis (now known as Oregon State University), from which he graduated in 1922 with a B.S. degree in chemical engineering. He then began research at the California Institute of Technology (Caltech) in Pasadena, earning his Ph.D. degree in 1925. From 1925 to 1927 he was a postdoctoral fellow in Europe, where he met the chief scientists of the day who were working on atomic and molecular structure, including Danish physicist Niels Bohr, British physicist William Henry Bragg, Austrian physicist Erwin Schrödinger, and German physicist Arnold Sommerfeld. He became a full professor at Caltech in 1931, but left teaching in 1936 to become the director at Caltech’s Gates and Crellin Laboratories. Pauling continued to work at the laboratories for the next 22 years.

In the 1960s Pauling spent several years researching the problems of war and peace at the Center for the Study of Democratic Institutions at Santa Barbara, California. He also held appointments at the University of California at San Diego from 1967 to 1969 and at Stanford University from 1969 to 1973. His last appointment was as director of the Linus Pauling Institute of Science and Medicine in Menlo Park, California, from 1973 until his death in 1994. In 1980 the Linus Pauling Institute of Science and Medicine moved to Palo Alto, California.

Pauling's early work reflects his European training in atomic and molecular structure. In 1931 he published a paper called “The Nature of the Chemical Bond,” which became a classic. In this paper Pauling used quantum mechanics to explain how atoms share electrons and how the electrons interact in a covalent bond, the link that holds atoms together in a molecule (see Chemical Reaction: Types of Bonds). Quantum mechanics is a theory that uses the concept of a discrete, or quantum, unit to describe how subatomic particles and energy interact, instead of a smooth, continuous scale. This paper was followed by the book Introduction to Quantum Mechanics (with E. Bright Wilson, 1935), which Pauling co-authored.

Pauling was a pioneer in the application of quantum mechanical principles to the structures of molecules. He examined the structures of molecules, and related quantum mechanical theories to the angles and distances he found between atoms in a molecule. One technique Pauling used to examine molecules is called electron diffraction. Electron diffraction involves studying the patterns that a stream of electrons produces when it passes between atoms in the molecules of a sample. As the electrons pass between atoms and through the molecules, the atoms affect the path of the electrons in such a way that the electron pattern reveals the inner structure of the molecule. Pauling also observed how the molecules reacted to chemical reactions or to regions of space affected by a magnet. The behavior of the molecules helped Pauling find out more about their structure.

Pauling also investigated electronegativity of atoms (the ease with which atoms attract extra electrons) and polarization in chemical bonds (the tendency for electrons to stay on one side of the molecule). He assigned electronegativities to atoms on a scale from 0 to 4.0. In a molecule, an atom with high electronegativity pulls electrons toward it, so the molecule becomes polarized, leaving one end of the molecule with a negative charge and one end with a positive charge. In hydrogen chloride (HCl), for example, hydrogen has an electronegativity of 2.1 and chlorine of 3.5. The bonding electrons are pulled toward the chlorine atom, giving it a small excess negative charge (and leaving the hydrogen atom with a small excess positive charge), polarizing the hydrogen-chlorine bond. The electronegativities of atoms that bond with hydrogen determine whether the hydrogen will be on the positive end or the negative end of the molecule. This helps predict how substances will react with water. Some substances, such as hydrogen chloride, react with water to form acids. Others, such as sodium hydroxide (NaOH) react with water to form bases.

These and Pauling's other ideas on chemical bonding are fundamental to modern theories of molecular structure. Much of this work was consolidated in his book The Nature of the Chemical Bond and the Structure of Molecules and Crystals (1939).

In the 1940s Pauling turned his attention to the chemistry of living tissues and systems. He applied his knowledge of molecular structure to the complexity of life, principally to proteins in blood. With American chemist Robert Corey, he worked on the structures of amino acids, which are the basic building blocks of proteins. They studied how amino acids form long, chainlike compounds called polypeptides which, in turn, link together to form proteins. Pauling and Corey proposed that many proteins have structures held together with hydrogen bonds, giving them helical (cylindrical spiral) shapes. This concept assisted British biochemist Francis Crick and American biochemist James Watson in their search for the structure of deoxyribonucleic acid (DNA). Watson and Crick eventually determined that the structure of the DNA molecule is a double helix.

In his research on blood, Pauling investigated immunology (the study of the body’s reaction to bacteria, viruses, and other foreign invaders) and the disease called sickle-cell anemia. Later work confirmed his hunch that sickle-cell anemia is genetic and that normal hemoglobin (the iron-protein compound in red blood cells that gives blood its red color) and the hemoglobin in abnormal “sickle” cells differ in electrical charge. Throughout the 1940s Pauling also carried out research on anesthesia. At the end of this period he published two textbooks, General Chemistry (1948) and College Chemistry (1950); both are still best-sellers.

Like many of his contemporaries, Pauling became concerned in the 1950s about the proliferation and atmospheric testing of nuclear weapons. He presented to the United Nations a petition signed by 11,021 scientists from throughout the world urging an end to nuclear weapons testing, and he reinforced this view in his book No More War (1958). For these efforts he was awarded the Nobel Peace Prize in 1962, the year in which the International Nuclear Test Ban Treaty was signed.

In the 1970s Pauling became an ardent advocate for huge doses of vitamin C, speculating that it could help prevent the common cold and help fight off cancer. He became so well known for his championship of vitamin C that many of his colleagues felt that it overshadowed his more important work in chemistry.