Linus Carl Pauling (February 28, 1901–August 19, 1994) was an American physical chemist. He was one of the first quantum chemists, and was awarded the Nobel Prize in Chemistry in 1954 for his work describing the nature of chemical bonds. He received the Nobel Peace Prize in 1962 for his campaign against above-ground nuclear testing, becoming one of only two people to receive the Nobel Prize in more than one field. Later in life, he became an advocate for regular consumption of massive doses of vitamin C (now regarded as medically unorthodox).
Pauling was born in Portland, Oregon. His father, an unsuccessful druggist, moved his family to a number of different cities in Oregon from 1903 to 1909, finally returning to Portland that year. When the elder Pauling died in 1910 of a perforated ulcer, Linus' mother was left to care for him and two younger siblings.
Pauling was a voracious reader as a child, and at one point his father wrote a letter to a local paper inviting suggestions of additional books that would occupy his time. A friend, Lloyd Jeffress, had a small chemistry laboratory in his bedroom when Pauling was in grammar school, and Jeffress' laboratory experiments inspired Pauling to plan to become a chemical engineer.
In high school, Pauling continued to experiment in chemistry, borrowing much of the equipment and materials from an abandoned steel company near which his grandfather worked as a night watchman.
Pauling failed to take some required American history courses and did not qualify for his high school diploma. The school awarded him the diploma 45 years later, only after he had won two Nobel Prizes.
College and graduate school
In 1917 Pauling entered the Oregon Agricultural College in Corvallis, now Oregon State University. Because of financial needs, he had to work full-time while attending a full schedule of classes. After his second year, he planned to take a job in Portland to help support his mother, but the college offered him a position teaching quantitative analysis (a course Pauling had just finished taking as a student). This allowed him to continue his studies at OAC.
In his last two years at OAC, Pauling became aware of the work of Gilbert N. Lewis and Irving Langmuir on the electronic structure of atoms and their bonding to form molecules. He decided to focus his research on how the physical and chemical properties of substances are related to the structure of the atoms of which they are composed, becoming one of the founders of the new science of quantum chemistry.
In his senior year he met Ava Helen Miller, a fellow student, and he married her on June 17, 1923; they had three sons and a daughter.
In 1922, Pauling graduated from OAC and went to graduate school at the California Institute of Technology ("Caltech") in Pasadena, California. His graduate research involved the use of X-ray diffraction to determine crystal structure. He published seven papers on the crystal structure of minerals while he was at CalTech. He received his Ph. D. degree, summa cum laude, in 1925.
Early scientific career
He then traveled to Europe to study under Arnold Sommerfeld in Munich, Niels Bohr in Copenhagen, and Erwin Schrödinger in Zürich. All three were working in the new field of quantum mechanics. It was while he was studying at OAC that Pauling had first been exposed to quantum mechanics, and he was now interested in seeing how it might help in the understanding of Pauling's chosen field of interest, the electronic structure of atoms and molecules. He devoted the two years of his European trip to this work, and decided to make this the focus of his future research, becoming one of the first scientists in the field of quantum chemistry. In 1927, he took a new position as an assistant professor at CalTech in theoretical chemistry.
Pauling began his faculty career at CalTech with a very productive five years, both continuing with his X-ray crystal studies and performing quantum mechanical calculations on atoms and molecules. He published approximately fifty papers in those five years. In 1929 he was promoted to associate professor, and in 1930, to full professor. By 1931, the American Chemical Society awarded Pauling the Langmuir Prize for the most significant work in pure science by a person 30 years of age or under.
In the summer of 1930 Pauling made another European trip, learning about the use of electrons in diffraction studies similar to the ones he had performed with X rays. With a student of his, L. O. Brockway, he built an electron diffraction instrument at CalTech and used it to study the molecular structure of a large number of chemical substances.
He introduced the concept of electronegativity in 1932. Using the various properties of molecules, such as the energy required to break bonds and the dipole moments of molecules, he established a scale and an associated numerical value for most of the elements, the Pauling Electronegativity Scale, which is useful in predicting the nature of bonds between atoms in molecules. (Another measure of electronegativity was defined by Robert S. Mulliken; the Mulliken scale generally correlates with Pauling's, but not perfectly. The Pauling scale is the more frequently cited electronegativity scale.)
Work on the nature of the chemical bond
In the 1930s he began publishing papers on the nature of the chemical bond, leading to his famous textbook on the subject published in 1939. It is based primarily on his work in this area that he received the Nobel Prize in Chemistry in 1954 "for his research into the nature of the chemical bond and its application to the elucidation of the structure of complex substances".
Part of Pauling's work on the nature of the chemical bond led to his introduction of the concept of hybridization. While it is normal to think of the electrons in an atom as being described by orbitals of types such as s, p, etc., it turns out that in describing the bonding in molecules, it is better to construct functions that partake of some of the properties of each. Thus the one 2s and three 2p orbitals in a carbon atom can be combined to make four equivalent orbitals (called sp3 hybrid orbitals), which would be the appropriate orbitals to describe carbon compounds such as methane, or the 2s orbital may be combined with two of the 2p orbitals to make three equivalent orbitals (called sp2 hybrid orbitals), with the remaining 2p orbital unhybridized, which would be the appropriate orbitals to describe certain unsaturated carbon compounds such as ethylene. Other hybridization schemes are also found in other types of molecules.
Another area which he explored was the relationship between ionic bonding, where electrons are transferred between atoms, and covalent bonding, where electrons are shared between atoms on an equal basis. Pauling showed that these were merely extremes, between which most actual cases of bonding fall. It was here especially that Pauling's electronegativity concept was particularly useful; the electronegativity difference between a pair of atoms will be the surest predictor of the degree of ionicity of the bond.
The third of the topics that Pauling attacked under the overall heading of "the nature of the chemical bond" was the accounting of the structure of aromatic hydrocarbons, particularly the prototype, benzene. The best description of benzene had been made by the German chemist Friedrich Kekulé. He had treated it as a rapid interconversion between two structures, each with alternating single and double bonds, but with the double bonds of one structure in the locations where the single bonds were in the other. Pauling showed that a proper description based on quantum mechanics was an intermediate structure containing some aspects of each. The structure was a superposition of structures rather than a rapid interconversion between them. The name "resonance" was later applied to this phenomenon. In a sense, this phenomenon resembles that of hybridization, described earlier, because it involves combining more than one electronic structure to achieve an intermediate result.
Work on biological molecules
In the mid-1930s, Pauling decided to strike out into new areas of interest. Early in his career, he had mentioned a lack of interest in studying molecules of biological importance. But as CalTech was developing a new strength in biology, and Pauling interacted with such great biologists as Thomas Hunt Morgan, Theodosius Dobzhanski, Calvin Bridges, and Alfred Sterdivant, he started to become interested in studying biological molecules. His first work in this area involved the structure of hemoglobin. He was able to demonstrate that the hemoglobin molecule changes structure when it gains or loses an oxygen atom. As a result of this observation, he decided to make a more thorough study of protein structure in general. He returned to his earlier use of X-ray diffraction analysis. But protein structures were far less amenable to this technique than the crystalline minerals of his former work. The best X-ray pictures of proteins in the 1930s had been made by the British crystallographer William Astbury, but when Pauling tried, in 1937, to account for Astbury's observations quantum mechanically, he could not.
It took eleven years for Pauling to explain the problem: his mathematical analysis was correct, but Astbury's pictures were taken in such a way that the protein molecules were tilted from their expected positions. Pauling had formulated a model for the structure of hemoglobin in which atoms were arranged in a helical pattern, and applied this idea to proteins in general. This helical arrangement suggested the double helix proposed by James D. Watson and Francis Crick for deoxyribonucleic acid (DNA), and Pauling had come close to this structure himself -- though his proposed structure for DNA was not quite correct, most people conversant with his work believe that if Watson and Crick had not put their model when they did, Pauling would soon have reached the same conclusion.
In 1951, based on the structures of amino acids and peptides and the planarity of the peptide bond, Pauling and colleagues correctly proposed the alpha helix and beta sheet as the primary structural motifs in protein secondary structure.
Pauling also studied enzyme reactions and showed that sickle-cell anemia was caused by a single amino acid change in the hemoglobin molecule.
Change of direction of his life
World War II produced a profound change in Pauling's life. He had been virtually apolitical to this point, but as a result of his experiences at this juncture Pauling became a peace activist. In 1946 he joined the Emergency Committee of Atomic Scientists, chaired by Albert Einstein, whose mission was to warn the public of the dangers associated with the development of nuclear weapons. His political activism prompted the U.S. State Department to deny him a visa in 1952 when he was invited to speak at a scientific conference in London, but his passport was restored in 1954, shortly before the ceremony in Stockholm where he received his first Nobel Prize.
In 1957, Pauling began a petition drive in cooperation with biologist Barry Commoner, who had studied radioactive strontium-90 in the milk teeth of children across North America and concluded that above-ground nuclear testing posed public health risks in the form of radioactive fallout. In 1958, Pauling and his wife presented the United Nations with a petition signed by more than 11,000 scientists calling for an end to nuclear-weapon testing. Public pressure subsequently led to a moratorium on nuclear weapons testing, followed by a partial test-ban treated signed in 1963 by John F. Kennedy and Nikita Khrushchev. On the day that the treaty went into force, the Nobel Prize Committee awarded Pauling its Peace Prize, describing him as "Linus Carl Pauling, who ever since 1946 has campaigned ceaselessly, not only against nuclear weapons tests, not only against the spread of these armaments, not only against their very use, but against all warfare as a means of solving international conflicts."
Many of Pauling's critics, including scientists who appreciated the contributions that he had made in chemistry, disagreed with his political positions and saw him as a naďve spokesman for Russian Communism. He was ordered to appear before the Senate Internal Security Subcommittee, which termed him "the number one scientific name in virtually every major activity of the Communist peace offensive in this country." An extraordinary headline in Life Magazine characterized his 1963 Nobel award as "A Weird Insult from Norway."
Pauling's scientific work in his later years generated controversy and was regarded by many scientists as outright quackery. In 1966, at the age of 65 when most people normally go into retirement, he began to champion the ideas of biochemist Irwin Stone, who proposed that massive doses of vitamin C could prevent colds. Eventually Pauling went beyond this, to the idea that vitamin C could prevent cancer. While most scientists do not believe that there is any validity in these claims, a few, convinced that this is one of a number of cases where substances naturally in the body can be used to prevent disease, established a new discipline called orthomolecular medicine. On Pauling's retirement in 1974, he and some of these scientists founded the Institute of Orthomolecular Medicine, now the Linus Pauling Institute of Science and Medicine, in Palo Alto, California. The Pauling Institute no longer subscribes to his recommendations for massive vitamin C supplementation. Dr. Matthias Rath, one of Pauling’s collaborators from this time, has continued research into the effects of large amounts of vitamin C on the human body.
Linus Pauling is one of only two people to have been awarded a Nobel Prize in more than one field, the other being Marie Curie.