Science Fair Project Encyclopedia
Linus Carl Pauling (February 28, 1901–August 19, 1994) was an American physical chemist, widely regarded as the premier chemist of the twentieth century. Pauling was a pioneer in the application of quantum mechanics to chemistry, and in 1954 was awarded the Nobel Prize in chemistry for his work describing the nature of chemical bonds. He also made important contributions to crystal and protein structure determination, and was one of the founders of molecular biology. Pauling received the Nobel Peace Prize in 1962 for his campaign against above-ground nuclear testing, becoming the only person in history to individually receive the Nobel Prize in more than one field (Marie Curie won Nobel Prizes in physics and chemistry, but shared the former and won the latter individually; John Bardeen won two Nobel Prizes, but both were in the field of physics, and both were shared; Frederick Sanger won two Nobel Prizes in chemistry). Later in life, he became an advocate for regular consumption of massive doses of Vitamin C, a regimen 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.
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 University
In 1917, Pauling entered the Oregon Agricultural College (OAC) 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 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
Pauling later traveled to Europe on a Guggenheim fellowship 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. In Europe, he was also exposed to one of the first quantum mechanical analyses of bonding in the hydrogen molecule, done by Walter Heitler and Fritz London. 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 and a pioneer in the application of quantum theory to the structure of molecules. 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 1932, he published what he regarded as his most important paper, in which he first laid out the concept of hybridization of atomic orbitals and analyzed the tetravalency of the carbon atom.
At Caltech, Pauling had struck a close friendship with Robert Oppenheimer, who was spending part of his research and teaching schedule away from Berkeley at Caltech every year. The two men planned to mount a joint attack on the nature of the chemical bond- apparently Oppenheimer would supply the mathematics and Pauling would interpret the results. However, this relationship was nipped in the bud when Pauling began to suspect that the theorist was probably becoming too close to his wife, Ava Helen; once when Pauling was at work, Oppenheimer had come to their place and blurted out an invitation to Ava Helen to join him on a tryst to Mexico. Although she flatly refused, she reported this incident to Pauling. This, and her apparent nonchalance about the incident, disquieted him, and he immediately cut off his relationship with the Berkeley professor, leading to a coolness between them that would last their lives, although Oppenheimer did invite Pauling to be the head of the Chemistry Division of the atomic bomb project (Pauling refused saying that he was a pacifist).
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". Pauling summarized his work on the chemical bond in The Nature of the Chemical Bond, a magnum opus which is probably the most influential chemistry book ever published. An idea of its importance can be gleaned from the fact that in the 30 years since its first edition was published in 1939, the book had been cited more than 16,000 times. Even today, it is remarkable how many modern scientific papers and articles in important journals cite this work, more than half a century after it was published.
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 revealed their model when they did, Pauling would soon have reached the same conclusion. One of the impediments facing him in this work was that he did not have access to the high quality X-Ray diffraction photographs of DNA taken by Rosalind Franklin, which Watson and Crick had seen. There is a touch of irony in the fact that he had a chance to attend a conference in England, where he could have seen them, but he could not do so because his passport was withheld at the time by the State Department, on specious suspicions that he had Communist sympathies. This was during the beginning of the McCarthy scare in the United States.
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. This work exemplified his ability to think unconventionally; central to the structure was the unorthodox assumption that one turn of the helix may well contain a non-integral number of amino acid residues.
Pauling also studied enzyme reactions and was among the first ones to point out that enzymes bring about reactions by stabilizing the transition state of the reaction, a view which is central to understanding their mechanism of action. He was also among the first scientists to postulate that the binding of antibodies to antigens would be due to a complementarity between their structures. Along the same lines, with the physicist turned biologist Max Delbruck, he wrote an early paper arguing that genetic replication was likely to be due to complementarity, rather than similarity, as suggested by a few researchers. This was made clear in the model of the structure of DNA that Watson and Crick discovered.
Pauling had been practically apolitical until World War II, but the war changed his life profoundly, and he became a peace activist. During the beginning of the Manhattan Project, Robert Oppenheimer invited him to be in charge of the Chemistry division of the project, but he declined saying that he was a pacifist. 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 passport in 1952, when he was invited to speak at a scientific conference in London. 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. He also participated in a public debate with the atomic physicist Edward Teller about the actual probability of fallout causing mutations. 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 above-ground nuclear weapons testing, followed by the Partial Test Ban Treaty, 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 the 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." Interestingly, the Caltech Chemistry Department, wary of his political views, did not even formally congratulate him. However, the Biology Department did throw him a small party, and one cannot help but think that they were more appreciative and sympathetic toward his work on mutations caused by radiation.
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 naïve spokesman for Soviet 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 1962 Nobel Prize as "A Weird Insult from Norway."
Work in alternative medicine
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, 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 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. One proposal put forward by Rath and Pauling includes the idea that humans naturally have elevated levels of cholesterol (and atherosclerotic plaque build-up in arteries) to prevent the negative effects of scurvy (extreme vitamin C deficiency), which would kill them much sooner than cardiovascular disease.
There is no doubt that Pauling was one of the finest scientific minds of the century. Nobel Laureate Max Perutz called him the greatest chemist of the century. Most scientists usually carve a niche of their own, and work in that niche. However, Pauling stands apart as having had an enormous range of interests; quantum mechanics, inorganic chemistry, organic chemistry, protein structure, molecular biology, and medicine. In all these fields, and especially on their boundaries, he made decisive contributions. His work on chemical bonding marks the beginning of modern quantum chemistry, and many of his contributions like hybridization and electronegativity have become part of standard chemistry textbooks. However, his valence bond approach to chemical bonding, though very useful, cannot explain quantitatively some of the characteristics of molecules, such as the paramagnetic nature of oxygen and the color of organometallic complexes. For these explanations, as well as for the explanation of chemical reactions, the Molecular Orbital Theory developed later by Robert Mulliken is more predictive. However, the strength of Pauling's theory lies in its simplicity. Pauling's work on crystal structure contributed significantly to the prediction and elucidation of the structures of complex minerals and compounds. His discovery of the alpha helix and beta sheet is a fundamental foundation for the study of protein structure. Pauling was also one of the founders of the science of molecular biology in the true sense of the term. His discovery of sickle cell anemia as a 'molecular disease' opened the way toward examining genetically acquired mutations at a molecular level. Pauling's work in orthomolecular medicine was more controversial and is still generating considerable debate.
- The Ava Helen and Linus Pauling Papers at the Oregon State University Libraries
- National Academy of Sciences biography
- Caltech oral history interview
- Scans of 46 of Pauling's notebooks from 1922 to 1994
- Linus Pauling and the Race for DNA
- Linus Pauling: The Nature of the Chemical Bond
- Linus Pauling, Hemoglobin and Sickle Cell Anemia: A Documentary History
- Linus Pauling's Honors, Awards and Medals
- Linus Pauling Centenary Exhibit
- The Dark Side of Linus Pauling's Legacy
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