February 28, 1901: Linus Pauling is born
Linus Carl Pauling (1901-1994)
Scientific field: Biology, Chemistry
Known for: Elucidating the nature of chemical bonds and the structures of molecules.
Linus Carl Pauling was an American chemist who applied quantum mechanics to the study of molecular structures, particularly in connection with chemical bonding. Pauling received the Nobel Prize for Chemistry in 1954 and the Nobel Prize for Peace in 1962 (the latter in recognition of his efforts on behalf of the international control of nuclear weapons and his campaigns against nuclear testing).
Pauling’s chemical work, for which he received his first Nobel Prize, dealt with the many aspects of molecular structure, ranging from simple molecules to proteins. He was among the first to apply the principles of quantum mechanics to the structure of molecules and effectively utilized X-ray diffraction (the alteration of the straight course of X rays by the interference of an atom or group of atoms), electron diffraction (interference with the course of electrons by atoms), magnetic effects, and the heat involved in forming chemical compounds for the calculation of interatomic distances and the angles between chemical bonds. He was successful in relating the distances and angles between chemical bonds to molecular characteristics and to interaction between molecules.
In order to account for the equivalency of the four bonds around the carbon atom, he introduced the concept of hybrid orbitals, in which electron orbits are moved from their original positions by mutual repulsion. Pauling also recognized the presence of hybrid orbitals in the coordination of ions or groups of ions in a definite geometric arrangement about a central ion. His theory of directed (positive and negative) valence (the capacity of an atom to combine with other atoms) was an outgrowth of his early work, as was the concept of the partial ionic character of covalent bonds—i.e., atoms sharing electrons. His empirical concept of electronegativity, the power of attraction for electrons in a covalent bond, was useful in further clarification of these problems. In the case of compounds whose molecules cannot be represented unambiguously by a single structure, he introduced the concept of resonance hybrids whereby the true structure of the molecule is regarded as an intermediate state between two or more depictable structures. The resonance theory came under heavy but unsuccessful attack in the U.S.S.R. in 1951 when doctrinaire scientists of the Communist Party argued that it conflicted with dialectical materialist principles. The ideas on bonding were developed serially in his numerous journal articles during his early career and were consolidated in his book The Nature of the Chemical Bond, and the Structure of Molecules and Crystals (1939), which grew out of lectures he gave in 1937 and 1938. The textbook proved to be one of the most influential of the century.
In 1934 Pauling began to apply his knowledge of molecular structure to the complex molecules of living tissues, particularly in connection with proteins. His studies of the magnetic susceptibility (the ease with which something can be magnetized) of the hemoglobin (the red protein in the red cells of the blood) molecule during oxygenation inaugurated a succession of studies that led to a theory of native proteins (active proteins as found in living organisms), denatured proteins (ones that through heat or chemical action have broken some of their bonds), and coagulated (solidified) proteins. He became interested in proteins involved in immunological reactions and in 1940, with a German-born biologist, Max Delbrück, developed a concept of molecular complementarity in antibody-antigen reactions (in which the production of antibodies is stimulated in an organism when foreign substances called antigens are introduced). He recognized the importance of hydrogen bonding in protein structure and in interactions between macromolecules (extremely large molecules usually built from repeating groups of smaller molecules). His work with an American chemist, Robert B. Corey, on the structure of amino acids and polypeptides (the chief components of proteins) led him to recognize that certain proteins have helical structures.
Late in the 1940s Pauling became interested in sickle-cell anemia when he learned that the red blood corpuscles show their abnormal crescent shape only in venous blood. Intuitively, he reasoned that the cause of the cell deformity must lie in a genetic defect associated with hemoglobin formation. His studies showed that the sickling effect was nullified by the presence of oxygen in the arterial blood.
Pauling also developed a molecular model for the explanation of anesthesia that was made public in 1961, introduced ideas toward the understanding of memory processes, and in 1965 postulated a theory of the atomic nucleus that had certain advantages over other models. His scientific career was characterized by the application of intuitive guesses aided by a phenomenal memory of chemical facts. Pauling referred to this as the stochastic method (from the Greek “apt to divine the truth by conjecture”).(1)
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