Speaking Out "Dr. Linus Pauling" - TVO - 1985 (Maig 2024)
Linus Pauling, completament Linus Carl Pauling, (nascut el 28 de febrer de 1901, Portland, Oregon, EUA, va morir el 19 d'agost de 1994 a Big Sur, Califòrnia), químic físic teòric nord-americà que es va convertir en l'única persona que va guanyar dos Premis Nobel no compartits.. El seu primer premi (1954) va ser guardonat per la investigació sobre la naturalesa de l'enllaç químic i el seu ús en l'estructura molecular dilucidant; el segon (1962) va reconèixer els seus esforços per prohibir la prova d’armes nuclears.
Vida i educació primerenques
Pauling va ser el primer dels tres fills i l’únic fill de Herman Pauling, farmacèutic, i de Lucy Isabelle (Darling) Pauling, filla d’un farmacèutic. Després de la seva primera educació a Condon i Portland, Oregon, va assistir a l'Oregon Agricultural College (actual Oregon State University), on va conèixer a Ava Helen Miller, que després es convertiria en la seva esposa, i on va obtenir la seva llicenciatura en ciències en enginyeria química summa. cum laude el 1922. Després assistí al Institut de Tecnologia de Califòrnia (Caltech), on Roscoe G. Dickinson li va mostrar com determinar les estructures dels cristalls mitjançant raigs X. Va rebre el seu doctorat. el 1925 per a una dissertació derivada dels seus papers d’estructura de cristall. Després d'un breu període com a National Research Fellow, va rebre una beca Guggenheim per estudiar mecànica quàntica a Europa.Va passar la majoria dels 18 mesos a l’Institut Arnold Sommerfeld de Física Teòrica de Munic, Alemanya.
Elucidació d’estructures moleculars
Després d’acabar els estudis postdoctorals, Pauling va tornar a Caltech el 1927. Allà va començar una llarga carrera de docència i investigació. L’anàlisi de l’estructura química es va convertir en el tema central del seu treball científic. Mitjançant la tècnica de difracció de raigs X, va determinar la disposició tridimensional dels àtoms en diversos minerals importants de silicats i sulfurs. El 1930, durant un viatge a Alemanya, Pauling va conèixer la difracció d’electrons i, al seu retorn a Califòrnia, va utilitzar aquesta tècnica de dispersió d’electrons des dels nuclis de molècules per determinar les estructures d’algunes substàncies importants. Aquest coneixement estructural el va ajudar a desenvolupar una escala d’electronegativitat en la qual assignava un número que representava la potència d’un àtom particular d’atracció d’electrons en un enllaç covalent.
To complement the experimental tool that X-ray analysis provided for exploring molecular structure, Pauling turned to quantum mechanics as a theoretical tool. For example, he used quantum mechanics to determine the equivalent strength in each of the four bonds surrounding the carbon atom. He developed a valence bond theory in which he proposed that a molecule could be described by an intermediate structure that was a resonance combination (or hybrid) of other structures. His book The Nature of the Chemical Bond, and the Structure of Molecules and Crystals (1939) provided a unified summary of his vision of structural chemistry.
The arrival of the geneticist Thomas Hunt Morgan at Caltech in the late 1920s stimulated Pauling’s interest in biological molecules, and by the mid-1930s he was performing successful magnetic studies on the protein hemoglobin. He developed further interests in protein and, together with biochemist Alfred Mirsky, Pauling published a paper in 1936 on general protein structure. In this work the authors explained that protein molecules naturally coiled into specific configurations but became “denatured” (uncoiled) and assumed some random form once certain weak bonds were broken.
On one of his trips to visit Mirsky in New York, Pauling met Karl Landsteiner, the discoverer of blood types, who became his guide into the field of immunochemistry. Pauling was fascinated by the specificity of antibody-antigen reactions, and he later developed a theory that accounted for this specificity through a unique folding of the antibody’s polypeptide chain. World War II interrupted this theoretical work, and Pauling’s focus shifted to more practical problems, including the preparation of an artificial substitute for blood serum useful to wounded soldiers and an oxygen detector useful in submarines and airplanes. J. Robert Oppenheimer asked Pauling to head the chemistry section of the Manhattan Project, but his suffering from glomerulonephritis (inflammation of the glomerular region of the kidney) prevented him from accepting this offer. For his outstanding services during the war, Pauling was later awarded the Presidential Medal for Merit.
While collaborating on a report about postwar American science, Pauling became interested in the study of sickle-cell anemia. He perceived that the sickling of cells noted in this disease might be caused by a genetic mutation in the globin portion of the blood cell’s hemoglobin. In 1949 he and his coworkers published a paper identifying the particular defect in hemoglobin’s structure that was responsible for sickle-cell anemia, which thereby made this disorder the first “molecular disease” to be discovered. At that time, Pauling’s article on the periodic law appeared in the 14th edition of Encyclopædia.
While serving as a visiting professor at the University of Oxford in 1948, Pauling returned to a problem that had intrigued him in the late 1930s—the three-dimensional structure of proteins. By folding a paper on which he had drawn a chain of linked amino acids, he discovered a cylindrical coil-like configuration, later called the alpha helix. The most significant aspect of Pauling’s structure was its determination of the number of amino acids per turn of the helix. During this same period he became interested in deoxyribonucleic acid (DNA), and early in 1953 he and protein crystallographer Robert Corey published their version of DNA’s structure, three strands twisted around each other in ropelike fashion. Shortly thereafter James Watson and Francis Crick published DNA’s correct structure, a double helix. Pauling’s efforts to modify his postulated structure had been hampered by poor X-ray photographs of DNA and by his lack of understanding of this molecule’s wet and dry forms. In 1952 he failed to visit Rosalind Franklin, working in Maurice Wilkins’s laboratory at King’s College, London, and consequently did not see her X-ray pictures of DNA. Frankin’s pictures proved to be the linchpin in allowing Watson and Crick to elucidate the actual structure. Nevertheless, Pauling was awarded the 1954 Nobel Prize for Chemistry “for his research into the nature of the chemical bond and its application to the elucidation of the structure of complex substances.”
