Scienziato americano Linus Pauling

Linus Pauling, in pieno Linus Carl Pauling, (nato il 28 febbraio 1901, Portland, Oregon, USA - morto il 19 agosto 1994, Big Sur, California), chimico fisico teorico americano che divenne l'unica persona ad aver vinto due premi Nobel non condivisi. Il suo primo premio (1954) fu assegnato per la ricerca sulla natura del legame chimico e il suo uso nel chiarire la struttura molecolare; il secondo (1962) ha riconosciuto i suoi sforzi per vietare i test sulle armi nucleari.

Vita e formazione

Pauling fu il primo di tre figli e l'unico figlio di Herman Pauling, un farmacista, e Lucy Isabelle (Cara) Pauling, la figlia di un farmacista. Dopo la sua prima educazione a Condon e Portland, Oregon, ha frequentato l'Oregon Agricultural College (ora Oregon State University), dove ha incontrato Ava Helen Miller, che sarebbe poi diventata sua moglie, e dove ha conseguito la laurea in ingegneria chimica summa cum laude nel 1922. Ha poi frequentato il California Institute of Technology (Caltech), dove Roscoe G. Dickinson gli ha mostrato come determinare le strutture dei cristalli usando i raggi X. Ha ricevuto il suo dottorato di ricerca. nel 1925 per una tesi derivata dalle sue carte di struttura cristallina. Dopo un breve periodo come National Research Fellow, ha ricevuto una Guggenheim Fellowship per studiare meccanica quantistica in Europa.Trascorse la maggior parte dei 18 mesi presso l'Istituto di fisica teorica di Arnold Sommerfeld a Monaco di Baviera, in Germania.

Chiarimento di strutture molecolari

Dopo aver completato gli studi post-dottorato, Pauling tornò a Caltech nel 1927. Lì iniziò una lunga carriera di insegnante e ricerca. L'analisi della struttura chimica è diventata il tema centrale del suo lavoro scientifico. Usando la tecnica della diffrazione dei raggi X, ha determinato la disposizione tridimensionale degli atomi in diversi importanti minerali di silicato e solfuro. Nel 1930, durante un viaggio in Germania, Pauling venne a conoscenza della diffrazione di elettroni e al suo ritorno in California usò questa tecnica di dispersione di elettroni dai nuclei delle molecole per determinare le strutture di alcune sostanze importanti. Questa conoscenza strutturale lo ha aiutato a sviluppare una scala di elettronegatività in cui ha assegnato un numero che rappresenta il potere di un particolare atomo di attrarre elettroni in un legame covalente.

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.”