Linusas Paulingas, visiškai gimęs Linusas Carlas Paulingas (g. 1901 m. Vasario 28 d. Portlandas, Oregonas, JAV - mirė 1994 m. Rugpjūčio 19 d., Big Sur, Kalifornija), Amerikos teorinis fizikas chemikas, kuris tapo vieninteliu asmeniu, laimėjusiu dvi nedalintas Nobelio premijas.. Jo pirmoji premija (1954 m.) Buvo paskirta už cheminės jungties prigimties ir jos panaudojimo išaiškinant molekulinę struktūrą tyrimus; antrasis (1962 m.) pripažino jo pastangas uždrausti branduolinių ginklų bandymus.
Ankstyvasis gyvenimas ir išsilavinimas
Paulingas buvo pirmasis iš trijų vaikų ir vienintelis vaistininko Hermano Paulingo ir vaistininko dukters Lucy Isabelle (Darling) Paulingo sūnus. Po ankstyvojo išsilavinimo Kondone ir Portlande, Oregone, jis lankėsi Oregono žemės ūkio koledže (dabar Oregono valstybinis universitetas), kur susitiko su Ava Helen Miller, kuri vėliau taps jo žmona, ir kur įgijo chemijos inžinerijos bakalauro laipsnį. Tada jis lankėsi Kalifornijos technologijos institute (Caltech), kur Roscoe G. Dickinsonas parodė jam, kaip rentgeno spinduliais nustatyti kristalų struktūras. Jam suteiktas daktaro laipsnis 1925 m. už disertaciją, gautą iš jo kristalinės struktūros dokumentų. Trumpam dirbdamas kaip nacionalinis mokslo darbuotojas, jis gavo Guggenheimo stipendiją studijuoti kvantinę mechaniką Europoje.Didžiąją 18 mėnesių dalį jis praleido Arnoldo Sommerfeldo teorinės fizikos institute Miunchene, Vokietijoje.
Molekulinių struktūrų elikidacija
Baigęs doktorantūrą, Paulingas grįžo į „Caltech“ 1927 m. Ten pradėjo ilgą mokymo ir tyrimų karjerą. Cheminės struktūros analizė tapo pagrindine jo mokslinio darbo tema. Taikydamas rentgeno spindulių difrakcijos metodą, jis nustatė trijų dimensijų atomų išdėstymą keliuose svarbiuose silikato ir sulfido mineraluose. 1930 m., Kelionėje į Vokietiją, Paulingas sužinojo apie elektronų difrakciją ir, grįžęs į Kaliforniją, pasinaudojo šia elektronų išsklaidymo iš molekulių branduolių technika, kad nustatytų kai kurių svarbių medžiagų struktūras. Šios struktūrinės žinios padėjo jam sukurti elektronegatyvumo skalę, kurioje jis priskyrė skaičių, nurodantį konkretaus atomo galią pritraukti elektronus kovalentiniame ryšyje.
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.”
