Si Linus Pauling scientist na Amerikano

Si Linus Pauling, sa buong Linus Carl Pauling, (ipinanganak noong ika-28 ng Pebrero, 1901, Portland, Oregon, US — namatay noong Agosto 19, 1994, Big Sur, California), Amerikanong teoretikal na pisikal na chemist na naging nag-iisang tao na nagwagi ng dalawang hindi nabantayan na Nobel Prize. Ang kanyang unang premyo (1954) ay iginawad para sa pananaliksik sa likas na katangian ng bono ng kemikal at ang paggamit nito sa pagpapalabas ng molekular na istruktura; ang pangalawa (1962) ay kinikilala ang kanyang pagsisikap na pagbawalan ang pagsubok ng mga sandatang nukleyar.

Maagang buhay at edukasyon

Si Pauling ang una sa tatlong anak at nag-iisang anak na si Herman Pauling, isang parmasyutiko, at Lucy Isabelle (Darling) Pauling, isang anak na parmasyutiko. Matapos ang kanyang maagang pag-aaral sa Condon at Portland, Oregon, nag-aral siya sa Oregon Agricultural College (na ngayon ay Oregon State University), kung saan nakilala niya si Ava Helen Miller, na kalaunan ay magiging asawa niya, at kung saan natanggap niya ang kanyang Bachelor of Science degree sa chemical engineering summa cum laude noong 1922. Pagkatapos ay dumalo siya sa California Institute of Technology (Caltech), kung saan ipinakita sa kanya ni Roscoe G. Dickinson kung paano matukoy ang mga istruktura ng mga kristal gamit ang X ray. Natanggap niya ang kanyang Ph.D. noong 1925 para sa isang disertasyon na nagmula sa kanyang mga papel na gawa sa kristal. Kasunod ng isang maikling panahon bilang isang National Research Fellow, nakatanggap siya ng isang Guggenheim Fellowship upang pag-aralan ang mga mekanika sa kabuuan sa Europa.Ginugol niya ang halos 18 buwan sa Arnold Sommerfeld's Institute for Theoretical Physics sa Munich, Germany.

Ang paglabas ng mga molekular na istruktura

Matapos makumpleto ang mga pag-aaral sa postdoctoral, si Pauling ay bumalik sa Caltech noong 1927. Doon nagsimula ang isang mahabang karera ng pagtuturo at pananaliksik. Ang pagtatasa ng istraktura ng kemikal ay naging pangunahing tema ng kanyang akdang pang-agham. Sa pamamagitan ng paggamit ng pamamaraan ng X-ray diffraction, tinukoy niya ang three-dimensional na pag-aayos ng mga atoms sa ilang mahahalagang mineral na silicate at sulfide. Noong 1930, sa isang paglalakbay sa Alemanya, nalaman ni Pauling ang tungkol sa pagkakaiba ng elektron, at sa kanyang pag-uwi sa California ginamit niya ang pamamaraang ito ng pagkalat ng mga electron mula sa nuclei ng mga molekula upang matukoy ang mga istruktura ng ilang mahahalagang sangkap. Ang kaalamang istruktura na ito ay tumutulong sa kanya sa pagbuo ng isang electronegativity scale kung saan siya ay nagtalaga ng isang numero na kumakatawan sa isang partikular na lakas ng atom na akitin ang mga electron sa isang covalent bond.

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.”