Линус Полинг американски учен

Линус Полинг, изцяло Линус Карл Полинг (роден на 28 февруари 1901 г., Портланд, Орегон, САЩ - умрял 19 август 1994 г., Биг Сур, Калифорния), американски теоретичен физически химик, който стана единственият човек, спечелил две неразделени Нобелови награди, Първата му награда (1954 г.) е присъдена за изследване на природата на химическата връзка и нейната употреба при изясняване на молекулната структура; вторият (1962 г.) признава усилията му да забрани изпитанията на ядрените оръжия.

Ранен живот и образование

Полинг беше първото от три деца и единственият син на Херман Полинг, фармацевт, и Люси Изабел (Дарлинг) Полинг, дъщеря на фармацевта. След ранното си образование в Кондън и Портланд, Орегон, той посещава селскостопански колеж в Орегон (сега Държавен университет в Орегон), където се запознава с Ава Хелън Милър, която впоследствие ще стане негова съпруга, и където получава степента си бакалавър по научно инженерство cum laude през 1922 г. След това посещава Калифорнийския технологичен институт (Калтех), където Роско Г. Дикинсън му показва как да определя структурите на кристалите с помощта на рентгенови лъчи. Той получи своя докторска степен. през 1925 г. за дисертация, получена от неговите документи за кристална структура. След кратък период като национален изследовател, той получава стипендия на Гугенхайм за изучаване на квантовата механика в Европа.Прекарва по-голямата част от 18-те месеца в Института за теоретична физика на Арнолд Сомерфелд в Мюнхен, Германия.

Изясняване на молекулните структури

След завършване на докторантура, Полинг се завръща в Калтех през 1927 г. Там той започва дълга кариера на преподаване и изследвания. Анализът на химическата структура стана централна тема на неговата научна работа. Използвайки техниката на рентгенова дифракция, той определи триизмерното подреждане на атомите в няколко важни силикатни и сулфидни минерали. През 1930 г., по време на пътуване до Германия, Полинг научава за електронната дифракция и след завръщането си в Калифорния използва тази техника на разсейване на електрони от ядрата на молекулите, за да определи структурите на някои важни вещества. Това структурно знание му помогнало в разработването на скала на електронегативност, в която той присвоил число, представляващо силата на определен атом за привличане на електрони в ковалентна връзка.

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.”