Linus Pauling e a natureza da ligação química: um percurso na história da descoberta do raio X à proposta estrutural dos ácidos nucléicos

Abstract

In 1962, the Nobel Prize in Physiology and Medicine was shared between three researchers: James Watson, Francis Crick, and Maurice Wilkins. The two initial researchers determined the spatial arrangement of the DNA macromolecule, while Wilkins justified, based on experimental data, Watson and Crick's proposal. For the development of the facts, some chemistry was necessary and we can take as a reference the contribution of Rosalind Franklin and her doctoral advisor, Raymond Gosling, in the process. The two produced high-resolution photographs through X-ray diffraction of crystallized DNA that enabled the interpretation of the molecule's structure by Watson, Crick, and Wilkins. For the development of the X-ray diffraction technique, which made it possible to interpret the location of atoms in a crystal, we highlight the contributions of many scientists such as William Henry Bragg and William Lawrence Bragg, father and son respectively. Henry Bragg improved the technique and X-ray equipment. At the same time, his son reinterpreted the X-ray diffraction data, which led to a law still used today, for a good approximation of the real arrangement of atoms in a crystalline lattice. Therefore, it is possible to verify the existence of a dependence on the technique for spatial determination of atoms, on the discovery of X-rays, by Wilhelm Röntgen. Using studies developed by William Crookes, and taking as a theoretical basis the productions of Heinrich Hertz and Phillip Lenard, Röntgen could verify the frequency of luminescence outside the glass tubes, leading to a prediction of this new type of radiation. We have Chemical Engineer Linus Carl Pauling, combining the developed technique of X-ray diffraction with the interpretation of the spatial arrangement of atoms. From an early age, he moved away from science and chemistry and became interested in understanding why atoms remain together in the formation of substances. Among all his productions, we highlight his research related to the nature of chemical bonds, a fundamental property for understanding the spatial configurations of atoms in chemical compounds. Pauling, through this understanding, developed his method for predicting spatial structures, in addition to taking Watson and Crick's proposal for the DNA double helix. Throughout Pauling's trajectory, we analyzed a single incident, the suggestion of a triple helix for DNA, and we sought to justify it within an entire historiographical reflection on this event. Considering the role of chemical bonds in understanding the spatial configurations of atoms in compounds, this thesis reflects on Pauling's error in the triple helix and the context that led him to determine the structure of the macromolecule, taking as a starting point the contribution of scientist in theoretical development, which justifies the union of atoms in substances. To this end, we analyzed primary and secondary historical sources, in the light of contemporary references in the historiography of science. Through discursive textual analysis, intending to produce a historical case study, Pauling's error was fundamental and justified, given the adversities that arose. We found that despite having made a mistake in proposing a triple helix, it would not have been possible to determine Watson and Crick's double helix without it.