Pauling’s Methodology: X-ray Crystallography

X-ray apparatus at Linus Pauling's desk, Gates Laboratory, California Institute of Technology. 1925.

X-ray apparatus at Linus Pauling's desk, Gates Laboratory, California Institute of Technology. 1925.

I was very fortunate in having A.A. Noyes suggest to me, or tell me, that I was to work with Roscoe Dickinson on x-ray crystallography, determination of the structure of crystals by x-ray diffraction. This technique gave for the first time detailed information about how atoms are related to other atoms in a crystal and how far apart they are from the other atoms.
Linus Pauling, 1988.

As a graduate student, well before Pauling began to research hemoglobin in earnest, he spent a great deal of his time using the technique of X-ray crystallography to determine the crystalline structure of a number of inorganic compounds. Pauling recalled that at that time X-ray crystallography “was a new technique, ten years old when I began. Quite a number of structures had been determined but there was a tremendous field open, a tremendous amount of work that could be done.”

Listen: Pauling discusses the importance of X-ray crystallography to his early structural chemistry research

The young Pauling obviously reveled in the excitement of being able to use a new and powerful technology. “We have a pretty extensive collection of apparatus” he once wrote to William Lawrence Bragg, the senior author of a 1922 textbook that started Pauling on X-ray crystallographic research. Any one of Bragg’s student’s, Pauling remarked, “no matter how physical his training,” need not “be frightened at coming to a chemical laboratory” so well-stocked with mechanical apparatus.

Initially Pauling used the technique of X-ray diffraction to determine the structures of fairly simple inorganic compounds, but later, as his own expertise grew and as he discovered new sources of funding, Pauling oriented this new technology toward complex organic compounds, including hemoglobin.

What was ultimately important to Pauling was not what X-ray crystallography could tell him about the size, structure, or relative placement of atoms within a molecule, but rather, what broader theories that information could then be used to support. His growing allegiance to structural chemistry, his developing ideas about the nature of the chemical bond, and his still nascent interest in biochemical interaction were all fed by his experience of rigorously determining molecular structure through new technological methods.

Pauling’s manuscript notes concerning his early experiments with hemochromogen, for instance, indicate the wide spectrum of experimental results he had to assimilate in order to create a coherent picture of the hemoglobin molecule.

"Outline of Experiments on Hemochromagen," pg. 1. June 25, 1935.

"Outline of Experiments on Hemochromagen," pg. 1. June 25, 1935.

The difficulties presented by the need to combine the information he had obtained from x-diffraction with information from other kinds of experimentation, including solubility and more traditional experimental methods, are readily apparent in Pauling’s notes.  Indeed, the impressive new technology of X-ray crystallography is relegated to just one entry in a list of experimental results.

Ultimately it wasn’t the technology at Pauling’s disposal that helped him become such a successful researcher, but rather his attitude in approaching technology and his ability to use the results it gave him to construct more broadly-applicable and intellectually-powerful theories.

To learn more about Linus Pauling’s use of x-ray crystallography, see the websites Linus Pauling and the Nature of the Chemical Bond: A Documentary History and It’s in the Blood!  A Documentary History of Linus Pauling, Hemoglobin and Sickle Cell Anemia.

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