Pauling had a strong interest in quantum physics, which he had studied in depth while
on a fellowship in Europe during the late 1920s. Quantum mechanical concepts framed
his important work on the chemical bond. Now, in 1940, quantum physics would affect
his ideas about protein structure.
It started with the work of Pascual Jordan, one of the important early quantum physicists.
He had recently turned his mind toward complex molecular structures, writing papers
promoting the idea that identical molecules might tend to stick together because of
quantum-mechanical resonance. Pauling learned of Jordan's ideas from a physicist
at Caltech who was working (oddly enough) on genetics: Max Delbrück, a brilliant German émigré who had arrived in California on a fellowship and never
Delbrück told Pauling about the Jordan papers one day when they ran into each other
on campus. This was during the period when Pauling was finishing his antibody paper,
and had been thinking hard about how proteins could bind to one another. Jordan's
idea of identical molecules sticking together was, of course, much different from Pauling's antibody-based
idea of complementary structures. He and Delbrück strolled to the Caltech library where Pauling found Jordan's
papers and started reading. Within a few minutes, Pauling decided that the ideas presented
were, as he put it later, "baloney."
He thought it worth writing a brief paper to let the world know why Jordan was wrong,
and after he did so, asked Delbrück to sign on as a coauthor. Delbrück, not wanting
to appear impolite to the great American chemist, made a few minor changes and signed
Their paper, "The Nature of the Intermolecular Forces Operative in Biological Processes,"
published in Science in the summer of 1940, effectively demolished Jordan's ideas about identical molecules,
clearly stated Pauling's views on the importance of complementary, die-and-coin relationships
between biological molecules (the same sort he had seen sticking together antibodies)
– and went almost unnoticed.
Now, however, it is cited as one of the founding documents of molecular biology, primarily
because of two sentences written by Pauling:
"The case might occur in which the two complementary structures happened to be identical;
however, in this case also the stability of the complex of two molecules would be
due to their complementariness rather than their identity. When speculating about
possible mechanisms of autocatalysis it would therefore seem to be most rational from
the point of view of the structural chemist to analyze the conditions under which
complementariness and identity might coincide."
A molecule making copies of itself - autocatalysis – is what happens when genes replicate.
Pauling was thinking about proteins when he wrote the paper. But his brief aside is
now seen as a remarkably prescient statement about the nature of the DNA double helix.