20th century / Science

Rosalind Franklin: Beyond the Helix

By Dan Hudson

“As a scientist Miss Franklin was distinguished by extreme clarity and perfection in everything she undertook”
– J. D. Bernal, Nature 1958

Dr. Rosalind Franklin (1920-58) is famously accredited with the original evidence for the B-DNA double helix (the most common form), a monumentally important revelation which served as the basis for modern molecular biology. Few are ignorant of Crick and Watson’s controversial use of Franklin’s X-Ray diffraction pattern in their 1952 Cold Spring Harbor seminar. They were awarded the Nobel Prize in physiology or medicine for this, while Franklin remained unacknowledged.

However, this London-born scientist was also a leading light in the field of physical chemistry, with contributions essential to the British war effort, most notably investigating the fine structures of coal, graphite and viral nucleic acid. This article aims to explore the unknown side to R. F.’s stellar scientific career.

From 1942-51, Franklin’s precise experiments on the nature of carbonaceous materials were to yield detailed models of their microstructure, thermal stability and reactivity. These were to contribute to the wartime economy (which was principally coal-dependant), the post-war rush for nuclear power, and modern industry.

Working for BCURA (British Coal Utilization Research Association) in their new Kingston-upon-Thames laboratory, Rosalind’s first work was directed at the density and porosity of various classes of coal. She obtained their true densities using a helium-displacement technique which corrected for air-containing pores in the sample. She went on to compare these densities with the apparent ‘lump’ density values from classical displacement studies. The comparison constitutes the first documented proof of ‘molecular sieve’ activity in carbon compounds, whereby large solvent molecules are shut out by the microscopic pores of some materials. Molecular sieves are vital to some modern industrial processes. For example, the separation of nitrogen from air, which is crucial in the synthesis of inorganic fertilizer via the Haber process.

Franklin expanded on these studies with analysis of coke; the heat treated/ carbonized form of coal used by the steel-making industry. Her results explained the decreased reactivity of coke relative to native coal: despite an increased pore density, the carbonization process seals the surface of coal particles, reducing the efficiency of combustion.

By 1950, the crystal structures of diamond and graphite had already been determined by Bragg (1913) and Bernal (1924) respectively. However, the microstructure of coal derivatives such as soot, coke and char remained uncharacterized. In this year Dr. Franklin published a seminal paper illustrating the primarily graphite-like nature of char, disproving the previously held assumption of structural disorder.

However, her most influential work was on the classification of “Graphitic” and “Non-graphitic” carbons. The post-war rush for nuclear energy research (for which synthetic graphite is essential) necessitated a purity classification system. This was provided by Franklin in 1951, working under Marcel Mathieu at the Laboratoire Central des Services Chemiques de l′Etat. Using an induction furnace capable of producing temperatures up to 3,000°C Franklin observed that carbon sources fell into one of two distinct classes.
• The microstructure of some carbons such as coke altered upon heating above ~2,200°C to closely resemble that of pure graphite (graphitising carbons).
• Other sources such as char were resistant to ‘graphitisation’ and refuse to attain an ordered crystal structure at temperatures up to 3000°C (non-graphitizing carbons).

Rosalind Franklin’s considerable experience in X-Ray diffraction and density studies helped her King’s College research team to obtain the infamous “Photo 51”- a clear X-ray diffraction pattern from sodium deoxyribonucleate crystals. This was used (some say without permission) by Crick and Watson in their 1952 address.

After disagreements with John Randall over the continuation of DNA research, Franklin joined a severely under-funded research group at Birkbeck College, headed by J.D. Bernal. Here she applied crystallographic techniques to uncover the 3D structure of Tobacco Mosaic Virus (TMV). With Aaron Klug, Rosalind revealed that TMV consists of a hollow protein capsule, previously thought to be rod-shaped, closely associated with viral RNA. She continued to study viruses until her death in 1958, most notably live polio- an extremely dangerous pursuit!

Dr. Franklin’s complete devotion to her work was demonstrated by her group’s publication of 13 papers in just two years, following her tragic diagnosis with aggressive bowel cancer. In conclusion, Rosalind Franklin’s contributions to science are numerous and of great importance, let them not be overshadowed by the theft of the helix by Crick and Watson.

References:
R.E. Franklin: ‘A study of the fine structure of carbonaceous solids by measurement of true and apparent densities’. Transactions of the Faraday Society (1949): 4; p.407
R.E. Franklin: ‘The structure of graphitic carbons’. Acta crystallographica (1950): 3; p107-12.
R.E. Franklin: ‘Crystallite growth in graphitizing and non-graphitizing carbons’. Proceedings of the Royal Society of London (1951): 209; p196-218.
P.J.F. Harris: ‘Rosalind Franklin’s work on coal, carbon and graphite’ Int Science Rev. (2001); 26(3).

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