Remembering Richard Marsh

Richard Marsh, 1960. Credit: Caltech Archives.

At the beginning of this year, on Tuesday, January 3rd, the highly accomplished crystallographer Richard E. Marsh passed away at the age of 94. During his impressive sixty-six-year career at Caltech, Marsh was influenced greatly by Linus Pauling’s work in crystallography, and eventually collaborated with him throughout the 1950s and early 1960s. Colleagues and admirers alike knew Marsh for his rigorous standards in investigating atomic structure, a discipline that resulted in his determination of over one-hundred crystal structures throughout his career and the improvement of at least that many more.

In a Caltech tenure that spanned more than six decades, Marsh also inspired generations of graduates and undergrads alike, teaching valuable techniques in crystallography and instilling in his students the rigor of his own research practice. His course “Methods of Structural Determination” was among the most popular graduate offerings in the Institute’s Chemistry division for a great many years. He leaves behind an impressive legacy for the crystallographers of today.

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Marsh, who went by Dick, was born in 1922 in Jackson, Michigan. By the time that he arrived at Caltech as an undergraduate in 1939, Pauling had already helped to established the Institute as among the premiere destinations for budding young crystallographers around the world. In particular, Pauling’s newly published Nature of the Chemical Bond had transformed crystallography from arcane to fundamental.

Though Pauling was certainly well known on campus when Marsh was an undergraduate, it would be another eleven years before Pauling and Marsh formally crossed paths. As a student, Marsh had identified an interest in chemistry, but hadn’t narrowed to a particular focus. He commented later that a technical drawing course at Caltech served as a precursor to his interest in crystallography. He graduated with his BS in applied chemistry in the midst of World War II (1943) and, upon graduation, enlisted in the US Navy, spending the next two years degaussing ships in New Orleans. This is where he met his wife Helena Laterriere, to whom he remained married for nearly seventy years.

Following his discharge, Marsh enrolled in graduate school at Tulane University so that he might remain in close proximity to his fiancée. Most of the courses that he needed were already full at the time of his enrollment, so Marsh signed up for an X-ray crystallography class at the nearby Sophie Newcomb College for women. It was there that he met the teacher who changed his life and cemented his interest in crystallography.

That teacher, Rose Mooney, had previously attempted to enroll at Caltech for graduate studies only to be turned away when she arrived in Pasadena and the administration realized that she was a female. Pauling himself stepped in at this point, giving her a temporary position in his laboratory until she was accepted into the graduate program at the University of Chicago. Her lab at Sophie Newcomb College was quite modest, containing only a Laue film holder and one x-ray tube, but for Marsh it was enough. Inspired, his course was set from then on, though he’d have to travel across the country to continue it.

After marrying Helena on August 11, 1947, Marsh enrolled at UCLA. He later called the 2,000-mile move across the southern United States the beginning of their honeymoon, joking that it was a wedding present to his new bride. At UCLA, Marsh studied crystallography under Jim McCullough and earned his Ph.D. in 1950. Caltech subsequently offered him a post-doctoral research appointment, and he remained at the Institute for his entire career, always in a non-tenured position until his retirement in 1990, when he named an emeritus professor.

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In the years immediately following World War II, Caltech was still very much the place to be for crystallographers. Thanks largely to Pauling, who returned to structural chemistry after his own war projects had wrapped up, scientists from all over the world travelled to Pasadena to conduct research and solve structures.

Marsh finally became associated with Pauling in 1950, when he arrived at the Institute as a post-doc. He published his first paper with Pauling, “The Structure of Chlorine Hydrate,” in 1952. A year later, the duo published “The crystal structure of β selenium,” which marked the first time that Marsh issued a correction of someone else’s work. Indeed, over the course of his career, Marsh became increasingly focused on policing the field for errors, always striving for maximum accuracy and precision. Pauling engaged in this work himself from time to time, although the various demands on his attention kept him too busy to make a full-time habit out of it.

Marsh at the famous Caltech Proteins Conference in 1953. To his right is Francis Crick.

Pauling and Marsh continued to collaborate on a number of other publications related to atomic structure between 1952 and 1955, at which point their interests began to diverge. Nonetheless, the two retained a degree of professional closeness throughout the following decades, often writing to compliment one another on various accomplishments, solicit advice, or suggest future projects. In one instance, Pauling provided the kernel of an idea that resulted in Marsh’s 1982 paper on N, N-Dimethylglycine hydrochloride. Likewise, Marsh helped pave the way for Pauling to publish one of his own articles in Acta Crystallography, where Marsh served as an editor for seven years.

In 1975, presented with the problem of solving of a compound that generates hydrazine from molecular nitrogen, Marsh devised and shared a method for determining the structure. This solution influenced the direction of study into hydrazine formation, creating the opportunity for further study. And although Marsh continued to solve structural problems in the years that followed, he also devoted countless hours – over half his career – to the pursuit and correction of published errors, usually pertaining to inaccurate space groups in important crystal structures. Pauling later described Marsh as the “conscience of crystallography.”

With time, he gained such a reputation that his colleagues in the field were perpetually anxious that they would be “Marshed,” or taken to task, for their errors. Marsh held his colleagues accountable to their calculations and believed firmly in checking a computer’s work, rather than the other way around. He is remembered today as having been responsible for many refinements in crystallographic discipline and for the high standards that make future refinements possible.

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Marsh in 2012. Photo by Rafn Stefansson.

In terms of organizational involvement, Marsh joined the American Crystallographic Association (ACA) shortly after starting at Caltech. Over the duration of his career, he became increasingly active in the group, and ultimately served as its president in 1993. He was also co-editor of Acta Crystallography from 1964-1971.

Marsh’s classroom lectures and his relationships with students were at least as influential as were his publications in crystallography. One colleague, B.C. Wang, recalled that Marsh summoned crystallographers of all stature – be they students, professors, or visiting scientists – to a group coffee at 10:30am every day, to encourage discussion and advancement within the field. Students also remembered him as critical but encouraging, his commitment to student success serving as an inspiration for their own hard work.

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Marsh and Pauling in 1986. Credit: Caltech Archives.

When queried by CRC Press in the early 1990s for his input on future publications, Pauling suggested that the press solicit a monograph from Marsh on the crystal structures that he had corrected thus far, arguing that a volume of this sort might help future crystallographers to avoid these errors. Pauling then wrote to Marsh, inquiring about the total number of crystal structures that Marsh had indeed corrected. Pauling had guessed that Marsh had published fixes for 25 to 30 structures and was surprised to learn that the actual number was between 110 and 120.

Although Marsh didn’t publish this proposed monograph, Pauling’s idea evidently inspired him. In 1995, he authored a substantial article on the subject, titled “Some thoughts on choosing the correct space group.” In the piece, Marsh discussed common types of errors as well as preferable techniques and methodology, including a few tables that documented space group revisions over time.

While at Caltech, Marsh worked closely with Verner Schomaker, another of Pauling’s graduate students. In 1991, the two teamed up to put together a festschrift honoring Pauling’s early work on crystallography. Pauling, a man who, by then, had received basically every award that a scientist can get, was immensely pleased and grateful for this honor.

In 2003, Marsh received the inaugural Kenneth Trueblood Award from the American Crystallographic Association for his outstanding achievements in chemical crystallography. Few other awards could be more fitting for a crystallographer of Marsh’s caliber and commitment. In announcing the prize, the chair of the selection committee identified Marsh as a “rare individual among crystallographers, an outstanding teacher and researcher who has greatly influenced so many students and faculty.” He will be remembered and missed for this indefatigable integrity, dedication, and mentorship.

Pauling Becomes a Researcher

Roscoe Dickinson, 1923.

[Part 2 of 3 in a series investigating Linus Pauling’s life as a graduate student]

As a graduate student at the California Institute of Technology (CIT), Linus Pauling tailored a research program that was focused on the properties of matter, with a particular emphasis placed on molecular structure. This interest and the techniques that he learned would shape Pauling’s scientific thinking for the rest of his life.

Pauling’s focus on the theoretical, and his questioning of why processes move forward as they do or why structures are built as they are, was in keeping with contemporary trends in physical chemistry. Pauling enrolled at Caltech with a strong desire to learn more about the discipline of physical chemistry and his early mentor, Caltech chemistry chair A.A. Noyes, encouraged him to build up his background in x-ray crystallography to further enable this pursuit.

When Pauling began classes in September 1922, he also began his research in x-ray crystallography under the direction of his major professor, Roscoe Gilkey Dickinson.  Not much older than Pauling and a recently minted PhD himself, Dickinson would soon become Pauling’s friend. Within weeks, Pauling began receiving invitations for dinners at the Dickinson house and was soon spending the odd weekend on camping trips with Dickinson and his wife.  After Ava Helen and Linus were married, she too joined in these social gatherings.

Dickinson and Pauling worked closely together for most of Pauling’s first year of grad school, but once Pauling had mastered the techniques necessary to prepare his own research, he mostly moved without Dickinson’s direct supervision. In a 1977 interview, Pauling recalled that Dickinson “was remarkably clear-headed, logical, and thorough” while working in the lab.  And as for the research,

Fortunately the field of x-ray diffraction was in an excellent state in that the procedures were rather complicated but they were thoroughly logical, [and] consisted of a series of logical tests.

The rigor and the logic that were fundamental to the field both pleased Pauling immensely.  And before long, the prodigious young student had moved beyond the expertise of his mentor and had begun to conduct original research that was outside of Dickinson’s own capability. In fact, Pauling’s acumen in the lab and facility as an x-ray crystallographer advanced so rapidly that, by his own recollection

…after about three years…I was making structure determinations of crystals that the technique was not powerful enough to handle, by guessing what the structure was and then testing it.

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

But in his earlier days, Pauling still needed some help. During November and December of his first year as a graduate student, Pauling prepared approximately twelve crystals and attempted to analyze them using x-rays, but none of the crystals yielded images sufficient enough to make a structure determination.

At this point, Dickinson stepped in and directed Pauling to the mineral molybdenite (MoS₂), in the process showing him how to take an adequate sample, mount it, and analyze it using x-ray crystallography. This assistance in hand, Pauling was able to determine the structure of the crystal and Dickinson returned to his own work, confident in his feeling that Pauling was capable of doing the crystallography himself.

Soon after completing the experiment, Pauling was confronted by a very different type of confusion. With a successful structure determination in hand, he assumed that the next step would be to publish the work. So too did he assume that Dickinson would provide him with more direction, but he found that none was offered.  As such, Pauling wrote up his findings and presented them for review to his major professor.

Not long after, A.A. Noyes summoned Pauling to his office and carefully explained to the young graduate student that he had written up a paper with only his name on it and in the process had failed to acknowledge the crucial help that Dickinson had provided. Chagrined, Pauling revised the paper and listed himself as a second author, behind Dickinson. The experience proved to be an important one for Pauling, who was reminded early on of how easy it can be to minimize or discount the role that colleagues can play in one’s own research.

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Molybdenite model, side view.

By the end of April 1923, Dickinson and Pauling had submitted their paper on the structure of molybdenite to the Journal of the American Chemical Society (JACS); it was published in June of that same year.  Together they had found the simplest crystal structure of molybdenite – which contains two molecules in a hexagonal unit – based on Laue and spectral photographs, and using the theory of space groups.  Although he published a piece on the manufacture of cement in Oregon while he was in undergrad at Oregon Agricultural College, the molybdenite paper was Pauling’s first true scientific publication.

Later that year, Pauling arrived at another milestone by publishing his first sole-author paper, one in which he described the structure of magnesium stannide (Mg₂Sn) as determined, once again, by using x-rays. The paper was a huge accomplishment for another reason as well: the x-ray processes used by Pauling had never been successfully deployed for the study of an intermetallic compound before.  And even though this was his first single author paper, Pauling still made sure to thank Roscoe Dickinson in his conclusion, taking pains to avoid another scholarly faux pas.  He would continue in this practice throughout his graduate career.

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Richard Tolman, 1931.

“The crystal structure of magnesium stannide,” was one of eight articles that Pauling published during his grad school years – he completed an impressive total of six structures before receiving his doctorate. Having authored these articles, Pauling found himself on the forefront of a shift in physical chemistry: as crystallography advanced, it was becoming increasingly clear that the properties of specific compounds were based on their structures, which could now be described with mounting confidence. Indeed, several of Pauling’s articles included reevaluations of existing structures, with revised explanations as to why the structures in question had not complied with the new data that Pauling collected.

One such article was “The Entropy of Supercooled Liquids at the Absolute Zero,” which Pauling wrote with CIT faculty member Richard C. Tolman.  In their paper, the two authors corrected an earlier claim made by Ermon D. Eastman, a professor of physical chemistry at Berkeley, who had stated that complicated crystals (those with large unit cells) have greater entropy at absolute zero than do simple crystals. Using statistical mechanical techniques, Pauling and Tolman were able to show that, at absolute zero, the entropy of all perfect crystals, even those with large unit cells, also has to be zero.

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Detail from ‘Atombau und Spektrallinien’ containing x-ray diffraction images.

Pauling had become familiar with Tolman through a different means. During his third term at Caltech, Spring of 1923, Pauling took Tolman’s course in advanced thermodynamics, an experience that boosted his subsequent interest in quantum theory. It was also during this period that he read Arnold Sommerfeld’s Atombau und Spektrallinien (Atomic Structure and Spectral Lines) and began to be exposed to cutting edge research in quantum theory through the numerous physics and chemistry research colloquia hosted by Caltech.

Sommerfeld would become a lasting influence on Pauling’s life and Pauling would eventually study with him in Germany while there on a Guggenheim Fellowship in 1926-27. But well before then, in 1923, Sommerfeld visited CIT to talk about his work with the new quantum theory. As an aid to his lectures, Sommerfeld used crystal models that he brought from Germany, which he hoped would help him to better explain this complicated work. Afterward, Pauling felt emboldened enough to to show Sommerfeld some of the models that he himself had made in the course of his own research; models that turned out to be much better than those constructed by Sommerfeld.

Max Perutz (1914-2002)

Max Perutz. Credit: Theresianische Akademie Wien.

[Ed Note: We mark the centenary of Max Perutz’ birth today with the first in a series of posts on his life and his associations with Linus Pauling. Today’s post focuses on his life from 1914-1941.]

Max Ferdinand Perutz was born May 19, 1914 in Vienna, the third child and second son of Hugo and Adele Perutz.  His birth came little more than a month before the assassination of Archduke Franz Ferdinand and the subsequent start of World War I. Vienna was largely untouched by the war, but suffered mightily from the economic depression that followed. The Perutzes, who had accumulated a substantial fortune from family textile concerns, lost their savings to the rapid postwar inflation. Nonetheless, according to biographer Georgina Ferry, the family managed to maintain an income and “within a few years of the war’s end, they were living as well as before.”

In a 2001 interview with Katherine Thompson for the British Library, Perutz said that he remembered little of these early years. He did recall being a “very delicate child,” contracting pneumonia three times before he was six and a very serious fever at age nine. Fortunately, he was able to recover from the fever after his nanny took him to a resort in the Alps for the winter. After World War II, chest x-rays revealed that Perutz had suffered from tuberculosis, the likely cause of his fever.

Perutz’s physical delicacy affected his social life as well; he described himself as a “weakling at school” who had no friends early on since he was sick so often. Because of his condition, Perutz did not excel at most sports. But his many holidays in the Alps led him to develop a lifelong love of rock climbing and skiing. These skills eventually earned Perutz the respect of his peers after he won a prize for the school skiing team.

Perutz attended private primary schools until entering the newly organized Realgymnasium, which brought a shift in focus from classics to modern languages and the sciences. Perutz described his early years of schooling as “eight years of unbearable boredom.” This boredom began to wane as Perutz gravitated toward English literature, an interest enabled by his Anglophile father who saw that he was tutored in English in addition to the more common French. Perutz secretly read Charles Dickens and other British novelists under the bench while at school, later furthering this passion with his first girlfriend, who was from England. Perutz’s parents expected him to take over the family textile business once he was old enough, and were heartened by his developing intellectual prowess.

However, the business route never appealed to Perutz, especially after he was exposed to chemistry by an influential teachers, and at eighteen he began formal pursuit of his interest in chemistry at the University of Vienna. (Protests from his parents were soothed by the help of a friend of Perutz’s older brother, a chemist at Dow.) As with his primary schooling, Perutz was not very impressed by the education that he received at university. He described the curriculum’s lack of mathematical training and decidedly practical emphasis as “chemistry done by heart” because of the reading and memorizing he was forced to do in lieu of actual laboratory work. But ultimately he made it through and, in the process, cultivated a new attraction to physics which he would later fulfill as a graduate student in England.

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Portrait of Perutz drawn by William Lawrence Bragg. Credit: MRC Laboratory of Molecular Biology

From Vienna, Perutz moved on to Cambridge, where he hoped to work with Frederick Gowland Hopkins, the university’s first chair of biochemistry and recipient of the 1929 Nobel Prize in Physiology for his work on the relation between vitamins and growth. Since Perutz showed up without letting anyone know, he did not find out that he could not work with Hopkins until he actually arrived. Chastened, Perutz looked elsewhere and ended up in the Cavendish Laboratory of Physics doing x-ray crystallography. “Without knowing it,” Perutz later recalled, this “was one of the best things I could have done.”  Supported by £500 sent by his father, Perutz settled in and was able to take care of his own finances for the duration of his doctoral studies.  His health continued to suffer though – once in England, he began to experience frequent and painful digestive problems.

The first project that interested Perutz was identifying radioactive deposits dug out from the cliffs in Cornwall. Perutz measured the half-life of the material, but found that it did not correspond to any known elements. Excited that he may have discovered a new element, Perutz shared his findings with Cambridge luminaries Ernest Rutherford and J. D. Bernal, who helped him to determine that the substance was, in fact, radium. Bernal also encouraged Perutz to publish his findings and to present them at a Royal Society soiree. This led to his first publication, “The Iron-Rhodonite from Slag,” which appeared in Mineralogy Magazine in 1937.

At the end of his first year at Cambridge, Perutz spent his summer holiday back in Austria and thought about what he might do for his doctoral dissertation. Felix Haurowitz, then at Charles University in Prague, suggested focusing on hemoglobin, telling Perutz that he could get crystallized hemoglobin from Gilbert Smithson Adair at Cambridge. When he returned and acquired the hemoglobin, Perutz says he “immediately got a lovely x-ray diffraction picture,” which “thrilled” Bernal.

In the midst of his hemoglobin research, Perutz also agreed to assist a man who came to the Cavendish Laboratory looking for researchers to satisfy his own interest in glacier development. Perutz saw this as a perfect opportunity to spend more time skiing in the Alps. He published his work in the Proceedings of the Royal Society in 1939, describing how melting and the movement of water contributed to glacier formation and flow.

In March 1940, Perutz wrapped up his Ph.D., which described the structure of hemoglobin and the x-ray methods used to develop the model. Yet the looming threat and subsequent reality of war overshadowed his findings and began to color components of his world that were much more important than his research.

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Credit: National Portrait Gallery, London.

As World War II approached, the Perutz family, still in Vienna, looked for ways to get out. The Perutzes were ethnic Jews, but Max’s parents were non-observant and Perutz himself had been baptized Catholic. As a young boy, Perutz was very devout, a character trait that he abandoned after his prayers that the Italians not invade Ethiopia were not answered. While his baptism was meant to protect him from anti-Semitism, he claimed that his family “very rarely” experienced discrimination before the Anschluss. Once the Nazis assumed power, the Perutz family quickly left with Max’s brother and sister going to the United States and his parents coming to stay in Cambridge. Hugo and Adele Perutz, used to supporting themselves, lost their businesses and spent all their money leaving Vienna – according to their son, they “were traumatized by suddenly being poor.”

To get them to England, Max both had to prove that he could support them and was also required to pay a thousand pounds, compelling him to sell some of his mother’s jewelry and to borrow funds to cover the rest. Around this time, William Lawrence Bragg, winner of the 1915 Nobel Prize in Physics, came to the Cavendish. Bragg was very excited about Perutz’s work with hemoglobin and helped him to secure a grant with the Rockefeller Foundation in New York. The grant provided £275 per year, enough for Perutz to prove that he could support his parents. But soon the family would come into even more trouble.

In May 1940, just two months after he finished his Ph.D., Perutz was interned by the British government. He was first taken and held in a school at Bury St. Edmunds, east of Cambridge, for one week before being transported to Liverpool. By July, Perutz, along with roughly twelve-hundred others, was shipped across the Atlantic to a camp near Quebec City, Canada, where the residents’ status was upgraded from “internee” to “civilian prisoner of war,” a change that promised access to clothing and army rations. In a 1985 essay for the New Yorker, titled “Enemy Alien,” Perutz wrote,

To have been arrested, interned, and deported as an enemy alien by the English, whom I had regarded as my friends, made me more bitter than to have lost freedom itself. Having first been rejected as a Jew by my native Austria, which I loved, I now found myself rejected as a German by my adopted country.

Perutz’s friends were working on his behalf to have him released, unknown to him since he could receive no communications.

Meanwhile, in Quebec, Perutz tried to make the best of things and organized a “camp university.” Hermann Bondi, a mathematician also from Vienna, taught on vector analysis, while Klaus Fuchs, a student at Bristol who fled Hitler’s persecution for being a communist, taught theoretical physics. For his part, Perutz drew on past research of his own, explaining the atomic structure of crystals to all who might be interested.

The Rockefeller Foundation did not forget about Perutz and arranged a professorship for him at the New School for Social Research in New York City. Hearing rumors that his father had also been interned and worried that he would not be able to obtain a visa to travel once he had been established in the United States, Perutz was eager to go back to England to check on his parents. After several delays and transfers, Perutz arrived back in Cambridge in January 1941, finding his father already released and his friends happy to see him.

Pauling and Proteins: Helices in the Air

Mounted models of the gamma helix and alpha helix, as housed in the Special Collections & Archives Research Center, Oregon State University Libraries.

[Part 2 of 3]

Linus Pauling sent shock waves through the scientific community when he published seven articles relating to the structure and function of proteins in the April-May 1951 issue of the Proceedings of the National Academy of Sciences. The first article of this volley was titled “The structure of proteins: Two Hydrogen-Bonded Helical Configurations of the Polypeptide Chain.” The second article was written by Pauling and Robert B. Corey, and was called “Atomic Coordinates and Structure Factors for Two Helical Configurations of Polypeptide Chains.” This paper was much more technical than was the first, and introduced two new important models developed by the Pauling group: the Gamma-helix and the Alpha-helix.

The article began by explaining in great detail Pauling’s idea for what he called the Gamma-helix (γ-helix). The γ-helix was the name assigned to the 5.1-residue helical configuration that Pauling, Corey, and Herman Branson had described in the first PNAS proteins article. The main difference between the γ-helix and the other configurations that they had proposed was that the bond angle between the C-N-C connection had been changed from 123˚ to 120˚. The authors explained that this small adjustment in the bond angle resulted in a miniscule change in the interatomic distances between various hydrogen bonds, but that these changes were significant enough to notably affect the number of residues per turn present within the structure.

(It is worth noting that the unit used to measure the distance between molecules is the Angstrom (Å). One Å equals 10^-10 m, or one ten-billionth of a meter. Considering the truly tiny sizes being measured, it is likewise worth noting that the changes between hydrogen bonds that Pauling was talking about were often measured in the thousandths of an Angstrom or ten-trillionths of a meter. One trillionth of a meter is known as a picometer.)

The article stressed that differences as small as 10 picometers could notably change bond angles, which would then change the number of residues per turn, thus dramatically affecting the shape of the helix. Next, the authors elaborated upon the likely arrangements of molecules within the helix due to symmetry or lack of symmetry in certain molecular bonds. Pauling and Corey further noted that they had used x-ray crystallography to validate their arguments and determine the crystal structures in question. From his earliest days as a scientist, Pauling had established himself as a major figure in x-ray crystallography, a technique by which an operator fires x-rays at a substance in question, then measures the way that the x-rays have deflected off of the substance. By analyzing these deflection patterns, researchers were then able to develop models of the shapes of molecular structures.

Once the γ-helix had been explained, the article moved on to discuss the Alpha-helix (α-helix). The group explained that the γ-helix and the α-helix were similar in terms of how the hydrogens bonded with other molecular groups, and how the residues fit under those configurations. They also detailed the exact interatomic distances between hydrogen and various other molecules in the structure, while pointing out that the distance between carbon and its other bonds determined the number of residues per turn. The number of turns, however, was variable; the smallest possible angle of 108.9˚ resulted in a residue of 3.6, while the largest possible angle of 110.8˚ resulted in a 3.67 residue.

William Lawrence Bragg, an internationally famous scientist and proteins researcher of great import, was impressed by the α-helix, though he felt his rival Pauling to be overly excited about it. The α-helix was not a complete protein, except in a few cases including fibers, hair, and horn.  The structure also did not explain the functioning of proteins. As such, Bragg felt the paper to be an important first step – no more, no less. The rest of the scientific community was more enthusiastic than was Bragg and his team. Pauling received a Nobel Prize in 1954 in Chemistry “for his research into the nature of the chemical bond and its application to the elucidation of the structure of complex substances,” the α-helix being among the most famous of these “complex structures.” The National Science Foundation even named a research vessel The Alpha Helix in honor of the discovery.

Bragg was even less generous regarding the γ-helix. Though in his very carefully worded congratulatory letter to Pauling he did not say so, he felt the γ-helix to be far-fetched, perhaps existing only in Pauling’s imagination. While this was not the case, the γ-helix ultimately made less of an impact on the scientific community.

Regardless, the import of Pauling’s work was felt throughout the profession.  Though Francis Crick would write that the alpha helix did not give him and Jim Watson the idea that DNA was a double helix, he did suggest that “helices were in the air,” at the time “and you would have to be either obtuse or very obstinate not to think along helical lines.”

New Insights into Metals and More

Linus and Peter Pauling at Warwick Castle, England. 1948.

[The Paulings in England: Part 3 of 5]

In his lab, a five minute walk from his office at Balliol College (where he was once caught boiling an egg on his electric space heater), Linus Pauling’s research took a turn from the contents of his lectures – intermolecular forces and biological specificity – and he found himself devoting his research time to metal theory. Pauling had planned to revise the index for his newly published freshman text, General Chemistry, during his Eastman Professorship, but couldn’t seem to get metals off his mind.  As he wrote in a letter to his Caltech colleague J. Holmes Sturdivant, “I thought that I would be doing work in connection with my freshman text while in England, but it has turned out that I have devoted all of my time, and presumably shall continue to do so, to work on the theory of metals and intermetallic compounds.”

He was aided in his lab by three other researchers – David Shoemaker, Hans Kuhn, and a young man from Holland, Dr. F. C. Romeyn. Pauling’s circumstances were proving to be highly productive, and in a March letter to Robert Corey, Pauling wrote of the impact that the change of setting was having in stimulating his thoughts:

I have been having wonderful success in my development of a theory of metals. I think that it has really been very much worthwhile for me to get away for this period of time, under circumstances favorable to my thinking over questions and trying to find their solution. The problem of metals has been on my mind for a number of years, and I haven’t been able to leave it alone, so it is a good thing that I have now managed to get it solved.

This new theory of metals was an extension of Pauling’s valence-bond approach to determining the structure of molecules, as initially developed in the late 1920s. Pauling was first exposed to quantum mechanics as an undergraduate at Oregon State University (then known as Oregon Agricultural College) and retained that interest as he transitioned to graduate studies and faculty employment at the California Institute of Technology.

In 1926 Pauling traveled on a Guggenheim Fellowship to study the developing field of quantum mechanics with physicists in Europe, and especially Germany. He brought these new ideas back to Caltech in the form of quantum chemistry, which he used to compute the electronic structures of molecules. This intuitive valence-bond approach was quickly judged a success and had been popular since the 1930s as a simple model for studying the electron dispersal in the bonds between molecules.

But all the while another chemist, Robert Mulliken (recipient of the 1966 Nobel Prize for Chemistry) had been steadily fostering a rival approach: the molecular orbital theory. While the Pauling family enjoyed springtime in Paris at the beginning of April, Pauling and Mulliken met head to head at a conference on Isotopic Exchange and Molecular Structure. There an entire day was devoted to the comparison of the two theories before a group of quantum chemists. Pauling had written earlier that molecular orbitals were confusing to students, but he learned at this meeting that one always has to stay one’s toes: with more mathematics under their belts, advanced chemistry students were increasingly hungry for the more quantitative approach that Mulliken’s theory offered.

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Sometimes ideas come upon the great thinker at surprising times, and Pauling experienced just such a eureka moment during one of his twice-weekly Oxford lectures in February.  As he wrote to Holmes Sturdivant,

I have just had a great stroke of luck. While giving my lecture on Tuesday I suddenly realized that a calculation about resonance energy of metals that I had just made and was reporting contained the key to the strange valence numbers and numbers of atomic orbitals and unused orbitals that have turned up in my theory of valency of metals.

Notes on intermetallic compounds by Linus Pauling, March 1948.

Pauling worked out his ideas on electron theory and the structure of metals and intermetallic compounds through pages and pages of careful handwritten calculations. In looking at each manuscript now, Pauling presents a hypothesis about some aspect of metal theory and then proceeds to calculate, revise, and recalculate until the theory and the experimental x-ray diffraction data line up. For instance, on one day in March, Pauling was exploring intermetallic compounds from several different angles.  He writes “I shall now treat intermetallic compounds, with my new ideas – resonance of bonds when an extra orbital is available, importance of n=1/2, 1/4 etc., concentration of bonding electrons into strong bonds (Zn-Zn, etc as compared with Na-Na) , transfer of electrons with increase in valence.” Hybrid orbitals, bond lengths, and the overall stability of structures were other items on Pauling’s research agenda.

Of course, not every idea is a winner and a few theories led Pauling down the wrong path; in one manuscript Pauling set out to, as he wrote, “consider sp hybridization – how can we set up a secular equation to give the results given by my bond-strength postulate?”  In the end Pauling found that “the ratio does not come out as desired. It is evident that my assumption that the energies can be taken proportional to ‘bond strengths’ is not right.”  Missteps such as these didn’t deter Pauling from pressing on with his research, for as he often said, “The way to have good ideas is to have lots of ideas, and throw away the bad ones.”

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Chemistry boasts its own special language, or nomenclature, and chemists like Pauling are to thank for the terms that make chemical jargon unique. As research advances, sometimes an entire new word is needed to describe an innovative concept. While tackling the nuances of metal theory at Oxford, Pauling wrote to Sturdivant about this very problem.

By the way, I think that we should do something toward improving the nomenclature. For example, coordination number is an awkward and unwieldy expression – we need one short, precise word for this concept. Perhaps ligancy could be used. It would fit in well with ligand and the verb to ligate. We also need some general words to express the bonds between one atom and the surrounding atoms – we now use the word bond to refer both to the electron pair bond that is resonating around among alternative positions and to the fraction of an electron pair bond that is a portion to a particular position. I have also felt troubled about using the word position in this way – to mean the region between two atoms. If we do introduce any change in nomenclature, it must be very well thought out, and must not involve too great a strain on the memory, or too great a departure from the past.

New fields also call for innovations in instrument development and research programs. Pauling was in constant communication with his colleagues back home about new tools that might be constructed to aid the researchers. He admired the Cavendish’s vast x-ray crystallography laboratory and also gained new insights from reading British journals devoted to scientific instrumentation. He would frequently send word back as to how Caltech workers could improve on a complex apparatus such as the specialized cameras for x-ray diffraction of metallic crystals.

Pauling was likewise intrigued by the English system of graduate education, wherein graduate students would take class work completely during the first year and then spend practically 100% of their time on research during the other two years. Pauling was always looking to improve upon existing programs, but as appealing as the English system was, he acknowledged that in implementing it one would run the risk of not knowing whether a student was an apt researcher for their entire first year!

Dorothy Crowfoot Hodgkin, 1910-1994

Linus Pauling and Dorothy Hodgkin, 1957.

[Part 1 of 2]

On May 12, 1910, Dorothy Crowfoot Hodgkin – a renowned X-ray crystallographer and long-time friend of both Linus and Ava Helen Pauling – was born in Cairo, Egypt. In honor of the hundredth anniversary of her birth, today’s and Thursday’s posts will be devoted to the discussion of not only Hodgkin’s life and extensive contributions to the scientific community, but also her friendship to the Pauling family.

Although Dorothy Crowfoot was born in Egypt, her parents were English and she spent most of her childhood in the United Kingdom. When World War I began in 1914, she and her two sisters were taken to England, where they lived for a time with their grandparents. After the war, Dorothy’s mother, who had moved to Sudan from Cairo with her husband in 1916, decided to return to England to be with her daughters. In 1920 the family moved to Beccles, England, and in 1921 Crowfoot entered the Sir John Leman Grammar School. During her time there, her interest in science grew immensely.

In 1928, after spending a year studying Latin and botany, Dorothy began to focus on chemistry at Oxford’s Somerville College, where she quickly became interested in X-ray crystallography. In 1932 Crowfoot left Oxford for Cambridge to work under J.D. Bernal. Two years later she returned to Oxford and after another two years of study was appointed a research fellow there, a position that she held until 1977.  During her time at Oxford, Dorothy supervised the work of many students, including a young Clara Brink, whose papers now reside in the Oregon State University Libraries Special Collections.

In 1937 Crowfoot married Thomas Hodgkin, with whom she had three children.

Throughout her lengthy scientific career, Hodgkin worked with great success on a wide variety of research projects pertaining to molecules such as sterols, vitamin B12 and insulin. She participated in the 1946 meetings that led to the formation of the International Union for Crystallography, and also became a member of various academies and societies, including the Royal Society and the American Academy of Arts and Sciences.

In 1964 Dorothy Crowfoot Hodgkin received her highest decoration: the Nobel Prize in Chemistry “for her determinations by X-ray techniques of the structures of important biochemical substances.” She also received the Order of Merit, the Lenin Peace Prize – for which she was nominated by Linus Pauling – the Copley Medal, and many other awards for her extensive research.

The first mention of Dorothy Hodgkin in the Pauling Papers appears in correspondence dated to 1947. In it, Pauling writes to Dr. H. Marshall Chadwell of the Rockefeller Foundation, asking for advice about Hodgkin, who will be coming to the U.S. in the fall on a grant from the Rockefeller Foundation. Pauling states that he has “known her work very well, and for a long time, and I have been looking forward to meeting her.” Not long after, Pauling and Hodgkin did meet, and they soon began personally exchanging letters. This process lasted essentially for the rest of their lives, and allows for direct observation of their developing friendship.

Letter from Pauling to Hodgkin, October 7, 1953.

Although much of the correspondence between Hodgkin and Pauling relates to research, they often discuss more personal matters. Alongside the numerous letters on Hodgkin’s work pertaining to Vitamin B12 and Pauling’s research on proteins, there are many letters discussing subjects such as health issues – not only their own but also those of their spouses – Pauling’s experience of being trapped on a cliff, and various travel plans – many of which set up visits to each other.

One specific letter of interest from Pauling to Hodgkin is dated September 14, 1955, in which Pauling writes

to congratulate you on the wonderful job that you have done on Vitamin B12. I find it hard to believe, although very satisfying, that the methods of x-ray crystallography can be used so effectively on such a complex molecule.

Hodgkin had begun work with the Vitamin B12 molecule in 1948.

Another interesting letter from Pauling to Hodgkin illustrates the extent to which the scientific viewpoint permeated Pauling’s thinking on a whole host of matters. In his letter dated January 27, 1959, Pauling thanks Hodgkin for a book that she had sent to him – Christopher Hill’s Puritanism and Revolution – and notes that “I have written to Christopher that I think that mad hatters are mad because of mercury poison – felt is made by treating the hair with mercuric nitrate. His chapter 11 is about a mad hatter.”

One last letter of note is written by Hodgkin on October 14, 1974, in which she informs Pauling that she “should be very happy indeed to be an Associate of the Linus Pauling Institute of Science and Medicine.” In this same letter, Vitamin B12 makes another appearance, demonstrating the longevity of her work with the molecule. This time, Hodgkin sends a stereo print of her structure of the Vitamin B12 coenzyme, which she calls “the most important naturally occurring form of the vitamin.”

Hodgkin and Pauling, 1986.

Unfortunately, not every letter between Pauling and Hodgkin comes under happy circumstances. On December 15, 1981, Hodgkin writes to Pauling to mourn the death of Ava Helen, which had occurred on December 7. Some six months later, on June 4, 1982, Pauling writes to Hodgkin in order to express his sympathy after hearing that her husband Thomas had died.

Hodgkin’s leading work in the field of X-ray crystallography made her one of the most decorated and successful scientists of the twentieth century, as well as a pioneering example of the role that women could play in the laboratory. Although a deep interest in science may have initially introduced Hodgkin and Pauling, our brief look at the correspondence between the two shows that their professional relationship quickly evolved into a long-lasting friendship.

Dorothy Crowfoot Hodgkin died on July 29, 1994, twenty-one days before Linus Pauling.

Check back on Thursday for our post on Hodgkin and Ava Helen Pauling, and make sure to visit the Linus Pauling Online portal for more information on Linus Pauling.

Two Years on the Pauling Beat

Today marks the second anniversary of the launching of the Pauling Blog.  In two years we have generated 214 posts, garnered over 63,000 views (not counting those accruing from syndication, which WordPress doesn’t include in its total statistics) and been graced with nearly 7,400 spam comments, most of which, thankfully, have been kept at bay by the good folks at Akismet.

We’re a bit less philosophical today than was the case one year ago, but we do want to take this moment to reflect back a bit.  Our readership has grown substantially over the past year and, as we enter our terrible twos, we figure this is a good opportunity to take another quick look at some writing that many of our readers may have never seen.  Here then, are ten worthwhile posts from the early days of the blog.

1. Visiting Albert Schweitzer:  a review of the Paulings’ trip to Schweitzer’s medical compound in central Africa – in Linus Pauling’s estimation, “one of the most inaccessible areas of the world.”
2. Pauling and the Presidents: the first in a series of three posts on Pauling’s relationship with this nation’s Commanders in Chief and with the office of the Presidency itself.  The other two posts focus on Pauling’s complicated interactions with John F. Kennedy, and with his own brief flirtation with the idea of running for the office himself.
3. Pauling’s Rules: among Pauling’s major early contributions to science was his formation of a set of rules used to guide one’s analysis of x-ray diffraction data in the determination of crystal structures.
4. The Guggenheim Trip: a three-part series detailing Linus and Ava Helen’s adventures as they toured through Europe for a year, meeting major scientific figures and absorbing the fledgling discipline of quantum mechanics.
5. The Darlings: Maternal Ancestors of Linus Pauling:  an entertaining look at the colorful characters residing further down Pauling’s family tree.  We also featured Pauling’s paternal ancestry as well as Ava Helen’s lineage in separate posts.
6. A Halloween Tale of Ice Cream and Ethanol:  Pauling’s typically detailed and ultra-rational recollection of a hallucination experienced late one November night.
7. Clarifying Three Widespread Quotes:  three quotes attributed to Linus Pauling are scattered across the Internet.  This post investigates whether or not Pauling actually authored them.
8. Pauling in the ROTC:  often accused of anti-Americanism due to his pacifist beliefs, few people know that Pauling actually served in the Reserve Officers Training Corps, ultimately rising to the rank of Major.  This post was among the first in our lengthy Oregon 150 series, celebrating Pauling’s relationship with his home state.
9. Mastering Genetics: Pauling and Eugenics:  a post that delves into what was among the more controversial stances that Pauling ever took.
10. Linus Pauling Baseball:  we can’t help it – the video is priceless.

As always, thanks for reading!

David and Clara Shoemaker

David and Clara Shoemaker working in an x-ray laboratory at Oregon State University, 1983.

Husband and wife crystallographers David and Clara Shoemaker were, in many respects, an unlikely couple.

David Shoemaker was born on May 12, 1920 in the tiny town of Kooskia, Idaho. Clara Brink was born on June 20, 1921 in Rolde, Holland. Both moved through their primary studies in orderly fashion and progressed to undergraduate work in chemistry – David at Reed College in Portland, Oregon, Clara at the University of Leiden.

In 1942 David received his bachelor’s degree from Reed and moved directly to the California Institute of Technology. Working under Linus Pauling, David quickly established himself as a promising doctoral candidate. His research was initially divided between Pauling’s expansive program of scientific war work and, later, a series of crystallographic investigations. While in Pasadena, David determined the structure of sixteen molecules, most notable among them threonine, an amino acid.

Upon receiving his Ph. D. in 1947, David – with the assistance of Pauling – was subsequently named a Guggenheim fellow, studying at both Oxford and the Institute for Theoretical Physics in Copenhagen. Aged 27, he was among the youngest of his era to receive a Guggenheim Fellowship.

Group photo of participants at the Conference on Current Problems of Physics. Copenhagen, Denmark. September 1947. Niels Bohr sits in the front row, far left. David Shoemaker is seated in the second row, fourth from right.

Clara’s path through graduate studies was somewhat less smooth. She completed her undergraduate work at the University of Leiden in 1941, shortly before the Nazi occupation of the Netherlands and the subsequent closing of the university. Despite the turbulence of World War II, Clara was able to commence her graduate studies through the University of Utrecht, though much of her coursework was self-taught, conducted in her parents’ home. Despite these handicaps, Clara completed her doctoral examinations on time, in 1946, after which point she assumed an assistantship at the University of Utrecht and learned the techniques of x-ray crystallography, commuting one day per week to Amsterdam to study under the renowned crystallographer Caroline MacGillavry.

The years immediately following the close of hostilities were fruitful ones for both David and Clara. Having returned home from his Guggenheim trip, David was named a Senior Research Fellow at Caltech, where he solved the difficult structure of DL-serine and began the research program that came to define much of his (and Clara’s) career – a broad series of investigations into the structures of complex transition-metal phases. In the meantime, Clara became a full-time crystallographer, first studying crystal structures of monovalent ions at the University of Leiden and later working for one year at Oxford, where she conducted research on the crystal structure of vitamin B12 under Dorothy Hodgkin, the 1964 Nobel laureate in Chemistry.

In 1951 David was hired away from Caltech by the Massachusetts Institute of Technology, where he began investigating zeolite structures as an Assistant Professor. Two years later, dissatisfied with the working environment at the University of Leiden, Clara took a one-year leave of absence to work on transition metals at M.I.T. Her laboratory in Cambridge was run by David Shoemaker.

In 1954 David renewed Clara’s leave of absence for an additional year and by 1955 it was clear that Clara would not be returning to Europe – on August 5th, the couple was married. Shortly thereafter Clara transferred to Harvard Medical School to work under the biochemist Barbara W. Low. One year later, Clara gave birth to the couple’s only son. While caring for the newborn Robert, Clara worked from home on the International Tables of Crystallography.

The Shoemakers enjoyed a productive tenure at M. I. T. – David was promoted to full professor, began a lengthy service on the U. S. National Committee for Crystallography (including a three-year term as President) and published widely, including a textbook titled Experiments in Physical Chemistry, which would eventually run through six editions.

In 1970 David was elected President of the American Crystallography Association. That same year, the Shoemakers relocated to Oregon State University, where David had been hired to chair the Department of Chemistry. In reaction to the university’s nepotism guidelines, Clara arranged to work as Research Associate under Dr. Ken Hedberg – like David Shoemaker, a former graduate student of Linus Pauling. The arrangement lasted for several years until the university’s rules were relaxed.

Model of the crystal structure and superstructure of the K Phase, Mn77Fe4Si19. Model built by Clara B. Shoemaker, David P. Shoemaker and Ted E. Hopkins.

During his tenure as department chair, David oversaw two major building projects – the construction of a new chemistry laboratory facility and the renovation of the chemistry offices and research building. Over that same period of time, Clara trained several graduate students in techniques of x-ray crystallography, publishing papers with many of her protégés. The couple retired in 1984, though they continued to conduct important work on transition metal phases as well as the controversial topic of quasicrystals.

The Shoemakers remained close friends with Linus Pauling, though they did dispute certain of Pauling’s claims about the nature of quasicrystals. In 1995 David Shoemaker, himself in fading health, spoke of his long association with Pauling at a memorial conference organized at Oregon State University. David’s comments detailing his recollection of the discovery of the alpha-helix caused something of a stir in the audience, as the provenance of the alpha-helix work has long been a matter of some dispute.

David Shoemaker on the Discovery of the Alpha Helix

Afterward, Shoemaker offered this clarification:

My memory may have been faulty in claiming to have seen Pauling actually taping his cardboard amide linkages together to form a helix, but Professor William Lipscomb, in a talk that preceded mine, showed a drawing in Pauling’s own hand of an alpha-helix rolled out flat, showing what points the polypeptide chain joined together in the helix. The drawing was titled ‘alpha helix. First drawn March 1948. Linus Pauling.’ My visit to Oxford was from January to March 1948.

David Shoemaker died of kidney failure on August 24, 1995, some six months after the Pauling memorial conference. His wife Clara, a close friend of our department, passed away on September 30, 2009. Over the course of their professional association, David and Clara published thirty-six scientific papers together.

The David and Clara Shoemaker Papers are just one of the many collections held in the OSU Libraries Special Collections.

The Pauling Centenary Conference

The date February 28, 2001 is meaningful to many residents of the Pacific Northwest.  At 10:54 AM that morning, the Nisqually earthquake, a magnitude 6.8 temblor located northwest of Olympia, Washington, shook the earth beneath the greater Seattle-Tacoma area and ultimately caused over $1 billion in damage.

Some 200 miles south in Corvallis, faint signs of the earthquake were noticed.  In the lobby of the LaSells Stewart Center, for instance, observers noted coats on a coat rack mysteriously swaying.  At the time, few thought much of what they were seeing however, given that an important local event (if something short of seismic) occupied the attentions of most.  February 28, 2001 was the one-hundredth anniversary of Linus Pauling’s birth and the LaSells Stewart Center was the site of a day-long conference honoring Pauling’s memory.

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“In 1986, just before [Lloyd] Jeffress died, Pauling wrote him a letter in which he caught him up on the events of the past year. The last paragraph of the letter related a recent article that Pauling had published in Nature magazine, which had stirred up controversy in the scientific community. A reporter had asked Pauling, ‘Do you have a liking for controversy?’ ‘No,’ replied Pauling. ‘I have a liking for the truth.’ This phrase, ‘a liking for the truth,’ and its surrogate implications of Pauling’s passion for discovery, even in the face of controversy, is a theme of this conference, and we hope that you will be enlightened and entertained by what is to follow.”

-Cliff Mead, centenary conference introductory remarks

“A Liking for the Truth: Truth and Controversy in the Work of Linus Pauling” assembled a multifaceted group of speakers who directly and indirectly reflected upon Pauling’s legacy as a scientist, activist and human being.  The day’s keynote speaker was Dr. Ahmed Zewail, the Linus Pauling Chair Professor of Chemistry and Professor of Physics at the California Institute of Technology, and the recipient of the 1999 Nobel Prize for Chemistry.  Zewail’s topic was the evolution of femtoscience, the study of atomic behaviors that occur in very short periods of time, a breathtaking field of research that allows scientists to, in Zewail’s words, “see bonds and atoms.”

Whereas Zewail spoke of time, another of the day’s presentations, by crystallographer and long-time Pauling family friend Dr. Jack Dunitz, focused on space.  Dunitz, Pauling and many others enmeshed in the practice of crystallography shared a deep interest in developing theories governing the rules that underlie “closest-packing” in molecules, work that Pauling and Max Delbrück extended into the realm of biology through their theory of molecular complementarity.

Jack Dunitz at a Caltech graduate student outing, ca. 1948.

Two Pauling biographers were likewise involved in the centenary activities.  Tom Hager spoke eloquently of the real world consequences that enveloped the Paulings as their peace work assumed international prominence.  Dr. Robert Paradowski reflected upon a turbulent period of the Paulings lives as a young couple, as the pair toured through Europe during Linus’s Guggenheim studies in 1926-1927.

Perhaps the day’s most broadly interesting talk, however, was delivered by Linus Pauling, Jr., the eldest of the four Pauling children.  Recalling memories as varied as Christmas traditions, the family cars and an eventful restaurant meal, Linus Jr. shed insight into a world hidden from even the closest of colleagues and most meticulous of biographers.  In the video excerpt below, Linus Jr. recounts the details of a cherished family tradition – regular vacations to the Painted Canyon desert.

Transcribed video of the Pauling Centenary Conference is available here.

The X-Ray Crystallography that Propelled the Race for DNA: Astbury’s Pictures vs. Franklin’s Photo 51

Rosalind Franklin, March 1956

During their so-called race to discover the structure of DNA, Linus Pauling and the unlikely pair of James Watson and Francis Crick utilized remarkably similar approaches in attempting to solve the riddle of the genetic material. In fact, one of the main tactics used by Watson and Crick was to approach the problem in the same manner that they assumed Pauling would. Although Pauling and Watson and Crick did, at one point, come up with nearly identical, yet incorrect, structures, it was Watson and Crick who would eventually solve DNA. Why then, if the pair were thinking like Pauling, were they able to beat him to the structure?

Although there were a variety of reasons behind Watson and Crick’s success, a good portion of it can be attributed to the relative superiority of resources available to them. Watson and Crick obviously had each other to keep themselves in check, but they also benefited from other voices of criticism such as Rosalind Franklin, Maurice Wilkins, and later Jerry Donohue. Linus Pauling also shared his ideas with his colleagues, but none of them were very familiar with DNA, and therefore couldn’t offer much feedback. (And they were largely ignored even when they did offer criticisms of Pauling’s structure.)

Another vital resource available to Watson and Crick was an excellent X-ray crystallography pattern, the famous photo 51, taken by Rosalind Franklin. Although, in all likelihood, Pauling could have also viewed Franklin’s photographs had he tried, he settled on using blurry patterns published by William T. Astbury several years before Franklin’s superior images. These X-ray photographs are the main topic of today’s post. In particular, the factors accounting for the difference in quality between Franklin’s and Astbury’s patterns will be discussed. Before delving into this subject, however, a brief overview of X-ray crystallography is necessary.

William T. Astbury, ca. 1950s.

X-ray crystallography, also sometimes known as X-ray diffraction, is used to determine the arrangement of atoms within a crystalline molecule. It is a rather complicated procedure, and the photos taken in the process can be interpreted only by a person with significant training. The steps to obtaining these photos are as follows.

First, an adequate crystal must be obtained. This is a very difficult step because the crystal must be large enough to observe and also sufficiently uniform. If it does not meet these specifications, errors – such as blurriness – will occur, often rendering the resulting crystallographic patterns useless, at least for purposes of determining atomic arrangement.

After an adequate crystalline specimen is obtained, a beam of X-rays is shined through it. When the beam strikes the electron clouds of the atoms in the crystal, it is scattered. These scattered beams can then be observed on a screen placed behind the crystal. Based on the angles and intensities of the scattered beams, a crystallographer can create a three dimensional picture of the electron density of the crystal.

Finally, from the electron density information, the mean positions of the atoms within a crystal can be determined, and the structure of the molecule can be considered “solved.” That said, just one image is not nearly enough to determine the structure of an entire crystal. Therefore, the crystal must be rotated stepwise through angles up to and even slightly beyond 180 degrees, depending on the specimen. Patterns are required at each step, and complete data sets may contain hundreds of photos.

Clearly, because the process of X-ray crystallography is so cumbersome, there are many opportunities for mistakes that may have led to the poor quality of Astbury’s photographs. However, Astbury’s techniques seem to have been excellent. He was a very experienced crystallographer, and had achieved great success in his earlier work with X-ray diffraction on substances such as keratin.

As it turns out, Astbury’s photos were of poor quality because of the DNA sample he was using. In the early 1950s, Rosalind Franklin had discovered that DNA came in two forms – a dry condensed form and a wet extended form. Astbury’s DNA sample was well prepared from calf thymus, but it contained a mixture of the two forms. This turned out to be the major reason why Astbury’s photographs were so blurry

Astbury's images, 1947. Plate 2.

It is important to note that, even if Astbury had known he was using a poor crystalline sample of DNA, he probably still wouldn’t have been able to compete with the quality of Franklin’s photos. In 1950, three years after Astbury’s images were published, Maurice Wilkins developed a way to obtain much better X-ray patterns of DNA through the use of a solution of sodium thymonucleate. This solution is highly viscous, and Wilkins found that thin strands could be drawn out by gently dipping a glass stirring rod into a sample and slowly pulling it out. These thin strands were pure DNA, and Wilkins was able to get excellent X-ray patterns from them.

Before long, Wilkins had also acquired better equipment and had also hired Rosalind Franklin to run it. Franklin, essentially working independently, used the same basic technique developed by Wilkins. She did, however, add several of her own smaller experimental refinements, which made the photographs even better. Eventually, she developed photo 51, which would later be shown to Watson and Crick. The rest, as they say, is history.

Rosalind Franklin and William Astbury were both excellent crystallographers, but Franklin’s experience with DNA gave her a clear advantage when working with the molecule. Her brilliant X-ray patterns would later prove to be a major determining factor in the “race for DNA”. For more information on DNA, please visit the Race for DNA website. For much more on Linus Pauling, check out the Linus Pauling Online portal.