NO ONE in the 20th century has contributed more to developments within the science of chemistry than Linus Pauling. He had a keenly focused but wide-ranging imagination which was coupled with great vitality. Any approach to a complete account of his fruitful interests would create a kaleidoscopic impression: several are of such a basic character that elementary chemistry suffices for their appreciation. The fact that he was self-motivated and initially self-taught gave him great confidence in his own outlook. It generated a momentum in his researches which led to his being a dominant influence in many areas of great importance, and not only in chemistry. On occasion it carried him into exposed and sometimes to untenable positions.
The layperson is often dissatisfied with scientists for not sufficiently concerning themselves with public aspects of their work. Pauling's long career shows what a rough ride can be given to one who does exactly that. Profoundly liberal in outlook, he was not an establishment figure. In that respect and in the context of chemistry, the great Joseph Priestley immediately comes to mind. There are parallel features in their characters and experiences and it was ultimately appropriate that it was only in 1984 that the American Chemical Society bestowed its greatest honour, the Priestley Medal, on Pauling. It was awarded 30 years after his Nobel Prize for Chemistry and 22 years after his Nobel Prize for Peace. Pauling had paid the price for speaking out against the nuclear arms race.
If much can be seen of the man in his roots, it is certainly true of Pauling. Born in 1901 in Condon, a small town in Oregon, he was the first of three children whose father, Herman, was a storekeeper also selling medicines. Herman Pauling died in 1910 leaving the family unprovided for. Linus and his mother, Lucy, did not get on well. She was naturally anxious for him to leave school and to start earning, but these early years saw him very self-determined. He took jobs, often of a physically demanding nature, to acquire the means to remain at school and, later, at what was then Oregon Agricultural College. One summer he worked as a roadways supervisor only to find that his mother had, necessarily it seems, spent the money he had sent home from the job.
His father's simple preparative items had made Linus Pauling aware of chemistry, and schoolboy expeditions had stimulated an interest in mineralogy. Pauling's teachers recognised his lively ability and, although his quantitative work was unimpressive, his grasp of chemical principles qualified him as a part-time instructor at college. His earnings from this covered his college fees when his resources were exhausted. It also led to his meeting Ava Miller, a student three years his junior, with whom he formed an instant attachment. When they married in 1923, she was only 19. It proved to be a very close partnership. Before his 22nd birthday Pauling was interviewed as a candidate for a Rhodes scholarship to Oxford. The story has it that the negative outcome derived from the question: 'How have you spent your time waiting for this interview?' and the reply, 'Reading La Vie Parisienne.' It should have gained him credit for his knowledge of French, to which he later added an excellent command of German.
The foundations of Pauling's scientific career were set when he went to the California Institute of Technology (Caltech) in 1922. There A. A. Noyes was head of Chemistry and he put Pauling to work for his PhD with Roscoe Dickenson, who was initiating studies of the structure of inorganic crystals by X-ray diffraction. In 1922 this method was in its early form. Success could depend upon finding solids of simple atomic arrangement which could then be deduced from the X-ray reflections from the crystal. This virgin field, pioneered by the Braggs father (W. H) and son (W. L), who shared the Nobel Prize for Physics in 1915, provided many rewards for the gifted empiricist Linus Pauling.
Concurrently he acquired an all-important grasp of theoretical methods in molecular statistics and, what proved even more significant, in quantum mechanics. RC Tolman was his masterly tutor. These foundations were extended in 1926-27. He spent nearly a year at Munich where X-ray diffraction by crystals was first observed, and where Arnold Sommerfeld was an established leader in quantum mathematics. This was soon extended in Pauling's armoury to Erwin Schrodinger's wave mechanics, acquired when he spent five months with Schrodinger and Peter Debye at Zurich. Even with hindsight, Pauling could not have spent his time in Europe more profitably.
While his mathematical experience did not suffice for the refinements of quantum physics, Pauling made excellent use of the methods he had learnt to achieve fruitful results in chemistry. In 1928, as a means of explaining the geometry of chemical bonding in molecules, he introduced the concept of electron hybridisation. In simple terms he showed how the orbitals of the four valence electrons of the carbon atom - one spherical, and three mutually at right angles - could be mixed (ie hybridised) to provide four carbon valencies directed to the corners of a tetrahedron. This provided the clearest basic insight into the framework structure of saturated and, also by modification, of all carbon compounds, that is, of the whole of organic chemistry.
Pauling went further. To approximate to the subtle state of electron distribution in polyatomic molecules he used an empirical method of calculation characterised by 'resonance' between electron states. This approximate method provided a simple means of representing the bonding of atoms throughout chemical structures and was extensively used for 30 years. Many genuinely new insights resulted for which Pauling must be credited: they extended both into the structure and reactivities of molecules. Not surprisingly, in view of the ease with which the 'resonating' structures could be represented, others exploited Pauling's concept in arbitrary, even naive ways. This modelling has since been replaced by other, sounder, methods.
Practical aspects of molecular structure studies were not neglected. Pauling took up the electron diffraction ('diffraction' is a species of selective reflection) method for gaseous molecules. With LO Brockway as his effective lieutenant at Caltech, nearly 200 molecules were measured by this method in 20 years. But of longer-term significance was Pauling's continuation of X-ray diffraction studies. In this R. B. Corey was his principal associate; the focus was on organic structures, most especially on the peptides, that is the precursors of proteins. The simultaneous and successful development of all these methods, experimental and theoretical, meant that the Gates and Crellin Laboratories at Caltech became a powerhouse on molecular structures. Then, in 1947, Pauling proffered the chemical world a survey of the whole field.
The Nature of the Chemical Bond was a magisterial statement on post-quantum theory evaluations of molecular and ionic structures which became the most influential chemistry text of the century. Pauling had systematically ordered the bond lengths and bond angles characterising chemical structures. Probably for the first time he made many aware of the packing size of various atom types. WL Bragg had earlier grasped this factor. Judicious use of these data could even predict the conformation and packing of molecules in the solid state.
Such considerations and Corey's X-ray work led to discoveries on the hugely important structures of proteins. Specific interactions between characteristic groups led to many protein chains forming helices whose pattern repeated along their lengths. The alpha-helix - on which Pauling published a paper in 1951 - proved to be the key to many protein structures, including hair, wool and muscle. The reversible coiling and uncoiling of helical units arranged along the lengths of fibres accounted for the stretching of stomach walls and of human hair when heated in steam for a 'permanent' wave. Another aspect: the protein in milk is present as a soluble particle. On heating or souring with traces of acid, the helices uncoil and their irregular long chains quickly become entangled with one another, producing an insoluble form, the skin or the curds. This 'denaturation' of the proteins is an important feature of biological systems.
Pauling was early convinced of the dependence of much biological activity upon specific molecular behaviour. His most striking illustration of this thesis was for sickle-cell anaemia. He showed that the abnormal cell shape resulted from its molecule containing one abnormal amino-acid residue: this genetically coded defect prevented it coiling to its usual form and resulted in 'a molecular disease'. The sickle-cell carried oxygen only inefficiently.
Not surprisingly, Pauling became interested in the form of molecule capable of transmitting the genetic code. He correctly delineated a type of structure which could so function by reproducing its own conformation, but he was late in accepting that the nucleic acids and not proteins were the molecules involved. When he commenced X-ray studies of DNA his diffraction patterns were poorer than those which initially guided Francis Crick and James Watson on the path to discovering the double helix of DNA. Watson's fear (described in The Double Helix, 1968) that Pauling was about to reveal the correct structure was mostly the product of Watson's imagination.
Later, Pauling pioneered the revealing use of changes of individual biomolecular types as evidence of evolutionary history. This insight has hugely extended and refined the details in the historical development of many biological families. These two items illustrate Pauling's ability to add chapters to biomolecular science.
For 30 years Pauling persistently advanced vitamin C as a prophylactic for the common cold, and even for cancer. The failure of extensive trials to confirm those benefits only partially reduced his enthusiasm. In 1941, when he suffered from a severe form of Bright's disease (glomurolo-
nephritis), Pauling associated his cure with massive doses of this same vitamin. His book Vitamin C and the Common Cold (1970) was widely read in the UK: it was followed by Cancer and Vitamin C (1979), written jointly with Dr Ewan Cameron of Lochlomondside Hospital. When in 1992 Pauling was told that he himself was afflicted with cancer, his immediate reply was to claim it would have struck much earlier had he not taken so much vitamin C. Others of his claims, such as the role of niacin (vitamin B3) in promoting normal mental health, and the significance of dietary factors in particular cases of mental abnormality, appear to be better founded.
The investigative pursuit of these medico-chemical interests led to many complications and confrontations in Pauling's later years - such as his eventual departure from Caltech and, more seriously, the dismissal of Dr Arthur Robinson from the Linus Pauling Institute of Science and Medicine at Palo Alto, in California. Robinson had been effective in obtaining grants even from the Federal Government for the institute. Having been an associate director he was obliged to leave, partly because his own work did not conform to Pauling's anticipations.
Pauling's public activities were a large element in his life from the 1950s. It seems he had been a Rooseveltian liberal until he married Ava Miller. Her family had distinctly radical sympathies. Pauling became a fully energised, self-determining, free-lance liberal. Associated with Bertrand Russell and Albert Einstein's Pugwash Conferences, which were aimed at defusing the nuclear confrontation of East and West in their early years, Pauling worked for a greater public impact than they achieved. His especial concern was the long-term human genetic damage resulting from atmospheric nuclear bomb tests. Here he conflicted with the whole US establishment and with several of his science colleagues. Pauling was never a communist nor even a unilateral disarmer, but he was for the unilateral abandonment of nuclear bomb tests if only because, he argued, there were already available ample supplies of adequately destructive weapons. One item in his sustained wide-ranging campaign was his book No More War] (1953). In 1961 he helped organise a conference in Oslo to argue against the nuclear arming of Nato.
The strain of his campaign, with its appeals, petitions, conferences, and Senate hearings, took its toll despite Pauling's extraordinary resilience. In the early 1960s he wrote: 'Each day brings more backward steps. I try to think of a new approach or new words and it seems we have used them all, and still events bring us closer and closer to the final agony.' As late as 1984 he was addressing over a hundred meetings a year on the threat of nuclear warfare.
These activities brought on Pauling the obloquy of the government and of the media throughout the United States. He was denounced as a pacifist, a fellow- traveller, as politically immature, and as a communist. His passport was withdrawn in 1952, for two years, and he was obliged to appear before the US Senate Internal Security Committee.
Pauling was awarded the Nobel Prize for Chemistry in 1954 for his work on chemical bonds and molecular structure, and the 1962 Nobel Prize for Peace. For the latter, Pauling's writings and lectures on the dangers of radioactive fallout in weapons testing and war were cited. Most of his science colleagues were not impressed by the Peace Prize. In his native state the Oregon Statesman averred that the award was for 'the extravagant posturings of a placarding peacenik', and Life called it 'an extraordinary insult to America'.
A reminder of his status in science is appropriate. For years the inert gases - which include argon, krypton, and xenon - were accepted as being incapable of forming any chemical compounds. In the early 1930s Pauling saw good reason to anticipate that krypton and xenon would form compounds with fluorine. This is so violently reactive a gas that special facilities are needed to handle it. Pauling suggested to one fluorine chemist that he should prepare the compounds with krypton and xenon, but no such attempt was made. Thirty years later Neil Bartlett, at the University of British Columbia, in Vancouver, succeeded with the preparation.
In 1988 two physicists in Switzerland startled the science world by reporting they had succeeded in producing electrical superconductivity at very much higher temperatures than ever before. The material with which they had succeeded was a complex of metal oxides including copper oxide. In 1987 Pauling had published an account of how, working with his valence bond method, this superconductivity might well be established in such materials.
Pauling gave a synopsis of his outlook:
I believe in non-violence . . . I accept the principle of the minimization of the amount of suffering in the world. I do not accept that we do not know what is good and what is evil . . . Science is the search for truth, that is the effort to understand the world: it involves the rejection of bias, of dogma, of revelation, but not the rejection of morality.
At the height of Pauling's denigration for supposed un-American activities, Albert Einstein wrote to President Eisenhower: 'I feel it to be my duty to testify that Professor Pauling is one of the most prominent and inventive scientists in this country. I have the highest esteem for his character and for his reliability as a man and as a citizen.' Such a statement from such a source leaves nothing further to be written.
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