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Linus Carl Pauling
The Greatest Architect of Modern Chemistry
 
 
 
Dr Subodh Mahanti

 


It is when we take some interest in the great discoverers and their lives that science becomes endurable and only when we begin to trace the developments of ideas that it becomes fascinating.

James Clerk Maxwell

The important thing in science is not so much to obtain new facts as to discover new ways of thinking about them.

William Lawrence Bragg in Beyond Reductionism (1968)

The personal lives of geniuses are as complex as those of ordinary mortals. Intellectual brilliance, after all, does not necessarily guarantee moral integrity, personal charm, political rectitude, or any other desirable character trait. So one should hardly be surprised that Linus Pauling's life and personality have been assessed in a myriad of ways by his contemporaries.

The one point on which no one disagrees is his brilliance as a scientist. Probably the most prolific and one of the best-known science writers of all time, Isaac Asimov, has called him "a first-class genius, "the greatest chemist of the 20th century". Pauling's numerous honorary degrees and awards confirm this judgment. His colleagues have honoured him at one time or another with every high honour in chemistry.


David E. Newton in his Linus Pauling: Scientist and Advocate, Universities Press (India) Ltd. 1999.

 


[The idea of writing on Pauling cropped up after writing on G.N. Ramachandran (Dream-2047, September 2001 Issue), who was greatly influenced by Pauling. We had reproduced the poem written by Ramachandran on Pauling. Moreover the year 2001 also happens to be the birth centenary of Pauling].

Linus Carl Pauling is the only person to have received two unshared Nobel Prizes - first 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', and the second one in 1962 in Peace for his ardent pacifist campaign against nuclear warfare. Pauling is widely regarded as one of the greatest scientists ever. Besides being the greatest architect of chemistry, Pauling was a founder of molecular biology and a pioneer in quantum mechanics. Pauling combined chemistry and physics to solve various puzzles related to the nature of chemical bond. As one of his biographers has written Pauling's understanding of the chemical bond and molecular architecture is probably unsurpassed in the history of chemistry. His ideas on chemical bonding are fundamental to modern theories of molecular structure. Pauling determined crystal structure by X-ray crystallography and the structure of gas molecules by electron diffraction. He ascertained the molecular cause of sickle-cell anaemia and his observation that a molecular disorder can explain the symptoms of an illness founded the discipline, molecular medicine. He developed an electronegativity scale to assigning electronegativities to atoms involved in covalent bonding. He extended the theory of covalent bonds to include metal and intermetallic compounds. It was Pauling who formulated the concept of resonance, a very important concept in structural chemistry. It refers to a state where none of the classical formulae of a chemical system is entirely consistent with observed properties. Pauling developed unique model building techniques that he put to use in his studies of proteins and nucleic acids. He proposed helical structures for proteins based on polarity of the atoms in the peptide bond. His monumental text book, The Nature of the Chemical Bond and the Structure of Molecules and Crystals, first published in 1939, is even today a classic in its field. The book is one of the most important books in the history of chemistry. It has been translated in many languages.

Pauling is much known for his controversial thesis proposing that high doses of vitamin-C would help not only in the prevention of common cold but also in the prevention of cancer. In 1973, he founded the Linus Pauling Institute of Science and Medicine in Palo Alto, California. Outside his scientific works, Pauling took a vital interest in public affairs, especially in the movement for world disarmament. His book No More War (1958) was a plea for international peace. It was an instant best-seller. He strongly opposed nuclear testing. He could gather signature and support of 11,000 scientists for his petition against nuclear testing in front of the United Nations. Pauling was well-known for his independence, courage, fighting qualities, brilliant wit and vigorous enthusiasm for his work. Isaac Asimov called him 'a gentleman in highest sense of the word." Pauling was a very controversial and outspoken person. His uncompromising nature was reflected even in his school days.

Pauling was born in Portland, Oregon, USA on 28th February 1901. His parents were Herman Henry William Pauling, a pharmacist and Lucy Isabelle Pauling usually called Belle. His father died when Pauling was 9 years old, forcing him to take up odd jobs to support his mother and sisters as well as pay for his education.

We are told that by the age of nine Pauling had read all the books available in his house. Pauling's father Herman Pauling, in his attempt to collect proper reading material for young Pauling, wrote to a local newspaper, the Oregonian : "I am a father and have an only son who is aged 9 years, in the fifth grade, a great reader and is deeply interested in ancient history….. In my desire to encourage and assist him in his prematurely developed inclinations I ask some of the Oregonian's interested readers to advise me regarding the proper or atleast the most comprehensive works to procure for him." we are told that Herman Pauling did not receive any response.

Pauling's interest in science developed at the very early age of 11. Pauling started collecting first insects and then minerals. It is said that he did not stop at collecting the objects but he proceeded to classify and catalogue them. However, in his own words Pauling was not successful as a collector. To quote Pauling: "I was not successful as a collector, but I got a book from the library on mineralogy and I copied out tables of properties, hardness and various properties, on to sheets of papers and glued the papers to the wall in my work room."

In 1914 Pauling graduated from the Sunnyside Grammar School and entered Portland's Washington High School. It is here that Pauling became interested in studying chemistry. He was influenced by one of his friends named Lloyd Jeffress, who had set up a small laboratory in the corner of his bedroom. Pauling became fascinated with chemistry after watching Jeffress conduct some simple experiments. To quote Pauling : "I decided then to be a chemist and to study chemical engineering, which was, I thought, the profession that chemists followed:" Following his friend Jeffress, Pauling also built a small laboratory in the basement of his house. He carried out a lot of experiments on his own. He borrowed the chemicals needed for his experiments from a small chemical laboratory at the abandoned Oregon Iron and Steel Company in Oswego. This was possible because Pauling's grandfather was a night watchman at a nearby plant. Later recalling his early interest in chemistry Pauling would write: "I was simply entranced by chemical phenomena, by the reaction in which substances disappear and other substances, often with strikingly different properties, appear."

Sickle-cell Anaemia: A Molecular Disease

Sickel-cell anaemia is a hereditary chronic blood disorder in which a person’s blood cells contain an abnormal form of haemoglobin, the protein that transports oxygen and which become incapable of carrying oxygen efficiently. This often results in anaemia. When the blood is deprived of oxygen the abnormal haemoglobin crystalises and distorts the red blood cells into a sickle shaped. The presence of sickle cells in the blood with or without accompanying anaemia, is called sicklemia. The disease principally affects the black population of Central Africa. Three different types of individuals occur in such populations – those who have two genes for normal haemoglobin and therefore do not suffer from the disease; those with one abnormal gene and one normal gene and are likely to suffer from anaemia and those with two abnormal genes who suffer a chronic and eventually fatal form of anaemia.

Pauling thought that it was an abnormality in oxygen-carrying haemoglobin molecule found in red blood cells and not the abnormality of the red blood cells themselves that caused the sickle cell anaemia. Before turning to sickle cell anaemia Pauling was working in haemoglobin. Pauling and his student Dr. Harvey Itano demonstrated that haemoglobin found in people having sickle cell anaemia actually differ from normal haemoglobin molecule. Though the difference was very modest. Only one of a total of 146 amino acids in such haemoglobin molecule is incorrect. But such a single error was enough to alter haemoglobin and reduce its ability to transport oxygen.

Here we will discuss in little detail how Pauling worked hard for continuing his education, with a view that it may act as a source of inspiration to younger people. Unlike many fortunate children, Pauling had to arrange money himself for his studies. Before joining Oregon Agricultural College at Corvallis, Pauling was working at a machine shop, where he was earning $100 a month and his employer had promised to increase his salary to $250 a month provided he decided to stay there. Pauling's mother was not in favour of his joining the college. As stated earlier Pauling's father died when he was nine years old. So his mother wanted Pauling to stay at home and help her financially as she still had two young children to raise. However, Pauling decided to join the college. Since his mother had no means to help him, Pauling had to earn enough to meet all his college expenses. The expenses were not very high. The college did not charge any tuition fees and the books were inexpensive. He lived in a cheap boarding house, where he shared a room with a fellow student. But still he had to work hard. Describing a job of delivering milk undertaken by him at the age of 18 he wrote: " a very hard job, working eight hours every night from about eight o'clock to about four o'clock with a horse pulling the milk wagon and delivering milk to about 500 customers."

Inspite of the hard work that he had to undertake to meet his college expenses, Pauling was able to impress his teachers and colleagues by his studies. He had very little social life. As his financial problem continued Pauling took up a job of paving-plant inspector of the State of Oregon during the summer of 1919. His job was to inspect new pavement and take samples back to the state laboratory for analysis. His salary for the job was $125 per month. He lived in a tent with the workmen and ate with them. He sent almost his entire salary to his mother, expecting that his mother would be able to help him to return to Oregon Agricultural College for his junior year. However, the financial crisis grew worse. His mother was suffering from pernicious anaemia. So he was compelled to decide to continue to work as leaving-plant inspector. But then he got an offer from Oregon Agricultural College to teach quantitative analysis in chemistry. The offer was really extraordinary considering the fact that Pauling was a student, who completed the course himself six months earlier. The salary for his new assignment was $100-a-month. His duties were to supervise laboratories and give lectures. He had to spend 40 hours a week with students. Besides his teaching assignment Pauling studied the works of two eminent chemists Gilbert Newton Lewis (1875-1946) and Irving Langmuir (1881-1957). Their works had a profound effect on Pauling. This had largely determined the course of his work for fifty years. As he later wrote by reading their works he developed "a strong desire to understand the physical and chemical properties of substances in relation to the structure of the atoms and molecules of which they are composed".

Resonance

Resonance means representation of the structure of a molecule by two or more conventional formulae. Whenever a molecule can be represented by two or more structures having the same arrangement of atomic nuclei but with different arrangement of electrons – there is resonance. In such a case the molecule is said to be a resonance hybrid of all these structures. The molecule is somewhere in between these structures and it cannot be represented satisfactorily by any one of them. For example, the formula of methanal or formaldehyde can be represented by H2 C=0, where there is a double bond in the carbonyl group. It is known that in such compound the oxygen atom carry some negative charge and the carbon has some positive charge. The true bonding in the compound is somewhere between H2C=0 and the ionic compound H2+C0- . The molecule is said to be a resonance hybrid of the two, indicated by H2C=0 <-> H2C+0-. The two possible structures need not contribute equally to the actual form. When the contributing structures are of about the same stability that is with same energy content, then resonance is important. The contribution of each structure to the resonance hybrid is dependent on the relative stability of that structure. If a particular structure is more stable it will make a larger contribution than the other structure(s). The resonance hybrid is more stable than any of the contributing structures. This increases in stability is called the resonance energy.


Pauling could begin his junior year in the college in the fall of 1920. On June 5, 1922 Pauling received his bachelor of science degree from the Oregon Agricultural College. Pauling failed to get Rhodes Scholarship inspite of being nominated by the faculty of his college with good recommendation. In the fall of 1922 Pauling enrolled as graduate student in the California Institute of Technology (Cal Tech) at Pasadena. Pauling's first choice was the University of California at Berkeley, where G.N. Lewis was the chairman of the department of chemistry, whose works had a decisive role on Pauling's scientific career. But Pauling did not get any response from Berkeley in time. His second choice was the University of California at Harvard but its scholarship offer was not matching Pauling's financial needs

The California Institute of Technology was originally established in 1891. Before 1920 it used to be known by various names like Throop University, Throop Polytechnique Institute and Throop College of Technology. In its early years its academic reputation was not very high. It became a leading research institution largely because of the initiatives taken by George Ellery Hale (1868-1938) , a member of the Throop Board of Trustees and then Director of Mount Wilson Observatory. In about 1907 Hale could persuade the other trustees to develop an outstanding institute for science and technology on their campus. Hale was also able to persuade some of the leading American researchers to come to Pasadena. Robert Andrews Millikan (1868-1953), who determined an accurate value for Planck's constant and originated the 'oil drop' experiment to measure electronic charge, left the University of Chicago in 1918 to become the first administrative head of the California Institute of Technology. Millikan got Nobel Prize in 1923. Arthur Amos Noyes left the Massachusetts Institute of Technology in 1917 to establish the Gates Chemical Laboratory at Throop. It was Noyes who had chosen Pauling as a graduate student. Noyes knew Pauling before his coming to Pasadena. He had sent Pauling the proofs of his new chemistry text, Chemical Principles, with the instruction to solve all the problems in the first nine chapters which numbered more than 500. Pauling solved all the problems. This helped Pauling to develop a strong background in physical chemistry. After coming to Cal Tech, Pauling realized that he lacked on many counts in his training at Oregon Agricultural College. To quote him : "There were so many gaps in understanding that …often I did not know whether to attribute this failure to myself or to the existing state of development of science".

In March 1926 Pauling sailed for Europe, on a two year Guggenheim Fellowship. First he went to Munich to work with Arnold Sommerfield (1868-1951) at his Institute of Theoretical Physics. At Munich he spent one year and wrote one of his most frequently cited research papers: "The Theoretical Prediction of the Physical Properties of Many-Electron Atom's and Ions". From Munich Pauling went to Copenhagen to spend a year with Niels Bohr (1885-1962) at the Institute of Theoretical Physics. At Copenhagen Pauling worked with Samuel Abraham Goudsmit (1902-78) whose work on spectral analysis eventually led to the discovery of the electron spin or fourth quantum number. From Copenhagen Pauling went to the University of Zurich, where he attended lectures by Erwin Schrodinger (1887-1961) and Peter Joseph William Debye (1884-1966). After completing his two-year European tour he came back to California Institute of Technology to join as Assistant Professor of Theoretical Chemistry and Mathematical Physics.

Pauling worked on a variety of problems in chemistry and biology. His early work in chemistry was on chemical bonding and molecular structure. Though Pauling consistently referred to himself as chemist or physical chemist, his early work involved mathematics and physics to a great extent. His research did not fit into any conventional definition of chemical studies. Once Pauling wrote :"Some people seem to think that work such as mine, dealing with the properties of atoms and molecules, should be classed with physics but I, as I have said before, feel that the study of chemical substances remains chemistry even though it reaches the state in which it requires the use of considerable mathematics." Pauling applied physical methods like X-ray diffraction, electron diffraction, and magnetic effects to determine molecular structures.

Electronegativity

Electronegativity denotes the easiness with which an atom can attract electrons to itself. Electronegative elements attract electrons, so forming negative ions. The halogens are typical electronegative elements. Pauling devised an electronegativity scale to indicate the relative power of attraction of elements for electron. Fluorine, the most non-metallic element has a value of 4.0 on this scale. Some other values on this scale are : boron(B) 2.0, carbon(C) 2.5, nitrogen (N) 3.0, oxygen (O) 3.5, silicon (Si) 1.8, phosphorus(P) 2.1, sulphur (S) 2.5, chlorine (Cl) 3.0, and bromine (Br) 2.8. In a covalent bond between two atoms of different electronegativities, the bonding electrons will be located close to the more electronegative atom, creating a dipole. Electronegativity values can be used to show why certain substances, such as hydrochloric acid, are acid, whereas others such as sodium hydroxide, are alkaline.

Pauling's interest in complex molecular structures led him to work in biology and medicine. He had a strong belief that all biological phenomena must have a molecular origin. He studied the properties of haemoglobin using magnetic measurements. This work led on to extensive studies of the nature and structure of proteins. Pauling jointly with Robert B. Corey showed that the amino acid chain in certain proteins can have helical structure. Pauling's work provided a powerful impact to F.H.C. Crick and J.D. Watson in their search for the structure of DNA.

Pauling made significant contributions to applying quantum mechanics to the bonding of chemical compounds. He developed almost all of the most fundamental principles of the modern theory of chemical bonding including the concept of the 'hybridization of orbital,' central to the understanding the shapes of molecules; resonance, a state where a molecule has a structure between two or different conventional structures and electronegativity. His book Introduction to Quantum Mechanics published in 1935 was quite influential .

Pauling studied the denaturation of proteins by heat, acids, bases or chemicals such as urea. He gave a correct interpretation of denaturation of proteins by applying the concept of weak bonds - it is due to the loss of a set of hydrogen bonds necessary for the stabilization of protein's three-dimensional structures. It does not involve the breaking of a covalent bond in the molecule or the separation of a colloidal aggregate.
Pauling explained the specificity of the antibody-antigen interaction by the formation of certain number of weak bonds, formed between atoms situated close together, in particular, hydrogen bonds between the antigen and the antibody. The complementary structure of antigen and antibody was evident from the existence of a large number of weak bonds.

What can we learn from Pauling's biography? Greatness can be achieved even through tremendous hardship. In fact many a great people had to struggle in the early years even for their bare survival. What is important is to have determination -determination to achieve something. But one needs to prepare for it. Self-teaching is very important. But then it has its own limitations. Proper training is important. Pauling could get opportunity to work with some of the best minds of his time. So it is also important to go where something is really happening, to get first hand experience and to be a part of it. Teachers can play a great role in shaping the careers of their students. This we see very often when we go through the biographies of great scientists. Unfortunately in India today teachers are hardly playing this role. Certainly there are exceptions. But the general trend is that by taking the name of 'professionalism' people are becoming more and more self-centered, often akin to being selfish. One cannot sustain an idea in vacuum. It needs a proper environment. In any case to achieve something one should, like Pauling, have enormous self-confidence and an urge to live a happy, useful and a satisfying life and help others to achieve the same. To quote Pauling : " The evidence of my senses tells me that I am a man like other men. When I cut myself, I am hurt, I suffer. I cry out. I see that that when someone else cuts himself, he cries out. I conclude from his behaviour that he is suffering in the same way that I was…I am led to believe that I am a man like other men.

The Chemical Bond

The chemical bond is the force that holds atoms together in a molecule or a mechanism by which atoms combine to form molecules. We will say that there is a chemical bond between two atoms or groups of atoms only when the forces acting between them are strong enough to form an aggregate of the atoms involved with sufficient stability to be regarded as an independent species.

The amount of energy required to break a bond and produce neutral atoms is known as bond energy. Atoms combine with each other because of their tendency of acquiring stable electronic configurations. Atoms with full outer shells, of electrons are more stable than those with partially filled outer shells. The noble gases or inert gases have full outer shells and are very stable. Other atoms can acquire stable electronic configuration by combining with other atoms to form chemical bonds. The principal types of chemical bonds are the ionic, covalent, metallic and hydrogen bonds. There are other types also. The ideal cases are ionic and covalent bonds and the remaining ones are of an intermediate type.

The Ionic Bond : results from the attraction of oppositely charged ions. Ionic bonds are formed by the transfer of electrons from a metallic element to a non-metallic element. The atoms of metallic elements lose their electrons to form positive ions while t he atom of non-metals gain electrons to form negative ions. The resulting highly stable ions retain their individual structures, as they approach one another to form stable molecule or crystal. An ionic crystal like sodium chloride is composed of independent sodium ion (Na+) and chlorine ion(Cl-). No discrete diatomic molecule exists and the entire crystal is a single giant molecule.

Covalent Bond : When a non-metal combines with another non-metal, they tend to share electrons so that the partner atoms each have a share in enough electrons to complete their outer shells. A single covalent bond is formed when two atoms share a pair of electrons. Unlike in ionic bond, in the formation of covalent bond there is no electron transfer. The attractive force is produced by interaction of the electron pair with the nuclei of both atoms. Double and triple bonds are formed when the atoms share more than two electrons. Generally in covalent bonding each atom contributes to the shared pair. Covalent bonds are of particular importance in organic chemistry because of the ability of the carbon atom to form four covalent bonds. But there are cases when both electrons come from the same atom. In such case the resulting bond has a partly ionic character and is called a co-ordinated link.

Metallic Bond : Metallic elements are held together by metallic bonding. The metallic bond is responsible for crystalline structure of pure metal. Metallic bond is not ionic because all the atoms are identical. It is also not covalent in the ordinary sense as the valency electrons are shared collectively by all the atoms in the crystal. Metal atoms are packed together where each atom loses its outer electrons into a ‘sea’ of free electrons or mobile electrons. These free electrons are delocalised, that is, not restricted to orbiting individual positive ions. The mobile electrons form a kind of electrostatic ‘glue’ holding the structure together.

Hydrogen Bond : Hydrogen bonding is a strong electrostatic attraction between two independent molecules in which the electric charges are unevenly distributed. Such molecules are called polar molecules and usually contain nitrogen, oxygen and fluorine. These elements have a strong tendency to draw electrons towards them. The hydrogen atom acts as bridge between them. Hydrogen bond is much weaker compared to ionic or covalent bonds. However, this plays an important role in molecular biology.

I want to be free of suffering to the greatest extent possible. I should like to live a happy, useful life, a satisfying life. I want other people to help keep my suffering to a minimum. It is my duty, accordingly, to help them, to strive to prevent suffering for other people".
For Further Reading

1. Serafini, Antony, Linus Pauling : A Man and His Science, New York : Paragaon House , 1989

2. White, Florence Meiman, Linus Pauling : Scientist and Crusador, New York: Walker & Co. 1980

3. Newton, David E. Linus Pauling : Scientist and Advocate, Hyderabad ; Universities Press (India) Ltd., 1999.