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Linus Carl Pauling
The Greatest Architect
of Modern Chemistry
Subodh Mahanti
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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.
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[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.
Linus Carl Pauling
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."
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Sickle-cell
Anaemia: A Molecular Disease
Sickel-cell anaemia is a hereditary chronic blood disorder in
which a persons 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.
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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".
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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.
Georg Ellery Hale |
Robert Andrews Millikan |
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.
Samuel Abraham Goudsmit |
Peter Joseph William Debye |
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.
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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.
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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 wasI
am led to believe that I am a man like other men.
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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 the 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.
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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. Attention
Attention
NCSTC is compiling
a National Directory of Organizations/Institutions active in
the field of S&T Communication/Popularization. This comprehensive
collection properly cross-indexed, will be valuable source of
reference to activists, academics and planners. For free registration
please send a request to :
Dr. A.P. Despande, Marathi Vidnyan Parishad,.
V,N. Purav Marg,
Sion - Chunabhatti, Mumbai - 400022
Phone Nos.: 022-5224714/5226268;
Fax: 022-5226268
E-mail: Vidnyan@Bom7.vsnl.net.in
This is a time
bound project and may not be possible to include entries received
after 15th December 2001.
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