LINUS PAULING was born in a small village in Oregon state (U.S.) on February 28, 1901, the son of a pharmacist. His father died when he was nine years old. He displayed early his interest in science; as a boy, he collected insects and minerals. When he was thirteen, Pauling began experiments at home using materials available from the kitchen.

 Pauling studied at the Washington high school in Portland but left without taking the diploma, as he had not completed a course in civics. Nevertheless he managed to enroll in the Oregon Agricultural College at Corvallis where he majored in chemical engineering and received a B.S. in 1992. He had to take a break because he had to support his mother by working, during spare hours, as an assistant in the college laboratory.

 Pauling was first a graduate student and then a teaching fellow in chemistry at the California Institute of Technology (Caltech) in Pasadena. He was awarded the Ph.D in chemistry (`summa cum laude' (1925)). For the next two years he was a research fellow at Caltech.

 During 1925-26 he worked in the laboratories of Sommerfeld (Munich), Niels Bohr (Copenhagen), Schroedinger (Zurich) and William Bragg (London). Schroedinger's wave mechanics and Pauli's exclusion principle were to have profound effects on his study of chemical bonding.

 Pauling held academic positions in three reputed institutions: Caltech (1927-63), University of California at San Diego (1967- 69), Stanford University (1969-73).

 Pauling founded in 1973 the Linus Pauling Institute of Science and Medicare at Palo Alto. Science late 1960, he became interested in the use of vitamin C, which he began to advocate for preventing the common cold. He and his wife began taking it regularly. He died at the ripe age of 93 (August 1994).

 The resonance theory

 During 1925-27, Pauling employed the techniques of X-ray crystallography to determine the structure of the molecules from the characteristic pattern they produce. He then studied the nature of chemical bonding in benzene and other aromatic compounds.

 In 1928 Pauling published his resonance theory of bonding which was based on the quantum mechanical concept of electron orbitals. In the older model of benzene, three of the six chemical bonds between adjacent carbon atoms were single bonds and three were double bonds. Pauling postulated a new concept that benzene rings can be viewed as hybrids of their structures. This has proved extremely useful in predicting the properties of aromatic compounds.

 Chemical structure of blood proteins

 In 1934 he turned his attention to biochemistry and formulated a theory of protein structure and function. Pauling initiated studies of the atomic and molecular structure of proteins and amino acids.

 He and Corey published in 1951 the first complete description of the molecular structure of proteins, which was the culmination of 14 years' research. This description of the three-dimensional structure of proteins marked a major advance in biochemistry. He published his ideas in The Nature of the Chemical Bond (1939), perhaps the most influential textbook in the field. For this work, he was awarded the Nobel Prize in Chemistry (1954).

 In 1949, he published a paper identifying the cause of sickle- cell anaemia as a molecular abnormality in hameoglobin. He then turned his attention to DNA, the biological molecule that carries the genetic code. He published a paper on the structure which he incorrectly described as a triple-stranded helix.

 Second Nobel prize

 In 1950, as the nuclear arms race gathered momentum, Pauling spoke against the U.S. Government's decision to develop the hydrogen bomb and advocated an end to testing of nuclear weapons. Pauling used his considerable oratorical skill to publicise the biological and genetic effects of radioactive fallout.

 In 1958 Pauling mobilised the support of over 11,000 scientists from 49 countries and presented a petition to the United Nations, protesting against nuclear tests. His efforts contributed the establishment of the Pugwash Movement (1957) which eventually promoted the nuclear test ban treaty (1963). His pacifist views estranged him from his contemporaries, causing personal suffering and harassment for long periods. Pauling was the sole winner of Noble for Peace, prize, the second time in 1962, an unparalleled record. He was awarded the International Lenin Peace Prize in 1972.

 Pauling received many honorary degrees and awards: the Davy Medal (1947) the National Medal of Science (1975), Lomonosov Medal of the Soviet Academy of Sciences and (1978) the Priestly Medal of the American Physical Society (1984).

 C.N.R. Rao, our Distinguished Scientist, has hailed Linus Pauling as ``the first person who made chemical bonding his primary concern through which he changed the course of chemistry. He created modern structural biology. Then he was a crusader for human rights and peace''. (Current Science Vol 67, 10 September 1994)

 R. Parthasarathy