After spending two years in Europe, he became a professor at the Californian Institute of Technology. His original work was on chemical bonding in terms of quantum mechanics; in the mid 1930s he turned to the structure of proteins. Pauling was also a leading figure in the early history of the determination of crystal structure using X-ray crystallography, work that led to his proposal of Pauling’s rules. He was awarded the 1954 Nobel Prize for chemistry. He was also an active campaigner against nuclear weapons and in 1962 was awarded the Nobel Peace Prize.