pling) provide information about the oxidation, spin,
and COORDINATIONstate of the ion.
mother nuclide The nuclide that undergoes actual
nuclear decay.
motif A pattern of amino acids in a protein SEQUENCE
that has a specific function, e.g., metal binding.
See alsoCONSENSUS SEQUENCE.
MRI SeeMAGNETIC RESONANCE IMAGING.
mRNA SeeMESSENGERRNA.
Müller, Paul Hermann(1899–1965) Swiss Chemist
Paul Hermann Müller was born at Olten, Solothurn,
Switzerland, on January 12, 1899. He attended pri-
mary school and the Free Evangelical elementary and
secondary schools. He began working in 1916 as a lab-
oratory assistant at Dreyfus and Company, followed by
a position as an assistant chemist in the Scientific-
Industrial Laboratory of their electrical plant. He
attended Basel University and received a Ph.D. in 1925.
He became deputy director of scientific research on
substances for plant protection in 1946.
Müller began his career with investigations of dyes
and tanning agents with the J.R. Geigy Company, Basel
(1925–65), and he concentrated his research beginning
in 1935 to find an “ideal” insecticide, one that had
rapid, potent toxicity for the greatest number of insect
species but would cause little or no damage to plants
and warm-blooded animals. He tested and concluded
that dichlorodiphenyltrichloroethane (DDT) was the
ideal insecticide.
In 1939 DDT was successfully tested against the
Colorado potato beetle by the Swiss government and
by the U.S. Department of Agriculture in 1943.
For this discovery of DDT’s potent toxic effects on
insects, he received the Nobel Prize for physiology or
medicine. However, DDT proved to be a two-edged
sword. With its chemical derivatives, DDT became the
most widely used insecticide for more than 20 years
and was a major factor in increased world food pro-
duction and suppression of insect-borne diseases, but
the widespread use of the chemical made it hazardous
to wildlife and it was banned in 1970. Müller died on
October 12, 1965, in Basel.Mulliken, Robert S.(1896–1986) AmericanChemist
Robert Sanderson Mulliken was born in Newburyport,
Massachusetts, on June 7, 1896, to Samuel Parsons Mul-
liken, a professor of organic chemistry, and Katherine W.
Mulliken. He received a B.Sc. degree in 1917 at the Mas-
sachusetts Institute of Technology, Cambridge, Mas-
sachusetts. He entered the chemical warfare service
during the war but left due to illness and then became
employed by New Jersey Zinc Company until he entered
graduate school at the University of Chicago in the fall of
1919, where he received a Ph.D. degree in 1921.
While a graduate student in chemistry at Chicago,
his research work on boundary layer or diffusion mem-
brane played an integral role in the Manhattan Project.
He also became interested in the interpretation of
valence and chemical bonding from the work of IRVING
LANGMUIRand G. N. Lewis. He taught at New York
University (1926–28) and then joined the faculty of the
University of Chicago (1928–85).
Mulliken worked on valence theory and molecular
structure starting in the 1920s. In 1952 he developed a
quantum-mechanical theory of the behavior of electron
orbitals as different atoms merge to form molecules,
and in 1966 he was awarded the Nobel Prize in chem-
istry “for his fundamental work concerning chemical
bonds and the electronic structure of molecules by the
molecular orbital method.”
In 1929 he married Mary Helen von Noé, the
daughter of a professor of paleobotany at the Univer-
sity of Chicago. They had two daughters.
Mulliken was a National Research Council fellow,
University of Chicago, and Harvard University,
1921–25; a Guggenheim fellow, Germany and Europe,
1930 and 1932–33; and a Fulbright scholar, Oxford
University, 1952–54. In 1975 the University of Chicago
Press published his selected papers.
He died on October 31, 1986.multicenter bond Representation of some MOLECU-
LAR ENTITIESsolely by localized two-electron two-cen-
ter BONDs appears to be unsatisfactory. Instead,
multicenter bonds have to be considered in which elec-
tron pairs occupy orbitals encompassing three or more188 mother nuclide