crystallization The process of forming crystals from
the melt or solution.
crystal systems The six (or seven) groupings of the
32 crystal classes based on the presence of common
symmetry elements: triclinic, monoclinic, orthorhombic,
tetragonal, hexagonal (rhombohedral), and isometric.
C-terminal amino acid residue See AMINO ACID
RESIDUE.
cubic close packing A way of packing atoms to
minimize unoccupied space that results in a crystal lat-
tice with cubic symmetry. There are three kinds of
cubic lattice: simple cubic, body-centered cubic, and
face-centered cubic, which is the close-packed type.
Many metals feature a cubic close-packed structure,
including gold (Au), silver (Ag), copper (Cu), aluminum
(Al), lead (Pb), nickel (Ni), and platinum (Pt).
curie (Ci) The basic unit used to describe the inten-
sity of radioactivity in a sample of material. One Ci =
3.700 ×1010 disintegrations per second. The unit used
in modern terminology is the Becquerel, which is 1 dps.
Curie, Marie (1867–1934) PolishChemist Marie
Curie (née Sklodowska) was born in Warsaw on
November 7, 1867, to a secondary school teacher. Edu-
cated in local schools, and by her father, she went to
Paris in 1891 to continue studying at the Sorbonne and
received licenciateships in physics and the mathematical
sciences.
She met her future husband Pierre Curie, a profes-
sor in the school of physics, in 1894, and they were
married the following year. She succeeded her husband
as head of the physics laboratory at the Sorbonne,
where she gained her doctor of science degree in 1903.
Following the death of her husband in 1906, she took
his place as professor of general physics in the faculty
of sciences, the first time a woman had held this posi-
tion. She was appointed director of the Curie Labora-
tory in the Radium Institute of the University of Paris,
founded in 1914.
Their early researches led to the isolation of polo-
nium, named after the country of Marie’s birth, and
radium, and she later developed methods for separating
radium from radioactive residues in sufficient quanti-
ties to allow for the study of its properties, and espe-
cially its therapeutic properties.
Throughout her life she actively promoted the use
of radium to alleviate suffering. She promoted this dur-
ing World War I, assisted by her daughter Iréne (who
won the Nobel Prize in chemistry in 1935).
Together with Pierre, she was awarded half of the
Nobel Prize for physics in 1903 for their study into the
spontaneous radiation discovered by Becquerel, who
was awarded the other half of the prize. In 1911 Marie
received a second Nobel Prize, in chemistry, in recogni-
tion of her work in radioactivity.
She received, jointly with her husband, the Davy
Medal of the Royal Society in 1903, and in 1921, Pres-
ident Harding of the United States, on behalf of the
women of America, presented her with one gram of
radium in recognition of her service to science. Marie
Curie died in Savoy, France, on July 4, 1934.Curie relation SeeMAGNETIC SUSCEPTIBILITY.Curtin-Hammett principle In a CHEMICAL REAC-
TIONthat yields one product (X) from one conforma-
tional ISOMER(A′) and a different product (Y) from
another conformational isomer (A′′) (and provided that
these two isomers are rapidly interconvertible relative to
the rate of product formation, whereas the products do
not undergo interconversion), the product composition
is not in direct proportion to the relative concentrations
of the conformational isomers in the SUBSTRATE; it is
controlled only by the difference in standard free ener-
gies (dćG) of the respective TRANSITION STATES.
It is also true that the product composition is for-
mally related to the relative concentrations of the con-
formational isomers A′and A′′(i.e., the conformational
equilibrium constant) and the respective rate constants
of their reactions. These parameters are generally,
though not invariably, unknown.
The diagram on page 66 represents the energetic
situation for transformation of interconverting isomers
A and A′into products X and Y.
See alsoCONFORMATION.Curtin-Hammett principle 65