CH 3 (CH 2 ) 9 CH:CH 2 , obtained from petroleum and used in making *dodecylbenzene.
dodecylbenzene A hydrocarbon,
CH 3 (CH 2 ) 11 C 6 H 5 , manufactured by a
Friedel–Crafts reaction between dodecene (CH 3 (CH 2 ) 9 CH:CH 2 ) and benzene. It can be sulphonated, and the
sodium salt of the sulphonic acid is
the basis of common *detergents.
dolomite A carbonate mineral consisting of a mixed calcium–magnesium carbonate, CaCO 3 .MgCO 3 ,
crystallizing in the rhombohedral
system. It is usually white or colourless. The term is also used to denote
a rock with a high ratio of magnesium to calcium carbonate. See limestone.
domain A functional unit of the
tertiary structure of a *protein. It
consists of chains of amino acids
folded into alpha helices and *beta
sheets to form a globular structure.
Different domains are linked together by relatively straight sections
of polypeptide chain to form the protein molecule. Domains allow a degree of movement in the protein
structure.
Donnan equilibrium The equilibrium set up when two solutions are
separated by a membrane permeable
to some but not all of the ions in the
solutions. In practice, the membrane
is often permeable to the solvent and
small ions but not to charged entities
of colloidal size or such polyelectrolytes as proteins. An electrical potential develops between the two
sides of the membrane with the two
solutions having varying osmotic
pressure. Donnan equilibrium is
named after the British chemist Frederick George Donnan (1870–1956),
who developed the theory of membrane equilibrium. Donnan equilibrium is important in biology.
donor An atom, ion, or molecule
that provides a pair of electrons in
forming a coordinate bond.
dopa (dihydroxyphenylalanine) A
derivative of the amino acid tyrosine.
It is found in particularly high levels
in the adrenal glands and is a precursor in the synthesis of *dopamine,
*noradrenaline, and *adrenaline.
The laevorotatory form, L-dopa, is administered in the treatment of
Parkinson’s disease, in which brain
levels of dopamine are reduced.
185
dose
d
C
H 2
NH 2
C
H 2
OH
O
H
O
H
Dopamine
O
H
O
H
C
H 2
CH 2
NH 2
Dopa
dopamine A *catecholamine that
is a precursor in the synthesis of *noradrenaline and *adrenaline. It also
functions as a neurotransmitter in
the brain.
d-orbital See orbital.
dose A measure of the extent to
which matter has been exposed to
*ionizing radiation. The absorbed
dose is the energy per unit mass absorbed by matter as a result of such
exposure. The SI unit is the gray, although it is often measured in rads (1
rad = 0.01 gray; see radiation units).
The maximum permissible dose is the
recommended upper limit of absorbed dose that a person or organ
should receive in a speciÜed period
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dodecylbenzene A hydrocarbon,
CH 3 (CH 2 ) 11 C 6 H 5 , manufactured by a
Friedel–Crafts reaction between dodecene (CH 3 (CH 2 ) 9 CH:CH 2 ) and benzene. It can be sulphonated, and the
sodium salt of the sulphonic acid is
the basis of common *detergents.
dolomite A carbonate mineral consisting of a mixed calcium–magnesium carbonate, CaCO 3 .MgCO 3 ,
crystallizing in the rhombohedral
system. It is usually white or colourless. The term is also used to denote
a rock with a high ratio of magnesium to calcium carbonate. See limestone.
domain A functional unit of the
tertiary structure of a *protein. It
consists of chains of amino acids
folded into alpha helices and *beta
sheets to form a globular structure.
Different domains are linked together by relatively straight sections
of polypeptide chain to form the protein molecule. Domains allow a degree of movement in the protein
structure.
Donnan equilibrium The equilibrium set up when two solutions are
separated by a membrane permeable
to some but not all of the ions in the
solutions. In practice, the membrane
is often permeable to the solvent and
small ions but not to charged entities
of colloidal size or such polyelectrolytes as proteins. An electrical potential develops between the two
sides of the membrane with the two
solutions having varying osmotic
pressure. Donnan equilibrium is
named after the British chemist Frederick George Donnan (1870–1956),
who developed the theory of membrane equilibrium. Donnan equilibrium is important in biology.
donor An atom, ion, or molecule
that provides a pair of electrons in
forming a coordinate bond.
dopa (dihydroxyphenylalanine) A
derivative of the amino acid tyrosine.
It is found in particularly high levels
in the adrenal glands and is a precursor in the synthesis of *dopamine,
*noradrenaline, and *adrenaline.
The laevorotatory form, L-dopa, is administered in the treatment of
Parkinson’s disease, in which brain
levels of dopamine are reduced.
185
dose
d
C
H 2
NH 2
C
H 2
OH
O
H
O
H
Dopamine
O
H
O
H
C
H 2
CH 2
NH 2
Dopa
dopamine A *catecholamine that
is a precursor in the synthesis of *noradrenaline and *adrenaline. It also
functions as a neurotransmitter in
the brain.
d-orbital See orbital.
dose A measure of the extent to
which matter has been exposed to
*ionizing radiation. The absorbed
dose is the energy per unit mass absorbed by matter as a result of such
exposure. The SI unit is the gray, although it is often measured in rads (1
rad = 0.01 gray; see radiation units).
The maximum permissible dose is the
recommended upper limit of absorbed dose that a person or organ
should receive in a speciÜed period
www.AzShimi.ir www.AzShimi.com