uranium series See radioactive
series.
urea (carbamide) A white crystalline
solid, CO(NH 2 ) 2 ; r.d. 1.3; m.p. 135°C.
It is soluble in water but insoluble in
certain organic solvents. Urea is the
major end product of nitrogen excretion in mammals, being synthesized
by the *urea cycle. Urea is synthesized industrially from ammonia and
carbon dioxide for use in *urea–
formaldehyde resins and pharmaceuticals, as a source of nonprotein nitrogen for ruminant livestock, and as
a nitrogen fertilizer.
urea cycle (ornithine cycle) The series of biochemical reactions that
converts ammonia to *urea during
the excretion of metabolic nitrogen.
Urea formation occurs in mammals
and, to a lesser extent, in some other
animals. The liver converts ammonia
to the much less toxic urea, which is
excreted in solution in urine.
urea–formaldehyde resins Synthetic resins made by copolymerizing
urea with formaldehyde (methanal).
They are used as adhesives or thermosetting plastics.
urea nitrate See unfo.
urethane resins (polyurethanes)
Synthetic resins containing the repeating group –NH–CO–O–. There are
numerous types made by copolymerizing isocyanate esters with polyhydric alcohols. They have a variety of
uses in plastics, paints, and solid
foams.
Urey, Harold Clayton (1894–1981)
US physical chemist, who became a
professor at the University of California in 1958. His best-known work
was the discovery of *deuterium
(heavy hydrogen) in 1932, for which
he was awarded the 1939 Nobel Prize
for physics.
uric acid The end product of purine
breakdown in most primates, birds,
terrestrial reptiles, and insects and
also (except in primates) the major
form in which metabolic nitrogen is
excreted. Being fairly insoluble, uric
acid can be expelled in solid form,
which conserves valuable water in
arid environments. The accumulation of uric acid in the synovial Ûuid
of joints causes gout.
543
UV–visible spectroscopy
u
N
H
N
H
N
H
N
H
O
O
O
Uric acid
OH
O
O
H
N
NH
OH
O
O
Uridine
uridine A nucleoside consisting
of one uracil molecule linked to a dribose sugar molecule. The derived
mucleotide uridine diphosphate
(UDP) is important in carbohydrate
metabolism.
UV See ultraviolet radiation.
UV–visible spectroscopy See ultraviolet–visible spectroscopy.
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series.
urea (carbamide) A white crystalline
solid, CO(NH 2 ) 2 ; r.d. 1.3; m.p. 135°C.
It is soluble in water but insoluble in
certain organic solvents. Urea is the
major end product of nitrogen excretion in mammals, being synthesized
by the *urea cycle. Urea is synthesized industrially from ammonia and
carbon dioxide for use in *urea–
formaldehyde resins and pharmaceuticals, as a source of nonprotein nitrogen for ruminant livestock, and as
a nitrogen fertilizer.
urea cycle (ornithine cycle) The series of biochemical reactions that
converts ammonia to *urea during
the excretion of metabolic nitrogen.
Urea formation occurs in mammals
and, to a lesser extent, in some other
animals. The liver converts ammonia
to the much less toxic urea, which is
excreted in solution in urine.
urea–formaldehyde resins Synthetic resins made by copolymerizing
urea with formaldehyde (methanal).
They are used as adhesives or thermosetting plastics.
urea nitrate See unfo.
urethane resins (polyurethanes)
Synthetic resins containing the repeating group –NH–CO–O–. There are
numerous types made by copolymerizing isocyanate esters with polyhydric alcohols. They have a variety of
uses in plastics, paints, and solid
foams.
Urey, Harold Clayton (1894–1981)
US physical chemist, who became a
professor at the University of California in 1958. His best-known work
was the discovery of *deuterium
(heavy hydrogen) in 1932, for which
he was awarded the 1939 Nobel Prize
for physics.
uric acid The end product of purine
breakdown in most primates, birds,
terrestrial reptiles, and insects and
also (except in primates) the major
form in which metabolic nitrogen is
excreted. Being fairly insoluble, uric
acid can be expelled in solid form,
which conserves valuable water in
arid environments. The accumulation of uric acid in the synovial Ûuid
of joints causes gout.
543
UV–visible spectroscopy
u
N
H
N
H
N
H
N
H
O
O
O
Uric acid
OH
O
O
H
N
NH
OH
O
O
Uridine
uridine A nucleoside consisting
of one uracil molecule linked to a dribose sugar molecule. The derived
mucleotide uridine diphosphate
(UDP) is important in carbohydrate
metabolism.
UV See ultraviolet radiation.
UV–visible spectroscopy See ultraviolet–visible spectroscopy.
www.AzShimi.ir www.AzShimi.com