carbon monoxide(CO) A colorless, odorless gas
that is toxic.
carbon monoxide dehydrogenases ENZYMEs that
catalyze the oxidation of carbon monoxide to carbon
dioxide. They contain IRON-SULFUR CLUSTERs and
either nickel and zinc or MOLYBDOPTERIN. Some nickel-
containing enzymes are also involved in the synthesis of
acetyl coenzyme A from CO 2 and H 2.
carbon sequestration The uptake and storage of
carbon. Trees and plants, for example, absorb CARBON
DIOXIDE, release the oxygen, and store the carbon.
Fossil fuels were at one time biomass and continue to
store the carbon until burned. Sometimes used to refer
to any way in which carbon can be removed from
active participation in the carbon cycle, such as by
injecting carbon dioxide into depleted oil wells or the
deep ocean as a means of controlling greenhouse gas
emissions.
See alsoGREENHOUSE EFFECT.
carbonyl group A functional group with an oxygen
atom double bonded to a carbon atom, e.g., aldehydes
(joined to at least one hydrogen atom) and ketones
(carbonyl group is joined to ALKYL GROUPs or ARYL
GROUPs).
carboplatin A second-generation platinum drug
effective in cancer chemotherapy named cis-diammine
(cyclobutane-1,1-dicarboxylato)platinum(II). Carbo-
platin is less toxic than the first-generation antitumor
drug, CISPLATIN.
carboxyl group A functional group that consists of
a carbon atom joined to an oxygen atom by a double
bond and to a HYDROXYL GROUP; present in all CAR-
BOXYLIC ACIDs.
carboxylic acid Organic molecules with a CAR-
BONYL GROUPin which the carbon is bonded to a
HYDROXYL GROUP.
carbyne Generic name for the species HC: and substi-
tution derivatives thereof, such as EtO 2 C–C: containing
an electrically neutral univalent carbon atom with three
nonbonding electrons. Use of the alternative name
methylidyneas a generic term is not recommended.carcinogen Any substance known that may produce
cancer.cardiotech A species radiolabeled with 99mT c with
the formula [T c(CNR) 6 ]+(Rtert-butyl) known for
IMAGINGthe heart after a heart attack.Carnot cycle Composed of four reversible pro-
cesses—two isothermal and two adiabatic—and can be
executed either in a closed or a steady-flow system.
First proposed in 1824 by French engineer Sadi Carnot
(1796–1832).carotenoids A large family of natural phytochemi-
cals, accessory pigments, found in plants (in chloro-
plasts) and animals. They are composed of two small
six-carbon rings connected by a carbon chain that must
be attached to cell membranes. Their variety of colors
absorb wavelengths that are not available to chloro-
phyll and so serve to transfer their captured energy
from the Sun to help in photosynthesis. Carotenoids
color fruits and vegetables and give them their charac-
teristic red, orange, and yellow colors and serve as
antioxidants in human nutrition. Over 600 carotenoids
are known.carrier-linked prodrug(carrier prodrug) A PRO-
DRUGthat contains a temporary linkage of a given
active substance with a transient carrier group that
produces improved physicochemical or pharmacoki-
netic properties and that can be easily removed in vivo,
usually by a hydrolytic cleavage.cascade prodrug A PRODRUGfor which the cleavage
of the carrier group becomes effective only after
unmasking an activating group.cascade prodrug 41