Caro’s acid See peroxo-
sulphuric(vi) acid.
carotene A member of a class of
*carotenoid pigments. Examples are
β-carotene and lycopene, which col-
our carrot roots and ripe tomato
fruits respectively. α- and β-carotene
yield vitamin A when they are bro-
ken down during animal digestion.
carotenoid Any of a group of yel-
low, orange, red, or brown plant pig-
ments chemically related to terpenes.
Carotenoids are responsible for the
characteristic colour of many plant
organs, such as ripe tomatoes, car-
rots, and autumn leaves. They also
absorb light energy and pass this on
to chlorophyll molecules in the light-
dependent reactions of photosynthe-
sis.
Carothers, Wallace Hume
(1896–1937) US industrial chemist,
who joined the Du Pont company
where he worked on polymers. In
1931 he produced neoprene, a syn-
thetic rubber. His greatest success
came in 1935 with the discovery of
the polyamide that came to be
known as nylon. Carothers, who
suffered from depression, committed
suicide.
carrageenanA naturally occurring
polysaccharide isolated from red
algae. The polymer is composed of d-
galactose units, many of which are
sulphated. K-carrageenan is a gelling
agent with uses similar to those of
*agar.
carrier gasThe gas that carries the
sample in *gas chromatography.
carrier molecule1.A molecule
that plays a role in transporting elec-
trons through the *electron trans-
port chain. Carrier molecules are
usually proteins bound to a nonpro-
tein group; they can undergo oxida-
tion and reduction relatively easily,
thus allowing electrons toÛow
through the system. 2.A lipid-
soluble molecule that can bind to
lipid-insoluble molecules and trans-
port them across membranes. Carrier
molecules have speciÜc sites that in-
teract with the molecules they trans-
port. Several different molecules may
compete for transport by the same
carrier.Carr–Purcell–Meiboom–Gill se-
quenceSee cpmg sequence.CARS(coherent anti-Stokes Raman
spectroscopy) A form of Raman spec-
troscopy (see raman effect) enabling
the intensity of Raman transitions to
be increased. In this technique two
laser beams with different frequen-
cies pass through a sample producing
electromagnetic radiation of several
frequencies. It is possible to adjust
the frequency of the lasers so that
one of the frequencies corresponds
to that of a Stokes line from the sam-
ple and the coherent emission has
the frequency of the anti-Stokes line
with a high intensity. CARS enables
Raman spectra to be obtained even
in the presence of other radiation.
One application of CARS is to obtain
Raman spectra from bodies inÛames.
Using this technique temperatures in
different parts of theÛame can be es-
timated from the intensity of the
transitions.cascade liqueÜerAn apparatus
for liquefying a gas of low *critical
temperature. Another gas, already
below its critical temperature, is
liquiÜed and evaporated at a reduced
pressure in order to cool theÜrst gas
to below its critical temperature. In
practice a series of steps is often
used, each step enabling the critical
temperature of the next gas to be
reached.
cascade process Any process that
takes place in a number of steps, usu-105 cascade process
c