197
10
amylose contained in the starch and
links the ends to form cycles. Mixtures of
products of different sizes are formed.
5 For producing pure cyclodextrins,
auxiliary substances can be added that
form complexes with the cyclodextrin of
the desired size that are hardly soluble.
Alternatively, specially modified enzymes
can be added.
5 Cyclodextrins are used, for example, to
remove cholesterol from fatty food by
precipitating the cyclodextrin/cholesterol
complex and separating it from the
substrate.
5 In pharmaceuticals, cyclodextrin/drug
complexes are used to increase the
stability and bioavailability of the active
pharmaceutical ingredients and to avoid
interaction with other substances.
5 “Empty” cyclodextrins can remove
unpleasant odors by selectively binding
odor-producing substances. This effect
is used, for example, in deodorants,
mouthwashes and textile sprays.
5 In homogeneous catalysis, cyclodextrins
can be used as phase-transfer catalysts
to increase the rate of an aqueous
biphasic reaction.
5 Like cellulose and starch, derivatives
of cyclodextrins can also be produced
by etherification, esterification and
cross-linking. In this way, the properties
of these compounds, such as their
solubility, can be specifically adjusted.
? Ten Quickies
1. Are cyclodextrins starch hydrolyzates?
Explain your answer!
2. Can cyclodextrins in principle also be
produced from cellulose?
3. What is the name of the cyclodextrin
with nine glucose monomers and how
many hydroxyl groups does it carry?
Estimate the external dimensions of this
cyclodextrin!
4. What are the differences between
amylases and cyclodextrin glycosyltransferases?
etherification or cross-linking. These reactions
can also be applied to cyclodextrins since they
also carry hydroxyl groups. In the case of cyclodextrins, these are basically located on the
outside, so that in most cases, the size and hydrophobicity of the cavity are not influenced by derivatization.
In principle, cyclodextrin derivatives are produced in the same way as cellulose and starch
derivatives (7 Chaps. 7 and 8). The rate of conversion is again expressed by the degree of substitution (DS).
One property of cyclodextrins, which can
be adjusted almost at will by derivatization, is
their solubility in certain solvents. For example, the 2,6-dimethyl ether of β-cyclodextrin is
much more soluble in cold water (570 g l −1 ) than
β-cyclodextrin itself. Methyl ethers of cyclodextrins are also soluble in organic solvents such
as methanol or acetone, which is interesting for
some applications (see phase-transfer catalysis). Another important cyclodextrin ether is
hydroxypropyl ether, which is used in the aforementioned textile spray, but also in pharmaceutical products.
Summary (Take-Home Messages)
5 Cyclodextrins are cyclic oligosaccharides
composed of typically six, seven or
eight glucose monomers linked via an
α-1,4-glycosidic bond.
5 The nomenclature is ascending with
Greek letters, starting with α for the
cyclodextrin with six glucose building
blocks.
5 Due to their cyclic structure, they form
a special geometric shape. As a result,
cyclodextrins have a hydrophilic shell
and a hydrophobic cavity.
5 By complexing apolar organic substances
within this cavity, cyclodextrins can form
inclusion or host-guest complexes.
5 The relative size of the compound to be
included and the size of the cavity are
decisive for the selectivity and stability of
the inclusion complex.
5 Cyclodextrins are produced enzymatically
from starch. The cyclodextrin glycosyltransferases used selectively cut the
10.4 · Derivatives of Cyclodextrins
10
amylose contained in the starch and
links the ends to form cycles. Mixtures of
products of different sizes are formed.
5 For producing pure cyclodextrins,
auxiliary substances can be added that
form complexes with the cyclodextrin of
the desired size that are hardly soluble.
Alternatively, specially modified enzymes
can be added.
5 Cyclodextrins are used, for example, to
remove cholesterol from fatty food by
precipitating the cyclodextrin/cholesterol
complex and separating it from the
substrate.
5 In pharmaceuticals, cyclodextrin/drug
complexes are used to increase the
stability and bioavailability of the active
pharmaceutical ingredients and to avoid
interaction with other substances.
5 “Empty” cyclodextrins can remove
unpleasant odors by selectively binding
odor-producing substances. This effect
is used, for example, in deodorants,
mouthwashes and textile sprays.
5 In homogeneous catalysis, cyclodextrins
can be used as phase-transfer catalysts
to increase the rate of an aqueous
biphasic reaction.
5 Like cellulose and starch, derivatives
of cyclodextrins can also be produced
by etherification, esterification and
cross-linking. In this way, the properties
of these compounds, such as their
solubility, can be specifically adjusted.
? Ten Quickies
1. Are cyclodextrins starch hydrolyzates?
Explain your answer!
2. Can cyclodextrins in principle also be
produced from cellulose?
3. What is the name of the cyclodextrin
with nine glucose monomers and how
many hydroxyl groups does it carry?
Estimate the external dimensions of this
cyclodextrin!
4. What are the differences between
amylases and cyclodextrin glycosyltransferases?
etherification or cross-linking. These reactions
can also be applied to cyclodextrins since they
also carry hydroxyl groups. In the case of cyclodextrins, these are basically located on the
outside, so that in most cases, the size and hydrophobicity of the cavity are not influenced by derivatization.
In principle, cyclodextrin derivatives are produced in the same way as cellulose and starch
derivatives (7 Chaps. 7 and 8). The rate of conversion is again expressed by the degree of substitution (DS).
One property of cyclodextrins, which can
be adjusted almost at will by derivatization, is
their solubility in certain solvents. For example, the 2,6-dimethyl ether of β-cyclodextrin is
much more soluble in cold water (570 g l −1 ) than
β-cyclodextrin itself. Methyl ethers of cyclodextrins are also soluble in organic solvents such
as methanol or acetone, which is interesting for
some applications (see phase-transfer catalysis). Another important cyclodextrin ether is
hydroxypropyl ether, which is used in the aforementioned textile spray, but also in pharmaceutical products.
Summary (Take-Home Messages)
5 Cyclodextrins are cyclic oligosaccharides
composed of typically six, seven or
eight glucose monomers linked via an
α-1,4-glycosidic bond.
5 The nomenclature is ascending with
Greek letters, starting with α for the
cyclodextrin with six glucose building
blocks.
5 Due to their cyclic structure, they form
a special geometric shape. As a result,
cyclodextrins have a hydrophilic shell
and a hydrophobic cavity.
5 By complexing apolar organic substances
within this cavity, cyclodextrins can form
inclusion or host-guest complexes.
5 The relative size of the compound to be
included and the size of the cavity are
decisive for the selectivity and stability of
the inclusion complex.
5 Cyclodextrins are produced enzymatically
from starch. The cyclodextrin glycosyltransferases used selectively cut the
10.4 · Derivatives of Cyclodextrins