Chemical and Functional Properties of Food Saccharides

© 2004 by CRC Press LLC
Methylated β-CD is more hydrophobic than the parent β-CD. Therefore, it forms
a more stable but still soluble cholesterol complex. Its high affinity to cholesterol
provides extraction of cholesterol from blood cell membranes, resulting in hemolysis
at ca. 1 mg/ml concentration.
One of the methylated β-CDs, heptakis (2,6-di-O-methyl-β-CD), called DIMEB,
is a crystalline product. It is extremely soluble in cold water but insoluble in hot
water; therefore, its purification and isolation of its complexes is technically very
simple. To date, it is the most superior solubilizer among CDs. It is available at an
isomeric purity above 95%, but for injecting drug formulations and widespread
industrial applications the cheaper randomly methylated β-CD (called RAMEB) is
produced and marketed.
In reaction of β-CD with starch in the presence of pullulanase, one or two either
maltosyl or glycosyl groups may be attached with the α-1,6 glycosidic linkage to
the primary side of the CD ring. The so-called branched CD (mono- or dimaltosyl
or mono- or diglucosyl CD) is very well soluble in water, heterogeneous, and a
noncrystallizing substance, produced and used in stable flavor powders for the food
industry.
The heptakis(sulfobutyl)β-CD is very well soluble in water. Even at extremely
high doses, it exhibits no toxic side effects. It can be used as a chiral separating
agent in capillary zone electrophoresis, but intensive research focuses on its application
as a parenteral drug carrier and component of aqueous injecting solutions of
poorly soluble drugs.
17.3 CYCLODEXTRIN INCLUSION COMPLEXES 9–14
In an aqueous solution, the slightly nonpolar CD cavity is occupied by water molecules,
which are energetically nonfavored guests because of polar–nonpolar interactions.
Therefore, water molecules can be readily substituted by other guests that
are less polar than water (Figure 17.5). One, two, or three CD molecules (hosts)
contain one or more entrapped guests. Most frequently, the host-to-guest ratio is
1:1. This is the essence of molecular encapsulation. However, commonly 2:1, 1:2,
2:2, or even more complicated associations and higher-order equilibria coexist.
FIGURE 17.5 Formation of the inclusion complex. Small circles represent water molecules,
which are repulsed both by the hydrophobic (potential guest) p-xylene and the hydrophobic
cavity of the truncated CD cylinder.