**1. Introduction**

Cyclodextrins (CDs) at times referred as Schardinger sugars or cycloamylose dextrins, were fortuitously discovered [1, 2] by Vielliers in 1891, who named these compounds as "cellulosing." Later on Schardinger, who is considered the founder of CD chemistry, gave a detailed description about preparation and separation of CD and, more recently, Kurkov and Loftsson [3] also made significant contributions to CD science.

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Franz Schardinger, studying microorganisms which play a role in the deterioration of foods and by action of cyclodextrinase-Bacillus macerans amylase on the starch, obtained two distinct crystalline substances with similar properties to the already known partial degradation products of starch, the dextrins, so he named them α-, and β-dextrin. The separation of the cycloalkyls may be carried out by selective precipitation by means of organic compounds or by high temperature chromatography on a cellulose column. French et al. demonstrated that CDs are cyclic oligosaccharides composed of several D-(+) glucopyranose units in the form of a saddle [4]. In the second half of the 1930s, Freudenberg and his co-workers elucidated the cyclic structure of α-, and β-dextrin [5]. They consist of (α-1,4)-linked glucose units. A Greek letter preceding the abbreviation CD—for cyclodextrin—indicates the number of glucose units (α for 6, β for 7, and γ for 8) entering the composition of the cycloamylose. CDs constituted of less than 6 glucopyranose units cannot be formed due to steric hindrances [6]. Approximately, 1500 CD derivatives have been reported [7] in the literature.

CDs have a truncated cone appearance [7–12], and a doughnut, toroidal- or cylinder-like shape, due to the spatial arrangement characteristic of the various functional groups of the glucose units. As a consequence of this conformation, all the secondary hydroxyl groups (corresponding to the C2 and C3 carbon atoms of the glucose units) are at one of the edges of the cavity, whereas the primary hydroxyls are in the other end of the cavity. Rotation of these –OH groups reduces the effective size of the cavity, making it have a more open conical truncated aspect [13] toward the side of the secondary hydroxyls (**Figures 1** and **2**).

can be established by the formation of hydrogen bridges between polar hosts and –OH of the primary hydroxyls. An endless number of physical and chemical processes [10, 14] are usually facilitated, that is, volatile substances may be stabilized by transforming in crystalline substances; oxygen-sensitive materials could find protection against oxidation; solubility and bioavailability of drugs could be improved [15–20] by participating in controlled

Cyclodextrins: Past and Present

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CDs have been the subject of a large number of studies dealing with complexation and molecular catalysis [21–25], as well as studies about hydrophobic effects and fine-tune models of biological processes. In 1953, the first patent on CDs and complexes was registered, but until 1970, only small amounts of relatively pure CDs were produced for industrial use due to their high production cost. Although in the beginning it was erroneously thought that CDs were toxic, currently, it is difficult to imagine a world without CDs [3] due to their potential use [26]. The number of possible applications seems to be unlimited, i.e., computer-aided drug design, pharmaceutical, medical, biomedical and biotechnological, drug and gene delivery, foods, foods additives and ingredients, food processing, cosmetic, textiles, industrial and ana-

An inherent interest surrounds these compounds due to their physical and chemicals properties [26–38]. The common feature of CDs is their ability to form inclusion complexes with a variety of molecules and ions, both in the solid state (crystalline substances) and in solution. As results of the structure of CDs, they can establish apolar-apolar interactions encapsulating other apolar molecules which may undergo structural changes [33–38], acting as molecular capsules [27–32]. However, the idea that one molecule could envelop another one to form a

lytical. Currently, patents on CDs are counted by thousands.

**Figure 2.** Steric structures of molecules from (a) α, (b) β, and (c) γ-CDs.

delivery processes.

**2. Inclusion complexes**

This spatial arrangement gives an apolar character to the interior of the cavity, whereas the presence of the –OH groups at the edges of the cone trunk makes them very water soluble. For instance, hydrophobic hosts will be housed inside the cavity because of the hydrophobic van der Waals type interactions, whereas simultaneously polar interactions

**Figure 1.** Molecular structure of (a) α, (b) β, and (c) γ-CDs.

Cyclodextrins: Past and Present http://dx.doi.org/10.5772/intechopen.72736 5

**Figure 2.** Steric structures of molecules from (a) α, (b) β, and (c) γ-CDs.

can be established by the formation of hydrogen bridges between polar hosts and –OH of the primary hydroxyls. An endless number of physical and chemical processes [10, 14] are usually facilitated, that is, volatile substances may be stabilized by transforming in crystalline substances; oxygen-sensitive materials could find protection against oxidation; solubility and bioavailability of drugs could be improved [15–20] by participating in controlled delivery processes.

CDs have been the subject of a large number of studies dealing with complexation and molecular catalysis [21–25], as well as studies about hydrophobic effects and fine-tune models of biological processes. In 1953, the first patent on CDs and complexes was registered, but until 1970, only small amounts of relatively pure CDs were produced for industrial use due to their high production cost. Although in the beginning it was erroneously thought that CDs were toxic, currently, it is difficult to imagine a world without CDs [3] due to their potential use [26]. The number of possible applications seems to be unlimited, i.e., computer-aided drug design, pharmaceutical, medical, biomedical and biotechnological, drug and gene delivery, foods, foods additives and ingredients, food processing, cosmetic, textiles, industrial and analytical. Currently, patents on CDs are counted by thousands.
