Cyclodextrin

Cyclodextrins (CD) are a class of compounds belonging to the cyclic oligosaccharides. Make ring degradation products of starch; they consist of α -1 ,4- glycosidically linked glucose molecules. The result is a toroidal structure with a central cavity. Cyclodextrins were first described by Villiers and Schardinger, but long remained a laboratory curiosity. They were first isolated by Villiers in 1891 and 1903 characterized by Schardinger as oligosaccharides.

Nomenclature

Depending on the number of their constituent glucose units, the cyclodextrins are named differently. Using a Greek letter as a prefix differentiates:

• α -cyclodextrin: n = 6 glucose molecules ( lumen diameter / height: 4.7 .. 5.3 / 7.9 Å)
• β -cyclodextrin: n = 7 glucose molecules ( lumen diameter / height: 6.0 .. 6.5 / 7.9 Å)
• γ -cyclodextrin: n = 8 glucose molecules ( lumen diameter / height: 7.5 .. 8.3 / 7.9 Å)
• δ -cyclodextrin: n = 9 glucose molecules

Cyclodextrins with much more glucose units are described in detail in the literature on the above-mentioned cyclodextrins addition. However, these are due to the small quantities and high prices are not of economic importance. The longest technical distribution have β -cyclodextrin and hydroxypropyl- β -cyclodextrin. In the food industry, α -cyclodextrin and γ -cyclodextrin are used. Since α -cyclodextrin is a soluble fiber, it can be it as such also listed in the table of contents, eg as alpha -cyclodextrin ( soluble fiber ).

Extraction and production

Cyclodextrins are produced biotechnologically by the enzymatic degradation of starch, such as corn or potatoes. The enzymes used for this purpose will be briefly referred to as cyclodextrin glycosyltransferases CGTases. When acting on the strength of CGTase cuts from the helically wound structure of the carbohydrate out individual pieces and combines them to form an annular oligosaccharide - the cyclodextrin. Is industrially interesting especially the varietal production of cyclodextrins in order to select the different cavity diameters depending on einzuschließender substance can. There are selective enzymes available that specifically produce α -, β - and γ -cyclodextrin, respectively. This is especially for the food industry is important because only α - and γ -cyclodextrin should be consumed indefinitely.

Properties

Allen lower cyclodextrins own the hydrophobic cavity in the interior and the polar outer surface. Wherein the cyclodextrins are able to form so-called inclusion compounds with apolar organic compounds.

In alkaline as well as acidic solutions up to pH 2 cyclodextrins are very stable. They have no fixed melting points, but are up to about 200 ° C stable. In addition they begin to decompose. They are considered non-toxic and are largely stable to human digestive enzymes, so α - cyclodextrin may be used as a soluble fiber.

Use

The ability to inclusion compounds with non-polar organic compounds and the water solubility of cyclodextrins to make an increasingly important subject of pharmaceutical research, since the complexes with pharmaceuticals are generally more soluble in water than the pure pharmaceuticals, and therefore also in the body are readily available. Continue their ability enclosed substance before surrounding compounds to protect (for example, oxygen), and the trapped substances over a long period of time to deliver, are of great interest.

α -cyclodextrin has been approved since 2008 in the European Union as a soluble dietary fiber. In June 2013, the Commission of the European Union α -cyclodextrin has certified a proven health benefit ( health claim ). The EU report confirms that α -cyclodextrin can reduce the rise in blood sugar after starchy meals. Due to its surface-active properties, it is used as emulsifying fiber in the food ( mayonnaise ) and cosmetics (skin creams), as well as whipping agents for desserts, confectionery and bakery products. Beta -cyclodextrin is approved in the EU as a food additive under the number E 459 with different maximum limits on certain foods, specifically in the aromatization of tea or instant beverage powders ( 0.5 milligrams per kilogram in the intended consumption preparation) and crisps (with 1 milligrams per kilogram ) and in tableted foods ( as needed - quantum satis ). Gamma - cyclodextrin was approved by the EU for Wacker Chemie AG as a novel food ingredient for food and beverage applications.

In addition, the consumer encounter cyclodextrins under the trade name Febreze, Bounce or Oust. The present in these products cyclodextrin derivatives bind the compounds responsible for unpleasant odors and are equally support of fragrances. In some countries (eg USA, Japan) cyclodextrins are approved as food additives, as they cancel among other things, the taste and smell of the trapped substances or can release it again. The range of applications of cyclodextrins today comprises of various drugs on preparations cardboard boxes to medicine, agriculture and various sensor applications. The German Textile Research Institute in Krefeld intensively researched the use of covalently bonded to the fabric fibers cyclodextrins for " intelligent" textiles. This can also prevent body odor both the skin absorbed drugs contain as.

In analytical chemistry, and especially with great success in gas chromatography special cyclodextrin derivatives are used to separate mixtures of enantiomers. Equally successful are established cyclodextrin derivatives in capillary electrophoresis ( CE English ). Sulfated, charged cyclodextrins even a separation of enantiomers neutral becomes possible that would otherwise not be accessible by CE.