Cyclodextrins ring formation

Other studies have included the formation of complexes using spray-drying techniques, including the preparation of cyclodextrin complexes. DSC may be used to determine the extent of drug inclusion within the cyclodextrin ring system, again via monitoring of the decrease in the heat of fusion (97). 

Cyclodextrins are well known [1] to form a number of crystalline adducts or inclusion complexes with a variety of substances. In the crystalline lattice, cyclodextrins form two types of packing One is a cage type where the cavity of one cyclodextrin molecule is closed on both sides by ad jacent molecules. The other is a channel-type, in which the cyclodextrin rings are packed on top of each other to produce cylinders with infinite centralcavity. Formation of one or the other type crystal structure depends on the size and molecular character of the guest molecule. 

As a final example we consider noncovalent molecular complex formation with the macrocyclic ligand a-cyclodextrin, a natural product consisting of six a-D-glucose units linked 1-4 to form a torus whose cavity is capable of including molecules the size of an aromatic ring. Table 4-3 gives some rate constants for this reaction, where L represents the cyclodextrin and S is the substrate ... 

Although Freudenberg s hypothesis that complex-formation occurred by inclusion within the cavity was generally accepted, there was no direct evidence for this, either in solution or in the solid state. Broser and Lautsch had found by spectrophotometric titration that the complexes of a series of dyes with the cyclodextrins in solution obeyed the mass action law with a stoichiometry of 1 1. They suggested that association on the outside of the ring might not have a defined stoichiometric composition, and they thus interpreted their results as being consistent with inclusion by cyclodextrin. Their results were not conclusive, however. 

Ueda, H. (2002) Physicochemical Properties and Complex Formation Abilities of Large-Ring Cyclodextrins, J. Incl. Phenom. 44, 53-56. 

Potential use of complexes of y - CD with organic compounds, including polymers, was also reviewed by Szejtli [6, 12, 13], y - CD are able to incorporate metal ions as ligands to prepare magnetic nano - particles [7,14], Harada and Ka-machi [8,15] first found that poly (ethylene oxide) (PEO) thread a- CD rings to form polymer - cyclodextrin complex. Since their finding of inclusion complex formation of polymer chains with a- CD, a large number of studies on inclusion complexes of... 

In the cyclodextrins readily obtainable from starch, the six (a-CD), seven (P-CD) and eight (y-CD) a(l- 4)-linked glucose units are "locked up" in a strait-jacket type belt due to adoption of 4Cj chair conformations of the pyranoid rings and a net of 2-OH — OH-3 hydrogen bonds (73, 74). As this structural rigidity even persists on inclusion complex formation, as exemplified by the three represenatives in Fig. 1 (75 - 78) ... 

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