Cyclodextrins and their Complexes

1. Cyclodextrins and their Complexes Molecules with holes... Stoddart: ‘‘Cyclodextrins are all-purpose molecular containers for organic, inorganic, organometallic, and metalloorganic compounds that may be neutral, cationic, anionic, or even radical”. α β glucopyranoside units γ

2. EASY name to remember... 5,10,15,20,25,30,35- heptakis-(hydroxymethyl)-2,4,7,9,12,14,17,19,22,24,27,29,32,34-tetradecaoxaoctacyclo[ 31.2.2.2.3;,6.28, 11.213, 16.218, 21.223, 26.228,31]nonatetracontane-36,37,38,39,40,41,42,43,44,45,46,47,48,49-tetradecol

5. In most cases these host molecules have an average structure of a truncated cone with a cavity lined with H3 and H5 protons and lone pairs of glycosidic oxygen atoms lying in a plane thus endowing the cavity with hydrophobic character, while the bases formed by the primary and secondary OH groups bestow a hydrophilic character

6. The great significance of CDs both in research and applications lies in their ability to selectively form inclusion complexes with other molecules, ions, or even radicals. This phenomenon bears the name molecular recognition

7. By appropriate choice of host and guest one can achieve a very high selectivity. 6 is complexed much more strongly by the dimeric host 7 than is 8.

9. Amazing sensitivity of CDs to the shapes of guest molecules or ions Most probably due to a difference in the stoichiometry of these complexes. Namely, the latter complexes are of 1:1 stoichiometry while in the former one guest molecule is mostly embedded in a capsule formed by two host CDs.

10. “flip-flop” mechanism

11. Molecular necklace

13. Chemosensors Using Modified Cyclodextrins

14. Numerous dye-modified CyDs were prepared as chemosensors for highly selective and sensitive molecular recognition 49 showed sensitivity for analytes such as steroids and terpenes with different selectivity from the native CD. 50 did not show any change in fluorescence intensity upon the addition of guests because of the strong inclusion of the dansyl group into the CD cavity

15. In the absence of guests effective quenching occurred between included nitrobenzene and pyrene, both closely located in the CD cavity. The fluorescence intensity dramatically increases with increasing concentration of a guest (e.g. lithocholic acid), because the nitrobenzene moiety is excluded from the CD cavity.

16. Cyclodextrins Conjugated with Other Kinds of Hosts

17. Metallocavitands Using Modified Cyclodextrins Metallocavitands are expected to lead to the development of new metal catalysts with enhanced selectivities and activities, in particular because of the protection against undesired side reactions provided by substrate inclusion into the CD cavity and by stabilization of unusual coordination modes.

19. Polymer Formation by Intermolecular Interactions

21. Regulation of Photoreactions

22. Host–Guest Interactions The intermolecular cavity of CDs includes H2O molecules which are surrounded by a hydrophobic wall mainly composed of hydrogen atoms. Therefore, these H2O molecules cannot fully form hydrogen bonds and are energetically less stable than bulk water molecules. When a guest molecule, of suitable size and preferably hydrophobic character, is added to a CD solution, H2O molecules in the CD cavity are replaced by the guest molecule..

24. Microcalorimetry

27. Pharmaceutical Applications of Cyclodextrins and Their Derivatives