Cydodextrin structure

Structures of the common cydodextrins and their larger analogs 98CRV1785. Synthetic cyclic oligosaccharides 98CRV1919. 

In addition to fluorescence methods, another study [27] developed a method to permit electron microscopic localization of Ras anchor domains on cytoplasmic membrane surfaces by immunogold labeling. The particle neighbor distances can be analyzed to obtain information about possible domain structure. Expressing H-Ras and K-Ras in baby hamster kidney cells, a nonrandom particle distribution was obtained from which the estimated mean raft size was 7.5-22 nm and about 35% of the membrane area consists of rafts. The same technique applied to cells that had been incubated with [3-cydodextrin to reduce cholesterol produced completely random distributions of H-Ras. This cholesterol dependence suggests some type of coupling of rafts across the inner and outer membrane leaflets. 

Fig. 1. Structural diagram of (a) p-cydodextrin and (b) two of the glucopyranose units illustrating details of the a-(l,4) glycosidic linkage, C-l (d) chair...

Fig. 15. Prototype examples of (a) cydodextrins and (b) calixarenes, showing conformational structures and dimensions.

Hydrogen-bonding patterns in crystal structures of the cydodextrins and the simpler carbohydrates differ. The infinite, homodromic chains are common both in the low molecular-weight carbohydrates and in the cydodextrins. The principal difference lies in the frequency of occurrence of the homodromic and antidromic cycles, which are common in the cyclodextrin crystal structures and rare in the mono-, di-, and trisaccharides. The cyclic patterns are the rule in the clathrate hydrates and in the ices. From this point of view, the hydrogen-bonding patterns of the hydrated cydodextrins lie between those of the simpler hydrated carbohydrates and those of the hydrate inclusion compounds, discussed in Part IV, Chapter 21. 

Fig. 7. A tethered cyclodextrin and the structure of p-cydodextrin, the most common cyclodextrin used as a bonded ligand in liquid chromatography.

An example of a STM manipulation on a jS-cydodextrin necklace has been given above (see Fig. 10.13) [75]. In further studies the same group further clarified the intramolecular structure of the cydodextrin polymer necklace with STM [158]. Head-to-head ( tail-to-tail ) to head-to-tail arrangement of the cydodextrin molecules were observed in the ratio (8 2). 

In situ STM has been applied [326] to study the potential-induced self-organization of (Z-cydodextrin on Au(lll) surfaces in NaClO4 solutions. The adsorbed molecules formed an ordered array of a cylindrical structure in the potential range 0.20 to —0.15 V (versus SCE), while they were desorbed at potentials lower than -0.40 V. 

Visualization of Cydodextrins in Supramolecular Structures by Scanning Probe Microscopy 319... 

In the next larger cydodextrin, j8-CyD, aliphatic inserts are less popular, although the crystal structures of [3]pseudorotaxanes with aliphatic mono- [25] and diacids [18, 26, 27], diols [28], and bis-imidazolyl hydrocarbons [29] have been reported. j8-CyD/monocarboxylic acid complexes pack in channel structures and create supramolecular polymers, whereas 8-CyD/diacid complexes break the channel structure, contrary to what could be anticipated based on the propensity of acids to dimerize. With the wide y-CyD and aromatic guests, such as Congo Red [14] and ( )-stilbene [15] dimerization of the guest inside y-CyD is observed to form [4] and [3]pseudorotaxanes. Irradiation of crystalline complexes of the latter yielded syn-tetraphenylcyclobutane as a single isomer. 

Fig. 12.7. Stoddart s cydodextrin [2]catenane 13, for which the X-ray structure is also available [66, 67].

Complexation of fuUerene C o with y-cydodextrin was attained by employment of high-speed vibrational milling (HSVM) by Komatsu et al. (Scheme 8.6) [14], Fullerene Cso was complexed within 10 min milling with fourfold excess of cyclodextrin, forming a 1 2 complex 25 with a bicapped structure. The solid-state... 

Using the simple approach of selective tosylation of primary hydroxyl sites followed by nucleophilic substitution by a tertiary amine reagent, quaternary ammonium salts of a wide range of structures derived from carbohydrate precursors have been prep>ared. for the cydodextrin derivatives, p>er-tosylation of the available hydroxylic sites was established by early efforts at generating cydodextrin derivatives (Cramer et al. 1969) with later modification to the procedure using aqueous medium. 

Hofmann BE, Bender H, Schulz GE (1989) Three-dimensional structure of cydodextrin glycosyltransferase from Bacillus circulans at 3.4 A resolution. J Mol Biol 209 793-800... 

If there were a generalized decrease in hydrophobidty because of a change in water structure, it would not be clear why this did not also affect the hydrophobidty of the cydodextrin interior. If it had, the effect on binding should have been larger than the effect on solubility. In support of this argument, the situation is quite different when ethanol is added to the water solutions. With 10% ethanol the solubility of t-butylbenzyl alcohol in water... 

---