Y-cydodextrin

Figure 10.38 shows modified / - and y-cydodextrins with two identical appended fluorophores that are able to form extimers (Ueno et al., 1997). They have been studied in 10% ethylene glycol aqueous solutions. /J-cyclodextrins with two 2-naphthylsulfonyl moieties linked to the smaller rim (compounds / -CDl, / -CD2, / -CD3), have a cavity that is too small to include both fluorophores one of them is outside the cavity and the other is inside. The latter can be excluded from the cavity upon inclusion of a guest molecule. Therefore, the excimer band in the fluorescence spectrum increases upon guest inclusion. 

Due to its distinctly hydrophobic character, C,5o is also practically insoluble in water. The concentration of a saturated solution is a homeopathic 3 x 10 molT. This value increases upon addition of amines as they may form donor-acceptor complexes with the fullerene. Colloidal solutions with particles measuring 0.22 pm and a concentration of 7 x 10" moll" have been obtained by the aid of ultrasound. Also did the application of complexing host molecules Uke y-cydodextrines lead to a higher solubihty. Surfactants serve to the same purpose. Strictly speaking, however, there are no real solutions in this case, but the fidlerene molecules are located inside of miceUes. 

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... 

Busche, B. J., Tonelli, A. E., and Balik, C. M. 2010. Rroperties of polystyrene/ polyjdimethyl siloxane) blends partially compatibilized with star polymers containing a y-cydodextrin core and polystyrene arms. Polymer 51 6013-6020. 

The cydodextrins are produced from starch by enzymatic conversions and are composed of 5-32 units, but the typical cydodextrins for chromatographic use consists of 6 units (a-cyclodextrin), 7 units (P-cydodextrin), or 8 units (y-cydodextrin). 

N. Rajagopalan, S.C. Chen, and W.S. Chow, A study of the inclusion complex of amphoter-icin-B with y-cydodextrin, Int. J. Pharm., 29,161-168,1986. 

The effect of methylated cydodextrins on the RhH(CO)(TPPTS)3 complex in hydroformylation conditions (50 bar, CO H2 = 1 1, and80°C) were investigated by high-pressure P NMR spectroscopy. It was found that the formation of the stable inclusion complex between methylated P-cyclodextrin and TPPTS influences the TPPTS dissociation equilibrium. The methylated a-cydodextrin does not interact with the TP PTS and the methylated y-cydodextrin can only weakly bind to the TP PTS. These results explain why a decrease in the normal-to-branched aldehydes ratio is always observed when cydodextrins are used as mass-transfer agents in aqueous biphasic hydroformylation processes [104]. 

TbADH Thermaonaerobium brockii alcohol dehydrogenase) and 12 other commercial CREDs were used to reduce phenylethyl ketone 46 as shown in Scheme 6.18. a-, 3- and y-Cydodextrins were used as additives to alter the enan-tiosdectivity and decrease the reaction rate. The studies showed that CRED 122, in the presence of increasing concentration of y-cyclodextrin, led to a decrease in enantiopurity of the desired (R) product however, when the molar ratio of cydodexuin reached 3.8, the configuration of the alcohol was swapped to (S). The decreased activity of the enzyme was attributed to transformation of the enzymes a-helix to the p-sheet or to a random coil. Maximum activity was as-sodated vdth maximum amount of a-helix content [28]. 

Another approach to increase the population of the photoreactive conformation is to include the compound into cyclodextrin cavities. Ct, ft and Y-Cydodextrins were added to aqueous solutions containing l,2-bis(2-methyl-l-benzothiophen-3-yl)perfluorocyclopentene having sulfonate groups, and the changes in the ratio of the two conformations were examined by NMR. By the addition of 10 equivalents of ft-cydodextrin, the Cj symmetry conformation ratio was increased from 0.64 to 0.94, and the cyclization quantum yield was increased from 0.32 to 0.49. 

Ueno, A., Tomita, Y., and Osa, T., Photoresponsive binding abflity of azobenzene-appended y-cydodextrin, Tetrahedron Lett., 24, 5245, 1983, and references died therein. 

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