Strong guest binding by cyclodextrin hosts in competing nonpolar solvents and the unique crystalline structure.

6-O-Modified ß-cyclodextrins, such as heptakis(6-O-triisopropylsilyl)-ß-cyclodextrin (TIPS-ß-CD) and heptakis(6-O-tert-butyldimethylsilyl)-ß-cyclodextrin (TBDMS-ß-CD), formed 2:1 inclusion complexes with pyrene in benzene and cyclohexane with high association constants. The X-ray crystalline structure of the TIPS-ß-CD-pyrene complex obtained from the benzene solution showed that one pyrene molecule was incorporated in the form of a sandwich-type complex with two benzene molecules within the cavity of the dimer formed by two TIPS-ß-CD molecules.

6-O-Modified beta-cyclodextrin enabling inclusion complex formation in nonpolar media.

Heptakis(6-O-tert-butyldimethylsilyl)-beta-cyclodextrin (TBDMS-beta-CD) effectively forms inclusion complexes with chlorinated benzenes in nonpolar solvents such as benzene-d(6) and cyclohexane-d(12). The inclusion selectivity toward 1,2- and 1,3-dichlorobenzenes can be switched by changing the solvent from benzene-d(6) to cyclohexane-d(12). Moreover, 1,2,4-trichlorobenzene (90 ppm) is perfectly removed from insulating oil by using TBDMS-beta-CD as an adsorbent.

Complete removal of chlorinated aromatic compounds from oils by channel-type gamma-cyclodextrin assembly.

This paper describes the complete removal of chlorinated aromatic compounds from insulating oil by a channel-type gamma-cyclodextrin (gamma-CD) assembly as a new adsorbent. Using this type of adsorbent (50-60 wt % of oil), 1,2,4- and 1,3,5-trichlorobenzenes, 2- and 4-chlorobiphenyls (2- and 4-MCBs), 4,4'-dichlorobiphenyl (4,4'-DiCB), and 3,4,4'-trichlorobiphenyl (3,4,4'-TrCB), whose initial concentrations were 100 ppm, were completely removed from the insulating oil. Competitive adsorption experiments using a mixture of 2-MCB and 4-MCB or a mixture of 4-MCB, 4,4'-DiCB, and 3,4,4'-TrCB revealed that selective adsorption based on the shape and size of the chlorinated aromatics was achieved by the channel-type gamma-CD assembly, implying that inclusion into the cavity of the channel-type gamma-CD was responsible for the removal of chlorinated aromatics from insulating oil. It was also found that more than 70% of adsorbed chlorinated aromatics was easily recovered from the channel-type gamma-CD by simply washing with n-hexane, and chlorinated aromatics were completely removed from the insulating oil even by the regenerated adsorbent, indicating that the gamma-CD assembly can be easily regenerated and recycled.