Modification of cyclodextrins to control their guest-host chemistry and their applications as chemosensors

Capped cyclodextrins are prepared by reaction with a planar porphine molecule capable of hydrogen bonding to hydroxyl groups of the torus-shaped cyclodextrin. Absorption, fluorescence and NMR data indicated the formation of a semi-closed assembly where the porphine molecule ''caps'' the cyclodextrin, closing off one end of the cyclodextrin host. A quantitative change in the absorption profile of an assembly prepared from highly water-soluble 2-hydroxypropyl-beta-CD and planar 4,4',4 '',4'''-(21H, 23H-porphine-5,10,15,20-tetrayl)tetrakis benzoic acid (FOR) occurred highly selectively in response to a guest-host complexation of pentachlorophenol. For the first time, solubilization of polynuclear aromatic hydrocarbons (PAHs), including the potent carcinogen benzo(a)pyrene, by modified cyclodextrins has enabled monitoring of these important environmental contaminants using lignin peroxidase. A separation and detection method using cyclodextrin modified capillary electrophoresis was also developed for analysis of the 16 US EPA priority pollutant PAHs. In this procedure, a mixture of negatively charged sulfobutylether-beta-cyclodextrin (SB-beta-CD) and neutral methyl-beta-cyclodextrin (M-beta-CD) was added to the running buffer and separation was effected based on differential distribution (partitioning) of the PAH components between the two CD types. Laser-induced fluorescence detection provided sensitive detection of 11 of the 16 components, with detection limits measured typically in the low mu g/L (ppb) range. Satisfactory separation of all 16 PAHs was achieved in under 20 min with 35 mM SB-beta-CD and 15 mM M-beta-CD, with efficiencies for all components greater than 10(5) theoretical plates.