Near-Infrared Spectroscopic Investigation of Inclusion Complexes between Cyclodextrins and Aromatic Compounds (original) (raw)

Near infrared (NIR) absorption in the 900-1800 nm region has been used to characterize and measure the association constants of the inclusion complexes between aromatic compounds (e.g., phenol, 4-chlorophenol, sodium 2-naphthalenesulfonate, and sodium 2-pyrenesulfonate) and a-, B-, and y -cyclodextrin. It was found that the NIR method is particularly suited for this type of study because upon forming complexes, the oscillator strengths of the C-H stretching [Av = 2 (at -1650 nm) and 3 (at -1 120 nm)] overtone bands of the aromatic guest compounds were increased by at least 2-5-fold. The observed increases are rationalized in terms of the enhancement in the anharmonicity and the libration motions of the guest molecule in the CD cavity.