Fluorescence Studies of the Effects of t -Butyl Functionalities on the Formation of Ternary β-Cyclodextrin Complexes with Pyrene

Abstract

The effects of t-butyl (TB) compounds on the formation of β-cyclodextrin (CD)/pyrene complexes have been examined by monitoring changes in the fluorescence I/III band ratio of 1.0 × 10⁻⁷ M pyrene in 0.075 M of the t-butyl compounds and in various concentrations of β-CD in a solvent mixture consisting of 60% v/v methanol/40% water solution. For the compounds tested, the strongest effects were observed in the presence of the following (in decreasing order): TB-carbamate, TB-carbazate, TB-(N-hydroxy) carbamate, TB-(N-butoxy carbonyl) glycine, and TB-formate. In terms of enhancement of the pyrene/β-CD binding constant, all exhibited effects stronger than those previously reported for t-butyl alcohol. In contrast, TB-amine, TB-acetic acid, and TB-acetoacetate exhibited very little effect. There appears to be a relationship between the chemical structure of the modifier molecules and the magnitude of their concomitant effects on the I/III ratio. In fact, the t-butyl modifiers which exhibited moderate to strong effects have a common caboxy, –C–O–, skeleton attached to the t-butyl moiety in their general structure: (CH₃)₃C–O–R. The modifier effect was also found to be independent of the pH of the solutions. A detailed explanation has been offered for the observed changes in the I/III ratio relative to t-butyl functionalities.