Application of solvent extraction and synchronous spectrofluorimetry to the determination of the formation constant for a 1:1 complex of carbazole with?-cyclodextrin in water-dimethyl sulfoxide medium

Abstract

Extraction of carbazole in heptane was performed at 25±1°C with an aqueous dimethyl sulfoxide (DMSO) medium containing β-cyclodextrin (βCD) at consecutive concentrations in the range of 0–10 mM. The fluorescence intensity of carbazole remaining in the heptane phase was measured by synchronous scanning fluorimetry. The apparent formation constant (Kf) for a 1:1 carbazole: βCD inclusion complex in water-DMSO medium was determined by using a linear plot of the distribution ratio calculated from the fluorescence intensities vs. the β-CD concentration. The values thus obtained ranged from 477 M−1 in a 10% v/v DMSO medium to 12.1 M−1 in a 60% v/v medium. Good linear relationships were observed between logKf and the DMSO concentration ([DMSO]), and also between logKf and the logarithm of the distribution coefficient (Kd) for carbazole. The formation constant in 100% water was estimated to be approximately 1.0×103 M−1 on the basis of the logKf vs. [DMSO] and the logKf vs. logKd correlations.