Guest–host interactions between tetrahydrobetacarboline and β-cyclodextrin

Abstract

The interactions between 1,2,3,4-tetrahydro-9H-pyrido[3,4-b]indole or tetrahydrobetacarboline, THBC, and cycloheptaamilose or β-cyclodextrin, β-CD, have been investigated using UV absorption, steady state and time resolved fluorescence measurements. The addition of β-cyclodextrin has very little effect on the absorption spectra of neutral and cationic THBC species. However, it induces a blue shift and pronounced fluorescence enhancements in the emission spectrum of the neutral substrate. Both, steady state and time resolved fluorescence studies show that neutral THBC species form 1:1 inclusion complexes with β-CD. Global analysis of the time resolved data provides evidence on the formation of two different types of 1:1 THBC–β-CD complexes. It is assumed that each one of these complexes corresponds to the two different topologies for the entry of the THBC molecule into the β-CD cavity, i.e. by its benzene or by its piperidinic moiety. Association constants of the complexes and other thermodynamic and photophysical parameters have been estimated from fluorescence measurements.