Abstract
Formation of a ternary complex by an ultrafast molecular rotor (UMR) with a macrocyclic cavitand has been investigated for the sensitive detection of the alkyl chain of a surfactant. A benzothiazole based UMR, Thioflavin-T (ThT), has been used as a fluorescent probe. It is shown that ThT forms a very weak inclusion complex with γ-cyclodextrin (γ-CD) with an association constant of 8.8 M(-1). However, the addition of a small amount of surfactant results in a significant increase in the emission intensity of ThT in γ-CD solution. From detailed steady-state and time-resolved fluorescence measurements and NMR studies, it has been inferred that the addition of the surfactant results in the formation of a ternary complex through the inclusion of its alkyl chain inside the γ-CD nanocavity. In such a ternary complex, the non-radiative torsional motion in ThT is largely prevented due to a large increase in the frictional force inside the nanocavity and results in a significant fluorescence enhancement. The formation of the binary and the ternary complexes in the present system has been further supported by the molecular docking and subsequent molecular dynamics simulation studies. The present result indicates that the inclusion complex with an UMR as a guest could be a potential candidate for the efficient detection of insoluble organic molecules, especially hydrocarbons.
Highlights
Cyclodextrins (CDs), made up of D-glucopyranose units, are well known macrocyclic host molecules and form inclusion complexes with several classes of guest molecules.[10,11] The exterior hydroxyl groups of CD make them soluble in water and their hydrophobic interior allows nonpolar organic molecules to reside in their nanocavity through hydrophobic interactions.[10,12] The most remarkable property of CDs is their ability to modify the physicochemical properties of guest molecules through several types of interactions
The photophysical properties of the ThT–g-CD inclusion complex have been investigated in the presence of different surfactants
The alkyl chain of the surfactant acts as a space regulator and occupy the empty space in the g-CD nanocavity. Such space regulation by the surfactant alkyl chain increases the frictional forces for the torsional motion of ThT and leads to an enormous increase in its emission quantum yield
Summary
Cyclodextrins (CDs), made up of D-glucopyranose units, are well known macrocyclic host molecules and form inclusion complexes with several classes of guest molecules.[10,11] The exterior hydroxyl groups of CD make them soluble in water and their hydrophobic interior allows nonpolar organic molecules to reside in their nanocavity through hydrophobic interactions.[10,12] The most remarkable property of CDs is their ability to modify the physicochemical properties of guest molecules through several types of interactions. With some exception,[14,15] its analyte sensing activity is mainly limited by the formation of a binary inclusion complex due to the fact that the size of its nanocavity can accommodate mostly one guest molecule
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