Cavity size dependent stoichiometry of probe–cyclodextrin complexation: Experimental and molecular docking demonstration

Abstract

Host-guest interaction of a newly synthesized intramolecular charge transfer (ICT) probe, namely (E)-4-(4-(diethylamino)benzylideneamino)-2-(trifluoromethyl)benzonitrile (DBTFB), with supramolecular assemblies like α- and β-cyclodextrin (CD) has been investigated exploiting various spectroscopic techniques. Steady state fluorescence studies reveal that depending on the different cavity sizes of the hosts, probe–CD inclusion complexes of different stoichiometries are formed. The stoichiometries and association constants of these complexes have been determined exploiting Benesi-Hildebrand equation and the stoichiometries are found to be 1:1 and 1:2 for probe–α-CD and probe–β-CD inclusion complexes respectively. Relatively higher steady state fluorescence anisotropy value of the probe in β-CD compared to that in α-CD substantiates the stoichiometrically different probe–CD interactions. Time resolved fluorescence study further corroborates the differential stoichiometry in the two cases. Hydrodynamic diameters of CD-encapsulated probe as obtained from dynamic light scattering (DLS) experiments demonstrate the cyclodextrin dependent stoichiometries. Molecular docking has been exploited to get a qualitative molecular based picture of the probe–CD complexations in the two cases.