Does degree of substitution on the cyclodextrin hosts impacts on their affinity towards guest binding?
Although cyclodextrins have been extensively utilized in various supramolecular fields due to their numerous attractive attributes, to achieve even advanced applications, they often need structural modification through substitutions of suitable functional groups at their rims. A systematic investigation on how the degree of substitution on the cyclodextrin rims affects the binding affinity for a given guest molecule, is however rarely been reported, especially from the perspective of the photophysical studies. Herein, we report the non-covalent interaction of a styryl based dye, LDS-798, with three different sulfobutylether beta cyclodextrin (SBEnβCD) derivates bearing varying degree of substitutions (n), using ground state absorption, steady-state emission, excited-state lifetime and time-resolved fluorescence anisotropy measurements. The dye-host binding constant values indicate that the strength of interaction between LDS-798 and SBEnβCD derivatives follows an increasing trend with the increasing number of the tethered sulfobutylether substituents on the cyclodextrin rims, which is attributed to the gradual increasing electrostatic interaction between the negatively charged sulfobutylether groups and the positively charged LDS-798. Excited state lifetime measurements and ionic strength dependent studies on the dye-SBEnβCD complexes further support the increased affinity between the dye and the host in the supramolecular complexes with the increasing number of sulfobutylether substituents on the βCD rims., Observed results suggest that the molecular recognition of LDS-798 with SBEnβCD derivatives can be tuned very effectively with the varying number of the sulfobutylether substituents in the cyclodextrin rims. Considering that SBE7CD is one of the FDA approved agents for drug formulation, the obtained results with other SBEnβCD hosts may be useful in designing selective drug delivery applications, drug formulations, as well as effective fluorescence on-off switches.