Organisation and complexation of mono- and bis-β-cyclodextrins without chromophores with a fluorescence-sensitive probe in aqueous solutions

The behaviour of mono- and bis-beta-cyclodextrin (CD) derivatives, namely 6(I)-deoxy-6(I)-[4-(hept-6-ynyl)-1H-1,2,3-triazolyl]-beta-CD and 1,5-bis((1-(6(I)-deoxy-beta-CD-6(I)-yl)-1H-1,2,3-triazol-4-yl)methoxy) pentyl, whose appended groups and inter-CD linkers, respectively, do not contain any chromophore, and their complexation with dimethyl-2,6-naphthalenedicarboxylate (DMN), a fluorescent polarity-sensitive probe in aqueous solutions, were investigated. Steady-state, time-resolved fluorescence, circular dichroism techniques, molecular mechanics (MM) and molecular dynamics (MD) simulations were employed. DMN appeared to slightly interact with the mono-beta-CD and only unstable non-covalent dimers were formed. On the contrary, stable 1:1 and 2:1 stoichiometry complexes were obtained with bis-beta-CD and DMN. A certain cooperativity due to the presence of both cavities and the linker favoured the formation of the complex 2:1 DMN:CD. DMN appeared to be axially oriented inside both CD cavities. MM and MD calculations also demonstrated the stability of the 1:1 and 1:2 stoichiometry complexes.