Rigid Organization of Fluorescence-Active Ligands by Artificial Macrocyclic Receptor to Achieve the Thioflavin T-Amyloid Fibril Level Association

Abstract

The push-pull molecules with an intramolecular charge transfer from donor to acceptor sides upon excitation exhibit a wide variety of biological and electronic activities, as exemplified by the in vivo fluorescence imaging probes for amyloid fibrils in the diagnosis and treatment of amyloid diseases. Interestingly, the structurally much simpler bis(4,8-disulfonato-1,5-naphtho)-32-crown-8 (DNC), in keen contrast to the conventional macrocyclic receptors, was found to dramatically enhance the fluorescence of twisted intramolecular charge-transfer molecules possessing various benzothiazolium and stilbazolium fluorophores upon complexation. Spectroscopic and microcalorimetric titrations jointly demonstrated the complex structures and the interactions that promote the extremely strong complexation, revealing that the binding affinity in these artificial host-guest pairs could reach up to a nearly 10(7) M(-1) order of magnitude in water, and the sandwich-type complexation is driven by electrostatic, hydrophobic, π-stacking, and hydrogen-bonding interactions. Quantum chemical calculations on free molecules and their DNC-bound species in both the ground and excited states elucidated that the encapsulation by DNC could greatly deter the central single and double chemical bonds from free intramolecular rotation in the singlet excited state, thus leading to the unique and unprecedented fluorescence enhancement upon sandwich-type complexation. This complexation-induced structural reorganization mechanism may also apply to the binding of other small-molecule ligands by functional receptors and contribute to the molecular-level understanding of the receptor-ligand interactions in many biology-related systems.

In Situ Photoconversion of Multicolor Luminescence and Pure White Light Emission Based on Carbon Dot-Supported Supramolecular Assembly

“…Upon complexation with CB[8], the fluorescence intensity of OF-1 2+ increases (Figure a) 16-fold as compared to the inherent fluorescence of OF-1 2+ , benefiting from the fact that free rotation of the CC double bond is restricted by CB[8] . The fluorescence quantum yield of OF-1 2+ ⊂CB­[8] was measured to be 12% (Table S3), a value which is considerably higher than that (0.63%) for free OF-1 2+ .…”

Supramolecular Luminescent Sensors

“…When the torsional motion is hindered, radiative decay pathways occur, resulting in strong fluorescence emission. Such restricted rotation can occur when the fluorophore is in viscous solvents, intercalated in DNA, or encapsulated in a macrocycle , or nanocavity . Thioflavin T has been used to study the formation, aggregation, and inhibition of amyloid fibrils, which are linked to neurodegenerative diseases such as Alzheimer’s disease. − …”

Binding of anions in triply interlocked coordination catenanes and dynamic allostery for dehalogenation reactions

“… 60 , 61 These results demonstrate that the dimerization of Tet -1 is an entropy-driven endothermic reaction, which is attributed to the increase of molecular disorder and release of solvents. 62 Similarly, the Δ G between the dimerization of Tet -1 with I – anions is –30.15 kJ mol –1 (Fig. S70 † ).…”