RESUMEN
The microviscosity of intracellular environments plays an important role in monitoring cellular function. Thus, the capability of detecting changes in viscosity can be utilized for the detection of different disease states. Viscosity-sensitive fluorescent molecular rotors are potentially excellent probes for these applications; however, the predictable relationships between chemical structural features and viscosity sensitivity are poorly understood. Here, we investigate a set of arylcyanoamide-based fluorescent probes and the effect of small aliphatic substituents on their viscosity sensitivity. We found that the location of the substituents and the type of π-network of the fluorophore can significantly affect the viscosity sensitivity of these fluorophores. Computational analysis supported the notion that the excited state rotational energy barrier plays a dominant role in the relative viscosity sensitivity of these fluorophores. These findings provide valuable insight into the design of molecular rotor-based fluorophores for viscosity measurement.
RESUMEN
The self-assembly of amyloid-ß (Aß) peptides into amyloid aggregates is a pathological hallmark of Alzheimer's Disease. We previously reported a fluorescent Aryl Cyano Amide (ARCAM) probe that exhibits an increase in fluorescence emission upon binding to Aß aggregates in solution and in neuronal tissue. Here, we investigate the effect of introducing small aliphatic substituents on the spectroscopic properties of ARCAM both free in solution and when bound to aggregated Aß. We found that introducing substituents designed to hinder the rotation of bonds between the electron donor and acceptor on these fluorophores can affect the overall brightness of fluorescence emission of the probes in amyloid-free solutions, but the relative fluorescence enhancement of these probes in amyloid-containing solutions is dependent on the location of the substituents on the ARCAM scaffold. We also observed the capability to tune the excitation or emission wavelength of these probes by introducing electron-donating or -withdrawing substituents that putatively affect either the energy required for photoexcitation or the stability of the photoexcited state. These studies reveal new design principles for developing ARCAM-based fluorescent Aß-binding probes with an enhanced fluorescence signal compared to background and tunable spectroscopic properties, which may lead to improved chemical tools for aiding in the diagnosis of amyloid-associated neurodegenerative diseases.
