Hybrid Synthetic and Computational Study of an Optimized, Solvent-Free Approach to Curcuminoids

Curcumin-based molecular probes for fluorescence imaging of fungi

Fluorescence imaging is a powerful and widely used method to visualize and study living organisms. However, fungi are notoriously difficult to visualize using fluorescence microscopy, given that their cell wall represents a diffusion barrier, and the synthetic organic dyes available are very limited when compared to molecular probes available for other organisms. Moreover, these dyes are usually available in only one colour, preventing co-staining experiments. To fill this gap, curcumin-based molecular probes were designed based on the rationale that curcumin is fluorescent and has moderate toxicity toward fungi, implying its ability to cross the cell wall to reach targets in the intracellular compartments. A family of boron diketonate complexes was synthesized, based on a curcumin backbone, tuning their emission color from blue to red. These probes did not present noticeable toxicity to filamentous fungus and, when applied to their visualization, readily entered the cells and precisely localized in sub-cellular organelles, enabling their visualization.

A curcumin-based AIEE-active fluorescent probe for Cu2+ detection in aqueous solution

Curcuminoids have been extensively investigated as metal ion probes, but the intrinsic aggregation-caused-quenching (ACQ) characteristic of curcumin would hinder their applications in aqueous solution. Fortunately, tetraphenylethylene (TPE) could endow the compounds with aggregation-induced emission (AIE)/aggregation-induced enhanced emission (AIEE) characteristics to eliminate the ACQ effect. According to this strategy, a series of TPE-modified curcumin derivatives L1–4 were prepared and studied for their AIEE properties. Among the four TPE-curcumin analogues, only L1 particles have been successfully used as an on-off fluorescence probe for detecting Cu²⁺ in aqueous solution. The fluorescence titration experiment determined its detection limit of 1.49 × 10⁻⁷ mol L⁻¹, and the binding ratio between L1 and Cu²⁺ was estimated as 2 : 1, which was in agreement with the results of high resolution mass spectrum and Job's plot. In addition, the binding constant was evaluated as 6.77 × 10² M⁻¹ using a Benesi–Hildebrand plot. Finally, the obtained L1-based indicator paper showed significant fluorescence response to Cu²⁺ aqueous solution. This TPE-modified strategy improves the detection capability of curcumin probe in aqueous solution and provides a feasible way to obtain other probes with ACQ characteristics.

A curcumin-based AIEE-active L1 was synthesized and used to prepare an on-off fluorescent probe for Cu²⁺ detection in aqueous solution.