Delineating a Tailor-Made Fluorescent Probe Designed for the Selective Detection of Tyrosinase.

A dicyanoisophorone based fluorescent probe (E)-2-(3-(4-hydroxystyryl)-5,5-dimethylcyclohex-2-en-1-ylidene)malononitrile (DCIP-OH) was developed for the selective sensing of tyrosinase in apple extract and live cells. The probe was obtained by the condensation of 2-(3,5,5-trimethylcyclohex-2-en-1-ylidene)malononitrile with 4-hydroxybenzaldehyde. Upon interaction with tyrosinase, the probe exhibited absorbance switching from 417 nm to 357 nm, accompanied by a slight increase in absorption value and an isosbestic point observed at 373 nm. Additionally, a reduction in emission intensity at 592 nm was observed. Furthermore, we successfully employed the probe for sensing of tyrosinase in apple extract and conducted inhibition studies by using kojic acid. LOD was determined to be ~0.4 nM. Moreover, the biocompatible nature of DCIP-OH enabled its effective localization in epithelial-like melanoma cells, B16F10, where it demonstrated successful fluorescent probing of intracellular tyrosinase.

Annulation-Induced Hidden Reactivity of the 1,2,4-Triazole Backbone.

Triazoles are an important class of compounds with widespread applications. Functionalization of the triazole backbone is thus of significant interest. In comparison to 1,2,3-triazoles, C-H activation-functionalization of the congeners 1,2,4-triazoles is surprisingly underdeveloped. Indeed, no such C-H activation-functionalization has been reported for 4-substituted 1,2,4-triazole cores. Furthermore, although denitrogenative ring-opening of 1,2,3-triazoles is well-explored, 1,2,4-triazole/triazolium substrates have not been known to exhibit N-N bond-cleaving ring-opening reactivity so far. In this work, we unveiled an unusual hidden reactivity of the 1,2,4-triazole backbone involving the elusive N-N bond-cleaving ring-opening reaction. This new reactivity was induced by a Satoh-Miura-type C-H activation-annulation at the 1,2,4-triazole motif appended with a pyridine directing group. This unique reaction allowed ready access to a novel class of unsymmetrically substituted 2,2'-dipyridylamines, with one pyridine ring fully-substituted with alkyl groups. The unsymmetrical 2,2'-dipyridylamines were utilized to access unsymmetrical boron-aza-dipyridylmethene fluorescent dyes. Empowered with desirable optical/physical properties such as large Stokes shifts and suitable hydrophobicity arising from optimal alkyl chain length at the fully-substituted pyridine-ring, these dyes were used for intracellular lipid droplet-selective imaging studies, which provided useful information toward designing suitable lipid droplet-selective imaging probes for biomedical applications.

AIEgens Based on Anion-π+ Interactions: Design, Synthesis, Photophysical Properties, and Their Applications in Material Science and Biology.

The design of novel aggregation-induced emission luminogens (AIEgens), has generally been facilitated by disrupting the possibility of π-π stacking. The recent literature describes a novel strategy to design AIEgens by introducing anion-π+ interactions to prevent the detrimental π-π stacking. This new strategy provides access to intrinsically charged AIEgens whose photophysical properties can be tuned either by incorporating different substituents on the π-molecular scaffold to modulate the acidity for tuning the interaction energy between a π-acceptor and counter-anions. This concept article provides a brief overview of the field, focusing on the synthesis of AIEgens, their photophysical properties, crystallography studies and their applications in live cell fluorescence imaging.

Interplay of Anion-π+ and π+ -π+ Interactions in Novel Pyrido[2,1-a]isoquinolinium-Based AIEgens - Substituent- and Counterion-Dependent Fluorescence Modulation and Applications in Live Cell Mitochondrial Imaging.

Recently, the concept of anion-π+ interactions has witnessed unique applications in the field of AIEgen development. In this contribution, we disclose a consolidated study of a library of N-doped ionic AIEgens accessed through silver-mediated cyclization of pyridino-alkynes. A thorough photophysical, computational and crystallographic study has been conducted to rationalize the observed substituent- and counterion-dependent fluorescence properties of these luminogens. We further elucidate the prominent role of anion-π+ interactions, π+ -π+ interactions and other non-covalent interactions, in inhibiting the undesired ACQ effect. Finally, we have also demonstrated the application of selected AIEgens for imaging of mitochondria in live cells.