Fluorogenic selective detection of Zn²⁺ using a pyrazole-ortho-vanillin conjugate: insights from DFT, molecular...

A fluorescent sensor, (E)-N'-(2-hydroxy-3-methoxybenzylidene)-3,5-dimethyl-1H-pyrazole-1-carbohydrazide (HMPC), was designed and synthesized for the selective fluorescence recognition of Zn²⁺ in semi-aqueous media. Notably, HMPC exhibited a red-shifted, two-fold fluorescence "turn-on" enhancement in response to Zn²⁺ at 490 nm, with a detection limit of 1.68 μM, which is significantly lower than the WHO guideline (76.0 μM). The binding constant of HMPC with Zn²⁺ was calculated to be 5 × 10⁴ M^-1. The fluorescence enhancement of HMPC in the presence of Zn²⁺ is attributed to the suppression of the PET process and the enhancement of ICT, leading to fluorescence via the CHEF mechanism. The sensing mechanism was demonstrated through UV-vis, fluorescence spectroscopy, Job plots, ESI-MS, and DFT calculations. For biological applications, cytotoxicity and cell imaging studies were performed using MCF-7 cells. Molecular docking studies revealed a high binding energy of HMPC (ΔG = -7.1 kcal mol^-1) with the 4,5-diaryl isoxazole HSP90 chaperone protein, suggesting its potential as an anticancer agent. Additionally, its binding energy of -6.5 kcal mol^-1 with the HDAC8 protein indicates greater efficacy than suberoylanilide hydroxamic acid (SAHA) in inhibiting HDAC, as it binds more strongly to the HDAC8 protein than SAHA (-7.4 kcal mol^-1). Furthermore, due to its favorable ADME profile, HMPC may be suitable for oral administration, enhancing its potential as an anticancer drug.