In this report, the interaction between a phenanthrene–pyrene-based fluorescent probe (PPI) and bovine serum albumin (BSA), a transport protein, has been explored by steady-state emission spectroscopy, fluorescence anisotropy, far-ultraviolet circular dichroism (CD), time-resolved spectral measurements, and molecular docking simulation study. The blue shift along with emission enhancement indicates the interaction between PPI and BSA. The binding of the probe causes quenching of BSA fluorescence through both static and dynamic quenching mechanisms, revealing a 1:1 interaction, as delineated from Benesi–Hildebrand plot, with a binding constant of ∼10 5 M –1 , which is in excellent agreement with the binding constant extracted from fluorescence anisotropy measurements. The thermodynamic parameters, Δ H °, Δ S °, and Δ G °, as determined from van’t Hoff relationship indicate the predominance of van der Waals/extensive hydrogen-bonding interactions for the binding phenomenon. The molecular docking and site-selective binding studies reveal the predominant binding of PPI in subdomain IIA of BSA. From the fluorescence resonance energy transfer study, the average distance between tryptophan 213 of the BSA donor and the PPI acceptor is found to be 3.04 nm. CD study demonstrates the reduction of α-helical content of BSA protein on binding with PPI, clearly indicating the change of conformation of BSA.

We report a novel phenazine-embedded fluorescent probe (2-[2-(pyridin-2-ylmethoxy)-phenyl]-1H-imidazo­[4,5-b]­phenazine, PIP), which upon complexation with Cu­(II)-ion-forming [(PIP)­CuII(Cl)] becomes nonfluorescent but regenerates fluorescence in a selective reaction with NO and HNO over different biologically reactive oxygen and nitrogen (ROS/RNS) species under physiological conditions. The fluorescence intensity of PIP gets quenched due to the formation of the [(PIP)­CuII(Cl)] complex, which regenerates the fluorescence by 67 and 84% upon reaction either with NO or HNO, respectively, in the presence of other biological reducing species. Details of photophysical properties of PIP, [(PIP)­CuII(Cl)], and [(PIP)­CuI] have been studied by density functional theory (DFT) calculations. The recognition efficacy of [(PIP)­CuII(Cl)] for exogenous and endogenous NO and HNO in A549 and RAW 264.7 cells with the flow cytometry application has also been demonstrated successfully.

We introduce herein, a novel copper complex-based fluorescent probe [CuII(DQ468)Cl]+ that exhibits a significant fluorescence turn-on response towards nitroxyl with high selectivity over other biological reactive oxygen, nitrogen and sulfur species, including nitric oxide.

A dual-emission pyrene-based new fluorescent probe ( N -(4-nitro-phenyl)- N ′-pyren-1-ylmethyl-ene-ethane-1,2-diamine (PyDA-NP)) displays green fluorescence for nitric oxide (NO) sensing, whereas it exhibits blue emission in the aggregated state. The mechanism of nitric oxide (NO/NO + ) sensing is based on N-nitrosation of aromatic secondary amine, which was not interfered by reactive oxygen species and reactive nitrogen species. The aggregation-induced enhancement of emission (AIEE) behaviors of the PyDA-NP could be attributed to the restriction of intramolecular rotation and vibration, resulting in rigidity enhancement of the molecules. The AIEE behavior of the probe was well established from fluorescence, dynamic light scattering, scanning electron microscopy, transmission electron microscopy, X-ray diffraction, optical fluorescence microscopy, and time-resolved photoluminescence studies. In a H 2 O/CH 3 CN binary mixture (8:2 v/v), the probe showed maximum aggregation with extensive (833-fold) increases in fluorescence intensity and high quantum yield (0.79). The aggregated state of the probe was further applied for the detection of nitroexplosives. It displayed efficient sensing of 2,4,6-trinitrophenol (TNP), corroborating mainly the charge-transfer process from pyrene to a highly electron-deficient TNP moiety. Furthermore, for the on-site practical application of the proposed analytical system, a contact-mode analysis was performed.

In this article, we have designed and synthesized a new, convenient and efficient phenanthroquinone-pyridoxal based fluorogenic probe PQPY, highly suitable for the selective and sensitive detection of nitric oxide in an aerated aqueous (7 : 3/H2O : MeCN) medium at pH 7.0 (10 mM HEPES buffer). Upon addition of nitric oxide, this probe exhibits emission in the green region (λem = 505 nm) which is ascribed to ICT (intramolecular charge transfer) from the phenanthroquinone moiety to the imidazole -N-N[double bond, length as m-dash]O fragment. The apparent formation constant, Kf, of the NO product of the ligand is (1.00 ± 0.2) × 105 M-1 and the LOD is 78 nM. The substantial enhancement of the life-time of the ligand (τ0 = 2.68 ns) occurs due to binding with nitric oxide (τ0 = 3.96 ns). This probe is low cytotoxicity, cell permeable and suitable for living cell imaging application.