4-(8-Quinolyl)amino-7-nitro-2,1,3-benzoxadiazole as a new colorimetric probe for rapid and visual detection of Hg2+

A pyridyl functionalized rhodamine chemodosimeter for selective fluorescent detection of mercury ions and cell imaging

Rhodamines gain sustained attention owing to their great potential for probe design applications. Herein, the facile preparation of a new pyridyl functionalized rhodamine dye PR is reported, which has stable fluorescence signal in water with maximum emission peak at 594 nm and Stokes shift of 81 nm. Based on dye PR, a new fluorescent probe PRHg has been developed by modifying the spirolactone of PR with hydrazine hydrate so as to produce spirolactam recognizing group for sensing of Hg²⁺. PRHg exhibits high selectivity and sensitivity towards Hg²⁺ in water/ethanol (v/v = 4/1, pH = 7.0) by a specific Hg²⁺-binding promoted spirolactam ring opening and hydrolyzing process. And, the detection limit for Hg²⁺ is evaluated to be 8.5 nM. Besides, the probe can respond to Hg²⁺ within 40 min and over a wide pH range from 4.0 to 10.0. Moreover, PRHg (40 µM) performs low cytotoxicity to HeLa cells (over 91.0 % cell survival rate), which allows the probe to be employed for tracing intracellular Hg²⁺ by fluorescence imaging.

A fluorimetric testing strip for the visual evaluation of mercury in blood using copper nanoclusters with DMSO-enhanced fluorescence and stability

A fluorimetric analytical method using test strips has been fabricated for detecting Hg²⁺ ions in blood by using copper nanoclusters (Cu NCs) prepared via a biomineralization route. Unexpectedly, the as-prepared Cu NCs displayed greatly amplified red fluorescence once dispersed in DMSO, the intensity of which decreased specifically in the presence of Hg²⁺. Moreover, the resultant Cu NCs were deposited onto test strips to be further fast dried on superhydrophobic substrates in vacuum. The test strip-based fluorimetry can allow for the direct analysis of Hg²⁺ in blood in the linear concentration range of 0.10-1000 nM. Importantly, this solvent-enhanced fluorescence protocol for different metal probes such as Cu NCs promises extensive analysis applications for designing numerous fluorimetric platforms such as test strips.

Intrabacterial Metabolism Obscures the Successful Prediction of an InhA Inhibitor of Mycobacterium tuberculosis

Tuberculosis, caused by Mycobacterium tuberculosis (M. tuberculosis), kills 1.6 million people annually. To bridge the gap between structure- and cell-based drug discovery strategies, we are pioneering a computer-aided discovery paradigm that merges structure-based virtual screening with ligand-based, machine learning methods trained with cell-based data. This approach successfully identified N-(3-methoxyphenyl)-7-nitrobenzo[c][1,2,5]oxadiazol-4-amine (JSF-2164) as an inhibitor of purified InhA with whole-cell efficacy versus in vitro cultured M. tuberculosis. When the intrabacterial drug metabolism (IBDM) platform was leveraged, mechanistic studies demonstrated that JSF-2164 underwent a rapid F₄₂₀H₂-dependent biotransformation within M. tuberculosis to afford intrabacterial nitric oxide and two amines, identified as JSF-3616 and JSF-3617. Thus, metabolism of JSF-2164 obscured the InhA inhibition phenotype within cultured M. tuberculosis. This study demonstrates a new docking/Bayesian computational strategy to combine cell- and target-based drug screening and the need to probe intrabacterial metabolism when clarifying the antitubercular mechanism of action.

A Unique Sensitive and Highly Selective Fluorescent Naphthodiaza-Crown Macrocyclic Ligand Chemosensor for Hg2+ in Water

The noticeable enhancement in fluorescence emission of O₂N₂-donor naphthodiaza-crown macrocyclic ligand (L) in the presence of Hg²⁺ was observed in which the fluorescence quantum yield of free ligand L as well as L/Hg²⁺ complex were found to be as 0.29 and 0.49, respectively. The observed ultra-low limit of detection (LOD) for Hg²⁺ by L was determined as low as 1.0 × 10^-11 M in water. A 1:1 stoichiometry was also established for L/Hg²⁺ together with a binding constant K _BH = 66,543 by employing fluorescence spectrophotometry. The competition experiments on L/Hg²⁺ demonstrated highly selective detection of Hg²⁺ in the presence of the library cations. A two path mechanism for detection of metal ion in terms of coordination of metal ion to L and/or the formation of counter ion was proposed by using of ¹H NMR and fluorescence spectroscopy. Graphical Abstract pH dependence mechanism of interaction between Hg²⁺ and macrocyclic ligand L.

A New Reactive 1,8-Naphthalimide Derivative for Highly Selective and Sensitive Detection of Hg2

A 1,8-naphthalimide derivative with a reactive aliphatic hydroxyl was designed and synthesized as a fluorescent probe. Its structure was characterized by IR, ¹H NMR, ¹³C NMR, LC-MS and HPLC. The probe showed high selectivity and sensitivity to Hg²⁺ over other metal ions such as Pb²⁺, Na⁺, K⁺, Cd²⁺, Cr³⁺, Zn²⁺, Cu²⁺, Ni²⁺, Ca²⁺, Fe³⁺, Fe²⁺, Co²⁺, Mn²⁺ and Mg²⁺ in MeCN/H₂O (15/85, v/v). The increase in fluorescence intensity was linearly proportional to the concentration of Hg²⁺ in the range of 18-40 μM with a detection limit of 1.38 × 10^-7 mol/L. The probe could work in a pH span of 4.3-9.0 and respond to Hg²⁺ quickly with strong anti-interference ability. Job's plot suggested a 1:2 complex of the probe and Hg²⁺.

4-(8-quinolyl)amino-7-nitro-2,1,3-benzoxadiazole as a new selective and sensitive fluorescent and colorimetric pH probe with dual-responsive ranges in aqueous solutions

Fluorescent and colorimetric pH probe possess many advantages including rapid response time, nondestructive testing, and excellent pH sensitivity. However, they usually cannot be utilized simultaneously in both acidic and basic pH ranges. In this study, a new selective and sensitive fluorescent and colorimetric pH probe, 4-(8-quinolyl)amino-7-nitro-2,1,3-benzoxadiazole (1), was designated and synthesized. The optical probe exhibited dual-responsive pH ranges to both acidic and basic aqueous solutions. When the solution pH was gradually increased from 8.5 to 13.3, the absorption spectra of 1 showed an obvious hyperchromicity, accompanied with a red shift of the absorption band at 340 nm, a blue shift of the absorption band at 482 nm, and a distinct color change from orange to violet pink to yellow. Within the pH range from 2.2 to 0.2, the fluorescent spectra of 1 showed a "turn-on" response signal to solution pH. In order to understand the response mechanism of the probe to solution pH, the probe molecule was split into two parts, 8-aminoquinoline (2) and 4-amino-7- nitro-benzofurazan (3). UV-vis absorption and fluorescent experiments of 2 and 3 indicated that both are sensitive optical pH probes. Furthermore, the NMR experiment of 1 was explored in basic and acidic conditions. The results indicated that the colorimetric responses of 1 to pH under basic condition should be attributed to the deprotonation of the imino group on the quinolyl ring, and the fluorescent recognition of 1 to pH under acidic condition was probably due to the protonation of the nitrogen atoms from the benzofurazan and quinolyl rings.

A Highly Selective Fluorescent Indicator for Copper Based on a Boron Complex

Condensation of 4-(diethylamino)salicylaldehyde with aqueous hydrazine, followed by complexation with BF3·OEt2 gives a fluorescent indicator highly selective for copper. The indicator forms a 2 : 1 complex with Cu2+ and displays a highly sensitive and selective fluorescent quenching action with Cu2+ upon excitation at 440 nm in water/THF (7 : 3, v/v) solution. This action is pH-independent over the range 4.5 < pH < 9.5.

Synthesis and Fluorescent Properties of a Novel Dansyl-based Fluorescent Probe for Hg2+

A novel turn-off fluorescent probe containing a dansyl fluorophore has been synthesised. Its recognition properties towards various metal ions have been studied by fluorescence spectrometry. The compound showed a high sensitivity and selectivity to Hg2+ ion and a complexation ratio towards Hg2+ of 2: 1. Its fluorescence intensity varied almost linearly versus the concentration of Hg2+ (0.8–8.4 μmol L−1), and the detection limit of Hg2+ was estimated to be 0.88 μmol L−1.

Synthesis, spectroscopic and DFT studies of novel fluorescent dyes: 3-aminoimidazo[1,2-a]pyridines possessing 4-pyrone moieties

A series of novel imidazo[1,2-a]pyridines possessing 4-pyrone ring were synthesized by three-component condensation of 4-pyrone carbaldehydes, 2-aminopyridines and isocyanides. Bismuth (III) chloride was used as a catalyst in these reactions and desired products were synthesized in good yields at a very short period of time under solvent free conditions. UV-Vis absorption and fluorescence emission spectra of these compounds were investigated. It shown that two of these compounds (10f and 10g) exhibit intense fluorescence in dichloromethane. Optimized ground-state molecular geometries and orbital distributions of these two fluorescent dyes were obtained using density functional theory (DFT). Thermogravimetric analysis and electrochemical properties of these compounds were also studied.