A colorimetric Pb2+ chemosensor: Rapid naked-eye detection, high selectivity, theoretical insights, and applications

Quinoline-quinoline schiff-base as an effective chromogenic, fluorogenic, and smartphone assisted RGB detection of Pb2+ ion in near aqueous medium

A novel multimode colorimetric and fluorescent chemosensor was developed using an 8-hydroxy quinoline carbaldehyde Schiff base with a quinoline hydrazide probe (E)-2-((2-(quinolin-2-yl)hydrazineylidene)methyl)quinolin-8-ol (L). NMR (1H & 13C), FTIR, and HR-mass spectral characterization techniques confirmed the probe L structural conformation. As Probe L contacts Pb2+ ions, a color change and turn-off emission can be visually detected in EtOH:H2O (1:1, v/v, pH = 7.21) medium. The probe displays a good emission at 440 nm due to the combined ESIPT and ICT process. The Pb2+ ion interacts with the probe and selectively quenches fluorescence by inhibiting ESIPT and >CN- isomerization. As per Job's plot, L-Pb2+ complex formation occurred in a 1:1 stoichiometric ratio, with association constant (Ka) and quenching constant (Ksv) estimated at 1.52 × 105 M-1 and 4.12 × 105 M, respectively. The detection limits of Pb2+ by spectrophotometric and spectrofluorometric were 1.99 μM (41 ppb) and 23.4 nM (485 ppt), respectively. Additionally, the test paper kit and RGB tool were used to monitor the color changes of L with Pb2+ and the LOD was found to be 5.99 μM (125 ppb). Its recognition mechanism has been verified by 1H NMR, ESI-mass, and theoretical studies.

A new benzothiazole azo dye colorimetric chemosensor for detecting Pb2+ ion

In this work, a new benzothiazole azo dye sensor (BTS) was synthesized, and its cation binding affinity was studied using the colorimetric method, UV-vis, and ¹H NMR spectral data. The results revealed that the sensor BTS exhibits a remarkable tendency for Pb²⁺ ion to perform spontaneous visual color change from blue (BTS) to pink (BTS + Pb²⁺), without any color change in the aqueous solutions of other cations such as Hg²⁺, Cu²⁺, Al³⁺, Ni²⁺, Cd²⁺, Ag⁺_, Ba²⁺, K⁺, Co²⁺, Mg²⁺, Na⁺, Ca²⁺, Fe²⁺, and Fe³⁺ ions. The observed selectivity could be due to the formation of the complex (BTS + Pb²⁺⁾, which led to a blue shift from 586 nm (BTS) to 514 nm (BTS + Pb²⁺) in the UV spectrum. The job's plot provided the stoichiometry ratio of the complex (BTS + Pb²⁺) to be 1:1. The limit of detection (LOD) of BTS for Pb²⁺ ion sensing was obtained at 0.67 µM. Additionally, the binding constant for BTS toward Pb ²⁺ ion was studied using the Benesi-Hildebrand equation. As a result of the BTS test paper strips investigations, it was found that the synthesized sensor BTS could be used as a rapid colorimetric chemosensor for the detection of the Pb²⁺ ions in the distilled, tap, and sea waters.

New tricks and emerging applications from contemporary azobenzene research

Azobenzenes have many faces. They are well-known as dyes, but most of all, azobenzenes are versatile photoswitchable molecules with powerful photochemical properties. Azobenzene photochemistry has been extensively studied for decades, but only relatively recently research has taken a steer towards applications, ranging from photonics and robotics to photobiology. In this perspective, after an overview of the recent trends in the molecular design of azobenzenes, we highlight three research areas where the azobenzene photoswitches may bring about promising technological innovations: chemical sensing, organic transistors, and cell signaling. Ingenious molecular designs have enabled versatile control of azobenzene photochemical properties, which has in turn facilitated the development of chemical sensors and photoswitchable organic transistors. Finally, the power of azobenzenes in biology is exemplified by vision restoration and photactivation of neural signaling. Although the selected examples reveal only some of the faces of azobenzenes, we expect the fields presented to develop rapidly in the near future, and that azobenzenes will play a central role in this development.

Determination of Tetraethyl Lead in Gasoline fuel

  Tetraethyl lead TEL is an organometallic component that is added to gasoline to improve engine performance. This material is also called an anti-knock because it reduces the knocking of the engine. The engine starts to throttle if the oil in its pistons burns quickly or after a short period of time from entering it. In this study, a sensitive,  simple, economical, fast and accurate, an indirect spectral analytical method has been developed  using Eriochrome Black T as chelating agent without use of separation and  isolation to estimate the amount of lead in the gasoline by using UV-Visible spectrophotometer instrument. The accuracy and sensitivity of the method were 99.9067 ± 0.09 and 0.0338 while the limits of detection (LOD) and qualification (LOQ) were 0.0721 and    0.2186 μg ml-1 respectively. The developed method can be applied to water, biological, environmental and fuel sample.

Novel Diazocrowns with Pyrrole Residue as Lead(II)Colorimetric Probes

Novel 18- and 23-membered diazomacrocycles were obtained with satisfactory yields by diazocoupling of aromatic diamines with pyrrole in reactions carried under high dilution conditions. X-ray structure of macrocycle bearing five carbon atoms linkage was determined and described. Compounds were characterized as chromogenic heavy metal ions receptors. Selective color and spectral response for lead(II) was found in acetonitrile and its mixture with water. Complexation properties of newly obtained macrocycles with a hydrocarbon chain were compared with the properties of their oligoether analogs. The influence of the introduction of hydrocarbon residue as a part of macrocycle on the lead(II) binding was discussed. Selective and sensitive colorimetric probe for lead(II) in aqueous acetonitrile with detection limit 56.1 μg/L was proposed.

A Visual and Ratiometric Chemosensor Using Thiophene Functionalized Hydrazone for the Selective Sensing of Pb2+ and F- Ions

Herein, a simple, efficient ratiometric chemosensor was reported for the selective sensing of Pb²⁺ and F^- ions using thiophene functionalized hydrazone as a chemical probe. Hydrazone moiety was developed by utilizing thiophene/naphthalene as a platform for the particular recognition of cation and anion. The structures of the precursor (Z)-(1-(5-bromothiophen-2-yl)ethylidene)hydrazine (ABTH) and the final probe 1-((Z)-(((Z)-1-(5-bromothiophen-2-yl)ethylidene)hydrazono)methyl)naphthalen-2-ol (NAPABTH) were confirmed by ¹H, ¹³C-NMR and LC-MS spectroscopic methods. The interaction of NAPABTH with Pb²⁺ and F^- ions was visually observed by the formation of pink and dark yellow solutions, respectively. The detection limits were found to be very low for Pb²⁺ as 1.06 ppm and for F^- ions as 3.72 nM. This visual detection of Pb²⁺/F^- ions with satisfactory outcomes obtained from UV-Vis titrations. The sensing mechanistic pathways and stoichiometric ratios were obtained from DFT and Job's plot, respectively. The observed results are highly promising as highly selective chemosensor with lower detection limits for Pb²⁺ and F^- ions. This strategy could exhibit tremendous applications for the selective sensing of heavy metal cations with rapid sensitivity for the design of new devices.

The remarkable selectivity of the 2-arylquinoline-based acyl hydrazones toward copper salts: exploration of their catalytic applications in the copper catalysed N-arylation of indole derivatives and C1-alkynylation of tetrahydroisoquinolines via the A3 reaction

Different selective 2-arylquinoline-based acyl hydrazones toward copper(i) salts were synthesised, characterized and studied their applicability as metal ligands in diverse chemical transformations.

Efficient one-pot synthesis and dehydrogenation of tricyclic dihydropyrimidines catalyzed by OMS-2-SO3H, and application of the functional-chromophore products as colorimetric chemosensors

An efficient and convenient one-pot multicomponent reaction (MCR) for the synthesis and dehydrogenation of tricyclic dihydropyrimidine derivatives, catalyzed by –SO₃H functionalized octahedral manganese oxide molecular sieves (OMS-2-SO₃H) as a novel solid acid catalyst, is reported. All of the organic products and the catalyst were unambiguously characterized with conventional techniques including Fourier-transform infrared spectroscopy (FT-IR), scanning electron microscopy (SEM), high-resolution transmission electron microscopy (HRTEM), X-ray diffraction analysis (XRD), ¹H NMR, and ¹³C NMR spectroscopy. The targeted dehydrogenated chromophore compounds were successfully used as colorimetric chemosensors for detection of transition metals in aqueous solution. For example, 1-[4-(4-hydroxy-3-methoxy-phenyl)-2-methyl-benzo[4,5]imidazo[1,2-a]pyrimidin-3-yl]-ethanone (7d), exhibited high sensitivity and selectivity toward detection of Cr³⁺ over a panel of other transition metal cations. The interference of foreign ions was found to be negligible. It was found that a 1 : 1 complex of Cr³⁺ and 7d is responsible for the color change of the solution from ochre to brown. These newly devised chemosensors can also exhibit significant wavelength shifts (up to 100 nm) when used as pH indicators. 7d for example, showed a vivid and sharp color change from pink to yellow in the pH range of 4 to 6.

Hyperconjugated products of dihydropyrimidines may act as colorimetric chemosensors.

Dual Colorimetric Sensor for Hg2+/Pb2+ and an Efficient Catalyst Based on Silver Nanoparticles Mediating by the Root Extract of Bistorta amplexicaulis

Environmental pollution derivated from toxic metals and organic toxins is becoming a serious issue worldwide because of their harmful effects on the ecosystem and human health. Here we are reporting an extremely selective and cost-effective colorimetric sensor for simultaneous recognition of Hg2+ and Pb2+ by using green synthesized silver nanoparticles (AgNPs) mediated from the environmental friendly roots extract of Bistorta amplexicaulis. Biogenic synthesized AgNPs were well-characterized by various spectroscopic techniques e.g., UV-vis, FT-IR, XRD, AFM, and Zetasizer. The photophysical potential of synthesized AgNPs toward common metal cations was explored via absorption spectroscopy and colorimetric assay. The hypsochromic shift in the SPR band of AgNPs can easily be detected through naked eyes vision from dark brown to light yellow in the case of Hg2+. A substantial reduction in the absorbance of AgNPs was recorded upon mixing with Pb2+. AgNPs based colorimetric sensor is highly sensitive toward Hg2+ and Pb2+ with a limit of detection (LOD) of 8.0 × 10-7 M and 2.0 × 10-7 M for Hg2+ and Pb2+, respectively. Furthermore, AgNPs showed promising catalytic activity for the degradation of methyl orange dye. These results demonstrate that Bistorta amplexicaulis stabilized silver nanoparticles have potential applications as a colorimetric sensor and an effective catalyst for the degradation of methyl orange.