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A new coumarin-based fluorescent chemosensor, 3, incorporating a hydrazone (-NH-N=C-), was designed and synthesized. The chemosensor displayed higher affinity towards Fe3+ in water-acetonitrile solution in the presence of other competing cations in emission and absorption essays. The binding stoichiometry between the chemosensor 3 and Fe3+ was shown to occur in a 1:1 ratio, and the binding modes of the chemosensor towards Fe3+ were identified through the emission response, ¹H NMR, FT-IR and molecular modelling studies. The hydroxyl and amine functionalities on 3 were recognized as possible binding sites. The chemosensor presented a limit of detection, a limit of quantification and the association constant of 0.45 µM, 1.50 µM and 3.01 x 10¹ M-1, respectively. [ABSTRACT FROM AUTHOR]

The green hydrogen economy offers synthetic green energy with significant impacts and is environmentally friendly compared to current fossil-based fuels. Exploration of green hydrogen energy in Southern Africa is still in the initial stages in many low-resourced settings aiming to benefit from sustainable green energy. At this early stage, potential benefits to society are yet to be understood. That is why the socio-economic impact of green hydrogen energy must be explored. This paper reviews the current literatures to describe the potential socio-economic effects in the Southern African Development Community (SADC). The review supports the view that green hydrogen will be beneficial and have great potential to revolutionise agricultural and industrial sectors, with advanced sustainable changes for both production and processing. This paper also examines how sustainable green hydrogen energy production in Southern Africa will provide economic value in the energy export sector around the world and support climate change initiatives. Further, it discusses the impacts of the green hydrogen value addition chain and the creation of green jobs, as well as the need for corresponding investments and policy reforms. It is also noted that the green hydrogen economy can contribute to job losses in fossil fuel-based industries, so that the workforce there may need re-skilling to take up green jobs. Such exchanges may deter efforts towards poverty alleviation and economic growth in SADC. [ABSTRACT FROM AUTHOR]

Pollution caused by the release of toxic heavy metals into the environment by industrial and farming processes has been regarded as a major problem worldwide. This has attracted a great deal of attention into restoration and remediation. Mercury is classified as a toxic heavy metal which has posed significant challenges to public and environmental health. To date, conventional methods for mercury detection rely on expensive, destructive, complex, and highly specialized methods. Evidently, there is a need to develop systems capable of easily identifying and quantifying mercury within the environment. In this way, organic-based colorimetric chemosensors are gaining increasing popularity due to their high sensitivity, selectivity, cost-effectiveness, ease of design, naked-eye, and on-site detection ability. The formation of coumarin-azo derivative AD1 was carried out by a conventional diazotization reaction with coumarin-amine 1c and N,N-dimethylaniline. Sensor AD1 displayed remarkable visual colour change upon mercury addition with appreciable selectivity and sensitivity. The detection limit was calculated as 0.24 µM. Additionally, the reversible nature of AD1 allowed for the construction of an IMPLICATION type logic gate and Molecular Keypad Lock. Chemosensor AD1 displayed further sensing applications in real-world water samples and towards on-site assay methods. Herein, we describe a coumarin-derived chemosensor bearing an azo (N = N) functionality for the colorimetric and quantitative determination of Hg2+ in organic and aqueous media. [ABSTRACT FROM AUTHOR]

C9H9IO3, orthorhombic, Pnma (no. 62), a = 10.9655(5) Å, b = 6.5768(3) Å, c = 13.3770(6) Å, V = 964.7 Å3, Z = 4, Rgt(F) = 0.0130, wRref(F2) = 0.0350, T = 200 K. [ABSTRACT FROM AUTHOR]

A novel colorimetric and fluorometric method based on coumarin as signalling unit was developed for Hg2+ recognition and quantification. Initially, the alkyne functionality was incorporated into a coumarin system and the resulting molecule showed higher specificity and sensitivity for Hg2+ over other cations in both absorption and emission sensing assays. The Hg2+ recognition was detected as visible colour change from colourless to yellow and as fluorescence quenching. The colour change was assigned to the increased intramolecular charge transfer (ICT) in the signalling unit upon Hg2+ binding whereas a decline in the fluorescence intensity was ascribed to the heavy atom effect from Hg2+. In order to generate a material with high sensing performance level, alkyne-functionalized molecule was hosted into a polymeric material. The resulting functionalized polymer showed higher sensitivity and selectivity for Hg2+ over its corresponding coumarin molecule. The investigation of the possible binding modes for Hg2+ suggested both alkyne and triazole functionalities as potential binding sites for Hg2+. The limit of detection (LOD) and limit of quantification (LOQ) of the proposed method were evaluated and values less than a recommended maximum level of Hg2+contaminant in drinking water (2.00 μg/L) were obtained (LOD = 0.44 μg/L and LOQ = 1.33μg/L). The real-life application of the method was investigated using natural water samples containing Hg2+ levels equivalent to the maximum tolerable concentration of Hg2+ in drinking water. The outcomes suggested that the method could be used in the sensing and determination of Hg2+ level of contaminant in the environment. [ABSTRACT FROM AUTHOR]

A novel fluorescent polymer for Hg2+ recognition was developed based on the phototautomerism mechanism of 7-hydroxycoumarin in aqueous solution. The developed system showed higher sensitivity and specificity towards Hg2+ in the acetonitrile/water mixture over various other metal ions, with a significant fluorescence quenching of the main emission band. It was shown that the presence of Hg2+ affects the chemical equilibrium of the 7-hydroxycoumarin phototautomers through the excited state intramolecular proton transfer (ESIPT) mechanism, which results in ratiometric fluorescence response upon stepwise addition of Hg2+. The occurrence of ESIPT mechanism was explained based on a comparison of the 1H NMR spectra of the starting alkynylated coumarin (4) in a non-polar aprotic solvent (CDCl3) and in a polar aprotic solvent (DMSO-d6). This was further confirmed by 1H NMR of 4 upon stepwise addition of Hg2+ in a polar aprotic solvent (DMSO-d6). From titration experiments, a higher sensitivity with a detection limit at the nanomolar level (50 nM) was observed and the response was fast and reversible. The real applications of the developed system were investigated in real samples and satisfactory results were obtained for both fresh and lake water samples. [ABSTRACT FROM AUTHOR]

A novel fluorescent polymer with pendant triazolyl coumarin units was synthesized through radical polymerization. The polymer showed reasonable sensitivity and selectivity towards Cu2+ in acetonitrile in comparison to other tested metal ions with a significant quenching effect on fluorescence and blue shifting in the range of 20 nm. The blue shift was assigned to the conformation changes of the diethylamino group from the coumarin moiety which led to planarization of the triazolyl coumarin units. The possible binding modes for Cu2+ towards the polymer were determined through the comparison of the emission responses of the polymer, starting vinyl monomer and reference compound, and the triazole ring was identified as one of the possible binding sites for Cu2+. The detection limits of the polymer and vinyl monomer towards Cu2+ were determined from fluorescence titration experiments and a higher sensitivity (35 times) was observed for the polymer compared with its starting monomer. [ABSTRACT FROM AUTHOR]

[Display omitted] • An azo dye of coumarin connected to phenolic derivative was synthesized via a conventional diazotization reaction in acidic medium. • Investigation of spectroscopic properties of the synthesized dye in different solvents indicated the possibility of azo-hydazone tautomerism to occur which was confirmed by spectroscopic assays such as 1H NMR, absorption and emission assays, and theoretical studies. • Influence of metal ions on the azo-hydrazone chemical equilibrium were studied and found Cu2+ as only metal ions which can affect established chemical equilibrium toward azo form and leads to the change in both visual appearance and spectroscopic properties of the dye. • The limit of detection (0.0779 mg/L) and limit of quantification (0.236 mg/L) for Cu2+ were determined and found to be much lower than the World Health Organization (WHO) guideline limit for Cu2+ levels in drinking water. • The dye showed potential applications as a sensor in colorimetric and spectroscopic detection and quantification of Cu2+ in domestic and environmental water samples, photo-imprinting and as a logic gate. A new tailor-made azo dye of coumarin connected to phenolic derivative is presented herein. Azo-hydrazone tautomerism in aqueous solution of the dye was observed and studied using spectroscopic assays such as 1H NMR, absorption and emission assays, and theoretical studies. Tautomerism was attributed to the presence of a labile phenolic hydrogen in the ortho position to the azo functionality and the hydrazone was found to be the more dominant tautomer. Influence of metal ions on the azo-hydrazone chemical equilibrium and how the accompanying colour and spectroscopic changes can be exploited for various functions, especially the detection and quantification of Cu2+ in aqueous environments was explored. The presence of Cu2+ affects the azo-hydrazone equilibrium resulting in visual appearance and spectroscopic changes and the likely binding sites for Cu2+ were evaluated. Cu2+ pushes the azo-hydrazone equilibrium towards the more conjugated form and the presence of other metal ions does not have any perceivable impact on this mechanism. The dye showed potential applications as a sensor in colorimetric and spectroscopic detection and quantification of Cu2+ in domestic and environmental water samples, photo-imprinting and as a logic gate. The limits of detection (LOD) and quantification (LOQ) for Cu2+ were found to be 0.0779 mg/L and 0.236 mg/L, respectively, much lower than the World Health Organization (WHO) guideline limit for Cu2+ levels in drinking water. [ABSTRACT FROM AUTHOR]

Iodine-methanol mediated oxidative-aromatization of 2-aryl-6,8-dibromo-2,3- dihydroquinolin-4(1H)-ones afforded the corresponding 2-aryl-6,8-dibromo-4-methoxyquinolines in high yield and purity. The isomeric 1-(2-amino-3,5-dibromophenyl)-3-aryl-2- propen-1-ones reacted with iodine in methanol afford in a single pot operation the corresponding 2-aryl-6,8-dibromo-4-methoxyquinoline (major) and 2-aryl-6,8- dibromoquinolin-4(1H)-one (minor) products that were separated in sequence by column chromatography on silica gel. Suzuki-Miyaura cross-coupling of the 6,8-dibromo-4- methoxyquinoline derivatives with excess arylvinylboronic acids afforded the corresponding 2-aryl-6,8-bis(2-arylethenyl)-4-methoxyquinolines. The absorption and fluorescence properties of these compounds were also determined. [ABSTRACT FROM AUTHOR]