Rationally designed
multiple hydroxyl-group-based chemosensors L1–L4 containing arene-based fluorophores are presented for the
selective detection of Al3+ and Ga3+ ions. Changes
in the absorption and emission spectra of L1–L4 in ethanol were easily observable upon the addition of
Al3+ and Ga3+ ions. Competitive binding studies,
detection limits, and binding constants illustrate significant sensing
abilities of these chemosensors with L4, showing the
best results. The interaction of Al3+/Ga3+ ions
with chemosensor L4 was investigated by fluorescence
lifetime measurements, whereas Job’s plot, high-resolution
mass spectrometry, and 1H NMR spectral titrations substantiated
the stoichiometry between L4 and Al3+/Ga3+ ions. The solution-generated [L-M3+] species further detected pyrophosphate ion (PPi) by exhibiting
emission enhancement and a visible color change. The binding of Al3+/Ga3+ ions with chemosensor L4 was
further supported by density functional theory studies. Reversibility
for the detection of Al3+/Ga3+ ions was achieved
by utilizing a suitable proton source. The multiionic response, reversibility,
and optical visualization of the present chemosensors make them ideal
for practical applications for real samples, which have been illustrated
by paper-strip as well as polystyrene film-based detection.
The present perspective focusses on a variety of scaffolds based on a pyridine-2,6-dicarboxamide fragment and their noteworthy roles in coordination chemistry, stabilization of reactive species, synthetic modelling of some metalloenzyme active sites, catalytic organic transformations, and sensing as well as recognition applications. These examples illustrate the significance of synthetic scaffolds based on the pyridine-2,6-dicarboxamide fragment in synthetic chemistry in general and coordination chemistry in particular.
This work presents the synthesis and characterization of two palladium-based fluorescent macrocycles offering hydrogen-bonding cavities of contrasting dimensions. Both palladium macrocycles function as chemosensors for the detection of nitroaromatics, whereas the larger macrocycle not only illustrates nanomolar detection of picric acid but also transports its significant amount from an aqueous to an organic phase.
Pyridine-2,6-dicarboxamide based scaffolds with appended naphthyl groups act as fluorescent probes for the selective detection of Pd2+ ions in aqueous medium and have applications as paper-strip sensors, as polystyrene films, and in cell imaging.
Two post-functionalized chemosensors display remarkable sensing of Zn2+ and Cd2+ ions via generating corresponding metal–organic frameworks (MOFs), whereas nitrate and nitrite ions reverse the MOF-polymerization process.
Amide based probes containing phenyl (L1), naphthyl (L2) and anthracenyl (L3) groups were screened towards metal ions. Probes L2 and L3 display sensing for Fe2+ and Fe3+ ions. The L3–Fe3+ system is shown to have potential applications in logic gates and cell imaging.
Pyridine-2,6-dicarboxamide based scaffolds with different appendages act as chemosensors for the selective detection of S2- ion, as well as gaseous H2S, in primarily aqueous media. Out of nine synthesized chemosensors, one with benzothiazole ring appendages was found to be highly selective for S2- ion and gaseous H2S. A series of spectroscopic studies confirmed that sulfide ion abstracts amidic N-H groups thus leading to the in situ generation of HS- ion, which remain bound to the pincer cavity of the resultant anionic chemosensor, and it was found that acetic acid could be used to reverse this process. It was essential for a chemosensor to feature a pincer cavity to recognize sulfide ion, whereas the sensing mechanism involved the deprotonation of the amidic N-H groups. We also illustrate the detection of sulfide ions and gaseous H2S in live cells and paper-strip sensing applications.
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