Novel symmetric diimine-Schiff bases and asymmetric triimine-Schiff bases as chemosensors for the detection of various metal ions

Heterocyclic fluorescent Schiff base chemosensors for the detection of Fe(III) and Cu(II) ions

Two new Schiff bases were synthesized from 1-(2,4-dihydroxyphenyl)ethanone and pyridine derivatives. Both compounds were characterized using infrared, UV-Vis., 1H NMR, 13C NMR and mass spectral studies. Density functional theory (DFT) calculations were performed for both the Schiff bases with 6-31G(d, p) as the basis set. Vibrational frequencies calculated using the theoretical method were in good agreement with the experimental values. Both the Schiff bases were highly fluorescent in nature. The cation-recognizing profile of the compounds was investigated in aqueous methanol medium. The Schiff base 4-(1-(pyridin-4-ylimino)ethyl)benzene-1,3-diol (PYEB) was found to interact with Fe(III) and Cu(II) ions, whereas the Schiff base 4,4'-((pyridine-2,3-diylbis(azanylylidene))bis(ethan-1-yl-1-ylidene))bis(benzene-1,3-diol) (PDEB) was found to detect Cu(II) ions. The mechanism of recognition was established as combined excited state intramolecular proton transfer (ESIPT)-chelation-enhanced fluorescence (CHEF) effect and chelation-enhanced quenching (CHEQ) process for the detection of Fe(III) and Cu(II) ions, respectively. The stability constant of the metal complexes formed during the sensing process was determined. The limit of detection for Fe(III) and Cu(II) ions with respect to Schiff base PYEB was found to be 1.64 × 10-6 and 2.16 × 10-7 M, respectively. With respect to Schiff base PDEB, the limit of detection for Cu(II) ion was found to be 4.54 × 10-4 M. The Cu(II) ion sensing property of the Schiff base PDEB was applied in bioimaging studies for the detection of HeLa cells.

Colorimetric Detection of Multiple Metal Ions Using Schiff Base 1-(2-Thiophenylimino)-4-(N-dimethyl)benzene

In this paper, a Schiff base ligand 1-(2-thiophenylimino)-4-(N-dimethyl)benzene (SL1) bearing azomethine (>C=N-) and thiol (-SH) moieties capable of coordinating to metals and forming colored metal complexes was synthesized and examined as a colorimetric chemosensor. The sensing ability toward the metal ions of Cu2+, Cr3+, Fe2+ Ni2+, Co2+, Mg2+, Zn2+, Fe2+, Fe3+, NH4VO3 (V5+), Mn2+, Hg2+, Pb2+, and Al3+ was investigated in a mixture of H2O and dimethylformamide (DMF) solvent using the UV–Visible spectra monitoring method. The synthesized Schiff base ligand showed colorimetric properties with Cr3+, Fe2+, Fe3+, and Hg2+ ions, resulting in a different color change for each metal that could be identified easily with the naked eye. The UV–Vis spectra indicated a significant red shift (~69–288 nm) from the origin after the addition of the ligand to these metal ions, which may be due to ligand-to-metal charge-transfer (LMCT). On applying Job’s plot, it was indicated that the ligand binds to the metal ions in a 2:1 ligand-to-metal molar ratio. SL1 behaves as a bidentate ligand and binds through the N atom of the imine group and the S atom of the thiol group. The results indicate that the SL1 ligand is an appropriate coordination entity and can be developed for use as a chemosensor for the detection of Cr3+, Fe2+, Fe3+, and Hg2+ ions.

A naphthoquinone based colorimetric probe for real-time naked eye detection of biologically important anions including cyanide ions in tap water: experimental and theoretical studies

A naphthoquinone based colorimetric sensor (N) bearing hydrazone receptors in aqueous media was developed and its recognition properties towards biologically important anions in DMSO–water mixture (9 : 1) were investigated using spectroscopic methods. The hydrazone based receptors showed selectivity towards anions (F⁻, OH⁻, CN⁻ and AcO⁻), through naked eye observable colour changes, from green to light blue (F⁻, CN⁻ and AcO⁻) and violet (OH⁻). The colour changes were concomitant with spectral changes. The sensor could also detect the presence of fluoride ions in commercially available toothpastes, through remarkable colour and spectral changes. In addition, test paper strips prepared from N were able to detect the presence of cyanide (KCN) and hydroxide (NaOH) in tap water. The study was complimented by density functional theory computations to have more insight in the interaction between N and the anions.

A naphthoquinone based colorimetric sensor (N) bearing hydrazone receptors in aqueous media was developed and its recognition properties towards biologically important anions in DMSO–water mixture (9 : 1) were investigated using spectroscopic methods.

Study of the structure–bioactivity relationship of three new pyridine Schiff bases: synthesis, spectral characterization, DFT calculations and biological assays

Schiff bases exhibit a broad range of applications, including their use as catalysts, stabilizers, dyes, and intermediates in organic synthesis; and biological activities, such as antifungal properties.

Selective detection of Cu2+ and Co2+ in aqueous media: Asymmetric chemosensors, crystal structure and spectroscopic studies

Two new azo-azomethine receptors, H₂L¹ and H₂L², containing hydrazine, naphthalene and different electron withdrawing groups, Cl and NO₂, have been designed and synthesized for qualitative and quantitative detection of Cu²⁺ and Co²⁺ in aqueous media. The crystal structure of H₂L¹is reported. The H₂L¹was used as a chemosensor for selective detection of trace amount of Cu²⁺ in aqueous media. H₂L² was also applied to naked-eye distinction of Cu²⁺ and Co²⁺ from other transition metal ions in aqueous media. Detection limit of Cu²⁺ is 1.13μM and 1.26μM, in water, for H₂L¹ and H₂L², respectively, which are lower than the World Health Organization (WHO) recommended level. The binuclear Cu²⁺ and Co²⁺ complexes of the receptors have been also prepared and characterized using spectroscopic methods and MALDI-TOF mass analysis. Furthermore, the binding stoichiometry between the receptors upon the addition Cu²⁺ and Co²⁺ has been investigated using Job's plot. Moreover, the fluorescence emission spectra of the receptors and their metal complexes are also reported.