Hugo Schiff (1864), was the first who synthesized Schiff bases by the condensation reaction of primary amines with carbonyl compounds (aldehyde or ketone). Schiff bases display several structural and electronic features that allow their application in different fields, ranging from medicinal to chemosensing. Schiff bases coordinate with various metal ions and form stable complexes. Due to their excellent coordination ability, Schiff bases are used as fluorescent turn-on/turn-off and colorimetric chemosensors for the detection of different metal cations including Ag+, Cu2+, Co2+, Mn2+, Cd2+, Hg2+, Ni2+, Zn2+, Pd2+, Fe3+, and Al3+ in different samples. This review article covers a wide range of Schiff bases used in chemosensing applications for various metal ions (e.g., monovalent, divalent and trivalent cations) in different biological, agricultural and environmental media.

Recent developments in fluorescent and colorimetric chemosensors based on schiff bases for metallic cations detection: A review

The Cambridge Crystallographic Database has been searched for the presence of intermolecular C–H⋯π(chelate ring) interactions, known to be stabilising, in the crystals of the first-row transition metal dithiocarbamates, i.e. containing anionic ligands of the type −S2CNR2, R = H, alkyl and aryl. A significant propensity to form C–H⋯π(chelate ring) interactions is noted, especially in crystals of nickel and copper dithiocarbamates. The participating hydrogen atoms are characterised as being near an electronegative atom/substituent encouraging their engagement in this supramolecular synthon. The survey shows that an open, square-planar geometry is not a prerequisite for a C–H⋯π(chelate ring) interaction but, allows, on average, more of these contacts leading to one- and two-dimensional architectures. It is concluded that a search for a C–H⋯π(chelate ring) supramolecular synthon should be included in any detailed analysis of the molecular packing of metal-containing crystals.

The remarkable propensity for the formation of C–H⋯π(chelate ring) interactions in the crystals of the first-row transition metal dithiocarbamates and the supramolecular architectures they sustain

Cadmium is a heavy metal which exists widely in industrial and agricultural production and can induce a variety of diseases in organisms. Therefore, its detection is of great significance in the fields of biology, environment and medicine. Fluorescent probe has been a powerful tool for cadmium detection because of its convenience, sensitivity, and bioimaging capability. In this paper, we reviewed 98 literatures on cadmium fluorescent sensors reported from 2017 to 2021, classified them according to different fluorophores, elaborated the probe design, application characteristics and recognition mode, summarized and prospected the development of cadmium fluorescent and colorimetric probes. We hope to provide some help for researchers to design cadmium fluorescent probes with higher selectivity, sensitivity and practicability.

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Recent progress in cadmium fluorescent and colorimetric probes

Integrated Spectroscopic, Bio-active Prediction and Analytics of Isoquinoline Derivative for Breast Cancer Mitigation

Coordination array for accurate colorimetric sensing of multiple heavy metal ions.

An alkyne arms containing salen-type Schiff base ligand, 6,6′-((1E,1′E)-(1,2-phenylenebis(azanylylidene))bis(ethan-1-yl-1-ylidene))bis(3-(prop-2-yn-1-yloxy)phenol) (H2L), is reported here as a dual chemosensor for CdII and PbII ions. The ligand H2L was characterized by various spectral methods. The ligand H2L acts as a dual sensor for CdII and PbII in methanol/HEPES buffer (5 mM, pH 7.3; 1 : 9 v/v) at room temperature with well-separated excitation and emission wavelengths. The emission intensity at 553 nm of H2L is shifted and a new band appeared at 578 nm with the increase in the presence of CdII when it is excited at 420 nm. With excitation at 410 nm, the emission intensity of H2L at 485 nm shifted and a new band appeared at 505 nm with the increase in the presence of PbII. The quantum yield of H2L increases considerably in the presence of CdII and PbII. The compound H2L is non-fluorescent; however, in the presence of CdII and PbII, the compound H2L is highly fluorescent with well-separated excitation and emission wavelengths, indicating that the metal ion is coordinated through phenolic oxygen and imine nitrogen of the Schiff base blocking the PET (Photoinduced Electron Transfer) process and stimulating the CHEF (Chelation Enhanced Fluorescence) process, to increase the fluorescence intensity of H2L. The detection limit values of H2L are in a nano-molar range for both metal ions, confirming very high sensitivity of H2L. The L·MII binding mode and the recognition mechanism of the sensor were explored by Job's plot, 1H NMR, FT-IR, pH and DFT calculations. Besides, H2L was successfully utilized in cell imaging studies for both metal ions in MCF 7 cells.

Biocompatible alkyne arms containing Schiff base fluorescence indicator for dual detection of CdII and PbII at physiological pH and its application to live cell imaging.

Spectral, NBO, NLO, NCI, aromaticity and charge transfer analyses of anthracene-9,10-dicarboxaldehyde by DFT.

Crystal structure and evaluating CH⋯π (aryl/chelate) interactions in bis(2-{[(2-hydroxyethyl)imino]-methyl}-4,6-diiodophenolato)-palladium(II) Schiff base complex derived from (E)-2-(((2-hydroxyethyl)imino)methyl)-4,6-diiodophenol

J. Winfred Jebaraj

Papers

Biocompatible alkyne arms containing Schiff base fluorescence indicator for dual detection of CdII and PbII at physiological pH and its application to live cell imaging.

Spectral, NBO, NLO, NCI, aromaticity and charge transfer analyses of anthracene-9,10-dicarboxaldehyde by DFT.

Crystal structure and evaluating CH⋯π (aryl/chelate) interactions in bis(2-{[(2-hydroxyethyl)imino]-methyl}-4,6-diiodophenolato)-palladium(II) Schiff base complex derived from (E)-2-(((2-hydroxyethyl)imino)methyl)-4,6-diiodophenol

Chemical synthesis, spectroscopic analysis, antioxidant, and antimicrobial activities of some hydrazones derived from 4-fluorobenzohydrazide