Sujan Biswas

Al3+ selective coumarin based reversible chemosensor: application in living cell imaging and as integrated molecular logic gate

An efficient coumarin based fluorescent ‘turn-on’ receptor (H2L) for the detection of Al3+ has been synthesized following simple Schiff base condensation of 4-hydroxy-3-acetylcoumarin with 2-amino-4-methylphenol. The receptor H2L shows about 21 fold increase in fluorescence intensity upon addition of Al3+ than in the case of other metals. The limit of detection is 0.39 μM. H2L is efficient in detecting Al3+ in the intracellular region of human cervical cancer cells and also exhibits an INHIBIT logic gate with Al3+ and EDTA as chemical inputs by monitoring both the absorption as well as emission mode. Theoretical calculations (DFT and TDDFT) are applied to interpret the sensing mechanism of the synthesized receptor.

Lewis base controlled supramolecular architectures via non-covalent interactions of dioxomolybdenum(VI) complexes with an ONS donor ligand: DFT calculations and biological study

Synthesis and characterization of five new mononuclear dioxomolybdenum(VI) complexes involving the Schiff base ligand (H2L) derived from 2-hydroxyacetophenone and S-benzyldithiocarbazate are reported. The ligand reacted with MoO2(acac)2 and a monodentate Lewis base forming cis-dioxo Mo(VI) complexes of the type [MoO2LB] (where B = THF, 1-methylimidazole, 1-allylimidazole, γ-picoline and pyridine). In all the complexes the ligand is coordinated to molybdenum via tridentate ONS donors phenolic oxygen, imine nitrogen and thioenolate sulfur. The crystal structures of the ligand and the five complexes have been determined by single crystal X-ray crystallography. These complexes are neutral with the metal having distorted octahedral geometry. All the complexes give rise to fascinating supramolecular architectures via hydrogen bonding and π–π stacking interactions. DFT calculations on the ligand and complexes are also carried out. The Schiff base ligand and its dioxomolybdenum(VI) complexes were tested against five human pathogenic bacteria Bacillus cereus, Bacillus subtilis, Proteus vulgaris, Escherichia coli, Pseudomonas aeruginosa and a fungi Candida albicans to assess their efficiency as antimicrobial agents. The MIC (minimum inhibitory concentration) for antimicrobial activity ranges from 1.0–10.0 μg per disc. They were also found to be effective antioxidants of the 2,2-diphenyl-1-picrylhydrazyl (DPPH) radical.

Supramolecular frameworks of binuclear dioxomolybdenum(VI) complexes with ONS donor ligands using 4,4′-azopyridine as a pillar: crystal structure, DFT calculations and biological study

Three new isostructural pillared binuclear dioxomolybdenum(VI) complexes [(MoO2L1)2(4,4′-azpy)] (1), [(MoO2L2)2(4,4′-azpy)] (2) and [(MoO2L3)2(4,4′-azpy)] (3) [where, 4,4′-azpy = 4,4′-azobis-(pyridine)] containing tridentate binegative Schiff base ligands (H2L1, H2L2 and H2L3) obtained by the condensation of salicylaldehyde and substituted salicylaldehyde with S-benzyl dithiocarbazate have been reported for the first time. These complexes have been characterized by spectroscopic and electrochemical studies. In all the complexes (1–3), 4,4′-azpy behaves as an auxiliary spacer and bridges the Mo(VI) centers giving rise to neutral 3D supramolecular frameworks. The cavities formed by hydrogen bonding interactions are capable of hosting guest molecules. The crystal structures reveal that each molybdenum site in the binuclear complexes adopts a distorted octahedral geometry. The morphology and structures of the complexes are further examined by SEM. Thermal behavior has been investigated to study the framework stabilities of these structures. Supportive DFT calculations on the complexes have been carried out. These ligands and complexes 1–3 have significant antimicrobial and antioxidant properties.

Novel pyridyl based azo-derivative for the selective and colorimetric detection of nickel(II).

A highly sensitive and selective pyridyl based colorimetric chemosensor (H2L) for the efficient detection of Ni(2+) has been reported. The synthesized chemosensor H2L is highly efficient in detecting Ni(2+) even in the presence of other metal ions that commonly co-exist with Ni(2+). H2L also shows distinct color change from green to deep red visible under naked eye due to specific binding with Ni(2+). This color change is due to formation of a new band at 510 nm upon gradual addition of Ni(2+). The association constant has been found to be 1.27×10(5) M(-1) with limit of detection (LOD) of 8.3×10(-7) M. Electronic structure of the H2L-Ni(2+) complex and sensing mechanism have been interpreted theoretically by DFT and TDDFT calculations.