Nikhil Ranjan Pramanik

Bio: Nikhil Ranjan Pramanik is an academic researcher from Bidhannagar College. The author has contributed to research in topics: Ligand & Schiff base. The author has an hindex of 10, co-authored 20 publications receiving 223 citations.

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

Abstract: 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.

Chemical, electrochemical and structural studies of some cis -dioxomolybdenum(VI) complexes of two tridentate ONS chelating ligands

Abstract: Several cis-dioxomolybdenum complexes of two tridentate ONS chelating ligands H2L1 and H2L2 (obtained by condensation of S-benzyl and S-methyl dithiocarbazates with 2-hydroxyacetophenone) have been prepared and characterized. Complexes 1 and 2 are found to be of the form MoO2 (CH3OH) L1 · CH3OH and MoO2L, respectively, (where L2– = dianion of H2L1 and H2L2). The sixth coordination site of the complexes acts as a binding site for various neutral monodentate Lewis bases, B, forming complexes 3–10 of the type MoO2LB (where B = γ-picoline, imidazole, thiophene, THF). The complexes were characterized by elemental analyses, various spectroscopic techniques, (UV-Vis, IR and 1H NMR), measurement of magnetic susceptibility at room temperature, molar conductivity in solution and by cyclic voltammetry. Two of the complexes MoO2(CH3OH) L1 · CH3OH (1) and MoO2L1(imz) (5) were structurally characterized by single crystal X-ray diffraction. Oxo abstruction reactions of 1 and 5 led to formation of oxomolybdenum(IV) compl...

Syntheses, crystal structures, DFT calculations, protein interaction and anticancer activities of water soluble dipicolinic acid-imidazole based oxidovanadium(iv) complexes.

Abstract: Three novel water soluble neutral mononuclear oxidovanadium(IV) complexes 1–3, [VOLB2] (where H2L = dipicolinic acid (DPA) and B = imidazole (1)/1-methylimidazole (2)/1-allylimidazole (3)), were synthesized by the reaction of [VOL(H2O)2] with imidazole/1-methylimidazole/1-allylimidazole in ethanol. The complexes were thoroughly characterized by elemental analysis, IR, UV-Vis and EPR spectroscopy, magnetic susceptibility, cyclic voltammetry and single crystal X-ray diffraction techniques. In all the complexes the vanadium(IV) centre assumes a distorted octahedral environment. All the three complexes have similar structures and contain a range of intramolecular interactions such as hydrogen bonding, C–H⋯π, and π⋯π stacking dominating their supramolecular architectures. A thermal study of the complexes was carried out to analyze their stability. The energy of non-covalent interactions and frontier orbitals for the complexes were also calculated by DFT. In order to investigate the binding interactions and conformational changes of the secondary structure of bovine serum albumin (BSA) with the complexes, absorption, fluorimetric titration and circular dichroism measurements in aqueous medium were carried out. Molecular docking studies have also been carried out to understand the binding modes and interaction patterns of the oxidovanadium(IV) complexes with BSA. The anticancer activities of the ligand and complexes 1–3 were tested against the human hepatic carcinoma cell line Hep3B. The complexes showed prominent cytotoxicity towards cancer cells.

New polymeric, dimeric and mononuclear dioxidomolybdenum(VI) complexes with an ONO donor ligand: crystal structures, DFT calculations, catalytic performance and protein binding study of the ligand

Abstract: Reaction of [MoO2(acac)2] with a new ONO donor Schiff base ligand (H2L), derived from 2-aminobenzoylhydrazide and benzoyl acetone in methanol under refluxing conditions, yields polymeric [MoO2L]n (1) and dimeric [MoO2L]2·THF (2) dioxidomolybdenum(VI) complexes. Complexes 1 and 2 undergo reaction with monodentate Lewis bases forming mononuclear complexes [MoO2L(3-pic)] (3), [MoO2L(1-allylimz)] (4) and [MoO2L(DMSO)] (5). In these complexes, the ligand is coordinated to the cis-[MoO2]2+ cores through enolic oxygens and an azomethine nitrogen. In complexes 3 and 4 the remaining sixth coordination site is occupied by the nitrogen atoms and in complex 5 by the oxygen atom of the Lewis base. The crystal structures of these complexes (1–5) have been determined by single crystal X-ray diffraction. The molybdenum atom exhibits a distorted octahedral coordination sphere. In complex 1, a 1D zigzag polymeric chain is formed through OMo–O interactions. In complex 2, a centrosymmetric dimer is formed through weak interaction of the non-coordinating amine nitrogen with the molybdenum centre. In contrast complexes 3, 4 and 5 are monomeric. The investigated complexes have also been characterized by elemental analysis, various spectroscopic techniques, thermogravimetric analysis and cyclic voltammetry. Supportive DFT calculations on the complexes have been carried out. The dioxidomolybdenum(VI) complexes have been tested for catalytic epoxidation and oxidative bromination of styrene. Fluorescence spectral measurements carried out by varying the concentration of the ligand indicate strong fluorescence resonance energy transfer (FRET) from BSA to the ligand and from the binding studies it is revealed that BSA has two binding sites for the ligand.

Thiosemicarbazones, semicarbazones, dithiocarbazates and hydrazide/ hydrazones: Anti - Mycobacterium tuberculosis activity and cytotoxicity

Abstract: The aim of this study was to identify a candidate drug for the development of anti-tuberculosis therapy from previously synthesized compounds based on the thiosemicarbazones, semicarbazones, dithiocarbazates and hydrazide/hydrazones compounds. The minimal inhibitory concentration (MIC) of these compounds against Mycobacterium tuberculosis was determined. Their in vitro cytotoxicity to J774 cells (IC50) was determined to establish a selectivity index (SI) (SI=IC50/MIC). The best compounds were the thiosemicarbazones (2, 3 and 4) and the hydrazide/hydrazones (14, 15, 16 and 18). The results are comparable to or better than those of "first line" or "second line" drugs commonly used to treat TB, suggesting these compounds as anti-TB drug candidates.

Transition metal complexes of symmetrical and asymmetrical Schiff bases as antibacterial, antifungal, antioxidant, and anticancer agents: progress and prospects

Abstract: Abstract The huge research on Schiff base coordination complexes in the past few decades has given rise to several new molecules that have been of biological importance. The ease with which the Schiff base ligands are designed and prepared and their pattern is elucidated have made them to be referred to as “fortunate ligands” possessing azomethine derivatives, the C=N linkage that is essential for biological activity, including antibacterial, antifungal, antioxidant, anticancer, and diuretic activities. A variety of Schiff base and its complexes have been studied as model molecules for biological oxygen carrier systems. The uses of Schiff bases as DNA-cleaving agents and its mode of interaction and free-radical scavenging properties are described. The review encapsulates the applications of Schiff bases and their complexes.