• BHASKAR BISWAS

      Articles written in Journal of Chemical Sciences

    • DNA binding and cleavage activity by a mononuclear iron(II)Schiff base complex: Synthesis and structural characterization

      Abhijit Pal Bhaskar Biswas Merry Mitra Subramaniyam Rajalakshmi Chandra Shekhar Purohit Soumitra Hazra Gopinatha Suresh Kumar Balachandran Unni Nair Rajarshi Ghosh

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      Synthesis and characterization of a mononuclear Fe(II) compound [Fe(L)](ClO4)2 (1) [L = N-(1-pyridin-2-yl-phenylidene)-N'-[2-({2-[(1-pyridin-2-ylphenylidene)amino]ethyl}amino)ethyl] ethane-1,2-diamine] (1) is reported. 1 crystallizes in P-1 space group with a = 11.9241(3) Å, b = 12.1994(3) Å and c = 13.0622(4) Å. The binding property of the complex with DNA has been investigated using absorption and emission studies, thermal melting, viscosity experiments and circular dichroism studies. The binding constant ($K_b$) and the linear Stern-Volmer quenching constant ($K_{\text{sv}}$) of the complex have been determined as $3.5 \times 10^3$M-1 and $2.73 \times 10^4$M-1, respectively. Spectroscopic and hydrodynamic investigations revealed intercalative mode of binding of 1 with DNA. 1 is also found to induce oxidative cleavage of the supercoiled pUC 18 DNA to its nicked circular form in a concentration dependent manner.

    • Synthesis, structural characterization and biological activity of a trinuclear zinc(II) complex: DNA interaction study and antimicrobial activity

      Bhaskar Biswas Niranjan Kole Moumita Patra Shampa Dutta Mousumi Ganguly

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      A trinuclear zinc(II) complex [Zn3L2(𝜇-O2CCH3)2(H2O)2]·H2O·2CH3OH (1) was synthesized from an in situ reaction between zinc acetate and a Schiff base ligand (H2L = 2-((2-hydroxyphenylimino) methyl)-6-methoxyphenol). The ligand was prepared by (1:1) condensation of ortho-vanillin and ortho-aminophenol. The ligand and zinc(II) complex were characterized by elemental analysis, Fourier Transform Infrared (FTIR), 1H-Nuclear Magnetic Resonance (NMR), UV-Vis spectroscopy, Powder X-ray Diffraction (PXRD) and thermogravimetric analysis. 1 crystallizes in P-1 space group with 𝑎 = 11.9241(3) Å, 𝑏 = 12.19746 Å, 𝑐 = 20.47784 Å with unit cell volume is 2674.440 (Å)3. Binding property of the complex with calf thymus DNA (CT-DNA) has been investigated using absorption and emission studies. Thermal melting and viscosity experiments were further performed to determine the mode of binding of 1 with CT-DNA. Spectroscopic and viscosity investigations revealed an intercalative binding mode of 1 with CT-DNA. The ligand and its zinc complex were screened for their biological activity against bacterial species and fungi. Activity data show that the metal complex has more antibacterial and antifungal activity than the parent Schiff base ligand and against those bacterial or fungi species.

    • Structural systematics of some metal complexes with 4,5-diazafluoren-9-one

      Abhijit Pal Bhaskar Biswas Merry Mitra Chandra Shekhar Purohit Chia-Her Lind Rajarshi Ghosh

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      Synthesis and X-ray structural characterization of three complexes of type cis-[M(dafone)2(NCS)2] (M = Co(II), 1; Ni(II), 2; Zn(II), 3; dafone = 4,5-diazafluoren-9-one) and a polymer cis-[Cd(dafone)(NCS)2]$_n$ (4) have been reported. Each of the four complexes is crystallized in orthorhombic crystal system. Structural study reveals that each metal(II) centre in the four complexes adopts distorted octahedral geometry with MN6 chromophore in 1-3 and MN4S2 chromophore in 4. The room temperature steady-state fluorescent intensity of dafone in dimethyl formamide at 402 nm is found to be quenched in these reported dafone complexes (1-4).

    • Synthesis and bio-catalytic activity of isostructural cobalt(III)-phenanthroline complexes

      Dhananjay Dey Arnab Basu Roy Anandan Ranjani Loganathan Gayathri Saravanan Chandraleka Dharumadurai Dhanasekaran Mohammad Abdulkader Akbarsha Chung-Yu Shen Hui-Lien Tsai Milan Maji Niranjan Kole Bhaskar Biswas

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      We have synthesized two isostructural mononuclear cobalt(III) complexes [1]NO3·3H2O and [1]NO3·CH3CO2H·H2O {[1]+ = [Co(1,10-phenanthroline)2Cl2]+} and characterized by single crystal X-ray structural analyses. Mass spectral studies of the complexes indicate both the compounds to produce identical cationic species viz., [Co(phen)2Cl2]+ in methanol solution. [1]+ has been evaluated as model system for the catechol oxidase enzyme by using 3,5-di-tert-butylcatechol (3,5-DTBC) as the substrate in methanol medium, which revealed that the cationic complex efficiently inhibits catalytic activity with kcat value 9.65 × 102 h−1. [1]+ cleaved pBR 322 DNA without addition of an activating agent. Further, the anti-cancer activity of [1]+ on human hepatocarcinoma cell line (HepG2) has been examined. The induction of apoptosis induced in the cell line was assessed base on the changes in cell morphology, which showed the efficacy of [1]+ to induce apoptosis in 53% of cells during 24 h treatment. Interestingly, the observed IC50 values reveal that [1]+ brings about conformational change on DNA strongly and exhibits remarkable cytotoxicity.

    • Recognition of self-assembled water-nitrate cluster in a Co(III)-2,2'-bipyridine host: Synthesis, X-ray structure, DNA cleavage, molecular docking and anticancer activity

      SUBRATA DAS ANANDAN RANJANI LOGANATHAN GAYATHRI SUBHASISH SAHA JORGE PASAN DHARUMADURAI DHANASEKARAN MOHAMMAD ABDULKADER AKBARSHA MILAN MAJI BHASKAR BISWAS

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      A mononuclear cobalt(III) complex [Co(bpy)₂Cl₂]NO₃·2H₂O (1) (bpy = 2,2'-bipyridine) has been synthesized and crystallographically characterized. Self-assembly of the lattice water molecules from rectangular tetrameric water cluster interacts with nitrate anion along the c-axis forming a six membered hexagonal water-nitrate cluster. It presents a new mode of association of water molecules with nitrate molecules which is not predicted theoretically or found experimentally. The molecule effectively cleaves bacterial genomic DNA and shows important cytotoxicity against human hepatocarcinoma cell (HepG2).

    • Unprecedented hetero-geometric discrete copper(II) complexes: Crystal structure and bio-mimicking of Catecholase activity

      ABHRANIL DE DHANANJAY DEY HARE RAM YADAV MILAN MAJI VINAYAK RANE R M KADAM ANGSHUMAN ROY CHOUDHURY BHASKAR BISWAS

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      An unprecedented solid of coper(II) complexes [Cu(dpa)₂NCS]₂[Cu(dpa)₂(NCS)₂](ClO₄)₂ (1) [dpa = 2,2'-dipyridylamine; SCN = thiocyanate], has been synthesized and crystallographically characterized with the aim to study the catecholase activity. The Cu(II) complex mimics the full catalytic cycle of the active site of catechol oxidase enzyme in acetonitrile medium with a turnover number of 4.788 × 10³ h⁻¹ along with the production of semiquinone radical and hydrogen peroxide. In situ generation of Cu(I) species in the catalytic pathway of catechol oxidation was established by electrochemical study and further confirmed by electron paramagnetic resonance (EPR) spectroscopy.

    • Synthesis and phosphatase activity of a Cobalt(II) phenanthroline complex

      MAMONI GARAI DHANANJAY DEY HARE RAM YADAV MILAN MAJI ANGSHUMAN ROY CHOUDHURY BHASKAR BISWAS

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      A mononuclear cobalt(II) complex, [Co(phen) ₂Cl ₂], (phen = 1,10-phenanthroline) has been synthesized and structurally characterized by different spectroscopic methods including single crystal X-ray structural study.X-ray crystal structural analysis revealed that the cobalt(II) complex crystallizes in amonoclinicsystem with C2/c space group and exists in cis-configuration in its crystalline state. Room temperature magnetic measurement accounts for 3e paramagnetism and indicates high spin cobalt(II) in the solid state. The cobalt(II) complex has been evaluated as a functional model for phosphatase enzyme by using 4-nitrophenylphosphate (PNPP) as a standard substrate in aqueous DMF medium. This mononuclear cobalt(II) complex exhibits good hydrolytic phosphoester cleavage efficiency with kcat value of 3.78 × 10 ²h ⁻¹.

    • Catalytic aspects of a copper(II) complex: biological oxidase to oxygenase activity

      BISWAJIT CHOWDHURY MILAN MAJI BHASKAR BISWAS

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      A coper(II) complex, [Cu(dpa)2(OAc)](ClO4) (1) [dpa =2, 2'-dipyridylamine; OAc = acetate], has been synthesized and crystallographically characterized. X-ray structure analysis revealed that this mononuclear Cu(II) complex crystallizes as a rare class of hexa coordination geometry named bicapped square pyramidalgeometry with P2₁/c space group. This copper complex displays excellent catalytic efficiency, kcat /KM (h⁻¹) = 6.17 × 10⁵ towards the oxidative coupling of 2-aminophenol (2-AP) to aminophenoxazin-3-one. Further, upon stoichiometric addition of copper(II) complex to 3,5-DTBC in presence of molecular oxygen in ethanol medium, the copper complex affords predominantly extradiol cleavage products along with a small amount of benzoquinone and a trace amount of intradiol cleavage products at a rate, kobs = 1.09 × 10⁻³ min ⁻¹, which provide substantial evidence for the oxygen activation mechanism. This paper presents a novel addition of a copper(II) complex having the potential to mimic the active site of phenoxazinone synthase and catechol dioxygenase enzymes with significant catalytic efficiency.

    • Gentisate-1,2-dioxygenase activity by an iron(II)-phenanthroline complex

      ABHRANIL DE DHANANJAY DEY AJIT DAS NIRANJAN KOLE BHASKAR BISWAS

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      In this work, we have synthesised and crystallographically characterized a mononuclear iron(II) complex, [Fe(phen)3](NO3)2 ·2H2O (1) (phen = 1,10-phenanthroline). Single crystal X-ray diffraction (SXRD) analysis revealed that 1 crystallizes in monoclinic system with P 1 space group. The lattice water molecules in 1 form a water-nitrate cluster, (H2O)2... (NO3)2 through strong H-bonding interaction mediated via iron(II) complex in a unique binding motif and provide additional stability to the compound in the solid state. This iron(II)complex is able to catalyze the cleavage of aromatic C-C linkage of 2,5-dihydroxybenzoic acid (Gentisic acid, GA) in oxygen environment. The iron(II) complex in the presence of two equivalent of triethylamine (Et3N) binds with GA stoichiometrically in acetonitrile medium at 25 C. Observation of GA-to-iron LMCT optical bands at 521 and 609 nm supports in situ generated iron-GA adduct in solution. This in situ generated iron-GA adduct reacts with molecular oxygen at the rate, kobs = 6.58×10−3 min−1 in acetonitrile and affords exclusively 2-oxo-4-hydroxy-hepta-3,5-dienedioic acid. The incorporation of both the oxygen atoms of molecular oxygen in the bio-mimicking activity of gentisate-1,2-dioxygenase by this iron(II)-phenanthroline complex remain arare example in scientific literature.

    • Phenoxazinone synthase and antimicrobial activity by a bis(1,3-diamino-2-propanolate) cobalt(III) complex

      BISWAJIT CHOWDHURY BIPLAB BHOWMIK AMRITA SAHU MAYANK JOSHI SUVENDU PAUL ANGSHUMAN ROY CHOUDHURY BHASKAR BISWAS

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      In this work, we have synthesised and structurally characterized a mononuclear cobalt(III) complex,[Co(2-O-pn)2] Cl 2H2O (1), (2-O-pn = 1,3-diamino-2-propanolate). From the X-ray structure of the cobalt complex, it is revealed that Co(III) ion in 1 adopts an octahedral geometry and crystallizes in the monoclinicsystem with C2/c space group. The lattice aqua molecule in combination with chloride ion in 1 forms a waterchloride cluster, (H2O)2 ··· (Cl)2 through strong H-bonding interaction mediated via cobalt(III) complex in a unique binding motif. This cobalt(III) complex has been tested as an effective catalytic system towards the oxidative coupling of 2-aminophenol (2-AP) in the MeCN medium. In situ mass spectral analysis confirms that 2-AP forms an adduct with cobalt ion and the course of catalysis proceeds through catalyst-substrate binding followed by oxidative coupling of 2-AP with iminobenzoquinone. This cobalt(III) catalyst affords exclusively aminophenoxazinone species with a significant turnover number, kcat: 6.37×102h-1 in the MeCN medium. This cobalt(III) complex is able to screen out the growth of some bacteria and fungi species. Quantum chemicalcalculations employing density functional theory is used to model structural parameters and spectroscopic behaviour. The theoretical findings corroborate well with the experimental results.

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