• BISWAJIT CHOWDHURY

      Articles written in Journal of Chemical Sciences

    • Relaxation of the excited 𝑁-(2-hydroxy benzylidene) aniline molecule: An ab initio and TD DFT study

      Biswajit Chowdhury Rina De Pinaky Sett Joydeep Chowdhury

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      The photophysical behaviour of N-(2-hydroxy benzylidene) aniline or most commonly known as salicylideneaniline (SA) has been investigated using the ab initio and DFT levels of theory. The quantum chemical calculations show that the optimized non planar enol ($C_1$) form of the SA molecule is the most stable conformer in the ground state and is marked by the twisting of the phenolic and anilino rings of the molecule. The geometry optimizations and the subsequent frequency calculations of the excited singlet electronic states of the various tautomeric forms of SA molecule were performed with the CIS level of theory. A detail theoretical investigation on the relaxation dynamics of the SA molecule has been presented. Possible explanation on the excitation wavelength dependence of the photochromic yield of the molecule is also reported.

    • TPR and TPD studies of effects of Cu and Ca promotion on Fe-Zn-based Fischer-Tropsch catalysts

      Olusola O James Biswajit Chowdhury Sudip Maity

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      Temperature-programmed reduction (TPR) and temperature-programmed desorption (TPD) were used to study the effects of Cu and Ca promotion on Fe-Zn-based Fischer-Tropsch catalysts. The reduction temperature for Fe2O3 → Fe3O4 was unaffected by Ca addition but decreased when promoted with Cu. Fe-Zn promoted with Cu and Ca showed even much lower reduction temperature for Fe2O3→Fe3O4. Ca promotion enhances carburization and increases surface acidity and basicity of the Fe-Zn oxide precursor. While Cu inhibits carburization and decreases the surface acidity and basicity of the Fe-Zn oxide precursor. The implications of these effects on the application of catalysts for FT are discussed.

    • 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.

    • 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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