• Manoj Kumar

      Articles written in Journal of Chemical Sciences

    • Maximization of yield of C-13 isotope by multiphoton dissociation of Freon-22 using high average power TEA CO2 laser

      Manoj Kumar Anant Deshpande Chintan Gupta A K Biswas A K Nath

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      Selective multi-photon dissociation (MPD) of Freon-22 (CF2HC1) molecules has been carried out using a TEA CO2 laser at various CO2 laser lines (9P(20)-9P(26)) in order to maximize the yield of C-13 isotope in the product (C2F4) at an enrichment factor of 100. The effects of laser pulse tail due to the presence of N2 in the laser mixture on the enrichment factor and yield of C-13 are investigated. It is found that the addition of a small amount of N2 is possible in the laser mixture without a significant drop in the yield at desired enrichment factor. Addition of a small amount of N2 improves the laser efficiency considerably. At a given pulse energy, a slight change in the near field intensity distribution of a laser severely affects the selectivity of C-13 isotope. The computed far-field intensity distributions of the measured near-field intensities show marked spatial variation in the focal spots that leads to a drop in selectivity. For macroscopic production of C-13 isotope a simple and novel multi-pass cavity has been designed and tested to focus the energy repeatedly keeping the optimum fluence constant at each focal spot.

    • Yield and enrichment studies of C-13 isotope by multi-photon dissociation of Freon-22 at low temperatures

      Manoj Kumar Anant Deshpande Chintan Gupta A K Nath

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      Multi-photon dissociation of Freon-22 (CF2HC1) at low temperatures has been carried out to separate the C-13 isotope using a TEA CO2 laser. Yield and enrichment of C-13 isotope in the product C2F4 are studied at 9P(22) laser line as a function of temperature (−50°C to 30°C). It is observed that at a given fluence when the temperature is lowered the yield decreases and the enrichment factor of C-13 increases.

      Room temperature irradiation of CF2HC1 towards the blue edge of C-13 absorption (i.e. at 9P(20) laser line) gives low yield of the product (C2F4) at a fluence, which produces the desired enrichment factor of 100. An increase in fluence gives very high yield of C2F4 but the enrichment factor is very low. Irradiating CF2HC1 at a temperature of −10°C enhances the enrichment factor to 100 and the yield obtained is comparable to that towards the red edge of C-13 absorption (i.e. at 9P(26) laser line).

      At a given enrichment factor higher enrichment efficiency is achieved when CF2HC1 is irradiated at lower temperature.

    • Effective Floquet Hamiltonian for spin 𝐼 = 1 in magic angle spinning NMR using contact transformation

      Manoj Kumar Pandey Mangala Sunder Krishnan

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      Contact transformation is an operator transformation method in time-independent perturbation theory which is used successfully in molecular spectroscopy to obtain an effective Hamiltonian. Floquet theory is used to transform the periodic time-dependent Hamiltonian, to a time-independent Floquet Hamiltonian. In this article contact transformation method has been used to get the analytical representation of Floquet Hamiltonian for quadrupolar nuclei with spin 𝐼 = 1 in the presence of an RF field and first order quadrupolar interaction in magic angle spinning NMR experiments. The eigenvalues of contact transformed Hamiltonian as well as Floquet Hamiltonian have been calculated and a comparison is made between the eigenvalues obtained using the two Hamiltonians.

    • Cu(II) complexes of glyco-imino-aromatic conjugates in DNA binding, plasmid cleavage and cell cytotoxicity

      Amit Kumar Atanu Mitra Amrendra Kumar Ajay Manoj Kumar Bhat Chebrolu P Rao

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      Binding of metal complexes of C2-glucosyl conjugates with DNA has been established by absorption and fluorescence studies. Conformational changes occurred in DNA upon binding have been studied by circular dichroism. All these studies are suggestive that the metal complexes bind to DNA through intercalation. Binding of di-nuclear copper complex 5 was found to be stronger when compared to the other complexes studied. Copper complexes were found to cleave the plasmid DNA in the absence of oxidizing or reducing agent, whereas, zinc complexes do not cleave. Metal complexes have shown toxicity to the HeLa and MCF-7 cell lines.Morphological studies, western blot and FACS analysis are suggestive of apoptotic cell death induced by the metal complexes. Di-nuclear copper complexes were found to be better as compared to the mononuclear ones in binding, plasmid cleavage and also in causing more cell death.

    • Effect of method of preparation on hydrodesulphurization activity of Co- or Ni-promoted MoS2/SBA-15 catalysts

      Shelu Garg Kapil Soni V V D N Prasad Manoj Kumar Thallada Bhaskar J K Gupta G Murali Dhar C S Gopinath

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      Ordered mesoporous material SBA-15 was synthesized and used as a support for the preparation of molybdenum sulphide catalysts through precipitation from homogeneous solution (PFHS) technique with the Mo content varying from 2-12 wt%. The prepared catalysts were evaluated for thiophene hydrodesulphurization catalytic activities at 400°RC. Catalysts prepared through PFHS method resulted in highly dispersed MoS2 catalysts, which were inferred from powder X-ray diffraction (XRD), X-ray photoelectron spectroscopy (XPS), low temperature oxygen chemisorptions (LTOC) and BET surface area analysis. The relationship between XPS intensity ratio, oxygen chemisorption and catalytic activities is discussed in terms of highly dispersed nano particles of MoS2 and its consequence in accommodating more promoted atoms at the edge sites.

    • Palladium complexes of a new type of N-heterocyclic carbene ligand derived from a tricyclic triazolooxazine framework

      Manoj Kumar Gangwar Alok Ch Kalita Prasenjit Ghosh

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      A new type of tricyclic triazolooxazine derived N-heterocyclic carbene precursors were developed by the alkylation reaction of a tricyclic triazolooxazine framework. In particular, the reaction of 5a,6,7,8,9,9ahexahydro-4𝐻-benzo[𝑏][1,2,3]triazolo[1,5-𝑑][1,4]oxazine with methyl iodide and ethyl iodide yielded the tricyclic triazolooxazine derived N-heterocyclic carbene precursors, (1−2)a, in 67−84% yield. The tricyclic triazolooxazinium iodide salts, (1−2)a, underwent metallation in a straight forward manner upon treatment with PdCl2 in the presence of K2CO3 in pyridine to give the trans-{3-(R)-5a,6,7,8,9,9a-hexahydro-4𝐻-benzo[𝑏][1,2,3]triazolo[1,5-𝑑][1,4]oxazin-4-ylidene} PdI2(pyridine) [R = Me (1b), Et (2b)] complexes in 23−25% yield. The new tricyclic triazolooxazine derived N-heterocyclic carbene moiety, as stabilized upon binding to palladium in the (1−2)b complexes, was structurally characterized by the X-ray single crystal diffraction studies.

    • A cross-linked manganese porphyrin as highly efficient heterogeneous catalyst for selective oxidation of cycloalkenes/alkanes

      Manoj Kumar Singh Debkumar Bandyopadhyay

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      The monomeric tetrakis (5,10,15,20-𝑝-bromophenyl) manganese porphyrin has been converted to a micro- and mesoporous material of surface area 1301m2/g by carefully manipulating the reaction conditions of Suzuki coupling. This material has been tested for its oxidizing ability of cycloalkenes/alkane by 𝑡-BuOOH, H2O2, CumOOH and m-CPBA. The catalyst is found to oxidize the alkenes selectively and it is not destroyed even 5% in 10 cycles of successive oxidation processes in one pot. The parent monomer gets destroyed appreciably under similar oxidizing conditions.

    • Design and synthesis of nanoporous perylene bis-imide linked metalloporphyrin frameworks and their catalytic activity

      Manoj Kumar Singh Debkumar Bandyopadhyay

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      Two nanoporous perylene bis-imide linked metalloporphyrin framework catalysts have been synthesized via condensation of 5,10,15,20-tetrakis-(4′-aminophenyl) iron(III) porphyrin chloride or 5,10, 15,20-tetrakis-(4′-aminophenyl) manganese(III) porphyrin chloride with perylene-3,4,9,10-tetracarboxylic dianhydride. Both the materials were crystalline in nature and were characterized by electron microscopy techniques, solid-state 1H-13C CP/MS NMR, powder X-ray diffraction (PXRD), and magnetic susceptibility measurements. The nitrogen gas physisorption study has indicated that both materials are porous in nature and have BET surface area with 653 m2/g and 974 m2/g with uniform pore size of 2.8 nm. These materials were found to act as very good heterogeneous catalysts for selective oxidation of alkanes and alkenes with tert-butyl hydroperoxide and were not degraded even after multiple uses up to 10 cycles.

    • A new Organopalladium compound containing four Iron (III) Porphyrins for the selective oxidation of alkanes/alkenes by t-BuOOH

      Manoj Kumar Singh Debkumar Bandyopadhyay

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      Two iron(III) tetraphenyl porphyrin catalytic units are connected by an azo-link to form the dimeric compound A. The compound A was then reacted with Pd2+ to make a tetrameric iron(III) porphyrin complex B with all four iron(III) catalytic sites open to the substrates and reactants. Both the compounds were characterized spectroscopically and the results of homogeneous oxidation of some alkanes and alkenes with t-BuOOH in presence of catalytic quantities of A and B have indicated remarkable improvement in selectivity and efficiency of A over the monomeric catalyst and B over A.

    • Validity of the Rosenfeld relationship: A comparative study of the network forming NTW model and other simple liquids

      ATREYEE BANERJEE MANOJ KUMAR NANDI SARIKA MAITRA BHATTACHARYYA

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      In this paper we explore the validity of the Rosenfeld and the Dzugutov relation for the Lennard- Jones (LJ) system, its repulsive counterpart, the WCA system and a network forming liquid, the NTW model. We find that for all the systems both the relations are valid at high temperature regime with an universalexponent close to 0.8. Similar to that observed for the simple liquids, the LJ and the WCA systems show a breakdown of the scaling laws at the low temperature regime. However for the NTW model, which is a simple liquid, these scaling laws are valid even at lower temperature regime similar to that found for ionic melts. Thus we find that the NTW model has mixed characteristics of simple liquids and ionic melts. Our study further reveals a quantitative relationship between the Rosenfeld and the Arrhenius relations. For strong liquids, the validity of the Rosenfeld relation in the low temperature regime is connected to it following the Arrhenius behaviour in that regime. Finally we explore the role of pair entropy and residual multiparticle entropy in the dynamics as a function of fragility of the systems.

    • Subtle interaction between Ag and O2: a near ambient pressure UV photoelectron spectroscopy (NAP-UPS) investigations

      MANOJ KUMAR GHOSALYA KASALA PRABHAKAR REDDY RUCHI JAIN KANAK ROY CHINNAKONDA S GOPINATH

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      The Ag-O2 interaction, which is at the center-stage of Ag-catalyzed partial oxidation reactions, is studied with NAP-UPS up to 0.2 mbar O2 pressure between 295 and 550 K. Three temperature regimes were identified for distinct Ag-O2 interaction, which are (a) 295–390 K, where mainly dissociative chemisorption of O2 happens, (b) 390–450 K, where diffusion of O-atoms into the sub-surfaces of Ag is prominent, and (c) >450 K, where metastable oxide forms on polycrystalline Ag surfaces. The work function (WF) of Ag changed from4.95 (<=390 K) to 5.30 eV (390–450 K), and then to 5.7 eV (>=450K) at 0.1mbar O2 pressure. Oxygen population in the sub-surfaces imparts crucial modifications to Ag at 390–450 K; it makes the surface to be electron-deficient that relates to the change in the WF of Ag and facilitates the formation of space charge layer on Ag surface. Oxygen adsorbed on such modified Ag-surfaces is electrophilic in nature, and this appears at a higher binding energy in core level XPS than the chemisorbed oxygen on metallic Ag. This is supported by angle-dependent NAP-XPS studies. The subsurface population of oxygen in Ag no longer persists at >410K when the O2 supply is removed. A high ratio of antibonding/bonding O 2p bands suggests the unique silver-oxygen interaction under the measurement conditions.

    • Some effects of (2s−2p) electron promotion in boron

      Ranjan Datta Manoj Kumar Datta Dulal C Ghosh

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      The wave function of the promoted (4p) state of boron of configuration (1s2; 2s1; 2p2) obtained as a result of promotion of one electron from 2s to 2p orbital in the ground state, is calculated. These results indicate that this promotion leads to a ‘contraction’ of both 2s and 2p orbitals.

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