• MANISH KUMAR

      Articles written in Journal of Chemical Sciences

    • Synthesis and characterisation of some hypervalent silicon compounds

      S P Narula Ravishankar Manish Kumar Meenu

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    • Ammonium derivatives of chromenones and quinolinones as lead antimicrobial agents

      Shilpi Gupta Seema Singh Abha Kathuria Manish Kumar Sweta Sharma Ram Kumar Virinder S Parmar Bharat Singh Anjali Gupta Erik Van Der Eycken Gainda L Sharma Sunil K Sharma

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      A series of novel ammonium derivatives were synthesized and examined for their antimicrobial efficacy. Comparison of antimicrobial spectrum revealed that compounds 9, 11, 16 and 23 had strong potential against pathogens in vitro. Cytotoxicity results showed compound 9 to be least toxic, it is non-toxic to A549 and U87 cells in MTT assay and exhibits marginal toxicity (15-20%) to human erythrocytes at a concentration of 1000 𝜇g/ml as compared to 100% lysis of cells by 31.25 𝜇g/ml of the standard drug amphotericin B. This compound has MIC values in the range of 1.95-31.25 𝜇g/disc in DDA against different pathogens and may considered to be an important lead antimicrobial molecule for further exploration.

    • Mechanisms of scavenging superoxide, hydroxyl, nitrogen dioxide and methoxy radicals by allicin: catalytic role of superoxide dismutase in scavenging superoxide radical

      MANISH KUMAR TIWARI NIHAR RANJAN JENA PHOOL CHAND MISHRA

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      The occurrence of free radicals such as superoxide radical anion (O2 ·-), hydroxyl radical (OH· ), methoxy radical (OCH3· ) and nitrogen dioxide radical (NO2· ) inside living cells can be very hazardous as these radicals can modify structures and functions of different biomolecules. Both exogenous antioxidantstaken as components of diet and endogenous enzyme antioxidants can scavenge O2·- separately. Mechanisms of scavenging O2 ·- by combinations of exogenous and endogenous enzyme antioxidants are not understood properly. In order to understand mechanisms of scavenging O2 ·-, OH · , OCH3 · , and NO2 · by allicin, and possible roles of superoxide dismutase (SOD) in scavenging O2 ·-, density functional theory was employed. Marcus theory was also employed to study scavenging of OH · , OCH3 · and NO2 · by electron transfer. In orderto find the most probable mechanisms of scavenging these radicals, different types of reactions such as one and two hydrogen atom transfer (HAT), single electron transfer (SET) and sequential proton loss electron transfer(SPLET) processes were investigated. It is found that allicin can scavenge O2 ·- via double hydrogen atom transfer catalyzed by Fe-SOD efficiently. Further, allicin can scavenge OH · by SET, and OCH3 · and NO2· by SPLET mechanisms most efficiently. Our results are in qualitative agreement with the available experimental data wherever these are available.

    • Theory for influence of uncompensated solution resistance on EIS of diffusion limited adsorption at rough electrode

      SHRUTI SRIVASTAV MANISH KUMAR RAMA KANT

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      Theory is developed for the electrochemical impedance spectroscopy (EIS) of the diffusion limited adsorption process coupled with reversible charge transfer at rough electrodes under the influence of ubiquitous uncompensated solution resistance. This study quantitatively relates the impedance response ofrough electrode to its phenomenological components, viz., diffusion limited adsorption, reversible charge transfer and uncompensated solution resistance. The random roughness of electrode is expressed by thesurface statistical property, i.e., power spectrum of roughness. The fractal nature of roughness is characterizedin terms of fractal dimension, lower cut-off length and topothesy length. The high-frequency regime iscontrolled by the uncompensated solution resistance whereas the low-frequency regime is governed by theadsorption process. The magnitude of impedance as well as phase decreases with rise in adsorption isotherm(length) parameter. The intermediate frequency regime is controlled by the coupling of adsorption and uncompensated solution resistance with the diffusion process. The fractal roughness parameters has quantitative influence on the magnitude of impedance over whole frequency regime while the phase plot shows qualitative difference in the intermediate frequency regime. The governing length scales which controls the characteristic crossover frequencies are: diffusion length, adsorption-ohmic coupling length and topothesy length (or width of interface). The three emergent crossover frequencies are: (i) ohmic reduced innercrossover frequency (ii) adsorption roughness topothesy dependent pseudo-quasireversibility characteristic frequency (iii) outer crossover frequency.

      Synopsis: This study quantitatively relates the impedance response of rough electrode to its phenomenological components, viz., diffusion limited adsorption, reversible charge transfer and uncompensated solution resistance. The random roughness of electrode is expressed by the surface statistical property, i.e., power spectrum of roughness.

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