• Title/Summary/Keyword: catalysis

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Understanding Enzyme Structure and Function in Terms of the Shifting Specificity Model

  • Britt, Billy Mark
    • BMB Reports
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    • v.37 no.4
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    • pp.394-401
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    • 2004
  • The purpose of this paper is to suggest that the prominence of Haldane's explanation for enzyme catalysis significantly hinders investigations in understanding enzyme structure and function. This occurs despite the existence of much evidence that the Haldane model cannot embrace. Some of the evidence, in fact, disproves the model. A brief history of the explanation of enzyme catalysis is presented. The currently accepted view of enzyme catalysis -- the Haldane model -- is examined in terms of its strengths and weaknesses. An alternate model for general enzyme catalysis (the Shifting Specificity model) is reintroduced and an assessment of why it may be superior to the Haldane model is presented. Finally, it is proposed that a re-examination of many current aspects in enzyme structure and function (specifically, protein folding, x-ray and NMR structure analyses, enzyme stability curves, enzyme mimics, catalytic antibodies, and the loose packing of enzyme folded forms) in terms of the new model may offer crucial insights.

Analytical Application of Glow Discharge Atomic Absorption Spectroscopy (GD-AAS) Using Three Types of Jet Configurations Under Power Mode

  • Hwang, Jun Ho;Lee, Ki Beom;Kim, Min Su;Lee, Seong Ro;Kim, Hasuck;Kim, Hyo Jin;Lee, Gae Ho
    • Analytical Science and Technology
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    • v.8 no.4
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    • pp.443-448
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    • 1995
  • Three anode configurations of six-jet, cone-jet and cylindrical-jet are tested for their analytical performance under power mode operation. The effect of pressure, power and gas flow rate on atomic absorption signals have been studied. The increase of atomic absorption signal of sample element is observed at a fixed pressure in all configurations as the gas flow rate increase up to 300-600 seem, and as the power dissipated in the glow discharge cell increase. The lower the pressure is in the glow discharge cell at a fixed discharge power and argon flow rate, the greater the absorbance of sample element is. The optimum conditions are taken from these data and a calibration curve of Cu in low-alloy steel sample is obtained. In this calibration curve, six-jet configuration shows the best analytical results varies as the sample element.

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Microwave Synthesis of a Porous Metal-Organic Framework, Nickel(II) Dihydroxyterephthalate and its Catalytic Properties in Oxidation of Cyclohexene

  • Lee, Ji-Sun;Halligudi, Shiva B.;Jang, Nak-Han;Hwang, Dong-Won;Chang, Jong-San;Hwang, Young-Kyu
    • Bulletin of the Korean Chemical Society
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    • v.31 no.6
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    • pp.1489-1495
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    • 2010
  • A porous coordination solid of nickel(II) dihydroxyterephthalate has been synthesized by the microwave-assisted (MW) method. The synthesized nickel(II) dihyroxylterephthalate was designated by the general formula of [$Ni_2$(dhtp) $(H_2O)_2]{\cdot}8H_2O$ (where, dhtp = 2,5-dihydroxyterephthalate, denoted by Ni-DHTP). The effect of microwave-irradiation temperature and time of irradiation on the porosity and morphological changes in the solids have also been investigated. The catalytic performance of Ni-DHTP synthesized by MW method has been studied in the oxidation of cyclohexene with aqueous $H_2O_2$, which gave cyclohexene oxide as the primary product and 2-cyclohexene-1-ol as a major product.

Styrene Epoxidation over Cobalt Cyclam Immobilized SBA-15 Catalyst

  • Sujandi;Prasetyanto, Eko Adi;Han, Sang-Cheol;Park, Sang-Eon
    • Bulletin of the Korean Chemical Society
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    • v.27 no.9
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    • pp.1381-1385
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    • 2006
  • Cobalt (cyclam) complex has been successfully immobilized onto SBA-15, and proven to be an active catalyst for the epoxidation of styrene with tert-butyl hydroperoxide as a terminal oxidant. The selectivity for styrene oxide was observed to be up to 66% with 40% styrene conversion after 12h reaction time. The reversible redox cycle between Co(III) and Co(II) couple which was supposed to play key role during the epoxidation reaction was supported by a cyclic voltametry analysis. The textural properties of the catalyst was characterized by XRD, N2 adsorption-desorption, and TEM analysis.

Dehydrogenation of Ethylbenzene with Carbon Dioxide as Soft Oxidant over Supported Vanadium-Antimony Oxide Catalyst

  • Hong, Do-Young;Vislovskiy, Vladislav P.;Park, Sang-Eon;Park, Min-Seok;Yoo, Jin-S.;Chang, Jong-San
    • Bulletin of the Korean Chemical Society
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    • v.26 no.11
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    • pp.1743-1748
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    • 2005
  • This work presents that carbon dioxide, which is a main contributor to the global warming effect, could be utilized as a selective oxidant in the oxidative dehydrogenation of ethylbenzene. The dehydrogenation of ethylbenzene over alumina-supported vanadium-antimony oxide catalyst has been studied under different atmospheres such as inert nitrogen, steam, oxygen or carbon dioxide as diluent or oxidant. Among them, the addition of carbon dioxide gave the highest styrene yield (up to 82%) and styrene selectivity (up to 97%) along with stable activity. Carbon dioxide could play a beneficial role of a selective oxidant in the improvement of the catalytic behavior through the oxidative pathway.

Diffusion-Influenced Kinetics of Reactions Involving Polymers

  • Sung, Jae-Young;Park, Pyeong-Jun;Lee, Jin-Uk;Lee, Woo-Jin;Kim, Ji-Hyun;Lee, Sang-Youb
    • Bulletin of the Korean Chemical Society
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    • v.24 no.6
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    • pp.843-852
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    • 2003
  • We present a brief account of the theory of diffusion-influenced kinetics of reactions involving polymers. The review will be based on the recent contributions from the authors. Both intrapolymer and interpolymer reactions are considered, and the effects of various physical factors, such as the chain length, chain stiffness, and hydrodynamic interactions, are described within a unified theoretical framework.