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( Stanfield Youngwon Lee ),( Christopher Bielawski ),정동영,강윤식,이명재,신희종,김미주,성영은 한국공업화학회 2014 한국공업화학회 연구논문 초록집 Vol.2014 No.1
Our work focused on determining if this outer Helmholtz plane reaction does indeedexist and play a significant role in non-precious metal catalysts. A three electrode half-cell was used tomeasure the oxygen reduction reaction activity of a non-precious metal catalystin different alkaline electrolytes. Using electrolytes with different cations altered the hydration energyas well as block or increase access of oxygen to the outer Helmholtzplane. Correlations between hydrationshell size and catalytic activity were observed.
Lee, Stanfield Youngwon,Chung, Dong Young,Lee, Myeong Jae,Kang, Yun Sik,Shin, Heejong,Kim, Mi-Ju,Bielawski, Christopher W.,Sung, Yung-Eun American Chemical Society 2016 The Journal of Physical Chemistry Part C Vol.120 No.43
<P>This study was focused On elucidating the origin of the catalytic activity displayed by non-precious-metal-based, oxygen reduction reaction (ORR) catalysts before and after heat treatment. Electrochemical measurements were recorded using a series of metal phthalocyanines calculated to exhibit varying oxygen adsorption energies before and after heat treatment at a temperature Sufficiently high to facilitate degradation. Collectively, the results indicate that while the oxygen adsorption is germane to the catalytic activity before heat, treatment, the ORR appears to proceed through. a different pathway that is not dependent on adsorption energy after heat treatment. These conclusions help to explain the high catalytic activities exhibited by carbon- or nitrogen-based materials containing metal ions after heat treatment and may lead to the realization of substitutes for ORB. catalysts that utilize precious transition metals.</P>
Lee, Stanfield Y.,Lyu, Jihong,Kang, Songsu,Lu, Sherilyn Jiawen,Bielawski, Christopher W. American Chemical Society 2018 The Journal of Physical Chemistry Part C Vol.122 No.22
<P>X-ray induced Auger electron spectroscopy was used to evaluate synthetic polymers containing carbons with differing degrees of sp-, sp<SUP>2</SUP>-, and sp<SUP>3</SUP>-hybridization states as well as heteroatoms. For comparison, a series of related small molecules was also studied. Linear correlations were observed and a universal calibration method for quantifying the average hybridization states of a wide variety of synthetic polymeric materials is offered.</P> [FIG OMISSION]</BR>
Multiple Residues in the P-Region and M2 of Murine Kir 2.1 Regulate Blockage by External $Ba^{2+}$
Lee, Young-Mee,Thompson, Gareth A.,Ashmole, Ian,Leyland, Mark,So, In-Suk,Stanfield, Peter R. The Korean Society of Pharmacology 2009 The Korean Journal of Physiology & Pharmacology Vol.13 No.1
We have examined the effects of certain mutations of the selectivity filter and of the membrane helix M2 on $Ba^{2+}$ blockage of the inward rectifier potassium channel, Kir 2.1. We expressed mutant and wild type murine Kir 2.1 in Chinese hamster ovary(CHO) cells and used the whole cell patch-clamp technique to record $K^+$ currents in the absence and presence of externally applied $Ba^{2+}$. Wild type Kir2.1 was blocked by externally applied $Ba^{2+}$ in a voltage and concentration dependent manner. Mutants of Y145 in the selectivity filter showed little change in the kinetics of $Ba^{2+}$ blockage. The estimated $K_d(0)$ was 108 ${\mu}M$ for Kir2.1 wild type, 124 ${\mu}M$ for a concatameric WT-Y145V dimer, 109 ${\mu}M$ for a WT-Y145L dimer, and 267 ${\mu}M$ for Y145F. Mutant channels T141A and S165L exhibit a reduced affinity together with a large reduction in the rate of blockage. In S165L, blockage proceeds with a double exponential time course, suggestive of more than one blocking site. The double mutation T141A/S165L dramatically reduced affinity for $Ba^{2+}$, also showing two components with very different time courses. Mutants D172K and D172R(lining the central, aqueous cavity of the channel) showed both a decreased affinity to $Ba^{2+}$ and a decrease in the on transition rate constant(${\kappa}_{on}$). These results imply that residues stabilising the cytoplasmic end of the selectivity filter(T141, S165) and in the central cavity(D172) are major determinants of high affinity $Ba^{2+}$ blockage in Kir 2.1.
Unveiling a Masked Polymer of Dewar Benzene Reveals <i>trans</i>-Poly(acetylene)
Seo, Jinwon,Lee, Stanfield Y.,Bielawski, Christopher W. American Chemical Society 2019 Macromolecules Vol.52 No.8
<P>A dibromo derivative of Dewar benzene, <I>trans</I>-5,6-dibromobicyclo[2.2.0]hex-1-ene, was polymerized using ring-opening metathesis polymerization (ROMP). The reaction proceeded in a controlled manner as changing the initial monomer-to-catalyst ratio afforded monodispersed polymers with tunable molecular weights and growing polymer chains were extended upon subsequent exposure to additional monomer. Treatment of the halogenated polymers with an alkyllithium reagent resulted in elimination followed by isomerization to afford <I>trans</I>-poly(acetylene). Based on a series of mechanistic and spectroscopic studies, the transformation was proposed to proceed through a cyclobutenyl intermediate that undergoes rearrangement. The methodology was found to be versatile as triblock copolymers containing the halogenated homopolymer were prepared and converted to their poly(acetylene)-containing derivatives. The polymers were characterized using gel permeation chromatography as well as a range of spectroscopic (NMR, FT-IR, UV-vis, and Raman) and analytical techniques.</P> [FIG OMISSION]</BR>
Young Mee Lee,Gareth A. Thompson,Ian Ashmole,Mark Leyland,Insuk So,Peter R. Stanfield 대한생리학회-대한약리학회 2009 The Korean Journal of Physiology & Pharmacology Vol.13 No.1
We have examined the effects of certain mutations of the selectivity filter and of the membrane helix M2 on Ba<sup>2+</sup> blockage of the inward rectifier potassium channel, Kir 2.1. We expressed mutant and wild type murine Kir 2.1 in Chinese hamster ovary (CHO) cells and used the whole cell patch-clamp technique to record K<sup>+</sup> currents in the absence and presence of externally applied Ba<sup>2+</sup>. Wild type Kir2.1 was blocked by externally applied Ba<sup>2+</sup> in a voltage and concentration dependent manner. Mutants of Y145 in the selectivity filter showed little change in the kinetics of Ba<sup>2+</sup> blockage. The estimated K<sub>d</sub>(0) was 108ՌM for Kir2.1 wild type, 124ՌM for a concatameric WT-Y145V dimer, 109ՌM for a WT-Y145L dimer, and 267ՌM for Y145F. Mutant channels T141A and S165L exhibit a reduced affinity together with a large reduction in the rate of blockage. In S165L, blockage proceeds with a double exponential time course, suggestive of more than one blocking site. The double mutation T141A/S165L dramatically reduced affinity for Ba<sup>2+</sup>, also showing two components with very different time courses. Mutants D172K and D172R (lining the central, aqueous cavity of the channel) showed both a decreased affinity to Ba<sup>2+</sup> and a decrease in the on transition rate constant (k<sub>on</sub>). These results imply that residues stabilising the cytoplasmic end of the selectivity filter (T141, S165) and in the central cavity (D172) are major determinants of high affinity Ba<sup>2+</sup> blockage in Kir 2.1.
김미주,강윤식,이명재,( Stanfield Youngwon Lee ),신희종,성영은 한국공업화학회 2014 한국공업화학회 연구논문 초록집 Vol.2014 No.1
Polymer electrolyte membrane fuel cells (PEMFC) are a sort of electrochemical devices that exerts the conversion of chemical energy into electrical energy under low operating temperatures. Due to the sluggish oxygen reduction reaction (ORR) in PEMFC, oxygen electrode catalysts that lower the overpotential are of significant importance. To reduce the usage of Pt, well known to be the best ORR catalyst but extremely expensive, research continues to be done to develop Pt-based catalysts that have been treated to create a Pt enriched surface. Herein we synthesized carbon supported Platinum-Cobalt nanoparticles and conducted acid and heat treatments to provide evidence of improved ORR activity due to a Pt rich surface structure. Physical and electrochemical characterizations were determined using tools such as X-ray diffraction, cyclic voltammetry (CV), and X-ray photoelectron spectroscopy (XPS).