• Proceedings of the Korean Vacuum Society Conference
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• 2016.02a
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• pp.292-292
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• 2016

Transition metal dichalcogenides (TMDs) with a two-dimensional layered structure have been considered highly promising materials for next-generation flexible, wearable, stretchable and transparent devices due to their unique physical, electrical and optical properties. Recent studies on TMD devices have focused on developing a suitable doping technique because precise control of the threshold voltage ($V_{TH}$) and the number of tightly-bound trions are required to achieve high performance electronic and optoelectronic devices, respectively. In particular, it is critical to develop an ultra-low level doping technique for the proper design and optimization of TMD-based devices because high level doping (about $10^{12}cm^{-2}$) causes TMD to act as a near-metallic layer. However, it is difficult to apply an ion implantation technique to TMD materials due to crystal damage that occurs during the implantation process. Although safe doping techniques have recently been developed, most of the previous TMD doping techniques presented very high doping levels of ${\sim}10^{12}cm^{-2}$. Recently, low-level n- and p-doping of TMD materials was achieved using cesium carbonate ($Cs_2CO_3$), octadecyltrichlorosilane (OTS), and M-DNA, but further studies are needed to reduce the doping level down to an intrinsic level. Here, we propose a novel DNA-based doping method on $MoS_2$ and $WSe_2$ films, which enables ultra-low n- and p-doping control and allows for proper adjustments in device performance. This is achieved by selecting and/or combining different types of divalent metal and trivalent lanthanide (Ln) ions on DNA nanostructures. The available n-doping range (${\Delta}n$) on the $MoS_2$ by Ln-DNA (DNA functionalized by trivalent Ln ions) is between $6{\times}10^9cm^{-2}$ and $2.6{\times}10^{10}cm^{-2}$, which is even lower than that provided by pristine DNA (${\sim}6.4{\times}10^{10}cm^{-2}$). The p-doping change (${\Delta}p$) on $WSe_2$ by Ln-DNA is adjusted between $-1.0{\times}10^{10}cm^{-2}$ and $-2.4{\times}10^{10}cm^{-2}$. In the case of Co-DNA (DNA functionalized by both divalent metal and trivalent Ln ions) doping where $Eu^{3+}$ or $Gd^{3+}$ ions were incorporated, a light p-doping phenomenon is observed on $MoS_2$ and $WSe_2$ (respectively, negative ${\Delta}n$ below $-9{\times}10^9cm^{-2}$ and positive ${\Delta}p$ above $1.4{\times}10^{10}cm^{-2}$) because the added $Cu^{2+}$ ions probably reduce the strength of negative charges in Ln-DNA. However, a light n-doping phenomenon (positive ${\Delta}n$ above $10^{10}cm^{-2}$ and negative ${\Delta}p$ below $-1.1{\times}10^{10}cm^{-2}$) occurs in the TMD devices doped by Co-DNA with $Tb^{3+}$ or $Er^{3+}$ ions. A significant (factor of ~5) increase in field-effect mobility is also observed on the $MoS_2$ and $WSe_2$ devices, which are, respectively, doped by $Tb^{3+}$-based Co-DNA (n-doping) and $Gd^{3+}$-based Co-DNA (p-doping), due to the reduction of effective electron and hole barrier heights after the doping. In terms of optoelectronic device performance (photoresponsivity and detectivity), the $Tb^{3+}$ or $Er^{3+}$-Co-DNA (n-doping) and the $Eu^{3+}$ or $Gd^{3+}$-Co-DNA (p-doping) improve the $MoS_2$ and $WSe_2$ photodetectors, respectively.

• KSBB Journal
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• v.8 no.3
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• pp.200-208
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• 1993

As a separation membrane for water-ethanol mixtures, alginic acid has been used which is hydrophilic polysaccharide and has excellent bonding capacity with divalent metal ions. Pervaporation characteristics of the alginic acid membrane were examined. The membrane was crosslinked with metal ions for the improvement of mechanical strength and chemical affinity. And its pervaporation characteristics were investigated. The first group(I A) metal complexed membrane cannot be used because of their brittleness and excessive swelling in low concentrations of ethanol solution. But the permeation characteristics of other metal complexed membrane were more improved than that of the alginic acid membrane because of their contraction of the membrane and hydrophilic property of metal ion.

• Bulletin of the Korean Chemical Society
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• v.33 no.8
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• pp.2669-2674
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• 2012

Crown ether is one of well-known host molecules and able to selectively sequester metal cation. We employed M06-2X density functional theory with IEFPCM and SMD continuum solvation models to study selectivity of dibenzo-18-crown-6-ether (DB18C6) for alkaline earth dications, $Ba^{2+}$, $Sr^{2+}$, $Ca^{2+}$, and $Mg^{2+}$ in the gas phase and in aqueous solution. $Mg^{2+}$ showed predominantly strong binding affinity in the gas phase because of strong polarization of CO bonds by cation. In aqueous solution, binding free energy differences became smaller among these dications. However, $Mg^{2+}$ had the best binding, being incompatible with experimental observations in aqueous solution. The enthalpies of the dication exchange reaction between DB18C6 and water cluster molecules were computed as another estimation of selectivity in aqueous solution. These results also demonstrated that $Mg^{2+}$ bound to DB18C6 better than $Ba^{2+}$. We speculated that the species determining selectivity in water could be 2:1 complexes of two DB18C6s and one dication.

• BMB Reports
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• v.31 no.4
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• pp.345-349
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• 1998

Aspartase (EC 4.3.1.1) from Hafnia alvei was purified to homogeneity by a combination of DEAE-cellulose, Red A-agarose, and Sepharose 6B chromatography. The purified enzyme appeared homogeneous on denatured SDS-polyacrylamide gel electrophoresis. The purified enzyme was a tetrameric protein composed of identical subunits with a molecular weight of 55,000 daltons. The optimum pH for the enzymatic reaction was 8.5 and the optimum temperature for maximum activity was $45^{\circ}C$. The enzyme has an absolute requirement of divalent metal ions ($Mg^{2+}$, $Mn^{2+}$) at the alkaline pH. The enzyme, however, was inactivated in the presence of other divalent cations such as $Zn^{2+}$, $Ca^{2+}$. The helical content of the purified enzyme was estimated by CD spectropolarimetry to be 61%.

• Journal of Environmental Science International
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• v.22 no.10
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• pp.1273-1278
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• 2013

Novel rhodamine 6G fluorescent chemosensors 1 and 2 for the detection of transition metal cations were synthesized through the condensation of rhodamine 6G ethylenediamine with each of 2-hydroxy-1-naphthaldehyde and 2,6-pyridinedicarbaldehyde, respectively. 1 and 2 were characterized using $^{13}C$ NMR, $^1H$ NMR and mass spectroscopy. Fluorometric and colorimetric measurements involving various metal ions revealed the ring opening of the rhodamine 6G spirocycle framework. In the absence of metal cations, 2 was colorless and non-fluorescent, whereas the addition of metal cations ($Hg^{2+}$ and others) changed the color to pink, accompanied by the appearance of an orange fluorescence. The chemosensors exhibited high selectivity for $Hg^{2+}$ over other divalent first-row transition metals. The complexes of $Hg^{2+}$ with 1 and 2 were successfully isolated. A huge enhancement in the fluorescence for both one- and two-photon excitations makes these compounds suitable candidates to be used for fluorescent labeling of biological systems.

• BMB Reports
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• v.38 no.5
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• pp.584-590
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• 2005

Glucose 6-phosphate dehydrogenase (EC 1.1.1.49) was purified from Aspergillus aculeatus, a filamentous fungus previously isolated from infected tongue of a patient. The enzyme, apparently homogeneous, had a specific activity of $220\;units\;mg^{-1}$/, a molecular weight of $105,000{\pm}5,000$ Dal by gel filtration and subunit size of $52,000{\pm}1,100$ Dal by sodium dodecyl sulphate-polyacrylamide gel electrophoresis. The substrate specificity was extremely strict, with glucose 6-phosphate (G6P) being oxidized by nicotinamide adenine dinucleotide phosphate (NADP) only. At assay pH of 7.5, the enzyme had $K_m$ values of $6\;{\mu}m$ and $75\;{\mu}m$ for NADP and G6P respectively. The $k_{cat}$ was $83\;s^{-1}$. Steady-state kinetics at pH 7.5 produced converging linear Lineweaver-Burk plots as expected for ternary-complex mechanism. The patterns of product and dead-end inhibition suggested that the enzyme can bind NADP and G6P separately to form a binary complex, indicating a random-order mechanism. The enzyme was irreversibly inactivated by heat in a linear fashion, with G6P providing a degree of protection. Phosphoenolpyruvate (PEP), adenosinetriphosphate (ATP), and fructose 6-phosphate (F6P), in decreasing order, are effective inhibitors. Zinc and Cobalt ions were effective inhibitors although cobalt ion was more potent; the two divalent metals were competitive inhibitors with respect to G6P, with $K_i$ values of $6.6\;{\mu}m$ and $4.7\;{\mu}m$ respectively. It is proposed that inhibition by divalent metal ions, at low NADPH /NADP ratio, is another means of controlling pentosephosphate pathway.

• Journal of the Korean Chemical Society
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• v.46 no.6
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• pp.515-522
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• 2002

Solid beta-dicalcium silicate hydrate $(\beta-C_2SH)$ synthesized under hydrothermal conditions at $240^{\circ}C$ and Ca/Si=2 molar ratio shows cation exchange properties towards divalent metal cations such as Fe, Cu, Zn, Cd, or Pb. The ability of metal cation uptake by the solid was found to be in the order: $Fe^{2+}$〉$Cu^{2+}$〉$Zn^{2+}$〉$Cd^{2+}$ = $Pb^{2+}$. Cesium selectivity of the solid was demonstrated in the presence of univalent cation such as $Li^+$, $Na^+$ and $K^+$ and divalent cations such as $Ca^{2+}$, $Mg^{2+}$ and $Ba^{2+}$, which are one hundred times more concentrated than the $Cs^+$. The uptake of $Cs^+$ is maximum in the presence of $Mg^{2+}$ whereas it is minimum in the presence of $K^+$. The different affinities of ${\beta}-C_2SH$ towards divalent metal cations can be used for the separation of those ions. Due to its selectivity for cesium it can be used in partitioning of radioactive Cs+ from nuclear wastes containing numerous cations. The mechanism of the metal cation exchange and cesium selectivity reactions by the solid is studied.

• The Korean Journal of Physiology and Pharmacology
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• v.9 no.2
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• pp.69-75
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• 2005

TRPM7, a cation channel protein permeable to various metal ions such as $Mg^{2+}$, is ubiquitously expressed in variety of cells including lymphocytes. The activity of TRPM7 is tightly regulated by intracellular $Mg^{2+}$, thus named $Mg^{2+}$-inhibited cation (MIC) current, and its expression is known to be critical for the viability and proliferation of B lymphocytes. In this study, the level of MIC current was compared between immature (WEHI-231) and mature (Bal-17) B lymphocytes. In both cell types, an intracellular dialysis with $Mg^{2+}$-free solution (140 mM CsCl) induced an outwardly-rectifying MIC current. The peak amplitude of MIC current and the permeability to divalent cation ($Mn^{2+}$) were several fold higher in Bal-17 than WEHI-231. Also, the level of mRNAs for TRPM7, a molecular correspondence of the MIC channel, was significantly higher in Bal-17 cells. The amplitude of MIC was further increased, and the relation between current and voltage became linear under divalent cation-free conditions, demonstrating typical properties of the TRPM7. The stimulation of B cell receptors (BCR) by ligation with antibodies did not change the amplitude of MIC current. Also, increase of extracellular $[Mg^{2+}]_c$ to enhance the $Mg^{2+}$ influx did not affect the BCR ligation-induced death of WEHI-231 cells. Although the level of TRPM7 was not directly related with the cell death of immature B cells, the remarkable difference of TRPM7 might indicate a fundamental change in the permeability to divalent cations during the development of B cells.

• Journal of the Korean Chemical Society
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• v.48 no.6
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• pp.577-582
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• 2004

The azacrown compounds, 1,4-dioxa-7,10,13-triazacyclopentadecane-N,N',N''-triacetic acid, $N-ac_3[15]aneN_3O_2(II_a)$ and 1,4-dioxa-7,10,13-triazacyclopentadecane-N,N',N''-tripropioc acid, $N-pr_3[15]aneN_3O_2(II_b)$ were synthesized by modified methods. Potentiometry was used to determine the protonation constant of the $N-ac_3[15]aneN_3O_2\;and\;N-pr_3[15]aneN_3O_2$. The stability constants of complexes of the trivalent metal ions of $Ce^{3+},\;Eu^{3+},Gd^{3+},and\;Yb^{3+}$ and divalent metal ions of $Co^{2+},\;Ni^{2+},\;Cu^{2+},\;and\;Zn^{2+}$ with the ligands $N-ac_3[15]aneN_3O_2\;and\;N-pr_3[15]aneN_3O_2$ have been determined at $25{\pm}0.1^{\circ}C$ in 0.1 M $NaClO_4$ solution by potentiometric methods. The metal ion affinities of the two triazamacrocyclic ligands with three pendant acetate or propionate groups are compared to those obtained for the similar ligands, 1,7-dioxa-4,10,13-triazacyclopentadecane-N,N',N''-triacetic acid, and 1,7-dioxa-4,10,13- triazacyclopentadecane-N,N',N''-tripropioc acid. The trends in stability of complexes for different metal ions due to changes in the nitrogen position of the donor atoms of the ligand are discussed.

• Korean Journal of Fisheries and Aquatic Sciences
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• v.51 no.5
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• pp.542-548
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• 2018

We investigated the effects of Na-alginates's average molecular weight (AMW), their concentrations and divalent metal ions on hydrophobic interaction of solution of Na-alginates in sea tangle produced Saccharina japonicus in East Coast of Korea. As the AMWs of Na-alginates decreased, the formations rates of hydrophobic micro domains and pre-micelles between intermoleculars of Na-alginates were increased. The pre-micelles between Na-alginates chains fully were formed when their concentrations reached 0.2%. In the effects of $Ca^{{+}{+}}$ and $Mg^{{+}{+}}$ on the hydrophobicity of Na-alginates solution, when the AMWs of Na-alginates were increased, the formation rates of hydrophobic micro domains produced by $Ca^{{+}{+}}$ and $Mg^{{+}{+}}$ in alginates chains were increased. When $Ca^{{+}{+}}$ and $Mg^{{+}{+}}$ concentrations that were needed to form gels of alginates solutions were insufficient, the formations of pre-micelle in alginates having large AMW were more incomplete than those of small AMW. In the increasing range from 0.01 to 0.1 mM in divalent metal ion concentration, the formation rate of pre-micelle in alginates solution added $Ca^{{+}{+}}$ were more faster than that of $Mg^{{+}{+}}$.