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Shin, Woonsup,Zhu, Enhua,Nagarale, Rajaram Krishna,Kim, Chang Hwan,Lee, Jong Myung,Shin, Samuel Jaeho,Heller, Adam American Chemical Society 2011 ANALYTICAL CHEMISTRY - Vol.83 No.12
<P>When a current or a voltage is applied across the ceramic membrane of the nongassing Ag/Ag<SUB>2</SUB>O-SiO<SUB>2</SUB>-Ag/Ag<SUB>2</SUB>O pump, protons produced in the anodic reaction 2Ag(s) + H<SUB>2</SUB>O → Ag<SUB>2</SUB>O(s) + 2H<SUP>+</SUP> + 2e<SUP>–</SUP> are driven to the cathode, where they are consumed by the reaction Ag<SUB>2</SUB>O(s) + H<SUB>2</SUB>O + 2e<SUP>–</SUP> → 2Ag(s) + 2 OH<SUP>–</SUP>. The flow of water is induced by momentum transfer from the electric field-driven proton-sheet at the surface of the ceramic membrane. About 10<SUP>4</SUP> water molecules flowed per reacted electron. Because dissolved ions decrease the field at the membrane surface, the flow decreases upon increasing the ionic strength. For this reason Ag<SUP>+</SUP> ions introduced through the anodic reaction and by dissolution of Ag<SUB>2</SUB>O decrease the flow. Their accumulation is reduced by applying Nafion-films to the electrodes. The 20 μL min<SUP>–1</SUP> flow rate of 6 mm i.d. pumps with Nafion coated electrodes operate daily for 5 min at 1 V for 1 month, for 70 h when the pump is pulsed for 30 s every 30 min, and for 2 h when operating continuously.</P><P><B>Graphic Abstract</B> <IMG SRC='http://pubs.acs.org/appl/literatum/publisher/achs/journals/content/ancham/2011/ancham.2011.83.issue-12/ac201118t/production/images/medium/ac-2011-01118t_0004.gif'></P><P><A href='http://pubs.acs.org/doi/suppl/10.1021/ac201118t'>ACS Electronic Supporting Info</A></P>
EPR Studies of the Active Sites of Carbon Monoxide Dehydrogenase from Clostridium thermoaceticum
Shin, Woonsup,Lindahl, Paul A. 한국분석과학회 1995 분석과학 Vol.8 No.4
The active sites of the nickel and iron-containing enzyme, carbon monoxide dehydrogenase (CODH) from clostridium thermoaceticum were investigated using Electron Paramagnetic Resonance (EPR) technique. CODH exhibits several spectral features called NiFeC, $g_{ave}=1.82$, $g_{ave}=1.86$. FCII signals which are originated from different clusters in this enzyme. CODH is know to catalyze two different kinds of reactions - acetyl-CoA synthesis and CO oxidation. The acetyl-CoA synthesis activity can be followed by monitoring CO/acetyl-CoA exchange. The addition of 1,10-phenanthroline (phen) to CODH selectively destroyed the CO/acetyl-CoA exchange activity and eliminated the NiFeC signal completely. CO oxidation activity and other EPR signals were unaffected. Such behavior demonstrates that CODH has two distinct active sites and that the NiFe complex is only responsible for the CO/acctyl-CoA exchange activity. Phen caused the removal of only 30% of Ni in the NiFe complex ($0.3Ni/{\alpha}{\beta}$) as shown by the quantitative metal analysis. The phen-treated CODH could be reactivated fully by incubation In $Ni^{2+}$ solution. Radioactive $^{63}Ni^{2+}$ was used to quantitate the amount of the $Ni^{2+}$ incorporated into phen-treated enzyme and showed that the amount was the same as the removed by the phen treatment. i.e. $0.3Ni/{\alpha}{\beta}$. This indicates that only 30% of NiFe complexes are labile and responsible for the CO/acctyl-CoA exchange activity, the other 70% are non-labile and have no exchange activity. This is the first clear evidence that the NiFe complex is heterogencous and labile and non-labile Ni sites arc interacting differently with substrates and chelating agents like phen.
Shin, Woonsup,Shin, Samuel Jaeho,Lee, Jong Myung,Nagarale, Rajaram Krishna,Heller, Adam Springer US 2011 Drug delivery and translational research Vol.1 No.4
<P>A programmable, skin-attached, 36??30??8?mm system for subcutaneous infusion of 1.2?mL of a drug solution is described. The system is intended to be replaced daily. It comprises a 20??14??8?mm electronic controller and power source, an 8?mm diameter 2?mm thick electroosmotic pump, a two-compartment reservoir for a pumped water and a drug solution, an adhesive tape for attachment to the skin, and a 6?mm long 27 gauge needle. Its removable electronic controller programs the dose rate and dose and is re-used. The electroosmotic pump consists of a porous ceramic membrane sandwiched between a pair of Ag/Ag2O plated carbon paper electrodes. It operates below 1.23?V, the thermodynamic threshold for water electrolysis without gassing. The flow rate can be adjusted between 4 and 30?μL?min(-1) by setting either by the voltage (0.2-0.8?V) or the current (30-200?μA). For average flow rates below 4?μL?min(-1), the pump is turned on and off intermittently. For example, a flow rate of 160?μL?day(-1), i.e., 0.13?μL?min(-1) for basal insulin infusion in type 1 diabetes management, is obtained when 10?s pulses of 75?μA is applied every 15?min. High flow rates of 10-30?μL?min(-1), required for prandial insulin administration, are obtained when the pump operates at 50-200?μA. To prevent fouling by the drug, only pure water passes the pump; the water pushes a drop of oil, which, in turn, pushes the drug solution.</P>
Quan De,Shin Woonsup The Korean Electrochemical Society 2004 한국전기화학회지 Vol.7 No.2
[ $DeniLite^{TM}$ ] laccase immobilized Pt electrode was used for amperometric detection of some catechol derivatives and o-aminophenol (OAP) derivative by means of substrate recycling. In case of catechol derivatives, the obtained sensitivities are 85, 79 and $57 nA/{\mu}M$ with linear ranges of $0.6\~30,\;0.6\~30\;and\; 1\~25 {\mu}M$ and detection limits (S/N=3) of 0.2, 0.2 and $0.3{\mu}M$ for 3,4-dihydroxycinnaminic acid (3,4-DHCA), 3,4-dihydroxybenzoic acid (3,4-DHBA) and 3,4-dihydroxyphenylacetic acid (3,4-DHPAA), respectively. In case of OAP derivative, the obtained sensitivity is $237 nA/{\mu}M$ with linear range of $0.2\~15{\mu}M$ and detection limit of 70 nM for 2-amino-4-chlorophenol (2-A-4-CP). The response time $(t_{90\%})$ is about 2 seconds for each substrate and the long-term stability is around 40-50days for catechol derivatives and 30 days for 2-A-4-CP with retaining $80\%$ of initial activity. The optimal pHs of the sensor for these substrates are in the range of 4.5-5.0, which indicates that stability of the enzymatically oxidized product plays a very important role in substrate recycling. The different sensitivity of the sensor for each substrate can be explained by the electronic effect of the sugstituent on the enzymatically oxidized form.
Baek, Jaewook,Shin, Woonsup The Korean Electrochemical Society 2018 Journal of electrochemical science and technology Vol.9 No.2
$MnO_2$, a metal oxide used as an electrode material in electrochemical capacitors (EDLCs), has been applied in binary oxide and conducting polymer hybrid electrodes to increase their stability and capacitance. We developed a method for electrodepositing Mn-Ni oxide/PANI, Mn-Ni oxide/PEDOT, and Mn-Ni-Ru oxide/PEDOT films on carbon paper in a single step using a mixed bath. Mn-Ni oxide/PEDOT and Mn-Ni-Ru oxide/PEDOT electrodes used in an electro-osmotic pump (EOP) have shown better efficiency compared to Mn-Ni oxide and Mn-Ni oxide/PANI electrodes through testing in water as a pumping solution. EOP using a Mn-Ni-Ru oxide/PEDOT electrode was also tested in a 0.5 mM $Li_2SO_4$ solution as a pumping solution to confirm the effect of the $Li^+$ insertion/de-insertion reaction of Ruthenium oxide on the EOP. Experimental results show that the flow rate increases with the increase in current in a 0.5 mM $Li_2SO_4$ solution compared to that obtained when water was used as a pumping solution.
Kim, Suk-Joon,Shin, Woonsup The Korean Electrochemical Society 2021 Journal of electrochemical science and technology Vol.12 No.2
Commercially available continuous glucose sensors require the operation stability for more than two weeks. Typically, the sensor comprises a sensing layer and an over-coating layer for the stable operation inside the body. In the sensing layer, enzymes and mediators are cross-linked together for the effective sensing of the glucose. The over-coating layer limits the flux of glucose and works as a biocompatible layer to the body fluids. Here, we report the simple preparation of the flux-limiting layer by the condensation of polyethyleneimine (PEI), tri-epoxide linker, and trimethylolpropane triglycidyl ether (PTGE). The sensor is constructed by a layer-by-layer drop-coating of the sensing layer containing glucose dehydrogenase and the PEI-derived blocking layer. It is stable for more than 14 days, which is enough for the sensor in the continuous monitor glucose monitoring (CGM) system.
Mercury Ion Monitoring in Mercury Plating Bath by Anodic Stripping Voltammetry
Park, Mijung,Yoon, Sumi,Shin, Woonsup The Korean Electrochemical Society 2016 Journal of electrochemical science and technology Vol.7 No.3
Anodic stripping voltammetry (ASV) is successfully applied in mM level detection of mercury ion in an electroplating bath which is currently used in preparing a cathodic electrolyzer. Glassy carbon electrode is used for the detection and the optimum condition obtained is 10 s deposition at −1.4 V vs. Ag/AgCl and stripping by scanning from −1.4 to +0.4 V vs Ag/AgCl at 50 mV/s. By applying the method, the mercury ion concentration in the electroplating bath could be successfully monitored during the plating.
Baek, Jaewook,Kim, Kyeonghyeon,Shin, Woonsup The Korean Electrochemical Society 2018 Journal of electrochemical science and technology Vol.9 No.2
Olivine structure of $LiFePO_4$ (LFP) is one of the most commonly used materials in aqueous rechargeable lithium batteries (ARLBs), and can store and release charge through the insertion/de-insertion of $Li^+$ between LFP and FP. We have fabricated LFP and LFP/FP electrodes on titanium paper and studied their electrochemical properties in 2 M $Li_2SO_4$. The LFP/FP electrode was determined to be a suitable electrode for electo-ostmotic pump (EOP) in terms of efficiency in water and 0.5 mM $Li_2SO_4$ solution. Experiments to determine the effect of cations and anions on the performance of EOP using LFP/FP electrode have shown that $Li^+$ is the best cation and that the anion does not significantly affect the performance of the EOP. As the concentration of $Li_2SO_4$ solution was increased, the current increased. The flow rate peaked at $4.8{\mu}L/30s$ in 1.0 mM $Li_2SO_4$ solution and then decreased. When the EOP was tested continuously in 1.0 mM $Li_2SO_4$ solution, the EOP transported approximately 35 mL of fluid while maintaining a stable flow rate and current for 144 h.