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Govindan Raghunathan,Sriram Sokalingam,Nagasundarapandian Soundrarajan,Ganapathiraman Munussami,Bharat Madan,이선구 한국생물공학회 2013 Biotechnology and Bioprocess Engineering Vol.18 No.2
Green fluorescent protein (GFP) has been used as a reporter marker in a wide range of biological and bioengineering studies. The expanded use of GFP in the field of biosensors, biochips and bio-conjugations requires the stability of GFP in organic co-solvent systems. This prompted us to examine the kinetic stability of two different GFP sequences, n-GFP and s-GFP, showing different folding robustness and thermodynamic stability, under a range of organic co-solvent systems. n-GFP and s-GFP are variants whose biophysical properties are comparable to wild type and super folder GFPs, respectively. The stability of n-GFP and s-GFP in 50% water-miscible organic solvents showed that s-GFP with higher thermodynamic stability exhibited much higher stability against organic solvents than n-GFP, which has lower thermodynamic stability. s-GFP was quite stable even in 90% organic solvents. Circular dichroism analysis confirmed that s-GFP maintained its native structure in organic co-solvent systems, whereas n-GFP showed structural variations under these conditions. Four highly fluctuating loop regions were identified from molecular dynamic simulations under the organic cosolvent conditions. A structural comparison of n-GFP and s-GFP suggested that the improved kinetic stability of s-GFP was due to its larger number of hydrogen bonds and salt-bridges that were present in four loop regions. This study suggests that thermodynamically stable s-GFP can be a good choice for use under harsh organic co-solvent conditions.
Govindan, Muthuraman,Adam Gopal, Ramu,Zhu, Bo,Duke, Mikel,Gray, Stephen,Moon, Il Shik Elsevier 2019 Journal of membrane science Vol.579 No.-
<P><B>Abstract</B></P> <P>Active ion crossover is a major obstacle in membrane electrolysis, which reduces the efficiency of the active mediator and increases operational cost. Using a prototype tubular cell divided with a MFI-zeolite-coated (shell side) ceramic tubular membrane, two active mediators, Co<SUP>3+</SUP> (Co<SUB>2</SUB>(SO<SUB>4</SUB>)<SUB>3</SUB>) in 5 M H<SUB>2</SUB>SO<SUB>4</SUB> at the anodic half-cell and Ni<SUP>1+</SUP> ([Ni(CN)<SUB>4</SUB>]<SUP>3-</SUP>) in 9 M KOH at the cathodic half-cell, were produced. The rate of Co<SUP>3+</SUP> production increased from 5.74 × 10<SUP>−3</SUP> M min<SUP>−1</SUP> to 7.11 × 10<SUP>−3</SUP> M min<SUP>−1</SUP> when the use of 9 M KOH at the cathodic half-cell instead of 5 M H<SUB>2</SUB>SO<SUB>4</SUB> at both half-cells and controlled migration due to the pH change. The absence of a UV–visible spectral peak for cobalt or nickel ions in the other side of the electrolyzed solution supports the lack of active metal ion crossover by the MFI-zeolite-coated ceramic membrane. In high acid and base electrolyte pH, the 5.6 fold higher resistance (5.13 Ω cm<SUP>−2</SUP>) than in high acid electrolytes in both half-cells (0.91 Ω cm<SUP>−2</SUP>) prevented proton and active mediator ion crossover. SEM-EDS and XRD data profiles found no cobalt or nickel ions on the membrane, which also supports the lack of migration, whereas the Al ion concentration decreased on the lumen side (9 M KOH containing the cathodic half-cell), demonstrating the dissolution of Al<SUB>2</SUB>O<SUB>3</SUB> in the KOH medium (uncoated MFI). The MFI-coated tubular membrane can be a good choice for the effective generation of two mediators by membrane electrolysis using high end pH electrolytes.</P> <P><B>Highlights</B></P> <P> <UL> <LI> MFI type zeolite membrane achieved for effective minimization of active ion crossover by pH variation. </LI> <LI> Two electron mediators have generated concurrently with high generation rate at each half-cells. </LI> <LI> No active ions migration evidenced by UV–visible analysis that were tested even during electrolysis. </LI> <LI> More than 1000 h operation in highly acid and base conditions confirm the effective stability of zeolite coating. </LI> </UL> </P>
Govindan, Muthuraman,Chung, Sang-Joon,Moon, Il-Shik American Chemical Society 2012 ACS combinatorial science Vol.14 No.6
<P>Electrochemically generated Co(III) mediated catalytic room temperature incineration of acetaldehyde, which is one of volatile organic compounds (VOCs), combined with wet scrubbing system was developed and investigated. Depending on the electrolyte’s type, absorption come removal efficiency is varied. In presence of electrogenerated Co(III) in sulfuric acid, acetaldehyde was mineralized to CO<SUB>2</SUB> and not like only absorption in pure sulfuric acid. The Co(III) mediated catalytic incineration led to oxidative absorption and elimination to CO<SUB>2</SUB>, which was evidenced with titration, CO<SUB>2</SUB>, and cyclic voltammetric analyses. Experimental conditions, such as current density, concentration of mediator, and gas molar flow rate were optimized. By the optimization of the experimental conditions, the complete mineralization of acetaldehyde was realized at a room temperature using electrochemically generated Co(III) with wet scrubber combinatorial system.</P><P><B>Graphic Abstract</B> <IMG SRC='http://pubs.acs.org/appl/literatum/publisher/achs/journals/content/acsccc/2012/acsccc.2012.14.issue-6/co300012a/production/images/medium/co-2012-00012a_0011.gif'></P>
Govindan, Muthuraman,Chung, Sang-Joon,Moon, Il-Shik American Chemical Society 2012 INDUSTRIAL & ENGINEERING CHEMISTRY RESEARCH - Vol.51 No.6
<P>The sustainable applicability of Ag(II)/Ag(I) redox mediator was studied in a semipilot-scale system for treatment of model artificial flue gases containing NO and SO<SUB>2</SUB>. Various discontinuous current supplies were tested for their effect on sustainable use of the electrogenerated mediator. Current density, cell volume, number of flow-through cell, and feed flow rates were varied in electrochemical thin layer cells to improve the applicability of the proposed current supply method. Discontinuing current flow every (5/5) min on–off (<I>i</I><SUB>DC5</SUB>) resulted in improved regeneration capacity of Ag(II) after 15 h. After extended operation (24 h), removal efficiencies of 62% NO and 100% SO<SUB>2</SUB> were achieved by mediated electrochemical oxidation both individually and simultaneously using the proposed discontinuous current supply, demonstrating the sustainable use of the mediator. This study will be taken as a pretest for long-term sustainability testing of the mediator, Ag(II), during industrial scaling up.</P><P><A href='http://pubs.acs.org/doi/suppl/10.1021/ie2015813'>ACS Electronic Supporting Info</A></P>
Govindan Muthuraman,문일식 한국공업화학회 2012 Journal of Industrial and Engineering Chemistry Vol.18 No.5
Mediated electrocatalytic oxidation (MEO) has been used for 150 years. Recently, the process was combined with scrubbing technology to allow the effective treatment of industrial air pollution. This review focuses on the development and applications of the MEO-assisted scrubbing process for the treatment of environmental air pollution. Particular focus was given to MEO using metal ions as mediators, influencing factors, such as electrolytes, electrode, flow method and rate, and the scrubbing column. More than 200 related publications were reviewed with 174 cited. Electro-scrubbing is considered as an advanced technology with possible further developments. Active electrodes, such as titanium-based Pt, DSA(RuO2/IrO2) film electrodes result in the complete mineralization of air pollutants in the MEO process. Air pollutants are removed with the assistance of electrogenerated high energy metal ions, such as Ag(II), Co(III) and Ce(IV), as well as by ozone and chlorine, as mediators in an acidic medium.