Name: a protocol for electrochemical evaluations and state of charge diagnostics of a symmetric organic redox flow battery
Uploaded: 2017-02-13T12:30:00
Description: Watch this Scientific Journal Video about A Protocol for Electrochemical Evaluations and State of Charge Diagnostics of a Symmetric Organic Redox Flow Battery at JoVE.com

This work was financially supported by Joint Center for Energy Storage Research (JCESR), an Energy Innovation Hub funded by the U.S. Department of Energy, Office of Science, Basic Energy Sciences. The authors also acknowledge Journal of Materials Chemistry A (a Royal Society of Chemistry journal) for originally publishing this research (<a href="http://pubs.rsc.org/en/content/articlehtml/2016/ta/c6ta01177b">http://pubs.rsc.org/en/content/articlehtml/2016/ta/c6ta01177b</a>). PNNL is a multi-program national laboratory operated by Battelle for DOE under Contract DE-AC05-76RL01830.

Note: All the solution preparations, cyclic voltammetry (CV) tests, and flow cell assembly and tests were carried out in an argon-filled glove box with water and O2 levels less than 1 ppm.
1. Electrochemical Evaluations of PTIO Flow Cells
<ol>
	<li>CV Test
	<ol>
		<li>Polish a glassy carbon electrode with 0.05 &#181;m gamma alumina powder, flush it with deionized water, put it in under vacuum at room temperature for overnight, and transfer it into a glove box.</li...

<ol>
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Soc. 136 (46), 16309-16316 (2014).</li><li>Wei, X., et al. <a target="_blank" href="http://www.ncbi.nlm.nih.gov/entrez/query.fcgi?db=PubMed&cmd=Search&doptcmdl=Citation&defaultField=Title+Word&term=TEMPO-Based+Catholyte+for+High-Energy+Density+Nonaqueous+Redox+Flow+Batteries.">TEMPO-Based Catholyte for High-Energy Density Nonaqueous Redox Flow Batteries.</a> Adv. Mater. 26 (45), 7649-7653 (2014).</li><li>Wei, X., et al. <a target="_blank" href="http://www.ncbi.nlm.nih.gov/entrez/query.fcgi?db=PubMed&cmd=Search&doptcmdl=Citation&defaultField=Title+Word&term=Towards+High-Performance+Nonaqueous+Redox+Flow+Electrolyte+Via+Ionic+Modification+of+Active+Species.">Towards High-Performance Nonaqueous Redox Flow Electrolyte Via Ionic Modification of Active Species.</a> Adv. Energy Mater. 5 (1), 1400678 (2015).</li><li>Fan, F. Y., et al. <a target="_blank" href="http://www.ncbi.nlm.nih.gov/entrez/query.fcgi?db=PubMed&cmd=Search&doptcmdl=Citation&defaultField=Title+Word&term=Polysulfide+Flow+Batteries+Enabled+by+Percolating+Nanoscale+Conductor+Networks.">Polysulfide Flow Batteries Enabled by Percolating Nanoscale Conductor Networks.</a> Nano Lett. 14 (4), 2210-2218 (2014).</li><li>Pan, H., et al. <a target="_blank" href="http://www.ncbi.nlm.nih.gov/entrez/query.fcgi?db=PubMed&cmd=Search&doptcmdl=Citation&defaultField=Title+Word&term=On+the+Way+Toward+Understanding+Solution+Chemistry+of+Lithium+Polysulfides+for+High+Energy+Li-S+Redox+Flow+Batteries.">On the Way Toward Understanding Solution Chemistry of Lithium Polysulfides for High Energy Li-S Redox Flow Batteries.</a> Adv. Energy Mater. 5 (16), 1500113 (2015).</li><li>Escalante-Garcia, I. L., Wainright, J. S., Thompson, L. T., Savinell, R. F. <a target="_blank" href="http://www.ncbi.nlm.nih.gov/entrez/query.fcgi?db=PubMed&cmd=Search&doptcmdl=Citation&defaultField=Title+Word&term=Performance+of+a+Non-Aqueous+Vanadium+Acetylacetonate+Prototype+Redox+Flow+Battery:+Examination+of+Separators+and+Capacity+Decay.">Performance of a Non-Aqueous Vanadium Acetylacetonate Prototype Redox Flow Battery: Examination of Separators and Capacity Decay.</a> J. Electrochem. Soc. 162 (3), 363-372 (2015).</li><li>Wei, X., et al. <a target="_blank" href="http://www.ncbi.nlm.nih.gov/entrez/query.fcgi?db=PubMed&cmd=Search&doptcmdl=Citation&defaultField=Title+Word&term=Microporous+Separators+for+Fe/V+Redox+Flow+Batteries.">Microporous Separators for Fe/V Redox Flow Batteries.</a> J. Power Sources. 218, 39-45 (2012).</li><li>Skyllas-Kazacos, M., Kazacos, M. <a target="_blank" href="http://www.ncbi.nlm.nih.gov/entrez/query.fcgi?db=PubMed&cmd=Search&doptcmdl=Citation&defaultField=Title+Word&term=State+of+Charge+Monitoring+Methods+for+Vanadium+Redox+Flow+Battery+Control.">State of Charge Monitoring Methods for Vanadium Redox Flow Battery Control.</a> J. Power Sources. 196 (20), 8822-8827 (2011).</li><li>Brooker, R. P., Bell, C. J., Bonville, L. J., Kunz, H. R., Fenton, J. M. <a target="_blank" href="http://www.ncbi.nlm.nih.gov/entrez/query.fcgi?db=PubMed&cmd=Search&doptcmdl=Citation&defaultField=Title+Word&term=Determining+Vanadium+Concentrations+Using+the+UV-Vis+Response+Method.">Determining Vanadium Concentrations Using the UV-Vis Response Method.</a> J. Electrochem. Soc. 162 (4), 608-613 (2015).</li><li>Petchsingh, C., et al. <a target="_blank" href="http://www.ncbi.nlm.nih.gov/entrez/query.fcgi?db=PubMed&cmd=Search&doptcmdl=Citation&defaultField=Title+Word&term=Spectroscopic+Measurement+of+State+of+Charge+in+Vanadium+Flow+Batteries+with+an+Analytical+Model+of+VIV-VV+Absorbance.">Spectroscopic Measurement of State of Charge in Vanadium Flow Batteries with an Analytical Model of VIV-VV Absorbance.</a> J. Electrochem. Soc. 163 (1), 5068-5083 (2016).</li><li>Duan, W., et al. <a target="_blank" href="http://www.ncbi.nlm.nih.gov/entrez/query.fcgi?db=PubMed&cmd=Search&doptcmdl=Citation&defaultField=Title+Word&term=A+Symmetric+Organic-Based+Nonaqueous+Redox+Flow+Battery+and+Its+State+of+Charge+Diagnostics+by+FTIR.">A Symmetric Organic-Based Nonaqueous Redox Flow Battery and Its State of Charge Diagnostics by FTIR.</a> J. Mater. Chem. A. 4 (15), 5448-5456 (2016).</li><li>Potash, R. A., McKone, J. R., Conte, S., Abru&#241;a, H. D. <a target="_blank" href="http://www.ncbi.nlm.nih.gov/entrez/query.fcgi?db=PubMed&cmd=Search&doptcmdl=Citation&defaultField=Title+Word&term=On+the+Benefits+of+a+Symmetric+Redox+Flow+Battery.">On the Benefits of a Symmetric Redox Flow Battery.</a> J. Electrochem. Soc. 163 (3), 338-344 (2016).</li><li>Kim, H. S., et al. <a target="_blank" href="http://www.ncbi.nlm.nih.gov/entrez/query.fcgi?db=PubMed&cmd=Search&doptcmdl=Citation&defaultField=Title+Word&term=A+Tetradentate+Ni(II)+Complex+Cation+as+a+Single+Redox+Couple+for+Non-aqueous+Flow+Batteries.">A Tetradentate Ni(II) Complex Cation as a Single Redox Couple for Non-aqueous Flow Batteries.</a> J. Power Sources. 283, 300-304 (2015).</li><li>Shinkle, A. A., Sleightholme, A. E. S., Griffith, L. D., Thompson, L. T., Monroe, C. 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As we demonstrated before,25 FTIR is capable of non-invasively detecting the SOC of the PTIO flow battery. As a diagnostic tool, FTIR is particularly advantageous because of its easy accessibility, fast response, low cost, small space requirement, facility for online incorporation, no detector saturation, and the ability to correlate structural information to investigate molecular evolutions during flow battery operation. Figure 3e illustrates a proposed flow battery device integr...

Redox flow batteries store energy in liquid electrolytes that are contained in external reservoirs and are pumped to internal electrodes to complete electrochemical reactions. The stored energy and power can thus be decoupled leading to excellent design flexibility, scalability, and modularity. These advantages make flow batteries well-suited for stationary energy storage applications for integrating clean yet intermittent renewable energies, increasing grid asset utilization and efficiency, and improving energy resiliency and security.1,2,3 Traditional aqueous flow batteries suffer from limited energy density, mostly due to the narrow voltage window to avoid water electrolysis.4,5,6,7,8 In contrast, non-aqueous electrolytes based flow batteries are being widely pursued because of the potential for achieving high cell voltage and high energy density.9,10 In these efforts, a variety of flow battery chemistries have been investigated, including metal-coordination complexes,11,12 all-organic,13,14 redox active polymers,15 and lithium hybrid flow systems.16,17,18,19
However, the potential of non-aqueous flow batteries has yet to be fully demonstrated due to the major technical bottleneck of limited demonstration under flow battery-relevant conditions. This bottleneck is closely associated with a number of performance-limiting factors. First, the small solubility of most electroactive materials leads to low energy density delivery by non-aqueous flow cells. Second, the rate capability of non-aqueous flow batteries is largely limited by the high electrolyte viscosity and resistivity at relevant redox concentrations. The third factor is the lack of high-performance membranes. Nafion and ceramic membranes show low ionic conductivity with non-aqueous electrolytes. Porous separators have demonstrated decent flow cell performance, but suffer considerable self-discharge because of relatively large pore size.14,20 Typically, mixed-reactant electrolytes containing both anolyte and catholyte redox materials (1:1 ratio) are used to reduce redox materials crossover, which however sacrifices the effective redox concentrations, typically by half.14,21 Overcoming the aforementioned bottleneck requires improvements in materials discovery, battery chemistry design, and flow cell architecture to achieve battery-relevant cycling.
Battery status monitoring is essentially important for reliable operations. Off-normal conditions including overcharge, gas evolution, and material degradation can cause damages to battery performance and even battery failure. Especially for large-scale flow batteries involving large amounts of battery materials, these factors can cause serious safety issues and investment loss. State of charge (SOC) describing the depth of charge or discharge of flow batteries is one of the most important battery status parameters. Timely SOC monitoring can detect potential risks before they reach threatening levels. However, this area seems to be under-addressed so far, especially in non-aqueous flow batteries. Spectrophotoscopic methods such as ultraviolet-visible (UV-vis) spectroscopy and electrolyte conductivity measurements have been evaluated in aqueous flow battery for SOC determination.22,23,24
We have recently introduced a novel symmetric non-aqueous flow battery design based on a new ambipolar redox material, 2-phenyl-4,4,5,5-tetramethylimidazoline-1-oxyl-3-oxide (PTIO).25 This flow battery holds the promise to address the aforementioned challenges of non-aqueous flow batteries. First, PTIO has a high solubility (2.6 M) in the battery solvent of acetonitrile (MeCN) that is promising to enable a high energy density. Second, PTIO exhibits two reversible redox pairs that are moderately separated and thus can form a symmetric battery chemistry by itself. We have also demonstrated that a distinguishable PTIO peak in the FTIR spectra can be correlated with the concentration of unreacted PTIO in the flow cell, which leads to spectroscopic determination of the SOC, as cross-validated by ESR results.26 Here we present a protocol to elaborate procedures for electrochemical evaluations and FTIR-based SOC diagnostics of the PTIO symmetric flow battery. This work is expected to trigger more insights in maintaining the safety and reliability during long-term flow battery operations, especially in real-world grid applications.

<table border="1" fo:keep-together.within-page="1" fo:keep-with-next.within-page="always">
	<tbody>
		<tr>
			<td>PTIO</td>
			<td>TCI America</td>
			<td>A5440</td>
			<td>&#62;98.0%</td>
		</tr>
		<tr>
			<td>Tetrabutylammonium hexafluorophosphate</td>
			<td>Sigma-Aldrich</td>
			<td>86879</td>
			<td>electrochemical grade, &#8805;99.0%</td>
		</tr>
		<tr>
			<td>MeCN</td>
			<td>BASF</td>
			<td>50325685</td>
			<td>Battery grade</td>
		</tr>
		<tr>
			<td>Silver nitrate</td>
			<td>Sigma-Aldrich</td>
			<td>204390</td>
			<td>99.9999% trace metals basis</td>
		</tr>
		<tr>
			<td>Gamma alumina powder</td>
			<td>CH Instruments</td>
			<td>CHI120</td>
			<td></td>
		</tr>
		<tr>
			<td>Graphite felt</td>
			<td>SGL</td>
			<td>GFD3</td>
			<td>Vacuum-dry at 70&#176;C for 24 h</td>
		</tr>
		<tr>
			<td>Porous separator</td>
			<td>Daramic</td>
			<td>AA800</td>
			<td>Vacuum-dry at 70&#176;C for 24 h</td>
		</tr>
		<tr>
			<td>Battery Tester</td>
			<td>Wuhan LAND electronics Co., Ltd.</td>
			<td>Lanhe</td>
			<td>1A current range</td>
		</tr>
		<tr>
			<td>Electrochemical Workstation</td>
			<td>Solartron Analytical</td>
			<td>ModuLab</td>
			<td></td>
		</tr>
		<tr>
			<td>glove box</td>
			<td>MBRAUN</td>
			<td>Labmaster SP</td>
			<td>oxygen and water levels &#60;1 ppm</td>
		</tr>
		<tr>
			<td>ESR spectrometer</td>
			<td>Bruker&#160;</td>
			<td>Elexsys 580&#160;</td>
			<td>Equipped with an SHQE resonator with microwave frequency ~9.85 GHz (X band) at 2 mW power, with 100 kHz field modulation</td>
		</tr>
	</tbody>
</table>

a protocol for electrochemical evaluations and state of charge diagnostics of a symmetric organic redox flow battery

Redox flow batteries have been considered as one of the most promising stationary energy storage solutions for improving the reliability of the power grid and deployment of renewable energy technologies. Among the many flow battery chemistries, non-aqueous flow batteries have the potential to achieve high energy density because of the broad voltage windows of non-aqueous electrolytes. However, significant technical hurdles exist currently limiting non-aqueous flow batteries to demonstrate their full potential, such as low redox concentrations, low operating currents, under-explored battery status monitoring, etc. In an attempt to address these limitations, we recently reported a non-aqueous flow battery based on a highly soluble, redox-active organic nitronyl nitroxide radical compound, 2-phenyl-4,4,5,5-tetramethylimidazoline-1-oxyl-3-oxide (PTIO). This redox material exhibits an ambipolar electrochemical property, and therefore can serve as both anolyte and catholyte redox materials to form a symmetric flow battery chemistry. Moreover, we demonstrated that Fourier transform infrared (FTIR) spectroscopy could measure the PTIO concentrations during the PTIO flow battery cycling and offer reasonably accurate detection of the battery state of charge (SOC), as cross-validated by electron spin resonance (ESR) measurements. Herein we present a video protocol for the electrochemical evaluation and SOC diagnosis of the PTIO symmetric flow battery. With a detailed description, we experimentally demonstrated the route to achieve such purposes. This protocol aims to spark more interests and insights on the safety and reliability in the field of non-aqueous redox flow batteries.

The unique advantages of the symmetric PTIO flow battery system are highly ascribed to the electrochemical properties of PTIO, an organic nitroxide radical compound. PTIO can undergo electrochemical disproportionation reactions to form PTIO+ and PTIO&#8722; (Figure 2a). These two redox pairs are moderately separated by a voltage gap of ~1.7 V (Figure 2b) and can be used as both anolyte and catholyte redox materials in a symmetric bat...

Watch this Scientific Journal Video about A Protocol for Electrochemical Evaluations and State of Charge Diagnostics of a Symmetric Organic Redox Flow Battery at JoVE.com

A Protocol for Electrochemical Evaluations and State of Charge Diagnostics of a Symmetric Organic Redox Flow Battery

We present the protocols for electrochemically evaluating a symmetric non-aqueous organic redox flow battery and for diagnosing its state of charge using FTIR.

Redox flow batteries have been considered as one of the most promising stationary energy storage solutions for improving the reliability of the power grid ...

The overall goal of this video protocol is to experimentally demonstrate the electrochemical performance and Fourier transform infrared based state of charge diagnostics of a symmetric, non-aqueous, PTIO based, redox flow battery. So this method can answer key questions in the grid energy storage field, such as how people can make sure the flow battery are running safely and reliably, especially in the long term operations. The main advantage for this technique is that the battery's state of charge can be determined through simple cost-effective Fourier transform infrared spectroscopy that is also integrable for real-time monitoring.Generally, individuals new to this technique will struggle because in flow batteries the solvent and supporting electrolytes will have very strong interferences during the quantification of the electroactive material. We first had this idea when we discover that PTIO has an absorption peak distinguishable from the solvent and the salt and is among the other oxidation states. All electrochemical tests, including cyclic voltammetry in flow cells, are performed in an argon filled glove box with water and oxygen levels of less than one ppm.Assemble the cyclic voltammetry setup in a 25 milliliter, three-neck, pear-shaped flask, with a polished glassy carbon working electrode, a graphite felt strip counter electrode, and a silver, silver nitrate 10 millimolar reference electrode. Next, dissolve 52 milligrams of PTIO and 0.87 grams of tetrabutylammonium hexafluorophosphate in 1.1 grams of acetonitrile. Add three milliliters of this solution to the flask to submerge the tips of the three electrodes.Connect the electrodes to an electrochemical work station. Measure the cyclic voltammetry curves in the voltage range of minus 1.75 to 0.75 volts at a scan rate of 100 millivolts per second. The potential gap between the two redox pairs is the theoretical cell voltage of the PTIO flow battery.To assemble the flow cell, first cut the graphite felt to an area of one by 10 square centimeters using a razor blade. Similarly, cut a porous separator to an area of three by 12 square centimeters and two gaskets, each with a hole of one by 10 square centimeters to accommodate the graphite felts. Dry the flow battery parts in a vacuum oven at 70 degrees Celsius overnight.The next day, move the parts into the glove box and allow them to cool down to the environmental temperature. Assemble the flow cell using a torque wrench, preset at 125 inch pounds. Then connect the electrolyte flow tubings to the flow cell.To perform the flow cell test, dissolve 1.05 grams of PTIO and 3.60 grams TBAPF6 in 3.60 grams of acetonitrile in the glove box. Then add four milliliters of the solution to each glass vial. Flow the electrolytes at 20 milliliters per minute.Connect the positive and negative current collectors of the flow cell to an electrochemical work station. Measure the electrochemical impedance spectroscopy of the flow cell in the frequency range from 100 kiloHertz to one Hertz at the open circuit potential. The voltage cutoffs of these flow cells are relatively sensitive to the cell by cell variation of impedance and need to be adjusted at the very first cycle of each cell to avoid overcharge.Connect the positive and negative current collectors of the flow cell to the battery tester. Set up voltage cutoffs of 0.8 and 2.2 volts in a constant current of 20 milliamps per square centimeter in the battery operation software. Repeatedly charge and discharge the PTIO flow cell.Prepare an acetonitrile solvent sample, a 1.0 molar TBAPF6 electrolyte solution, and a 0.5 molar PTIO, 1.0 molar TBAPF6 electrolyte solution in the glove box. Because the charge of PTIO species are air sensitive, sealable FTIR cells should be used to avoid air contact. An air tight container is recommended when transporting the FTIR cell out of the glove box to the FTIR spectrometer.Add a small volume of each solution to a sealable FTIR cell with potassium bromide windows and a path length of 0.2 millimeters. Seal the FTIR cell and put the FTIR cell in a storage container and transfer it out of the glove box. Mount the FTIR cell to a spectrometer and proceed to collect the FTIR spectrum.Then compare the acquired FTIR spectra of acetonitrile, 1.0 molar TBAPF6 and 0.5 molar PTIO, 1.0 molar TBAPF6 electrolyte. Next add 4.0 milliliters of the 0.5 molar PTIO, 1.0 molar TBAPF6 solution to each glass vial. Flow the electrolytes at 20 milliliters per minute.Fully charge the flow cell until the voltage reaches 2.2 volts. Then stop the charging in the pump and collect the positive and negative electrolytes. Measure the FTIR spectra for both the positive and negative electrolytes as before.Compare their FTIR spectra with that of the original PTIO solution. Working in a glove box, prepare a series of PTIO solutions in 1.0 molar TBAPF6 in acetonitrile. Measure and compare the FTIR spectra of each of the solutions to obtain the calibration curve.To measure the state of charge, first assemble another flow cell. Add 11 milliliters of the 0.5 molar PTIO, 1.0 molar TBAPF6 solution to each glass vial. Flow the electrolytes at 20 milliliters per minute.Charge the flow cell at a constant current of 10 milliamps per square centimeter. At various charge times, stop the cell charge and electrolyte flow and take small aliquots of the electrolytes from anolyte and catholyte side glass vials before resuming the cell. Finally, measure and compare the FTIR spectra of the five sample aliquots.The electrochemical performance of the PTIO flow cell is shown here. The PTIO cell shows a theoretical cell voltage of 1.73 volts from cyclic voltammetry. Cycling at 20 milliamps per square center for the 0.5 molar cell led to an average coulombic efficiency of 90%a voltaic efficiency of 67%and an energy efficiency of 60%However, the flow cell exhibited a capacity fading.The feasibility for using FTIR to determine the SOC is validated by the FTIR peaK at 1218 inverse centimeters. Here, the solvents and salt have minimal interference to PTIO. The three oxidation states of PTIO can be distinguished from each other.The logarithm of the peak intensity exhibits a linear dependence on the PTIO concentration and be used as the calibration curve. The PTIO concentration and state of charge of a PTIO flow cell at several time intervals during charging were determined by FTIR measurements. The accuracy of FTIR based SOC determination is cross-validated by electron spin resonance measurements.Once mastered, this technique can be done in eight hours if it is performed properly. While attempting this procedure it's important to remember to avoid oxygen or moisture exposure to the samples. Following this procedure, other methods, like measuring FTIR as function of cycle number can be performed in order to answer additional questions, like state of health and material's degradation.After watching the video, you should have a good understanding of how to evaluate the electrochemical performance of a given redox flow battery chemistry and how to measure the SOC of redox flow batteries that use FTIR sensitive redox materials.

a-protocol-for-electrochemical-evaluations-state-charge-diagnostics

Research

JoVE Journal

Chemistry

Steady-state, Pre-steady-state, and Single-turnover Kinetic Measurement for DNA Glycosylase Activity

Human 8-oxoguanine DNA glycosylase (OGG1) excises the mutagenic oxidative DNA lesion 8-oxo-7,8-dihydroguanine (8-oxoG) from DNA. Kinetic characterization of OGG1 is undertaken to measure the rates of 8-oxoG excision and product release. When the OGG1 concentration is lower than substrate DNA, time courses of product formation are biphasic; a rapid exponential phase (i.e. burst) of product formation is followed by a linear steady-state phase. The initial burst of product formation corresponds to the concentration of enzyme properly engaged on the substrate, and the burst amplitude depends on the concentration of enzyme. The first-order rate constant of the burst corresponds to the intrinsic rate of 8-oxoG excision and the slower steady-state rate measures the rate of product release (product DNA dissociation rate constant, koff). Here, we describe steady-state, pre-steady-state, and single-turnover approaches to isolate and measure specific steps during OGG1 catalytic cycling. A fluorescent labeled lesion-containing oligonucleotide and purified OGG1 are used to facilitate precise kinetic measurements. Since low enzyme concentrations are used to make steady-state measurements, manual mixing of reagents and quenching of the reaction can be performed to ascertain the steady-state rate (koff). Additionally, extrapolation of the steady-state rate to a point on the ordinate at zero time indicates that a burst of product formation occurred during the first turnover (i.e. y-intercept is positive). The first-order rate constant of the exponential burst phase can be measured using a rapid mixing and quenching technique that examines the amount of product formed at short time intervals (&lt;1 sec) before the steady-state phase and corresponds to the rate of 8-oxoG excision (i.e. chemistry). The chemical step can also be measured using a single-turnover approach where catalytic cycling is prevented by saturating substrate DNA with enzyme (E&gt;S). These approaches can measure elementary rate constants that influence the efficiency of removal of a DNA lesion.

Time courses for the glycosylase activity of 8-oxoguanine DNA glycosylase are biphasic exhibiting a burst of product formation and a linear steady-state phase. Utilizing quench-flow techniques, the burst and the steady-state rates can be measured, which correspond to excision of 8-oxoguanine and release of the glycosylase from the product DNA, respectively.

Human 8-oxoguanine DNA glycosylase (OGG1) excises the mutagenic oxidative DNA lesion 8-oxo-7,8-dihydroguanine (8-oxoG) from DNA. Kinetic characterization ...

Analysis of Volatile and Oxidation Sensitive Compounds Using a Cold Inlet System and Electron Impact Mass Spectrometry

This video presents a protocol for the mass spectrometrical analysis of volatile and oxidation sensitive compounds using electron impact ionization. The analysis of volatile and oxidation sensitive compounds by mass spectrometry is not easily achieved, as all state-of-the-art mass spectrometric methods require at least one sample preparation step, e.g., dissolution and dilution of the analyte (electrospray ionization), co-crystallization of the analyte with a matrix compound (matrix-assisted laser desorption/ionization), or transfer of the prepared samples into the ionization source of the mass spectrometer, to be conducted under atmospheric conditions. Here, the use of a sample inlet system is described which enables the analysis of volatile metal organyls, silanes, and phosphanes using a sector field mass spectrometer equipped with an electron impact ionization source. All sample preparation steps and the sample introduction into the ion source of the mass spectrometer take place either under air-free conditions or under vacuum, enabling the analysis of compounds highly susceptible to oxidation. The presented technique is especially of interest for inorganic chemists, working with metal organyls, silanes, or phosphanes, which have to be handled using inert conditions, such as the Schlenk technique. The principle of operation is presented in this video.

This video presents a protocol for the mass spectrometrical analysis of volatile and oxidation sensitive compounds using electron impact ionization. The presented technique is especially of interest for inorganic chemists, working with metal organyls, silanes, or phosphanes which have to be handled using inert conditions, such as the Schlenk technique.

This video presents a protocol for the mass spectrometrical analysis of volatile and oxidation sensitive compounds using electron impact ionization. The ...

Dynamic Electrochemical Measurement of Chloride Ions

This protocol describes the dynamic measurement of chloride ions using the transition time of a silver silver chloride (Ag/AgCl) electrode. Silver silver chloride electrode is used extensively for potentiometric measurement of chloride ions concentration in electrolyte. In this measurement, long-term and continuous monitoring is limited due to the inherent drift and the requirement of a stable reference electrode. We utilized the chronopotentiometric approach to minimize drift and avoid the use of a conventional reference electrode. A galvanostatic pulse is applied to an Ag/AgCl electrode which initiates a faradic reaction depleting the Cl&#713; ions near the electrode surface. The transition time, which is the time to completely deplete the ions near the electrode surface, is a function of the ion concentration, given by the Nernst equation. The square root of the transition time is in linear relation to the chloride ion concentration. Drift of the response over two weeks is negligible (59 &#181;M/day) when measuring 1 mM [Cl&#713;]using a current pulse of 10 Am-2. This is a dynamic measurement where the moment of transition time determines the response and thus is independent of the absolute potential. Any metal wire can be used as a pseudo-reference electrode, making this approach feasible for long-term measurement inside concrete structures.

Dynamic measurement of chloride ions is presented. Transition time of an Ag/AgCl electrode, during a chronopotentiometric technique, can give the concentration of chloride ions in electrolyte. This method does not require a stable conventional reference electrode.

This protocol describes the dynamic measurement of chloride ions using the transition time of a silver silver chloride (Ag/AgCl) electrode. Silver silver ...

Glycan Node Analysis: A Bottom-up Approach to Glycomics

Synthesized in a non-template-driven process by enzymes called glycosyltransferases, glycans are key players in various significant intra- and extracellular events. Many pathological conditions, notably cancer, affect gene expression, which can in turn deregulate the relative abundance and activity levels of glycoside hydrolase and glycosyltransferase enzymes. Unique aberrant whole glycans resulting from deregulated glycosyltransferase(s) are often present in trace quantities within complex biofluids, making their detection difficult and sometimes stochastic. However, with proper sample preparation, one of the oldest forms of mass spectrometry (gas chromatography-mass spectrometry, GC-MS) can routinely detect the collection of branch-point and linkage-specific monosaccharides ("glycan nodes") present in complex biofluids. Complementary to traditional top-down glycomics techniques, the approach discussed herein involves the collection and condensation of each constituent glycan node in a sample into a single independent analytical signal, which provides detailed structural and quantitative information about changes to the glycome as a whole and reveals potentially deregulated glycosyltransferases. Improvements to the permethylation and subsequent liquid/liquid extraction stages provided herein enhance reproducibility and overall yield by facilitating minimal exposure of permethylated glycans to alkaline aqueous conditions. Modifications to the acetylation stage further increase the extent of reaction and overall yield. Despite their reproducibility, the overall yields of N-acetylhexosamine (HexNAc) partially permethylated alditol acetates (PMAAs) are shown to be inherently lower than their expected theoretical value relative to hexose PMAAs. Calculating the ratio of the area under the extracted ion chromatogram (XIC) for each individual hexose PMAA (or HexNAc PMAA) to the sum of such XIC areas for all hexoses (or HexNAcs) provides a new normalization method that facilitates relative quantification of individual glycan nodes in a sample. Although presently constrained in terms of its absolute limits of detection, this method expedites the analysis of clinical biofluids and shows considerable promise as a complementary approach to traditional top-down glycomics.

This article presents an enhanced form of a novel bottom-up glycomics technique designed to analyze the pooled compositional profile of glycans in unfractionated biofluids through the chemical breakdown of glycans into their constituent linkage-specific monosaccharides for detection by GC-MS. Potential applications include early detection of cancer and other glycan-affective disorders.

Synthesized in a non-template-driven process by enzymes called glycosyltransferases, glycans are key players in various significant intra- and ...

Synthesis of Cyclic Polymers and Characterization of Their Diffusive Motion in the Melt State at the Single Molecule Level

We demonstrate a method for the synthesis of cyclic polymers and a protocol for characterizing their diffusive motion in a melt state at the single molecule level. An electrostatic self-assembly and covalent fixation (ESA-CF) process is used for the synthesis of the cyclic poly(tetrahydrofuran) (poly(THF)). The diffusive motion of individual cyclic polymer chains in a melt state is visualized using single molecule fluorescence imaging by incorporating a fluorophore unit in the cyclic chains. The diffusive motion of the chains is quantitatively characterized by means of a combination of mean-squared displacement (MSD) analysis and a cumulative distribution function (CDF) analysis. The cyclic polymer exhibits multiple-mode diffusion which is distinct from its linear counterpart. The results demonstrate that the diffusional heterogeneity of polymers that is often hidden behind ensemble averaging can be revealed by the efficient synthesis of the cyclic polymers using the ESA-CF process and the quantitative analysis of the diffusive motion at the single molecule level using the MSD and CDF analyses.

A protocol for the synthesis and characterization of diffusive motion of cyclic polymers at the single molecule level is presented.

We demonstrate a method for the synthesis of cyclic polymers and a protocol for characterizing their diffusive motion in a melt state at the single ...

Using Capillary Electrophoresis to Quantify Organic Acids from Plant Tissue: A Test Case Examining Coffea arabica Seeds

Carboxylic acids are organic acids containing one or more terminal carboxyl (COOH) functional groups. Short chain carboxylic acids (SCCAs; carboxylic acids containing three to six carbons), such as malate and citrate, are critical to the proper functioning of many biological systems, where they function in cellular respiration and can serve as indicators of cell health. In foods, organic acid content can have significant impact on taste, with increased SCCA levels resulting in a sour or &#34;acid&#34; taste. Because of this, methods for the rapid analysis of organic acid levels are of particular interest to the food and beverage industries. Unfortunately, however, most methods used for SCCA quantification are dependent on time-consuming protocols requiring the derivatization of samples with hazardous reagents, followed by costly chromatographic and/or mass spectrometric analyses. This method details an alternate method for the detection and quantification of organic acids from plant material and food samples using free zonal capillary electrophoresis (CZE), sometimes simply referred to as capillary electrophoresis (CE). CZE provides a cost-effective method for measuring SCCAs with a low limit of detection (0.005 mg/ml). This article details the extraction and quantification of SCCAs from plant samples. While the method provided focuses on measurement of SCCAs from coffee beans, the method provided can be applied to multiple plant-based food materials.

Using Capillary Electrophoresis to Quantify Organic Acids from Plant Tissue: A Test Case Examining Coffea arabica Seeds

This article presents a method for the detection and quantification of organic acids from plant material using free zonal capillary electrophoresis. An example of the potential application of this method, determining the effects of a secondary fermentation on organic acid levels in coffee seeds, is provided.

Carboxylic acids are organic acids containing one or more terminal carboxyl (COOH) functional groups. Short chain carboxylic acids (SCCAs; carboxylic ...

Electrochemical Impedance Spectroscopy as a Tool for Electrochemical Rate Constant Estimation

Electrochemical impedance spectroscopy (EIS) was used for advanced characterization of organic electroactive compounds along with cyclic voltammetry (CV). In the case of fast reversible electrochemical processes, current is predominantly affected by the rate of diffusion, which is the slowest and limiting stage. EIS is a powerful technique that allows separate analysis of stages of charge transfer that have different AC frequency response. The capability of the method was used to extract the value of charge transfer resistance, which characterizes the rate of charge exchange on the electrode-solution interface. The application of this technique is broad, from biochemistry up to organic electronics. In this work, we are presenting the method of analysis of organic compounds for optoelectronic applications.

Electrochemical impedance spectroscopy (EIS) of species that undergo reversible oxidation or reduction in solution was used for determination of rate constants of oxidation or reduction.

Electrochemical impedance spectroscopy (EIS) was used for advanced characterization of organic electroactive compounds along with cyclic voltammetry (CV). ...

Controlled Photoredox Ring-Opening Polymerization of O-Carboxyanhydrides Mediated by Ni/Zn Complexes

Here, we describe an effective protocol that combines photoredox Ni/Ir catalysis with the use of a Zn-alkoxide for efficient ring-opening polymerization, allowing for the synthesis of isotactic poly(&#945;-hydroxy acids) with expected molecular weights (&#62;140 kDa) and narrow molecular weight distributions (Mw/Mn &#60; 1.1). This ring-opening polymerization is mediated by Ni and Zn complexes in the presence of an alcohol initiator and a photoredox Ir catalyst, irradiated by a blue LED (400 - 500 nm). The polymerization is performed at a low temperature (-15 &#176;C) to avoid undesired side reactions. The complete monomer consumption can be achieved within 4 - 8 hours, providing a polymer close to the expected molecular weight with narrow molecular weight distribution. The resulted number-average molecular weight shows a linear correlation with the degree of polymerization up to 1000. The homodecoupling 1H NMR study confirms that the obtained polymer is isotactic without epimerization. This polymerization reported herein offers a strategy for achieving rapid, controlled O-carboxyanhydrides polymerization to prepare stereoregular poly(&#945;-hydroxy acids) and its copolymers bearing various functional side-chain groups.

Controlled Photoredox Ring-Opening Polymerization of O-Carboxyanhydrides Mediated by Ni/Zn Complexes

A protocol for the controlled photoredox ring-opening polymerization of O-carboxyanhydrides mediated by Ni/Zn complexes is presented.

Here, we describe an effective protocol that combines photoredox Ni/Ir catalysis with the use of a Zn-alkoxide for efficient ring-opening polymerization, ...

Ion Mobility-Mass Spectrometry Techniques for Determining the Structure and Mechanisms of Metal Ion Recognition and Redox Activity of Metal Binding Oligopeptides

Electrospray ionization (ESI) can transfer an aqueous-phase peptide or peptide complex to the gas-phase while conserving its mass, overall charge, metal-binding interactions, and conformational shape. Coupling ESI with ion mobility-mass spectrometry (IM-MS) provides an instrumental technique that allows for simultaneous measurement of a peptide&#8217;s mass-to-charge (m/z) and collision cross section (CCS) that relate to its stoichiometry, protonation state, and conformational shape. The overall charge of a peptide complex is controlled by the protonation of 1) the peptide&#8217;s acidic and basic sites and 2) the oxidation state of the metal ion(s). Therefore, the overall charge state of a complex is a function of the pH of the solution that affects the peptides metal ion binding affinity. For ESI-IM-MS analyses, peptide and metal ions solutions are prepared from aqueous-only solutions, with the pH adjusted with dilute aqueous acetic acid or ammonium hydroxide. This allows for pH dependence and metal ion selectivity to be determined for a specific peptide. Furthermore, the m/z and CCS of a peptide complex can be used with B3LYP/LanL2DZ molecular modeling to discern binding sites of the metal ion coordination and tertiary structure of the complex. The results show how ESI-IM-MS can characterize the selective chelating performance of a set of alternative methanobactin peptides and compare them to the copper-binding peptide methanobactin.

Ion mobility-mass spectrometry and molecular modeling techniques can characterize the selective metal chelating performance of designed metal-binding peptides and the copper-binding peptide methanobactin. Developing new classes of metal chelating peptides will help lead to therapeutics for diseases associated with metal ion misbalance.

Electrospray ionization (ESI) can transfer an aqueous-phase peptide or peptide complex to the gas-phase while conserving its mass, overall charge, ...

Evaluation of Oxidative Stress in Biological Samples Using the Thiobarbituric Acid Reactive Substances Assay

Despite its limited analytical specificity and ruggedness, the thiobarbituric acid reactive substances (TBARS) assay has been widely used as a generic metric of lipid peroxidation in biological fluids. It is often considered a good indicator of the levels of oxidative stress within a biological sample, provided that the sample has been properly handled and stored. The assay involves the reaction of lipid peroxidation products, primarily malondialdehyde (MDA), with thiobarbituric acid (TBA), which leads to the formation of MDA-TBA2 adducts called TBARS. TBARS yields a red-pink color that can be measured spectrophotometrically at 532 nm. The TBARS assay is performed under acidic conditions (pH = 4) and at 95 &#176;C. Pure MDA is unstable, but these conditions allow the release of MDA from MDA bis(dimethyl acetal), which is used as the analytical standard in this method. The TBARS assay is a straightforward method that can be completed in about 2 h. Preparation of assay reagents are described in detail here. Budget-conscious researchers can use these reagents for multiple experiments at a low cost rather than buying an expensive TBARS assay kit that only permits construction of a single standard curve (and thus can only be used for one experiment). The applicability of this TBARS assay is shown in human serum, low density lipoproteins, and cell lysates. The assay is consistent and reproducible, and limits of detection of 1.1 &#956;M can be reached. Recommendations for the use and interpretation of the spectrophotometric TBARS assay are provided.

The goal of the thiobarbituric acid reactive substances assay is to assess oxidative stress in biological samples by measuring the production of lipid peroxidation products, primarily malondialdehyde, using visible wavelength spectrophotometry at 532 nm. The method described here can be applied to human serum, cell lysates, and low density lipoproteins.

Despite its limited analytical specificity and ruggedness, the thiobarbituric acid reactive substances (TBARS) assay has been widely used as a generic ...