SR acknowledges the support of the Israel science foundation, grant no. 280/12.

1. Preparing Carbon Samples
<ol>
	<li>Grind the carbon samples to the desired fraction size (here, coal samples were ground to a fraction size of between 74-250 mm).</li>
	<li>During the grinding process the grinder should be held in a regulated environment (AC cooled to 20 &#176;C). Additionally, purging the grinder chamber with a flow of nitrogen gas prior to grinding minimizes oxidation at this stage.</li>
	<li>Transfer the carbon samples to sealable canisters and replace the air atmosphere with nitrogen. Keep the samples in a temperature regulated room (AC cooled to 20 &#176;C).&#160;</li>
	<li>Prepare the carbon samples for EPR measurements by heating the carbon samples under an inert environment in the vacuum oven. (In order to remove the adsorbed water in the system.)</li>
	<li>Place each of the samples in an open glass vial inside the vacuum oven (Figure 1A).</li>
	<li>Close the vacuum oven door and replace atmosphere in the chamber with nitrogen or argon, then heat to 60 &#186;C.</li>
	<li>Hold these conditions for 24 hr.</li>
	<li>Turn off the oven and allow the temperature to reach room temperature. Then, open the oven and remove the sample vials.</li>
	<li>Stopper the sample vials with rubber septa and an aluminum cap (Figure 1B).</li>
	<li>Use a vacuum system (Figure 1C) to remove all traces of oxygen.</li>
	<li>Connect the vial to the system and seal valves 1-5.</li>
	<li>Turn on the vacuum pump and pressure gauges.</li>
	<li>Open valve 1 and wait till the monitors show a vacuum of ~0.1 mbar.</li>
	<li>Make sure leakage is minimal by closing valve 1 and counting to 30. If the increase in pressure is not more than 3 mbar than the seal of the system is sufficient.</li>
	<li>Open valve 2 and remove the atmosphere in the vial &#8211; wait till the pressure returns to the initial pressure value determined in step 1.14 and again test for leakage.</li>
	<li>If multiple vials are being done at the same time (valves 2-4) then repeat step 1.15 for each valve.</li>
	<li>After achieving a vacuum and effectively purging the vials of the remaining atmosphere, replace the atmosphere with a desired gas.</li>
	<li>Close valve 1 and immediately open valve 5 and allow the pressure to reach 0.5 atm.</li>
	<li>Close valve 5 and open valve 1 to remove the gas, and wait until return to the starting vacuum valve (purge 1).</li>
	<li>Close valve 1 and immediately open valve 5 and allow the pressure to reach 0.5 atm.</li>
	<li>Close valve 5, open valve 1 to remove the gas and wait until return to the starting vacuum valve (purge 2).</li>
	<li>Close valve 1 and immediately open valve 5, and allow the pressure to reach 1.0 atm, then close valve 5.</li>
	<li>Close valve 2 and remove the vial by gently pulling downward and removing the needle.</li>
	<li>After removing the vial open valve 1 and purge the gas from the vacuum system.</li>
	<li>Before turning off the vacuum pump open valve 2 to allow air into the system and simultaneously turn off the pump (this prevents a backflow of the oil).</li>
</ol>
2. Loading EPR 3 mm Quartz Tubes
<ol>
	<li>Rinse the EPR tube with ethanol and dry with N2.</li>
	<li>Remove the aluminum seal from the desired coal sample.</li>
	<li>Gently turn the open end of the EPR tube into the vial filled with the carbon sample.</li>
	<li>Depress and turn the EPR tube, then gently tap until the sample has evenly dispersed at the bottom.</li>
	<li>Fill the tube in this manner up to a length of at least 1.5 cm.</li>
	<li>Seal the tip of the tube with rubber Teflon putty of about 0.5-1.0 cm length of putty (Figure 2A).</li>
</ol>
3. Setting Up the Flow System
<ol>
	<li>Insert the quartz tube into the EPR resonator, make sure that the section of the EPR tube filled with the coal is filling the entire resonator cavity.</li>
	<li>The EPR measurements reported here were conducted at room temperature 292-297 K.</li>
	<li>Set up a tank with the desired flow gas (N2, CO2, He) make sure there are 2 operation valves in order to control the flow (Figure 2B).</li>
	<li>Connect a rubber tubing to the tank. Ensure that the length reaches the tip of the EPR quartz tube with enough pull so as not to put strain on the quartz tube.</li>
	<li>Connect a flow controller to the rubber tubing to monitor gas flow.</li>
	<li>Insert the tube through the rubber Teflon putty by using a small gauge needle.</li>
	<li>Insert the needle until it is in close proximity (about 3-4 cm above the coal surface) to the sample but far enough away from the sample so as not to affect the magnetic field (Figure 2C).</li>
	<li>Leave flow off&#160; (turn on flow ONLY after tuning).</li>
	<li>Poke a hole in the rubber putty to release the outflow gas.</li>
</ol>
4. EPR Measurement
<ol>
	<li>Turn on the EPR spectrometer.</li>
	<li>Tune with no gas flow. Open the microwave tuning panel, locate the dip at 33.0 dB power, and use auto tune for obtaining the best tuning conditions..</li>
	<li>Set the microwave power to 2.0 mW, at this power there is no saturation.</li>
	<li>Open 2D experiment, as a function of magnetic field and time.</li>
	<li>Set the parameters of the experiment as follows: 
	Microwave power = 2.0 mW 
	Modulation amplitude = 1.0 G 
	Time constant = 60 msec 
	Sweep width = 100 G 
	Delay = 120 sec 
	No. of points for a field sweep scan = 1024 
	No. of points as a function of time = 50</li>
	<li>Start measurement cycle.</li>
	<li>Turn on gas flow.</li>
	<li>After the sample has reached equilibrium and there is no further change in the EPR line shape, at these parameters after about 25 CW-EPR spectra that were measured with 120 sec delay between them, stop the gas flow. Expose the sample to an air atmosphere and continue with the measurements until 50 spectra are obtained, or until equilibrium is reached. There is no need to tune again after stopping the gas flow. The measurement is continuing automatically, with 120 sec delay between each CW-EPR spectrum.</li>
	<li>If equilibrium is reached at a slower rate, increase the number&#160;of points as a function of time.</li>
	<li>If equilibrium is reached at much faster rate, decrease the delay time between each scan.</li>
</ol>
5. Data Analysis
<ol>
	<li>Simulate each EPR field sweep spectrum using the easyspin toolbox implemented on MATLAB23. Take two species into account, where for each species the g-value, the line width, and the extent of contribution to the EPR spectrum is fitted by writing the program file as follows: 
	clear, clf, clc 
	% Load experimental file 
	expdata= load(&#39;t0s.txt&#39;); 
	%Define spin system of species one 
	SysC.g = 2.004; 
	SysC.lwpp =0.62; 
	%Define experiment parameters for species one 
	Exp.mwFreq = 9.85764;&#160;&#160; %in GHz 
	Exp.Range=[347 357];&#160;&#160;&#160;&#160;&#160; %in mT 
	Exp.Harmonic=1; 
	%calculate CW EPR spectrum for species one 
	[Bx,specX] = pepper(SysC,Exp); 
	%Define spin system of species two 
	SysC2.g = 2.0028; 
	SysC2.lwpp =0.145; 
	%Define experimental parameters for species two 
	Exp2.mwFreq = 9.85764; 
	Exp2.Range=[347 357]; 
	Exp2.Harmonic=1; 
	%calculate CW EPR spectrum for species two 
	[Bx2,specX2] = pepper(SysC2,Exp2); 
	x=0:0.1:1; 
	% combine the spectrum of the two species. 
	spectot=1.0*specX+0.0*specX2; 
	%plotting the experimental and simulated spectra. 
	Bx*10,spectot,expdata(:,1),expdata(:,2));</li>
</ol>

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No conflicts of interest declared.

Surface oxidation of carbon materials is of significant industrial and academic interest. The effects of carbon substrate oxidation have been characterized with a wide range of analytical techniques including EPR. When investigating the interaction of molecular oxygen with carbon substrate such as coal which has a propensity to undergo oxidation (hence its main utilization as an energy resource) sample preparation and storage is extremely important.
Our samples are coal substrates that have be...

Substrates of varying (wt%) ratios of C/H/O atoms present different types and concentrations of stable radicals that are detectable via Electron Paramagnetic Resonance (EPR)8. These radicals depend on the structure of the macromolecules and are highly influenced by their aromatic nature. The EPR spectrum of coal radicals is characterized by a single broad resonance. In such cases, only the g-value, the line width and the spin concentration can be obtained. The g-values of EPR spectra can be used to determine whether a radical is carbon-centered or oxygen-centered. The basic equation for the electron Zeeman interaction <img alt="Equation 1" fo:content-width="0.8in" src="/files/ftp_upload/51548/51548eq1.jpg" /> defines the g-value, where h is the Planck constant, v is the constant mw frequency applied in the experiment, B0 is the resonance magnetic field and &#946;e is the Bohr magneton. For free electrons the g-value is 2.00232. Variations in the g-value from the 2.00232 are related to magnetic interactions involving the orbital angular momentum of the unpaired electron and its chemical environment. Organic radicals usually have g-values close to the free electron g, which depends on the location of the free radical in the organic matrix3,8-10. Carbon-centered radicals have g-values that are close to the free electron g-value 2.0023. Carbon-centered radicals with an adjacent oxygen atom have higher g-values in the range of 2.003-2.004, while oxygen centered radicals have g-values that are &#62;2.004. The g-value of 2.0034-2.0039 is characteristic for carbon-centered radicals in a nearby oxygen heteroatom that results in increased g-values over that of purely carbon-centered radicals11-15. Line-width is governed by the spin-lattice relaxation process. Therefore, an interaction between adjacent radicals or between a radical and paramagnetic oxygen results in a decrease in the spin lattice relaxation time, and hence, an increase in the line-width4-6.
Stopped flow experiments with EPR detection allow the observation of time-dependent changes in the amplitude of an EPR signal at a distinct field value during the interaction of two phases by time sweep acquisition (kinetic display). The result of such a measurement is a rate constant for the formation, decay or conversion of a paramagnetic species. The procedure is analogous to the well-established case of stopped flow operation with optical detection in which a time-dependence of the optical absorption at a distinct wavelength is observed. Typically stopped flow experiments are conducted in a liquid state as radicals that are not EPR detected in liquid state due to short relaxation time T1, as e.g.&#160;hydroxyl (OH&#215;) or superoxide (O2-) cannot be studied directly by EPR-stopped flow techniques. It is, however, possible to study the spin-adducts of these radicals with nitrones, yielding nitroxide-type radicals (spin-traps), as they are EPR-active and their kinetics can be monitored also by stopped flow EPR16-18.
The method of measurement of rates of chemical reactions using fast-flow gaseous techniques with EPR detection has also previously been established19-22. In essence, the method depends on the measurement, by EPR, of the concentration of a reactant as a function of distance (and thus at a constant velocity, the time) over which the reactant has been in contact with a reactive gas in the flow tube. Conditions whereby the concentration of the reactive gas is approximately constant are usually employed so that the measured decay is pseudo first order.
In the current work, a simple gas flow setup was implemented and a constant flow of gas was introduced to the surface of the solid carbon substrate.
With the method detailed in the current work we succeeded in achieving interesting results where this interaction of molecular oxygen with a certain part of the existing stable radical structure can be reversibly affected simply by flowing a diamagnetic gas through the carbon samples at STP. As a result of this method the removal of the interacting paramagnetic gas uncovers a new radical surface with a g value, which is closer to that of a free electron.

<table><tbody><tr><td>EPR spectrometer</td><td>Bruker</td><td>Elexsys E500</td><td></td></tr><tr><td>EPR quartz tube</td><td>Wilmad-Lab Glass</td><td></td><td></td></tr><tr><td>Vacuum oven&amp;nbsp;</td><td>Heraeus</td><td>VT6060</td><td></td></tr><tr><td>Balance</td><td>Denver Instrument</td><td>100A</td><td></td></tr><tr><td>High Vacuum Silicone Grease</td><td>VWR International</td><td>59344-055</td><td></td></tr><tr><td>Teflon putty&amp;nbsp;</td><td></td><td></td><td></td></tr><tr><td>Laboratory (Rubber) Stoppers</td><td>Sigma-Aldrich</td><td>Z114111</td><td></td></tr><tr><td>Aluminum Crimp seals&amp;nbsp;</td><td>Sigma-Aldrich</td><td>Z114146</td><td></td></tr><tr><td>Hand Crimper</td><td>Sigma-Aldrich</td><td>Z114243</td><td></td></tr><tr><td>Borosilicate vials&amp;nbsp;</td><td>Sigma-Aldrich</td><td>Z11938</td><td></td></tr><tr><td>Rubber tubing&amp;nbsp;</td><td></td><td></td><td></td></tr><tr><td>Aluminum hose clamps</td><td></td><td></td><td></td></tr><tr><td>Screwdriver&amp;nbsp;</td><td></td><td></td><td></td></tr><tr><td>Custom made vacuum system&amp;nbsp;</td><td></td><td></td><td></td></tr><tr><td>Glass storage cylinders&amp;nbsp;</td><td></td><td></td><td></td></tr><tr><td>BD Regular Bevel Needles</td><td>BD</td><td>305122</td><td></td></tr><tr><td>Helium&amp;nbsp;&amp;nbsp;</td><td>Oxar Ltd</td><td></td><td></td></tr><tr><td>Argon&amp;nbsp;&amp;nbsp;&amp;nbsp;&amp;nbsp;</td><td>Oxar Ltd</td><td></td><td></td></tr><tr><td>CO&lt;sub&gt;2&lt;/sub&gt; 99.99%</td><td>Maxima</td><td></td><td></td></tr><tr><td>N&lt;sub&gt;2&lt;/sub&gt; 99.999%</td><td>Oxar Ltd</td><td></td><td></td></tr><tr><td>O&lt;sub&gt;2&lt;/sub&gt;</td><td>Maxima</td><td></td><td></td></tr><tr><td>Air</td><td>Maxima</td><td></td><td></td></tr></tbody></table>

exploring the radical nature of a carbon surface by electron paramagnetic resonance and a calibrated gas flow

While the first Electron Paramagnetic Resonance (EPR) studies regarding the effects of oxidation on the structure and stability of carbon radicals date back to the early 1980s the focus of these early papers primarily characterized the changes to the structures under extremely harsh conditions (pH or temperature)1-3. It is also known that paramagnetic molecular oxygen undergoes a Heisenberg spin exchange interaction with stable radicals that extremely broadens the EPR signal4-6. Recently, we reported interesting results where this interaction of molecular oxygen with a certain part of the existing stable radical structure can be reversibly affected simply by flowing a diamagnetic gas through the carbon samples at STP7. As flows of He, CO2, and N2 had a similar effect these interactions occur at the surface area of the macropore system.
This manuscript highlights the experimental techniques, work-up, and analysis towards affecting the existing stable radical nature in the carbon structures. It is hoped that it will help towards further development and understanding of these interactions in the community at large.

When preforming the EPR experiments on various coal samples, as a function of the exposure time to a diamagnetic gas flow it was noted that during the gas flow, a second species at g~2.0028 appeared. This g-value is close to the value of a free electron and consistent with unsubstituted aliphatic carbon centered radicals. However, the total spin concentration for each sample remained constant within our experimental error (&#177;10%). Figure 3A presents two scans: 0 sec and 1,900 sec after the coal sampl...

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Exploring the Radical Nature of a Carbon Surface by Electron Paramagnetic Resonance and a Calibrated Gas Flow

Stable radicals that are present in carbon substrates interact with paramagnetic oxygen through a Heisenberg spin exchange. This interaction can be significantly reduced under STP conditions by flowing a diamagnetic gas over the carbon system. This manuscript describes a simple method to characterize the nature of those radicals.

While the first Electron Paramagnetic Resonance (EPR) studies regarding the effects of oxidation on the structure and stability of carbon radicals date ...

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10.7K Views.  The Hebrew University of Jerusalem. Stable radicals that are present in carbon substrates interact with paramagnetic oxygen through a Heisenberg spin exchange. This interaction can be significantly reduced under STP conditions by flowing a diamagnetic gas over the carbon system. This manuscript describes a simple method to characterize the nature of those radicals.

Video: Exploring the Radical Nature of a Carbon Surface by Electron Paramagnetic Resonance and a Calibrated Gas Flow

A Protocol for Detecting and Scavenging Gas-phase Free Radicals in Mainstream Cigarette Smoke

Cigarette smoking is associated with human cancers. It has been reported that most of the lung cancer deaths are caused by cigarette smoking 5,6,7,12. Although tobacco tars and related products in the particle phase of cigarette smoke are major causes of carcinogenic and mutagenic related diseases, cigarette smoke contains significant amounts of free radicals that are also considered as an important group of carcinogens9,10. Free radicals attack cell constituents by damaging protein structure, lipids and DNA sequences and increase the risks of developing various types of cancers. Inhaled radicals produce adducts that contribute to many of the negative health effects of tobacco smoke in the lung3. Studies have been conducted to reduce free radicals in cigarette smoke to decrease risks of the smoking-induced damage. It has been reported that haemoglobin and heme-containing compounds could partially scavenge nitric oxide, reactive oxidants and carcinogenic volatile nitrosocompounds of cigarette smoke4. A 'bio-filter' consisted of haemoglobin and activated carbon was used to scavenge the free radicals and to remove up to 90% of the free radicals from cigarette smoke14. However, due to the cost-ineffectiveness, it has not been successfully commercialized. Another study showed good scavenging efficiency of shikonin, a component of Chinese herbal medicine8. In the present study, we report a protocol for introducing common natural antioxidant extracts into the cigarette filter for scavenging gas phase free radicals in cigarette smoke and measurement of the scavenge effect on gas phase free radicals in mainstream cigarette smoke (MCS) using spin-trapping Electron Spin Resonance (ESR) Spectroscopy1,2,14. We showed high scavenging capacity of lycopene and grape seed extract which could point to their future application in cigarette filters. An important advantage of these prospective scavengers is that they can be obtained in large quantities from byproducts of tomato or wine industry respectively11,13

Spin-trapping ESR spectroscopy was used to study the effect of plant antioxidants lycopene, pycnogenol and grape seed extract on scavenging gas-phase free radicals in cigarette smoke.

Cigarette smoking is associated with human cancers. It has been reported that most of the lung cancer deaths are caused by cigarette smoking 5,6,7,12.  ...

Bioengineering

Measurement of Ultrafast Vibrational Coherences in Polyatomic Radical Cations with Strong-Field Adiabatic Ionization

We present a pump-probe method for preparing vibrational coherences in polyatomic radical cations and probing their ultrafast dynamics. By shifting the wavelength of the strong-field ionizing pump pulse from the commonly used 800 nm into the near-infrared (1200-1600 nm), the contribution of adiabatic electron tunneling to the ionization process increases relative to multiphoton absorption. Adiabatic ionization results in predominant population of the ground electronic state of the ion upon electron removal, which effectively prepares a coherent vibrational state (&#34;wave packet&#34;) amenable to subsequent excitation. In our experiments, the coherent vibrational dynamics are probed with a weak-field 800 nm pulse and the time-dependent yields of dissociation products measured in a time-of-flight mass spectrometer. We present the measurements on the molecule dimethyl methylphosphonate (DMMP) to illustrate how using 1500 nm pulses for excitation enhances the amplitude of coherent oscillations in ion yields by a factor of 10 as compared to 800 nm pulses. This protocol may be implemented in existing pump-probe setups through the incorporation of an optical parametric amplifier (OPA) for wavelength conversion.

We present a protocol for probing ultrafast vibrational coherences in polyatomic radical cations that result in molecular dissociation.

We present a pump-probe method for preparing vibrational coherences in polyatomic radical cations and probing their ultrafast dynamics. By shifting the ...

In situ FTIR Spectroscopy as a Tool for Investigation of Gas/Solid Interaction: Water-Enhanced CO2 Adsorption in UiO-66 Metal-Organic Framework

In situ infrared spectroscopy is an inexpensive, highly sensitive, and selective valuable tool to investigate the interaction of polycrystalline solids with adsorbates. Vibrational spectra provide information on the chemical nature of adsorbed species and their structure. Thus, they are very useful for obtaining molecular level understanding of surface species. The IR spectrum of the sample itself gives some direct information about the material. General conclusions can be drawn concerning hydroxyl groups, some stable surface species and impurities. However, the spectrum of the sample is &#34;blind&#34; with respect to the presence of coordinatively unsaturated ions and gives rather poor information about the acidity of surface hydroxyls, species decisive for the adsorption and catalytic properties of the materials. Furthermore, no discrimination between bulk and surface species can be made. These problems are solved by the use of probe molecules, substances that interact specifically with the surface; the alteration of some spectral features of these molecules as a result of adsorption provides valuable information about the nature, properties, location, concentration, etc., of the surface sites.
The experimental protocol for in-situ IR studies of gas/sample interaction includes preparation of a sample pellet, activation of the material, initial spectral characterization through the analysis of the background spectra, characterization by probe molecules, and study of the interaction with a particular set of gas mixtures. In this paper we investigate a zirconium terephthalate metal organic framework, Zr6O4(OH)4(BDC)6 (BDC = benzene-1,4-dicarboxylate), namely UiO-66 (UiO refers to University of Oslo). The acid sites of the UiO-66 sample are determined by using CO and CD3CN as molecular probes. Furthermore, we have demonstrated that CO2 is adsorbed on basic sites exposed on dehydroxylated UiO-66. Introduction of water to the system produces hydroxyl groups acting as additional CO2 adsorption sites. As a result, CO2 adsorption capacity of the sample is strongly enhanced.

In situ FTIR Spectroscopy as a Tool for Investigation of Gas/Solid Interaction: Water-Enhanced CO2 Adsorption in UiO-66 Metal-Organic Framework

The use of FTIR spectroscopy for investigation of the surface properties of polycrystalline solids is described. Preparation of sample pellets, activation procedures, characterization with probe molecules and model studies of CO2 adsorption are discussed.

In situ infrared spectroscopy is an inexpensive, highly sensitive, and selective valuable tool to investigate the interaction of polycrystalline solids ...

Rapid Scan Electron Paramagnetic Resonance Opens New Avenues for Imaging Physiologically Important Parameters In Vivo

We demonstrate a superior method of 2D spectral-spatial imaging of stable radical reporter molecules at 250 MHz using rapid-scan electron-paramagnetic-resonance (RS-EPR), which can provide quantitative information under in vivo conditions on oxygen concentration, pH, redox status and concentration of signaling molecules (i.e., OH&#8226;, NO&#8226;). The RS-EPR technique has a higher sensitivity, improved spatial resolution (1 mm), and shorter acquisition time in comparison to the standard continuous wave (CW) technique. A variety of phantom configurations have been tested, with spatial resolution varying from 1 to 6 mm, and spectral width of the reporter molecules ranging from 16 &#181;T (160 mG) to 5 mT (50 G). A cross-loop bimodal resonator decouples excitation and detection, reducing the noise, while the rapid scan effect allows more power to be input to the spin system before saturation, increasing the EPR signal. This leads to a substantially higher signal-to-noise ratio than in conventional CW EPR experiments.

Rapid Scan Electron Paramagnetic Resonance Opens New Avenues for Imaging Physiologically Important Parameters In Vivo

A new electron paramagnetic resonance (EPR) method, rapid scan EPR (RS-EPR), is demonstrated for 2D spectral spatial imaging which is superior to the traditional continuous wave (CW) technique and opens new venues for in vivo imaging. Results are demonstrated at 250 MHz, but the technique is applicable at any frequency.

We demonstrate a superior method of 2D spectral-spatial imaging of stable radical reporter molecules at 250 MHz using rapid-scan ...

High-Temperature and High-Pressure In situ Magic Angle Spinning Nuclear Magnetic Resonance Spectroscopy

Nuclear magnetic resonance (NMR) spectroscopy represents an important technique to understand the structure and bonding environments of molecules. There exists a drive to characterize materials under conditions relevant to the chemical process of interest. To address this, in situ high-temperature, high-pressure MAS NMR methods have been developed to enable the observation of chemical interactions over a range of pressures (vacuum to several hundred bar) and temperatures (well below 0 &#176;C to 250 &#176;C). Further, the chemical identity of the samples can be comprised of solids, liquids, and gases or mixtures of the three. The method incorporates all-zirconia NMR rotors (sample holder for MAS NMR) which can be sealed using a threaded cap to compress an O-ring. This rotor exhibits great chemical resistance, temperature compatibility, low NMR background, and can withstand high pressures. These combined factors enable it to be utilized in a wide range of system combinations, which in turn permit its use in diverse fields as carbon sequestration, catalysis, material science, geochemistry, and biology. The flexibility of this technique makes it an attractive option for scientists from numerous disciplines.

The molecular structures and dynamics of solids, liquids, gases, and mixtures are of critical interest to diverse scientific fields. High-temperature, high-pressure in situ MAS NMR enables detection of the chemical environment of constituents in mixed phase systems under tightly controlled chemical environments.

Nuclear magnetic resonance (NMR) spectroscopy represents an important technique to understand the structure and bonding environments of molecules. There ...

Performing In Situ Closed-Cell Gas Reactions in the Transmission Electron Microscope

Gas reactions studied by in situ electron microscopy can be used to capture the real-time morphological and microchemical transformations of materials at length scales down to the atomic level. In situ closed-cell gas reaction (CCGR) studies performed using (scanning) transmission electron microscopy (STEM) can separate and identify localized dynamic reactions, which are extremely challenging to capture using other characterization techniques. For these experiments, we used a CCGR holder that utilizes microelectromechanical systems (MEMS)-based heating microchips (hereafter referred to as &#34;E-chips&#34;). The experimental protocol described here details the method for performing in situ gas reactions in dry and wet gases in an aberration-corrected STEM. This method finds relevance in many different materials systems, such as catalysis and high-temperature oxidation of structural materials at atmospheric pressure and in the presence of various gases with or without water vapor. Here, several sample preparation methods are described for various material form factors. During the reaction, mass spectra obtained with a residual gas analyzer (RGA) system with and without water vapor further validates gas exposure conditions during reactions. Integrating an RGA with an in situ CCGR-STEM system can, therefore, provide critical insight to correlate gas composition with the dynamic surface evolution of materials during reactions. In situ/operando studies using this approach allow&#160;for detailed investigation of the fundamental reaction mechanisms and kinetics that occur at specific environmental conditions (time, temperature, gas, pressure), in real-time, and at high spatial resolution.

Performing In Situ Closed-Cell Gas Reactions in the Transmission Electron Microscope

Here, we present a protocol for performing in situ TEM closed-cell gas reaction experiments while detailing several commonly used sample preparation methods.

Gas reactions studied by in situ electron microscopy can be used to capture the real-time morphological and microchemical transformations of materials at ...

Engineering

Microscopic Visualization of Porous Nanographenes Synthesized through a Combination of Solution and On-Surface Chemistry

On-surface synthesis has recently been regarded as a promising approach for the generation of new molecular structures. It has been particularly successful in the synthesis of graphene nanoribbons, nanographenes and intrinsically reactive and instable, yet attractive species. It is based on the combination of solution chemistry aimed at preparation of appropriate molecular precursors for further ultra-high vacuum surface assisted transformations. This approach also owes its success to an incredible development of characterization techniques, such as scanning tunneling/atomic force microscopy and related methods, which allow detailed, local characterization at atomic scale. While the surface-assisted synthesis can provide molecular nanostructures with outstanding precision, down to single atoms, it suffers from basing on metallic surfaces and often limited yield. Therefore, the extension of the approach away from metals and the struggle to increase productivity seem to be significant challenges toward wider applications. Herein, we demonstrate the on-surface synthesis approach for generation of non-planar nanographenes, which are synthesized through a combination of solution chemistry and sequential surface-assisted processes, together with the detailed characterization by scanning probe microscopy methods.

A combination of solution and surface assisted synthesis opens new directions in the atomically precise synthesis of nanostructures. Scanning tunneling microscopy (STM) supplemented by non-contact atomic force microscopy (nc-AFM) enables detailed characterization of newly designed and generated carbon-based nano-objects.

On-surface synthesis has recently been regarded as a promising approach for the generation of new molecular structures. It has been particularly ...

Raman Spectroscopy for Chemical Analysis

Source: Laboratory of Dr. Ryoichi Ishihara &#8212; Delft University of Technology
Raman spectroscopy is a technique for analyzing vibrational and other low frequency modes in a system. In chemistry it is used to identify molecules by their Raman fingerprint. In solid-state physics it is used to characterize materials, and more specifically to investigate their crystal structure or crystallinity. Compared to other techniques for investigating the crystal structure (e.g. transmission electron microscope and x-ray diffraction) Raman micro-spectroscopy is non-destructive, generally requires no sample preparation, and can be performed on small sample volumes.
For performing Raman spectroscopy a monochromatic laser is shone on a sample. If required the sample can be coated by a transparent layer which is not Raman active (e.g., SiO2) or placed in DI water. The electromagnetic radiation (typically in the near infrared, visible, or near ultraviolet range) emitted from the sample is collected, the laser wavelength is filtered out (e.g., by a notch or bandpass filter), and the resulting light is sent through a monochromator (e.g., a grating) to a CCD detector. Using this, the inelastic scattered light, originating from Raman scattering, can be captured and used to construct the Raman spectrum of the sample.
In the case of Raman micro-spectroscopy the light passes through a microscope before reaching the sample, allowing it to be focused on an area as small as 1 &#181;m2. This allows accurate mapping of a sample, or confocal microscopy in order to investigate stacks of layers. Care has to be taken, however, that the small and intense laser spot does not damage the sample.
In this video we will briefly explain the procedure for obtaining a Raman spectra, and an example of a Raman spectrum captured from carbon nanotubes will be given.

Source: Laboratory of Dr. Ryoichi Ishihara &#8212; Delft University of Technology
Raman spectroscopy is a technique for analyzing vibrational and other ...

JoVE Science Education

Analytical Chemistry

Electron Paramagnetic Resonance (EPR) Spectroscopy

Source: David C. Powers, Tamara M. Powers, Texas A&#38;M
In this video, we will learn the basic principles behind Electron Paramagnetic Resonance (EPR). We will use EPR spectroscopy to study how dibutylhydroxy toluene (BHT) behaves as an antioxidant in the autoxidation of aliphatic aldehydes.

EPR Spectroscopy, Paramagnetic Molecule and Zeeman Effect

Source: David C. Powers, Tamara M. Powers, Texas A&#38;M
In this video, we will learn the basic principles behind Electron Paramagnetic Resonance (EPR). ...

Inorganic Chemistry

Radicals: Electronic Structure and Geometry

This lesson delves into the geometry of a radical, which is influenced by the electronic structure of the molecule. The principle is similar to that of a lone pair, where the unpaired electron influences the geometry at the radical center.
Accordingly, the structure of a trivalent radical lies between the geometries of carbocations and carbanions. An sp2-hybridized carbocation is trigonal planar, while an sp3-hybridized carbanion is trigonal pyramidal. Here, the difference in geometry is attributed to the difference in the number of nonbonding electrons. While the former has nil, the latter has two nonbonding electrons. Hence, a carbon radical with one nonbonding electron present in the p orbital falls between these two cases.
It is therefore reasonable to expect the radical geometry of a trivalent carbon species to lie between trigonal planar and trigonal pyramidal. As observed experimentally, the trivalent carbon-centered radicals typically possess superficially pyramidal geometry but are nearly planar. For instance, this is observed in oxygenated radicals like &#8226;CH2OH and &#8226;CMe2OH. Certain carbon-centered radicals, such as &#8226;CF3, are closer in geometry to the sp3-hybridized carbanions, which are trigonal pyramidal. In contrast, the methyl radical is fully trigonal planar like an sp2-hybridized carbocation.
The chirality of radicals is also a good indicator of the geometry. While the carbanion could be chiral given its resistance to pyramidal inversion, radicals can be achiral, since carbon-centered radicals with alkyl substituents that are superficially pyramidal readily undergo pyramidal inversion to become nearly planar.

This lesson delves into the geometry of a radical, which is influenced by the electronic structure of the molecule. The principle is similar to that of a ...

Exploring the Radical Nature of a Carbon Surface by Electron Paramagnetic Resonance and a Calibrated Gas Flow

Summary

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Chapters in this video

A Protocol for Detecting and Scavenging Gas-phase Free Radicals in Mainstream Cigarette Smoke

Measurement of Ultrafast Vibrational Coherences in Polyatomic Radical Cations with Strong-Field Adiabatic Ionization

In situ FTIR Spectroscopy as a Tool for Investigation of Gas/Solid Interaction: Water-Enhanced CO₂ Adsorption in UiO-66 Metal-Organic Framework

Rapid Scan Electron Paramagnetic Resonance Opens New Avenues for Imaging Physiologically Important Parameters In Vivo

High-Temperature and High-Pressure In situ Magic Angle Spinning Nuclear Magnetic Resonance Spectroscopy

Performing In Situ Closed-Cell Gas Reactions in the Transmission Electron Microscope

Microscopic Visualization of Porous Nanographenes Synthesized through a Combination of Solution and On-Surface Chemistry

Raman Spectroscopy for Chemical Analysis

Electron Paramagnetic Resonance (EPR) Spectroscopy

Radicals: Electronic Structure and Geometry