This work was supported by the HAS-JSPS bilateral joint research project. Financial support from grants NKFIH PD 121019 and FK 125134 is acknowledged.

1. Preparation of rubbed surfaces for aligning LC molecules planarly
<ol>
	<li>Prepare clean glass substrates.
	<ol>
		<li>Cut glass substrates using a diamond-based glass cutter (Table of Materials) into small square pieces with averages sizes of 1 cm x 1 cm. Wash them by sonication at 38 kHz or 42 kHz in an alkaline detergent (Table of Materials, diluted in water at a detergent:water volume ratio of 1:3) and rinse with distilled water repeatedly (typically, more than 10x with 5 min of sonication for each rinse).</li>
		<li>Subject the substrates to ultraviolet-ozone (UV-O3) cleaner (Table of Materials) for more than 10 min.</li>
	</ol>
	</li>
	<li>Coat planar alignment layer onto clean glass substrates.
	<ol>
		<li>Drip 20 &#181;L of 1 mL of a polyimide planar alignment solution (Table of Materials, used as is) with a pipette onto the cleaned glass substrates. Immediately spin-coat the solution, using a spin coater (Table of Materials) at 3,000 rpm and room temperature (RT) for 70 s. 
		NOTE: The typical thickness of the alignment layer is about 20 nm.</li>
		<li>Bake the coated glass substrates at 80 &#176;C for 60 min to remove the solvent and at 180 &#176;C for &#62;60 min for curing. Rub the substrates using a rayon-cloth rubbing machine (Table of Materials) with the following parameters: rotation speed = 300 rpm, plate speed = 20 mm/s, and impression = 0.3 mm to realize uniaxial alignment of LC materials.</li>
	</ol>
	</li>
</ol>
2. Preparation of LC cells
<ol>
	<li>Place a glass substrate coated with the alignment layer onto another substrate, with the alignment layers face-to-face, and ensure that they are 80% overlapped to form a cell. 
	NOTE: The 20% nonoverlapped surfaces are to be used for introducing LC materials into the cell.</li>
	<li>Place 100 &#181;L of a photoreactive adhesive (Table of Materials) and 0.1 mg of micrometer-sized glass particles (diameter = 5 &#181;m) onto a clean glass substrate and mix them manually using the tip of a paper clip. Move the mixed material to four corners of the cell to adjust the cell gap and illuminate the cell using a low-pressure mercury vapor short arc lamp (Table of Materials) with a wavelength of 365 nm (1.1 W/cm2). Place the cell under the LED lamp at a distance of 1 cm for 5 min.</li>
	<li>After illumination, place the cell onto a hot stage and set the target temperature of the stage to heat the cell to a temperature above the isotropic liquid (I)-nematic (N) phase transition (typically at 160 &#176;C). Transfer the LC material (1-[4-butoxyazobenzene-4&#8217;-yloxy]-6-[4-cyanobiphenyl-4&#8217; yl]hexane; CB6OABOBu; 0.2&#8722;10.0 &#181;L) onto one open surface of the cell and push the materials towards the cell entrance using a microspatula to obtain contact between the LC material and entrance of the cell. Wait for the LC materials to be filled in the cell by capillary force. 
	NOTE: CB6OABOBu has a phase sequence: Cry 100.3 &#176;C TB 105.2 &#176;C N 151.7 &#176;C I on heating and I 151.4 &#176;C N 104.5 &#176;C TB 83 &#176;C Cry on cooling. Do not introduce CB6OABOBu into the N phase or TB phase because flow-induced alignment is promoted.</li>
</ol>
3. Texture characterization by polarizing optical microscopy
<ol>
	<li>Observe the LC cells placed on the hot stage to control the sample temperature (40&#8722;180 &#176;C) with &#177; 0.1 K accuracy under a polarizing light microscope (POM, Table of Materials) using 4x&#8722;100x objective lenses. Record textures using a digital color camera sequentially during cooling and heating.</li>
	<li>Use a UV epi-illuminator (Table of Materials) equipped on the POM with a wavelength of 365 nm (50 mW/cm2).</li>
</ol>
4. Photorheological measurements
<ol>
	<li>Prepare of rheological measurements.
	<ol>
		<li>Before placing any sample onto the stage of the rheometer (Table of Materials), perform geometry inertia calibration and zero gap calibration controlled by a software according to manufacturer&#8217;s instructions to ensure accuracy of the rheological study. Weigh 250 mg of the CB6OABOBu powder sample and load it onto the base quartz plate of the rheometer. 
		NOTE: For the present study, a plate with a diameter of 50 mm is used.</li>
		<li>Set the temperature of the sample chamber to a value above the I-N phase transition point (&#62;160 &#176;C). Set a gap value for approaching the measuring plate to the base quartz plate to sandwich the sample (typical gap value used = 20 &#181;m). Trim excess sample (e.g., by using paper wipes) that is outside of the gap when the measuring plate stops at the trimming position, which is 25 &#181;m above the targeted gap. 
		NOTE: Do not allow excess amount of CB6OABOBu to be introduced to the sample chamber, as this makes the measurements inaccurate.</li>
	</ol>
	</li>
	<li>Perform rheological measurements.
	<ol>
		<li>Irradiate UV light at 365 nm (1&#8722;100 mW/cm2), measuring photorheological switching of CB6OABOBu using the high-pressure mercury vapor short arc lamp. 
		NOTE: The light will be guided from beneath the sample container through the base quartz plate.</li>
		<li>Perform measurements in 1) oscillatory mode for extracting dynamic restoring information of the material and 2) steady rotational mode for obtaining effective rotational viscosity. For measurements in rotational mode, apply a constant shear stress of 13 Pa to the sample to ensure that the measurement is made in the Newtonian regime. 
		NOTE: The selection of the modes is performed by a software according to the manufacturer&#8217;s instructions.</li>
	</ol>
	</li>
</ol>
5. Photo-differential scanning calorimetry
<ol>
	<li>Weigh 10 mg of CB6OABOBu powder sample and load it into a gold differential scanning calorimetry (DSC) pan. Heat the sample to 170 &#176;C in the isotropic phase and ensure that there is no inhomogeneous sample distribution in the DSC pan as observed by the naked eye. Cover the DSC pan with a quartz plate.</li>
	<li>Perform photo-DSC measurements according to the manufacturer&#8217;s instructions (Table of Materials). Measure DSC data at a scan of 10 &#176;C/min. 
	NOTE: The photo-DSC machine is equipped with a UV light intensity of 50 mW/cm2.</li>
</ol>
6. X-ray diffraction characterization
<ol>
	<li>Heat the powder CB6OABOBu sample using the hot stage at 170 &#176;C and suck the sample into an XRD capillary (diameter = 0.5 mm) by capillary force.</li>
	<li>Attach the capillary to a sample holder equipped with a temperature controller. Set the chamber temperature (60 &#176;C, 70 &#176;C, 80 &#176;C, 90 &#176;C, 100 &#176;C, 110 &#176;C, 120 &#176;C, 130 &#176;C, 140 &#176;C, 150 &#176;C, 160 &#176;C, and 170 &#176;C for each X-ray diffraction measurement).</li>
	<li>Irradiate the sample by X-ray and detect the diffracted X-ray beams by a detector without UV irradiation and under a UV light intensity of 10 mW/cm2 for 1 min and 10 min. 
	NOTE: The current study was conducted in RIKEN beamline BL45XU. The light source was the SPring-8 standard in-vacuum undulator. A liquid nitrogen-cooled Si double crystal monochromator was used to monochromatize the beam. The wavelength was 1 &#197;.</li>
</ol>

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The authors have nothing to disclose.

As revealed in Figure 1, CB6OABOBu is a photo-responsive material with I, N, TB, and Cry phase sequences upon cooling. Since local ordering of these phases differs significantly, the photo-driven switching of rheological properties is expected to exhibit good viscoelastic contrast. To quantitatively investigate this, photo-rheology measurements were performed.
First, we consider the rheological data measured in the dark (Figure 2<stro...

Smart mechanical materials with the capability to change their viscoelastic properties in response to environmental variation have generated tremendous interest among researchers. Switchability is considered to be the most important material factor, which offers robustness of repetitive mechanical response in living organisms. To date, artificial switchable materials with versatile functions have been designed by utilizing soft matter (i.e., photoresponsive hydrogels1,2,3, polymers4,5,6,7,8,9,10,11, liquid crystals [LCs]9,10,11,12,13,14,15,16,17, pH-responsive micelles18,19,20,21,22, and surfactants23). However, these materials suffer from more than one of the following problems: lack of reversibility, low switching contrast ratio of viscoelasticity, low adaptivity, and slow switching speed. In conventional materials, a tradeoff exists between the switching contrast ratio of viscoelasticity and switching speed; thus, designing materials covering all of these criteria with high performance is challenging. To realize materials with the aforementioned omnicapability, selecting or designing molecules that carry emergent natures of both high fluidity (viscous property) and rigidity (elastic property) is essential.
Liquid crystals are ideal systems with a potentially large number of liquid crystalline and solid phases that can be tuned by molecular design. This allows for self-assembled structures at different length scales in particular LC phases. For example, while high-symmetry nematic LCs (NLCs) exhibit low viscosity and elasticity because of their short-range spatial order, low-symmetry columnar or smectic LCs show high viscosity and elasticity due to one- and two-dimensional long-range periodicities. It is expected that if LC materials can be switched between two phases with large differences in their viscoelastic properties, then a viscoelastic smart material with high performance can be achieved. A few examples have been reported9,10,11,12,13,14,15.
This article demonstrates the preparation of a photorheological LC material with a phase sequence of isotropic (I)-nematic (N)-twist-bend nematic (TB)24-crystal (Cry) upon cooling (and vice versa upon heating), which exhibits fast and reversible viscoelastic switching in response to light. Presented here are the methods for measuring viscoelasticity and an illustration of the microscopic structure-viscoelasticity relationship. Details are described in the representative results and discussion sections.

<table>
	<tbody>
		<tr>
			<td>21-401-10</td>
			<td>AS ONE</td>
			<td></td>
			<td>Microspatula</td>
		</tr>
		<tr>
			<td>AL1254</td>
			<td>JSR</td>
			<td></td>
			<td>Planar alignment agent for liquid crystals</td>
		</tr>
		<tr>
			<td>BX53P</td>
			<td>Olympus</td>
			<td></td>
			<td>Polarising microscope with transmission/epi-illumination units</td>
		</tr>
		<tr>
			<td>Discovery DSC 25P</td>
			<td>TI instruments</td>
			<td></td>
			<td>Photo-DSC equipment</td>
		</tr>
		<tr>
			<td>Glass cutter PRO-1A</td>
			<td>Sankyo</td>
			<td></td>
			<td>A diamond-based glass cutter</td>
		</tr>
		<tr>
			<td>HS82</td>
			<td>Mettler Toledo</td>
			<td></td>
			<td>hot stage</td>
		</tr>
		<tr>
			<td>MCR502</td>
			<td>Anton Paar</td>
			<td></td>
			<td>A commercial rheometer</td>
		</tr>
		<tr>
			<td>MRJ-100S</td>
			<td>EHC</td>
			<td></td>
			<td>Rubbing machine</td>
		</tr>
		<tr>
			<td>Norland Optical Adhesive 65, 81</td>
			<td>Norland Products</td>
			<td></td>
			<td>Photoreactive adhesions</td>
		</tr>
		<tr>
			<td>OmniCure S2000</td>
			<td>Excelitas Technologies</td>
			<td></td>
			<td>A commericial high-pressure mercury vapor short arc lamp. Maximum 70 mW/cm^2.</td>
		</tr>
		<tr>
			<td>PILATUS 6M</td>
			<td>Dectris</td>
			<td></td>
			<td>Hybrid photon counting detector for X-ray diffraction dectection</td>
		</tr>
		<tr>
			<td>S1126</td>
			<td>Matsunami Glass</td>
			<td></td>
			<td>Glass substrate</td>
		</tr>
		<tr>
			<td>SC-158H</td>
			<td>EHC</td>
			<td></td>
			<td>Spin coater</td>
		</tr>
		<tr>
			<td>SCAT-20X</td>
			<td>DKS</td>
			<td></td>
			<td>Alkaline detergent</td>
		</tr>
		<tr>
			<td>SLUV-4</td>
			<td>AS ONE</td>
			<td></td>
			<td>Low-pressure mercury vapor short arc lamp</td>
		</tr>
		<tr>
			<td>UV-208</td>
			<td>Technovision</td>
			<td></td>
			<td>Ultraviolet-ozone (UV-O3) cleaner</td>
		</tr>
	</tbody>
</table>

high-contrast and fast photorheological switching of a twist-bend nematic liquid crystal

Smart viscoelastic materials that respond to specific stimuli are one of the most attractive classes of materials important to future technologies, such as on-demand switchable adhesion technologies, actuators, molecular clutches, and nano-/microscopic mass transporters. Recently it was found that through a special solid-liquid transition, rheological properties can exhibit significant changes, thus providing suitable smart viscoelastic materials. However, designing materials with such a property is complex, and forward and backward switching times are usually long. Therefore, it is important to explore new working mechanisms to realize solid-liquid transitions, shorten the switching time, and enhance the contrast of rheological properties during switching. Here, a light-induced crystal-liquid phase transition is observed, which is characterized by means of polarizing light microscopy (POM), photorheometry, photo-differential scanning calorimetry (photo-DSC), and X-ray diffraction (XRD). The light-induced crystal-liquid phase transition presents key features such as (1) fast switching of crystal-liquid phases for both forward and backward reactions and (2) a high contrast ratio of viscoelasticity. In the characterization, POM is advantageous in offering information on the spatial distribution of LC molecule orientations, determining the type of liquid crystalline phases appearing in the material, and studying the orientation of LCs. Photorheometry allows measurement of a material&#8217;s rheological properties under light stimuli and can reveal the photorheological switching properties of materials. Photo-DSC is a technique to investigate thermodynamic information of materials in darkness and under light irradiation. Lastly, XRD allows studying of microscopic structures of materials. The goal of this article is to clearly present how to prepare and measure the discussed properties of a photorheological material.

POM images, photorheometric data, photo-DSC data, and XRD intensity profiles were collected in darkness during temperature variation and while shining UV light. Figure 1a,b represents the structure of CB6OABOBu, with its phase sequence and possible conformations optimized by the MM2 forcefield in the modeling program (e.g., ChemBio3D).
When CB6OABOBu is in the trans-state, two energy-plausible conformational states appear, and the twisted conforma...

Watch this Scientific Journal Video about High-Contrast and Fast Photorheological Switching of a Twist-Bend Nematic Liquid Crystal at JoVE.com

High-Contrast and Fast Photorheological Switching of a Twist-Bend Nematic Liquid Crystal

This protocol demonstrates the preparation of a photorheological material that exhibits a solid phase, various liquid crystalline phases, and an isotropic liquid phase by increasing temperature. Presented here are methods for measuring the structure-viscoelasticity relationship of the material.

Smart viscoelastic materials that respond to specific stimuli are one of the most attractive classes of materials important to future technologies, such ...

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Research

JoVE Journal

Chemistry

6.3K Views.  RIKEN Center for Emergent Matter Science (CEMS). This protocol demonstrates the preparation of a photorheological material that exhibits a solid phase, various liquid crystalline phases, and an isotropic liquid phase by increasing temperature. Presented here are methods for measuring the structure-viscoelasticity relationship of the material.

Video: High-Contrast and Fast Photorheological Switching of a Twist-Bend Nematic Liquid Crystal

Untargeted Metabolomics from Biological Sources Using Ultraperformance Liquid Chromatography-High Resolution Mass Spectrometry (UPLC-HRMS)

Here we present a workflow to analyze the metabolic profiles for biological samples of interest including; cells, serum, or tissue. The sample is first separated into polar and non-polar fractions by a liquid-liquid phase extraction, and partially purified to facilitate downstream analysis. Both aqueous (polar metabolites) and organic (non-polar metabolites) phases of the initial extraction are processed to survey a broad range of metabolites. Metabolites are separated by different liquid chromatography methods based upon their partition properties. In this method, we present microflow ultra-performance (UP)LC methods, but the protocol is scalable to higher flows and lower pressures. Introduction into the mass spectrometer can be through either general or compound optimized source conditions. Detection of a broad range of ions is carried out in full scan mode in both positive and negative mode over a broad m/z range using high resolution on a recently calibrated instrument. Label-free differential analysis is carried out on bioinformatics platforms. Applications of this approach include metabolic pathway screening, biomarker discovery, and drug development.

Untargeted Metabolomics from Biological Sources Using Ultraperformance Liquid Chromatography-High Resolution Mass Spectrometry UPLC-HRMS

Untargeted metabolomics provides a hypothesis generating snapshot of a metabolic profile. This protocol will demonstrate the extraction and analysis of metabolites from cells, serum, or tissue. A range of metabolites are surveyed using liquid-liquid phase extraction, microflow ultraperformance liquid chromatography/high-resolution mass spectrometry (UPLC-HRMS) coupled to differential analysis software.

Here we present a workflow to analyze the metabolic profiles for biological samples of interest including; cells, serum, or tissue. The sample is first ...

Isolation and Preparation of Bacterial Cell Walls for Compositional Analysis by Ultra Performance Liquid Chromatography

The bacterial cell wall is critical for the determination of cell shape during growth and division, and maintains the mechanical integrity of cells in the face of turgor pressures several atmospheres in magnitude. Across the diverse shapes and sizes of the bacterial kingdom, the cell wall is composed of peptidoglycan, a macromolecular network of sugar strands crosslinked by short peptides. Peptidoglycan&#8217;s central importance to bacterial physiology underlies its use as an antibiotic target and has motivated genetic, structural, and cell biological studies of how it is robustly assembled during growth and division. Nonetheless, extensive investigations are still required to fully characterize the key enzymatic activities in peptidoglycan synthesis and the chemical composition of bacterial cell walls. High Performance Liquid Chromatography (HPLC) is a powerful analytical method for quantifying differences in the chemical composition of the walls of bacteria grown under a variety of environmental and genetic conditions, but its throughput is often limited. Here, we present a straightforward procedure for the isolation and preparation of bacterial cell walls for biological analyses of peptidoglycan via HPLC and Ultra Performance Liquid Chromatography (UPLC), an extension of HPLC that utilizes pumps to deliver ultra-high pressures of up to 15,000 psi, compared with 6,000 psi for HPLC. In combination with the preparation of bacterial cell walls presented here, the low-volume sample injectors, detectors with high sampling rates, smaller sample volumes, and shorter run times of UPLC will enable high resolution and throughput for novel discoveries of peptidoglycan composition and fundamental bacterial cell biology in most biological laboratories with access to an ultracentrifuge and UPLC.

The bacterial cell wall is composed of peptidoglycan, a macromolecular network of sugar strands crosslinked by peptides. Ultra Performance Liquid Chromatography provides high resolution and throughput for novel discoveries of peptidoglycan composition. We present a procedure for the isolation of cell walls (sacculi) and their subsequent preparation for analysis via UPLC.

The bacterial cell wall is critical for the determination of cell shape during growth and division, and maintains the mechanical integrity of cells in the ...

Synthesis and Exfoliation of Discotic Zirconium Phosphates to Obtain Colloidal Liquid Crystals

Due to their abundance in natural clay and potential applications in advanced materials, discotic nanoparticles are of interest to scientists and engineers. Growth of such anisotropic nanocrystals through a simple chemical method is a challenging task. In this study, we fabricate discotic nanodisks of zirconium phosphate [Zr(HPO4)2&#183;H2O] as a model material using hydrothermal, reflux and microwave-assisted methods. Growth of crystals is controlled by duration time, temperature, and concentration of reacting species. The novelty of the adopted methods is that discotic crystals of size ranging from hundred nanometers to few micrometers can be obtained while keeping the polydispersity well within control. The layered discotic crystals are converted to monolayers by exfoliation with tetra-(n)-butyl ammonium hydroxide [(C4H9)4NOH, TBAOH]. Exfoliated disks show isotropic and nematic liquid crystal phases. Size and polydispersity of disk suspensions is highly important in deciding their phase behavior.

A two dimensional model material of discotic zirconium phosphate was developed. The inorganic crystal with lamellar structure was synthesized by hydrothermal, reflux, and microwave-assisted methods. On exfoliation with organic molecules, layered crystals can be converted to monolayers, and nematic liquid crystal phase was formed at sufficient concentration of monolayers.

Due to their abundance in natural clay and potential applications in advanced materials, discotic nanoparticles are of interest to scientists and ...

A Method to Manipulate Surface Tension of a Liquid Metal via Surface Oxidation and Reduction

Controlling interfacial tension is an effective method for manipulating the shape, position, and flow of fluids at sub-millimeter length scales, where interfacial tension is a dominant force. A variety of methods exist for controlling the interfacial tension of aqueous and organic liquids on this scale; however, these techniques have limited utility for liquid metals due to their large interfacial tension.
Liquid metals can form soft, stretchable, and shape-reconfigurable components in electronic and electromagnetic devices. Although it is possible to manipulate these fluids via mechanical methods (e.g., pumping), electrical methods are easier to miniaturize, control, and implement. However, most electrical techniques have their own constraints: electrowetting-on-dielectric requires large (kV) potentials for modest actuation, electrocapillarity can affect relatively small changes in the interfacial tension, and continuous electrowetting is limited to plugs of the liquid metal in capillaries.
Here, we present a method for actuating gallium and gallium-based liquid metal alloys via an electrochemical surface reaction. Controlling the electrochemical potential on the surface of the liquid metal in electrolyte rapidly and reversibly changes the interfacial tension by over two orders of magnitude ( &#820;500 mN/m to near zero). Furthermore, this method requires only a very modest potential (&#60; 1 V) applied relative to a counter electrode. The resulting change in tension is due primarily to the electrochemical deposition of a surface oxide layer, which acts as a surfactant; removal of the oxide increases the interfacial tension, and vice versa. This technique can be applied in a wide variety of electrolytes and is independent of the substrate on which it rests.

We present a method to control the interfacial energy of a liquid metal in an electrolyte via electrochemical deposition (or removal) of a surface oxide layer. This simple method can control the capillary behavior of gallium-based liquid metals by tuning the interfacial energy rapidly, significantly, and reversibly using modest voltages.

Controlling interfacial tension is an effective method for manipulating the shape, position, and flow of fluids at sub-millimeter length scales, where ...

Microfluidic Pneumatic Cages: A Novel Approach for In-chip Crystal Trapping, Manipulation and Controlled Chemical Treatment

The precise localization and controlled chemical treatment of structures on a surface are significant challenges for common laboratory technologies. Herein, we introduce a microfluidic-based technology, employing a double-layer microfluidic device, which can trap and localize in situ and ex situ synthesized structures on microfluidic channel surfaces. Crucially, we show how such a device can be used to conduct controlled chemical reactions onto on-chip trapped structures and we demonstrate how the synthetic pathway of a crystalline molecular material and its positioning inside a microfluidic channel can be precisely modified with this technology. This approach provides new opportunities for the controlled assembly of structures on surface and for their subsequent treatment.

Herein, we describe the fabrication and operation of a double-layer microfluidic system made of polydimethylsiloxane (PDMS). We demonstrate the potential of this device for trapping, directing the coordination pathway of a crystalline molecular material and controlling chemical reactions onto on-chip trapped structures.

The precise localization and controlled chemical treatment of structures on a surface are significant challenges for common laboratory technologies. ...

High Pressure Single Crystal Diffraction at PX^2

In this report we describe detailed procedures for carrying out single crystal X-ray diffraction experiments with a diamond anvil cell (DAC) at the GSECARS 13-BM-C beamline at the Advanced Photon Source. The DAC program at 13-BM-C is part of the Partnership for Extreme Xtallography (PX^2) project. BX-90 type DACs with conical-type diamond anvils and backing plates are recommended for these experiments. The sample chamber should be loaded with noble gas to maintain a hydrostatic pressure environment. The sample is aligned to the rotation center of the diffraction goniometer. The MARCCD area detector is calibrated with a powder diffraction pattern from LaB6. The sample diffraction peaks are analyzed with the ATREX software program, and are then indexed with the RSV software program. RSV is used to refine the UB matrix of the single crystal, and with this information and the peak prediction function, more diffraction peaks can be located. Representative single crystal diffraction data from an omphacite (Ca0.51Na0.48)(Mg0.44Al0.44Fe2+0.14Fe3+0.02)Si2O6 sample were collected. Analysis of the data gave a monoclinic lattice with P2/n space group at 0.35 GPa, and the lattice parameters were found to be: a = 9.496 &#177;0.006 &#197;, b = 8.761 &#177;0.004 &#197;, c = 5.248 &#177;0.001 &#197;, &#946; = 105.06 &#177;0.03&#186;, &#945; = &#947; = 90&#186;.

In this report, we describe detailed procedures for carrying out single crystal X-ray diffraction experiments with a diamond anvil cell at the GSECARS 13-BM-C beamline at the Advanced Photon Source. ATREX and RSV programs are used to analyze the data.

In this report we describe detailed procedures for carrying out single crystal X-ray diffraction experiments with a diamond anvil cell (DAC) at the ...

A Straightforward Method for Glucosinolate Extraction and Analysis with High-pressure Liquid Chromatography (HPLC)

Glucosinolates are a well-studied and highly diverse class of natural plant compounds. They play important roles in plant resistance, rapeseed oil quality, food flavoring, and human health. The biological activity of glucosinolates is released upon tissue damage, when they are mixed with the enzyme myrosinase. This results in the formation of pungent and toxic breakdown products, such as isothiocyanates and nitriles. Currently, more than 130 structurally different glucosinolates have been identified. The chemical structure of the glucosinolate is an important determinant of the product that is formed, which in turn determines its biological activity. The latter may range from detrimental (e.g., progoitrin) to beneficial (e.g., glucoraphanin). Each glucosinolate-containing plant species has its own specific glucosinolate profile. For this reason, it is important to correctly identify and reliably quantify the different glucosinolates present in brassicaceous leaf, seed, and root crops or, for ecological studies, in their wild relatives. Here, we present a well-validated, targeted, and robust method to analyze glucosinolate profiles in a wide range of plant species and plant organs. Intact glucosinolates are extracted from ground plant materials with a methanol-water mixture at high temperatures to disable myrosinase activity. Thereafter, the resulting extract is brought onto an ion-exchange column for purification. After sulfatase treatment, the desulfoglucosinolates are eluted with water and the eluate is freeze-dried. The residue is taken up in an exact volume of water, which is analyzed by high-pressure liquid chromatography (HPLC) with a photodiode array (PDA) or ultraviolet (UV) detector. Detection and quantification are achieved by conducting comparisons of the retention times and UV spectra of commercial reference standards. The concentrations are calculated based on a sinigrin reference curve and well-established response factors. The advantages and disadvantages of this straightforward method, when compared to faster and more technologically advanced methods, are discussed here.

A Straightforward Method for Glucosinolate Extraction and Analysis with High-pressure Liquid Chromatography HPLC

Here, we describe in great detail an established and robust protocol for the extraction of glucosinolates from ground plant materials. After an on-column sulfatase treatment of the extracts, the desulfoglucosinolates are eluted and analyzed by high-pressure liquid chromatography.

Glucosinolates are a well-studied and highly diverse class of natural plant compounds. They play important roles in plant resistance, rapeseed oil ...

A Convenient Method for Extraction and Analysis with High-Pressure Liquid Chromatography of Catecholamine Neurotransmitters and Their Metabolites

The extraction and analysis of catecholamine neurotransmitters in biological fluids is of great importance in assessing nervous system function and related diseases, but their precise measurement is still a challenge. Many protocols have been described for neurotransmitter measurement by a variety of instruments, including high-pressure liquid chromatography (HPLC). However, there are shortcomings, such as complicated operation or hard-to-detect multiple targets, which cannot be avoided, and presently, the dominant analysis technique is still HPLC coupled with sensitive electrochemical or fluorimetric detection, due to its high sensitivity and good selectivity. Here, a detailed protocol is described for the pretreatment and detection of catecholamines with high pressure liquid chromatography with electrochemical detection (HPLC-ECD) in real urine samples of infants, using electrospun composite nanofibers composed of polymeric crown ether with polystyrene as adsorbent, also known as the packed-fiber solid phase extraction (PFSPE) method. We show how urine samples can be easily precleaned by a nanofiber-packed solid phase column, and how the analytes in the sample can be rapidly enriched, desorbed, and detected on an ECD system. PFSPE greatly simplifies the pretreatment procedures for biological samples, allowing for decreased time, expense, and reduction of the loss of targets. 
Overall, this work illustrates a simple and convenient protocol for solid-phase extraction coupled to an HPLC-ECD system for simultaneous determination of three monoamine neurotransmitters (norepinephrine (NE), epinephrine (E), dopamine (DA)) and two of their metabolites (3-methoxy-4-hydroxyphenylglycol (MHPG) and 3,4-dihydroxy-phenylacetic acid (DOPAC)) in infants' urine. The established protocol was applied to assess the differences of urinary catecholamines and their metabolites between high-risk infants with perinatal brain damage and healthy controls. Comparative analysis revealed a significant difference in urinary MHPG between the two groups, indicating that the catecholamine metabolites may be an important candidate marker for early diagnosis of cases at risk for brain damage in infants.

We present a convenient solid-phase extraction coupled to high-pressure liquid chromatography (HPLC) with electrochemical detection (ECD) for simultaneous determination of three monoamine neurotransmitters and two of their metabolites in infants' urine. We also identify the metabolite MHPG as a potential biomarker for the early diagnosis of brain damage for infants.

The extraction and analysis of catecholamine neurotransmitters in biological fluids is of great importance in assessing nervous system function and ...

Total Internal Reflection Absorption Spectroscopy (TIRAS) for the Detection of Solvated Electrons at a Plasma-liquid Interface

The total internal reflection absorption spectroscopy (TIRAS) method presented in this article uses an inexpensive diode laser to detect solvated electrons produced by a low-temperature plasma in contact with an aqueous solution. Solvated electrons are powerful reducing agents, and it has been postulated that they play an important role in the interfacial chemistry between a gaseous plasma or discharge and a conductive liquid. However, due to the high local concentrations of reactive species at the interface, they have a short average lifetime (~1 &#181;s), which makes them extremely difficult to detect. The TIRAS technique uses a unique total internal reflection geometry combined with amplitude-modulated lock-in amplification to distinguish solvated electrons&#39; absorbance signal from other spurious noise sources. This enables the in situ detection of short-lived intermediates in the interfacial region, as opposed to the bulk measurement of stable products in the solution. This approach is especially attractive for the field of plasma electrochemistry, where much of the important chemistry is driven by short-lived free radicals. This experimental method has been used to analyze the reduction of nitrite (NO2-(aq)), nitrate (NO3-(aq)), hydrogen peroxide (H2O2(aq)), and dissolved carbon dioxide (CO2(aq)) by plasma-solvated electrons and deduce effective rate constants. Limitations of the method may arise in the presence of unintended parallel reactions, such as air contamination in the plasma, and absorbance measurements may also be hindered by the precipitation of reduced electrochemical products. Overall, the TIRAS method can be a powerful tool for studying the plasma-liquid interface, but its effectiveness depends on the particular system and reaction chemistry under study.

Total Internal Reflection Absorption Spectroscopy TIRAS for the Detection of Solvated Electrons at a Plasma-liquid Interface

This article presents a total internal reflection absorption spectroscopy (TIRAS) method for measuring short-lived free radicals at a plasma-liquid interface. In particular, TIRAS is used to identify solvated electrons based on their optical absorbance of red light near 700 nm.

The total internal reflection absorption spectroscopy (TIRAS) method presented in this article uses an inexpensive diode laser to detect solvated ...

Using Graphene Liquid Cell Transmission Electron Microscopy to Study in Situ Nanocrystal Etching

Graphene liquid cell electron microscopy provides the ability to observe nanoscale chemical transformations and dynamics as the reactions are occurring in liquid environments. This manuscript describes the process for making graphene liquid cells through the example of graphene liquid cell transmission electron microscopy (TEM) experiments of gold nanocrystal etching. The protocol for making graphene liquid cells involves coating gold, holey-carbon TEM grids with chemical vapor deposition graphene and then using those graphene-coated grids to encapsulate liquid between two graphene surfaces. These pockets of liquid, with the nanomaterial of interest, are imaged in the electron microscope to see the dynamics of the nanoscale process, in this case the oxidative etching of gold nanorods. By controlling the electron beam dose rate, which modulates the etching species in the liquid cell, the underlying mechanisms of how atoms are removed from nanocrystals to form different facets and shapes can be better understood. Graphene liquid cell TEM has the advantages of high spatial resolution, compatibility with traditional TEM holders, and low start-up costs for research groups. Current limitations include delicate sample preparation, lack of flow capability, and reliance on electron beam-generated radiolysis products to induce reactions. With further development and control, graphene liquid cell may become a ubiquitous technique in nanomaterials and biology, and is already being used to study mechanisms governing growth, etching, and self-assembly processes of nanomaterials in liquid on the single particle level.

Using Graphene Liquid Cell Transmission Electron Microscopy to Study in Situ Nanocrystal Etching

Graphene liquid cell electron microscopy can be used to observe nanocrystal dynamics in a liquid environment with greater spatial resolution than other liquid cell electron microscopy techniques. Etching premade nanocrystals and following their shape using graphene liquid cell Transmission Electron Microscopy can yield important mechanistic information about nanoparticle transformations.

Graphene liquid cell electron microscopy provides the ability to observe nanoscale chemical transformations and dynamics as the reactions are occurring in ...