Name: novel techniques for observing structural dynamics of photoresponsive liquid crystals
Uploaded: 2018-05-29T14:00:00
Description: Watch this Scientific Journal Video about Novel Techniques for Observing Structural Dynamics of Photoresponsive Liquid Crystals at JoVE.com

We thank Dr. S. Tanaka at Tokyo Institute of Technology for time-resolved IR vibrational spectroscopy measurements and Prof. M. Hara and Dr. K. Matsuo at Nagoya University for XRD measurements. We also thanks Prof. S. Yamaguchi at Nagoya University, Prof. R. Herges at Kiel University and Prof. R. J. D. Miller at the Max Planck Institute for the Structure and Dynamics of Matter for valuable discussion.
This work is supported by the Japanese Science Technology (JST), PRESTO, for funding the projects "Molecular technology and creation of new functions" (Grant Number of JPMJPR13KD, JPMJPR12K5, and JPMJPR16P6) and "Chemical conversion of light energy". This work is also partially supported by JSPS Grant Numbers JP15H02103, JP17K17893, JP15H05482, JP17H05258, JP26107004, and JP17H06375.

1.Time-Resolved Infrared Vibrational Spectroscopy
<ol>
	<li>Sample preparation
	<ol>
		<li>Solution: Dissolve the &#960;-extended cyclooctatetraene (&#960;-COT) molecules into dichloromethane with proper concentration (1 mmol/L).</li>
		<li>LC phase: Melt the &#960;-COT powder on a calcium fluoride (CaF2) substrate using hot plate at the temperature of 100 &#176;C. Cool the sample at a room temperature. 
		Note: We need to choose a material (CaF2 or barium fluoride (BaF2...

The crucial step of the process during the time-resolved electron diffraction measurements is maintaining the high voltage (75 keV) without current fluctuation since the distance between the photocathode and anode plate is only ~10 mm. If the current fluctuates above the range of 0.1 &#181;A before or during the experiments, increase the acceleration voltage up to 90 keV to discharge and set it again to 75 keV. This conditioning process has to be done until the current fluctuates in the range of 0.1 &#181;A. The proper d...

Liquid crystals (LCs) have a variety of functions and are widely used in scientific and technological applications1,2,3,4,5,6. The behavior of LCs can be attributed to their orientational ordering as well as to the high mobility of their molecules. A molecular structure of LC materials is typically characterized by a mesogen core and long flexible carbon chains that ensure high mobility of the LC molecules. Under external stimuli7,8,9,10,11,12,13,14,15, such as light, electric fields, temperature changes, or mechanical pressure, small intra- and intermolecular motions of the LC molecules cause drastic structural reordering in the system, leading to its functional behavior. To understand the functions of LC materials, it is important to determine the molecular scale structure in the LC phase and identify the key motions of the molecular conformations and packing deformations.
X-ray diffraction (XRD) is commonly employed as a powerful tool for determining structures of LC materials16,17,18. However, the diffraction pattern originating from a functional stimuli-responsive core is often concealed by a broad halo pattern from the long carbon chains. An effective solution to this problem is provided by time-resolved diffraction analysis, which enables direct observations of molecular dynamics using photoexcitation. This technique extracts structural information about the photoresponsive aromatic moiety using the differences between the diffraction patterns obtained before and after photoexcitation. These differences provide the means both to remove the background noise and to directly observe the structural changes of interest. Analyses of the differential diffraction patterns reveal the modulated signals from the photoactive moiety alone, thereby excluding the deleterious diffraction from the non-photoresponsive carbon chains. A description of this method of differential diffraction analysis is provided in Hada, M. et al19.
Time-resolved diffraction measurements can provide structural information about the atomic rearrangements that occur during the phase transition in materials20,21,22,23,24,25,26,27,28,29 and chemical reactions among molecules30,31,32,33,34. With these applications in mind, remarkable progress has been made in the development of ultrabright and ultrashort-pulsed X-ray35,36 and electron37,38,39,40 sources. However, time-resolved diffraction has only been applied to simple, isolated molecules or to single- or poly-crystals, in which highly ordered inorganic lattice or organic molecules produce well-resolved diffraction patterns providing structural information. In contrast, ultrafast structural analyses of more complex soft materials have been hampered because of their less ordered phases. In this study, we demonstrate the use of time-resolved electron diffraction as well as transient absorption spectroscopy and time-resolved infrared (IR) vibrational spectroscopy to characterize the structural dynamics of photoactive LC materials using this diffraction-extracted methodology19.

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novel techniques for observing structural dynamics of photoresponsive liquid crystals

We discuss in this article the experimental measurements of the molecules in liquid crystal (LC) phase using the time-resolved infrared (IR) vibrational spectroscopy and time-resolved electron diffraction. Liquid crystal phase is an important state of matter that exists between the solid and liquid phases and it is common in natural systems as well as in organic electronics. Liquid crystals are orientationally ordered but loosely packed, and therefore, the internal conformations and alignments of the molecular components of LCs can be modified by external stimuli. Although advanced time-resolved diffraction techniques have revealed picosecond-scale molecular dynamics of single crystals and polycrystals, direct observations of packing structures and ultrafast dynamics of soft materials have been hampered by blurry diffraction patterns. Here, we report time-resolved IR vibrational spectroscopy and electron diffractometry to acquire ultrafast snapshots of a columnar LC material bearing a photoactive core moiety. Differential-detection analyses of the combination of time-resolved IR vibrational spectroscopy and electron diffraction are powerful tools for characterizing structures and photoinduced dynamics of soft materials.

We chose a saddle-shaped &#960;-COT skeleton43,44 as a photoactive core unit of the LC molecule, because it forms a well-defined columnar stacking structure and because the central eight-membered COT ring is expected to show a photoinduced conformational change into a flat form owing to the excited-state aromaticity19,45. Synthetic process of this material is provided in p...

Watch this Scientific Journal Video about Novel Techniques for Observing Structural Dynamics of Photoresponsive Liquid Crystals at JoVE.com

Novel Techniques for Observing Structural Dynamics of Photoresponsive Liquid Crystals

Here, we present the protocols of differential-detection analyses of time-resolved infrared vibrational spectroscopy and electron diffraction which enable observations of the deformations of local structures around photoexcited molecules in a columnar liquid crystal, giving an atomic perspective on the relationship between the structure and the dynamics of this photoactive material.

We discuss in this article the experimental measurements of the molecules in liquid crystal (LC) phase using the time-resolved infrared (IR) vibrational ...

This method can help address a common problem in the liquid crystal research. Which is that peak molecular motion during the photoresponse cannot be determined by conventional methods. The main advantage of these techniques is that the structure and the ultrafast dynamics of photoexcited liquid crystal are obtained both from differential IR spectrum and differential electron diffraction patterns.I will be demonstrating the time-resolved IR vibration spectroscopy. To prepare a solution phase sample for time-resolved IR vibrational spectroscopy, dissolve 0.025 millimoles of pi-COT in 25 milliliters of dichloromethane, to obtain a 1 millimole per liter solution. To prepare a liquid crystal phase sample, cover a 3 millimeter thick calcium fluoride substrate in pi-COT powder.Place the substrate on a hot plate, and melt the powder at 100 degrees Celsius. Turn off the hot plate, and allow the sample to cool to room temperature. After preparing the sample, turn on the titanium-sapphire laser and the chirped pulse amplifier and allow them to thermally stabilize.Set the pulse duration to 120 femtoseconds, the repetition rate to 500 Hertz, and the incident fluence to 1 millijoule per square centimeter. Check the power and stability of the UV pump, and mid-IR probe pulses, and realign the optical paths as needed. Cool the mercury-cadmium-tellurium IR detector with liquid nitrogen.Position the spectrometer in line with the optical path and calibrate the spectrometer. Then, mount a 1 millimeter thick silicone wafer on the sample holder as a test sample. Set the pump-probe delay to a positive value.Optimize the pump-probe overlap by adjusting the mirror directing the pump beam to the sample, to obtain the maximal transient signal intensity. Set up a scan, starting at minus 100 picoseconds and ending at 1000 picosends, with a step time of 5 picoseconds. Scan the test sample, and identify the temporal position where the transient signal starts to emerge or time zero.Then, if using a solution phase sample, mount a flow cell with barium fluoride windows in the instrument and begin pumping the sample through the flow cell. If using a liquid crystal phase sample, mount the sample on a motorized stage to allow continuous movement of the laser spot position on the sample, to minimize laser induced damage. Confirm the time zero temporal position with the sample, and set the start, end and step times.Select a directory for the data file, and run the data acquisition process. First, etch and clean a silicone nitride coated wafer, to obtain a substrate with silicone nitride windows. Place the substrate on a spin coater chuck with the silicone nitride windows facing up.Spin coat the substrate with a 10 milligram per milliliter solution of pi-COT in chloroform. Place the spin coated substrate on a hot plate, and heat the hot plate to 100 degrees Celsius to melt the pi-COT. Turn off the hot plate when it reaches 100 degrees Celsius and let the sample cool in place, to obtain a pi-COT liquid crystal film.To begin the measurement, mount the sample on the instrument sample holder. Place the sample holder in the vacuum chamber and close the chamber. Use a rotary pump to evacuate the chamber to less than 1000 pascals or 10 millibars.Then, use a turbomolecular pump to evacuate the electron gun chamber to about 10 to the minus 6 pascals. Next, turn on the titanium-sapphire laser, and the chirped pulse amplifier, and allow them to thermally stabilize for one hour. Set the repetition rate to 500 hertz.Turn on the CCD camera chiller, and cool the device to 10 degrees Celsius. Then, turn on the electrical power supply, and set the voltage to 75 kilovolts. Open the special overlap software, and set the exposure time to 50 milliseconds.To find the probe electron beam position, first set the start type to z-overlap, and click start. When that process finishes, select y-overlap and click start again. Then, set the electron beam to the sample holder pinhole position, and align the pump laser with the reflected pump light by the pinhole.Next, switch to the time-resolved electron diffraction program. Set the start type to time-resolved and the pump influence to 2 millijoules per square centimeter. Click start to measure the time zero position based on an inorganic standard material fixed on the sample holder.Then, insert the Faraday cup into the electron beam path and measure the fluence with the picoammeter. Rotate the neutral density filter to adjust the electron beam fluence to 3 picoamperes. Adjust the pump pulse fluence to 1.67 milliwatts by rotating the wave plate on the pump beam line.Then, in the time-resolved electron diffraction software, move to the sample position. Set the CCD camera exposure time to 1 second. Set the start type to single, and click start to obtain a static electron diffraction image.Then, turn on the Peltier element of the CCD camera and cool the device to minus 20 degrees Celsius. Once the CCD camera has cooled, set the number of patterns to collect at each step, and the number of steps for the time-resolved measurements. Set the start type to time-resolved, and click start to collect the time-resolved electron diffraction images.When the experiment has finished, turn off the electron acceleration power supply. Collect the time-resolved image in the same way to obtain a background. The differential IR vibrational spectrum of a pi-COT based liquid crystal thin film had peaks corresponding to the stretching modes of the COT and thiazole rings, and of the biphenyl moyades, which are strongly IR active in the flat T1 form of pi-COT.The time-dependent evolution of the peak intensity had a wave number of 1338 reciprocal centimeters. It's consistent with the saddle to flat confirmational change within 2 picoseconds. Followed by relaxation to the initial saddle form in 10 to 20 picoseconds for single molecules, or 150 picoseconds for stacked molecules.The electron diffraction peaks from the photoresponsive moyades were extracted from the long pattern dominated by long carbon chains, by subtracting the initial diffraction pattern from a pattern obtained 500 picoseconds after UV pulse radiation. The positive and negative peaks indicated the formation and loss, respectively, of structural features by 500 picoseconds after irradiation. Th formation of a new ordered structure began about 200 picoseconds after photoexcitation, consistent with the relaxation to the initial saddle form in stacked molecules.The loss of the pi-pi stacking order on a 300 picoseconds timescale, was attributed to a small number of flat conformers, with 300 to 1000 picoseconds lifetimes, twisting to minimize steric hindrance. We first had the idea for this method when we discussed liquid crystals, which are not usually examined by times of diffraction because they do not provide good electron diffraction patterns. Our methodology allows changes in liquid crystal diffraction patterns to be identified, allowing access to important structure information and ultrafast molecule dynamics.Once mastered, these techniques can be done in a half day if they are performed properly. These techniques can potentially be used to answer further questions about the structure and ultrafast dynamics of more complex biomaterials.

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Research

JoVE Journal

Chemistry

Production of Disulfide-stabilized Transmembrane Peptide Complexes for Structural Studies

Physical interactions among the lipid-embedded alpha-helical domains of membrane proteins play a crucial role in folding and assembly of membrane protein complexes and in dynamic processes such as transmembrane (TM) signaling and regulation of cell-surface protein levels. Understanding the structural features driving the association of particular sequences requires sophisticated biophysical and biochemical analyses of TM peptide complexes. However, the extreme hydrophobicity of TM domains makes them very difficult to manipulate using standard peptide chemistry techniques, and production of suitable study material often proves prohibitively challenging. Identifying conditions under which peptides can adopt stable helical conformations and form complexes spontaneously adds a further level of difficulty. Here we present a procedure for the production of homo- or hetero-dimeric TM peptide complexes from materials that are expressed in E. coli, thus allowing incorporation of stable isotope labels for nuclear magnetic resonance (NMR) or non-natural amino acids for other applications relatively inexpensively. The key innovation in this method is that TM complexes are produced and purified as covalently associated (disulfide-crosslinked) assemblies that can form stable, stoichiometric and homogeneous structures when reconstituted into detergent, lipid or other membrane-mimetic materials. We also present carefully optimized procedures for expression and purification that are equally applicable whether producing single TM domains or crosslinked complexes and provide advice for adapting these methods to new TM sequences.

Biophysical and biochemical studies of interactions among membrane-embedded protein domains face many technical challenges, the first of which is obtaining appropriate study material. This article describes a protocol for producing and purifying disulfide-stabilized transmembrane peptide complexes that are suitable for structural analysis by solution nuclear magnetic resonance (NMR) and other analytical applications.

Physical  interactions among the lipid-embedded alpha-helical domains of membrane  proteins play a crucial role in folding and assembly of membrane ...

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 ...

Structure and Coordination Determination of Peptide-metal Complexes Using 1D and 2D 1H NMR

Copper (I) binding by metallochaperone transport proteins prevents copper oxidation and release of the toxic ions that may participate in harmful redox reactions. The Cu (I) complex of the peptide model of a Cu (I) binding metallochaperone protein, which includes the sequence MTCSGCSRPG (underlined is conserved), was determined in solution under inert conditions by NMR spectroscopy.
NMR is a widely accepted technique for the determination of solution structures of proteins and peptides. Due to difficulty in crystallization to provide single crystals suitable for X-ray crystallography, the NMR technique is extremely valuable, especially as it provides information on the solution state rather than the solid state. Herein we describe all steps that are required for full three-dimensional structure determinations by NMR. The protocol includes sample preparation in an NMR tube, 1D and 2D data collection and processing, peak assignment and integration, molecular mechanics calculations, and structure analysis. Importantly, the analysis was first conducted without any preset metal-ligand bonds, to assure a reliable structure determination in an unbiased manner.

Structure and Coordination Determination of Peptide-metal Complexes Using 1D and 2D 1H NMR

The NMR-solution structure of a metallochaperone model peptide with Cu (I) was determined, and a detailed protocol from sample preparation and 1D and 2D data collection to a three-dimensional structure is described.

Copper (I) binding by metallochaperone transport proteins prevents copper oxidation and release of the toxic ions that may participate in harmful redox ...

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 ...

From Constructs to Crystals &#8211; Towards Structure Determination of &#946;-barrel Outer Membrane Proteins

Membrane proteins serve important functions in cells such as nutrient transport, motility, signaling, survival and virulence, yet constitute only ~1% percent of known structures. There are two types of membrane proteins, &#945;-helical and &#946;-barrel. While &#945;-helical membrane proteins can be found in nearly all cellular membranes, &#946;-barrel membrane proteins can only be found in the outer membranes of mitochondria, chloroplasts, and Gram-negative bacteria. One common bottleneck in structural studies of membrane proteins in general is getting enough pure sample for analysis. In hopes of assisting those interested in solving the structure of their favorite &#946;-barrel outer membrane protein (OMP), general protocols are presented for the production of target &#946;-barrel OMPs at levels useful for structure determination by either X-ray crystallography and/or NMR spectroscopy. Here, we outline construct design for both native expression and for expression into inclusion bodies, purification using an affinity tag, and crystallization using detergent screening, bicelle, and lipidic cubic phase techniques. These protocols have been tested and found to work for most OMPs from Gram-negative bacteria; however, there are some targets, particularly for mitochondria and chloroplasts that may require other methods for expression and purification. As such, the methods here should be applicable for most projects that involve OMPs from Gram-negative bacteria, yet the expression levels and amount of purified sample will vary depending on the target OMP.

From Constructs to Crystals &amp;#8211; Towards Structure Determination of &amp;#946;-barrel Outer Membrane Proteins

&#946;-barrel outer membrane proteins (OMPs) serve many functions within the outer membranes of Gram-negative bacteria, mitochondria, and chloroplasts. Here, we hope to alleviate a known bottleneck in structural studies by presenting protocols for the production of &#946;-barrel OMPs in sufficient quantities for structure determination by X-ray crystallography or NMR spectroscopy.

Membrane proteins serve important functions in cells such as nutrient transport, motility, signaling, survival and virulence, yet constitute only ~1% ...

Post Column Derivatization Using Reaction Flow High Performance Liquid Chromatography Columns

A protocol for the use of reaction flow high performance liquid chromatography columns for methods employing post column derivatization (PCD) is presented. A major difficulty in adapting PCD to modern HPLC systems and columns is the need for large volume reaction coils that enable reagent mixing and then the derivatization reaction to take place. This large post column dead volume leads to band broadening, which results in a loss of observed separation efficiency and indeed detection in sensitivity. In reaction flow post column derivatization (RF-PCD) the derivatization reagent(s) are pumped against the flow of mobile phase into either one or two of the outer ports of the reaction flow column where it is mixed with column effluent inside a frit housed within the column end fitting. This technique allows for more efficient mixing of the column effluent and derivatization reagent(s) meaning that the volume of the reaction loops can be minimized or even eliminated altogether. It has been found that RF-PCD methods perform better than conventional PCD methods in terms of observed separation efficiency and signal to noise ratio. A further advantage of RF-PCD techniques is the ability to monitor effluent coming from the central port in its underivatized state. RF-PCD has currently been trialed on a relatively small range of post column reactions, however, there is currently no reason to suggest that RF-PCD could not be adapted to any existing one or two component (as long as both reagents are added at the same time) post column derivatization reaction.

A protocol for the use of reaction flow high performance liquid chromatography columns for methods employing post column derivatization (PCD) is presented.

A protocol for the use of reaction flow high performance liquid chromatography columns for methods employing post column derivatization (PCD) is ...

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 ...

From Molecules to Materials: Engineering New Ionic Liquid Crystals Through Halogen Bonding

Herein, we demonstrate that a bottom-up approach, based on halogen bonding (XB), can be successfully applied for the design of a new type of ionic liquid crystals (ILCs). Taking advantages of the high specificity of XB for haloperfluorocarbons and the ability of anions to act as XB-acceptors, we obtained supramolecular complexes based on 1-alkyl-3-methylimidazolium iodides and iodoperfluorocarbons, overcoming the well-known immiscibility between hydrocarbons (HCs) and perfluorocarbons (PFCs). The high directionality of the XB combined with the fluorophobic effect, allowed us to obtain enantiotropic liquid crystals where a rigid, non-aromatic, XB supramolecular anion acts as mesogenic core.
X-ray structure analysis of the complex between 1-ethyl-3-methylimidazolium iodide and iodoperfluorooctane showed the presence of a layered structure, which is a manifestation of the well-known tendency to segregation of perfluoroalkyl chains. This is consistent with the observation of smectic mesophases. Moreover, all the reported complexes melt below 100 &#176;C, and most are mesomorphic even at room temperature, despite that the starting materials were non-mesomorphic in nature.
The supramolecular strategy reported here provides new design principles for mesogen design allowing a totally new class of functional materials.

A protocol for the synthesis of a new type of mesogens, based on the halogen-bonded supramolecular anion [CnF2n+1-I&#183;&#183;&#183;I&#183;&#183;&#183;I-CnF2n+1]&#8722;, is reported.

Herein, we demonstrate that a bottom-up approach, based on halogen bonding (XB), can be successfully applied for the design of a new type of ionic liquid ...

Liquid-cell Transmission Electron Microscopy for Tracking Self-assembly of Nanoparticles

Drying a nanoparticle dispersion is a versatile way to create self-assembled structures of nanoparticles, but the mechanism of this process is not fully understood. We have traced the trajectories of individual nanoparticles using liquid-cell transmission electron microscopy (TEM) to investigate the mechanism of the assembly process. Herein, we present the protocols used for liquid-cell TEM studies of the self-assembly mechanism. First, we introduce the detailed synthetic protocols used to produce uniformly sized platinum and lead selenide nanoparticles. Next, we present the microfabrication processes used to produce liquid cells with silicon nitride or silicon windows and then describe the loading and imaging procedures of the liquid-cell TEM technique. Several notes are included to provide helpful tips for the entire process, including how to manage the fragile cell windows. The individual motions of nanoparticles tracked by liquid-cell TEM revealed that changes in the solvent boundaries caused by evaporation affected the self-assembly process of nanoparticles. The solvent boundaries drove nanoparticles to primarily form amorphous aggregates, followed by flattening of the aggregates to produce a 2-dimensional (2D) self-assembled structure. These behaviors are also observed for different nanoparticle types and different liquid-cell compositions.

Here we introduce experimental protocols for the real-time observation of a self-assembly process using liquid-cell transmission electron microscopy.

Drying a nanoparticle dispersion is a versatile way to create self-assembled structures of nanoparticles, but the mechanism of this process is not fully ...

Preparation of Graphene-Supported Microwell Liquid Cells for In Situ Transmission Electron Microscopy

The fabrication and preparation of graphene-supported microwell liquid cells (GSMLCs) for in situ electron microscopy is presented in a stepwise protocol. The versatility of the GSMLCs is demonstrated in the context of a study about etching and growth dynamics of gold nanostructures from a HAuCl4 precursor solution. GSMLCs combine the advantages of conventional silicon- and graphene-based liquid cells by offering reproducible well depths together with facile cell manufacturing and handling of the specimen under investigation. The GSMLCs are fabricated on a single silicon substrate which drastically reduces the complexity of the manufacturing process compared to two-wafer-based liquid cell designs. Here, no bonding or alignment process steps are required. Furthermore, the enclosed liquid volume can be tailored to the respective experimental requirements by simply adjusting the thickness of a silicon nitride layer. This enables a significant reduction of window bulging in the electron microscope vacuum. Finally, a state-of-the-art quantitative evaluation of single particle tracking and dendrite formation in liquid cell experiments using only open source software is presented.

Preparation of Graphene-Supported Microwell Liquid Cells for In Situ Transmission Electron Microscopy

A protocol for preparation of graphene-supported microwell liquid cells for in situ electron microscopy of gold nanocrystals from HAuCl4 precursor solution is presented. Furthermore, an analysis routine is presented to quantify observed etching and growth dynamics.

The fabrication and preparation of graphene-supported microwell liquid cells (GSMLCs) for in situ electron microscopy is presented in a stepwise protocol. ...