Name: direct imaging of laser-driven ultrafast molecular rotation
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This work was supported in part by grants-in-aid KAKENHI from the Japan Society for the Promotion of Science (JSPS) and the Ministry of Education, Culture, Sports, Science, and Technology (MEXT) Japan (#26104539, #26620020, #26810011, #15H03766, #15KT0060, #16H00826, and #16K13927); the Konica Minolta Science and Technology Foundation; the "Planting Seeds for Research" program of TokyoTech; the Imaging Science Project of the Center for Novel Science Initiatives (CNSI) at the National Institutes of Natural Sciences (NINS) (#IS261006); the RIKEN-IMS joint program on "Extreme Photonics;" and the Consortium for Photon Science and Technology (CPhoST).

NOTE: Through this protocol, we clarify what we actually did to develop the present method. Exact parameters, including chamber and optical setup design and the sizes and types of the parts, are not always essential to apply the present system to the reader&#39;s apparatus. The essence of the procedures will be given as notes in each step.
1. Construction of a 2D-slice Imaging Apparatus
NOTE: Throughout this step, all the commercially available parts and equipment, su...

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The present procedure enables us to capture a real-time movie of molecular rotation with a slit-based 2D imaging setup. Because the observed ions pass through the slit, step 1.5 is one of the critical steps. The edges of the slit blades must be sharp. When there is a small defect, such as a 0.3 mm dent in the slit, a scratch is observed in the ion image (Figure 6). In such a case, the slit blade should be polished with 2,000-grit wet sandpaper.
Apart from the unique camera ang...

For a deeper understanding and better use of the dynamic nature of molecules, it is essential to clearly visualize molecular motions of interest. Time-resolved Coulomb explosion imaging is one of the powerful approaches to achieve this objective1,2,3. In this approach, the molecular dynamics of interest are initiated by a pump ultrashort laser field and are then probed by a time-delayed probe pulse. Upon probe irradiation, molecules are multiply ionized and broken into fragment ions due to the Coulomb repulsion. The spatial distribution of the ejected ions is a measure of the molecular structure and spatial orientation at the probe irradiation. A sequence of measurement scanning the pump-probe delay time leads to the creation of a molecular movie. It is noteworthy that, for the simplest case &#8211; diatomic molecules &#8211; the angular distribution of the ejected ions directly reflects the molecular axis distribution (i.e., the squared rotational wave function).
With regard to the pump process, recent progress in the coherent control of molecular motion using ultrashort laser fields has led to the creation of highly controlled rotational wave packets4,5. Furthermore, the direction of rotation can be actively controlled by using a polarization-controlled laser field6,7,8. It has therefore been expected that a detailed picture of molecular rotation, including wave natures, could be visualized when the Coulomb explosion imaging technique is combined with such a pump process9,10,11,12,13. However, we sometimes encounter experimental difficulties associated with the existing imaging methods, as mentioned below. The purpose of this paper is to present a new way of overcoming these difficulties and of creating a high-quality movie of molecular rotational wave packets. The first experimental movie of molecular rotation taken with the present method, along with its physical implications, were presented in our previous paper11. The background of development, the detailed theoretical aspect of the present imaging technique, and a comparison with other existing techniques will be given in a forthcoming paper. Here, we will mainly focus on the practical and technical aspects of the procedure, including the combination of the typical pump-probe optical setup and the new imaging apparatus. As in the previous paper, the target system is unidirectionally rotating nitrogen molecules11.
The main experimental difficulty of the existing imaging setup, schematically shown in Figure 1, has to do with the position of the detector, or the camera angle. Because the rotational axis coincides with the laser propagation axis6,7,8 in laser-field-induced molecular rotation, it is not practical to install a detector along the rotational axis. When the detector is installed so as to avoid laser irradiation, the camera angle corresponds to a side observation of rotation. In this case, it is impossible to reconstruct the original orientation of molecules from the projected (2D) ion image14. A 3D imaging detector14,15,16,17,18,19, with which the arrival time to the top detector and the ion impact positions can be measured, offered a unique way to directly observe molecular rotation using Coulomb explosion imaging10,12. However, the acceptable ion counts per laser shot are low (typically &#60; 10 ions) in the 3D detector, meaning that it is difficult to create a long movie of molecular motion with high image quality14. The dead time of the detectors (typically ns) also affects the image resolution and imaging efficiency. It is also not a simple task to make a good pump-probe beam overlap by monitoring a real-time ion image with a laser repetition rate of &#60;~1 kHz. Although several groups have observed rotational wave packets using the 3D technique, the spatial information was limited and/or direct, and a detailed visualization of wave nature, including complicated nodal structures, was not achieved10,12.
The essence of the new imaging technique is the use of the &#34;new camera angle&#34; in Figure 1. In this configuration, laser beam exposure to a detector is avoided while the 2D detector is parallel to the rotational plane, leading to the observation from the rotational axis direction. The slit allows only the ion in the rotational plane (the polarization plane of the laser pulses) to contribute to an image. A 2D detector, which offers a higher count rate (typically ~100 ions) than a 3D detector, can be used. The setup of the electronics is simpler than in the case of 3D detection, while the measurement efficiency is higher. Time-consuming mathematical reconstruction, such as Abel inversion14, is also not needed to extract angular information. These features lead to the easy optimization of the measurement system and to the production of high-quality movies. A standard 2D/3D charged-particle imaging apparatus can be easily modified to the present setup without the use of expensive equipment.

<table border="0" cellpadding="0" cellspacing="0" width="618">
	<tbody>
		<tr height="42">
			<td height="42" style="height:42px;width:249px;">CMOS camera</td>
			<td style="width:83px;">Toshiba TELI</td>
			<td style="width:119px;">BU-238M-ES</td>
			<td style="width:167px;">equipped with SONY IMX174 sensor</td>
		</tr>
		<tr height="21">
			<td height="21" style="height:21px;width:249px;">High voltage switch</td>
			<td style="width:83px;">Behlke</td>
			<td style="width:119px;">HTS-41-03-GSM</td>
			<td></td>
		</tr>
		<tr height="21">
			<td height="21" style="height:21px;width:249px;">High voltage switch</td>
			<td style="width:83px;">Behlke</td>
			<td style="width:119px;">HTS-80-03</td>
			<td></td>
		</tr>
		<tr height="63">
			<td height="63" style="height:63px;width:249px;">Digital delay generator</td>
			<td style="width:83px;">Stanford research systems</td>
			<td style="width:119px;">DG535</td>
			<td></td>
		</tr>
		<tr height="63">
			<td height="63" style="height:63px;width:249px;">Digital delay generator</td>
			<td style="width:83px;">Stanford research systems</td>
			<td style="width:119px;">DG645</td>
			<td></td>
		</tr>
		<tr height="21">
			<td height="21" style="height:21px;width:249px;">Microchannel plate</td>
			<td style="width:83px;">Photonis</td>
			<td align="right" style="width:119px;">3075</td>
			<td></td>
		</tr>
		<tr height="42">
			<td height="42" style="height:42px;width:249px;">Pulsed valve</td>
			<td style="width:83px;">LAMID LTD</td>
			<td style="width:119px;">Even-Lavie valve&#160;</td>
			<td style="width:167px;">High repetition, room temperature model</td>
		</tr>
		<tr height="84">
			<td height="84" style="height:84px;width:249px;">Molecular beam skimmers</td>
			<td style="width:83px;">Institute for Molecular Science</td>
			<td style="width:119px;">13C11</td>
			<td style="width:167px;">3 and 1.5 mm center hole, 25 degrees full inner angle, and ~50 mm length</td>
		</tr>
		<tr height="21">
			<td height="21" style="height:21px;width:249px;">Optical Comparator</td>
			<td style="width:83px;">Nikon</td>
			<td style="width:119px;">V-24B</td>
			<td style="width:167px;"></td>
		</tr>
		<tr height="42">
			<td height="42" style="height:42px;width:249px;">DPSS laser</td>
			<td style="width:83px;">Lighthouse Photonics</td>
			<td style="width:119px;">Sprout</td>
			<td></td>
		</tr>
		<tr height="21">
			<td height="21" style="height:21px;width:249px;">Femtosecond Ti:Sapphire oscillator</td>
			<td style="width:83px;">KMLabs</td>
			<td style="width:119px;">Halcyon</td>
			<td></td>
		</tr>
		<tr height="21">
			<td height="21" style="height:21px;width:249px;">Femtosecond Ti:Sapphire amplifier</td>
			<td style="width:83px;">Quantronix</td>
			<td style="width:119px;">Odin-II HE</td>
			<td></td>
		</tr>
		<tr height="21">
			<td height="21" style="height:21px;width:249px;">Motorized linear stage</td>
			<td style="width:83px;">Sigma Koki</td>
			<td style="width:119px;">KST(GS)-100X</td>
			<td></td>
		</tr>
		<tr height="21">
			<td height="21" style="height:21px;width:249px;">Manual X-stage</td>
			<td style="width:83px;">Sigma Koki</td>
			<td style="width:119px;">TSD-601S</td>
			<td></td>
		</tr>
		<tr height="42">
			<td height="42" style="height:42px;width:249px;">High resolution mirror mount</td>
			<td style="width:83px;">Newport</td>
			<td style="width:119px;">Suprema SX100-F2KN-254</td>
			<td></td>
		</tr>
		<tr height="42">
			<td height="42" style="height:42px;width:249px;">High resolution mirror mount</td>
			<td style="width:83px;">LIOP-TEC GmbH</td>
			<td style="width:119px;">SR100-100R-2-HS</td>
			<td></td>
		</tr>
		<tr height="63">
			<td height="63" style="height:63px;width:249px;">Polarization checker</td>
			<td style="width:83px;">Paradigm Devices, Inc.</td>
			<td style="width:119px;">O-tool VIS</td>
			<td></td>
		</tr>
		<tr height="44">
			<td height="44" style="height:44px;width:249px;">Instrument communication interface</td>
			<td style="width:83px;">National Instruments</td>
			<td style="width:119px;">NI-MAX</td>
			<td></td>
		</tr>
		<tr height="45">
			<td height="45" style="height:45px;width:249px;">Graphical development environment for measurement programs</td>
			<td style="width:83px;">National Instruments</td>
			<td style="width:119px;">LabVIEW 2014</td>
			<td></td>
		</tr>
		<tr height="42">
			<td height="42" style="height:42px;width:249px;">Laser line dielectric mirror</td>
			<td style="width:83px;">CVI/LEO</td>
			<td style="width:119px;">TLM2-400/800-45UNP</td>
			<td></td>
		</tr>
		<tr height="21">
			<td height="21" style="height:21px;width:249px;">Laser line dielectric mirror</td>
			<td style="width:83px;">Altechna</td>
			<td colspan="2">Low GDD Ultrafast mirror</td>
		</tr>
		<tr height="21">
			<td height="21" style="height:21px;width:249px;">Laser line dielectric mirror</td>
			<td style="width:83px;">Altechna</td>
			<td colspan="2">Low GDD Ultrafast mirror</td>
		</tr>
		<tr height="42">
			<td height="42" style="height:42px;width:249px;">Femtosecond polarizer</td>
			<td style="width:83px;">Advanced Thin Films</td>
			<td style="width:119px;">PBS-GVD</td>
			<td></td>
		</tr>
	</tbody>
</table>

direct imaging of laser-driven ultrafast molecular rotation

We present a method for visualizing laser-induced, ultrafast molecular rotational wave packet dynamics. We have developed a new 2-dimensional Coulomb explosion imaging setup in which a hitherto-impractical camera angle is realized. In our imaging technique, diatomic molecules are irradiated with a circularly polarized strong laser pulse. The ejected atomic ions are accelerated perpendicularly to the laser propagation. The ions lying in the laser polarization plane are selected through the use of a mechanical slit and imaged with a high-throughput, 2-dimensional detector installed parallel to the polarization plane. Because a circularly polarized (isotropic) Coulomb exploding pulse is used, the observed angular distribution of the ejected ions directly corresponds to the squared rotational wave function at the time of the pulse irradiation. To create a real-time movie of molecular rotation, the present imaging technique is combined with a femtosecond pump-probe optical setup in which the pump pulses create unidirectionally rotating molecular ensembles. Due to the high image throughput of our detection system, the pump-probe experimental condition can be easily optimized by monitoring a real-time snapshot. As a result, the quality of the observed movie is sufficiently high for visualizing the detailed wave nature of motion. We also note that the present technique can be implemented in existing standard ion imaging setups, offering a new camera angle or viewpoint for the molecular systems without the need for extensive modification.

Figure 4A shows a probe-only raw image of the N2+ ion ejected upon probe irradiation (Coulomb explosion), taken for one probe laser shot. Each bright spot corresponds to one ion. Figure 4B shows a summed image of 10,000 binarized raw camera images. These images show that our imaging setup can monitor the molecules of all the orientation angles in the polarization plane. Figure 4C shows the normalized polar plot correspo...

Watch this Scientific Journal Video about Direct Imaging of Laser-driven Ultrafast Molecular Rotation at JoVE.com

Direct Imaging of Laser-driven Ultrafast Molecular Rotation

We present a protocol for creating a real-time movie of a molecular rotational wave packet using a high-resolution Coulomb explosion imaging setup.

We present a method for visualizing laser-induced, ultrafast molecular rotational wave packet dynamics. We have developed a new 2-dimensional Coulomb ...

Overall, the goal of this experiment is to take high resolution, real time snapshots of ultrafast molecular rotation. This method can help answer key questions in the field of Quantum Mechanics and Physical Chemistry such as the connection between the quantum molecular motion and the classical mechanics world. The main advantage of this technique is that we can carry out high resolution, high throughput realtime imaging of molecules from a camera angle which has not been previously realized.This method can provide insight into rotation dynamics of molecules. It can also be applied to other systems such as oriented molecules and photo resource actions. The equipment needed for the experiment has two main components.The first is a two dimensional slice imaging apparatus constructed in a vacuum chamber. This schematic provides an idea of what is inside the chamber. After lasers, ionized diatomic molecules.There are ion optical elements to guide the ionization products. There is a slit to select ions in the laser polarization plane and an electrode that acts as a pulsed repeller. It directs ions to a parallel detector consisting of microchannel plates backed by a phosphor screen.The second component is the pump probe optical setup. As depicted in the schematic, the setup employs a titanium sapphire laser amplifier to create three colinear femptosecond pulses. The first pulse is linearly polarized with a center wavelength of 820 nanometers and is for molecular alignment.The second pulse if for direction control. It is a delayed replica of the first pulse, except the linear polarization is tilted 45 degrees with respect to the first. The third pulse is the Coulomb explosion imaging probe.It is at 407 nanometers, circularly polarized, and lasts 100 femtoseconds. These three pulses enter the vacuum chamber along the same path. An important step is to adjust the polarization state of the pulses using a polarization checker.This checker allows visualization of the polarization state by the polarization angle dependent transmission intensity. Install the polarization checker in the beam path just before it enters the chamber. Focus on the polarization state of the imaging probe.The goal is circular polarization. To change the polarization, use the wave plates in the pulse's path. Adjust the wave plates in their rotational optic mounts.Stop when the checker indicates the polarization is circular. Follow a similar procedure with pulse one by adjusting its wave plates. In the end, its polarization angle should be vertical.Manipulate the wave plates of the second pulse to produce linear polarization where the angle is at 45 degrees with respect to that of pulse one. Remove the polarization checker and dumps from the beam path and complete other setup preparations. The time overlap of the pulses must be roughly optimized.To do this, four elements should be mounted just before the focusing lens in the system. The first in the path is an optical window as thick as the focusing lens and the chamber window combined. Next is a nonlinear crystal with a nonlinear response only when the pump and probe interact simultaneously.Third along the path is a dispersion prism. Finally, there's a sheet of white paper to register the nonlinear signal. Work with the pump one beam and the probe pulse by placing a beam dump on pump two beam.Search for a third harmonic signal using the motorized stage. Press the move button on the stage controller to scan and search for the third signal. The paper in the beam path will indicate the harmonic signal with a white blue fluorescence.Next, unblock pump two and block pump one with a beam dumper. Use the manual stage in the pump two line to adjust the beam path. Scan the micrometer based stage until the third harmonic emission occurs.Determination of the time zero or temporal overlap is complete when fluorescence is visible on the paper. Before continuing, remove all of the elements that were added to the beam line to find the temporal overlap. The unique aspect of the measurement setup is the camera placement.As suggested in this schematic, the detector surface is perpendicular to the laser polarization plane. The camera axis is perpendicular to the detector's surface and thus parallel to the line of the laser propagation. Install a digital camera on the optical post in front of the vacuum view port ensuring it is properly oriented.In addition, install a cooling fan behind the camera. To reduce unwanted light, drape a curtain over the region between the view port and the lens. With the camera connected to the computer, start the control software and maximize the gain of the camera.Start capturing images resulting from the molecular ionization. The camera images should cover the entire surface of the detector when the camera is properly positioned. Continue to monitor the captured images to adjust the camera focus.The size of the spots due to the ions should be as sharp and as small as possible. For measurements, first find the signal and optimize the ion imaging settings. To do this, use only the probe pulse by blocking the pump pulse beams.The pulse travels through a plano convex lens to focus it on the molecular beams. A pulse generator sets the time of the high voltage switches for the ion optics. Set it to the estimated arrival time of the Nitrogen molecule ions.Monitor the ion image while adjusting the lens position and gas pulse time to achieve the largest and brightest image. Next use the pulse generator to change the time of the high voltage switches. Use the time for the Coulomb exploded doubly ionized Nitrogen channel.At the computer, decrease the camera frame rate and increase the exposure time. In addition, adjust the ion optic biases so the observed ion distribution becomes an undistorted ellipse. Move on to finding the pump probe spatial overlap.Unblock pump one, but keep pump two blocked. Make use of the telescope to position the pump pulse beam waste in high resolution mirror mount one to alter the beam position. As the telescope is adjusted, monitor the spot due to the pump pulses.When the smallest spot size is seen, the beam waste is in the molecular beam. Continue by ensuring the probe pulse images the molecules irradiated by the pump pulse. This requires moving the delay stage from its zero position.For Nitrogen, move the motorized stage about 600 micrometers forward. As in this example, the previously isotropic image should become strongly anisotropic along the direction of pump one polarization. At this point, block pump one and unblock pump two.Use high resolution mirror mount two to find the pump probe overlap. Adjust the mirror while keeping the optical path of pump one unchanged. The alignment should be along the oblique angle of pump two's polarization direction with respect to the polarization of pump one.To observe the unidirectional rotation dynamics, unblock both pump beams. Use the manual delay stage to set the delay between the pump beams. Adjust the stage to four picoseconds in the case of molecular Nitrogen.Set up the motorized stage in the probe beam to scan probe delays. Check to determine if unidirectional rotation can be recognized in camera images as the probe delay is scanned. For a movie of unidirectional molecular rotation change the camera frame rate and exposure time.Use computer control to collect data and step through probe time values. This is a probe only raw image of doubly ionized Nitrogen that was ejected after one shot of probe irradiation. Each bright spot corresponds to an ion.This image is produced when 10, 000 such binarized images are summed over. The real space size is 80 millimeters by 50 millimeters. Note that false color is used to show signal intensity.Ultimately the data can be used to generate a normalized polar plot with the radial value proportional to an angle dependent probability. Clear evidence of unidirectional molecular rotation is presented in this series of selected snapshots taken after irradiation with two pump pulses. There are three series.One has the ion image in which the elliptical shape has been converted to a circle. The second has a corresponding polar plot. Finally, there is a series created with a model constructed using overlapped images of dumbbells at various orientation angle, weighted with observed angular probabilities.After it's debutment, this technique paved the ways for researcher in the field of molecular science to explore the quantum nature of molecular rotation. After watching this video, you should have a good understanding of how to control and visualize the ultrafast molecular rotation using phaser gun laser pulses.

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Measurements of Long-range Electronic Correlations During Femtosecond Diffraction Experiments Performed on Nanocrystals of Buckminsterfullerene

The precise details of the interaction of intense X-ray pulses with matter are a topic of intense interest to researchers attempting to interpret the results of femtosecond X-ray free electron laser (XFEL) experiments. An increasing number of experimental observations have shown that although nuclear motion can be negligible, given a short enough incident pulse duration, electronic motion cannot be ignored. The current and widely accepted models assume that although electrons undergo dynamics driven by interaction with the pulse, their motion could largely be considered &#39;random&#39;. This would then allow the supposedly incoherent contribution from the electronic motion to be treated as a continuous background signal and thus ignored. The original aim of our experiment was to precisely measure the change in intensity of individual Bragg peaks, due to X-ray induced electronic damage in a model system, crystalline C60. Contrary to this expectation, we observed that at the highest X-ray intensities, the electron dynamics in C60 were in fact highly correlated, and over sufficiently long distances that the positions of the Bragg reflections are significantly altered. This paper describes in detail the methods and protocols used for these experiments, which were conducted both at the Linac Coherent Light Source (LCLS) and the Australian Synchrotron (AS) as well as the crystallographic approaches used to analyse the data.

We describe an experiment designed to probe the electronic damage induced in nanocrystals of Buckminsterfullerene (C60) by intense, femtosecond pulses of X-rays. The experiment found that, surprisingly, rather than being stochastic, the X-ray induced electron dynamics in C60 are highly correlated, extending over hundreds of unit cells within the crystals1.

The precise details of the interaction of intense X-ray pulses with matter are a topic of intense interest to researchers attempting to interpret the ...

Microfluidic Chips for In Situ Crystal X-ray Diffraction and In Situ Dynamic Light Scattering for Serial Crystallography

This protocol describes fabricating microfluidic devices with low X-ray background optimized for goniometer based fixed target serial crystallography. The devices are patterned from epoxy glue using soft lithography and are suitable for in situ X-ray diffraction experiments at room temperature. The sample wells are lidded on both sides with polymeric polyimide foil windows that allow diffraction data collection with low X-ray background. This fabrication method is undemanding and inexpensive. After the sourcing of a SU-8 master wafer, all fabrication can be completed outside of a cleanroom in a typical research lab environment. The chip design and fabrication protocol utilize capillary valving to microfluidically split an aqueous reaction into defined nanoliter sized droplets. This loading mechanism avoids the sample loss from channel dead-volume and can easily be performed manually without using pumps or other equipment for fluid actuation. We describe how isolated nanoliter sized drops of protein solution can be monitored in situ by dynamic light scattering to control protein crystal nucleation and growth. After suitable crystals are grown, complete X-ray diffraction datasets can be collected using goniometer based in situ fixed target serial X-ray crystallography at room temperature. The protocol provides custom scripts to process diffraction datasets using a suite of software tools to solve and refine the protein crystal structure. This approach avoids the artefacts possibly induced during cryo-preservation or manual crystal handling in conventional crystallography experiments. We present and compare three protein structures that were solved using small crystals with dimensions of approximately 10-20 &#181;m grown in chip. By crystallizing and diffracting in situ, handling and hence mechanical disturbances of fragile crystals is minimized. The protocol details how to fabricate a custom X-ray transparent microfluidic chip suitable for in situ serial crystallography. As almost every crystal can be used for diffraction data collection, these microfluidic chips are a very efficient crystal delivery method.

Microfluidic Chips for In Situ Crystal X-ray Diffraction and In Situ Dynamic Light Scattering for Serial Crystallography

This protocol describes in detail how to fabricate and operate microfluidic devices for X-ray diffraction data collection at room temperature. Additionally, it describes how to monitor protein crystallization by dynamic light scattering and how to process and analyze obtained diffraction data.

This protocol describes fabricating microfluidic devices with low X-ray background optimized for goniometer based fixed target serial crystallography. The ...

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 ...

Automation of a Positron-emission Tomography (PET) Radiotracer Synthesis Protocol for Clinical Production

The development of new positron-emission tomography (PET) tracers is enabling researchers and clinicians to image an increasingly wide array of biological targets and processes. However, the increasing number of different tracers creates challenges for their production at radiopharmacies. While historically it has been practical to dedicate a custom-configured radiosynthesizer and hot cell for the repeated production of each individual tracer, it is becoming necessary to change this workflow. Recent commercial radiosynthesizers based on disposable cassettes/kits for each tracer simplify the production of multiple tracers with one set of equipment by eliminating the need for custom tracer-specific modifications. Furthermore, some of these radiosynthesizers enable the operator to develop and optimize their own synthesis protocols in addition to purchasing commercially-available kits. In this protocol, we describe the general procedure for how the manual synthesis of a new PET tracer can be automated on one of these radiosynthesizers and validated for the production of clinical-grade tracers. As an example, we use the ELIXYS radiosynthesizer, a flexible cassette-based radiochemistry tool that can support both PET tracer development efforts, as well as routine clinical probe manufacturing on the same system, to produce [18F]Clofarabine ([18F]CFA), a PET tracer to measure in vivo deoxycytidine kinase (dCK) enzyme activity. Translating a manual synthesis involves breaking down the synthetic protocol into basic radiochemistry processes that are then translated into intuitive chemistry &#34;unit operations&#34; supported by the synthesizer software. These operations can then rapidly be converted into an automated synthesis program by assembling them using the drag-and-drop interface. After basic testing, the synthesis and purification procedure may require optimization to achieve the desired yield and purity. Once the desired performance is achieved, a validation of the synthesis is carried out to determine its suitability for the production of the radiotracer for clinical use.

Automation of a Positron-emission Tomography PET Radiotracer Synthesis Protocol for Clinical Production

Positron-emission tomography (PET) imaging sites that are involved in multiple early clinical research trials need robust and versatile radiotracer manufacturing capabilities. Using the radiotracer [18F]Clofarabine as an example, we illustrate how to automate the synthesis of a radiotracer using a flexible, cassette-based radiosynthesizer and validate the synthesis for clinical use.

The development of new positron-emission tomography (PET) tracers is enabling researchers and clinicians to image an increasingly wide array of biological ...

Light-driven Molecular Motors on Surfaces for Single Molecular Imaging

The design and synthesis of a synthetic system that aims for the direct visualization of a synthetic rotary motor at the single molecule level on surfaces are demonstrated. This work requires careful design, considerable synthetic effort, and proper analysis. The rotary motion of the molecular motor in solution is shown by 1H NMR and UV-vis absorption spectroscopy techniques. In addition, the method to graft the motor onto an amine-coated quartz is described. This method helps to gain more insight into molecular machines.

The manuscript describes how to synthesize and graft a molecular motor on surfaces for single molecular imaging.

The design and synthesis of a synthetic system that aims for the direct visualization of a synthetic rotary motor at the single molecule level on surfaces ...

Imaging Corrosion at the Metal-Paint Interface Using Time-of-Flight Secondary Ion Mass Spectrometry

Corrosion developed at the paint and aluminum (Al) metal-paint interface of an aluminum alloy is analyzed using time-of-flight secondary ion mass spectrometry (ToF-SIMS), illustrating that SIMS is a suitable technique to study the chemical distribution at a metal-paint interface. The painted Al alloy coupons are immersed in a salt solution or exposed to air only. SIMS provides chemical mapping and 2D molecular imaging of the interface, allowing direct visualization of the morphology of the corrosion products formed at the metal-paint interface and mapping of the chemical after corrosion occurs. The experimental procedure of this method is presented to provide technical details to facilitate similar research and highlight pitfalls that may be encountered during such experiments.

Time-of-flight secondary ion mass spectrometry is applied to demonstrate the chemical mapping and corrosion morphology at the metal-paint interface of an aluminum alloy after being exposed to a salt solution compared with a specimen exposed to air.

Corrosion developed at the paint and aluminum (Al) metal-paint interface of an aluminum alloy is analyzed using time-of-flight secondary ion mass ...

Ultrafast Time-resolved Near-IR Stimulated Raman Measurements of Functional &#960;-conjugate Systems

Femtosecond time-resolved stimulated Raman spectroscopy is a promising method of observing the structural dynamics of short-lived transients with near infrared (near-IR) transitions, because it can overcome the low sensitivity of spontaneous Raman spectrometers in the near-IR region. Here, we describe technical details of a femtosecond time-resolved near-IR multiplex stimulated Raman spectrometer that we have recently developed. A description of signal generation and optimization, measurement, data acquisition, and calibration and correction of recorded data is provided as well. We present an application of our spectrometer to analyze the excited-state dynamics of &#946;-carotene in toluene solution. A C=C stretch band of &#946;-carotene in the second lowest excited singlet (S2) state and the lowest excited singlet (S1) state is clearly observed in the recorded time-resolved stimulated Raman spectra. The femtosecond time-resolved near-IR stimulated Raman spectrometer is applicable to the structural dynamics of &#960;-conjugate systems from simple molecules to complex materials.

Ultrafast Time-resolved Near-IR Stimulated Raman Measurements of Functional &amp;#960;-conjugate Systems

Details of signal generation and optimization, measurement, data acquisition, and data handling for a femtosecond time-resolved near-IR stimulated Raman spectrometer are described. A near infrared stimulated Raman study on the excited-state dynamics of &#946;-carotene in toluene is shown as a representative application.

Femtosecond time-resolved stimulated Raman spectroscopy is a promising method of observing the structural dynamics of short-lived transients with near ...

A Microwave-Assisted Direct Heteroarylation of Ketones Using Transition Metal Catalysis

Heteroarylation introduces heteroaryl fragments to organic molecules. Despite the numerous available reactions reported for arylation via transition metal catalysis, the literature on direct heteroarylation is scarce. The presence of heteroatoms such as nitrogen, sulfur and oxygen often make heteroarylation a challenging research field due to catalyst poisoning, product decomposition and the rest. This protocol details a highly efficient direct &#945;-C(sp3) heteroarylation of ketones under microwave irradiation. Key factors for successful heteroarylation include the use of XPhos Palladacycle Gen. 4 Catalyst, excess base to suppress side reactions and the high temperature and pressure achieved in a sealed reaction vial under microwave irradiation. The heteroarylation compounds prepared by this method were fully characterized by proton nuclear magnetic resonance spectroscopy (1H NMR), carbon nuclear magnetic resonance spectroscopy (13C NMR) and high-resolution mass spectrometry (HRMS). This methodology has several advantages over literature precedents including broad substrate scope, rapid reaction time, greener procedure and operational simplicity by eliminating the preparation of intermediates such as silyl enol ether. Possible applications for this protocol include, but are not limited to, diversity-oriented synthesis for the discovery of biologically active small molecules, domino synthesis for the preparation of natural products and ligand development for new transition metal catalytic systems.

Heteroaryl compounds are important molecules utilized in organic synthesis, medicinal and biological chemistry. A microwave-assisted heteroarylation using palladium catalysis provides a rapid and efficient method to attach heteroaryl moieties directly to ketone substrates.

Heteroarylation introduces heteroaryl fragments to organic molecules. Despite the numerous available reactions reported for arylation via transition metal ...

Hyperspectral Imaging as a Tool to Study Optical Anisotropy in Lanthanide-Based Molecular Single Crystals

In this work, we describe a protocol for a novel application of hyperspectral imaging (HSI) in the analysis of luminescent lanthanide (Ln3+)-based molecular single crystals. As representative example, we chose a single crystal of the heterodinuclear Ln-based complex [TbEu(bpm)(tfaa)6] (bpm=2,2&#8217;-bipyrimidine, tfaa&#8211; =1,1,1-trifluoroacetylacetonate) exhibiting bright visible emission under UV excitation. HSI is an emerging technique that combines 2-dimensional spatial imaging of a luminescent structure with spectral information from each pixel of the obtained image. Specifically, HSI on single crystals of the [Tb-Eu] complex provided local spectral information unveiling variation of the luminescence intensity at different points along the studied crystals. These changes were attributed to the optical anisotropy present in the crystal, which results from the different molecular packing of Ln3+ ions in each one of the directions of the crystal structure. The HSI herein described is an example of the suitability of such technique for spectro-spatial investigations of molecular materials. Yet, importantly, this protocol can be easily extended for other types of luminescent materials (such as micron-sized molecular crystals, inorganic microparticles, nanoparticles in biological tissues, or labelled cells, among others), opening many possibilities for deeper investigation of structure-property relationships. Ultimately, such investigations will provide knowledge to be leveraged into the engineering of advanced materials for a wide range of applications from bioimaging to technological applications, such as waveguides or optoelectronic devices.

Here, we present a protocol to obtain luminescent hyperspectral imaging data and to analyze optical anisotropy features of lanthanide-based single crystals using a Hyperspectral Imaging System.

In this work, we describe a protocol for a novel application of hyperspectral imaging (HSI) in the analysis of luminescent lanthanide (Ln3+)-based ...

Computation of Atmospheric Concentrations of Molecular Clusters from ab initio Thermochemistry

The computational study of the formation and growth of atmospheric aerosols requires an accurate Gibbs free energy surface, which can be obtained from gas phase electronic structure and vibrational frequency calculations. These quantities are valid for those atmospheric clusters whose geometries correspond to a minimum on their potential energy surfaces. The Gibbs free energy of the minimum energy structure can be used to predict atmospheric concentrations of the cluster under a variety of conditions such as temperature and pressure. We present a computationally inexpensive procedure built on a genetic algorithm-based configurational sampling followed by a series of increasingly accurate screening calculations. The procedure starts by generating and evolving the geometries of a large set of configurations using semi-empirical models then refines the resulting unique structures at a series of high-level ab initio levels of theory. Finally, thermodynamic corrections are computed for the resulting set of minimum-energy structures and used to compute the Gibbs free energies of formation, equilibrium constants, and atmospheric concentrations. We present the application of this procedure to the study of hydrated glycine clusters under ambient conditions.

Computation of Atmospheric Concentrations of Molecular Clusters from ab initio Thermochemistry

The atmospheric concentrations of weakly bound molecular clusters can be computed from the thermochemical properties of low energy structures found through a multi-step configurational sampling methodology utilizing a genetic algorithm and semi-empirical and ab initio quantum chemistry.

The computational study of the formation and growth of atmospheric aerosols requires an accurate Gibbs free energy surface, which can be obtained from gas ...