This research is supported by the National Key Research and Development Program of China (2017YFA0206801, 2018YFA0208600), Natural Science Foundation of Jiangsu Province,&#160;and National Natural Science Foundation of China (91645116). L.X is the Zhong-Wu Specially Appointed Professor of the Jiangsu University of Technology. The authors acknowledge the suggestions from Dr. Hao Hu and Dr. Mingjun Yang.

1. Building model
<ol>
	<li>Build porphycene structure: Open GaussView software by double-click the mouse. Then click Element Fragment button in the menu of the GaussView to choose the needed elements. Construct porphycene. Then click File button to save as the pdb file.</li>
	<li>Solvate the model: Solvate porphycene in a cubic TIP3P21 water box with an edge length of 38 &#197; by issuing the command in the linux operating system: genbox_d -cp prp-vac.pdb -cs spc216.gro -o solv.pdb -maxsol 1484 -box 3.8.</li>
	<li>Build deuterium porphycene: Issue the following command to generate topology file: cns &#60; ppi_solv.inp. Then open prp-wat.psf with vi command and change the mass of H1 from 1.00800 to 2.01600 to replace one intramolecular hydrogen atom of porphycene with deuterium to build single deuterium substituted porphycene.</li>
	<li>Set normal MD simulation parameters: Input method scctb, integral 0.5 fs, and cutoff 12 in the MD input file by opening it with vi command. 
	NOTE: Adopt a cutoff distance of 12 &#197; for calculating both vdW and electrostatic interactions. Simulate the porphycene molecule with DFTB/MIO method22. Set the integration time step as 0.5 fs for MD simulations. Maintain the temperature of the simulation system at 300 K with Langevin thermostat. Then perform the simulations with QM4D software following the steps below.</li>
</ol>
2. Pre-sits
<ol>
	<li>Set up temperature parameters: Input templow 260, temphigh 1100 and ntemp 160 in the input file. 
	NOTE: The temperature range from 260K to 1100K was spread out by QM4D software to 160 temperature points during MD simulations. The template input files are included in Supplementary Files.</li>
	<li>Initiate the pre-sits: Set runtype 100 and step 120,000 in the input file. Then issue the following command: $PATH/qm4d $INPUTFILE &#62; $OUTPUTFILE. 
	NOTE: The total step is 120,000 but can be adjusted depending on the specific need. The suggested parameters of MD simulations are saved in the $INPUTFILE. The same command is also used in the following opt-sits and production simulation steps, with the input file modified accordingly.</li>
	<li>Calculating the decomposed energies
	<ol>
		<li>Extract energy changes: During the pre-sits stage, monitor the energy of each term to calculate the mean values, as shown in Figure 1. Use grep Linux command to extract the energy as follows: 
		grep &#8216;SITS-ener0&#8217; $INPUTFILE | awk &#8216;{a+=$3;b+=$4;c+=$5}END{print a/NR,b/NR,c/NR}.</li>
		<li>Modify average energies in the MD input file: Calculate the average energies based on the output of the command line above, and modify the line vshift0 -30801.95; vshift1 -26.88; vshift2 -13888.28 in the input file with the newly generated averages. 
		NOTE: Numbers -30801.85, -26.88 and -13888.28 are the average energies in the current model system. Please modify the values based on the specific systems.</li>
	</ol>
	</li>
</ol>
3. Opt-sits
<ol>
	<li>Initiate opt-sits: Set runtype 0 in the input file. Then initiate the QM4D program by typing the command as shown in step 2.2 to start the optimization step.</li>
	<li>Monitoring the energy changes and nk values.
	<ol>
		<li>Plot the energy propagation with &#8220;grace&#8221; program and make sure the energy fluctuation can cover the lowest and the highest ends of the temperature range.</li>
		<li>After optimization, save the final nk values of the opt-sits step into a new file, which is named as nk.dat in this protocol.</li>
	</ol>
	</li>
</ol>
4. Running production simulations
<ol>
	<li>Prepare MD input file: Set runtype 1 in the new input file to start the production simulation step. Specify the file name of stored nk file as nkfile nk.dat in the input file. The number of time steps was set as 6,400,000 in the present systems.</li>
	<li>Initiate production MD simulation: Issue the following command to start MD simulations: $PATH/qm4d $INPUTFILE &#62; $OUTPUTFILE. 
	NOTE: Make sure the nk values can be read in by the QM4D software. The simulation time is system dependent so change the simulation step based on specific demands. Select a proper number of time steps to ensure enough simulation time for your own system. This step is likely time consuming, so save restart files to avoid restarting the production from the very beginning once being disrupted.</li>
</ol>
5 Data analysis
<ol>
	<li>Monitoring the distance changes
	<ol>
		<li>Monitor the bond forming and breaking process during the production phase, use the grep command to check the distance changes of H1-N1 and H1-N2 along the simulation time. The same operation can be conducted for H2-N3 and H2-N4. Then plot the distance propagation using the accumulated distance value during the production simulations.</li>
	</ol>
	</li>
	<li>Extracting reaction coordinates
	<ol>
		<li>Extract the reaction coordinates and the energy terms from the production output file generated by QM4D by grep command: 
		grep &#8216;dist 1&#8217; $OUTPUTFILE | awk &#8216;{print $5}&#8217; &#62; distance1; 
		grep &#8216;ener0&#8217; $OUTPUTFILE &#62; ener0.</li>
		<li>Organize data in four columns: q1, q2, U0 and U&#8217; (U0 and U&#8217; are the output normal energy and weighted energy), and write them into the data file at each time frame.</li>
	</ol>
	</li>
	<li>Calculating Free energy
	<ol>
		<li>Calculate the free energy by issuing the following command: 
		sits-pmf 300 $INPUTFILE PMF2 [hist_minx hist_maxx num_binsx] [hist_miny hist_maxy num_binsy] &#62; $OUTPUTFILE. 
		NOTE: sits-pmf is the histogram-based analysis method. [hist_minx hist_maxx num_binsx] defines the range and number of bins for the first reaction coordinate. The second reaction coordinates can be set by [hist_miny hist_maxy num_binsy].</li>
		<li>To project the free energy on the two-dimensional landscape, type the following command: 
		sits-pmf 300 h1-2d.dat PMF2 -0.6 0.6 24 2.45 4.25 36 &#62; sits-pmf.out. 
		NOTE: Use a total of 24 bins and 36 bins to cover the distance changes in two selected reaction coordinates, q1 and q2, respectively. Save the 2D PMF data for each hydrogen/deuterium to the sits-pmf.out file.</li>
	</ol>
	</li>
</ol>

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The authors have nothing to disclose.

The structure of porphycene was shown in Figure 1. The electrostatic embedding QM/MM hybrid potential with SITS method was used to describe the chemical reactions in water23,24. The proton transfer occurs within porphycene3 and thus porphycene is set as QM region and the reminding water is set as MM region. Herein we adopted DFTB/MIO as our QM method to treat the porphycene by balancing the efficiency and accu...

The proton transfer process in porphycenes holds potential applications in developing molecular switches, transistors and information storage devices1,2. In particular, tautomerization in porphycenes through double proton transfer process has attracted wide interest in the fields of spectroscopy and photophysics2. The inner hydrogen atoms of porphycene can migrate from one trans isomer to the other equivalent trans isomer through double proton transfer process as shown in Figure 1. Two mechanisms have been proposed for the double proton transfer process: the concerted and the stepwise mechanism3,4. In the concerted double proton transfer process, both proton atoms move to the transition state synchronously in a symmetric way, whereas one proton completes the transfer before the other proton in a stepwise process. Two hydrogen atoms can transfer simultaneously or stepwise depending on the correlation strength between two hydrogen atoms5.
Isotopic substitution has been used to detect the structural properties of molecules and rate constants of reaction kinetics6. Single deuterium substitution in the inner hydrogen of porphycene leads to an asymmetric shape of the molecule. The hydrogen bond may expand or contract because of mass difference between the hydrogen and deuterium atoms. The isotopic substitution introduces a perturbation in the scaffold of porphycene. The question arises that whether asymmetric structure would affect the proton transfer process. Limbach and coworkers reported that the replacement of hydrogen with deuterium will compress both hydrogen bonds, and the cooperative coupling of two hydrogen bonds in porphycene may favor concerted mechanism7, whereas Yoshikawa stated the deuteration would make the stepwise mechanism contribute more than the concerted mechanism8. Experimental techniques, such as force spectroscopy, have been developed to capture tautomerization details in a single porphycene9. However, it is still challenging to determine the atomic details of proton transfer experimentally because of its transient nature.
Theoretical calculations and simulations can act as complementary tools in elucidating the reaction mechanisms of proton transfer. Among different theoretical methods, molecular dynamics (MD) simulations can monitor dynamic motions of each atom, and has been widely used to reveal complex mechanisms in chemical and enzymatic reactions. However, regular MD simulations tend to suffer from insufficient sampling issue, especially when high energy barrier exists in the process of interest. Therefore, enhanced sampling methods have been developed, which include transition path sampling10,11, umbrella sampling (US)12,13, and integrated tempering sampling (ITS)14,15. Combination of different enhanced sampling methods can further increase sampling efficiency16,17,18. To harness the enhanced sampling algorithms in simulating chemical reactions, we have implemented the selective integrated tempering sampling (SITS) method with quantum mechanical and molecular mechanical (QM/MM) potentials recently19. The proposed SITS-QM/MM method combines the advantages from both methods: the SITS method accelerates the sampling and can explore all possible reaction channels without prior knowledge of the reaction mechanism, and QM/MM provides more accurate description of the bond forming and bond breaking process, which cannot be simulated by MM methods solely. The implemented SITS-QM/MM approach has successfully uncovered concerted double proton transfer, uncorrelated and correlated stepwise double proton transfer mechanism in different systems, without pre-defining reaction coordinates19. For porphycene, the stepwise but correlated proton transfer character has been reported19. The hybrid SITS-QM/MM method was used to investigate the isotopic effect in porphycene in our study, and below are the detailed descriptions of the algorithm and protocol of our method.
We have implemented SITS method with hybrid QM/MM potentials. The effective potential of SITS was defined to include the potential energy at different temperatures with the weighting factors nk to cover wider temperature ranges,
<img alt="Equation 1" src="/files/ftp_upload/60040/60040equ01.jpg" />
where, N is the number of canonical terms, &#946;k is the inverse temperature, and nk is the corresponding weighting factor for each canonical component. UE(R) and&#160;UN(R) represent the enhanced and non-enhanced terms in SITS and are defined as,
<img alt="Equation 2" src="/files/ftp_upload/60040/60040equ02.jpg" />
Us, Use and Ue are the potential energy of sub-system, the interaction between sub-system and the environment, and the potential energy of environment. QM/MM potential is expressed as a hybrid summation of three components,
<img alt="Equation 3" src="/files/ftp_upload/60040/60040equ03.jpg" />
where Uqm, Uqm/mm, and&#160;Umm are the internal energy term of the QM subsystem, the interaction energy between the QM and MM regions, and the interaction energy within the MM subsystem, respectively. The&#160;Uqm/mm term can be further divided into three components, which include the electrostatic, van der Waals, and covalent interaction energy terms between the QM and MM atoms,
<img alt="Equation 4" src="/files/ftp_upload/60040/60040equ04.jpg" />
We assign <img alt="Equation 5" src="/files/ftp_upload/60040/60040equ05.jpg" />, and <img alt="Equation 6" src="/files/ftp_upload/60040/60040equ06.jpg" /> into one&#160;Us term in SITS,
<img alt="Equation 7" src="/files/ftp_upload/60040/60040equ07.jpg" />
The full potential of the system was then decomposed into the energy of subsystem Us, the interaction energy between the subsystem and the environment Use, and the energy of environment Ue. For instance, in the system of the present work, the subsystem is the porphycence, and the environment the water.
The PMF profile along a collective variable&#160;&#964;(R) is derived as,
<img alt="Equation 8" src="/files/ftp_upload/60040/60040equ08.jpg" />
The generally used reaction coordinates for each hydrogen transfer of N1&#8722;H1&#183;&#183;&#183; N2 are q1 = (r1&#8722;r2)/2 and q2 = r1 + r2, where r1 is the distance of N1-H1 and r2 is the distance of H1-N2.
The method has been implemented in the QM/MM MD simulation package QM4D20. The complete source code and documentation can be found here: http://www.qm4d.info/.
Generally, the SITS-QM/MM MD simulations involve four steps: pre-equilibrium (pre-sits); optimization nk (opt-sits); production simulation and data analysis.

<table>
	<tbody>
		<tr>
			<td>operating system</td>
			<td>CentOS Linux release 6.0</td>
			<td></td>
			<td></td>
		</tr>
		<tr>
			<td>QM4D software</td>
			<td>http://www.qm4d.info/</td>
			<td></td>
			<td>in-house program</td>
		</tr>
		<tr>
			<td>Computer desktop</td>
			<td>HP</td>
			<td></td>
			<td></td>
		</tr>
	</tbody>
</table>

isotopic effect in double proton transfer process of porphycene investigated by enhanced qm/mm method

The single deuterium substitution in porphycene leads to an asymmetric molecular geometry, which may affect the double proton transfer process in the porphycene molecule. In this study, we applied an enhanced QM/MM method called SITS-QM/MM to investigate hydrogen/deuterium (H/D) isotope effects on the double proton transfer in porphycene. Distance changes in SITS-QM/MM molecular dynamics simulations suggested that the deuterium substituted porphycene adopted the stepwise double proton transfer mechanism. The structural analysis and the free energy shifts of double proton transfer process indicated that the asymmetric isotopic substitution subtly compressed the covalent hydrogen bonds and may alter the original transition state location.

The single deuterium substitution effect on double proton transfer process in porphycene was examined in the current protocol (Figure 1). The potential energy of QM sub-system and the water during pre-equilibrium and optimization step were checked to make sure the energy has been broadened to a wider energy range (Figure 2). The representative distance and angle changes (Figure 3 and Figure 4), and the ...

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Isotopic Effect in Double Proton Transfer Process of Porphycene Investigated by Enhanced QM/MM Method

A protocol that uses enhanced QM/MM method to investigate the isotopic effect on the double proton transfer process in porphycene is presented here.

The single deuterium substitution in porphycene leads to an asymmetric molecular geometry, which may affect the double proton transfer process in the ...

isotopic-effect-double-proton-transfer-process-porphycene

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6.2K Views.  Chinese Academy of Sciences. A protocol that uses enhanced QM/MM method to investigate the isotopic effect on the double proton transfer process in porphycene is presented here.

Video: Isotopic Effect in Double Proton Transfer Process of Porphycene Investigated by Enhanced QM/MM Method

High Precision Zinc Isotopic Measurements Applied to Mouse Organs

We present a procedure to measure with high precision zinc isotope ratios in mouse organs. Zinc is composed of 5 stable isotopes (64Zn, 66Zn, 67Zn, 68Zn and 70Zn) which are naturally fractionated between mouse organs. We first show how to dissolve the different organs in order to free the Zn atoms; this step is realized by a mixture of HNO3 and H2O2. We then purify the zinc atoms from all the other elements, in particular from isobaric interferences (e.g., Ni), by anion-exchange chromatography in a dilute HBr/HNO3 medium. These first two steps are performed in a clean laboratory using high purity chemicals. Finally, the isotope ratios are measured by using a multi-collector inductively-coupled-plasma mass-spectrometer, in low resolution. The samples are injected using a spray chamber and the isotopic fractionation induced by the mass-spectrometer is corrected by comparing the ratio of the samples to the ratio of a standard (standard bracketing technique).&#160;This full typical&#160;procedure produces an isotope ratio with a 50 ppm (2 s.d.) reproducibility.

We present the technique to measure with high precision zinc isotope ratios in mouse organs.

We present a procedure to measure with high precision zinc isotope ratios in mouse organs. Zinc is composed of 5 stable isotopes (64Zn, 66Zn, 67Zn, 68Zn ...

Layer-by-layer Synthesis and Transfer of Freestanding Conjugated Microporous Polymer Nanomembranes

CMP as large surface area materials have attracted growing interest recently, due to their high variability in the incorporation of functional groups in combination with their outstanding thermal and chemical stability, and low densities. However, their insoluble nature causes problems in their processing since usually applied techniques such as spin coating are not available. Especially for membrane applications, where the processing of CMP as thin films is desirable, the processing problems have hindered their commercial application.
Here we describe the interfacial synthesis of CMP thin films on functionalized substrates via molecular layer-by-layer (l-b-l) synthesis. This process allows the preparation of films with desired thickness and composition and even desired composition gradients.
The use of sacrificial supports allows the preparation of freestanding membranes by dissolution of the support after the synthesis. To handle such ultra-thin freestanding membranes the protection with sacrificial coatings showed great promise, to avoid rupture of the nanomembranes. To transfer the nanomembranes to the desired substrate, the coated membranes are upfloated at the air-liquid interface and then transferred via dip coating.

In this paper we describe the interfacial synthesis of conjugated microporous polymers (CMP) on sacrificial substrates, and the dissolution of the substrate for the preparation of freestanding CMP nanomembranes. In addition, we will describe how the fragile nanomembranes can be transferred to other substrates.

CMP as large surface area materials have attracted growing interest recently, due to their high variability in the incorporation of functional groups in ...

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 ...

Radiolabeling and Quantification of Cellular Levels of Phosphoinositides by High Performance Liquid Chromatography-coupled Flow Scintillation

Phosphoinositides (PtdInsPs) are essential signaling lipids responsible for recruiting specific effectors and conferring organelles with molecular identity and function. Each of the seven PtdInsPs varies in their distribution and abundance, which are tightly regulated by specific kinases and phosphatases. The abundance of PtdInsPs can change abruptly in response to various signaling events or disturbance of the regulatory machinery. To understand how these events lead to changes in the amount of PtdInsPs and their resulting impact, it is important to quantify PtdInsP levels before and after a signaling event or between control and abnormal conditions. However, due to their low abundance and similarity, quantifying the relative amounts of each PtdInsP can be challenging. This article describes a method for quantifying PtdInsP levels by metabolically labeling cells with 3H-myo-inositol, which is incorporated into PtdInsPs. Phospholipids are then precipitated and deacylated. The resulting soluble 3H-glycero-inositides are further extracted, separated by high-performance liquid chromatography (HPLC), and detected by flow scintillation. The labeling and processing of yeast samples is described in detail, as well as the instrumental setup for the HPLC and flow scintillator. Despite losing structural information regarding acyl chain content, this method is sensitive and can be optimized to concurrently quantify all seven PtdInsPs in cells.

Phosphoinositides are signaling lipids whose relative abundance rapidly changes in response to various stimuli. This article describes a method to measure the abundance of phosphoinositides by metabolically labeling cells with 3H-myo-inositol, followed by extraction and deacylation. Extracted glycero-inositides are then separated by high-performance liquid chromatography and quantified by flow scintillation.

Phosphoinositides (PtdInsPs) are essential signaling lipids responsible for recruiting specific effectors and conferring organelles with molecular ...

Characterization, Quantification and Compound-specific Isotopic Analysis of Pyrogenic Carbon Using Benzene Polycarboxylic Acids (BPCA)

Fire-derived, pyrogenic carbon (PyC), sometimes called black carbon (BC), is the carbonaceous solid residue of biomass and fossil fuel combustion, such as char and soot. PyC is ubiquitous in the environment due to its long persistence, and its abundance might even increase with the projected increase in global wildfire activity and the continued burning of fossil fuel. PyC is also increasingly produced from the industrial pyrolysis of organic wastes, which yields charred soil amendments (biochar). Moreover, the emergence of nanotechnology may also result in the release of PyC-like compounds to the environment. It is thus a high priority to reliably detect, characterize and quantify these charred materials in order to investigate their environmental properties and to understand their role in the carbon cycle.
Here, we present the benzene polycarboxylic acid (BPCA) method, which allows the simultaneous assessment of PyC&#39;s characteristics, quantity and isotopic composition (13C and 14C) on a molecular level. The method is applicable to a very wide range of environmental sample materials and detects PyC over a broad range of the combustion continuum, i.e., it is sensitive to slightly charred biomass as well as high temperature chars and soot. The BPCA protocol presented here is simple to employ, highly reproducible, as well as easily extendable and modifiable to specific requirements. It thus provides a versatile tool for the investigation of PyC in various disciplines, ranging from archeology and environmental forensics to biochar and carbon cycling research.

Characterization, Quantification and Compound-specific Isotopic Analysis of Pyrogenic Carbon Using Benzene Polycarboxylic Acids BPCA

We present the benzene polycarboxylic acid (BPCA) method for assessing pyrogenic carbon (PyC) in the environment. The compound-specific approach uniquely provides simultaneous information about the characteristics, quantity and isotopic composition (13C and 14C) of PyC.

Fire-derived, pyrogenic carbon (PyC), sometimes called black carbon (BC), is the carbonaceous solid residue of biomass and fossil fuel combustion, such as ...

Determination of Carbonyl Functional Groups in Bio-oils by Potentiometric Titration: The Faix Method

Carbonyl compounds present in bio-oils are known to be responsible for bio-oil property changes upon storage and during upgrading. Specifically, carbonyls cause an increase in viscosity (often referred to as &#39;aging&#39;) during storage of bio-oils. As such, carbonyl content has previously been used as a method of tracking bio-oil aging and condensation reactions with less variability than viscosity measurements. Additionally, carbonyls are also responsible for coke formation in bio-oil upgrading processes. Given the importance of carbonyls in bio-oils, accurate analytical methods for their quantification are very important for the bio-oil community. Potentiometric titration methods based on carbonyl oximation have long been used for the determination of carbonyl content in pyrolysis bio-oils. Here, we present a modification of the traditional carbonyl oximation procedures that results in less reaction time, smaller sample size, higher precision, and more accurate carbonyl determinations. While traditional carbonyl oximation methods occur at room temperature, the Faix method presented here occurs at an elevated temperature of 80 &#176;C.

Here we present a potentiometric titration technique for accurately quantifying carbonyl compounds in pyrolysis bio-oils.

Carbonyl compounds present in bio-oils are known to be responsible for bio-oil property changes upon storage and during upgrading. Specifically, carbonyls ...

Observation and Analysis of Blinking Surface-enhanced Raman Scattering

From a single molecule at a silver nanoaggregate junction, blinking surface-enhanced Raman scattering (SERS) is observed. Here, a protocol is presented on how to prepare the SERS-active silver nanoaggregate, record a video of certain blinking spots in the microscopic image, and analyze the blinking statistics. In this analysis, a power law reproduces the probability distributions for bright events relative to their duration. The probability distributions for dark events are fitted by a power law with an exponential function. The parameters of the power law represent molecular behavior in both bright and dark states. The random walk model and the speed of the molecule across the entire silver surface can be estimated. It is difficult to estimate even when using averages, autocorrelation functions, and super-resolution SERS imaging. In the future, power law analyses should be combined with spectral imaging, because the origins of blinking cannot be confirmed by this analysis method alone.

This protocol describes the analysis of blinking surface-enhanced Raman scattering due to the random walk of a single molecule on a silver surface using power laws.

From a single molecule at a silver nanoaggregate junction, blinking surface-enhanced Raman scattering (SERS) is observed. Here, a protocol is presented on ...

Photoelectron Imaging of Anions Illustrated by 310 Nm Detachment of F&#8722;

Anion photoelectron imaging is a very efficient method for the study of energy states of bound negative ions, neutral species and interactions of unbound electrons with neutral molecules/atoms. State-of-the-art in vacuo anion generation techniques allow application to a broad range of atomic, molecular, and cluster anion systems. These are separated and selected using time-of-flight mass spectrometry. Electrons are removed by linearly polarized photons (photo detachment) using table-top laser sources which provide ready access to excitation energies from the infra-red to the near ultraviolet. Detecting the photoelectrons with a velocity mapped imaging lens and position sensitive detector means that, in principle, every photoelectron reaches the detector and the detection efficiency is uniform for all kinetic energies. Photoelectron spectra extracted from the images via mathematical reconstruction using an inverse Abel transformation reveal details of the anion internal energy state distribution and the resultant neutral energy states. At low electron kinetic energy, typical resolution is sufficient to reveal energy level differences on the order of a few millielectron-volts, i.e., different vibrational levels for molecular species or spin-orbit splitting in atoms. Photoelectron angular distributions extracted from the inverse Abel transformation represent the signatures of the bound electron orbital, allowing more detailed probing of electronic structure. The spectra and angular distributions also encode details of the interactions between the outgoing electron and the residual neutral species subsequent to excitation. The technique is illustrated by the application to an atomic anion (F&#8722;), but it can also be applied to the measurement of molecular anion spectroscopy, the study of low lying anion resonances (as an alternative to scattering experiments) and femtosecond (fs) time resolved studies of the dynamic evolution of anions.

Here, we present a protocol for photoelectron imaging of anionic species. Anions generated in vacuo and separated by mass spectrometry are probed using velocity mapped photoelectron imaging, providing details of anion and neutral energy levels, anion and neutral structure and the nature of the anion electronic state.

Anion photoelectron imaging is a very efficient method for the study of energy states of bound negative ions, neutral species and interactions of unbound ...

Synthesis of Soft Polysiloxane-urea Elastomers for Intraocular Lens Application

This study discusses a synthesis route for soft polysiloxane-based urea (PSU) elastomers for their applications as accommodating intraocular lenses (a-IOLs). Aminopropyl-terminated polydimethylsiloxanes (PDMS) were previously prepared via the ring-chain equilibration of the cyclic siloxane octamethylcyclotetrasiloxane (D4) and 1,3-bis(3-aminopropyl)-tetramethyldisiloxane (APTMDS). Phenyl groups were introduced into the siloxane backbone via the copolymerization of D4 and 2,4,6,8-tetramethyl-2,4,6,8-tetraphenyl-cyclotetrasiloxane (D4Me,Ph). These polydimethyl-methyl-phenyl-siloxane-block copolymers were synthesized for increasing the refractive indices of polysiloxanes. For applications as an a-IOL, the refractive index of the polysiloxanes must be equivalent to that of a young human eye lens. The polysiloxane molecular weight is controlled by the ratio of the cyclic siloxane to the endblocker APTMDS. The transparency of the PSU elastomers is examined by the transmittance measurement of films between 200 and 750 nm, using a UV-Vis spectrophotometer. Transmittance values at 750 nm (upper end of the visible spectrum) are plotted against the PDMS molecular weight, and &#62; 90% of the transmittance is observed until a molecular weight of 18,000 g&#183;mol&#8722;1. Mechanical properties of the PSU elastomers are investigated using stress-strain tests on die-cut dog-bone-shaped specimens. For evaluating mechanical stability, mechanical hysteresis is measured by repeatedly stretching (10x) the specimens to 5% and 100% elongation. Hysteresis considerably decreases with the increase in the PDMS molecular weight. In vitro cytotoxicity of some selected PSU elastomers is evaluated using an MTS cell viability assay. The methods described herein permit the synthesis of a soft, transparent, and noncytotoxic PSU elastomer with a refractive index approximately equal to that of a young human eye lens.

This study describes synthetic routes for aminopropyl-terminated polydimethylsiloxanes and polydimethyl-methyl-phenyl-siloxane-block copolymers and for soft polysiloxane-based urea (PSU) elastomers. It presents the application of PSUs as accommodating an intraocular lens. An evaluation method for in vitro cytotoxicity is also described.

This study discusses a synthesis route for soft polysiloxane-based urea (PSU) elastomers for their applications as accommodating intraocular lenses ...

Niobium Oxide Films Deposited by Reactive Sputtering: Effect of Oxygen Flow Rate

Reactive sputtering is a versatile technique used to form compact films with excellent homogeneity. In addition, it allows easy control over deposition parameters such as gas flow rate that results in changes on composition and thus in the film required properties. In this report, reactive sputtering is used to deposit niobium oxide films. A niobium target is used as metal source and different oxygen flow rates to deposit niobium oxide films. The oxygen flow rate was changed from 3 to 10 sccm. The films deposited under low oxygen flow rates show higher electrical conductivity and provide better perovskite solar cells when used as electron transport layer.

Here, we present a protocol for niobium oxide films deposition by reactive sputtering with different oxygen flow rates for use as an electron transport layer in perovskite solar cells.

Reactive sputtering is a versatile technique used to form compact films with excellent homogeneity. In addition, it allows easy control over deposition ...