This research was carried out at the Jet Propulsion Laboratory, California Institute of Technology, under a contract with the National Aeronautics and Space Administration. We acknowledge the support by the NASA Astrobiology Institute (Icy Worlds). L.M.B. is supported by the NAI through the NASA Postdoctoral Program, administered by Oak Ridge Associated Universities through a contract with NASA. J.E.N. was supported through a US Department of Education PR/Award #: P031C110019 administered through Citrus College. We acknowledge useful discussions with members of the NAI Thermodynamics, Disequilibrium, and Evolution Focus Group and the Blue Marble Space Institute of Science.

1. Safety Considerations
<ol>
	<li>Use personal protective equipment (lab coat, goggles, nitrile gloves, proper shoes) to prevent against chemical spills or injury. Use syringes and needles, and take care to not puncture gloves. Take care during experiment setup to check the apparatus for leaks by performing the injection first with double distilled H2O (ddH2O), and to check the stability of the reaction vials on the stand, before adding chemicals.</li>
	<li>Undertake this experiment with any chem...

<ol>
	<li>Leduc, S. <a target="_blank" href="http://www.ncbi.nlm.nih.gov/entrez/query.fcgi?db=PubMed&cmd=Search&doptcmdl=Citation&defaultField=Title+Word&term=.">.</a> The Mechanism of Life. , (1911).</li><li>Coatman, R. D., Thomas, N. L., Double, D. D. <a target="_blank" href="http://www.ncbi.nlm.nih.gov/entrez/query.fcgi?db=PubMed&cmd=Search&doptcmdl=Citation&defaultField=Title+Word&term=Studies+of+the+growth+of+&#8216;&#8216;silicate+gardens&#8217;&#8217;+and+related+phenomena.">Studies of the growth of &#8216;&#8216;silicate gardens&#8217;&#8217; and related phenomena.</a> J. Mater. Sci. 15, 2017-2026 (1980).</li><li>Barge, L. M., et al. <a target="_blank" href="http://www.ncbi.nlm.nih.gov/entrez/query.fcgi?db=PubMed&cmd=Search&doptcmdl=Citation&defaultField=Title+Word&term=From+Chemical+Gardens+to+Chemobrionics.">From Chemical Gardens to Chemobrionics.</a> Chem. Rev. 115 (16), 8652-8703 (2015).</li><li>Russell, M. J., Hall, A. 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E., Escribano, B., Sainz-D&#237;az, I. <a target="_blank" href="http://www.ncbi.nlm.nih.gov/entrez/query.fcgi?db=PubMed&cmd=Search&doptcmdl=Citation&defaultField=Title+Word&term=Chemical-Garden+Formation,+Morphology,+and+Composition.+I.+Effect+of+the+Nature+of+the+Cations.">Chemical-Garden Formation, Morphology, and Composition. I. Effect of the Nature of the Cations.</a> Langmuir. 27, 3286-3293 (2011).</li><li>Stone, D. A., Goldstein, R. E. <a target="_blank" href="http://www.ncbi.nlm.nih.gov/entrez/query.fcgi?db=PubMed&cmd=Search&doptcmdl=Citation&defaultField=Title+Word&term=Tubular+precipitation+and+redox+gradients+on+a+bubbling+template.">Tubular precipitation and redox gradients on a bubbling template.</a> P. Natl. Acad. Sci. 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E., et al. <a target="_blank" href="http://www.ncbi.nlm.nih.gov/entrez/query.fcgi?db=PubMed&cmd=Search&doptcmdl=Citation&defaultField=Title+Word&term=Iron-Sulfide-Bearing+Chimneys+as+Potential+Catalytic+Energy+Traps+at+Life&#8217;s+Emergence.">Iron-Sulfide-Bearing Chimneys as Potential Catalytic Energy Traps at Life&#8217;s Emergence.</a> Astrobiology. 11, 933-950 (2011).</li><li>Roszol, L., Steinbock, O. <a target="_blank" href="http://www.ncbi.nlm.nih.gov/entrez/query.fcgi?db=PubMed&cmd=Search&doptcmdl=Citation&defaultField=Title+Word&term=Controlling+the+Wall+Thickness+and+Composition+of+Hollow+Precipitation+Tubes.">Controlling the Wall Thickness and Composition of Hollow Precipitation Tubes.</a> Phys. Chem. Chem. Phys. 13, 20100 (2011).</li><li>Ludwig, K. A., Kelley, D. S., Butterfield, D. A., Nelson, B. 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Chemical Gardens in Microgravity.</a> Langmuir. 27, 3294-3300 (2011).</li><li>Thouvenel-Romans, S., Steinbock, O. <a target="_blank" href="http://www.ncbi.nlm.nih.gov/entrez/query.fcgi?db=PubMed&cmd=Search&doptcmdl=Citation&defaultField=Title+Word&term=Oscillatory+Growth+of+Silica+Tubes+in+Chemical+Gardens.">Oscillatory Growth of Silica Tubes in Chemical Gardens.</a> J. Am. Chem. Soc. 125, 4338-4341 (2003).</li><li>Batista, B. 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The formation of a chemical garden structure via injection method can be accomplished by interfacing any two solutions containing reactive ions that produce a precipitate. There are many possible reaction systems that will produce precipitate structures and finding the right recipe of reactive ions and concentrations to grow a desired structure is a matter of trial and error. The flow rate of the injection solution is controlled by a programmable syringe pump and this can also be varied between experiments to simulate di...

&#8220;Chemical gardens&#8221; are self-assembling inorganic precipitates developed where two fluids of contrasting chemistries interact1,2. These self-assembling inorganic structures have been the subject of scientific interest for over a century partly due to their biomimetic appearance, and many experimental and theoretical studies have been pursued to understand the various complex aspects and possible functions of chemical garden systems3. Natural examples of chemical gardens include mineral &#8220;chimney&#8221; precipitates that grow around hydrothermal springs and seeps, and it has been argued that these could provide plausible environments for life to emerge4. To grow a chemical garden simulating a natural hydrothermal vent chimney, a reservoir solution should represent a simulated ocean composition and an injection solution should represent the hydrothermal fluid that feeds into the ocean. The versatility of this type of experiment to different reaction systems allows for simulation of almost any proposed ocean / hydrothermal fluid chemistry, including environments on the early Earth or on other worlds. On the early Earth, the oceans would have been anoxic, acidic (pH 5-6), and would have contained dissolved atmospheric CO2 and Fe2+, as well as FeIII, Ni2+, Mn2+, NO3-, and NO2-. Chemical reactions between this seawater and the ultramafic ocean crust would have produced an alkaline hydrothermal fluid containing hydrogen and methane, and in some cases sulfide (HS-)4-8. The chimneys formed in early Earth alkaline vent environments could thus have contained ferrous/ferric oxyhydroxides and iron/nickel sulfides, and it has been proposed that these minerals might have served particular catalytic and proto-enzymatic functions toward harnessing geochemical redox / pH gradients to drive the emergence of metabolism5. Likewise, on other worlds such as that may host (or may have hosted) water/rock interfaces &#8212; such as early Mars, Jupiter&#8217;s moon Europa, or Saturn&#8217;s moon Enceladus &#8212; it is possible that water/rock chemistry could generate alkaline vent environments capable of driving prebiotic chemistry or even providing habitable niches for extant life5,9-11.
The classic chemical garden experiment involves a seed crystal of a metal salt, e.g. ferrous chloride tetrahydrate FeCl2&#8226;4H2O, submerged in a solution containing reactive anions, e.g. sodium silicate or &#8220;water glass&#8221;. The metal salt dissolves, creating an acidic solution containing Fe2+ that interfaces with the more alkaline solution (containing silicate anions and OH-) and an inorganic membrane precipitate is formed. The membrane swells under osmotic pressure, bursts, then re-precipitates at the new fluid interface. This process repeats until the crystals are dissolved, resulting in a vertically oriented, self-organized precipitate structure with complex morphology at both macro and micro scales. This precipitation process results in the continued separation of chemically contrasting solutions across the inorganic chemical garden membrane, and the difference of charged species across the membrane yields a membrane potential12-14. Chemical garden structures are complex, exhibiting compositional gradients from interior to exterior13,15-19, and the walls of the structure maintain separation between contrasting solutions for long periods while remaining somewhat permeable to ions. In addition to being an ideal experiment for educational purposes (as they are simple to make for classroom demonstrations, and can educate students about chemical reactions and self-organization), chemical gardens have scientific significance as representations of self-assembly in dynamic, far-from-equilibrium systems, involving methods that can lead to the production of interesting and useful materials20,21.
Chemical gardens in the laboratory can also be grown via injection methods, in which the solution containing one precipitating ion is slowly injected into the second solution containing the co-precipitating ion (or ions). This results in the formation of chemical garden structures similar to those of crystal growth experiments, except that the properties of the system and the precipitate can be better controlled. The injection method has several significant advantages. It allows one to form a chemical garden using any combination of precipitating or incorporated species; i.e., multiple precipitating ions can be incorporated into one solution, and/or other non-precipitating components can be included in either solution to adsorb / react with the precipitate. The membrane potential generated in a chemical garden system can be measured in an injection experiment if an electrode is incorporated into the interior of the structure, thus enabling electrochemical study of the system. Injection experiments offer the ability to feed the injection solution into the interior of the chemical garden for controlled time frames by varying the injection rate or total injected volume; it is therefore possible to feed through different solutions sequentially and use the precipitated structure as a trap or reactor. Combined, these techniques allow for laboratory simulations of the complex processes that could have occurred in a natural chemical garden system at a submarine hydrothermal vent, including a chimney formed from many simultaneous precipitation reactions between ocean and vent fluid (e.g., producing metal sulfides, hydroxides, and/or carbonates and silicates)5,22. These techniques can also be applied to any chemical garden reaction system to allow for formation of new types of materials, e.g., layered tubes or tubes with adsorbed reactive species20,23.
We detail here an example experiment that includes the simultaneous growth of two chemical gardens, Fe2+-containing structures in an anoxic environment. In this experiment we incorporated trace amounts of polyphosphates and/or amino acids into the initial injection solution to observe their effect on the structure. After initial formation of the chemical garden we then switched the injection solution to introduce sulfide as a secondary precipitating anion. Measurements of membrane potentials were made automatically throughout the experiment. This protocol describes how to run two experiments at once using a dual syringe pump; the data shown required multiple runs of this procedure. The relatively high flow rates, low pH of the reservoir and reactant concentrations employed in our experiments are designed to form large chimney precipitates on time scales suitable for one-day laboratory experiments. However, fluid flow rates at natural hydrothermal springs can be much more diffuse and the concentrations of precipitating reactants (e.g., Fe and S in an early Earth system) could be an order of magnitude lower4; thus, structured precipitates would form over longer timescales and the vent could be active for tens of thousands of years24,25.

<table border="0" cellpadding="0" cellspacing="0">
	<tbody>
		<tr>
			<td>Syringe Pump</td>
			<td>Fisher</td>
			<td>14-831-3</td>
			<td>Dual or multiple channel, depending on desired number of simultaneous experiments</td>
		</tr>
		<tr>
			<td>Ferrous chloride tetrahydrate</td>
			<td>Fisher</td>
			<td>I90500</td>
			<td>Ferrous Chloride Tetrahydrate (Crystalline/Certified)</td>
		</tr>
		<tr>
			<td>Ferric chloride hexahydrate</td>
			<td>Fisher</td>
			<td>I88-100&#160;</td>
			<td>Ferric&#160;Chloride&#160;Hexahydrate&#160;(Lumps/Certified ACS)</td>
		</tr>
		<tr>
			<td>Sodium hydroxide</td>
			<td>Sigma-Aldrich</td>
			<td>S5881</td>
			<td>reagent grade, &#8805;98%, pellets (anhydrous)</td>
		</tr>
		<tr>
			<td>Sodium sulfide nonahydrate</td>
			<td>Fisher</td>
			<td>S425212</td>
			<td>Sodium Sulfide Nonahydrate (Crystalline/Certified ACS).&#160; Store at -20C. Only open in a glove box or fume hood. Releases toxic H2S gas; all sulfide-containing solutions must be kept in a glove box or fume hood.</td>
		</tr>
		<tr>
			<td>Potassium pyrophosphate</td>
			<td>Sigma-Aldrich</td>
			<td align="right">322431</td>
			<td>97%, http://www.sigmaaldrich.com/catalog/product/aldrich/322431?lang=en&#38;region=US</td>
		</tr>
		<tr>
			<td>L-Alanine</td>
			<td>Sigma-Aldrich</td>
			<td>A7627</td>
			<td>http://www.sigmaaldrich.com/catalog/product/sigma/a7627?lang=en&#38;region=US</td>
		</tr>
		<tr>
			<td>Syringes (10cc)</td>
			<td>Fisher</td>
			<td>14-823-16E</td>
			<td>BD&#8482; Syringe with Luer-Lok Tips (Without Needle)</td>
		</tr>
		<tr>
			<td>Syringe needles (16 gauge)</td>
			<td>Fisher</td>
			<td>14-826-18B</td>
			<td>BD&#8482; General Use and PrecisionGlide Hypodermic Needles, 16 G x 1.5 in. (38mm)</td>
		</tr>
		<tr>
			<td>Tubing</td>
			<td>Cole Parmer</td>
			<td>EW-06407-71</td>
			<td>Tygon Lab Tubing, Non-DEHP, 1/16&#34;ID X 1/8&#34;OD</td>
		</tr>
		<tr>
			<td>Aluminum seals</td>
			<td>Fisher</td>
			<td>0337523C</td>
			<td>Thermo Scientific&#8482; National&#8482; Headspace 20mm Crimp Seals</td>
		</tr>
		<tr>
			<td>Gray butyl stoppers</td>
			<td>Fisher</td>
			<td>0337522AA</td>
			<td>Thermo Scientific&#8482; National&#8482; 20mm Septa for Headspace Vials</td>
		</tr>
		<tr>
			<td>Serum bottles</td>
			<td>Sigma-Aldrich</td>
			<td>33110-U</td>
			<td>Vials, crimp top, serum bottle, size 100 mL, clear glass, O.D. &#215; H 51.7 mm &#215; 94.5 mm. For these experiments, the bottom of the serum bottle should be cut off.</td>
		</tr>
		<tr>
			<td>Pipette tips</td>
			<td>VWR</td>
			<td>53511-682</td>
			<td>pipette tips 0.5-10 microliters</td>
		</tr>
		<tr>
			<td>Wire</td>
			<td>McMaster-Carr</td>
			<td>8073K661</td>
			<td>Solid Single-Conductor Wire, UL 1007/1569, 20 AWG, 300 VAC</td>
		</tr>
	</tbody>
</table>

chemical gardens as flow-through reactors simulating natural hydrothermal systems

Here we report experimental simulations of hydrothermal chimney growth using injection chemical garden methods. The versatility of this type of experiment allows for testing of various proposed ocean / hydrothermal fluid chemistries that could have driven reactions toward the origin of life in environments on the early Earth, early Mars, or even other worlds such as the icy moons of the outer planets. We show experiments that include growth of chemical garden structures under anoxic conditions simulating the early Earth, inclusion of trace components of phosphates / organics in the injection solution to incorporate them into the structure, a switch of the injection solution to introduce a secondary precipitating anion, and the measurement of membrane potentials generated by chemical gardens. Using this method, self-assembling chemical garden structures were formed that mimic the natural chimneys precipitated at submarine hydrothermal springs, and these precipitates can be used successfully as flow-through reactors by feeding through multiple successive &#8220;hydrothermal&#8221; injections.

Once the injection solution started to feed into the reservoir solution, a chemical garden precipitate began to form at the fluid interface and this structure continued to grow over the course of the injection (Figures 4-7). In the experiments reported here, the first injection was sodium hydroxide (which can be modified to include L-alanine and/or pyrophosphate), and the reservoir solution was a 1:3 mixture of Fe3+/Fe2+, yielding a mixed-redox-state iron oxyhydroxide precipitate. T...

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Chemical Gardens as Flow-through Reactors Simulating Natural Hydrothermal Systems

We describe chemical garden formation via injection experiments that allow for laboratory simulations of natural chemical garden systems that form at submarine hydrothermal vents.

Here we report experimental simulations of hydrothermal chimney growth using injection chemical garden methods. The versatility of this type of experiment ...

chemical-gardens-as-flow-through-reactors-simulating-natural

Research

JoVE Journal

Chemistry

14.3K ビュー.  California Institute of Technology. We describe chemical garden formation via injection experiments that allow for laboratory simulations of natural chemical garden systems that form at submarine hydrothermal vents.

ビデオ: Chemical Gardens as Flow-through Reactors Simulating Natural Hydrothermal Systems

Free Radicals in Chemical Biology: from Chemical Behavior to Biomarker Development

The involvement of free radicals in life sciences has constantly increased with time and has been connected to several physiological and pathological processes. This subject embraces diverse scientific areas, spanning from physical, biological and bioorganic chemistry to biology and medicine, with applications to the amelioration of quality of life, health and aging. Multidisciplinary skills are required for the full investigation of the many facets of radical processes in the biological environment and chemical knowledge plays a crucial role in unveiling basic processes and mechanisms. We developed a chemical biology approach able to connect free radical chemical reactivity with biological processes, providing information on the mechanistic pathways and products. The core of this approach is the design of biomimetic models to study biomolecule behavior (lipids, nucleic acids and proteins) in aqueous systems, obtaining insights of the reaction pathways as well as building up molecular libraries of the free radical reaction products. This context can be successfully used for biomarker discovery and examples are provided with two classes of compounds: mono-trans isomers of cholesteryl esters, which are synthesized and used as references for detection in human plasma, and purine 5',8-cyclo-2'-deoxyribonucleosides, prepared and used as reference in the protocol for detection of such lesions in DNA samples, after ionizing radiations or obtained from different health conditions.

Radical-based biomimetic chemistry has been applied to building-up libraries necessary for biomarker development.

The involvement of free radicals in life sciences has constantly increased with time and has been connected to several physiological and pathological ...

High-pressure Sapphire Cell for Phase Equilibria Measurements of CO2/Organic/Water Systems

The high pressure sapphire cell apparatus was constructed to visually determine the composition of multiphase systems without physical sampling. Specifically, the sapphire cell enables visual data collection from multiple loadings to solve a set of material balances to precisely determine phase composition. Ternary phase diagrams can then be established to determine the proportion of each component in each phase at a given condition. In principle, any ternary system can be studied although ternary systems (gas-liquid-liquid) are the specific examples discussed herein. For instance, the ternary THF-Water-CO2 system was studied at 25 and 40&#160;&#176;C and is described herein. Of key importance, this technique does not require sampling. Circumventing the possible disturbance of the system equilibrium upon sampling, inherent measurement errors, and technical difficulties of physically sampling under pressure is a significant benefit of this technique. Perhaps as important, the sapphire cell also enables the direct visual observation of the phase behavior. In fact, as the CO2 pressure is increased, the homogeneous THF-Water solution phase splits at about 2 MPa. With this technique, it was possible to easily and clearly observe the cloud point and determine the composition of the newly formed phases as a function of pressure.
The data acquired with the sapphire cell technique can be used for many applications. In our case, we measured swelling and composition for tunable solvents, like gas-expanded liquids, gas-expanded ionic liquids and Organic Aqueous Tunable Systems (OATS)1-4. For the latest system, OATS, the high-pressure sapphire cell enabled the study of (1) phase behavior as a function of pressure and temperature, (2) composition of each phase (gas-liquid-liquid) as a function of pressure and temperature and (3) catalyst partitioning in the two liquid phases as a function of pressure and composition. Finally, the sapphire cell is an especially effective tool to gather accurate and reproducible measurements in a timely fashion.

High-pressure Sapphire Cell for Phase Equilibria Measurements of CO2/Organic/Water Systems

The high pressure sapphire cell apparatus is a unique tool to study, without sampling, phase behavior under a wide range of pressures. Using a cathetometer, very precise volume measurements can be recorded to measure liquid expansion and phase composition. Thus, this synthetic method enables the study of (1) phase equilibria of multi-component mixtures and (2) the partition behavior of catalyst or model compounds as a function of pressure.

The high pressure sapphire cell apparatus was constructed to visually determine the composition of multiphase systems without physical sampling. ...

Ethylene Polymerizations Using Parallel Pressure Reactors and a Kinetic Analysis of Chain Transfer Polymerization

We demonstrate a method for high-throughput catalyst screening using a parallel pressure reactor starting from the initial synthesis of a nickel &#945;-diimine ethylene polymerization catalyst. Initial polymerizations with the catalyst lead to optimized reaction conditions, including catalyst concentration, ethylene pressure and reaction time. Using gas-uptake data for these reactions, a procedure to calculate the initial rate of propagation (kp) is presented. Using the optimized conditions, the ability of the nickel &#945;-diimine polymerization catalyst to undergo chain transfer with diethylzinc (ZnEt2) during ethylene polymerization was investigated. A procedure to assess the ability of the catalyst to undergo chain transfer (from molecular weight and 13C NMR data), calculate the degree of chain transfer, and calculate chain transfer rates (ke) is presented.

A protocol for the high-throughput analysis of polymerization catalyst, chain transfer polymerizations, polyethylene characterization, and reaction kinetic analysis is presented.

We demonstrate a method for high-throughput catalyst screening using a parallel pressure reactor starting from the initial synthesis of a nickel ...

Development of a Backbone Cyclic Peptide Library as Potential Antiparasitic Therapeutics Using Microwave Irradiation

Protein-protein interactions (PPIs) are intimately involved in almost all biological processes and are linked to many human diseases. Therefore, there is a major effort to target PPIs in basic research and in the pharmaceutical industry. Protein-protein interfaces are usually large, flat, and often lack pockets, complicating the discovery of small molecules that target such sites. Alternative targeting approaches using antibodies have limitations due to poor oral bioavailability, low cell-permeability, and production inefficiency.
Using peptides to target PPI interfaces has several advantages. Peptides have higher conformational flexibility, increased selectivity, and are generally inexpensive. However, peptides have their own limitations including poor stability and inefficiency crossing cell membranes. To overcome such limitations, peptide cyclization can be performed. Cyclization has been demonstrated to improve peptide selectivity, metabolic stability, and bioavailability. However, predicting the bioactive conformation of a cyclic peptide is not trivial. To overcome this challenge, one attractive approach it to screen a focused library to screen in which all backbone cyclic peptides have the same primary sequence, but differ in parameters that influence their conformation, such as ring size and position.
We describe a detailed protocol for synthesizing a library of backbone cyclic peptides targeting specific parasite PPIs. Using a rational design approach, we developed peptides derived from the scaffold protein Leishmania receptor for activated C-kinase (LACK). We hypothesized that sequences in LACK that are conserved in parasites, but not in the mammalian host homolog, may represent interaction sites for proteins that are critical for the parasites&#39; viability. The cyclic peptides were synthesized using microwave irradiation to reduce reaction times and increase efficiency. Developing a library of backbone cyclic peptides with different ring sizes facilitates a systematic screen for the most biological active conformation. This method provides a general, fast, and facile way to synthesize cyclic peptides.

A simple and general method for the synthesis of cyclic peptides using microwave irradiation is outlined. This procedure enables the synthesis of backbone cyclic peptides with a collection of different conformations while retaining the side chains and the pharmacophoric moieties., and therefore, allows to screen for the bioactive conformation.

Protein-protein interactions (PPIs) are intimately involved in almost all biological processes and are linked to many human diseases. Therefore, there is ...

Synthesis and Characterization of Supramolecular Colloids

Control over colloidal assembly is of utmost importance for the development of functional colloidal materials with tailored structural and mechanical properties for applications in photonics, drug delivery and coating technology. Here we present a new family of colloidal building blocks, coined supramolecular colloids, whose self-assembly is controlled through surface-functionalization with a benzene-1,3,5-tricarboxamide (BTA) derived supramolecular moiety. Such BTAs interact via directional, strong, yet reversible hydrogen-bonds with other identical BTAs. Herein, a protocol is presented that describes how to couple these BTAs to colloids and how to quantify the number of coupling sites, which determines the multivalency of the supramolecular colloids. Light scattering measurements show that the refractive index of the colloids is almost matched with that of the solvent, which strongly reduces the van der Waals forces between the colloids. Before photo-activation, the colloids remain well dispersed, as the BTAs are equipped with a photo-labile group that blocks the formation of hydrogen-bonds. Controlled deprotection with UV-light activates the short-range hydrogen-bonds between the BTAs, which triggers the colloidal self-assembly. The evolution from the dispersed state to the clustered state is monitored by confocal microscopy. These results are further quantified by image analysis with simple routines using ImageJ and Matlab. This merger of supramolecular chemistry and colloidal science offers a direct route towards light- and thermo-responsive colloidal assembly encoded in the surface-grafted monolayer.

A protocol for the synthesis and characterization of colloids coated with supramolecular moieties is described. These supramolecular colloids undergo self-assembly upon the activation of the hydrogen-bonds between the surface-anchored molecules by UV-light.

Control over colloidal assembly is of utmost importance for the development of functional colloidal materials with tailored structural and mechanical ...

Laser-heating and Radiance Spectrometry for the Study of Nuclear Materials in Conditions Simulating a Nuclear Power Plant Accident

Major and severe accidents have occurred three times in nuclear power plants (NPPs), at Three Mile Island (USA, 1979), Chernobyl (former USSR, 1986) and Fukushima (Japan, 2011). Research on the causes, dynamics, and consequences of these mishaps has been performed in a few laboratories worldwide in the last three decades. Common goals of such research activities are: the prevention of these kinds of accidents, both in existing and potential new nuclear power plants; the minimization of their eventual consequences; and ultimately, a full understanding of the real risks connected with NPPs. At the European Commission Joint Research Centre&#39;s Institute for Transuranium Elements, a laser-heating and fast radiance spectro-pyrometry facility is used for the laboratory simulation, on a small scale, of NPP core meltdown, the most common type of severe accident (SA) that can occur in a nuclear reactor as a consequence of a failure of the cooling system. This simulation tool permits fast and effective high-temperature measurements on real nuclear materials, such as plutonium and minor actinide-containing fission fuel samples. In this respect, and in its capability to produce large amount of data concerning materials under extreme conditions, the current experimental approach is certainly unique. For current and future concepts of NPP, example results are presented on the melting behavior of some different types of nuclear fuels: uranium-plutonium oxides, carbides, and nitrides. Results on the high-temperature interaction of oxide fuels with containment materials are also briefly shown.

We present experiments in which real nuclear fuel, cladding, and containment materials are laser heated to temperatures beyond 3,000 K while their behavior is studied by radiance spectroscopy and thermal analysis. These experiments simulate, on a laboratory scale, the formation of a lava-phase following a nuclear reactor core meltdown.

Major and severe accidents have occurred three times in nuclear power plants (NPPs), at Three Mile Island (USA, 1979), Chernobyl (former USSR, 1986) and ...

Minimum Burning Pressures of Water-based Emulsion Explosives

This manuscript describes a protocol to measure the minimum pressure required for sustained burning of water-based emulsion explosives. Pumping water-based emulsion explosives for blasting applications can be very hazardous, as demonstrated by a number of pump accidents around the globe in the last decades, including some that resulted in fatalities. In Canada, the recognition of this hazard has led to the development of pumping guidelines that were endorsed by both the explosives industry and the Explosive Regulatory Division of the Canadian government. In these guidelines, it was noted that the minimum burning pressures (MBP) measured in a laboratory would provide a good guide to characterize the behaviour of these products in pumping systems. The same guidelines also call for the design of pump systems that prevent, whenever possible, pressures from exceeding the MBP of the product being pumped. At the time of publication of these guidelines, a methodology existed for measuring such MBP values but it had never been validated to measure the MBP of ammonium nitrate water-based emulsions (AWEs). AWEs are now used much more widely than any other water-based explosives and precursors in on-site bulk loading operations.
The Canadian Explosives Research Laboratory (CanmetCERL) has been conducting research over the last ten years to develop a validated testing protocol to measure and interpret representative MBP values for AWEs. The test, as it is performed today, will be described and the critical components will be justified by reference to recent published data. Results of MBP measurements, for a range of AWE products, will be presented. Inclusion of the MBP test in the test standards for the authorization of high explosives in Canada will also be discussed.

We present an apparatus based on hot-wire ignition in a pressurized enclosure and an associated methodology to measure the minimum pressure required to induce sustained combustion in water-based emulsion explosives. This method improves product characterization to allow one to use them more safely during pumping and mixing operations.

This manuscript describes a protocol to measure the minimum pressure required for sustained burning of water-based emulsion explosives. Pumping ...

Controlled Photoredox Ring-Opening Polymerization of O-Carboxyanhydrides Mediated by Ni/Zn Complexes

Here, we describe an effective protocol that combines photoredox Ni/Ir catalysis with the use of a Zn-alkoxide for efficient ring-opening polymerization, allowing for the synthesis of isotactic poly(&#945;-hydroxy acids) with expected molecular weights (&#62;140 kDa) and narrow molecular weight distributions (Mw/Mn &#60; 1.1). This ring-opening polymerization is mediated by Ni and Zn complexes in the presence of an alcohol initiator and a photoredox Ir catalyst, irradiated by a blue LED (400 - 500 nm). The polymerization is performed at a low temperature (-15 &#176;C) to avoid undesired side reactions. The complete monomer consumption can be achieved within 4 - 8 hours, providing a polymer close to the expected molecular weight with narrow molecular weight distribution. The resulted number-average molecular weight shows a linear correlation with the degree of polymerization up to 1000. The homodecoupling 1H NMR study confirms that the obtained polymer is isotactic without epimerization. This polymerization reported herein offers a strategy for achieving rapid, controlled O-carboxyanhydrides polymerization to prepare stereoregular poly(&#945;-hydroxy acids) and its copolymers bearing various functional side-chain groups.

Controlled Photoredox Ring-Opening Polymerization of O-Carboxyanhydrides Mediated by Ni/Zn Complexes

A protocol for the controlled photoredox ring-opening polymerization of O-carboxyanhydrides mediated by Ni/Zn complexes is presented.

Here, we describe an effective protocol that combines photoredox Ni/Ir catalysis with the use of a Zn-alkoxide for efficient ring-opening polymerization, ...

Utilization of Stop-flow Micro-tubing Reactors for the Development of Organic Transformations

A new reaction screening technology for organic synthesis was recently demonstrated by combining elements from both continuous micro-flow and conventional batch reactors, coined stop-flow micro-tubing (SFMT) reactors. In SFMT, chemical reactions that require high pressure can be screened in parallel through a safer and convenient way. Cross-contamination, which is a common problem in reaction screening for continuous flow reactors, is avoided in SFMT. Moreover, the commercially available light-permeable micro-tubing can be incorporated into SFMT, serving as an excellent choice for light-mediated reactions due to a more effective uniform light exposure, compared to batch reactors. Overall, the SFMT reactor system is similar to continuous flow reactors and more superior than batch reactors for reactions that incorporate gas reagents and/or require light-illumination, which enables a simple but highly efficient reaction screening system. Furthermore, any successfully developed reaction in the SFMT reactor system can be conveniently translated to continuous-flow synthesis for large scale production.

A protocol for organic reaction screening using stop-flow micro-tubing (SFMT) reactors employing gaseous reactants and/or visible-light mediated reactions is presented.

A new reaction screening technology for organic synthesis was recently demonstrated by combining elements from both continuous micro-flow and conventional ...

Reducing Willow Wood Fuel Emission by Low Temperature Microwave Assisted Hydrothermal Carbonization

Biomass is a sustainable fuel, as its CO2 emissions are reintegrated in biomass growth. However, the inorganic precursors in the biomass cause a negative environmental impact and slag formation. The selected short rotation coppice (SRC) willow wood has a high ash content (<img alt="Equation 1" src="/files/ftp_upload/58970/58970eq1.jpg" /> = 1.96%) and, therefore, a high content of emission and slag precursors. Therefore, the reduction of minerals from SRC willow wood by low temperature microwave assisted hydrothermal carbonization (MAHC) at 150 &#176;C, 170 &#176;C, and 185 &#176;C is investigated. An advantage of MAHC over conventional reactors is an even temperature conductance in the reaction medium, as microwaves penetrate the whole reactor volume. This allows a better temperature control and a faster cooldown. Therefore, a succession of depolymerization, transformation and repolymerization reactions can be analyzed effectively. In this study, the analysis of the mass loss, ash content and composition, heating values and molar O/C and H/C ratios of the treated and untreated SCR willow wood showed that the mineral content of the MAHC coal was reduced and the heating value increased. The process water showed a decreasing pH and contained furfural and 5-methylfurfural. A process temperature of 170 &#176;C showed the best combination of energy input and ash component reduction. The MAHC allows a better understanding of the hydrothermal carbonization process, while a large-scale industrial application is unlikely because of the high investment costs.

A protocol for the emission precursor depletion from low quality biomass by low temperature microwave assisted hydrothermal carbonization treatment is presented. This protocol includes the microwave parameters and the analysis of the biocoal product and process water.

Biomass is a sustainable fuel, as its CO2 emissions are reintegrated in biomass growth. However, the inorganic precursors in the biomass cause a negative ...