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>
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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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The authors declare that they have no competing financial interests.

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...

Watch this Scientific Journal Video about Chemical Gardens as Flow-through Reactors Simulating Natural Hydrothermal Systems at JoVE.com

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 Görüntüleme.  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.