Name: Chemical Gardens as Flow-through Reactors Simulating Natural Hydrothermal Systems (Video) | JoVE Journal
Uploaded: 2015-11-18T14:00:00.000+00:00
Duration: 12 min 55 s
Description: Explore chemical garden simulations of submarine hydrothermal vents using flow-through injection methods. This technique helps researchers study self-assembling mineral structures and early Earth conditions relevant to origins of life.

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5 minutes

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 chemical garden recipe, but one of the reactants we use to simulate deep-sea vents is a hazardous chemical, sodium sulfide; therefore do the entire experiment inside a fume hood to prevent exposure.
	<ol>
		<li>Only open the bottle of sodium sulfide in the fume hood and place a balance inside the fume hood for weighing sulfide. Always keep sulfide-containing solutions inside the fume hood as they release toxic H2S gas, and also keep sulfide liquid, sharps, and solid waste containers in the fume hood. Another reactant of interest is Fe(II)Cl2&#8226;4H2O, which oxidizes upon exposure to air, so take care to keep solutions anoxic and to grow chemical gardens under an anoxic headspace (e.g., N2 or Ar), always within a fume hood or glove box.</li>
	</ol>
	</li>
</ol>
2. Setup for Injection Experiments
<ol>
	<li>Create glass &#8220;injection vials&#8221; by cutting off the bottom 1 cm of a 100 ml clear glass crimp top serum bottle (20 mm crimp seal closure type) with a glass cutter so that, when inverted, the vessel is open to the air. As these are reusable, clean the vials in a 1 M HCl acid bath O/N, and then rinse well with ddH2O before a new experiment.</li>
	<li>Prepare the injection vials (Figure 1).
	<ol>
		<li>Collect a 20 mm septum, 20 mm aluminum crimp seal, and a 0.5-10 &#181;l plastic pipette tip. Using a 16 G syringe needle, carefully puncture a hole through the center of the septum, then remove and discard the needle in the appropriate sharps waste container.</li>
		<li>Insert the pipette tip into the needle hole, into the side of the rubber septum that will face inside the crimp top of the vial. Push the pipette tip through the septum so that it pokes out the other side.</li>
		<li>Crimp-seal the septum with pipette tip onto the injection vessel to make a watertight seal. When sealed, push the pipette tip further through the septum so that it protrudes outside.</li>
		<li>Affix 1/16&#8221; inner diameter clear flexible chemical-resistant tubing to the pipette tip (tubing length should reach from the injection vial to the syringe pump); slide it up for a watertight seal. 
		Note: This will be the injection tube, fed from the other end by a syringe with 16 G needle.</li>
		<li>Check for leaks: Insert a 10 ml syringe filled with ddH2O with a 16 G needle into the other end of the tubing (smoothly slide the tubing straight onto the needle and be careful not to puncture the wall of the tubing). Slowly inject so that the ddH2O moves up the tubing and into the bottom of the reaction vessel. Ensure that the syringe/tube, tube/tip, and crimp seals are watertight.</li>
	</ol>
	</li>
	<li>Clamp the injection vials on a stand in a fume hood, so that the injection will feed in from the bottom of the vial. 
	Note: Multiple vials can be set up at once and fed simultaneously by separate syringes.</li>
	<li>Set up electrodes for measuring membrane potential across the wall of the chemical gardens. Always use the same convention for which lead is &#8220;inside&#8221; and which is &#8220;outside&#8221; of the chemical gardens.
	<ol>
		<li>Cut lengths of insulated wire (e.g., copper) that reach from inside the reaction vessels to the lead of the multimeter or data logger. Leave a little bit of slack in the wires for positioning.</li>
		<li>Strip ~3 mm of the wire bare at the ends that will be located inside the reaction vial. At the other ends that will be connected to the multimeter leads, strip ~1 cm of wire.</li>
		<li>Fix the wires in place to measure membrane potential across the chemical garden. For the wire that will go inside the chemical garden: insert it into the opening of the pipette tip from which fluid will feed into the vessel.</li>
		<li>Push the wire in lightly to ensure contact with the injection solution, but not so far that it will clog the injection flow. For the outside wire: place it so that it will be in contact with the solution reservoir but not with the chemical garden precipitate.</li>
		<li>Tape or otherwise secure the wires so that they cannot move inside the injection vial during the experiment (Figure 2).</li>
		<li>Attach the other ends of the wires to the multimeter, and secure the wires so that those ends also do not move throughout the experiment.</li>
	</ol>
	</li>
	<li>Set up N2 gas lines that will each feed into one of the injection vials.
	<ol>
		<li>Split the gas feed from a N2 source into several tubes, so that there is one N2 feed for each injection vial.</li>
		<li>Place each N2 tube so that it feeds into the headspace of one of the injection vials.</li>
	</ol>
	</li>
</ol>
3. Preparation of Solutions for Chemical Garden Growth
<ol>
	<li>Prepare the reservoir solution, 100 ml for each experiment. Note: In this example, use 75 mM Fe2+ and 25 mM Fe3+ as the precipitating cations (Table 1).
	<ol>
		<li>Create anoxic solutions by first bubbling the ddH2O with N2 gas for ~15 min per 100 ml.</li>
		<li>Weigh out and add the FeCl2&#8226;4H2O and FeCl3&#8226;6H2O, stirring gently to dissolve (not vigorously so as to not introduce oxygen).</li>
		<li>After reagents are dissolved, immediately resume light bubbling of the Fe2+/Fe3+ solution with N2 gas while injections are prepared.</li>
	</ol>
	</li>
	<li>Choose any two of the primary injection solutions shown in Table 1, and prepare 10 ml of each. Fill a 10 ml syringe to the 7 ml mark with each of the solutions (one syringe for each solution). Replace the needle caps and set aside.</li>
	<li>Prepare 20 ml of the secondary injection solution (sodium sulfide &#8212; CAUTION) shown in Table 1. Fill two 10 ml syringes to the 7 ml mark with this solution, replace the needle caps and set aside. Always keep sulfide-containing solutions and syringes in the fume hood.</li>
	<li>Refill the ddH2O syringes from Step 2.2.5; these will be used to flush the injection tube.</li>
</ol>
4. Starting the Primary Injection
<ol>
	<li>Use desired data logger for membrane potential measurements; measure each experiment&#8217;s potential on a separate channel, and set the scan rate to give the desired amount of data points (e.g., for a 2-hr injection, recording potential every 30 sec would be sufficient).</li>
	<li>Secure the primary injection syringes on the programmable syringe pump in the fume hood.</li>
	<li>Use a waste beaker to catch drips and set the syringe pump to inject at a fast rate until the syringes both begin to drip into the beaker. Then stop the injection (in order to ensure that the two syringes begin injecting at exactly the same level).</li>
	<li>Re-program the syringe pump to inject at 2 ml per hour (calibrate for the type of syringe being used), but do not hit start.</li>
	<li>Insert the ddH2O syringes into the two plastic injection tubes, and inject so that the water fills the clear tubing up to the aperture where it enters the main reservoir. Place the syringes on the stand, above the injection vials.</li>
	<li>Pour 100 ml of the Fe2+/Fe3+ reservoir solution into each vial.</li>
	<li>Adjust the flow of the N2 gas lines as desired to keep the experiment anoxic for the duration of the injections.</li>
	<li>Carefully cover the reservoir vials with an airtight seal (e.g., using Parafilm; not obstructing the view through the glass) and insert an N2 feed into each vial (Figure 3).</li>
	<li>Bring the ddH2O syringes (still inserted in the tubing) down next to the primary injection syringes. Carefully slide the plastic injection tubing off the ddH2O syringe needle, and immediately transfer it directly onto one of the primary injection syringe needles. (Take care to not puncture the wall of the tubing.)</li>
	<li>Start the injection, and start recording of membrane potential.</li>
</ol>
5. Starting the secondary injection:
<ol>
	<li>Hit stop on the syringe pump after 3 hr (after 6 ml have been injected), once chemical garden structures have formed (Figure 4), continually generating a membrane potential (Figure 5).</li>
	<li>Carefully remove the primary injection syringes from the syringe pump (but leave them connected to the tubing so the structures are not disturbed); set them on the stand above the level of the fluid in the vials so that the fluid cannot flow back into the syringe.</li>
	<li>Secure the secondary injection sulfide syringes to the syringe pump, and repeat Steps 4.3 and 4.4.</li>
	<li>Remove the secondary syringes one at a time from the syringe pump, and, while holding the syringes above the level of the fluid in the vials, repeat Step 4.9, transferring the tubing from the primary syringes to the secondary syringes (Figure 6). Be vigilant that the fluid pressure from the reservoir into the syringe does not cause fluid to flow back into the syringe as this could collapse the chemical garden.</li>
	<li>When the transfer is complete, carefully secure the secondary syringes to the syringe pump.</li>
	<li>Re-program the syringe pump to inject at 2 ml per hour, and hit start to continue the injection with the new injection solution.</li>
	<li>Safely dispose of the primary injection syringes.</li>
</ol>
6. Ending the Experiment
<ol>
	<li>First stop the syringe pump, then stop recording of the membrane potential and save the data.</li>
	<li>Turn off the N2 flow and remove the lines and the Parafilm from the injection vessels.</li>
	<li>If desired, sample the reservoir solution or precipitate for further analysis. To carefully remove the reservoir solution and not disturb the precipitate, use a 25 ml pipette to carefully pipette off the reservoir solution in several aliquots, and discard the solution in a waste beaker.</li>
	<li>Unclamp the injection vessels one at a time and pour the solution into a waste transfer beaker in the fume hood. Use ddH2O to rinse out pieces of precipitate.</li>
	<li>Remove the syringes from the syringe pump, and extract them from the tubing, letting extra injection fluid run off into the waste transfer beaker. Empty the syringes into the waste beaker, and dispose of the syringes in a sulfide sharps container kept in the fume hood.</li>
	<li>Remove the tubing from the experiment vial and dispose of it in a solid waste bag. Uncrimp the seal and dispose of the septum, seal, and pipette tip.</li>
	<li>Rinse out the glass experiment vial and soak it in a 1 M HCl acid bath O/N. (CAUTION &#8212; glassware that has been in contact with sodium sulfide will release toxic H2S gas when placed in acid. Keep acid baths inside the fume hood.)</li>
</ol>

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<li>Hansen, H. C. B., Guldberg, S., Erbs, M., Koch, C. B. <a target="_blank" href="http://www.ncbi.nlm.nih.gov/pubmed?term=((Kinetics+of+nitrate+reduction+by+green+rusts%E2%80%94effects+of+interlayer+anion+and+Fe+%28II%29%3A+Fe+%28III%29+ratio%5BTitle%5D)+AND+%22Appl.+Clay+Sci%22%5BJournal%5D)">Kinetics of nitrate reduction by green rusts—effects of interlayer anion and Fe (II): Fe (III) ratio.</a> Appl. Clay Sci. 18 (1), 81-91 (2001).</li>
<li>Trolard, F., Bourrié, G. Fougerite a natural layered double hydroxide in gley soil: habitus, structure, and some properties. <a target="_blank" href="http://scholar.google.com/scholar?hl=en&safe=off&q=author%3aTrolard%2C+F+%22Clay+Minerals+in+Nature+-+Their+Characterization%2C+Modification+and+Application%22">Clay Minerals in Nature - Their Characterization, Modification and Application</a>. , InTech. (2012).</li>
<li>van Oss, C. J. Specifically Impermeable Precipitate Membranes. <a target="_blank" href="http://scholar.google.com/scholar?hl=en&safe=off&q=author%3avan+Oss%2C+CJ+%22Surface+and+Colloid+Science%22">Surface and Colloid Science</a>. , Springer. US. 115-144 (1984).</li>
<li>Baaske, P., et al. <a target="_blank" href="http://www.ncbi.nlm.nih.gov/pubmed?term=((Extreme+accumulation+of+nucleotides+in+simulated+hydrothermal+pore+systems%5BTitle%5D)+AND+%22P.+Natl.+Acad.+Sci.+USA%22%5BJournal%5D)">Extreme accumulation of nucleotides in simulated hydrothermal pore systems.</a> P. Natl. Acad. Sci. USA. 104, 9346-9351 (2007).</li>
</ol>

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><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</td><td>Ferric&amp;nbsp;Chloride&amp;nbsp;Hexahydrate&amp;nbsp;(Lumps/Certified ACS)</td></tr><tr><td>Sodium hydroxide</td><td>Sigma-Aldrich</td><td>S5881</td><td>reagent grade, &amp;ge;98%, pellets (anhydrous)</td></tr><tr><td>Sodium sulfide nonahydrate</td><td>Fisher</td><td>S425212</td><td>Sodium Sulfide Nonahydrate (Crystalline/Certified ACS). Store at -20&amp;nbsp;&amp;#176;C. Only open in a glove box or fume hood. Releases toxic H&lt;sub&gt;2&lt;/sub&gt;S 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>&lt;a href=&quot;http://www.sigmaaldrich.com/catalog/product/aldrich/322431?lang=en&amp;amp;region=US&quot;&gt;322431&lt;/a&gt;</td><td>97%</td></tr><tr><td>L-Alanine</td><td>Sigma-Aldrich</td><td>&lt;a href=&quot;http://www.sigmaaldrich.com/catalog/product/sigma/a7627?lang=en&amp;amp;region=US&quot;&gt;A7627&lt;/a&gt;</td><td></td></tr><tr><td>Syringes (10&amp;nbsp;cc)</td><td>Fisher</td><td>14-823-16E</td><td>BD&amp;trade; Syringe with Luer-Lok Tips (Without Needle)</td></tr><tr><td>Syringe needles (16&amp;nbsp;gauge)</td><td>Fisher</td><td>14-826-18B</td><td>BD&amp;trade; General Use and PrecisionGlide Hypodermic Needles, 16&amp;nbsp;G x 1.5 in. (38&amp;nbsp;mm)</td></tr><tr><td>Tubing</td><td>Cole Parmer</td><td>EW-06407-71</td><td>Tygon Lab Tubing, Non-DEHP, 1/16&quot; ID x 1/8&quot; OD</td></tr><tr><td>Aluminum seals</td><td>Fisher</td><td>0337523C</td><td>Thermo Scientific&amp;trade; National&amp;trade; Headspace 20&amp;nbsp;mm Crimp Seals</td></tr><tr><td>Gray butyl stoppers</td><td>Fisher</td><td>0337522AA</td><td>Thermo Scientific&amp;trade; National&amp;trade; 20&amp;nbsp;mm 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. &amp;times; H 51.7 mm &amp;times; 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 &amp;#956;l</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

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...

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 ...

The overall goal of the following experiment is to simulate natural chimneys precipitated at submarine hydrothermal vents of early earth using chemical garden experiments to generate the self assembling structures on a small scale. This is achieved by first preparing two solutions. One solution simulates the composition of early earth seawater, and one solution simulates an alkaline hydrothermal fluid produced by water rock reactions.Next, an apparatus is set up so that the hydrothermal like fluid can be injected into a reservoir of the simulated ocean under an anoxic atmosphere. As a third step, electrodes are set up to measure the voltage between hydrothermal and ocean solutions during the injection. Finally, the hydrothermal like solution is slowly injected into the base of a vial containing the simulated ocean solution, mimicking the natural seepage of vent fluid out of the ocean crust and into the surrounding sea water.The results show that a mineral precipitate forms at the interface of the ocean and hydrothermal solutions, and this develops into a self assembling chemical garden structure resembling a natural hydrothermal chimney Submarine. Hydrothermal chimneys are just like natural chemical gardens. They were generated, we think on earth about 4.4 billion years ago, and they're made of iron sulfides and iron hydroxides, to the most part with a little bit of silica.And they behave like a skin they're generated where alkaline solutions come up into the ocean, which is somewhat acidic. And at the interface between the two, they precipitate these minerals, as I say, looking rather like a skin. In fact, one could compare them to life as we know it today.And that is life tends to have an alkaline interior as we do, for example. And it tends to rather like acidic exteriors. I mean, I can say flippantly perhaps that we like a pH shampoo of pH 5.5.We like acidic soda pops for example. But also we like to have alkaline drinks to keep us healthy because after all, our interiors are healthy, just like natural chemical gardens. And what we've seen in the lab today is the fact that the interior of these chemical gardens is alkaline.The exterior is acid. It's somewhat oxidized, and we have, what happens is these chemical gardens impose a chemical gradient across the two, that chemical gradients of pH and Redox, and they summed to about half a volt, which is about the amount of electrochemical energy required to drive life. And we feel that this was just right to drive life to be into being in the first place in one of these chemical gardens on the ocean floor 4 billion years ago.This experiment allows us to simulate different planetary conditions like oceans, hydrothermal fluids, atmospheres, but also allows us to simulate the effects of changing specific experimental parameters and what effect that will have on the system. Originally, we were studying chemical gardens that grew directly from crystals inside test tubes, but we weren't able to measure the membrane potential because we couldn't get a wire directly inside the membrane itself. So in order to do this, we developed a new method.It's an injection method where we injected hydrothermal simulant into ocean fluid in a reservoir. This allowed us to use an automated data logger to measure the membrane potential over the growth of the membrane. Those who are New to this method may struggle for growing nicely structured chemical gardens and positioning virus into the chi needs for voltage measurement.However, by troubleshooting, they can solve all these problems. Begin by using a glass cutter to cut the bottom off of a 100 milliliter clear glass crimp top serum bottle for uses the injection vial. Also collect a 20 millimeter septum, 20 millimeter aluminum crimp seal, and a 0.5 to 10 microliter plastic pipette tip.Using a 16 gauge syringe needle, carefully puncture a hole through the center of the septum, then remove and discard the needle in the appropriate sharps waste container. Next, insert the pipette tip into the needle hole and push the pipette tip through the septum so that it pokes out the other side. Crimp seal the septum with the pipette tip onto the injection vessel.To make a watertight seal wind sealed, push the pipette tip further through the septum so that it protrudes to the outside. Then affix a one 16th inch inner diameter, clear, flexible, and chemical resistant tube to the pipette tip. Slide the tubing up onto the pipette tip In order to create a watertight seal, ensure that the tubing is long enough to reach from the injection vial to the syringe pump.Next, clamp the injection vials on a stand inside a fume hood so that the injection will feed in from the bottom of the vial. Cut two lengths of insulated wires so they are long enough to reach from inside the reaction vessels to the data logger. Leave a little bit of slack in the wires for positioning.Next, strip about three millimeters of insulation from the end of each wire that will be located inside the reaction vial at the other ends. That will be connected to the multimeter leads. Strip about one centimeter of the wire insert one wire the wire that will be inside the chemical garden close to the opening of the pipette tip to ensure contact with the injection solution, but not so far that it will clog the injection flow.And then secure both ends of the wires in place using tape. Then place the outside wire so that it will contact the solution reservoir, but not the chemical garden precipitate. Next, attach the free ends of the wires to the data logger to keep the headspace above the solution reservoir.And IC set up nitrogen gas lines. Split the gas feed from a nitrogen source tank into several tubes so that there is one feed for each injection vial. Prepare 200 milliliters of the reservoir solution, also known as the ocean simulant for each reaction vial by first bubbling deionized water with nitrogen gas for about 15 minutes per 100 milliliters.This ensures that the experiment will remain anoxic throughout the injection. Then weigh out and add 25 millimolar of iron, two chloride tetra and 75 millimolar of iron. Three chloride hexahydrate to the water.Stir the mixture gently to dissolve the ions without introducing oxygen into the mixture. After the ions are dissolved immediately resume light bubbling of the solution with nitrogen gas. While the injections are prepared, choose any two of the primary injection solutions from the table shown here and prepare 10 milliliters of each solution.Then fill a 10 milliliter syringe to the seven milliliter mark with each of the solutions, cap them and set them aside. Next, prepare 20 milliliters of 50 millimolar sodium sulfide in the fume hood as the secondary injection. Fill two 10 milliliter syringes to the seven milliliter mark With the solution, replace the needle caps and set them aside.Secure the primary injection syringes onto a programmable syringe pump that is located inside the fume hood. Set the injection rate to one milliliter per minute and turn on the pump until both syringes begin to drip into the waste beaker. Then stop the injection.Next, insert the syringes containing deionized water into the two plastic injection tubes and inject so that the water fills the clear tubing up to the aperture where it enters the main reservoir. Then place the syringes on the stand above the injection vials. Then carefully pour 100 milliliters of the iron containing reservoir solution into each vial.Carefully create an airtight seal over the vials using perfil and insert a nitrogen feed into each vial. Adjust the flow of the nitrogen gas lines as desired to keep the experiment anoxic for the duration of the injections. Next, bring the water filled syringes one at a time down next to the primary injection syringes.Carefully slide off the plastic injection tubing and immediately transfer it directly onto one of the primary injection syringe needles. Taking care not to puncture the wall of the tubing. Then set the syringe pump to run at two milliliters per hour for three hours and start the injection at the same time.Start the recording of the membrane potential. Hit stop on the syringe pump after three hours. Once the chemical garden structures have formed, carefully remove the primary injection syringes from the syringe pump, but leave them connected to the tubing so the structures are not disturbed.Set them on the stand above the level of the fluid in the vials so that the fluid does not flow back into the syringe. Next, secure the secondary injection syringes, which in this case consist of sodium sulfide to the syringe pump and prime the needle until both begin to drip dispose of the sulfide solution in a special hazardous waste container. Then remove the syringes one at a time from the syringe pump and transfer the tubing from the primary injection syringe to the sodium sulfide containing syringe.Reprogram the syringe pump to inject the solution at two milliliters per hour and hit start to inject the sodium sulfide solution at this rate for three hours. Once the primary injection solution is fed into the reservoir solution, a chemical garden precipitate begins to form at the fluid interface, and this structure continues to grow over the course of the injection under environmental scanning electron microscopy, the primary precipitates formed in the presence of alanine appeared more rounded in amorphous, whereas pure iron oxy hydroxide precipitates as well as those containing pyrophosphate appeared more crystalline following the primary injection. The potential tended to peak immediately around 0.45 to 0.55 volts, and then decreased for about an hour before stabilizing around 0.1 to 0.2 volts for the rest of the primary injection.When the primary syringes were switched to the secondary syringes containing sodium sulfide, the chemical garden continued to grow except that visible new growths were now black iron sulfide. Rather than contributing to the existing walls, the black sulfide portions of the chemical garden appeared to branch off and grow separately. As soon as the sulfide injection solution reached the chemical garden, the membrane potential immediately jumped to about 0.9 volts.There are many possible combinations of solutions that you can use to grow your chemical gardens. It is also possible to change the injection rate from a faster rate to a slower rate and change the primary injection to a secondary one at any time during the experiment, as long as your chemical garden structure is completely formed. Sodium sulfide solutions release hydrogen sulfide gas, which is extremely hazardous.Open sodium sulfide containers and sulfide containing solutions must be used inside of fume hood and handled according to material safety data sheet guidelines both used and unused solutions must be disposed of as hazardous waste. Hydrothermal chimneys we've just seen being grown in the lab are made of porous minerals, basically iron sulfides and iron hydroxides. And they thi, we think they'll act as catalysts on early life, and they're very similar in structure to the catalysts and enzymes we have even in our own skin to this day.This experiment can be used to simulate different geological environments, but is also applicable from a material science because there's a lot of interest in learning how to control the growth of these self assembling structures by manipulating the parameters of the experiment, and also perhaps for creating structures and materials that could act as catalysts for different reactions.

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