Chemical Gardens as Flow-through Reactors Simulating Natural Hydrothermal Systems

Summary

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

Abstract

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 “hydrothermal” injections.

Introduction

“Chemical gardens” are self-assembling inorganic precipitates developed where two fluids of contrasting chemistries interact^1,2. 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 “chimney” precipitates that grow around hydrothermal springs and seeps, and it has been argued that these could provide plausible environmen....

Protocol

1. Safety Considerations

1. 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.
2. 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 experi....

Results

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.......

Discussion

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.......

Materials

List of materials used in this article

Name	Company	Catalog Number	Comments
Syringe Pump	Fisher	14-831-3	Dual or multiple channel, depending on desired number of simultaneous experiments
Ferrous chloride tetrahydrate	Fisher	I90500	Ferrous Chloride Tetrahydrate (Crystalline/Certified)
Ferric chloride hexahydrate	Fisher	I88-100	Ferric Chloride Hexahydrate (Lumps/Certified ACS)
Sodium hydroxide	Sigma-Aldrich	S5881	reagent grade, ≥98%, pellets (anhydrous)
Sodium sulfide nonahydrate	Fisher	S425212	Sodium Sulfide Nonahydrate (Crystalline/Certified ACS). Store at -20 °C. 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.
Potassium pyrophosphate	Sigma-Aldrich	322431	97%
L-Alanine	Sigma-Aldrich	A7627
Syringes (10 cc)	Fisher	14-823-16E	BD™ Syringe with Luer-Lok Tips (Without Needle)
Syringe needles (16 gauge)	Fisher	14-826-18B	BD™ General Use and PrecisionGlide Hypodermic Needles, 16 G x 1.5 in. (38 mm)
Tubing	Cole Parmer	EW-06407-71	Tygon Lab Tubing, Non-DEHP, 1/16" ID x 1/8" OD
Aluminum seals	Fisher	0337523C	Thermo Scientific™ National™ Headspace 20 mm Crimp Seals
Gray butyl stoppers	Fisher	0337522AA	Thermo Scientific™ National™ 20 mm Septa for Headspace Vials
Serum bottles	Sigma-Aldrich	33110-U	Vials, crimp top, serum bottle, size 100 ml, clear glass, O.D. × H 51.7 mm × 94.5 mm. For these experiments, the bottom of the serum bottle should be cut off.
Pipette tips	VWR	53511-682	pipette tips 0.5-10 μl
Wire	McMaster-Carr	8073K661	Solid Single-Conductor Wire, UL 1007/1569, 20 AWG, 300 VAC