The flow-reactor, a better hydrothermal vent simulator, part 1

flow-reactor (HCFR) build by Ei-ichi Imai at Nagaoka Institute of Technology.
flow-reactor (HCFR) build by Ei-ichi Imai at Nagaoka Institute of Technology.

In the previous post, i wrote about a conventional kind of submarine hydrothermal simulator (SHS) called the autoclave. In today’s post i will talk about the flow kind of reactor which is more realistic compared to the autoclave. Jack Corliss, the man who discovered a real SHS, came up with the notion that a flow-type reactor is essential for new origin of life experiments, as he argued that the quenching effect of the cold seawater is important to hold the short-lived intermediates (hydrogen cyanide, sugars and etc) or as he calls it “quasi-species” in prebiotic synthesis of bio-molecules. This essentially means that a flow kind of simulators are required to better represent a real SHS to  produce more reliable results than the autoclave.

Initial Schematics of Jack Corliss in his paper
Initial Schematics of Jack Corliss in his paper

Co-incidentally, Koichiro Matsuno, designed a principle idea of a flow reactor which could reflow the fluids repeatedly in heat and cold (i will name here-forth as hydrothermal circulation flow-reactor (HCFR) for convenience). Ei-Ichi Imai, Koichiro Matsuno and co-workers went on to build  (image above, schematics diagram below) the reactor and experimented using many bio-molecules.

Their first paper which made it to Nature (big thing for scientist), reported that oligomerization of glycine could occur at 200-250°C, where a monomer glycine solution was circulating for 2 hours or so. Oligomers up to Hexaglycine was reported when metal (Cu2+) and controlled pH was introduced. Without them, only oligomers up to triglycine could be obtained. They also tried the same experiment using  glycine and alanine. They observed oligomerzation products such as

Schematic diagram of the HCFR system from Nagaoka Institute of Technology
Schematic diagram of the HCFR system from Nagaoka Institute of Technology

diketopiperaxine, gly-ala, ala-gly, gly-ala-ala, ala-ala, ala-ala-ala and ala-ala-ala- ala was created when the solution was heated with similar conditions. What i described abover is a big thing in origin of life studies. This land-mark discovery, was the first to show that oligomerization (a shorter version of polymerization) could occur using basic amino acid (gly), without the help of DNA and RNA molecules which are crucial in making proteins in life.

In their other works, oligomerization of nucleotide up to trimers (basic monomer of DNA) was also observed when 20mM of adenosine monophosphate was used with 1mM ZnCl2 were reflowed at 110°C.

Despite the findings made by HCFR, the system is rather hypothetical, since we know that real live vents don’t really circulate in that manner (shown below) however, this kind of reactor is useful when it comes to monitor chemical changes in the system. In my next post, i will review another kind of flow-reactor in Japan which i have also worked on in the past.

HCFR mimicking a circulatory system in a real life vent.
HCFR mimicking a hypothetical circulatory system in a real life vent.

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Making life in a pot

In the last few posts, i wrote about the basics of submarine hydrothermal vents (SHS), here i will be posting about the simulators that we use in the lab to recreate this environment. This is useful as we can use many kinds of basic chemicals to test how they react when directed to massive heat and pressure similar to SHS. Today’s post will be about the most basic of simulator, we call it the autoclave; I will be also describing some of the experiments done in an autoclave system to date.; which literally a boiling pot.

Autoclave at Kensei Kobayashi lab at Yokohama National University, Japan
Autoclave at Kensei Kobayashi lab at previous university, Yokohama National University, Japan

When the hypothesis that life could have started at SHS was proposed; Miller and Bada was one of the first to come with real experimental simulations. They  argued that biomolecules decompose at high temperature and pressure, thus making SHS an unreliable spot for origins. They carried out the experiment at 250°C and 26 Mpa for about 6 hours, and adjusted the pH to neutral of amino acids, leucine, alanine, serine and aspartic acid. The experiment was conducted in an autoclave; a device conventionally used to sterilize equipment and supplies by subjecting them to high pressure and temperature (figure on the left and below, you can’t miss it!!). They showed that aspartic acid and serine decomposed rapidly, and the half life of leucine was about 15-20 min; and alanine appears to be much stable than the rest. Glycine, which was not part of the starting material, was produced during the course of the experiments. From this experiment, They went on to conclude that SHS is not ideal for origin of life, because amino acid being an monomer to proteins will be destroyed at high heat and pressure.

This finding, however received much criticism, some scientists mentioned that the duo did not control the redox conditions in their simulations, and started at a neutral pH; this is very much unlikely in a real situation hence, their results are not very realistic. Kohara and and his buddies showed that if a reducing condition (adding hydrogen) is introduced to an autoclave (similar to a real SHS), amino acid are better conserved up to 300°C. The stability of amino acids was dependent on the fugacity of hydrogen in the system compared to inert conditions shown by Miller and Bada. This is shown in Kohara and co workers’ work, that hydrolyzed samples exhibits higher recovery compared to the non-hydrolyzed ones.

Schemetic diagram of a simple autoclave
Schemetic diagram of a simple autoclave

Moving on, in 1992, RJC Hennet and friends managed to show that by using some basic chemicals found in the ocean (KCN with NH4CL and HCHO together with pyrite, pyrrhotite and magnetite to be precise) at 150°C, could form a variety of amino acids in an autoclave. Similarly, David Marshall also showed how amino acids and amines could be formed using aqueous NH4HCO3 solutions were reacted with gaseous C2H2, H2, and O2 at 200-275°C for 0.2-2 hours. These experiments seems to be supporting that bio-molecules especially amino acids (so far), could be formed in such conditions which could have existed on early earth.

Now on the cons of autoclave. Despite being robust and proven useful, the autoclaves severely lacks a cooling device. Conventionally, once the heating vessel is removed from the furnace of an autoclave, a fan is usually placed to cool it down for a few hours. This is not exactly how a real SHS will function, one could easily imagine that the hot fluids emitted by the vents will be rapidly cooled down by the near freezing water of the ocean. This limitation made researchers to come with a more dynamic system, which i will write about in the next post.

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Submarine Hydrothermal system (SHS) and the link to origin of life

http://www.whoi.edu/cms/images/lstokey/2005/1/v41n2-tivey1en_5063.jpg

Plate tectonic is the theory which unified on how the earth worked. The theory has always been there (since 1879)1,2 and was only accepted in the 1950‘s. The theory also predicted the existence of hydrothermal vents; a deep-sea hot springs is formed when cold seawater seeps into magma-emitting cracks on the oceanic surface, heats up, and rises. Although scientists had been actively searching for vents since the early 1960s, it wasn’t until the 1977; when the Galápagos Hydrothermal Expedition led by Richard Von Herzen and Robert Ballard of the Woods Hole Oceanographic Institution, that confirmed their existence using the famous submersible, Alvin ,3,4.

The relationship between SHS and origin of life on the other hand, first came out through Jack Corliss, John Baross and Sarah Hoffman5. They claimed that the conditions surrounding the vent area provided all the conditions for life’s creation on earth. Over time this idea has sprouted and have been elaborated with many in-situ integration with simulation data. I will elaborate more on this in the next post.

  1. Darwin, G.H (1879) On the procession of viscous spheroid, and on the remote History of the Earth.Philosophical Transactions of the Royal Society of London Vol. 170, 447-538
  2. McKenzie, D. P (1969) Speculations on the consequences and causes of plate motions. Geophysical Journal International, 18(1), 1–32.
  3. Corliss, J. B. J, Baross, J.A and Hoffman, S.E (1981) An hypothesis concerning the relationship between submarine hot springs and the origin of life on Earth.  Oceanologica Acta 4, 59-69.
  4. Corliss, J.B, Lyle, M, Dymond. J and Crane, K (1978) The chemistry of hydrothermal mounds near the Galapagos Rift. Earth and Planetary Science Letters, Volume 40, Issue 1,12–24.
  5. Corliss, J.B, Baross, J.A. and Hoffman, S.E (1981) An hypothesis concerning the relationship between submarine hot springs and the origin of life on Earth, Oceanologica Acta 4, 59–69