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I have been putting together an alternate biochemistry, one that is suited for an environment with lots of fluorine. I have a "model" of sorts for how it works, and I would like to know if there are any glaring problems that I am overlooking.

So you have the cell, lets name him Adam, after the Adam from the Christian Bible.

Adam uses liquid Hydrogen Fluoride as its solvent instead of water, the temperature of the environment is low, about -60 to -50 Celsius, so the Hydrogen Fluoride can be a liquid. And at the current moment, the atmosphere is composed of various fluorine-nonmetal compounds(like CF4, NF3, etc.) but no actual F2 gas.

Adam is also a very primitive cell, it only consists of the cell membrane, a nucleolus, and some ribosome analogues. Adam uses difluorophosphates as a replacement for normal phosphates, and HFCs(Hydrofluorocarbons) as a replacement for sugars. His Cell Membrane is made of a phospholipid analogue, using the difluorophosphate replacement. His is made of a chain of HFCs and difluorophosphates, with the bases being attached the the HFCs, there are 10 bases as opposed to our 4, because of this, Adam's nucleolus is smaller than one of our biochemistry, and his codons are a combination of 2 bases instead of our 3.

Adam uses a Fermentation analogue to make 3 of an ATP analogue, which uses a chain of difluorophosphates rather than regular phosphates.

Are there any glaring problems with what I just described?

NOTE: yes, I know that it is unusual/unlikely for such a planet to exist, as fluorine is not that abundant, but just assume that the planet does exist.

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  • $\begingroup$ The biggest problem is how are you going to maintain all of that elemental fluorine? It's literally the most electronegative substance in existence and pretty much the most reactive. $\endgroup$
    – stix
    Commented Aug 2, 2022 at 17:35
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    $\begingroup$ @stix He explicitly mentions that there is no F2 on the planet. But fluorine is not a very abundant element in the universe, so a planet with an HF ocean is very unusual to say the least. HF occurs in minor amounts in comets and probably generally on icy bodies of the solar system. $\endgroup$
    – Avun Jahei
    Commented Aug 2, 2022 at 18:20
  • $\begingroup$ I don't know much about biochemistry, but what I do know about fluorine is best summed up as OH GOD OH GOD SO REACTIVE OH GOD $\endgroup$
    – KEY_ABRADE
    Commented Aug 3, 2022 at 4:08

3 Answers 3

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I am not enough of a chemist to give meaningful avice. There are a few issues though that come to my mind and that may (or may not) be relevant.

"Adam uses ... HFCs as a replacement for sugars"

Sugar is a form of energy storage in terrestrial organisms. It is used as energy source by oxidation.

How is the hydrofluorocarbon used a energy source? The H-F bond is stronger than he H-O bond and I think that is also true for H-C. (EDIT: maybe you mean HFCs replace ribose in the genetic apparatus or cellulose, hemicellulose and other sugar derivates as structural element)

If HF is used as solvent in your biochemistry, does that mean that it is the dominant liquid on the planet? I do not know how likely that is. Fluorine is not a very abundant element in the universe.

In case the atmosphere is reducing one would expect ammonia or carbon compounds like methanol, ethanol and propane to be orders of magnitude more abundant than HF. They are all liquid in the given temperature range.

In case the atmosphere is oxidizing there are actually not many liquids left. CO2 is liquid only under high atmospheric pressure. One may expect liquid SO2 to be way more abundant than HF, although it can well be the case that the crust is strongly depleted in sulfur. That would not be unusual, because sulfur likes to combine with iron and may end up in the core as iron sulfide as is probably the case in many bodies of the solar system.

HF also has a strong tendency to react with sulfate which would form fluoride and sulfuric acid, so the HF would get mineralized very quickly (for example 2 HF + CaSO4 -> CaF2 + H2SO4). I would recommend that your planet is poor in sulfur.

(EDIT: This part is questionable; point is, HF is very corrosive toward a lot of minerals)

HF also attacks silicate, again mineralizing the fluorine. Fluorine is a highly lithophile element, it really wants to be a rock.

Given its temperature the planet is likely covered with a layer of water ice which would protect the HF from the rocks but would also limit the availability of mineral nutrients on the surface.

But wait: HF is denser than ice, so it would sink below the ice crust whenever it can and would then react with the rock anyway.

I can't see a way for your HF to be stable in geological timescales. It has to be permanently produced in the crust by geochemical processes and than transported to the surface, for example by volcanic erruptions.

In any case I would not expect oceans of HF to exist, rather small ponds at best.

Finally, there is a reason why our biochemistry only has 4 base pairs: it is the minimum you need for a genetic code. Which selection pressure led to the evolution of no less than 10 base pairs?

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  • $\begingroup$ Yes, HF would be the dominant liquid on the planet(I get its not very abundant, but I want to explore it, not dismiss it because its uncommon, it not impossible for it to happen, buts its handwave-y). It definitely seems like a good idea to have a sulfur poor crust, so I will go with that. I meant for the planet to have been formed fluorine rich, so there was already a large quantity of the elements that had reacted, but I looked at the densities of the fluorine compounds of the top ten most abundant elements of earths crust(excluding oxygen and hydrogen), and with all of them, their ... $\endgroup$
    – KaffeeByte
    Commented Aug 2, 2022 at 22:40
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    $\begingroup$ @Logan R. Kearsley CaF2 is the main source of fluorine and fluorine products. The reaction you quote is a forced one, it needs a lot of energy to proceed. The reverse reaction therefore releases a lot of energy, so that would be the natural direction of the equation. I could look up the Gibbs free energy change of the reaction if you want me to. Actually, it does not matter if it is CaSO4, CaCO3 or CaSiO3, since fluorine is the most electronegative element it will kick everything else out and form CaF2. $\endgroup$
    – Avun Jahei
    Commented Aug 3, 2022 at 18:52
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    $\begingroup$ @AvunJahei That seems very weird to me, because sodium fluoride will react at low temperatures to produce HF and sodium bisulfate... but I guess the energy difference is much smaller in that case. $\endgroup$ Commented Aug 3, 2022 at 19:53
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    $\begingroup$ @AvunJahei So it's not so much a matter of the planet being poor in sulfur, as being poor in calcium (and magnesium?) so as to not soak up all the fluorine. Lot's of sulfur would then assist in preventing fluorine from binding to sodium, potassium, etc. $\endgroup$ Commented Aug 3, 2022 at 21:02
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    $\begingroup$ @Logan R. Kearsley Lol, that's literally what I just thought, including the magnesium part. But HF also reacts with SiO2 to silicon tetrafluoride and water. That would be the main concern, don't know why I focused on sulfur. $\endgroup$
    – Avun Jahei
    Commented Aug 3, 2022 at 21:19
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It is unlikely that silicon tetrafluoride would exist freely in the atmosphere. SiF4 will react with the HF in the ocean, producing quantities of H2SiF6.

Information from Silicon Tetrafluoride Generation

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  • $\begingroup$ HFCs and CF4 are also extremely potent greenhouse gases. It'd make keeping the planet at the cold temperature stated by OP somewhat difficult. $\endgroup$
    – stix
    Commented Aug 2, 2022 at 22:09
  • $\begingroup$ @stix There’s no problem at all with keeping the planet cold, it can be as far from its sun as is necessary. $\endgroup$
    – Mike Scott
    Commented Aug 3, 2022 at 4:41
  • $\begingroup$ @rubpy32 Wouldn't F2 gas react with the H2SiF6? $\endgroup$
    – KaffeeByte
    Commented Mar 22, 2023 at 15:11
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The lack of oxygen and nitrogen in the classes of biomolecules you've described so far is a little weird. Fluorine can replace oxygen as an oxidizer, but not in structural roles, and it can only sometimes replace -OH groups. Similarly, nitrogen is a ridiculously useful heteroatom for controlling the properties of rings and polymers, and switching the solvent won't change that. I'd expect to see at least a few nitrogen centers, NF or NH bridges, and NF2, NH2, or NFH side groups.

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  • $\begingroup$ Well, there would be definitely nitrogen in the bases used in the genetic material, and definitely in amino acid analogues, just like earth cells, and nitrogen would also be in plenty of other things that just didn't mention. As for oxygen, maybe it would be better to include a dash of it in the role of sugars, so instead of HFCs, you use oxy-Hydrofluorocarbons, or whatever that would be called. Its just I have some loose chemical structures I sketched, and I had imagined for the carbon to replace the structural role of Oxygen, and fluorine to replace the -OH groups. $\endgroup$
    – KaffeeByte
    Commented Aug 3, 2022 at 18:26

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