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What kind of inorganic materials might be used instead of phospholipid bilayer? It should be able to function in ammonia-environment. I had an idea of using phosphotungsic acid's anions based on this https://www.newscientist.com/article/dn20906-life-like-cells-are-made-of-metal/, but I don't think they would be able to connect to each other. I really need inorganic polymer, don't I?

phospholiopiids

https://www.phospholipid-research-center.com/phospholipid/types/

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    $\begingroup$ What problem do you anticipate with regular phospholipids in an ammonia environment? $\endgroup$
    – Willk
    Commented Jun 29, 2022 at 17:13
  • $\begingroup$ @Willk, I don't expect problems, I don't want to use organic molecules. $\endgroup$
    – Baldo
    Commented Jun 29, 2022 at 17:15
  • $\begingroup$ No organic molecules means to me no carbon. For aesthetics or is there some biochemical issue with carbon? Low carbon planet? $\endgroup$
    – Willk
    Commented Jun 29, 2022 at 17:23
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    $\begingroup$ Idea is that one of spirits that created life decided to show others how life can be different than their creations so they found place with almost no carbon and tried to create something. Note that spirits can't escape physical possibilities of world and only allow creatures to happen so it is not explained by "magic". $\endgroup$
    – Baldo
    Commented Jun 29, 2022 at 17:27
  • $\begingroup$ @Baldo (1/2) No organic material means no carbon, which is possibly a fatal restriction as you'll have a very hard time forming polymers. Carbon is relatively rare on Earth (to the point of being "almost no carbon"), and is about a THOUSAND times less common than silicon, which also forms tetravalent bonds, but life still prefers carbon over silicon. However, I'd say the most unrealistic part of your premise is a complete lack of carbon, as it's fairly easily formed in every star and is the 4th most abundant atom in the universe. $\endgroup$
    – stix
    Commented Aug 1, 2022 at 15:31

2 Answers 2

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Perfluoroalkyl Amides

enter image description here

Phospholipid bilayers rely on molecules with a hydrophilic head and hydrophobic tail. In an aqueous environment, these molecules form a two layer structure with the hydrophobic side of each molecule facing toward the center and the hydrophilic side facing outwards and inwards.

Cells in an ammonia environment could rely on molecules with ammonophilic heads and ammonophobic tails to form similar structures. Compounds known as perfluorinated long chain alkyl amides possess ammonophilic amide heads and ammonophobic fluorocarbon tails. Some examples of these compounds include perfluoroheptanamide, perfluorooctanamide, and perfluorodecanamide.

Information and picture from Micelle Formation in Liquid Ammonia

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  • $\begingroup$ The molecule you've suggested is organic. OP specifically states "no organic molecules" Which, admittedly makes the question much more difficult as it will be hard to form polymers. $\endgroup$
    – stix
    Commented Aug 1, 2022 at 15:28
  • $\begingroup$ That's the kind of paper that makes one wonder "why did they bother to test that specifically?" It even says " it is difficult to envisage how such perfluorinated systems could readily be formed"; like, where is all of that fluorine going to come from? $\endgroup$
    – Logan R. Kearsley
    Commented Aug 1, 2022 at 18:49
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Silane chains

Congratulations, you've discovered a justification for properly silicon-based life!

Silanes are unstable in the presence of oxygen or water, but as long as you've got mostly-anhydrous ammonia, at low temperatures, they should be fine. In fact, they have some nice advantages over organic alkane chains for use in ammonia: they've got lower melting and boiling points, so you can make them longer to maximize ammonophobicity and ease micelle formation without making them too rigid to form liquid-crystal membranes.

Now, what do you stick on the end for the ammonophillic part? Phosphates or sulfates should work fine, but if you like the idea of metal inclusions, you could go with double-tailed lithium, sodium, or potassium bis(silyl) amides, with the general formula $MN((SiH_2)_XSiH_3)_2$, where $M$ is some metal ion.

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  • $\begingroup$ Silane chains (hydrosilanes) are unstable in ammonia and react with it. The ammonia based solvent requirement of OP would not be feasible with hydrosilanes. In addition, silicon-silicon bonds (as in silane chains) are very rigid and unlikely to be flexible enough to form analogs of proteins and other molecular machinery critical to life processes. $\endgroup$
    – stix
    Commented Aug 1, 2022 at 19:56
  • $\begingroup$ @stix We don't need it to form proteins, just cell membranes, for the purposes of this question. All I can find on silane-ammonia reactions is about gas-phase reactions at high temperatures; is it still unstable at low temperatures in liquid ammonia? $\endgroup$
    – Logan R. Kearsley
    Commented Aug 1, 2022 at 20:22
  • $\begingroup$ Even as a cell membrane, or especially as a cell membrane, flexible bonds are a must. $\endgroup$
    – stix
    Commented Aug 1, 2022 at 20:25
  • $\begingroup$ @stix Flexible inter-molecular bonds are a must, so the bulk membrane can flow to allow insertion of new units for growth. Intramolecular flexibility is considerably less important. $\endgroup$
    – Logan R. Kearsley
    Commented Aug 1, 2022 at 20:39
  • $\begingroup$ Incidentally, polysilazanes (polymers & rings with a repeating Si-N backbone) look to be suitable stable-in-ammonia, flexible, and structurally diverse to serve as a basis for protein-equivalents--and they even have a nice built-in repeating dipole! Probably not great for making micelles for the same reason, though. $\endgroup$
    – Logan R. Kearsley
    Commented Aug 1, 2022 at 20:46

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