Nitrous oxide based respiration?

[Linguofreak]

In this post from the "Terrestrial Planet with a Terrestrial Moon" thread, I mooted the idea of an alien biology in which photosynthesis produces N2O, which is then used for respiration as an oxidizer.

So I'd like to ask the chemists and biologists on the board: Is this at all plausible?

First of all, is there a workable set of reactions for such a biology? (My own thoughts so far are at the end of the post).

Secondly, I know that N2O decomposes exothermally and can be used as a monopropellant. Wkipedia says:

Nitrous oxide can also be used in a monopropellant rocket. In the presence of a heated catalyst, N2O will decompose exothermically into nitrogen and oxygen, at a temperature of approximately 1300 °C[citation needed]. Because of the large heat release, the catalytic action rapidly becomes secondary as thermal autodecomposition becomes dominant.

The last sentence concerns me greatly: Does this mean that an atmosphere with significant amounts of N2O would be a planet-wide bomb waiting for a lightning bolt?

Thirdly, I know that N2O attacks ozone. Is there any plausible UV blocker for an atmosphere with large quantities of N2O?

Fourthly, are there any other possible deal-breakers?

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Going back to the question of the reactions such a biology would be based on, I assume that photosynthesis would look something like:

CO2 + Nitrogen source + H2O -> N2O + Food

And respiration would look like:

N2O + Food -> CO2 + H2O + Nitrogen sink

The nitrogen sink in respiration would preferably be something heavy and/or non-gaseous, and the photosynthesis process would preferably be able to use either N2 or the nitrogen sink from the respiration reaction as a nitrogen source, as the point of this whole idea is a biology that can slow down nitrogen escape on worlds with shallow gravity wells, so it's desirable for photosynthesis to consume N2 while respiration produces a heavier nitrogen compound.

Would glucose be a good food for this reaction as on Earth? Can anybody suggest a good nitrogen sink?

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Another possible process might be something like this, assuming some method of capturing N2 from the atmosphere to form N2O were available:

Carbon/Nitrogen compound + H2O <-> N2O + Food

One implementation of which could be:

EDIT: Here I thought I had a reaction of the form HCN + H2O <-> N2O + glucose, but I made an arithmetic error.

EDIT2: I did find another reaction, which I think I did the math right on, using ethanol:

N2O + C2H6O <-> 2 HCN + 2 H2O

The atom counts check out (I hope! I was quite embarrassed to find an arithmetic error after making that assertion in the original version of this post), but I'm not enough of a chemist to evaluate other metrics of its favorability as as a photosynthesis/respiration process (such as whether it actually delivers any energy). Can anybody comment on that?

 

[statickid]

If a human visited that planet and they got a leak in their space suit it would be HILARIOUS!

:lol: :lol: :rofl: :rofl: :lol: :lol:

I apologize this post is not helpful in any way.

 

[thepenguin]

First of all, is there a workable set of reactions for such a biology? (My own thoughts so far are at the end of the post).
see below

The last sentence concerns me greatly: Does this mean that an atmosphere with significant amounts of N2O would be a planet-wide bomb waiting for a lightning bolt?
yes.

Thirdly, I know that N2O attacks ozone. Is there any plausible UV blocker for an atmosphere with large quantities of N2O?
Not to my knowledge, short of spraying sunscreen in the upper atmosphere...
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Would glucose be a good food for this reaction as on Earth? Can anybody suggest a good nitrogen sink?
perhaps N2 gas is your best bet.
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Ethanol: N2O + C2H5OH <-> 2 HCN + 2 H2O
Its favorability as as a photosynthesis/respiration process (such as whether it actually delivers any energy). Can anybody comment on that?
82.05−277.0=2*(130.5−241.818)+X
-194.95=-222.636+X
-194.95+222.636=X
X=27.686 kJ energy released per mole "burned" in N2O
VS. 1368 kJ energy released per mole burned in traditional air.
The reaction yields heat, but is 50x less effective than traditional burning.

Just my :2cents: on it. I would appreciate it if someone would check my enthalpies of formation and reaction.

 

[Linguofreak]

Does this mean that an atmosphere with significant amounts of N2O would be a planet-wide bomb waiting for a lightning bolt?

yes.

I was afraid of that.

perhaps N2 gas is your best bet.

N2 defeats the whole excercise, if it isn't doomed from the start, as the point is to figure out a means of putting oxygen and nitrogen into heavier or higher-boiling-point chemicals so they can be retained by a low escape velocity world. N2O is desirable for this purpose because it's one chemical that takes care of both elements (while also meeting the requirement that the chemical that is used to store oxygen must be an oxidizer).

The reaction yields heat, but is 50x less effective than traditional burning.

I wasn't sure how the HCN reaction would do, it was just an idea. I have a feeling other reactions would probably do better. At the very least decomposition of N2O followed by more "traditional" oxygen burning would do as long as elemental oxygen and nitrogen didn't escape into the atmosphere. The only problem with that path would be justifying the production of N2O in photosynthesis. What would the most likely products and yield of a straight N2O/glucose reaction be? And, in general, what would the most favorable (and plausible) photosynthesis/respiration reaction set involving N2O?

 

[thepenguin]

What would the most likely products and yield of a straight N2O/glucose reaction be?
8 N2O + 2 C6H12O6 -> 8 NH3 + 8 CO2 + 4 CO
of course, the COs would probably strip the surrounding "air"
4 CO + 4 N2O -> 4 CO2 + 4 N2
However, that leaves remaining nitrogen.
Also, the reaction could occur with a better energy yield if there were some chlorine gas in the atmosphere as well, forming NH4Cl instead of regular ammonia. Is chlorine "allowed" in your atmosphere? It could give us ~200kJ more energy yield, assuming that the creatures have a method to dispose of the NH4Cl (solid) that is released as a by-product of the reaction. If I had chlorine, I could probably also do something with phosgene as a carbon sink.

Whatever this biology looks like, almost all of it is toxic to earth life.

 

[Linguofreak]

What would the most likely products and yield of a straight N2O/glucose reaction be?
8 N2O + 2 C6H12O6 -> 8 NH3 + 8 CO2 + 4 CO
of course, the COs would probably strip the surrounding "air"
4 CO + 4 N2O -> 4 CO2 + 4 N2
However, that leaves remaining nitrogen.

If the CO stripping can occur in the cell as part of respiration and the nitrogen can be fixed into something heavy immediately, or if local photosynthesis does a good enough job of drawing down N2 in producing N2O, that isn't necessarily a deal breaker.

On the flip side, is a photosynthetic reaction that's producing N2O as an oxidizer likely to produce glucose as a fuel? The initial atmospheric components for a terrestrial planet will generally be lots of CO2 and water with some N2 thrown in. If the planet is in the habitable zone, the water will rain out, leaving CO2 and some N2, at which point CO2 will begin to be sequestered in carbonate minerals, leaving a lower pressure atmosphere progressively more enriched in N2 as CO2 is drawn down. Photosynthesis will initially be operating in this environment (N2/CO2 atmosphere over H2O ocean), so if it's producing N2O, it will initially look something like: H2O + N2 + CO2 -> N2O + ???, so respiration and subsequent photosynthetic processes (operating on heavier nitrogen sources) should probably be similar in form. What's plausible in that regard?

Also, the reaction could occur with a better energy yield if there were some chlorine gas in the atmosphere as well, forming NH4Cl instead of regular ammonia. Is chlorine "allowed" in your atmosphere?

Is N2O/glucose low on energy yield? Do we need the extra yield? Cl is not really allowed as a primordial component (too reactive, like oxygen), but if a biological process can establish and maintain its presence in the atmosphere and the resulting acidity from chlorine compounds can be dealt with, why not?

I do understand that Cl2 photodissociates under UV, which could solve our no-ozone problem, but would also introduce monatomic chlorine into the atmosphere.

By the way, are there any atmospheric components that could stabilize the decomposition of N2O (so that a lightning bolt just produces a local cloud of N2 + O2, rather than producing a planet-wide fireball)?

It could give us ~200kJ more energy yield, assuming that the creatures have a method to dispose of the NH4Cl (solid) that is released as a by-product of the reaction. If I had chlorine, I could probably also do something with phosgene as a carbon sink.

Would it have any advantages over CO2 as a carbon sink?

Whatever this biology looks like, almost all of it is toxic to earth life.

Indeed.

 

[thepenguin]

If the CO stripping can occur in the cell as part of respiration and the nitrogen can be fixed into something heavy immediately, or if local photosynthesis does a good enough job of drawing down N2 in producing N2O, that isn't necessarily a deal breaker.

On the flip side, is a photosynthetic reaction that's producing N2O as an oxidizer likely to produce glucose as a fuel? The initial atmospheric components for a terrestrial planet will generally be lots of CO2 and water with some N2 thrown in. If the planet is in the habitable zone, the water will rain out, leaving CO2 and some N2, at which point CO2 will begin to be sequestered in carbonate minerals, leaving a lower pressure atmosphere progressively more enriched in N2 as CO2 is drawn down. Photosynthesis will initially be operating in this environment (N2/CO2 atmosphere over H2O ocean), so if it's producing N2O, it will initially look something like: H2O + N2 + CO2 -> N2O + ???, so respiration and subsequent photosynthetic processes (operating on heavier nitrogen sources) should probably be similar in form. What's plausible in that regard?

generally, nitrogen compounds might first go to ammonia.
6 H2O + 2 N2 -> 4 NH3 + 3 O2
O2 + 2 N2 -> 2 N2O
So I guess we could say that an ammonia+nitrous oxide system would be sensible.
6 H2O + 6 N2 + 6 CO2 -> C6H12O6 + 6 N2O
Just going with water, nitrogen, and co2, this looks like a good chance of happening.

Is N2O/glucose low on energy yield? Do we need the extra yield? Cl is not really allowed as a primordial component (too reactive, like oxygen), but if a biological process can establish and maintain its presence in the atmosphere and the resulting acidity from chlorine compounds can be dealt with, why not?

I do understand that Cl2 photodissociates under UV, which could solve our no-ozone problem, but would also introduce monatomic chlorine into the atmosphere.

monatomic chlorine is fiction. you will never get free Cl1 gas in an atmosphere, it will usually form into Cl2 molecules or chain itself onto another molecule, forming something like phosgene, or something like chloric acid (in this case, it would be an upper-atmospheric phenomenon, so there is little problem with it harming life, assuming that this life has evolved to live under acidic conditions like some organisms on earth have).

By the way, are there any atmospheric components that could stabilize the decomposition of N2O (so that a lightning bolt just produces a local cloud of N2 + O2, rather than producing a planet-wide fireball)?
not if you want to have life there.

Would it have any advantages over CO2 as a carbon sink?
It just provides a convenient way to deal with all of this carbon and chlorine. It also provides a sufficiently heavy chemical. Officially, you could probably use chlorine as your oxidizer and not bother with the N2O, but that would wreck our conventional notions of metabolism, and defeat the purpose of doing it like this. chlorine is also used for more complex biological functions.

Here's an idea: use the dinitrogen trioxide, dinitrogen tetraoxide and dinitrogen pentoxide molecules as a way of storing the oxygen for a more classical metabolism. I think the N2O4 <-> N2O5 chain is practical, but N2O3 has too much energy to be used as a carrier. You were in the right ballpark, but I think we may do better by using heavier molecules that work on their own.