Metabolism In a Reducing Atmosphere

Question

Recently I have been looking for metabolic processes that might emerge on a planet with a reducing atmosphere and have come up empty-handed. There are some other questions out there that have been answered such as energetics in a reducing atmosphere, but the conditions of my planets are wildly different and would not be able to support the same means as other similar questions asked on this platform.

My planet has a reducing atmosphere but has low concentrations of carbon. So something like Acetylene will play a much smaller role in metabolic processes than is addressed in similar questions. The biosolvent utilized in my world is anhydrous ammonia.

This lifeform will be nitroborane-based. So it uses nitrogen and boron as the base substitutes for carbon. I am in search of two things: a way to extract energy from certain resources present, and how those resources might be captured.

So for the first part of my question, I'm looking for an alternative to fermentation or the Krebs cycle, so that oxidizing is removed from the equation, and substances like hydrocarbons are other carbon compounds are not utilized as much as possible. I'm looking for something completely new and foreign from what we have here on Earth. Resources in high abundance on my world are metal ammine complexes, nitrogen and boron compounds, and relatively low in oxygen and carbon.

For the second part of my question I mean to say how will the reagents used in these metabolic processes be captured by the life there. Will it be gas exchange and diffusion like we are used to on Earth, maybe liquid diffusion?

The world is relatively colder and has a higher pressure and this life will be in the deep where the ammonia is viscous and pressures extreme. Could this by chance change the way reagents for the metabolism are absorbed? Thanks for your answers in advance.

Answer 1

Is hydrogen available? If not, what are the major reducing species available?

If hydrogen is available, you can still expect to get energy by hydrogenation, transforming nitroborane compounds into ammonia and either elemental boron or diborane; at STP, diborane has a small positive heat of formation, but the reaction might become favorable at high pressures due to volume reduction.

Fermentation doesn't depend on oxygen or hydrogen anyway, and you can certainly expect the general principle of breaking down large complex molecules into smaller, simpler, lower-energy ones to still work. The exact processes are highly contingent (note the wide variety of fermentation products produced by Earthling biology--lactate, acetate, alcohol, etc.), but presuming optimal results and depending on the energetic favorability of diborane vs. elemental boron and hydrogen, I would expect final fermentation products to be either diborane, nitrogen, and a smidgen of ammonia, or boron and ammonia--and possibly extra nitrogen anyway, depending on exactly what energy-rich molecules you are using. E.g., hydrogen-poor, azide-rich energy storage molecules would produce primarily nitrogen waste upon fermentative decomposition.