Any fluorine alternatives to the phosphate chain of ATP?

Question

From what I know, the energy in ATP comes from the phosphate chain, which can be cleaved for energy using water(more specifically the energy comes the from the formation of new molecules upon cleaving the chain, as the cleavage itself takes energy.), and then the cleaved phosphates can be added back into the chain to release water and take energy. I have been spending a little bit trying to find a replacement for the phosphates, but I come up empty, So is there some replacement to the phosphate chain (that ideally won’t react with F2 gas)?

Some Clarity to the question:

I am looking for some molecule that can be put into a chain and will be cleaved by the addition of a simple molecule[that’s not so reactive in fluorine environment it’ll explode] to release energy [the energy will probably come from then formation of new bonds after cleaving the chain] and un-cleaved to release the same simple molecule and take energy

Edit: The cells’ solvent is liquid hydrogen fluoride(HF) at about -30 to -50 Celsius.

Answer 1

Nobody knows, but that won't keep me from making a wild guess!

The obvious first thing to try is short fluorophosphine chains, like $P_3F_5$.You could turn that into a $-P_3F_4$ group ($R-PF-PF-PF_2$) attached to an appropriate carrier molecule. That's stable enough to not immediately dissociate like polyfluoronitrogens, and maybe you could get energy out of it by reacting with $HF$? To produce $R-PF-PFH + PF_3$, or $R-PF-PF_2 + F_2HP$. You'd get better solubility and more consistent chemical behavior by allowing a hydrogen substitution, so you end up with $R-PF-PF-PFH + HF \Leftrightarrow R-PF-PFH + F_2HP$.

I am disinclined to bother trying to figure out the energetics of such a reaction, though, because it has some significant problems; phosphate is just a generally useful ion to have around. It's charged, and participates in a bunch of catalytic reactions and it can form multiple bonds to build bridges between other molecular groups--like nucleic acid backbones. Phosphines are polar but uncharged, and don't have the same kind of functional diversity. It all comes down to fluorine just not being a good substitute for oxygen. However, if there is oxygen around (which there should be, because it's more abundant than fluorine and fluorine will displace it from water and silicates), then fluorophosphines will react with oxygen to form difluorphosphates ($F_2PO_2^-$), which is hydrolytically unstable in water (it wants to form regular phosphates and more hydrofluoric acid), but it is stable in hydrofluoric acid. These could probably be chained to produce something much more similar to terrestrial phosphate chains. Rather than

$R-O-PO(OH)-O-PO(OH)_2 + H_2PO_3 \Leftrightarrow R-O-PO(OH)-O-PO(OH)-O-PO(OH)_2 + H_2O$

you'd get

$R-O-POF-O-POF_2 + F_2PO(OH) \Leftrightarrow R-O-POF-O-POF-O-POF_2 + HF$

In which we replace, not the oxygens, but specifically the hydroxyl groups with fluorines. Synthesis occurs by removing a fluorine from the chain and a hydrogen from the fluorphosphoric acid, using them to form new HF, and forming a new ester bond between the oxygen from which the hydrogen was removed and the phosphorus from which the fluorine was removed. Hydrolysis is the reverse.

I have no idea how to look up the actual energetics of such a molecule--I would be surprised if anyone has ever actually synthesized and studied it--but on general principle it should be slightly more rigid and have comparable if not slightly higher bond energy than Earthling phosphate chains.

And just to throw it out there, since I'm looking at it now, maybe you could do something useful with the nitrogen difluoride radical ('cause unlike polyfluorophosphines, polyfluoronitrogens like to dissociate).

Answer 2

Nitrogen trifluoride.

https://en.wikipedia.org/wiki/Nitrogen_trifluoride

It proved to be far less reactive than the other nitrogen trihalides nitrogen trichloride, nitrogen tribromide and nitrogen triiodide, all of which are explosive. Alone among the nitrogen trihalides it has a negative enthalpy of formation.

Enthalpy of formation is -31kJ/moles. The formation (starting with ammonia) gives off a little energy when fluorinated. Wikipedia says "It is a rare example of a binary fluoride that can be prepared directly from the elements only at very uncommon conditions, such as an electric discharge.". That is good because it means under ordinary conditons NH3 is safe from getting fluorinated. I propose that in your biology, an electric discharge or catalysts which can produce something similar are used to produce your NF3 from NH3 and harvest energy, then regenerate the NH3.

Reaally your energy storage molecule is not the NF3 but good old ammonia. A mellow way to get a little and give a little would be for one of the fluorines to reversibly trade places with a hydrogen. Ammonia has 3 hydrogens, NF3 has 3 fluorides and so you can have intermediates mirroring ATP ADP and AMP. Replacing one hydrogen with one fluoride should give you about 10 kJ/moles. Thus ammonia would be the most energetic molecule (probably ammonium fluoride in an HF solution) and you would replace H with F as you need energy. Instead of making sugar, your autotrophs make ammonia.