Melgar
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Could you survive a year with only the chemicals you could make from a hydrocarbon feedstock?
Let's assume you're stranded on Saturn's moon Titan, in a base that has access to hydrocarbons, water, ammonia, nitrogen, and varying amounts of
minerals. You have mineral supplements, lots of inorganic chemicals, plenty of chemistry equipment, as well as the electrical output of a
recently-fueled nuclear reactor. There's a basic atmospheric life-support system in place that should continue to function, but no food, no plants
(or anything else that's photosynthetic), and no seeds. Could you make it a year, waiting for the resupply?
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CharlieA
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Very interesting thought experiment! I assume you have enough sustenance to hold you until your first syntheses are complete. I think this will
require some thought I suppose for starters that you will want to make some simple sugars (e.g. glucose), a simple fat, and simple protein from amino
acids. My ignorance of biochemistry doesn't tell me what simple protein(s) and fats you would require to sustain yourself.
...I guess there isn't any simple, one-step synthesis of pizza and chianti!
[Edited on 3-29-2017 by CharlieA]
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macckone
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How many crew mates?
Amino acids are going to be difficult to synthesize.
Might need an alternate source. Mmmm long pig.
Humans also require fatty acids and of course vitamins.
Some of the vitamins are tricky.
Honestly, I don't know enough biology to know what
To synthesize.
Tryptophan was banned in the US after a manufacturing
Error poisoned a bunch of people, if I remember right.
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Melgar
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The question is mainly posed this way to prevent people from deciding to become farmers rather than chemists, by extracting seeds from food, or
whatever they might think to do. Some people don't seem to like the idea of subsisting on synthetic chemicals. You're at a normal weight, and have
plenty of water and minerals, but your immediate problem is calories. If I remember right, most people can live for at least two weeks on stored
calories, as long as they stay hydrated.
I like this question because shorter syntheses can provide for short-term needs, and vice versa. The longer time goes on, the harder it gets.
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clearly_not_atara
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Triacetin would be your first stop. Propylene is passed over SeO2 to convert it to allyl alcohol and treated with peroxide or osmium to glycerol.
Reaction with acetyl-X gives you the simplest edible molecule that isn't ethanol.
Once you've got that you might want to work on some carbohydrates. Oxidation of allyl alcohol or pyrolysis of glycerol gives acrolein, which doesn't
sound like a food, but dimerizing acrolein gives the much tastier 3,4-dihydropyran-6-carboxaldehyde... which you can reduce to the alcohol, eliminate
and dehydrogenate to a very reactive 6-methylenepyran. Assuming it works on conjugated alkenes (heh) OsO4 will convert this to
1,5-dioxo-2,3,4,6-tetrahydroxyhexane, which can be easily reduced to isomers of fructose.
This isn't quite a diet, but with a few ammonium salts and a sample of your own feces it should be enough to get a bacterial culture going... you can
grow samples and use established procedures to separate amino acids. Vitamins would be the next challenge.
Yeah, I cheated as soon as I got to fructose. Lol, feces.
[Edited on 29-3-2017 by clearly_not_atara]
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Melgar
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@atara: That's very close to my conclusion as well, although propylene glycol is also a viable energy source, since it's metabolized to pyruvate.
However, there's an aldehyde intermediate that should probably be avoided when possible, as it would tend to stress your liver. Really though, you
wouldn't need to go all the way to triacetin, since your body can convert glycerol to carbohydrates on its own, quite easily really. Maybe flavor it
with some lactic or citric acid, some compressed CO2, and you've got yourself something about as tasty as whatever Aldi's calls its Sprite knockoff.
I opted to colonize acetobacter from my skin microbiota, since they're aerobic at least, and thus could probably survive on little more than
a glycerol solution with a bit of ammonia in it, along with trace minerals. They're also cellulose-forming, so yay, fiber!
Mostly, the exercise kind of wrapped itself up when I realized that glycerol worked just fine on its own as an energy source. Even if you posit that
colonizing bacteria is cheating, and I don't really think it is, all you'd need to do is synthesize any of the multitude of chemicals that your gut
flora can use but aren't absorbed by your intestines. The gas and bloating would be pretty bad, I imagine, but humans evolved that sort of symbiosis
for a reason! Our ancestors has to subsist on very limited diets for long periods of time as well.
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j_sum1
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When I consider how long some people manage to live on very little except flavoured ethanol I would say that the above two posts are quite plausible.
Surviving would be one thing. Staying healthy would be quite another.
Once you have glycerol, I can't imagine that synthesising lipids would be all that hard. Getting a suitable mix of fatty acids might be a trick
tough. A lot would depend on exactly what your hydrocarbon feedstock was.
The really tough one would be proteins. Whatever you do you would need to ingest some nitrogen-containing compounds of some sort. The body can
synthesise some amino acids but not all. I am not sure where you would start to redress this. Protein deficiency would knock you out eventually. I
think I would begin with a bit of urine recycling but that would obviously be a short-term measure.
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Herr Haber
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Clearly Not Atara:
DIY Chemistry certainly means something to you that it doesnt mean to others 
In a previous post you suggested using vomit, now feces... I cant wait for the next one !
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XeonTheMGPony
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Quote: Originally posted by clearly_not_atara  | Triacetin would be your first stop. Propylene is passed over SeO2 to convert it to allyl alcohol and treated with peroxide or osmium to glycerol.
Reaction with acetyl-X gives you the simplest edible molecule that isn't ethanol.
Once you've got that you might want to work on some carbohydrates. Oxidation of allyl alcohol or pyrolysis of glycerol gives acrolein, which doesn't
sound like a food, but dimerizing acrolein gives the much tastier 3,4-dihydropyran-6-carboxaldehyde... which you can reduce to the alcohol, eliminate
and dehydrogenate to a very reactive 6-methylenepyran. Assuming it works on conjugated alkenes (heh) OsO4 will convert this to
1,5-dioxo-2,3,4,6-tetrahydroxyhexane, which can be easily reduced to isomers of fructose.
This isn't quite a diet, but with a few ammonium salts and a sample of your own feces it should be enough to get a bacterial culture going... you can
grow samples and use established procedures to separate amino acids. Vitamins would be the next challenge.
Yeah, I cheated as soon as I got to fructose. Lol, feces.
[Edited on 29-3-2017 by clearly_not_atara] |
That'd be my first go too as well, Algae is dam near omnipresent once you have a slurry going you can start to grow an amazing variety off it.
Just need a bit of fuel (Sugars) and ph modifiers.
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Melgar
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| Quote: Originally posted by XeonTheMGPony | That'd be my first go too as well, Algae is dam near omnipresent once you have a slurry going you can start to grow an amazing variety off it.
Just need a bit of fuel (Sugars) and ph modifiers. |
Technically, algae is photosynthetic, and thus you don't have access to it. If you need a technical reason, let's say that everything was thoroughly
sterilized except people, who still had to shower in a disinfectant solution. They're pretty serious about making sure their search for life doesn't
get repeatedly invalidated by Earth microbes.
| Quote: Originally posted by j_sum1 | A lot would depend on exactly what your hydrocarbon feedstock was.
The really tough one would be proteins. Whatever you do you would need to ingest some nitrogen-containing compounds of some sort. The body can
synthesise some amino acids but not all. I am not sure where you would start to redress this. Protein deficiency would knock you out eventually. I
think I would begin with a bit of urine recycling but that would obviously be a short-term measure. |
You can get protein by colonizing your skin bacteria. In my case, I opted for acetobacter because it's specialized for living under aerobic,
acidic conditions, isn't toxic to people, and the acidic conditions generally prevent contamination by other microbes. They also can produce
cellulose and break down ethanol into acetic acid. I heard that bacterial protein sources aren't necessarily at the right ratio for people to survive
on, and often contain a bunch of crap that isn't good for our livers, but plenty of biochem reagents could certainly be extracted from
acetobacter colonies.
As far as hydrocarbons, on Titan, there's plenty of methane and ethane, as well as a large quantity of difficult-to-characterize chemicals called Tholins. Pyrolysis of this stuff would likely lead to a large variety of chemicals, similar to what's found in coal tar.
[Edited on 3/31/17 by Melgar]
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Texium
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Reading that Wikipedia page, it's stated that Titan's tholins are nitrogen rich, so a source of organic nitrogen containing compounds is already
present en masse, but what form most of it is in appears to be unknown. It seems likely that they contain PAH's as well as possibly azo compounds,
based on the orangey color.
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Melgar
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Ok, to make this more interesting, let's say you have virtually unlimited amounts of every saturated hydrocarbon with five carbons or less, and lots
of gooey tar-like stuff that pyrolyzes into a substance with a composition similar to coal tar, along with lots of HCN gas (fume hood not optional!).
Additionally, the entire base is automatically sterilized every 24 hours, since they were really quite serious about not wanting to contaminate Titan
with Earth microbes. So no bacterial colonies. 
Now, of the 20 amino acids our bodies use, we can make 11 of them. The nine amino acids humans cannot synthesize are phenylalanine, valine,
threonine, tryptophan, methionine, leucine, isoleucine, lysine, and histidine. Here are the structures.
Could you synthesize the nine essential amino acids, while subsisting on a diet of water and glycerol?
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