Organic chemistry question

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Organic chemistry question

Post by Sirius_Alpha on 7th August 2008, 11:51 pm

I know this is perhaps a rather broad question, but what organic molecules have thus far been detected in space? I'm trying to brush up on exobiology and organic chemistry. I figured Titan's atmosphere is a good place to start.

So far I have:
diacetylene,
methylacetylene
acetylene
propane
cyanoacetylene
hydrogen cyanide
cyanogen

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Re: Organic chemistry question

Post by Juramike on 10th August 2008, 8:38 am

Here is a list of some predicted more complex organic compounds from Titan spark tholin experiments:
(Where an electric discharge is shot through a gas mixture under conditions thought to simulate a planetary atmosphere):

(amounts in parentheses are detected amounts relative % normalized to glycine)

Urea (194)
Glycine [Gly] (100)
Beta-alanine (22)
Orotic acid (22) [heterocycle, whoo-hoo!)
Aspartic acid [Asp] (21)
Glutamic acid [Glu] (8)
Gamma aminobutyric acid [GABA] (6)
Xanthine (5)
5-Aminoorotic acid (4)
beta-Aminobutyric acid (4)
N-Methylglycine (3)
Adenine [A] (3)
beta-Aminoisobutyric acid (3)
2,6-Diaminopurine (2)
alpha-Aminobutyric acid (2)
3-Aminoalanine (2)
Hypoxanthine (1)
2-Methylalanine (1)
5-Aminouracil (1)
Guanine [G] (1)
Alanine (Ala) (1)
Uracil [U] (<1)
Diamino n-butyric acid (<1)
Valine [Val] (trace)
Threonine [Thr] (trace)
Isovaline (trace)

Similar compounds are also detected in Jovian and Triton atmosphere simulations, although the ratios are different.
Pyruvic acid (69) and Maelic acid (47) are major products of Jovian spark tholin experiments - again scaled to Glycine (100).

References:
Macdonald and Sagan Icarus 94 (1991) 354-367.
Sagan et al. Acc. Chem. Res. 25 (1992) 286-292.
Macdonald et al. Icarus 108 (1994) 137-145.

[I have a really spiffy EXCEL table that includes structures, but I can't figure how to attach it. ]

-Mike

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Re: Organic chemistry question

Post by Sirius_Alpha on 10th August 2008, 2:06 pm

O_o Thank-you for that. I read somewhere that glycine was detected a while back, but a later search failed to produce those findings.

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Re: Organic chemistry question

Post by Juramike on 10th August 2008, 4:43 pm

Glycine has been detected in interstellar clouds. It was detected by the radio emmissions of the conformation changes in the gas phase.

Check out:
Snyder Origins of Life and Evolution of Biospheres 27 (1997) 115-133. The search for interstellar glycine.
(pay-for article here: http://www.springerlink.com/content/h2035j1365v2244h/)


and also:
Ohishi and Isikawa Origins of Life and Evolution of Biospheres 26 (1996), 161. (detected using radio line spectral analysis around Sgr B2 cloud)

The Murchison meteorite contained a whole slew of organic compounds. But this was stuff brought down to earth, not remotely detected.

Wikiepedia: http://en.wikipedia.org/wiki/Murchison_meteorite
and the pay-for Nature article:
Kvenvolden et al Nature 228 (1970) 923-926. "Evidence for extraterrestrial amino-acids and hydrocarbons in the Murchison meteorite." http://www.nature.com/nature/journal/v228/n5275/pdf/228923a0.pdf

-Mike

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Re: Organic chemistry question

Post by Juramike on 10th August 2008, 4:55 pm

Link to a free article on how glycine could be formed from UV irradiation of interstellar ices:

Bernstein et al Nature 416 (2002) 402-403. "Racemic amino acids from the ultraviolet photolysis of interstellar ice analogues."
Freely availalble here: http://astrochem.org/PDF/Bernsteinetal2002.pdf

-Mike

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Re: Organic chemistry question

Post by Sirius_Alpha on 10th August 2008, 7:04 pm

Juramike wrote:Glycine has been detected in interstellar clouds. It was detected by the radio emmissions of the conformation changes in the gas phase.
This is what I was referring to earlier. Unfortunately, since then the Glycine detection was found to be spurious.

A Rigorous Attempt to Verify Interstellar Glycine
http://www.journals.uchicago.edu/doi/abs/10.1086/426677

Abstract wrote:In 2003, Kuan and coworkers reported the detection of interstellar glycine (NH2CH2COOH) based on observations of 27 lines in 19 different spectral bands in one or more of the sources Sgr B2(N-LMH), Orion KL, and W51 e1/e2. They supported their detection report with rotational temperature diagrams for all three sources. In this paper we present essential criteria that can be used in a straightforward analysis technique to confirm the identity of an interstellar asymmetric rotor such as glycine. We use new laboratory measurements of glycine as a basis for applying this analysis technique, both to our previously unpublished 12 m telescope data and to the previously published Swedish-ESO Submillimetre Telescope (SEST) data of Nummelin and colleagues. We conclude that key lines necessary for an interstellar glycine identification have not yet been found. We identify some common molecular candidates that should be examined further as more likely carriers of several of the lines reported as glycine. Finally, we illustrate that a rotational temperature diagram used without the support of correct spectroscopic assignments is not a reliable tool for the identification of interstellar molecules.
Emphasis mine.


Thank-you for those links, too. =)

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Re: Organic chemistry question

Post by Juramike on 10th August 2008, 8:41 pm

Well, golly...

It looks like the detection of interstellar glycine in a gas cloud is in dispute. Nice ref.
(But when/if they do manage to confirm it, I won't be real surprised.)

For detecting glycine on an extrasolar planet: that's going to be tough and need a different technique.

The blackbody radio emissions would probably swamp out any rotational signals (I'm guessing, I have no clue - this is the first time I was aware of looking at rotamer conformation transitions using radio waves).

More likely for a planetary surface you'd need to switch to vibrational transistions in the infrared spectrum. But the amino group and the carboxylic acid group of glycine are shared by many other molecules as well. (Acetic acid, formic acid, methyl amine, alanine, etc.). Even if you could get a clear/clean high res reflectance spectrum, it would be difficult to say "Ah ha! Glycine!"

Maybe the next mission to Titan will carry a lander equipped to separate and detect molecules such as glycine and friends. In situ analysis (HPLC? GCMS? IR? RAMAN?) following a chemical separation will probably be the best way to identify stuff from the murk. If it's that tough in our own solar system I can only imagine the difficulties beyond...

-Mike

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