Glycolaldehyde

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Glycolaldehyde
IUPAC name

2-hydroxyacetaldehyde

Identifiers
CAS number 141-46-8 YesY
PubChem 756
ChemSpider 736 YesY
KEGG C00266 YesY
ChEBI CHEBI:17071 YesY
Jmol-3D images Image 1
Properties
Molecular formula C2H4O2
Molar mass 60.052 g/mol
Density 1.065 g/mL
Boiling point 131.3 °C; 268.3 °F; 404.4 K
Related compounds
Related aldehydes 3-Hydroxybutanal

Lactaldehyde

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Except where noted otherwise, data are given for materials in their standard state (at 25 °C (77 °F), 100 kPa)
Infobox references

Glycolaldehyde (HOCH2-CH=O) is the smallest possible molecule that contains both an aldehyde group and a hydroxyl group. It is the only possible diose, a 2-carbon monosaccharide, although a diose is not strictly a saccharide. While not a true sugar, it is the simplest sugar-related molecule.[2] Glycolaldehyde is an intermediate in the formose reaction. In the formose reaction two formaldehyde molecules condense to make glycolaldehyde. Glycolaldehyde then is converted to glyceraldehyde. The presence of thisglycolaldehyde in this reaction demonstrates how it might play an important role in the formation of the chemical building blocks of life. Nucleotides, for example, rely on the formose reaction to attain its sugar unit. Nucleotides are essential for life, because they compose the genetic information and coding for life.

Glycolaldehyde forms from many precursors, including the amino acid glycine. It can form by action of ketolase on fructose 1,6-bisphosphate in an alternate glycolysis pathway. This compound is transferred by thiamine pyrophosphate during the pentose phosphate shunt.

In purine catabolism, xanthine is first converted to urate. This is converted to 5-hydroxyisourate, which decarboxylates to allantoin and allantoic acid. After hydrolyzing one urea, this leaves glycolureate. After hydrolyzing the second urea, glycolaldehyde is left. Two glycolaldehydes condense to form erythrose 4-phosphate, which goes to the pentose phosphate shunt again.

Glycolaldehyde is the second most abundant chemical formed when preparing pyrolysis oil (up to 10% by weight).[3]

Formation in Space

Formation of Glycolaldehyde in star dust

Glycolaldehyde was found in a low-mass molecular cloud of a forming star (IRAS 16293-2422). More recently it was found in a high-mass cores as well. Since the detection of this organic compound many research groups have attempted to theorize various chemical routes to explain its formation in stellar systems.

One theory is glycolaldehyde formed on the surface of dust grains. Dust grains allow molecules to grow and react, such as hydrogenation in the case of glycolaldehyde. A particular research group focused on constant temperature collapse of massive molecular cores. When conditions like decreased temperature and appropriate densities, similar to those of massive cores, are considered, only a few reactions supported grain-surface synthesis. A theorized intermediate is formyl radical (CHO). This intermediate is a well-known compound to exist in cold, photon-dominated regions of stellar clouds. HCO is theorized to have reacted with itself on a grain of dust and gained hydrogen's forming glycolaldehyde. The star must maintain lower temperatures for this theory to be plausible, and the longer the star collapses at this temperature (3-15 K) the more time for complicated compound to form.

Glycolaldehyde may also be formed through grain surface reactions in ices containing methanol. It was found that UV-irradiation of methanol ices containing CO yielded organic compounds such as glycolaldehyde and methyl formate, the more abundant isomer of glycolaldehyde. The abundances of the products slightly disagree with the observed values found in IRAS 16293-2422, but this can be accounted for by temperature changes. Ethylene Glycol and glycolaldehyde require temperatures above 30 K.[4][5] The general consensus among the astrochemistry research community is in favor of the grain surface reaction hypothesis. However, some scientists believe the reaction occurs within denser and colder parts of the core. The dense core will not allow for irradiation as stated before. This change will completely alter the reaction forming glycolaldehyde.[6]

The different conditions studied indicate how problematic it could be to study chemical systems that are light-years away. The conditions for the formation of glycolaldehyde are still unclear. At this time the most consistent formation reactions seems to be on the surface of ice in stardust.

Formation on Prebiotic Earth

When Earth was first formed the atmosphere has been theorized to consist of gases such as methane, (CH4), ammonia (NH3), water vapor, and other simple gases. These gases were exposed to electrical discharge following the formation of formaldehyde in abundance and glycolaldehyde in lesser amounts. This theory is similar to that of Miller-Urey. After the electrical discharge to early Earth’s atmosphere, formaldehyde and glycolaldehyde then rained down to Earth and were deposited in aquifers that theoretically contained other solvents such as formamide. Formamide has been shown to provide an electrophilic background that is necessary for simple sugars to react further, producing more complex sugars.

The aquifers had a high alkaline environment. The Earth’s atmosphere, consisting of CO2, was able to lower the aquifers pH enabling formation of complex sugars. Some scientists speculate borates in these aquifers were able to permit formation of complex sugars, such as ribose, by forming borate complexes with the final pentose. Glycolaldehyde bound to borate enolized, meaning the carbon oxygen bond gave electrons to the neighboring carbon creating a double bond. The oxygen received hydrogen due to the creation of the double bond. Glycolaldehyde then participated in aldol reactions acting as a nucleophile. This process yielded the first complex sugar on Earth.[7][8]

Some scientists hypothesize that sugars were not actually made in early Earth’s atmosphere like explained above, but rather occurred during early metabolism. Short dipeptides could facilitate the formation of complex sugars. Specifically L-valyl-L-valine was used as a catalyst to form pentoses from glycolaldehyde. This formation actually shows stereo specificity. The only naturally occurring isomer of ribose is the D-enantiomer, and when L-valyl-L-valine is used as a catalyst the D enantiomer is the only product. This is a nice explanation as to why the specific enantiomer occurs in nature.[9]

In space

Sugar molecules in the gas surrounding a young Sun-like star.[1]

Glycolaldehyde has been identified in gas and dust near the center of the Milky Way galaxy,[10] in a star-forming region 26000 light-years from Earth,[11] and around a protostellar binary star, IRAS 16293-2422, 400 light years from Earth.[12][13] Observation of in-falling glycolaldehyde spectra 60 AU from IRAS 16293-2422 suggests that complex organic molecules may form in stellar systems prior to the formation of planets, eventually arriving on young planets early in their formation.[5]

Detection

The interior region of a dust cloud is known to be relatively cold. With temperatures as cold as 4 Kelvin the gases within the cloud will freeze and fasten themselves to the dust, which provides the reaction conditions conclusive for the formation of complex molecules such as glycolaldehyde. When a star has formed from the dust cloud the temperature within the core will increase. This will cause the molecules on the dust to evaporate and be released. The molecule will emit radio waves that can be detected and analyzed. Atacama Large Millimeter/submilliter Array also known as ALMA first detected glycolaldehyde. ALMA consists of 66 antennas that can detect the radio waves emitted from the stardust.[14]

References

  1. ↑ "Sweet Result from ALMA". ESO Press Release. Retrieved 3 September 2012. 
  2. ↑ Carroll, P., Drouin, B., and Widicus Weaver, S., (2010). "The Submillimeter Spectrum of Glycolaldehyde". Astrophys. J. 723: 845–849. Bibcode:2010ApJ...723..845C. doi:10.1088/0004-637X/723/1/845. 
  3. ↑ Moha, Dinesh; Charles U. Pittman, Jr. & Philip H. Steele (March 2006). "Pyrolysis of Wood/Biomass for Bio-oil:  A Critical Review". Energy & Fuels 206 (3): 848–889. doi:10.1021/ef0502397. Retrieved 5 September 2013. 
  4. ↑ Öberg, K. I.; Garrod, R. T., van Dishoeck, E. F. & Linnartz, H. (09 2009). "Formation rates of complex organics in UV irradiation CH_3OH-rich ices. I. Experiemtns". Astronomy and Astrophysics 504 (3): 891–913. doi:10.1051/0004-6361/200912559. 
  5. ↑ 5.0 5.1 Jørgensen, J. K.; Favre, C.; Bisschop, S.; Bourke, T.; Dishoeck, E.; Schmalzl, M. (2012). Detection of the simplest sugar, glycolaldehyde, in a solar-type protostar with ALMA. eprint. 
  6. ↑ Woods, P. M; Kelly, G. Viti, S., Slater, B., Brown, W. A., Puletti, F., Burke, D. J., & Raza, Z. (2013). "Glycolaldehyde Formation via the Dimerisation of the Formyl Radical". The Astrophysical Journal 777 (50). doi:10.1088/0004-637X/777/2/90. 
  7. ↑ Kim,, H.; Ricardo, A., Illangkoon, H. I., Kim, M. J., Carrigan, M. A., Frye, F., & Benner, S. A. (2011). "Synthesis of Carbohydrates in Mineral-Guided Prebiotic Cycles". Journal of the American Chemical Society 133 (24)): 9457–9468. doi:10.1021/ja201769f. 
  8. ↑ Benner,, S. A.; Kim, H.; Carrigan, M. A. (2012). "Asphalt, Water, and the Prebiotic Synthesis of Ribose, Ribonucleosides, and RNA". Accounts of Chemical Research 45 (12): 2025–2034. doi:10.1021/ar200332w. 
  9. ↑ Cantillo,, D.; Ávalos, M.; Babiano, R.; Cintas, P.; Jiménez, J. L.; Palacios, J. C. (2012). "On the Prebiotic Synthesis of D-Sugars Catalyzed by L-Peptides Assessments from First-Principles Calculations". Chemistry a European Journal 18: 8795–8799. doi:10.1002/chem.201200466. 
  10. ↑ Hollis, J.M., Lovas, F.J., & Jewell, P.R. (2000). "Interstellar Glycolaldehyde: The First Sugar". The Astrophysical Journal 540 (2): 107–110. Bibcode:2000ApJ...540L.107H. doi:10.1086/312881. 
  11. ↑ Beltran, M. T.; Codella, C.; Viti, S.; Neri, R.; Cesaroni, R.; (11/2008). First detection of glycolaldehyde outside the Galactic Center. eprint arXiv:0811.3821. 
  12. ↑ Than, Ker (August 29, 2012). "Sugar Found In Space". National Geographic. Retrieved August 31, 2012. 
  13. ↑ Staff (August 29, 2012). "Sweet! Astronomers spot sugar molecule near star". AP News. Retrieved August 31, 2012. 
  14. ↑ "Building blocks of life found around young star". Retrieved 11 December 2013. 

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