Forum for Science, Industry and Business

Sponsored by:     3M 
Search our Site:

 

Researchers discover novel chemical route to form organic molecules

16.01.2012
An international team of scientists led by University of Hawai'i at Mânoa Professor Ralf I. Kaiser, Alexander M. Mebel of Florida International University, and Alexander Tielens of Leiden Observatory in the Netherlands, discovered a novel chemical route to form polycyclic aromatic hydrocarbons (PAHs) – complex organic molecules such as naphthalene carrying fused benzene rings – in ultra-cold regions of interstellar space. The team announced their findings in the January 3 issue of Proceedings of the National Academy of Sciences. Funding for the study was provided by the U.S. Department of Energy, Basic Energy Sciences.

These findings have crucial implications not only to reduce the emission of PAHs as toxic byproducts from internal combustion engines, but also rationalize the synthetic routes to a key class of organic molecules in the interstellar medium associated with the origins of life.


This graphic depicts PAH formation from combustion processes to interstellar space. Credit: Ralf Kaiser

On Earth, PAHs are associated with incomplete com­bus­tion processes and can be formed readily at elevated temperatures in combustion engines of cars and in cigarette smoke. Once liberated into the am­bient environ­ment, PAHs can be transferred into the lungs by inhalation and are strongly implicated in the degradation of hu­man health, particularly due to their high carcino­ge­nic risk po­­ten­­tial. PAHs are also se­rious water pollutants of marine ecosystems and bioaccumulate in the fatty tissue of living organisms. Together with leafy vegetables, where PAHs deposit easily, they have been further linked to soil contamination, food poisoning, liver lesions, and tumor growth.

Whereas on Earth, PAHs are classified as highly toxic, PAHs have been dubbed as the 'cradle of life' in the interstellar medium and are considered as key players in the astrobiological evolution. On the molecular level, functionalized PAHs carrying carbonyl and hydroxyl groups were found in organic extracts from the Murchison meteorite and form membrane-like boundary structures, the first in­dica­tions of a cell type structure, which are requisite to the origin of life. The compounds that are water soluble form non-soluble vesicles, constituting molecules that possess both polar and non-polar components. The hollow droplets formed by this lipid multilayer are essential for the origin of life process since they provide an environment in which the functionalized PAHs can evolve by isolating and protecting them from the surrounding medium.

Scientists have been researching the formation of PAHs in combustion flames and in the interstellar medium for decades, but the formation mechanism of even the simplest PAH prototype – the naphthalene molecule (C10H8) as present in earthly mothballs - has remained an open question. Textbook knowledge postulates that classical reaction mechanisms involve complex reactions following hydrogen abstraction and acetylene addition (HACA) sequences with substantial 'activation energies.' These processes can only operate at high temperatures of a few 1,000 K as present, for instance, in combustion processes and in the outflows of carbon-rich stars and planetary nebulae. However, in recent years it has become quite clear that interstellar PAHs are rapidly destroyed in the interstellar medium upon photolysis, interstellar shock waves driven by supernova explosions, and energetic cosmic rays. The destruction time scales are much shorter than the timescale for injection of new material into the interstellar medium by carbon-rich Asymptotic Giant Branch (AGB) stars and carbon-rich planetary nebulae as the descendants of AGB stars. Therefore, the ubiquitous presence of PAHs in the interstellar medium implies a cru­cial, previously unexplained route to a fast chemical growth of PAHs in the cold environment of the interstellar medium at temperatures down to 10 K, where the classical HACA reaction mechanism cannot function, since entrance barriers (classical 'activation energies') cannot be overcome.

To unravel the formation of naphthalene as the simplest representative of PAHs, University of Hawai'i at Mânoa chemists Dorian S.N. Parker, Fangtong Zhang, Seol Kim, and Ralf I. Kaiser conducted gas phase crossed molecular beam experiments in their laboratory and presented that naphthalene can be formed as a consequence of a single collision event via a barrier-less and exoergic reaction between the phenyl radical and vinylacetylene involving a van-der-Waals complex and submerged barrier in the entrance channel. Angular resolved mass spectrometer measurements of the reaction products together with isotopic labeling confirmed that naphthalene plus a single hydrogen atom, were produced. To support the derived mechanism involved in the formation of naphthalene, theoretical chemists at Florida International University (Alex Landera, Vadim V. Kislov, Alexander Mebel), merged the experimental results with theoretical computations. Theoretical computations also provide the three-dimensional distribution of electrons in atoms and thus the overall energy level of a molecule. Mebel's computations showed that naphthalene is formed from the reaction of a single phenyl radical colliding with vinylacetylene. Most importantly, since the temperatures of cold molecular clouds are very low (10 K), the computations indicate that the reaction has no entrance barrier ('activation energy').

"These findings chal­len­ge conventional wisdom that PAH-formation only occurs at high tem­pe­ra­tures such as in combustion systems and implies that low tem­pe­ra­tu­re chemistry can initiate the synthesis of the very first PAH in the interstellar medium," said co-author Tielens.

In the future, the team plans to expand these studies to unravel the formation routes to more complex PAHs like phenan­thre­ne and anthracene, and also to nitrogen-substituted PAHs such as indole and quinoline. This concept can be also expanded to functionalized PAHs with organic side chains thus bringing researchers closer to solving the decade old puzzle of how complex PAHs and their derivatives can be synthesized in combustion flames and in cold interstellar space.

Ralf Kaiser | EurekAlert!
Further information:
http://www.hawaii.edu

More articles from Life Sciences:

nachricht What the world's tiniest 'monster truck' reveals
23.08.2017 | American Chemical Society

nachricht Treating arthritis with algae
23.08.2017 | Empa - Eidgenössische Materialprüfungs- und Forschungsanstalt

All articles from Life Sciences >>>

The most recent press releases about innovation >>>

Die letzten 5 Focus-News des innovations-reports im Überblick:

Im Focus: Fizzy soda water could be key to clean manufacture of flat wonder material: Graphene

Whether you call it effervescent, fizzy, or sparkling, carbonated water is making a comeback as a beverage. Aside from quenching thirst, researchers at the University of Illinois at Urbana-Champaign have discovered a new use for these "bubbly" concoctions that will have major impact on the manufacturer of the world's thinnest, flattest, and one most useful materials -- graphene.

As graphene's popularity grows as an advanced "wonder" material, the speed and quality at which it can be manufactured will be paramount. With that in mind,...

Im Focus: Exotic quantum states made from light: Physicists create optical “wells” for a super-photon

Physicists at the University of Bonn have managed to create optical hollows and more complex patterns into which the light of a Bose-Einstein condensate flows. The creation of such highly low-loss structures for light is a prerequisite for complex light circuits, such as for quantum information processing for a new generation of computers. The researchers are now presenting their results in the journal Nature Photonics.

Light particles (photons) occur as tiny, indivisible portions. Many thousands of these light portions can be merged to form a single super-photon if they are...

Im Focus: Circular RNA linked to brain function

For the first time, scientists have shown that circular RNA is linked to brain function. When a RNA molecule called Cdr1as was deleted from the genome of mice, the animals had problems filtering out unnecessary information – like patients suffering from neuropsychiatric disorders.

While hundreds of circular RNAs (circRNAs) are abundant in mammalian brains, one big question has remained unanswered: What are they actually good for? In the...

Im Focus: RAVAN CubeSat measures Earth's outgoing energy

An experimental small satellite has successfully collected and delivered data on a key measurement for predicting changes in Earth's climate.

The Radiometer Assessment using Vertically Aligned Nanotubes (RAVAN) CubeSat was launched into low-Earth orbit on Nov. 11, 2016, in order to test new...

Im Focus: Scientists shine new light on the “other high temperature superconductor”

A study led by scientists of the Max Planck Institute for the Structure and Dynamics of Matter (MPSD) at the Center for Free-Electron Laser Science in Hamburg presents evidence of the coexistence of superconductivity and “charge-density-waves” in compounds of the poorly-studied family of bismuthates. This observation opens up new perspectives for a deeper understanding of the phenomenon of high-temperature superconductivity, a topic which is at the core of condensed matter research since more than 30 years. The paper by Nicoletti et al has been published in the PNAS.

Since the beginning of the 20th century, superconductivity had been observed in some metals at temperatures only a few degrees above the absolute zero (minus...

All Focus news of the innovation-report >>>

Anzeige

Anzeige

Event News

Call for Papers – ICNFT 2018, 5th International Conference on New Forming Technology

16.08.2017 | Event News

Sustainability is the business model of tomorrow

04.08.2017 | Event News

Clash of Realities 2017: Registration now open. International Conference at TH Köln

26.07.2017 | Event News

 
Latest News

What the world's tiniest 'monster truck' reveals

23.08.2017 | Life Sciences

Treating arthritis with algae

23.08.2017 | Life Sciences

Witnessing turbulent motion in the atmosphere of a distant star

23.08.2017 | Physics and Astronomy

VideoLinks
B2B-VideoLinks
More VideoLinks >>>