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Organic molecules (DOC)

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Organic molecules (DOC) Powered By Docstoc
					Students: Alberty Pit, Reuland Yves, Heinrichs Martin

Teacher:   Daman Pascal

School:    Lycée de garçons de Luxembourg


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SUMMARY
The purpose of our presentation is to analyze the existence and the constitution of
organic molecules in the molecular clouds in space.

New discoveries made with GBT (Green Bank Telescope) have proved the existence
of organic molecules in the interstellar molecular clouds. In fact in the cloud called
Sagittarius B2(N), that is near the centre of our galaxy, organic molecules were
discovered.

The discovery of those organic molecules in the coldest regions of the interstellar
medium has certainly forced scientists to rethink their view of the interstellar
chemistry.

These large molecules were accumulated by some chemical reactions during the gas
phase. The presence of H2 molecules is essential for this synthesis, but to form H2
molecules energy is needed, which is not present in the interstellar medium. The
formation of interstellar H2 is produced on the surface of grains of dust (in fact the
mass of an interstellar cloud is constituted by 99 % of gas and 1 % of dust).
The hydrogen atoms that travel in the interstellar medium because of the thermal
agitation enter in collision with a grain of dust and fix themselves at the surface. This
is called absorption.




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History
In 1990 two professors of the University of Rennes (CNRS) Ian Smith and Bertrand
Rowe discovered that in the presence of carbonized dust like soot, silicates, ice and
benzenes, neutral molecules are constituted. This reaction is held faster when the
temperature is lower, between 10 and 40 K. They found organic molecules like NH3,
C2N2, C2H4, C2H6, prebiotic neutral complexes in the whole. The explanation of
this phenomenon is that the temperature was so low that the two molecules had, when
they entered in collusion, plenty of time to find the right spatial configuration to make
a chemical reaction possible.


New discoveries made with GBT (Green Bank Telescope) have proved the existence
of organic molecules in the interstellar molecular clouds. In fact in the cloud called
Sagittarius B2(N), that is near the centre of our galaxy, organic molecules like e.g.
acetamide (CH3CONH2), cyclopropénone (H2C3O), propénal (CH2CHCHO),
propanal (CH3CH2CHO), and kéténimine (CH2CNH) were discovered.

In 2004, a team of scientists found a new class of organics in comet dust captured
from comet Wild 2 by NASA’s stardust spacecraft. Scott Sandford, the study's lead
author and a scientist from NASA's Ames Research Center in California's Silicon
Valley said about this discovery: “A portion of the organic material in the samples is
unlike anything seen before in extraterrestrial materials”. The analysis of these
Stardust samples indicated that they contain molecules made of carbon and hydrogen
that are common in interstellar space. These molecules are called: Polycyclic aromatic
hydrocarbons (PAHs). Certain of those PAHs contain as well oxygen and nitrogen,
which play important rules in terrestrial biochemistry. So scientists believe that
comets are largely made of the original material of which our solar system formed.
According to those scientists further analysis of comet dust may help them to get
important insights into the evolution of the sun, its planets and possibly the origin of
life.




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Explanations

      Cosmic Dust:

Cosmic dust is composed of particles in space which are a few molecules to 0.1 mm
in size. Cosmic dust can be further distinguished by its astronomical location; for
example: intergalactic dust, interstellar dust and dust clouds around other stars.
Stardust grains are contained within the meteorites, from which they are extracted in
terrestrial laboratories from meteorites. The meteorites were formed along with the
sun and planets and have essentially the same ages. Each Stardust grain existed before
the earth was formed. The meteorites have preserved the previously interstellar
Stardust grains since that time. Stardust is a scientific term rather than a poetic one,
referring to refractory dust grains that condensed from cooling ejected gases from
individual presolar stars.

An important property of Stardust is the hard, refractory, high-temperature nature of
the grains. Prominent are silicon carbide, graphite, aluminum oxide, aluminum spinel,
and other such grains that would condense at high temperature from a cooling gas,
such as in stellar winds or in the decompression of the inside of a supernova. They
differ greatly from the solids formed at low temperature within the interstellar
medium.

(Wikipedia)



      Acetamide (CH3CONH2):

It is a white crystalline solid in a pure form. On earth it
is used as a plasticizer and in the synthesis of many
other organic compounds.


Recent work on the Robert C. Byrd Green Bank
Telescope has resulted in the discovery of several
organic (carbon-based) compounds near the center of
the Milky Way galaxy. Acetamide has been detected.
This is particularly important as acetamide has a peptide bond, the essential bond
between amino acids in proteins. This supports the theory that organic molecules that
can lead to life (as we know it on Earth) can form in space.




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       Propionaldehyde (Propanal) (CH3CH2CHO):

It is a colorless liquid with a fruity odour.




       Propenal or Acrolein (CH2=CH-CHO):

This is the simplest unsaturated aldehyde (An aldehyde is
an organic compound containing a terminal carbonyl
group. The word aldehyde seems to have arisen from
alcohol dehydrogenated) in organic chemistry. Propenal
is described as having a disagreeable, acrid smell. It can
cause serious damage in contact with the skin.

In World War I it was used as a chemical weapon.

Glycerol, heated to 553 °K, decomposes into acrolein.



       Ketenimines:

Those are a group of organic compounds sharing a common functional group with the
general structure R1 R2 C=C=NR3 . The parent compound is ketenimine or CH2CNH.




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Formation of organic molecules in outer space
    Formation of H2

The hydrogen atoms that cross the interstellar medium, because of the thermal
agitation enter in collusion with grains of cosmic dust and stick at their surface. This
phenomenon is called absorption. They don’t stay motionless, but on the contrary they
are animated with a great mobility on the surface. They change rapidly from one place
to another. It happens that two hydrogen atoms, present at the same moment and the
same place, recombine to form a molecule. The grain of dust is used as a sort of
catalyst. The formed molecule can be reinjected into space, this process is called
desorption. Laboratory experiments have shown that the formation of H2 molecules
on grains of dust is an effective process, to such a point that if the conditions are
favorable (in particular the absence of UV radiation in deep molecular clouds), all the
hydrogen exists in the molecular form. This hydrogen molecule is at the origin of the
interstellar chemistry in gas phase and the formation of more and more complex
molecules. The process leading to the formation of H2 is also able to form other
molecules even the most complex organic molecules that have been observed yet.

This chemical process, possible even in the very extreme conditions of the interstellar
medium, contributes to the complexity of cosmic matter which leads from the
elementary particles to the components of life.




    Traces of possible prebiotic forms of life

Thanks to the dipole moment of the asymmetric molecules the radio astronomer can
detect their presence in the Milky Way on their milimetric stripes and trace the lines
of isodensity of the clouds that they are observing. They have already found hundreds
of molecular stripes in space and thousands of molecular clouds in infra-red. Old stars
eject into space the heavy compounds that they have produced during their lifetime.
This phenomenon also exists for supernovae which create the mean part of the
elements of Mendeleev table in a fragment of a second. Among the elements
produced is carbon.

As we have already explained, hydrogen atoms are very abundant in space, so the
carbon atoms produced by the supernovae can interact rapidly.



Most of the molecular stripes discovered in space are in relation with the prebiotic
processes (as carbon monoxide (CO), hydrocyanic acid (HCN) or formaldehyde
(HCHO)).

We cannnot say that those molecules interact in the interstellar medium to form
polymers or aromatic components based on benzene (C6H6) but the hydrogen –
nitrogen - carbon sequence to HCN and HCHO shows that this interaction is not
impossible.


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The most troubling fact and at the same time the fact which should keep the
professionals maintaining their research is the medium in which the organic
molecules exist and which is strongly hostile to them especially because those
molecules are very fragile. The interstellar medium is frozen and not very dense. The
molecules exist in gas fields that are at a temperature that varies between 10 and 100
K (more then 160° below 0). At such low temperatures it seems miraculous that the
matter is not inert. There are 100 to 10,000 molecules/cm3 against 1019 molecules/cm3
in the air on earth. The frequency of meetings is very low, at most one every thousand
years.

To explain this we have to say that in space the ejected photons of the stars can hit the
atoms or the molecules and tear off their electrons. Consequently the matter has an
electric charge and is ionized. Until now astronomers have considered that interstellar
chemistry could only proceed by this mechanism. In such a rarified and frozen
medium the thermal energy is incompetent to create any chemical reaction.



Prospects:
The Atacama Large Millimeter Array (ALMA), which will cover a frequency range
from 30 to 950 GHz, will be able to study and to analyze much more organic
molecules emitting in frequency ranges which are not covered by classic radio-
telescopes. The opportunity of being able to arrange the movable antennas and the
remarkable accuracy of pointing will allow us to penetrate into space regions never
explored until now and maybe to find new organic molecules, thus bringing us nearer
to the origins of life.



SOURCES:

http://media4.obspm.fr/public/IUFM/chapitre3/souschapitre2/section4/page11/section
3_2_4_11.html

http://www.astrosurf.com/luxorion/bioastro-contaminatioet5.htm


http://www.techno-science.net/?onglet=news&news=3040

http://www-dapnia.cea.fr/Sap/Activites/Projets/ISOCAM/composition.shtml

http://stardust.jpl.nasa.gov/ .

http://stardust.jpl.nasa.gov/news/news108.html

http://wikipedia.com




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