Transcript Chemistry in protostellar disks

Hunt for molecules
at the origin of life
-93.10
ion
R
D
-93.20
-93.30
-93.40
Energy
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-93.50
-93.60
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-4.0
-3.0
HNC+H
-2.0
-1.0
0.0
1.0
2.0
3.0
4.0
HCN+H
Y. Ellinger, M. Lattelais, G. Berthier
Laboratoire d’Etude Théorique
des Milieux Extrêmes
Cet exposé s’appuie sur le travail réalisé au LETMEX par
G. Berthier, JM. Chiaramello, C. Dimur, Y. Ellinger, M. Lattelais, F. Pauzat, D. Talbi,
dans le cadre des Programmes Nationaux PCMI, Planétologie et du GDR Exobiologie.
What do we mean by molecules at the origin of life ?
HN-C-O
Prebiotic molecules on Earth: The Miller/Urey Experiments
By the 1950, scientists were in hot pursuit of the origin of life. Around the world, the scientific
community was examining what kind of environment would be needed to allow life to begin. In
1953, Miller and Urey conducted an experiment which would change the approach of scientific
investigation into the origin of life*.
Miller took molecules which were
believed to represent the major
components of the early Earth’s
atmosphere and confined them in a
closed system: CH4, NH3, H2, H2O.
Electric discharges were run in the
system to simulate lightning storms
believed to be common on the early
Earth.
After a week 10-15% of the carbon
was in the form of organic materials.
About 2% of the carbon was in the
form of some amino acids.
In 1961, Oro found that amino acids could be made from HCN and NH3 in aqueous solution. He also
found a large amount of Adenine, a major component of DNA, RNA and ATP and the genetic code.
* In fact the first such experiment is that of Urea synthesis in 1820.
Prebiotic molecules in space: Meteorites, Comets, ISM
In 1969, a meteorite fell over Murchison, Australia.
It is a type of meteorite known as a carbonaceous
chondrite. It appears to be older than the solar system
- over 4.5 billion years.
In addition, meteorites of this type contain many of
the same amino acids that are found in living tissue.
About 70 amino acids have been identified, including
8 out of the 20 present in living organisms.
In 1971, the simplest species containing the peptide
bond H2N-CH=O (formamide) was identified in the
ISM (but none of its isomers has been detected).
Meteorite found in Allende, Mexico.
In 1972, a precursor of the peptide bond, HNCO has
been identified in the ISM.
In 1997-98, the same molecules were found in
comets Haukutake and Hale-Bopp.
The more elaborate material has only been found associated with solids.
The weight of prebiotic molecules in astrochemistry
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From 1998 to 2005
The possible contributions of Quantum Chemistry
Avoid erroneous conclusions.
Propose new molecules to be
searched.
Interpret/explain observations
But
How do we compare to
observations ?
Precision and error bars
Spectroscopic Data :
Requested
Delivered
Rotational constants
Dipole moment
<1%
5%
possible
possible
Vibrational frequencies
Absolute intensities
<1%
10%
almost
Not yet
Electronic transitions
Transition moments
<0.2 eV
<0.1%
need work
sometimes
Precision and error bars
Energetical Data:
Requested
Delivered
Proton affinities
1 kcal/mol
possible
Isomerization energies
1 kcal/mol
possible
Dissociation energies
1 kcal/mol
almost
Physisorption energies
Ionisation energies
Activation barriers
0.1 kcal/mol
5 kcal/mol
0.2 kcal/mol
possible
not yet
need work
About the production of Adenine in ISM
(according to Chakrabarti et al 2000)
The “oligomerization” of HCN provides a particularly intriguing route to
chemical evolution because it could lead to the production of Adenine.
HCN + HCN  CH(NH)CN
CH(NH)CN + HCN  NH2CH(CN)2
NH2
NH2CH(CN)2 + HCN  NH2(CN)C=C(CN)NH2
N
NH2(CN)C=C(CN)NH2 + HCN  C5H5N5 ( Adenine) 
N
H
N
N
Assuming for each step a temperature-independent rate coefficient of
k = 10-10 cm3 s-1, they found considerable formation of Adenine on
relatively short time-scale (188 yr).
Can this reaction really occur efficiently under the 10-100 K conditions
of the ISM?
About the feasability of HCN + HCN  CH(NH)CN
(Theory:
I.W.M. Smith, D. Talbi, E. Herbst, A & A, 369, 611 (2001) )
The reaction is endothermic
There is an activation barrier of 71 kcal/mol (36000 K)
The rate coefficient of the dimer kdim (cm3 s-1) is given by
kdim(T) = 10-10 exp(-36000/T)
The reaction cannot really occur under the 10-100 K of the ISM
I
H C
N
H C
H
N
II
C
C
N
C
N
C
N
H
III
N
C
H
H
H
H
C
N
IV
H
H
V
N
C
H
N
C
N
Looking for prebiotic phosphorus
Most stable molecule [C H O N] :
Most stable molecule [C H O P] :
HNCO
HPCO
Rotational constants of HNCO (GHz)
Be
CCSD
6-311G**
B 11.085
C 10.932
6-311++G**
11.068
10.915
« Experiment »
CCSD(T)
6-311G**
DFT/B3LYP
6-311++G**
6-311G**
6-311++G**
10.955
10.804
11.091
10.954
11.078
10.943
10.972
10.820
B = 11.071
C = 10.911
Prediction of rotational constants for HPCO (GHz)
Be
B
C
CCSD
6-311G**
6-311++G**
DFT/B3LYP)
6-311G**
6-311++G**
5.5165
5.4005
5.5212
5.4049
5.5357
5.4169
« Best estimate »
B = 5.519 ± 0.005
5.5017
5.3842
C = 5.402 ± 0.005
Theory: C. Dimur, F. Pauzat, Y. Ellinger, G. Berthier , Spectr. Chim. Acta A, 57, 851 (2001)
Origin of the peptide bond
H
Relative energy (Kcal/mol)
H
80
O
HH
C
H
H
60
N H
C
C
H
H
O
C
N
H
N
OH
H
N
O
The most stable compound that can
be formed from [C,3H,O,N] is :
formamide.
It is the simplest example of peptide
bond.
40
The peptide bond is the most
stable link.
20
Only the lowest energy isomer is
observed. Predictions (GHz, D):
H
N C
H
H
N
H
0
H
C
O
OH
Exp:
Theo:
B=11.3738
B=11.3321
C=9.8337
C=9.8246
Theory: J.M. Chiaramello, D. Talbi, G. Berthier, Y. Ellinger, Int. J. Astrobiology, in press (2005)
Relative energy (Kcal/mol)
Sulphur analogues of the peptide bond
80
The most stable compound that can
be formed from [C,3H,S,N] is :
thio-formamide.
60
It is the simplest example of peptide
bond with a sulphur atom.
HH
C
H
H
H
N H
C
S
40
H
H
C N
H
C
H
N
H
S
N
The peptide bond is the most
stable link.
S
SH
H
20
N
H
H
H
C
SH
Best chance for observation is
H2N-CH=S.
Predictions(GHz, D):
N C
H
0
S
Theo:
B=6.0342
µ=4.9
C=5.4921
Theory: J.M. Chiaramello, D. Talbi, G. Berthier, Y. Ellinger, Int. J. Astrobiology, in press (2005)
Phosphorus compounds
Relative energy (Kcal/mol)
The most stable compound that can
be formed from [C,3H,O,P] is :
methyl-phosphine-oxide.
80
It has no relation with the peptide
bond.
It may be an intermediate on the
route to prebiotic phosphorus
compounds.
60
40
H
P
20
H
P
H
0
HH
C
H
C
O
H
H
H
P
C
O
H
C
OH
Best chance for observation is
H3C-P=O.
Predictions(GHz, D):
OH
P
Theo:
B=8.0275
µ=3.5
C=6.4779
Theory: J.M. Chiaramello, D. Talbi, G. Berthier, Y. Ellinger, Int. J. Astrobiology, in press (2005)
Origin of the peptide bond
80
E(kcal/mol)
H3C
H
70
H3C
N
H3C
H3C
H3 C
H3 C
60
O
O
H
O
O
H3C
CH3
CH3
N
N
H3C
N
H
The most stable compound
that can be formed from
[3C,7H,O,N] is :
N-methyl acetamide.
H3 C
O
H
N
H3C
N
O CH3
H
O
N
CH3
H
50
H3C
H3C
40
The order of stability shows :
N
OH
H
N
OMe
H3C
30
H
20
H3C
N
CH3
HN
CH3
1rst : N-C-O connectivity
peptide bond
2nd : C-N-O connectivity
OMe
OH
3rd : 3-membered rings
10
0
O
N
H3C
N
H
CH3
O
Theory: M. Lattelais, DEA (Paris VI), (2005)
Relative energies of selected isomers
of Glycine
E (kcal/mol)
HO-CH2-C(NH2)=O
12.1
H2N-CH2-COOH
10.0
CH3- O-C(NH2)=O
4.5
CH3- NH-COOH
0.0
Theory: M. Lattelais, DEA (Paris VI), (2005)
Comparison Glycine/Alanine
E (kcal/mol)
E (kcal/mol)
CH3-O-CH2-C(NH2)=O
22.0
HO-CH2-C(NH2)=O
12.1
CH3-NH-CH2-COOH
19.2
H2N-CH2-COOH
10.0
NH2-CH(CH3)-COOH
12.4
CH3- O-C(NH2)=O
4.5
NH2-CH2-CH2-COOH
11.6
CH3- NH-COOH
0.0
OH-CH(CH3)-C(NH2)=O
11.1
CH3-CH2-OC(NH2)=O
3.7
CH3-CH2-NH-COOH
0.0
Theory: M. Lattelais, DEA (Paris VI), (2005)
Comparison between protonated Glycine and Alanine
E(kcal/mol)
E (kcal/mol)
HO-CH2-C(NH3
+)=O
CH3- O-C(NH3+)=O
CH3- NH2
+-COOH
H3N+-CH2-COOH
CH3-O-CH2-C(NH3+)=O
39.6
OH-CH(CH3)-C(NH3+)=O
28.2
CH3-CH2-OC(NH3+)=O
22.2
CH3-CH2-NH2+-COOH
17.5
CH3-NH2+-CH2-COOH
10.7
+NH -CH(CH )-COOH
3
3
6.6
22.1
16.0
10.6
0.0
+NH -CH -CH -COOH
3
2
2
0.0
Theory: M. Lattelais, DEA (Paris VI), (2005)
Comparison between ionized Glycine and Alanine
E(kcal/mol)
E (kcal/mol)
[CH3- O-C(NH2)=O]
+
[HO-CH2-C(NH2)=O]
[CH3- NH-COOH]
[H2N-CH2-COOH]
+
+
17.9
+
8.8
4.7
0.0
[CH3-CH2-OC(NH2)=O] +
24.2
[CH3-O-CH2-C(NH2)=O] +
22.9
[OH-CH(CH3)-C(NH2)=O] +
12.3
[CH3-CH2-NH-COOH] +
11.3
[NH2-CH(CH3)-COOH] +
6.3
[CH3-NH-CH2-COOH] +
4.1
[NH2-CH2-CH2-COOH]+
0.0
Theory: M. Lattelais, DEA (Paris VI), (2005)
CONCLUSIONS and PERSPECTIVES
The peptide bond type of linkage is more common than originally thought.
The simplest molecule containing this bond, H2N-CH=O is more stable
than any of its isomers. This result is confirmed on N-methyl acetamide.
Neutral Glycine and -Alanine are not the most stable compounds.
Protonated Glycine and -Alanine are the most stable species.
Biological protonated -Alanine is found 6.6 kcal/mol higher in energy.
Ionized Glycine and -Alanine are the most stable species.
Biological ionized -Alanine is found 6.3 kcal/mol higher in energy.
Results are consistent with the analysis showing that
Glycine and -Alanine are the major components in chondrites CI.
Analysis of interstellar grains may be a decisive step in
the understanding of the origin of prebiotic material.
END
Common point in Miller/Devienne type of
experiments
Miller : presence of WATER
Devienne : NO WATER





Electric discharges to simulate
lightnings.
Particle beams to simulate
cosmic rays:
X and  rays,
electrons ~5 MeV,
protons ~12 MeV.
UV at < 2000 Å to create free
radicals.
Thermal energy to simulate
volcanism.
Impact of high energy beams of
nitrogen, hydrogen on a graphite
surface in presence of thermal
oxygen.
There is enough energy to
overcome any energy barrier and
reach the most stable species.
Science fiction: life based on silicon ?
Relative energy (Kcal/mol)
HH
Si
H
80
H
Si
H
O
N
H
N
O
H
H
N
OH
The most stable compound that can be
formed from [Si,3H,O,N] is :
sila-formamide.
It is the simplest example of peptide
bond with a silicon atom.
N H
Si
H
Si
H
O
60
The peptide bond is the most
stable link that can be formed.
40
H
N Si
20
H
H
OH
Best chance for observation is
H2N-SiH=O.
Predictions(GHz, D):
H
N Si
H
0
O
Theo:
B=7.2292
µ=5.3
C=6.1164
Theory: J.M. Chiaramello, D. Talbi, G. Berthier, Y. Ellinger, Int. J. Astrobiology, in press (2005)
Comparaison between Glycine and Alanine
E (kcal/mol)
E (kcal/mol)
CH3-O-CH2-C(NH2)=O
22.0
HO-CH2-C(NH2)=O
12.1
CH3-NH-CH2-COOH
19.2
H2N-CH2-COOH
10.0
NH2-CH(CH3)-COOH
12.4
CH3- O-C(NH2)=O
4.5
NH2-CH2-CH2-COOH
11.6
CH3- NH-COOH
0.0
OH-CH(CH3)-C(NH2)=O
11.1
CH3-CH2-OC(NH2)=O
3.7
CH3-CH2-NH-COOH
0.0
Theory: M. Lattelais, DEA (Paris VI), (2005)