Hunt for molecules at the origin of life Y. Ellinger, M. Lattelais, G. Berthier Laboratoire...

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Hunt for moleculesat the origin of life

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.

HN-C-O

What do we mean by molecules at the origin of life ?

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 on Earth: The Miller/Urey Experiments

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.

Prebiotic molecules in space: Meteorites, Comets, ISM

Meteorite found in Allende, Mexico.

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).

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





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

Rotational constants <1%Dipole moment 5%

Vibrational frequencies <1%Absolute intensities 10%

Electronic transitions <0.2 eVTransition moments <0.1%

Delivered

possiblepossible

almostNot yet

need worksometimes

Energetical Data: Requested

Proton affinities 1 kcal/mol

Isomerization energies 1 kcal/mol

Dissociation energies 1 kcal/mol Physisorption energies 0.1 kcal/mol

Ionisation energies 5 kcal/mol Activation barriers 0.2 kcal/mol

Delivered

possible

possible

almost

possible

need work

not yet

Precision and error bars

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

NH2CH(CN)2 + HCN NH2(CN)C=C(CN)NH2

NH2(CN)C=C(CN)NH2 + HCN C5H5N5 ( Adenine)

N

N

N

H

N

N H2

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?

I

II

III

IV

V

H

NC C N

H

N CC N

HH

C N

H

NC N C

H

C NHC NH

N

H

CH

H

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

Looking for prebiotic phosphorus

Most stable molecule [C H O N] : HNCOMost stable molecule [C H O P] : HPCO

Prediction of rotational constants for HPCO (GHz)

Be CCSD DFT/B3LYP)6-311G** 6-311++G** 6-311G** 6-311++G**

B 5.5165 5.5212 5.5357 5.5017C 5.4005 5.4049 5.4169 5.3842

« Best estimate » B = 5.519 ± 0.005 C = 5.402 ± 0.005

Rotational constants of HNCO (GHz)

Be CCSD CCSD(T) DFT/B3LYP 6-311G** 6-311++G** 6-311G** 6-311++G** 6-311G** 6-311++G**

B 11.085 11.068 10.972 10.955 11.091 11.078 C 10.932 10.915 10.820 10.804 10.954 10.943« Experiment » B = 11.071 C = 10.911

Theory: C. Dimur, F. Pauzat, Y. Ellinger, G. Berthier , Spectr. Chim. Acta A, 57, 851 (2001)

Rel

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(K

cal/

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0

20

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H

CN

H O

H

NC

O

HHH

H

CN

H OH

NC

H OH

HN

H

C

HH O H

NC

H O

H

Origin of the peptide bond

Theory: J.M. Chiaramello, D. Talbi, G. Berthier, Y. Ellinger, Int. J. Astrobiology, in press (2005)

The peptide bond is the most stable link.

Only the lowest energy isomer is observed. Predictions (GHz, D):

Exp: B=11.3738 C=9.8337Theo: B=11.3321 C=9.8246

The most stable compound that can be formed from [C,3H,O,N] is : formamide.

It is the simplest example of peptide bond.

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0

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H

CN

H S

H

H

CN

H SH

NC

H SH

H

H

NC

H S

H

N

H

C

HH S

NC

S

HHH

Sulphur analogues of the peptide bond


The peptide bond is the most stable link.

Best chance for observation is H2N-CH=S. Predictions(GHz, D):

Theo: B=6.0342 C=5.4921µ=4.9

The most stable compound that can be formed from [C,3H,S,N] is : thio-formamide.

It is the simplest example of peptide bond with a sulphur atom.

Phosphorus compounds


Best chance for observation is H3C-P=O. Predictions(GHz, D):

Theo: B=8.0275 C=6.4779µ=3.5

Rel

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0

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P

H

C

HH OPC

H OH

H

H

CP

H O

H

H

CP

H OH

The most stable compound that can be formed from [C,3H,O,P] is : methyl-phosphine-oxide.

It has no relation with the peptide bond.It may be an intermediate on the route to prebiotic phosphorus compounds.

E(kcal/mol)

0

20

50

70

80

CH3 NOH

CH3 NHCH3

OMe

CH3 NH

OMe O

NH

CH3

CH3

NO

H

CH3

HN

O

CH3

CH3

CH3

NO

CH3

CH3

NOH

CH3 NH

O

CH3

CH3 NO CH3H

O

NCH3

CH3H O

NCH3

HCH3

O

NH

CH3CH3

60

40

30

10

The most stable compound that can be formed from [3C,7H,O,N] is :N-methyl acetamide.

The order of stability shows :

1rst : N-C-O connectivitypeptide bond

2nd : C-N-O connectivity

3rd : 3-membered rings

Origin of the peptide bond

Theory: M. Lattelais, DEA (Paris VI), (2005)

Relative energies of selected isomers of Glycine

HO-CH2-C(NH2)=O 12.1

H2N-CH2-COOH 10.0

CH3- O-C(NH2)=O 4.5

CH3- NH-COOH 0.0

E (kcal/mol)


H2N-CH2-COOH 10.0

CH3- O-C(NH2)=O 4.5

CH3- NH-COOH 0.0

E (kcal/mol)


E (kcal/mol)

CH3-O-CH2-C(NH2)=O 22.0

CH3-NH-CH2-COOH 19.2

NH2-CH(CH3)-COOH 12.4

NH2-CH2-CH2-COOH 11.6

OH-CH(CH3)-C(NH2)=O 11.1

CH3-CH2-OC(NH2)=O 3.7

CH3-CH2-NH-COOH 0.0

E (kcal/mol)

CH3-O-CH2-C(NH2)=O 22.0






CH3-CH2-NH-COOH 0.0


H2N-CH2-COOH 10.0

CH3- O-C(NH2)=O 4.5

CH3- NH-COOH 0.0

E (kcal/mol)


H2N-CH2-COOH 10.0

CH3- O-C(NH2)=O 4.5

CH3- NH-COOH 0.0

E (kcal/mol)

Comparison Glycine/Alanine


HO-CH2-C(NH3+)=O 22.1

CH3- O-C(NH3+)=O 16.0

CH3- NH2+-COOH 10.6

H3N+-CH2-COOH 0.0

E (kcal/mol)

E(kcal/mol)

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

+NH3-CH(CH3)-COOH 6.6

+NH3-CH2-CH2-COOH 0.0

Comparison between protonated Glycine and Alanine


Comparison between ionized Glycine and Alanine

E(kcal/mol)

[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

[CH3- O-C(NH2)=O] + 17.9

[HO-CH2-C(NH2)=O] + 8.8

[CH3- NH-COOH] + 4.7

[H2N-CH2-COOH] + 0.0

E (kcal/mol)


Analysis of interstellar grains may be a decisive step in the understanding of the origin of prebiotic material.

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.

Common point in Miller/Devienne type of experiments

Miller : presence of 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.

Devienne : NO WATER

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.


The peptide bond is the most stable link that can be formed.

Best chance for observation is H2N-SiH=O. Predictions(GHz, D):

Theo: B=7.2292 C=6.1164µ=5.3

Rel

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cal/

mol

)

0

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H

SiN

H O

H

H

SiN

H OH

NSi

O

HHH

N

H

Si

HH O

HNSi

H O

H NSi

H OH

H

Science fiction: life based on silicon ?

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.

E (kcal/mol)

CH3-O-CH2-C(NH2)=O 22.0






CH3-CH2-NH-COOH 0.0

E (kcal/mol)

CH3-O-CH2-C(NH2)=O 22.0






CH3-CH2-NH-COOH 0.0


H2N-CH2-COOH 10.0

CH3- O-C(NH2)=O 4.5

CH3- NH-COOH 0.0

E (kcal/mol)


H2N-CH2-COOH 10.0

CH3- O-C(NH2)=O 4.5

CH3- NH-COOH 0.0

E (kcal/mol)

Comparaison between Glycine and Alanine


Hunt for molecules at the origin of life Y. Ellinger, M. Lattelais, G. Berthier Laboratoire...

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Transcript of Hunt for molecules at the origin of life Y. Ellinger, M. Lattelais, G. Berthier Laboratoire...