Searching for the Origins of Life in Interstellar Space

Centre for Research in Mass Spectrometry, York University

Michael Jarvis & the Research Group of Professor D. K. Bohme

Thursday, April 26, 2007.

NGC 4526

What is the chemical composition of our galaxy?

Composition of the stars:•90% hydrogen

•10% helium

•trace amounts of heavy elementsOur Sun

Composition of interstellar clouds:•gas and dust grains

•mostly hydrogen and helium

•trace amounts of small molecules (H2O, CH2O, CH4, NH3, CO2, and CH3OH), in gas-phase and on the surface and in the interior of dust grains

H H

O H H

H

H

HN

HH

H H

OH

H Horsehead nebula

Proteins

DNA,RNA

In our galaxy, Earth is a very special place.Complex organic molecules are abundant!

Earth atmosphere:N2 (78%), O2 (21%), Ar (0.9%), CO2 (0.04%)

H2O, O3, CFCs...

LIFE is abundant!

What are the fundamental requirements for life?

(DNA,RNA) (proteins)

“Bradykinin”: arg–pro–pro–gly–phe–ser–pro–phe–arg

4-memberoligonucleotide

Topic of this presentation.

(1) water

(2) nucleic acids and amino acids (organic polymers)

Where were organic compounds such as amino acids first formed? On Earth? Elsewhere?

There are two (competing) theories:

Organic compounds were delivered to Earth by interplanetary dust, meteorites, comets and asteroids: “Panspermia”

(1)

Organic compounds were synthesized on Earth. The required energy is provided by lightning, UV, cosmic radiation, thermal energy or radioactive decay. “Homegrown synthesis”.

(2)

“Many of the interstellar molecules discovered to date are the same kinds detected in laboratory experiments specifically designed to synthesize prebiotic molecules. This fact suggests a universal prebiotic chemistry.”

- Jan M. Hollis, NASA Goddard Space Flight Centre

The planetary nebula K3-35. The colors show the 3.6 cm emission.

The various colours represent different intensities of emission.

Can we “see” molecules in the interstellar medium?

The Very Large Array (VLA), consisting of 27 radio antennas on the Plains of San Agustin, New Mexico, is one of the world’s premier astronomical radio observatories. Each antenna is 25 meters in diameter.

Radioastronomy is used to identify molecules based on unique “fingerprint” emissions or absorptions.

2-carbonsugar

3-carbonsugar+

5-carbon sugar(ribose)

The synthesis of ribose molecules is important because these molecules form the backbone structure of both DNA and RNA, the carriers of all genetic information.

• Molecules rotate end-over-end.

• When they change from a higher rotational energy level to a lower rotational level, they emit radio waves (photons) at precise frequencies.

In 2004, glycolaldehyde was discovered in a cold region (8 K) of the gas-and-dust cloud Sagittarius B2, 26,000 light years away, near the centre of our own Milky Way Galaxy. The discovery was made using the National Science Foundation’s giant Robert C. Byrd Green Bank Telescope (GBT).

A recent discovery:

Have amino acids been detected in the interstellar medium?

INTERSTELLAR GLYCINE

Y.-J. Kuan, S.B. Charnley, et al.

Astrophys. J. 593: 848-867 (2003)

“…27 glycine lines were detected …in one or more sources..”

A RIGOROUS ATTEMPT TO VERIFYINTERSTELLAR GLYCINE

L.E. Snyder et al.

Astrophys. J. 619: 914-930 (2005)

“We conclude that key lines necessary for an interstellar glycine identification have not yet been found.”

Thus, the presence of glycine in the interstellar medium has not yet been confirmed, but the possibility cannot be ruled out…

Nonetheless, biological material has been found in ppm quantities in meteorites that have impacted on Earth.

• more than 70 different amino acids• carboxylic acids• pyrimidine• purine

The “carbonaceous chondrite” class of meteorites have been found to contain up to 60 ppm of amino acids!

CI Chondrites:

CM Chondrites:

•cometary origin (material from interstellar medium)

•asteroidal origin (material from solar system)

Amino acid composition in two CI (Ivuna and Orgeuil) and two CM (Murchison* and Murray) meteorites:

Amino acid CI(%) CM(%)Glycine 17 17-amino acids 17 63,-amino acids 66 20

*More than 70 different amino acids were detected in the Murchison meteorite!

Sept. 28, 1969Murchison, Australia

Why are ion/molecule reactions important in the ISM?

• They are largely unaffected by extreme low temperatures (10-20K).

• They are ~100 times faster than neutral/neutral reactions.

Let’s see if we can generate amino acids from starting materials, involving ions, that are known to exist in the ISM.

•gas and dust grains

•mostly hydrogen and helium

•trace amounts of small molecules (H2O, CH2O, CH4, NH3, CO2, and CH3OH), in gas-phase and on the surface and in the interior of dust grains

H H

O H H

H

H

HN

HH

H H

OH

H

CH+ (vis), CF+, CO+, NO+, SO+, H3+ (IR),

HCO+, COH+, HCS+, N2H+, H3O+, HOCO+, HCNH+, H2COH+, HC3NH+, C6H-, C4H-, C8H-

In our laboratory we study gas-phase ion chemistry.

Selected-ion flow tube/triple quadrupole mass spectrometer (SIFT/QqQ)

“Simulating” the environment of the interstellar medium:

Ions enter instrument

reagent molecules(variable flow)

Analysis and quantitation in

quadrupole mass spectrometer

Fixed reaction time

To Roots Blower

• He as a buffer gas.• Pressure of only 0.35 Torr (0.0005 atm).• Reacting ions and molecules have no translational kinetic energy

Several attempts to generate glycine were unsuccessful:

CH3NH2+ + HCOOH

CH3NH2+ + CO2

CH3NH2+ + CO + H2O

NH3+ + CH3COOH

CH2COOH+ + NH3

N-O bond formation is preferred over C-C and N-C bond formation.

OH

O

NH2

(Blagojevic et al., Mon. Not. R. Astron. Soc. 339 (2003) L7-L11.)

NH2OH+ + CH3COOH NH2CH2COOH+ (ionized glycine)

NH2OH2+ + CH3COOH NH3CH2COOH+ (protonated glycine)

• OH+O bonding allows N-C bond formation

Success!!

Some background on the precursors:

Acetic acid: CH2+ + CO CH2CO+ + hv

CH2CO+ + 2H2O CH3COOH+ + H2O

Has been detected in ISM (1997)Hydroxylamine:

NH3(s) + H2O(s) + hv NH2OH(g) + other products

Nishi et al. (J. Chem. Phys., 80, 3898, 1984)

Undetected in ISM (so far)• NH2OH will be made in irradiation of interstellar ice (as shown by Nishi et al.).

• Charnley et al. (Sept. 2001) proposed that NH2OH should be one of the major components of interstellar ice. It can be formed by radical hydrogenation of NO on the surface of dust grains.

NH2OH+ + CH3COOH NH2CH2COOH+

Comparing the fragmentation of our product ion with that of commercial (ie. purchased) glycine:

0 5 10 15 20 25 30 35 40 45

0.0

0.2

0.4

0.6

0.8 Gly+ CH2NH+

0.0

0.2

0.4

0.6

0.8

Gly+

CH2NH+

Nose cone potential (/-V)R

elat

ive

abun

danc

e

• Increasing the voltage on the nose cone induces energetic collisions between ions and the neutral buffer gas.

• The specific fragmentation patterns and appearance energies can be used as a “chemical fingerprint” to identify unknowns.

Potential energy landscape for the reaction between

protonated hydroxyl amine and acetic acid to produce

GlyH+

B3LYP/6-311++G(df,pd)

(Galina Orlova)

Computational Chemistry results: (NH2OH)H+ + CH3COOH

-54.1

23.124.3

TS1

H2O

-27.2

-18.8

0.0

H0, kcal mol-1

PRC2

TS2

-13.7

Larger amino acids: Synthesizing alanine

Buoyed by our great success synthesizing glycine via a gas-phase ion/molecule reaction, we have attempted to synthesize alanine in a similar manner.

NH2OH+ + CH3CH2COOH NH2CH2CH2COOH+ (ionized alanine)

NH2OH2+ + CH3CH2COOH NH3CH2CH2COOH+ (protonated alanine)

The isomer formed is -alanine...

(protonated)-alanine

(protonated)-alanine

Biologicalisomer

Non-biologicalisomer

… this can be confirmed from the observed fragmentation pattern.

The “carbonaceous chondrite” class of meteorites have been found to contain up to 60 ppm of amino acids!

CI Chondrites:

CM Chondrites:

•cometary origin (material from interstellar medium)

•asteroidal origin (material from solar system)

Amino acid composition in two CI (Ivuna and Orgeuil) and two CM (Murchison and Murray) meteorites:

Amino acid CI(%) CM(%)Glycine 17 17-amino acids 17 63-alanine 40 1other ,-amino acids 26 19

Sept. 28, 1969Murchison, Australia

H2O

TS1

TS2-ß

H0, kcal mol-1

12.4

24.3

-65.3

ß-AlaH+

TS2-a

17.4

0.0

-59.5

a-AlaH+

-27.2

-14.5-19.4

TS2-a TS2-ß

Computational Chemistry results: (NH2OH)H+ + CH3CH2COOH

Potential energy landscape for the reaction between protonated hydroxyl amine and propanoic

acid to produceβ-AlaH+ (solid line) and α-

AlaH+ (dotted line)

B3LYP/6-311++(df,pd)

(Galina Orlova)

NH3(s) + H2O(s) NH2OHhv hv NO + 3H

hv, heat

NH2OH

Interstellar ice

Interstellar gas

hv/A+ RH+

NH2OH2+NH2OH+

CH3COOHCH3CH2COOH

CH3COOHCH3CH2COOH

NH2CH2COOH+

NH2CH2CH2COOH+

NH3CH2COOH+

NH3CH2CH2COOH+

-H2O-H2O

MM+

NH2CH2COOHNH2CH2CH2COOH

e-

H

M and A represent any neutral atom / molecule with a suitable IE. RH+ represents a proton carrier with PA(R) < PA(NH2OH).

(Blagojevic et al., Mon. Not. R. Astron. Soc. 339 (2003) L7-L11.)

Some Conclusions• “Precursors to life” such as amino acids may have been delivered to Earth by meteorites, comets, etc.

• Remote sensing of amino acids in the ISM with radiotelescopes has proved inconclusive. However, analysis of meteorites provides direct evidence of their presence.

• The synthesis of specifically -alanine supports the hypothesis that “CI chondrite” meteorites have interstellar origins.

• From starting materials that are present in the ISM, we have demonstrated a mechanism for the interstellar synthesis of glycine and -alanine!!!

NH2,3OH+ + CH3COOH NH2,3CH2COOH+

NH2,3OH+ + CH3CH2COOH NH2,3CH2CH2COOH+

Acknowledgements

York University• Professor D.K. Bohme• Dr. Voislav Blagojevic

• Bohme research group

Australian National University• Dr. Simon Petrie St Francis Xavier University• Professor Galina Orlova