Transcript - Department of Chemistry, York University

Searching for the Origins of
Life in Interstellar Space
Michael Jarvis & the Research Group of
Professor D. K. Bohme
Centre for Research in Mass Spectrometry, York University
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 elements
Composition of interstellar clouds:
Our Sun
•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
H
N
H
OH
H
H
H
H
Horsehead nebula
In our galaxy, Earth is a very special place.
Complex organic molecules are abundant!
LIFE is abundant!
Earth atmosphere:
N2 (78%), O2 (21%), Ar (0.9%), CO2 (0.04%)
H2O, O3, CFCs...
Proteins
DNA,RNA
What are the fundamental requirements for life?
(1) water
(2) nucleic acids and amino acids (organic polymers)
(DNA,RNA)
4-member
oligonucleotide
(proteins)
Topic of this
presentation.
“Bradykinin”:
arg–pro–pro–gly–phe–ser–pro–phe–arg
Where were organic compounds such as amino acids first
formed? On Earth? Elsewhere?
There are two (competing) theories:
(1) Organic compounds were delivered to
Earth by interplanetary dust, meteorites,
comets and asteroids: “Panspermia”
(2) Organic compounds were synthesized
on Earth. The required energy is
provided by lightning, UV, cosmic
radiation, thermal energy or radioactive
decay. “Homegrown synthesis”.
“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
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.
The planetary nebula K3-35. The colors show the 3.6 cm emission.
The various colours represent different intensities of emission.
Radioastronomy is used to identify molecules based on unique
“fingerprint” emissions or absorptions.
• 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.
A recent discovery:
In 2004, glycolaldehyde was discovered in a cold region (8 K) of the gasand-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).
2-carbon
3-carbon
+
sugar
sugar
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.
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 VERIFY
INTERSTELLAR 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:
•cometary origin (material from interstellar medium)
CM Chondrites:
•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
Sept. 28, 1969
Murchison, Australia
*More than 70 different amino acids were
detected in the Murchison meteorite!
In our laboratory we study gas-phase ion chemistry.
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
H
N
H
OH
H
H
H
H
CH+ (vis), CF+, CO+, NO+, SO+, H3+
(IR), HCO+, COH+, HCS+, N2H+, H3O+,
HOCO+, HCNH+, H2COH+, HC3NH+,
C6H-, C4H-, C8H-
Selected-ion flow tube/triple quadrupole mass spectrometer
(SIFT/QqQ)
“Simulating” the environment of the interstellar medium:
• He as a buffer gas.
• Pressure of only 0.35 Torr (0.0005 atm).
• Reacting ions and molecules have no translational kinetic energy
reagent molecules
(variable flow)
To Roots Blower
Analysis and
quantitation in
quadrupole mass
spectrometer
Ions enter
instrument
Fixed reaction time
Several attempts to generate glycine were unsuccessful:
O
CH3NH2+ + HCOOH
CH3NH2+ + CO2
CH3NH2+ + CO + H2O
NH2
NH3+ + CH3COOH
CH2COOH+ + NH3
OH
N-O bond formation is preferred over C-C and N-C bond formation.
Success!!
NH2OH+ + CH3COOH  NH2CH2COOH+ (ionized glycine)
NH2OH2+ + CH3COOH  NH3CH2COOH+ (protonated glycine)
• OH+O bonding allows N-C bond formation
(Blagojevic et al., Mon. Not. R. Astron. Soc. 339 (2003) L7-L11.)
NH2OH+ + CH3COOH  NH2CH2COOH+
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.
Comparing the fragmentation of our product ion with that of
commercial (ie. purchased) glycine:
0.8
CH2NH+
0.6
Relative abundance
0.4
Gly+
0.2
0.0
• 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.
0.8
Gly+
0.6
CH2NH+
0.4
0.2
0.0
0
5
10 15 20 25 30 35 40 45
Nose cone potential (/-V)
Computational Chemistry results: (NH2OH)H+ + CH3COOH
H0, kcal mol-1
TS2
24.3
Potential energy landscape
for the reaction between
protonated hydroxyl amine
and acetic acid to produce
GlyH+
23.1
0.0
-13.7
-18.8
-27.2
B3LYP/6-311++G(df,pd)
TS1
-54.1
PRC2
(Galina Orlova)
H2O
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...
… this can be confirmed from the observed fragmentation pattern.
Biological
isomer
Non-biological
isomer
(protonated)
-alanine
(protonated)
-alanine
The “carbonaceous chondrite” class of meteorites have been
found to contain up to 60 ppm of amino acids!
CI Chondrites:
•cometary origin (material from interstellar medium)
CM Chondrites:
•asteroidal origin (material from solar system)
Amino acid composition in two CI (Ivuna and Orgeuil) and two CM
(Murchison and Murray) meteorites:
Amino acid
Glycine
-amino acids
-alanine
other ,-amino acids
Sept. 28, 1969
Murchison, Australia
CI(%) CM(%)
17
17
17
63
40
1
26
19
Computational Chemistry results: (NH2OH)H+ + CH3CH2COOH
H0, kcal mol-1
TS2-a
TS2-ß
TS2-a
17.4
24.3
TS2-ß
12.4
0.0
-14.5
Potential energy landscape for
the reaction between protonated
hydroxyl amine and propanoic
acid to produce
β-AlaH+ (solid line) and αAlaH+ (dotted line)
-19.4
-27.2
B3LYP/6-311++(df,pd)
TS1
-59.5
-65.3
a-AlaH +
ß-AlaH+
H2 O
(Galina Orlova)
NH2CH2COOH
M+ NH2CH2CH2COOH
H
M
e-
NH2CH2COOH+
NH2CH2CH2COOH+
NH3CH2COOH+
NH3CH2CH2COOH+
CH3COOH
-H2O CH3CH2COOH
hv/A+
NH2OH+
Interstellar gas
Interstellar ice
NH3(s) + H2O(s) hv
CH3COOH
CH3CH2COOH -H2O
RH+
NH2OH2+
NH2OH
hv, heat
NH2OH
hv
NO + 3H
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.
• 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+
• The synthesis of specifically -alanine supports the hypothesis that “CI
chondrite” meteorites have interstellar origins.
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