1. Astrobiology, homochirality, and origin of life
Axel Brandenburg, based on work with Anja Andersen, Martin Nilsson, Susanne Höfner, Tuomas Multamäki, Harry and Kirsi Lehto (Nordita)
Astrobiology in Nordic countries
Role of Nordita
Meetings: Copenhagen, Turku, Oslo, Stockholm
Winter school last January
Our current interests:
homochirality and origin of life
peptide world, RNA world
Stockholm Observatory, Astronomy seminar, September 29, 2006
Int. J. Astrobio. 3, 209 (2004), 4, 75 (2005),
Orig. Life Evol. Biosph. 35, 225 (2005), 35, 507 (2005)

2. Astrophysics: staff and duties
Nordita in Copenhagen

3. Nordita in Stockholm Expected developments
~6 new post-docs Nordic+non-Nordic
~2 new assist. profs
~5 programs/year
visiting professors (1/2-2yr)
Nordita-days next August

4. AB-School Jan 2004 Copenhagen Aug 2004 Turku Jan 2005 Copenhagen
Nov 2005 Oslo
Jan 2006 Kittilä

5. Topics at Nordic AB meetings
Atmospheric
escape
Martian gullies
Icelandic analogues
Subglacial lakes
Geological
evolution
Cyanobacteria
Deep biosphere
Extremophiles
Deep biosphere
Meteorites
stardust
RNA world
geochemistry
Nucleotide
Synthesis
In space
Deep
biosph
Ancient DNA, PNA,
Early life evidence
Climate, exoplanets
Mars simulator
Interstellar chem.

6. Frozen/liquid water on Mars
On Earth: Life 3.8 Gyr ago
Frozen/liquid water on Mars

7. Astrobiology: The range of problems
From dust to planets
Exoplanets
Water delivery
Habitable worlds
Archaen world
Volcanoes, carbon cycle
Impacts, panspermia
Greenhouse effect
Miller experiment
Amino acids, chemistry
Artificial life
Origin of life
RNA world, TNA, PNA
homochirality
Early life
Extremophiles
Cyanobacteria
Oxygen, methane evol.

8. Remaining dust settles
Time line
104 yr yr yr yr
First life
planetesimals
Sun ignites
T0=1010 yr after Big Bang
All gas gone
Remaining dust settles

9. Amino acids in proteins: left-handed Sugars in DNA and RNA: right-handed
Is chirality:
(i) prerequisite
(ii) consequence
of life?
carboxyl
group
Louis Pasteur
( )
animo
group
chlorophyll

10. Producing enantiomeric excess (e.e)
Life only develops in homochiral environment
Homochirality is a prerequisite
However: no mechanism produces 100% e.e.
only minute partial excess possible (electroweak)
slightly bigger for large Z, goes like Z5  Cu (II) ions
Still need amplification mechanism
Frank (1953) model (plus extensions): nucleotides
Autocatalysis and enantiomeric cross inhibition
Plasson, Bersini, Commeyras (2004): peptides

11. Chirality selection during polymerization of the first replicating molecule?
lipid world?
Peptide world,
PNA world
RNA world
dual world
achiral
RNA
DNA
RNA
proteins
chiral
Rasmussen et al (2003
Artif. Life 9, )
Isotactic polymer
(same chirality) R
Monomers
to dimers
“waste”
(enantiomeric
cross-inhibition) L

12. RNA and peptide worlds Polycondensation reactions
Isotractic chains strongly preferred
Self-amplification conceivable
Initially (nonliving): e.e.=0
During polycondensation: e.e. ~ exp(lt)
l is the growth rate

13. RNA versus peptide worlds
RNA world
peptide world
Activation D  D*, L  L*
Polymerization D+D DD, L+L  LL
Epimerization DL  LL, LD  DD
Depolymerization DD  D+D, LL  L+L
Template-directed (PCR-like)
Enantiomeric cross-inhibition
Autocatalytic production of new mono-nucleotides ( but uncertain)
APED model (Plasson et al.)

14. Recap of Frank-type model (Frank 1953)
auto-catalysis alone
kinetic equation
exponential
growth
enantiomeric excess:
catalyst

15. Need mutual antagonism
add cross-inhibition
kinetic equation
unspecific antagonism

16. Initial bias not necessary
Exponential amplification
Initial excess can be virtually zero
Initial bias may not change this
depends on strength
Second genesis: other chirality?
would be cool
but is not necessary
Bifurcation diagram
with Andersen, Höfner, Nilsson
Orig. Life Evol. Biosph. 35, 225 (2005)
fidelity

17. Relevant experiments: autocatalysis
now also: proline-catalyzed reaction (Blackmond 2004)
pyrimidine-5-carboxylaldehyde
with diisopropylzinc
 autocatalytic self-amplification
cf. Frank (1953), Goldanskii & Kuzmin (1989), …
Soai et al. (1995)
self-amplification
+ competition important

18. Relevant experiments: nucleotides
 Mononucleotides with wrong
chirality terminate chain growth ok
poisoned
template-directed oligomerization
poly (CD)  oligo (GD)
(using HPLC)
 enantiomeric cross-inhibition
cytosine
guanine
Joyce et al. (1984)

19. Contergan: was sold as racemic mixture
Cures morning sickness
during pregnancy
causes misformations
(abandoned in December 1961)

20. Relevant experiments: crystals
Crystal growth, many different
nucleation sites: racemic mixture
Crystal growth with stirring:
primary nucleation suppressed
Kondepudi et al. (1990)
 competition important

21. APED model (Plasson et al. 2004)
a: activation
p: polymer.
a: inhibition
h: depolym.
e: epimerization
on N-terminal
DLLL
not
DL DD

22. APED model equations
Consider limit
of large h and e

23. APED model equations limit of large h and e corresponding reaction
 D catalyzes conversion
of both D* and L* into D

24. APED model equations additional limit of large p
corresponding reaction
APED model is
auto-catalytic after all!
subtract

25. Where could this work? a) hydrothermal vents b) Tides
Braun & Libchaber (2003)
b) Tides
Lathe (2003)

26. Early forms of protocells
Michael J. Russell (2006, Am. Sci. 94, 32-39)

27. Spatially extended model
with Tuomas Multamäki, Int. J. Astrobio. 3, 209 (2004)
Reaction-diffusion equation
1350
1349
Proto type: Fisher’s equation
1348
Propagating front solutions
wave speed
1347
Spread of the black death

28. 1D and 2D models (reaction-diffusion equation)
Propagation into racemic
environment
Disappearence of
isolated islands

29. Piecewise linear increase
Reduced equations
add/subtract:

30. Effects of turbulence

31. Pencil Code Started in Sept. 2001 with Wolfgang Dobler
High order (6th order in space, 3rd order in time)
Cache & memory efficient
MPI, can run PacxMPI (across countries!)
Maintained/developed by ~20 people (CVS!)
Automatic validation (over night or any time)
Max resolution so far , 256 procs
Isotropic turbulence
MHD, passive scl, CR
Stratified layers
Convection, radiation
Shearing box
MRI, dust, interstellar
Sphere embedded in box
Fully convective stars
geodynamo
Other applications
Homochirality
Spherical coordinates

32. Conclusions Astrobiology: need to be prepared… Polymerization model:
Based on measurable processes
Reduction to accurate simplified model
Homochirality in space (earth, interstellar, etc)
Timescales 500 Myr; fossil evidence of spatially fragmented homochirality?
Pencil Code: just google for it
Detailed manual, …