Homochirality without autocatalysis or cross-inhibition

1. Homochirality withoutautocatalysis or cross-inhibition • Standard approach: spontaneous symmetry breaking • Result of (proto)life • New results (fluctuations important, dilute systems) • Homochirality as biomarker ( Mars experiment) A. Brandenburg Int. J. Astrobio. 3, 209 (2004), 4, 75 (2005), Orig. Life Evol. Biosph. 35, 225 (2005), 35, 507 (2005) Astrobiology 7, 725 (2007) • Homochirality: result of spontaneous symmetry breaking • Result of (proto)life • Contrast Frank (1953) with modified mechanism • Similarity to magnetohydrodynamics • Spatially extended systems

2. 3 different classes of mechanisms • Autocatalysis and mutual antagonism- - Frank (1953) model - Grow both, and dump pairs - Has been applied to RNA world • crystal growth with stirring - larger crystals spawn more nucelation sites • constructive autocatalysis (indirect) - has been applied to peptides

3. Pathway to homochirality • Instability (to tap energy, both D&L grow, but still no preference for either) • Nonlinearity (competition between D&L) • Example I: nucleotides autocatalysis & enantiomeric cross-inhibition (Frank 1953, Sandars 2003, Joyce et al. 1984) • Example II: peptides activation/polymerization/epimerization/depolymerization (APED) (Plasson et al. 2004)

4. Prebiotic experiments: nucleotides template-directed polymerization ~polymerase chain reaction (PCR) Serious difficulty: requires building blocks of the same chirality  Mononucleotides with wrong chirality terminate chain growth Joyce et al. (1984) ok poisoned poly (CD)  oligo (GD) (HPLC) guanine cytosine

5. New developments • Cross inhibition not likely? • Can be avoided in dilute systems (rare reactions) • 2015 and 2017 papers • Even auto-catalysis not needed? • Also dilute systems • 2008 paper

6. Net reactions in APED model Brandenburg, Lehto, & Lehto (2007)

7. Rare reactions: homochirality

8. Net reactions in APED model

9. Modeling the reactions State vector ([A], [D], [L]) Different reactions A  D: f  f + (-1, 1, 0) A  L: f  f + (-1, 0, 1) D A: f  f + (1, -1, 0) L A: f  f + (1, 0, -1) Prob: k+ Prob: k-

10. Auto-catalytic & Cross inhib. State vector ([A], [D], [L]) Different reactions A  D: f  f + (-1, 1, 0) A  L: f  f + (-1, 0, 1) Cross-inhibition D+L  2A: f  f + (2, -1, -1) Prob: k+[D]/N Prob: k+[L]/N Prob: kX

11. Four experiments • Auto-catalysis & cross inhibition • Auto-catalysis & no cross-inhib. (just decay) • No auto-catalysis, but cross inhib. • No auto-catalysis nor cross-inhib.

12. Four cases II I IV III

13. No autocatalysis:  slow • Auto-catalysis & cross inhibition • Auto-catalysis & no cross-inhib. (just decay) • No auto-catalysis, but cross inhib. • No auto-catalysis nor cross-inhib.

14. Usage as biomarkers • Search for chiral remains (e.g. DNA in permafrost) • Search for extant life that selects one chirality

15. Stereospecific uptake

16. Stereospecific uptake

17. Stereospecific uptake

18. The Viking labs (1976) • Gas chomatograph - mass spectrometer (GCMS) • No organics detected (less than on moon!) • Decisive reason why conclusion: no life

19. The Label Release Experiment • Supply “nutrients” (amino acids, etc) • Control experiment + = CO2+…

20. Control Experiment • Soil heated to 140 C, later 40 – 50 C • To sterilize soil + = nothing

21. HW5: working with a paper

23. Quote from Sagan • … the more extraordinary the claim, the more extraordinarily well-tested the evidence must be. • The person making the extraordinary claim has the burden of proving to the experts at large that his or her belief has more validity than the one almost everyone else accepts…

24. Phoenix lander discovered perchlorates • Explains why no (not much) organics are found • Might also explain results of Viking Experiments

25. Perchlorates: KClO4 • Claim for life not generally accepted • But it does remain somewhat puzzling

26. x

27. Low temperature experiments

28. Conclusions • Homochirality as result of protolife • Potentially a biomarker • New labeled release experiments Background figure: Brandenburg & Multamake (2004)

29. Stereospecific uptake

30. Net reactions in APED model Brandenburg, Lehto, & Lehto (2007) inhibition step Effectively like auto-catalysis epimerization on N-residue

31. Reduced APED model a one way round-about For nearly racemic state:

32. new Lows (L) in North & South counter clockwise clockwise

33. (iii) 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 1347 wave speed Spread of the black death

34. An unexpected lesson learnt • Magnetic fields and flows can also be chiral • Helicity important for solar dynamo • Important topic at Nordita  zero at the equator? No! (Chatterjee et al 2011) north equator south

35. Analogies with homochirality? • Chatterjee et al (2011): magnetobuoyancy • Both chiralities • Initial conditions • fairly complicated • Simpler systems? • Gellert et al (2011): instability of toroidal field