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The Origin of Chirality

The Origin of Chirality. Anne-Catherine Bédard Charette Group Meeting Jan 25 th 2012. “ Any man who, upon looking down at his bare feet, doesn't laugh, has either no sense of symmetry or no sense of humour ” (Descartes, cf. Walker 1979). About Me !. Ottawa

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The Origin of Chirality

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  1. The Origin of Chirality Anne-Catherine Bédard Charette Group Meeting Jan 25th 2012 “Any man who, upon looking down at his bare feet, doesn't laugh, has either no sense of symmetry or no sense of humour” (Descartes, cf. Walker 1979)

  2. About Me ! Ottawa Biopharmaceuticals Sciences - COOP Québec Montréal Paris Honours Project JCEMolChem

  3. Outline Terrestrial vs ExtraterrestrialTheories • Stereochemistry in Life • Minority report : opposite handedness • Difference in energy of enantiomers • Chiralityformpolarized light • Chiral field : Magnetism • Amplification and transfert of chirality • Crystallization • Unidirectional rotation of Earth

  4. Louis Pasteur • 1848 : Pasteur 1st to draw attention to the homochirality in nature • Optical purity is inherent to life • Failure of other planets to yield optically active material = evidence for the absence of life of complexity comparable to earth’s • 1874 : Van’t Hoff = assymmetry on carbon atom. • Dextrogyre (+)-D • Levogyre (-)-L 1822-1895 France Tartaric Acid

  5. Enantiotopic TS

  6. Diastereotopic TS

  7. Biomolecular Homochirality • Basic elementsof biochemistry • 20 (L)-aminoacids • 5 bases (A, G, C, U, T) • (D)-Ribose • (D)-Glucose • Fats • Phosphatides • Formation of proteins, enzymes, DNA, RNA, sources and storagesof metabolicenergy!

  8. Chirality and Physical Property R-Carvone : caraway odour S-Carvone : spearmint odour Thalidomide (1957-1961) Morning sickness treatment Cause congenital abnormalities

  9. D-Amino Acids • Ingestion of D-A.A. in food • Racemization with vinegar, yogurt, potatoes… • Enzyme : D-A.A. oxidase • Babies : 60% of D-aspartic acid in prefrontal cortex at 14th week of gestation • Decreased by birth to traces amount • Alzheimer’s : accelerated racemisation of aspartic acid residue • Racemisation is linked to the process of ageing… • A. A. clock : complementary to 14C-dating method

  10. Racemisation • Thermodynamically favored process • Gain of entropy (in the solid state) • Room temperature racemisation of alanine • Thousand of years!

  11. Difference in Free Energiesof Enantiomers

  12. The Weak (Nuclear) Force – Parity Violation • 4thfundamental force of physics • Influence electronsinsideatomscausingthem to travelhelicalpathsthatgives all atoms a handedness • 1013 time weakerthan the strong force thatholds protons and neutrons in the nucleus • Discovery in 1956 by • TsungDao Lee (Columbia U.) • Chen NingYang (Princeton) • Nobel prize of Physics in 1957! • Lee (30) and Yang (34) Lee, T. D.; Yang, C. N. Phys Rev 1956, 104, 254

  13. The Weak (Nuclear) Force – Parity Violation • Most familiar effect : β-decay (60Co, 14C) • Inherently left-handed! Conservation of momentum

  14. 60Co Beta-Decay – Wu’s Experiment • If parity is conserved, then the probability of electron emission at θ is equal to that at 180o - θ. Nucleipolarisedthrough spin alignment in a large magnetic fieldat 0.01oK Wu, C. S. and al. Phys Rev 1957, 105, 1413 Bonner, W. A. Chirality2000, 12, 114

  15. Difference in Energy of Enantiomers • Femtojoule (10-15) to picojoule (10-12) scale • L-A.A. and D-sugars are more stable ! • No experiment has been successful in confirming the effect. MacDermott, A. J. Orig Life Evol Biosphere, 1995,25, 191 Quack, M. Angew. Chem. Int. Ed. 2002, 41, 4618 Salam, A. J Mol Evol 1991, 33, 105

  16. ChiralityfromPolarized Light Chemicaleffect of polarized radiation Photochemicalasymmetricsynthesis Photochemicaldecomposition of racemates

  17. Kagan’s Decomposition of Camphor 290-370 nm CPL (UV) 20% ee 99% decomp Balavoine, G.; Moradpour, A.; Kagan, H. B. J. Am. Chem. Soc. 1974, 96, 16.

  18. Bonner’s Polarised Light Exp. • Selective destruction of D enantiomer of A.A. withright circularlypolarized light (UV) • Exact and opposite effect of RCPL and LCPL • Leucine has the highestmolecularabsoption coefficient • Predicted = 2% eeat 80% photolyzed Flores, J. J.; Bonner, W. A.; Massey, G. A.; J. Am. Chem. Soc. 1977, 99, 11

  19. Leucine’s Photolysis • 212.8 m, CPL Photodecomposition vs photosynthesis Flores, J. J.; Bonner, W. A.; Massey, G. A.; J. Am. Chem. Soc. 1977, 99, 3622

  20. AssymmetricPhotosynthesis • Photocyclisation of alkenes in solution Bernstein, W. J.; Calvin, M.; Bechardt, O. J. Am. Chem. Soc. 1973, 95, 527

  21. Circularly Polarized Light (CPL) • Sunlight is polarized linearly (LPL) and non-assymmetric • Right or left CPL is a result of natural (LPL) sunlight reflexion at the earth’s surface and earth’s magnetic field (0,1%) • Sunlight is considered insufficient for enantioselective photochemistry.

  22. Circular Polarization in Space • Strong IR circular polarisation resulting from dust scattering in Orion OMC-1 star-formation region Baileys, J. and al. Science 1998, 281, 672

  23. Extraterestrial A.A. Meteorite • Meteorite : Murchinson Autralia in 1970 • Issue of terrestrial contamination… • 5 α-Me A.A. (extremely rare or unreported) Cronin, J. R. ; Pizzarello, S. Science1997, 275, 951.

  24. Strecker Synthesis in Space Silicate grains of sub-micrometer diameter coated with ice layer Contains H2O, CO2, CO, CH3OH, NH3 Subsequent aggregation = formation of comets !

  25. Strecker Synthesis in Space Interstellar conditions in the lab: • Vaccum (10-7 mbar) • Lowtemperature (12K) • Mixture : H2O, NH3, CH3OH, CO, CO2 • Irradiation with UV light for 24h • Warmed slowly up to room temperature. • Photochemically formed radicals are assumed to recombine in order to form oligomers and polymers Caro, M. and co. Chem Eur J 2005, 11, 4895

  26. GC-MS Analysis • 16 amino acids were formed • 5/20 protein-constituent • Glycine = most abundant

  27. Chiral field : Magnetism

  28. Magnetochiral Photochemistry • 0.2M aq. solution Cr(III)tris-oxalato complex • Dissociation and reassociation of the ligands • Laser (unpolarized) around 696 nm (vis rouge) • Magnetic field (B) at 7,5T Rikken, G. L. J. A.; E. Raupach E. Nature, 2000, 405, 932

  29. Magnetochiral Photochemistry Enantioselectivity as a fct. of the magnetic field (B) Enantioselectivity as a fct. of the wavelenght (λ) Rikken, G. L. J. A.; E. Raupach E. Nature, 2000, 405, 932

  30. Magnetochiral Photochemistry • Does the magnetic field convert unpolarized light in CPL ? • Earth’s magnetic field : 10-4 T … (vs 7.5 T) Photoresolution time : 6min Racemization : 70min Rikken, G. L. J. A.; E. Raupach E. Nature, 2000, 405, 932

  31. Amplification andTransfert of Chirality

  32. Adsorption of Chiral OrganicMolecules on EnantiomorphousCrystals • Quartz = most abondant mineral on Earth • Can be helically chiral in the solid form • 1974 (Bonner) : preferential adsorption of one a.a. enantiomer out of a racemate on the crystal • Leads to enrichement of the solution in one enantiomer ! • Drawback : anhydrous conditions… Bonner, W. A. and al. Science 1974, 186, 143

  33. Amplification Reaction - Saoi • Discovered in 1995 • Autocatalytic reaction

  34. Saoi on Crystals Saoi, K. and al. Orig Life Evol Biosph, 2010, 40, 65

  35. Snail Shells • Right-helical shells are stereoselectively preferred and dominant • 1 ‘racemic’ snail (Cuban tree) • Helically chiral CaCO3 !

  36. What About Sugars !?!

  37. Prebioticsynthesis: Formose Reaction • Ribose (C5H10O5) is a formal pentamer of formaldehyde (CH2O) Northrup, A. B.; MacMillan, D. W. C., J.A.C.S. 2002, 124, 6798 Breslow, R. Tetrahedron Letters 52 (2011) 2028–2032 Breslow, R. Tetrahedron Lett. 1959, 21, 22.

  38. A.A. as Asymmetric Catalysts • Alanine : most common in protein • Isovaline : most common in meteorite • Aldol condensation of glycoaldehyde in water L-A.A. gives D-sugars ! Pizzarello, S.; Weber, A. L. Science 2004, 303, 1151

  39. Enantioselective Formose Reaction L-A.A. catalyzethe formation of D-glyceraldehyde preferentially? 21% ee Breslow, R. Tetrahedron Letters 52 (2011) 2028–2032

  40. Enantioselective Formose Reaction • Only small ee was obtained … amplification by selective solubilisation • D-glyceraldehyde = complete water solubility • DL-glyceraldehyde = limited water solubility • 61/39 (21% ee) can become 92/8 (84% ee) after slow water evaporation Breslow, R. Tetrahedron Letters 52 (2011) 2028–2032

  41. Crystallization

  42. Morowithz Treatment – A. A. • Most A.A. formracemic compound crystals are less solubles (and higherm.p.) than L or D enantiomers • Ex : 1% ee solution of D and L-A.A (in H2O) • As the water evaporates the less soluble crystalswouldprecipitatesleavingincreasedrichness in one enantiomers Morowitz, H. J. Theor. Biol. 1969, 25, 491

  43. Example • 500mg of phenylalanine with 1% ee • Dissolved in water • Slow evaporation until the bulk of the material had crystallized (>400mg) • Solution is now 40% ee … repeat • Solution is now 90,9% ee • Recovered mass is 20mg Breslow, R.; Levine, M. S. PNAS 2006, 35, 12979

  44. Precipitation of A.A. • 2001 (Viedma) • D-tyrosine crystallized faster than L-tyrosine • Parity non-conserving energy • 2006 (Scolnik): repeated experiment • Same result ! • ‘undetectable impurities’… Viedma, C. Orig Life Evol Biosphere 2001, 31, 501 Scolnik, Y. and al. Phys Chem 2006, 8, 333

  45. Unidirectional Rotation of Earth

  46. Unidirectional Rotation of Earth • Tornado have a ‘prefered’ rotation that are opposite from Northern and Southern hemisphere. • Due to ‘not well understood’ amplification mechanism Kovacs, K. L.; Keszthelyi, L. Origin of Life 1981, 11, 93

  47. NaClO3 • 100g of NaClO3 in 120mL of H2O at 50oC • Induce precipitation = racemic • Stirred solution • 99,7% ee in 32 differents crystallisations • 18 (L) ; 14 (R) • Unpredicable and random Kondepudi, D. K. and al. Science 1990, 250, 975

  48. Unidirectional Rotation of Earth • 1981 : Clockwise stirring = preference for the incorporation of D-isomers into the polymers and longer polymers • Not convincing enough to conclude unequivocally… Kovacs, K., L.; Keszthelyi, L.; Goldanskii, V. J.; Origin of Life 1981, 11, 93-103

  49. Aggregation of Disk-ShapedPorphyrins • Stacks (electrostatic and H-bonding interactions) • Small aggregates assemble into fiberlike structures with helical orientation • controlled by the direction of the vortex motion • Orientations detected by the absorption of circularly polarized light. Ribo, J. M. et al. Science 2001, 292, 2063

  50. Aggregation of Disk-Shaped Porphyrins • How ? a particular handedness is imposed by the stirring direction • 1st unequivocal demonstration of chiral selection induced by stirring. • The supramolecular structure may act as a homochiral template for subsequent asymmetric reactions or may function as a chiral catalyst. Ribo, J. M. et al. Science 2001, 292, 2063

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