Download The Origin of Chirality

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)
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About Me !
Québec
Paris
Honours Project
JCEMolChem
Ottawa
Biopharmaceuticals Sciences - COOP
Montréal
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Outline
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Terrestrial vs Extraterrestrial Theories
Stereochemistry in Life
Minority report : opposite handedness
Difference in energy of enantiomers
Chirality form polarized light
Chiral field : Magnetism
Amplification and transfert of chirality
Crystallization
Unidirectional rotation of Earth
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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
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Enantiotopic TS
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Diastereotopic TS
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Biomolecular Homochirality
• Basic elements of biochemistry
▫ 20 (L)-amino acids
▫ 5 bases (A, G, C, U, T)
▫ (D)-Ribose
▫ (D)-Glucose
▫ Fats
▫ Phosphatides
• Formation of proteins, enzymes,
DNA, RNA, sources and
storages of metabolic energy !
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Chirality and Physical Property
R-Carvone : caraway odour
S-Carvone : spearmint odour
Thalidomide (1957-1961)
Morning sickness treatment
Cause congenital abnormalities
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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
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Racemisation
• Thermodynamically favored process
• Gain of entropy (in the solid state)
• Room temperature racemisation of alanine
▫ Thousand of years!
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The Weak (Nuclear) Force – Parity Violation
• 4th fundamental force of physics
• Influence electrons inside atoms causing them to travel
helical paths that gives all atoms a handedness
• 1013 time weaker than the strong force that holds
protons and neutrons in the nucleus
• Discovery in 1956 by
• Tsung Dao Lee (Columbia U.)
• Chen Ning Yang (Princeton)
• Nobel prize of Physics in 1957!
• Lee (30) and Yang (34)
Lee, T. D.; Yang, C. N. Phys Rev 1956, 104, 254
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The Weak (Nuclear) Force – Parity Violation
• Most familiar effect : β-decay (60Co, 14C)
• Inherently left-handed!
Conservation
of momentum
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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.
Nuclei polarised through spin alignment in a large magnetic field
at 0.01oK
Wu, C. S. and al. Phys Rev 1957, 105, 1413
Bonner, W. A. Chirality 2000, 12, 114
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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
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Chemical effect of polarized radiation
Photochemical asymmetric synthesis
Photochemical decomposition of racemates
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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.
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Bonner’s Polarised Light Exp.
• Selective destruction of D enantiomer of A.A. with
right circularly polarized light (UV)
• Exact and opposite effect of RCPL and LCPL
▫ Leucine has the highest molecular absoption coefficient
▫ Predicted = 2% ee at 80% photolyzed
Flores, J. J.; Bonner, W. A.; Massey, G. A.; J. Am. Chem. Soc. 1977, 99, 11
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Leucine’s Photolysis
• 212.8 m, CPL
Light polarization
% Decomposition
Enantiomeric Excess
RCPL
59
1,98 ± 0,31
LCPL
75
2,50 ± 0,35
Unpolarized
54
0,30 ± 0,33
Photodecomposition vs photosynthesis
Flores, J. J.; Bonner, W. A.; Massey, G. A.; J. Am. Chem. Soc. 1977, 99, 3622
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Assymmetric Photosynthesis
• Photocyclisation of alkenes in solution
Bernstein, W. J.; Calvin, M.; Bechardt, O. J. Am. Chem. Soc. 1973, 95, 527
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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.
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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
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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. Science 1997, 275, 951.
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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 !
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Strecker Synthesis in Space
Interstellar conditions in the lab :
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Vaccum (10-7 mbar)
Low temperature (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
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GC-MS Analysis
• 16 amino acids were formed
• 5/20 protein-constituent
• Glycine = most abundant
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Magnetochiral Photochemistry
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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
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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
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Magnetochiral Photochemistry
Photoresolution time : 6min
Racemization : 70min
• Does the magnetic field convert unpolarized light in CPL ?
• Earth’s magnetic field : 10-4 T … (vs 7.5 T)
Rikken, G. L. J. A.; E. Raupach E. Nature, 2000, 405, 932
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Adsorption of Chiral Organic Molecules
on Enantiomorphous Crystals
• 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
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Amplification Reaction - Saoi
• Discovered in 1995
• Autocatalytic reaction
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Saoi on Crystals
Saoi, K. and al. Orig Life Evol Biosph, 2010, 40, 65
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Snail Shells
• Right-helical shells are stereoselectively
preferred and dominant
• 1 ‘racemic’ snail (Cuban tree)
• Helically chiral CaCO3 !
•
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Prebiotic synthesis : 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.
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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
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Enantioselective Formose Reaction
L-A.A. catalyze the formation of D-glyceraldehyde
preferentially?
Amino acid
Ratio (D/L)
L-Serine
50,3/49,7
L-Alanine
50,8/49,2
L-Phenylalanine
52,2/47,8
L-Valine
52,2/47,8
L-Leucine
54,4/45,6
L-Glutamic Acid
60,7/39,3
L-Proline
28,9/71,1
Breslow, R. Tetrahedron Letters 52 (2011) 2028–2032
21% ee
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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
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Morowithz Treatment – A. A.
• Most A.A. form racemic compound crystals are less
solubles (and higher m.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 crystals
would precipitates leaving increased richness in one
enantiomers
Morowitz, H. J. Theor. Biol. 1969, 25, 491
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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
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Precipitation of A.A.
• 2001 (Viedma)
• D-tyrosine crystallized faster than Ltyrosine
• 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
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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
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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
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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
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Aggregation of Disk-Shaped Porphyrins
• Stacks (electrostatic and Hbonding 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
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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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Conclusion
• No hypothesis has been accepted yet
• Terrestrial vs Extraterrestrial theory
1.
2.
3.
4.
5.
6.
Difference in energy of enantiomers : Parity violation
Chirality form polarized light : Selective degradation
Chiral field : Magnetism
Amplification and transfert of chirality
Crystallization
Unidirectional rotation of Earth