150 180 210 240 270 300 330 0.010 L-Alanine D-Alanine 0.005
0.000 g
-0.005
-0.010
Søren Vrønning Hoffmann Nyk Jones
Uwe Meierhenrich Laurent Nahon Cornelia Meinert Introduction: Chirality Many biomolecules are chiral
L-Alanine D-Alanine Mirror
r-CPL Circularly polarized light l-CPL is also chiral Introduction • Homochirality in life: Almost exclusively single enantiomers: L-form of amino acids in proteins L-Ala D-Ala D-form of sugars in DNA
• Many theories for origin of this racemic symmetry breaking. By chance: Stochastic fluctuations breaking symmetry Beta decay: Parity violation in weak nuclear force
Asymmetric photochemistry with circularly polarized light (CPL) • Absolute Asymmetric Photochemistry model: Possible extra-terrestrial origin of homochirality Ice of molecules on particles and comets Origin of pre-biotic molecules on Interstellar Dust Particles (IDP)
H2O, CO2, CO, NH3 Irradiated with UV light Photo-reactions form and CH3OH on IDP organic molecules
Amino acids have been observed in simulated, UV irradiated Interstellar Ice Analogues
Meierhenrich U.J. Amino Acids and the Asymmetry of Life. Springer-Verlag Berlin Heidelberg 2008 Circular Dichroism
The CD signal: CD = AL-AR The Absolute Asymmetric Photochemistry model Photolysis upon absorption by energetic UV light
Solution (water) D/L-Phe
A chiral molecule with a CD signal would photo- decompose asymmetrically under irradiation with CPL. The devils advocate
Is there really Circularly Polarized UV light in interstellar space? The Absolute Asymmetric Photochemistry model The OMC-1 star forming region in Orion
Total IR Intensity (2.2 mm) Percentage circular polarization Calculated CPL from Mie scattering of aligned ellipsoidal grains extends into the VUV-UV spectral region… Bailey J. Science 281 (1998) 672 The Absolute Asymmetric Photochemistry model
Photo chemical reactions are governed not by CD but by anisotropy, g
k s Photolysed L-Alanine
Photolysed D-Alanine kr D/L-Alanine
CD De (k -k ) g = = = r s Abs e ½(kr+ks) Anisotropy Spectroscopy
Circular Dichroism
Absorbance Full spectra of anisotropy are recorded: g(l) g = De/e = DA/A enhances CD bands of low absorption
Anisotropy The g(l) spectrum shows that even a broad band uniform UV source can induce an e.e. in Phenylalanine in solution. CPL induced ee in Amino Acids Anisotropy Spectra of amino acids
D-Ala
L-Ala
The L-Alanine Anisotropy Spectrum falls in the RED areas.
The D-Alanine Anisotropy Spectrum falls in the BLUE areas. CPL induced ee in Amino Acids Anisotropy Spectra of amino acids
D-Ala
L-Ala
D-Val L-Ser L-Pro
L-Val
Similar tendencies are found in other amino acids CPL induced ee in Amino Acids UV irradiation of Alanine
Meinert, Hoffmann, Cassam-Chena, Evans, Giri, Nahon, Meierhenrich Angew. Chem. Int. Ed. 2014, 53, 210 –214 Rosetta mission 2014-2016 Comet 67P/Churyumov–Gerasimenko
Observed amino acids and many other organic molecules relevant to life The Rosetta mission
…. dust from the landing(s) was analysed
Glycolaldehyde reaction
Glyceraldehyde (chiral) Formose Formose
Ribose several steps The chiral unit of RNA! UV induced formation of sugars
UV induced formation of H2O Glycolaldehyde MeOH Glyceraldehyde NH3 and RIBOSE
… and many others…
H2 UV lamp Liquid nitrogen 3.5% of the sample is sugars cooled plate
Meinert C., Myrgorodska I., de Marcellus P., Buhse T., Nahon L., Hoffmann S.V., d’Hendecourt L., Meierhenrich U.J. Science 352, 2016, 208-212.. The ExoMars mission A new and ongoing mission to Mars by the European Space Agency (ESA). Look for life, past or present
ExoMars rover in 2021 ”Rosalind Franklin” discovery of the structure of DNA