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.