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: Many biomolecules are chiral

L-Alanine D-Alanine Mirror

r-CPL Circularly polarized light l-CPL is also chiral Introduction • in : 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 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 (ESA). Look for life, past or present

ExoMars rover in 2021 ”Rosalind Franklin” discovery of the structure of DNA