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Biologische Systeme und Medizin Poster: Mi., 14:00–16:30 M-P184
Chiral discrimination and structural analysis of RNA by Raman spectroscopy
and x-ray crystallography
Sarah Bolik 1 , Benjamin Schulz 1 , Michael Ruebhausen 1 , Mathias Kramer 2 ,
Markus Perbandt 2 , Christian Betzel 2 , V.E. Erdmann 3 , Sven Klussmann 4
1 Insitut für Angewandte Physik, Universität Hamburg – 2 Institut für Biochemie, Univeristät
Hamburg – 3 Institut für Biochemie, Freie Universität Berlin – 4 Noxxon Pharma
AG, Berlin
Amino acids found in living organisms occur almost exclusively as L-enantiomers and
nucleic acids as D-enantiomers. The origins of this pervasive homochirality have never
been explained satisfactorily. Because there is no obvious biochemical reason for choosing
one enantiomer over the other, numerous physical and biochemical mechanisms
have been invoked to explain the phenomenon. Chirality is a fundamental aspect of
chemical biology, and is of central importance in pharmacology. We have analysed the
L- and the D- enantiomer of an RNA molecule with the sequence (r(CUGGGCGG)x
r(CCGCCUGG)) by X-ray crystallography and Raman spectroscopy. The combined
results of these experiments reveal new insights about the nature of chirality in nucleic
acids. X-ray crystallography is a technique in crystallography in which the pattern
produced by the diffraction of X-rays through the closely spaced lattice of atoms in a
crystal is recorded and then analyzed to reveal the nature of that lattice. Since electrons
more or less surround atoms uniformly, it is possible to determine where atoms
are located. This generally leads to an understanding of the material and molecular
structure of a substance. This technique is widely used in chemistry and biochemistry
to determine the structures of inorganic compounds, DNA/RNA, and proteins. X-ray
diffraction is commonly carried out using single crystals of a material. Inelastic light
scattering can reveal structural changes as well as changes in the electronic structure of
the investigated system due to its coupling to electronic matrix elements. We use incident
photons around 5 eV, where specific chromophores within the enantiomer exhibit
a resonance. Spectra could be described by taking into account oscillation modes of the
included bases. These modes are superpositions of modes originating from the different
possible vibrations of atoms in the complex structured bases. We find that there is
no sign of a structural difference in the spectra of L- and D-RNA. Nevertheless, small
changes in the modes between the two forms enable us to calculate a Raman Difference
Spectrum (RDS). The RDS is dependent on the incident photon energy. We suggest
that electronic configuration between L- and D-RNA is different due to charge transfer
effects that modify the electronic structure to which the Raman probe couples. We
outline how to use this matrix element effect for the study of bio-organic matter.