Photocatalysis and the origin of life: Synthesis of
nucleoside bases from formamide on TiO2(001)
single surfaces
Ana Patricia Gámiz-Hernández
Department of Chemistry
University of Basel
AG Meuwly
A. P. Gámiz Hernández (UniBasel)
Senanayake PNAS 2006
August 15th 2013
1/9
Outline
1
Background
2
Results
3
Conclusions
A. P. Gámiz Hernández (UniBasel)
Senanayake PNAS 2006
August 15th 2013
2/9
Background
Theories about the origin of Life
Oparin and Haldane
hypothesized that conditions on
the primitive Earth favored
chemical reactions that
synthesized organic compounds
from inorganic precursors.
The Miller-Urey experiment
simulated the conditions to be
present on the early Earth, and
tested for the occurrence of
chemical origins of life.
H2 O, CH4 , NH3 , and H2 , heat,
electrodes and cooling obtaining
amino acids (G), sugars and
other biomolecules.
A. P. Gámiz Hernández (UniBasel)
Senanayake PNAS 2006
August 15th 2013
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Results
Photoreaction of formamide (HNCO) in TiO2 layers
Previous studies of photoreaction of organic
molecules have been carried out in liquid phase.
Here, they report the first experiments performed in a
clean surface at ultra-high vacuum conditions.
Among the theories of the origin of life, those
considering mineral surfaces are appealing because
of their simplicity.
Minerals act as template providing directionality and
as catalytic materials reducing the activation energy
for the formation of reaction intermediates.
A. P. Gámiz Hernández (UniBasel)
Senanayake PNAS 2006
August 15th 2013
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Results
Photoreaction of formamide (HNCO) in TiO2 layers
Products desorbing after
formamide adsorption at 300 K
over the TiO2 single crystal in
dark conditions: CO, H2 , NH3 ,
HCN and traces of H2 O.
The reactions are temperature
dependent; no reaction occurs at
84 K while the reaction occurred
at 300K and above.
A. P. Gámiz Hernández (UniBasel)
Senanayake PNAS 2006
August 15th 2013
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Results
Photoreaction of formamide (HNCO) in TiO2 layers
When the adsorption of
formamide is subjected to UV
irradiation for 15 min, the
desorption shows considerable
masses above 45 m/z, larger
than formamide.
Anaylisis using mass
spectrometry shows evidence of
NH2 CO and some products have
been identify as nucleic acids:
Cytosine, Uracil, Thymine,
Adenine and Guanine.
Some of these products have
been already identify in other
reactions of HCN polimerization.
A. P. Gámiz Hernández (UniBasel)
Senanayake PNAS 2006
August 15th 2013
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Results
Photoreaction of formamide
Using High-resolution x-ray
analysis shows a larger
concentration of A and G nucleic
acids than U and C. The opposite
is observed in gas-phase.
A. P. Gámiz Hernández (UniBasel)
Senanayake PNAS 2006
August 15th 2013
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Conclusions
Conclusions
After photoexcitation of a TiO2 surface, the productos accumulate
with time and may not be subject to decomposition from the
excitation source.
The formation of these molecules, by surface reaction of
formamide, is proof that some minerals in the form of oxide
semiconductors are active materials for making
high-molecular-weight organic molecules that may have acted as
precursors for biological compounds required for life in the
universe.
A. P. Gámiz Hernández (UniBasel)
Senanayake PNAS 2006
August 15th 2013
8/9