2 research outputs found
Abilities of elastic peak electron spectroscopy in the field of thin films growth investigation: Au on Al and Al2O3
International audienc
Adsorption of Cytosine and AZA Derivatives of Cytidine on Au Single Crystal Surfaces
The adsorption of cytosine on the
Au(111) and Au(110) surfaces
has been studied using both aqueous deposition and evaporation in
vacuum to prepare the samples. Soft X-ray photoelectron spectroscopy
(XPS) and near edge X-ray absorption fine structure spectroscopy (NEXAFS)
were used to determine the electronic structure and orientation of
the adsorbates. In addition, three derivatives of cytosine, 6-azacytosine,
6-azacytidine, and 5-azacytidine, were studied. Monolayer films of
the latter three samples were adsorbed on Au(111) from aqueous solution,
and the nature of bonding was determined. Spectra have been interpreted
in the light of published calculations of free cytosine molecules
and new ab initio calculations of the other compounds. Surface core
level shifts of Au 4f imply that all of these compounds are chemisorbed.
Cytosine adsorbs as a single tautomer but in two chemical states with
different surface-molecule bonding. For deposition in vacuum, a flat-lying
molecular state bonded through the N<sub>(3)</sub> atom of the pyrimidine
ring dominates, but a second state is also present. For deposition
from solution, the second state dominates, with the molecular plane
no longer parallel to the surface. This state also bonds through the
N<sub>(3)</sub> atom, but in addition interacts with the surface via
the amino group. Two tautomers of 6-azacytosine were observed, and
they and 6-azacytidine adsorb with similar geometries, chemically
bonding via the azacytosine ring. The ribose ring does not appear
to perturb the adsorption of azacytidine compared with azacytosine.
The azacytosine ring is nearly but not perfectly parallel to the surface,
like 5-azacytidine, which adsorbs as an imino tautomer. This work
highlights the complications, which can occur when medicinally significant
compounds are adsorbed on gold, for example, in drug delivery systems,
but also the amount of chemical information and detailed understanding
that can be extracted from such complex systems