XPS characterization of (copper-based) coloured stains formed on limestone surfaces of outdoor Roman monuments

Limestone basements holding bronzes or other copper alloys artefacts such as sculptures, decorations and dedicatory inscriptions are frequently met both in modern and ancient monuments. In outdoor conditions, such a combination implies the corrosion products of the copper based alloy, directly exposed to rainwater, will be drained off and migrate through the porous surfaces, forming stains of different colours and intensities, finally causing the limestone structures to deteriorate

Structural analysis of Cu(II) ligation to the 5'-GMP nucleotide by pulse EPR spectroscopy

Simple copper salts are known to denature poly d(GC). On the other hand, copper complexes of substituted 1,4,7,10,13-pentaazacyclohexadecane-14,16-dione are able to convert the right-handed B form of the same DNA sequence to the corresponding left-handed Z form. A research program was started in order to understand why Cu(II) as an aquated ion melts DNA and induces the conformational change to Z-DNA in the form of an azamacrocyclic complex. In this paper, we present a continuous wave and pulse electron paramagnetic resonance study of the mononucleotide model system Cu(II)-guanosine 5'-monophosphate . Pulse EPR methods like electron-nuclear double resonance and hyperfine sublevel correlation spectroscopy provide unique information about the electronic and geometric structure of this model system through an elaborate mapping of the hyperfine and nuclear quadrupole interactions between the unpaired electron of the Cu(II) ion and the magnetic nuclei of the nucleotide ligand. It was found that the Cu(II) ion is directly bound to N7 of guanosine 5'-monophosphate and indirectly bound via a water of hydration to a phosphate group. This set of experiments opens the way to more detailed structural characterization of specifically bound metal ions in a variety of nucleic acids of biological interest, in particular to understand the role of the metal-(poly)nucleotide interaction