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A spectroscopic (UV-Vis, CD and EPR), thermodynamic and voltammetric study of the copper(ii) complexes with the Ac-PHPGGSNWGQ-NH2polypeptide (L), a fragment of the opossum PrP protein N-terminal four-repeat region, was carried out in aqueous solution. It suggests the formation of a highly distorted [Cu(L)H−2] complex species in the neutral region, the stereochemistry of which is ascribable to a square base pyramid and a CuN3O2chromophore, resulting from the coordination of a histidine imidazole and two peptide nitrogen atoms and probably oxygen atoms from water molecules. At basic pH values a [Cu(L)H−3]−species with a pseudo-octahedral geometry was also obtained, with four nitrogen donor atoms in its equatorial plane, coming from the histidine residue and from peptidic nitrogen atoms. Interestingly, at pH values relatively higher than the neutrality, the coordination sphere of the copper complex in the [Cu(L)H−2] species changes its stereochemistry towards a pseudo-octahedron, as suggested by the change in the parallel copper hyperfine coupling constant of the EPR spectra at low temperature. A slight difference in the redox potentials between this two-faced [Cu(L)H−2] complex species seems to confirm this behaviour. Both potentiometric and spectroscopic data were compared with the analogous species obtained with the Ac-PHGGGWGQ-NH2peptide, belonging to the octarepeat domain of the human prion protein (hPrP) N-terminal region. The [Cu(L)H−2] species formed by the Ac-PHPGGSNWGQ-NH2decapeptide, having a slightly lower stability, turned out to be less abundant and to exist within a narrow pH range. [ABSTRACT FROM AUTHOR]

The I–V behavior of self-assembled monolayers of a 1,3-alternate bis(dipyridyl)calix[4]arene derivative and its Cu2+ complex have been studied by conducting-atomic force microscopy; theoretical calculations have been carried out to simulate I–V curves. The experimental data show that the two systems have different conductive properties, the Cu2+ complex monolayer having a lower resistance. Theoretical calculations demonstrate that the difference between the two simulated systems results from the different position of their Fermi level. Such a different response to charge transfer may be of interest for the fabrication of molecular electronics devices based on calixarenes. [ABSTRACT FROM AUTHOR]