The thermodynamic parameters for the inclusion of some naturally occurring amino acids into a series of p-sulfonated calix[4]arenes, were determined via both ¹H NMR and calorimetric titrations in buffered aqueous solution at 25 °C. The calorimetric data show that inclusion is enthalpically driven in all cases, regardless of flexibility of the host and the nature of the guest. The most efficient receptor is the calix[4]arene tetrasulfonate 1, which exists in solution at pH 7 in a cone conformation, stiffened by H-bonding at the lower rim. Molecular mechanics data help in the understanding of why some hosts do not form inclusion complexes at all. The comparison of our data with literature reports shows that there are dramatic buffer-dependent changes in the binding affinities.

Copper(ii) coordination to human amylin has an influence on the aggregation and cytotoxic features of the polypeptide. Comparative investigations, carried out on a model peptide encompassing the 17–29 aminoacid region of amylin containing the putative metal binding site, support the non-fibrillar nature of the copper(ii) complexes.

An aqueous solution spectroscopic (Vis and EPR) study of the copper(II) complexes with the Ac-HGGG-NH₂ and Ac-PHGGGWGQ-NH₂ polypeptides (generically designated as L) suggests square base pyramids ascribable to [Cu(L)H₋₂] complex species, which contain three nitrogen donor atoms, arising from imidazole and peptide groups, in the equatorial plane and for a pseudo-octahedral geometry in the case of [Cu(L)H₋₃]⁻ and [Cu(L)H₋₄]²⁻ which have four nitrogen donor atoms in their equatorial plane. The coordination sphere of the copper complex in the [Cu(L)H₋₂] species, which is present at neutral pH values, is completed by two oxygen donor atoms. ESI-MS spectra ascertained that water molecules are not present in the coordination equatorial plane of this latter species, in comparison with other copper(II) complexes with ligands bearing nitrogen and oxygen donor atoms and surely having equatorial water molecules. This indicates the coordination of a carbonyl oxygen atom in the equatorial plane has to be invoked. However, no direct proof about the involvement of a carbonyl group oxygen donor atom apically linked to copper was obtained, due to the flexibility of these structures at room temperature. Additionally, the low A_‖ value leads one to consider another oxygen atom of a carbonyl group being involved in the apical bond to copper in a fast exchange fashion. This apical interaction, which may also involve a water molecule, is more pronounced in the Cu–Ac-HGGG-NH₂ than in the analogous Cu–Ac-PHGGGWGQ-NH₂ system, probably because of the presence of tryptophan and proline in the polypeptide sequence.