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 [CuLH-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(ll) 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.

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In this work, three modified CDs (mCDs), namely 6-deoxy-6-[1-(2-amino)ethylamino]-beta-CD, 6-deoxy-6-[N-(2-methylamino)pyridine)]-beta-CD and 3-monodeoxy-3-monoamino-beta-CD, are investigated as chiral selectors for CE with LIF (CE-LIF) and CE-TOF-MS. The potential of these three mCDs as chiral selectors in CE was also compared with the unmodified beta-CD and gamma-CD. A group of ten different D- and L-amino acids derivatized with FITC was selected as case-study for CE-LIF and CE-MS comparison. The analyte group includes negatively (D/L-Glu and D/L-Asp), neutral (D/L-Ala and D/L-Asn) and positively (D/L-Arg) charged amino acids. Chiral separation conditions compatible with CE-TOF-MS could be achieved based on the figures of merit obtained by CE-LIF using the different CDs. Interestingly, LOD values obtained by chiral CE-TOF-MS were in the nM range comparable or only slightly worse to those obtained by CE-LIF. Moreover, the time of analysis using mCDs was reduced more than 30% compared with the non-chiral conditions (19.2 versus 28.4 min, respectively), with resolution and efficiency values as high as 5.15 and 843 000 plates/m, respectively. The usefulness of this chiral CE-TOF-MS method was corroborated through the detection of the main D- and L-amino acids found in different real samples including transgenic versus wild soy and vinegar.

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A beta-cyclodextrin substituted by an imidazole-bound histamine (CDmh) was successfully used to separate underivatised tryptophan racemate in capillary electrophoresis in the presence of copper(II) ion by the ligand exchange mechanism. To the best of our knowledge, this is the first example of a cyclodextrin derivative behaving as the first coordination sphere ligand in the complex added to the background electrolyte (BGE).