These show that the mobility of the complexes decreased in the order Complex I > Complex II > Complex III for both polyphenols, and that the mobility of the EGCG complexes was considerably less than for the corresponding GA complexes. The presence of three distinct mononuclear Cu(II) complexes HKI-272 order was identified from the frozen solution spectra of the products of reactions with Cu(II) with both EGCG and GA, and

the corresponding complexes from each polyphenol had similar values for their g- and hyperfine parameters. These results are consistent with the unpaired electron residing primarily in the 3dx2-y2 orbital in all of the complexes, and the similarities in the results from the two polyphenols suggests that the binding with Cu is similar with both, and hence

that both involve chelation with a pyrogallol entity. The values for the spectral parameters observed in the present measurements are similar to those reported by Oess et al. [1] and [2] for the Cu(II)-GA system. Based on the reported trends in g- and A(Cu)-values with coordination environment for Cu(II) amino acid complexes [23], [24], [25] and [26], Complexes I and II can be assigned respectively to mono- and bis- Cu(II) polyphenol complexes in both the EGCG and GA systems. selleck chemicals The spectral parameters for Complex III are similar to those of Complex II, although Complex III has slightly larger A// and Aiso and slightly smaller g//- and giso-values with each polyphenol. The value of (A//-Aiso) is proportional to the 3dx2-y2 electron density and the fact that its magnitude changes in the same direction as that of Aiso is consistent with core polarization of inner shell s-orbitals being the main source of Aiso (e.g. [27]) in these complexes. The fact that similar numbers are obtained for Complexes II and III for both GA and EGCG ( Table 1) strongly suggests that they all have similar Cu coordination environments, and that there is no major change in symmetery between Complexes II and III. Since it is well known that dimeric and polymeric species

are formed as a result of autoxidation of polyphenols at high pH values [28], it is possible that Complex III involves one or more Vasopressin Receptor dimers of GA or EGCG attached to the Cu, although it is also possible that the differences between Complexes II and III simply represent a change in the phenolic groups coordinated to the copper. We do not consider that Complex III corresponds to the coordination of a third bidentate ligand to the Cu-atom as suggested by Oess et al. [1] and [2]. Such a complex should have some population of the Cu 4 s orbital, and hence a much reduced value of Aiso (since polarization of inner shell orbitals give the opposite sign to population of the 4 s orbital [27]). Finally, we cannot exclude the possibility that Complex III corresponds to a mixed polyphenol/glycerol complex, but in the absence of further evidence any assignment must be regarded as speculative.