On 2014 Feb 12, Ferenc Zsila commented:

This text is shown on the page 24, in the paper of Ma et al. (see above):

"Figure 2C shows the change in intensity of CD bands in the presence of 1.0 mol equiv of Cu²⁺ at 252, 312, and 514 nm. Relatively strong CD bands are often for d-d transitions of Cu²⁺ tetragonal complexes.²⁹ However, these complexes involve main-chain amide coordination as well as histidine coordination via the imidazole ring. In these cases, the dominant contribution to optical activity observed is due to the vicinal contributions resulting from the asymmetric alpha carbon held in a chelate ring between two chelating donor atoms, such as adjacent main-chain amides.⁴³ At physiological pH and below, the lack of optical activity from the d-d transition of the complex suggests that backbone amide coordination is absent. At pH 8.5 and above, amide proton is deprotonated, which promotes copper coordination by the main chain, resulting in a negative CD band appearing at 514 nm. Clearly, Aβ(1-16) forms a type II square-planar coordination geometry with Cu^2+, and the coordination geometry is 3N1O at pH 7.5. Both visible absorption and CD spectra indicate that the coordinating ligands are strongly pH dependent, a mixed species is present at physiological pH, and main-chain amide coordination is absent at lower pH values."

The following text is shown on the page 18171, in the paper of Syme et al. Syme CD, 2004:

"The insets in Fig. 2 show the change in the intensity of CD bands in the presence of 1 eq of Cu²⁺ at 252, 312, and 514 nm. Relatively strong CD bands are often observed for d-d transitions of Cu²⁺ tetragonal complexes (36, 37). However, these complexes involve main-chain amide coordination as well as histidine coordination via the imidazole ring. In these cases, the dominant contribution to optical activity observed is due to the vicinal contributions resulting when the asymmetric α-carbon is held in a chelate ring between two chelating donor atoms (e.g. adjacent main-chain amides) (38). At physiological pH and below, the lack of optical activity from the d-d transition of the Cu-Aβ complex suggests that backbone amide coordination is not taking place. It is likely that raising the pH above 8 promotes amide deprotonation and copper coordination by the main chain, resulting in a CD band being observed at 514 nm. In summary, it is clear that Aβ forms a TypeII square-planar coordination geometry with Cu^2+, and both EPR and CD measurements indicate that the coordinating ligands are highly pH-dependent, a mixed species is present at physiological pH, and main-chain amide coordination is not present at lower pH values."

[Syme CD, Nadal RC, Rigby SE, Viles JH. Copper binding to the amyloid-β (Aβ) peptide associated with Alzheimer's disease: folding, coordination geometry, pH dependence, stoichiometry, and affinity of Abeta-(1-28): insights from a range of complementary spectroscopic techniques. J. Biol. Chem. 2004 (279) 18169-18177.]

On 2014 Feb 01, Ferenc Zsila commented:

None

On 2014 Feb 01, Ferenc Zsila commented:

None

On 2014 Feb 12, Ferenc Zsila commented:

This text is shown on the page 24, in the paper of Ma et al. (see above):

"Figure 2C shows the change in intensity of CD bands in the presence of 1.0 mol equiv of Cu²⁺ at 252, 312, and 514 nm. Relatively strong CD bands are often for d-d transitions of Cu²⁺ tetragonal complexes.²⁹ However, these complexes involve main-chain amide coordination as well as histidine coordination via the imidazole ring. In these cases, the dominant contribution to optical activity observed is due to the vicinal contributions resulting from the asymmetric alpha carbon held in a chelate ring between two chelating donor atoms, such as adjacent main-chain amides.⁴³ At physiological pH and below, the lack of optical activity from the d-d transition of the complex suggests that backbone amide coordination is absent. At pH 8.5 and above, amide proton is deprotonated, which promotes copper coordination by the main chain, resulting in a negative CD band appearing at 514 nm. Clearly, Aβ(1-16) forms a type II square-planar coordination geometry with Cu^2+, and the coordination geometry is 3N1O at pH 7.5. Both visible absorption and CD spectra indicate that the coordinating ligands are strongly pH dependent, a mixed species is present at physiological pH, and main-chain amide coordination is absent at lower pH values."

The following text is shown on the page 18171, in the paper of Syme et al. Syme CD, 2004:

"The insets in Fig. 2 show the change in the intensity of CD bands in the presence of 1 eq of Cu²⁺ at 252, 312, and 514 nm. Relatively strong CD bands are often observed for d-d transitions of Cu²⁺ tetragonal complexes (36, 37). However, these complexes involve main-chain amide coordination as well as histidine coordination via the imidazole ring. In these cases, the dominant contribution to optical activity observed is due to the vicinal contributions resulting when the asymmetric α-carbon is held in a chelate ring between two chelating donor atoms (e.g. adjacent main-chain amides) (38). At physiological pH and below, the lack of optical activity from the d-d transition of the Cu-Aβ complex suggests that backbone amide coordination is not taking place. It is likely that raising the pH above 8 promotes amide deprotonation and copper coordination by the main chain, resulting in a CD band being observed at 514 nm. In summary, it is clear that Aβ forms a TypeII square-planar coordination geometry with Cu^2+, and both EPR and CD measurements indicate that the coordinating ligands are highly pH-dependent, a mixed species is present at physiological pH, and main-chain amide coordination is not present at lower pH values."

[Syme CD, Nadal RC, Rigby SE, Viles JH. Copper binding to the amyloid-β (Aβ) peptide associated with Alzheimer's disease: folding, coordination geometry, pH dependence, stoichiometry, and affinity of Abeta-(1-28): insights from a range of complementary spectroscopic techniques. J. Biol. Chem. 2004 (279) 18169-18177.]