Spectroscopic and potentiometric study of copper(II) complexes with l-histidyl-glycyl-l-histidyl-glycine in aqueous solution

Cu nanocrystal growth on peptide nanotubes by biomineralization: Size control of Cu nanocrystals by tuning peptide conformation

“…Because the size of Cu nanocrystals was changed on the HG12 peptide nanotubes by pH change, it is likely that the HG12 peptide-Cu(II) complex undergoes the conformation change on the nanotubes between the lower pH range and the higher pH range. This conformation change is supported by the report that the free HG12 peptide molecules in aqueous solution formed complexes with Cu(II) and folded into the compact form by means of ligation between histidines and Cu(II) in the lower pH range, whereas the HG12 peptideCu(II) complexes were aggregated in the higher pH range (39,57). To confirm that this peptide conformation change by pH change also occurs on the nanotubes, Fourier transform IR spectra of the HG12 peptide-Cu(II) complexes on the nanotubes at pH 6 and pH 8 were compared in Fig.…”

“…6 Left). This folded conformation of the HG12 peptide-Cu(II) complex is adapted from the complex conformation observed in the free suspension (39,57). The compacted HG12 peptide chain by folding may also contribute reduction of the aggregation between the regularly spaced peptide chains on the nanotubes.…”

“…5, solid line), indicating that fewer Cu ions bind the glycine amides in the basic condition (58). The 1,625 cm Ϫ1 peak is the amide vibration of ␤-sheet conformation of peptide backbone aggregation by hydrogen bonding (57,60), and the increase of this IR intensity by increasing pH indicates that the HG12 peptide chains on the nanotubes were aggregated in the higher pH range. The increase of IR intensity at a 1,604 cm Ϫ1 peak by pH increase is due to the formation of intermolecular N(His)-Cu(II)-N(His) bonds between the peptide chains by means of the aggregation (57,58).…”

“…The 1,625 cm Ϫ1 peak is the amide vibration of ␤-sheet conformation of peptide backbone aggregation by hydrogen bonding (57,60), and the increase of this IR intensity by increasing pH indicates that the HG12 peptide chains on the nanotubes were aggregated in the higher pH range. The increase of IR intensity at a 1,604 cm Ϫ1 peak by pH increase is due to the formation of intermolecular N(His)-Cu(II)-N(His) bonds between the peptide chains by means of the aggregation (57,58). This observation is consistent with the loss of IR intensity at a 1,550 cm Ϫ1 peak, the imidazole side chain vibrational mode of histidine without the Cu(II) ligation, by way of pH increase (61).…”

Size‐Controlled Ni Nanocrystal Growth on Peptide Nanotubes and Their Magnetic Properties

“…[14,22±24] The HG12 peptides were immobilized on the template nanotubes by incubating the peptides in the nanotube solution for 24 h at pH values between 4 and 10, and the resulting HG12-peptide nanotubes were examined using Raman microscopy and atomic force microscopy before growing Ni nanocrystals on the nanotube surfaces. Previously, the HG12 peptides were shown to aggregate in basic solution, [19,25,26] and we hypothesized that the degree of the peptide aggregation controls the size of the Ni nanocrystal on the nanotube, as proposed in Figure 1. Recently, a synthetic peptide, Ala±His±His±Ala±His±His±Ala±Ala±Asp, was immobilized on nanotubes for Au-nanocrystal growth, and Au nanocrystals grown on the nanotubes were observed to be located between the peptides that were attached to the nanotube in a regular fashion.…”