The AuNPs prepared with PBHs containing Met residue were stabilised with a lower number of ligands on each AuNP surface compared to the AuNPs capped with other PBH ligands. A direct comparison of Au[(Met)2B] and Au[(TrCys)2B] revealed fewer ligands for the Met-containing PBH-AuNP, despite both having the same diameter. 1H NMR spectra and FT-IR absorption spectra of free PBHs and of the PBH-capped AuNPs were measured to identify the interactions between the gold

surface and the capping ligand. The NMR spectra of the AuNPs showed broad signals PF-02341066 clinical trial compared to the free PBHs. Figure 3 shows 1H NMR spectra of Au[(Gly-Tyr-Met)2B] and its free PBH (Gly-Tyr-Met)2B in DMSO-d 6. The signal of the H-α of the Met residue appeared at approximately 1.5 ppm in the PBH (Gly-Tyr-Met)2B NMR spectrum and was significantly broadened in that

of Au[(Gly-Tyr-Met)2B]. A similar line broadening was also BAY 73-4506 observed in the NMR spectrum of Au[(Gly-Trp-Met)2B] (Figure 3) and of Au[(Met)2B] (see Additional file 2: Figure S1). These observations indicate that the PBH was attached to the gold surface through the Met residue [46]. Analogous results were observed for the NMR spectra of Au[(Gly-Tyr-TrCys)2B] and Au[(TrCys)2B] [9], where the sulphur atom of the TrCys residue is see more involved in the surface binding. Figure 3 1 H NMR spectra of Epothilone B (EPO906, Patupilone) free PBHs and PBH-capped AuNPs. (a) Free PBH (Gly-Tyr-Met)2B (top) and 1H NMR spectrum of AuNP Au[(Gly-Tyr-Met)2B] (bottom) in DMSO-d6, and (b) 1H NMR spectrum of free PBH (Gly-Trp-Met)2B (top)

and 1H NMR spectrum of AuNP Au[(Gly-Trp-Met)2B] (bottom) in DMSO-d6. Table 1 Structural characteristics of the AuNPs from elemental analysis and TEM data AuNP Size (nm) Calculated m/na from %Nb Number of Au atomsc PBH units per Au nanoparticle Mw Au[(Gly-Trp-Met)2B] 1.6 0.062 126 8 32,106 Au[(Gly-Tyr-TrCys) 2 B] 1.8 0.22 180 40 90,397 Au[(Gly-Tyr-Met)2B] 1.5 0.064 104 7 27,100 Au[(Met)2B] 2.3 0.154 375 57 102,625 Au[(TrCys)2B] 2.3 0.26 375 97 164,377 Bold emphasis is used to signal the most stable AuNP; a m, Number of PBH units; n, Number of Au atoms; b%N from elemental analysis; cestimated supposing spherical particles and applying N = 30.89602 D3 [47]. The FT-IR spectra are shown in Figure 4. For Au[(Gly-Tyr-Met)2B], Au[(Gly-Trp-Met)2B] and Au[(Met)2B], the band caused by the C = O stretching mode of the carboxylic group was absent. However, two bands were observed around 1,600 and 1,398 cm−1, assigned to the asymmetric and symmetric stretching vibrations of carboxylate anions [48]. These results suggest that the carboxylic groups are also involved in PBH interactions with the gold surface. Significant changes were observed in the amide I band in the spectra of capped NPs compared with those of the free PBHs.