X-ray diffraction of histidine-silver(?) The different X-ray diffraction patterns of the histidine-silver(I) complex and the histidine blank ligand (Figures 1A and 1B, respectively) showed that histidine has reacted with silver(?) to form a new species[12]. The products were metallic silver and silver oxide. The average crystallite sizes were calculated from the peak broadening of X-ray diffraction patterns by the Scherrer equation (D=57.3×kλ/βcosθ)[13]. The mean particle size of histidine-silver(I) was 34.6 nm. The Ag colloids aggregated with the histidine solution."

Ultrastructure of histidine-silver(?) complex The transmission electron microscope image of histidine-silver(I) (Figure 2) showed that histidine-silver(?) nanoparticles were granular and tend to aggregate, and then absorbed on the columnar surface. The size distribution of single particles was found to be 16% < 20 nm, 21% between 20-40 nm, 23% between 40-60 nm, 26% between 60-80 nm, and 14% >80 nm. The mean particle size was 39.2 nm. The size of the aggregated samples was 300-500 nm."

Irfrared spectra of histidine-silver(?) complex The interaction of silver(I) with histidine was investigated furtherly by infrared. The infrared spectra of blank histidine (Figure 3A) was compared with that of histidine-silver(I) (Figure 3B). Blank histidine displayed a shoulder peak at 3 016.30 cm−1, which corresponded to O-H stretching vibrations. After contacted with silver(I), the interaction of silver(I) with the oxygen of the carboxyl group caused a clear shift and splitting of the δOH+νCH2, which moved from 3 016.30 cm−1 to 3 012.98 cm−1 and 2 879.28 cm−1. The infrared spectra showed no shift of the amido bond νC-O band at 1 634.12 cm−1 after contacted with silver(I). The band at 1 111.78 cm−1 assigned to -NH2 twisting or -NH3+ in-plane wagging shifted to lower frequencies, which indicated that the -amino-group coordinates with silver(I). In the spectra of histidine, five bands between 732.59-852.58 cm−1 were assigned to out of plane deformation vibrations of the imidazole ring CH bonds. In the spectra of histidine-silver(I), these bands decreased in number and intensity with a frequency difference of approximately 20-40 cm−1. In the spectra of histidine in this range, the most intense band was at 830.63 cm−1, while the band closed to 833.29 cm−1 had a quarter intensity of the band at 830.63 cm−1, and there was no band at 852.58 cm−1 in the spectra of histidine-silver(I). A band of moderate intensity was observed at 732.59 cm−1, which was the characteristic of histidine. A narrow band at 778.38 cm−1 was observed for histidine-silver(I), and assigned to the stretching (ring) of imidazole ring. In the spectra of histidine-silver(I), these bands were present at about the same frequency but decreased in number and intensity. The ring band of the imidazole ring was observed at 421.43 cm−1 in histidine spectra and at 472.82 cm−1 in the histidine-silver(I) spectra."