Chitosan is water soluble in acidic conditions
due to protonation of primary amines in the chitosan chains. The Ag NP suspension was also acidic (pH 5.23 to 6.25) . Although the acidity of these two solutions was maintained during mixing, partial precipitation of the Ag NP/Ch composites was observed at all conditions tested, suggesting that decreased solubility of the chitosan chains was induced by the binding of Ag NPs to selleck chemicals the chitosan amino and hydroxyl groups . Addition of excess NaOH completely precipitated the composite. Figure 1 shows a typical SEM micrograph of the composite. Ag NP/Ch composites were obtained as flocculated, aggregated, spherical sub-micrometer particles. The composites were yellow or brown; darker composites were obtained when larger amounts of Ag NPs were reacted with the chitosan. Figure 2 shows UV-visible spectra of the original Ag NP suspension and of the reaction mixes containing high amounts of Ag NP. Since spherical Ag NPs provide a peak near 400 nm [25, 29], the absence of this peak shows that
Ag NPs are not present in the supernatant of the post-reaction mixture and that the Ag NPs were completely bound to the chitosan. Figure 1 A SEM micrograph of chitosan/SN129. Weight ratio of Ag NPs in the composite is 23.5 wt%. Figure 2 UV-visible spectra of the original Ag NP suspension and of the post-reaction mixture supernatant. Procaspase activation Solid line and dashed line correspond to the original Ag NP suspension and the post-reaction mixture supernatant, respectively. (a) SN35 and the supernatants obtained from 1 mg of chitosan and 328.5 μg of SN35, (b) SN65 and the supernatants obtained from 1 mg of chitosan and 279 g μof SN65, (c) SN129 and the supernatants obtained from 1 mg of chitosan and 308 μg of SN129. The peak due to Ag NPs is marked with a vertical line. The supernatants were obtained from
the post-reaction mixture of 1 mg of chitosan Phospholipase D1 and 328.5 μg of SN35 (dotted line), 279 μg of SN65 (short dashed line), and 308 μg of SN129 (long dashed line). The solid line corresponds to the original suspension of SN129. TEM micrographs of the Ag NPs and Ag NP/Ch composites are shown in Figure 3. Compared to Ag NPs before reaction, Ag NPs in the composites are dispersed in the chitosan matrix and appear as uneven gray domains. The thickness of the TEM specimen of the composites is uneven due to the direct casting of the composite floc. Uneven contrast of the chitosan domains is due to the uneven thickness of the specimen. Ag NPs in thick areas of the chitosan matrix are overlapped. Meanwhile, Ag NPs in thin areas appeared non-overlapped. The particle sizes of Ag NPs in the composites are similar to that of the original Ag NPs. Although some minor aggregation of Ag NPs was observed, there was no macroscopic aggregation, showing that the particle size of the Ag NPs in the Ag NP/Ch composites was controlled. Figure 3 TEM micrographs of Ag NPs. (a) SN35, (b) SN65, (c) SN129; Ag NP/Ch composites (d) 24.7 wt% of SN35, (e) 21.