*3.3. X-Ray Diffraction*

The spectra of chitosan and POX-1 are very similar. Both diffractograms show similar stretched peaks at 10–30◦ 2θ, which are attributed to chitosan (Figure 3A) [38].

The maxima of the spectra of both chitosan and deferoxamine are in the same region (15–27◦ 2θ). The spectrum of chitosan displays a double wide peak with the left-shouldered maximum at 20◦ 2θ, while the diffractogram of deferoxamine at the same region exhibits four peaks with the main one at ca. 21.2◦ 2θ. Thus, the maximum and the shoulders of the deferoxamine-conditioned signals are right-shifted as compared to those of chitosan (Figure 3B).

The maxima of the spectra of both POX-2 and deferoxamine are located at ca. 21◦ 2θ. The spectrum of the POX-1 sample does not display any significant peak at this region. This fact indicates the presence of deferoxamine in POX-2 and its absence in POX-1 (Figure 3C).

The X-ray diffraction spectra of POX-2 and POX-3 samples are very similar. However, the diffractogram of POX-3 displays a broader maximum peak at 18–25◦. 2θ. This indicates the presence of smaller, crystallographically active structural units in the main particles of the sample (for example, in the POX-3 nanoparticles, probably, there are smaller nanolevel particles) (Figure 3D). The described differences do not refute our assumption about the identity of the chemical structure of POX-2 and POX-3.

Generally, the X-ray diffraction study confirms the identical chemical structures of POX-2 and POX-3, and allows us to conclude that both POX-2 and POX-3 contain chitosan and deferoxamine.
