2.2.3. PXRD Studies

X-ray diffractometry has been used as a complementary tool for evaluating the possible interactions between the RSP/RM-β-CD inclusion complex and the excipients, which correlate with changes in the crystallinity profile of the samples.

The X-ray diffraction patterns of the RSP/RM-β-CD inclusion complex, selected excipients, and their physical mixtures are depicted in Figure 10a–d.

**Figure 10.** X-ray diffraction profiles of RSP/RM-β-CD inclusion complex, selected excipients, and their physical mixtures: starch (STR) (**a**); microcrystalline cellulose (CEL) (**b**); magnesium stearate (MgSTE) (**c**); lactose (LCT) (**d**).

The diffraction profile of the RSP/RM-β-CD inclusion complex presents three characteristic reflections of higher intensity at 9.42, 11.42, and 17.48 2*θ* and others of lower intensity at 14.17, 19.87, and 21.47 2*θ*. In the diffractograms of STR and CEL, there are several main broad peaks and numerous undefined ones, with low intensities indicating the amorphous nature of the excipients (Figure 10a,b). In the case of physical mixture of the RSP/RM-β-CD inclusion complex with STR, the diffraction pattern reveals the disappearance of the high intensity crystalline reflection of the inclusion complex from 9.42 2*θ*; the other two characteristic peaks of the inclusion complex can be observed at 11.64 and 14.47 2*θ*, while the rest of the bands are overlapped over the broad bands of excipient. The PXRD pattern of the inclusion complex–CEL physical mixture exhibits an overlap of characteristic peaks of both the RSP/RM-β-CD inclusion complex observed at 9.45, 11.50,

14.29, 17.52, 19.90, 21.32 2*θ*, and the excipient, indicating a lack of interaction between the components.

The diffractogram of MgSTE shows characteristic crystalline reflections at 2*θ* of 5.35, 7.20, 8.90, 21.78, and 22.53, suggesting its crystalline state [18] (Figure 10c). The diffraction profile of physical mixtures of the inclusion complex with MgSTE represents a sum of characteristic peaks of KP that appear at 2*θ* of 9.42, 11.45, 14.27, 17.47, 19.84, and 21.30, and excipient peaks that appear at 5.41, 7.23, 9.02, 21.93, and 22.71 2*θ*, highlighting no interaction between the inclusion complex and MgSTE.

The crystalline profile of LCT is demonstrated by the high intensity crystalline reflections at 19.22, 19.69, 20.11, 20.77, and 21.09 2*θ* and other peaks with lower intensity at 10.61, 12.62, 16.53, 23.85, 24.75, 25.67, 31.85, and 33.32 2*θ*, which are present in its diffraction pattern (Figure 10d). The diffractogram of the inclusion complex–LCT mixture shows all the characteristic crystalline reflections of excipient (at 10.57, 12.58, 16.48, 19.17, 19.63, 20.06, 20.72, 21.03, 23.84, 24.71, 25.61, 31.78, and 33.24 2*θ*), but some corresponding to RSP/RM-β-CD KP are greatly attenuated (at 14.14 and 21.30 2*θ*) or shifted (9.36, 11.36, and 17.17 2*θ*), confirming the interaction in solid state between the inclusion complex and LCT that was previously demonstrated by thermal analysis and UATR-FTIR spectroscopy.
