# Immobilization of Levocyetririzine on Mesoporous Silica for Antiallergenic Gel Formulation
## 3 Results and Discussions
### Immobilization of Levb on Mesoporous Material
The layer thickness values are shown in Figure 6 as the function of the preparation (mixing) time. Evidently, the Levo does not form a uniform and coherent layer on the surface, but the thickness of the layer can help approximate the adsorbed quantity. The trend of increasing the layer thickness with mixing time is in good agreement with the results of adsorption measurements, as illustrated in Figure 7. \begin{table}
\begin{tabular}{c c c c c c} \hline \multicolumn{2}{c}{**Sample**} & **O** & **N** & **C** & **Cl** & **Si** \\ \hline Uncorrected & _SyLev6_ & 50.3 & 2.1 & 24.2 & 0.7 & 22.7 \\  & _SyLev7_ & 46.9 & 3.0 & 27.6 & 0.9 & 21.5 \\  & _SyLev8_ & 44.0 & 2.5 & 30.6 & 1.2 & 21.7 \\  & _SyLev9_ & 43.1 & 3.2 & 32.1 & 1.2 & 20.5 \\ \hline Pure base & Theoretical & 11.1 & 7.4 & 77.8 & 3.7 & \\  & Measured & 12.6 & 9.6 & 74.5 & 3.3 & \\ \hline Corrected & _SyLev6_ & 12.0 & 6.9 & 78.9 & 2.2 & SiO\({}_{2.3}\) \\  & _SyLev7_ & 11.2 & 8.5 & 77.8 & 2.5 & SiO\({}_{2.2}\) \\  & _SyLev8_ & 11.9 & 6.4 & 78.8 & 3.0 & SiO\({}_{2.1}\) \\  & _SyLev9_ & 11.3 & 7.7 & 78.0 & 2.9 & SiO\({}_{2.2}\) \\ \hline \end{tabular}
\end{table} 
Table 4: Surface composition (_atomic_ %) of the immobilized levocetriazine base samples calculated by the _infinitely thick homogeneous sample_ model. Figure 5: Adsorption isotherms of levocetriazine base–MSM and Syloid materials. The FTIR analysis provides complementary information about the immobilization of the drug (Figure S6). In Syloid, the SiO\({}_{4}\)\({}^{4-}\) tetrahedrons form long Si-O-Si chains, typically resulting in bands at 1074 cm\({}^{-1}\) and 804 cm\({}^{-1}\) as asymmetric and symmetric stretches, respectively (Figure 8). The strong band at 464 cm\({}^{-1}\) is attributed to a bending vibration of the Si-O-Si chain. A silica surface usually reacts with the humidity of air to form Si-OH bonds, and this stretch gives a band at 973 cm\({}^{-1}\) here. Moreover, there are two broader bands with lower intensity at 3350 cm\({}^{-1}\) and 1630 cm\({}^{-1}\), which can be attributed to adsorbed water, as inorganic materials always contain it. The IR spectrum of Levo is richer than that of Syloid owing to the numerous functional groups. Therefore, the additional peaks that cannot be seen on the carrier but are present in the immobilized sample are attributed to Levo, providing evidence of immobilization of the drug. Based on the DSC measurement results (Figure S7), variable amounts of physically bound water could be detected in all samples. This is confirmed by the variable amount of mass losses (determined between 30 and 125 \({}^{\circ}\)C, hot presented here) and the intense  
Figure 6: Thickness of the levocetririzine layers adsorbed on silica, calculated from X-ray photoelectron intensity data, as function of preparation (mixing) time. Figure 7: Changes in results of adsorption measurements (total and mesopore volume, specific surface area; relative to Syloid) as function of preparation (mixing) time. absorption bands in the IR spectrum around 3400 cm\({}^{-1}\) and 1640 cm\({}^{-1}\). The highest amount of moisture (18.3 m/m\(\%\)) was contained by the sample SyLev8, which also explains the broad endotherm noticeable on its corresponding heat flow curve (Figure S7). On the heat flow curve of the other three samples (_SyLev6, SyLev7, and SyLev9_) a small and broad endotherm is visible, with a peak maximum in the range of 72-86 \({}^{\circ}\)C, corresponding to the evaporation of water, while the other endotherm, at higher temperatures, described above, is noticeable only in the case of sample _SyLev7_. Based on the IR recordings, the presence of the active ingredient could be detected in each sample. The fact that the melting endotherm of the active ingredient is not visible in all cases can be explained by the fact that in such cases, a small amount of the active ingredient may be present only on the surface of the Syloid and possibly in amorphous form. The morphologies of the Levb on Syloid were studied by SEM, and are shown in Figure S8 for all samples and Figure 9 for _sample SyLev8_.