# Encapsulation of \(\alpha\)-Lipoic Acid in Halloysite Nanotubes
## 3 Results  
The morphology of the halloysite sample used in this work was imaged by electron microscopy (Figure 2). The length of the nanotubes ranges between 0.3 and 5 \(\upmu\)m. The hollow cavity is clearly visible in the TEM image (Figure 2). A proper statistical treatment evidencing the average size of the nanotubes was provided in a recent report [14]. Research activities were used to identify \(\alpha\)-lipoic acid. High-performance liquid chromatography with UV detection is the method used in this study. A chromatogram with \(\alpha\)-lipoic acid is shown in Figure 3, with a peak time of approximately 2.7 min. The peak parameters are shown in Table 1. The optimal chromatographic conditions were selected to ensure effective separation of the component. The suitability of the chromatographic system for the characteristics of the identified peak meets the requirements of the European Pharmacopoeia 11.0, which indicates that the method developed by us gives correct values. Figure 2: Microscopic images of halloysite: SEM (left hand side), TEM (right hand side). \(\alpha\)-lipoic acid was irradiated with UV light in its native form in a solution and in a suspension of halloysite nanocomposite with \(\alpha\)-lipoic acid. The total exposure time was 24 h. Control of the concentration of \(\alpha\)-lipoic acid was carried out after 1, 2, 5, 12 and 24 h of testing. Studies show that \(\alpha\)-lipoic acid degrades quite quickly under the influence of ultraviolet radiation. After a day of irradiation, its concentration in the solution decreased by 54.2%. The most significant degradation occurs in the first 12 h of exposure, when the amount of destroyed substance is reduced by more than half. The degradation of \(\alpha\)-lipoic acid in halloysite under the influence of UV light is much slower. Up to 12 h of irradiation tests, the concentration of \(\alpha\)-lipoic acid in the solution did not change significantly. It should be noted that after UV irradiation for 24 h, 84.4% of \(\alpha\)-lipoic acid is preserved (Figure 4). \begin{table}
\begin{tabular}{c c c c c} \hline \hline
**Sample** & **RT (min)** & **Area** & **Peak Height** & **Tail Factor** & **Theoretical Plates EP** \\ \hline \(\alpha\)-lipoic acid & 2.738 & 718.83 & 270.829 & 1.0 & 25,769 \\ \hline \end{tabular}
\end{table} 
Table 1: Peak characteristics of \(\alpha\)-lipoic acid from HPLC analysis. Figure 4: Degradation of \(\alpha\)-lipoic acid under the influence of UV radiation. Figure 3: Chromatogram of \(\alpha\)-lipoic acid identification. According to the scientific literature, mineral clays provide good protection against the photodegradation of photolabile organic substances used in pharmaceuticals and cosmetics. Thus, [PERSON], in co-authorship, investigated the role of montmorillonite and haloysite in the photostability of piroxicam, which is a non-steroidal anti-inflammatory drug [39]. Piroxicam was introduced into clays by mechanical mixing followed by intercalation in solution. Photostability tests using a xenon lamp showed that hybrids based on montmorillonite showed greater photostability than hybrids based on halloysite. The authors claim that in montmorillonite there were \"specific interactions\" between organic molecules and clay layers, whereas in halloysite there were none. The occurrence of specific bonds in montmorillonite during the encapsulation of photostable tetracycline is evidenced by the authors' research [40]. It was shown that the effect of increasing photostability is provided by the lamellar structure of montmorillonite, which ensures the placement of organic molecules in the interlayer space as well as a certain chemical composition with the ability for cation exchange. Other clays, such as palygorskite and sepiolite, which have a fibrous structure, did not provide effective photoprotection. [PERSON], in co-authorship [41], obtained successful results on the protection against photodegradation of promethazine (a phenothiazazine drug) intercalated in montmorillonite.