## 4 Bionanosystems
### Bionanosystems for RA
#### 4.1.2. Bionanosystems Based on Inorganic Carriers
The protective effect was attributed at the precipitation of Fe\({}^{2+}\)/basil extract chelates on the superficial active region [142]. In particular, it was found that the formation of chelates occurs precisely with RA and Fe\({}^{2+}\). Possibly RA in neutral electrolytes is in the carboxylate anion form because its 1 st dissociation constant (pKa1) is 2.92 [102], and the chelates are formed by interaction between RA and empty orbital of transition metal. The chelates can precipitate on the steel coupon surface, especially at active corrosion regions. In addition, the interaction between the -OH active groups present in the RA structure and Fe\({}^{2+}\) cations are another possible mechanism for chelate formation. Halloysite (HNT) is a two-layered aluminosilicate clay similar to kaolin with the form of hollow tubes with an external diameter of about 50-80 nm, an internal diameter of 10-15 nm and a length of about 1000 nm. HNT nanotubes can effectively encapsulate active agents in the hollow structure due to a high adsorption capacity that is higher than that observed for other clays, which results in a slower release rate of any active agent from HNT [143]. Films containing HNT as a carrier for rosemary essential oil [144] and peppermint oil [145] have been reported describing the controlled release of the active components such as RA. Among the inorganic lamellar-structured reservoirs, the layered double hydroxides (LDHs), also called hydrotalcites, deserve special attention because they are very effective in adsorbing and intercalating organic molecules, as well as in releasing them in a controlled manner, and protecting them from external agents. LDHs are anionic clays consisting of positively charged and pillared hydroxide lamellae balanced by hydrated anions intercalated between the layers. The interlayer anions can be easily exchanged to produce intercalated systems containing both inorganic and organic anions, which are firmly anchored by ionic bond [146]. LDHs have been used as nanocarriers of antioxidants such as carnosine acid, gallic acid, vanmillic acid, ferulic acid, caffeic acid, and many others [147; 148; 149]. The intercalation between the layers not only protects these molecules from oxidation and thermal degradation, but it also reduces the effects of migration, and shows release behavior suitable for their use in controlled delivery systems. Furthermore, the organo-modification of LDH improves the compatibility with polymer matrices, thus making LDHs particularly interesting and versatile as additives for polymer composites. Modification of LDH with salicate anions [150] and benzoic acid derivatives [151; 152; 153], known for antibacterial properties, is described in the literature. Additionally, these functional fillers have successfully dispersed in various polymer matrices, demonstrating that the functional host-guest systems slowly release their contents to maintain antimicrobial agent concentrations at desired levels over a long period of time. Interestingly, polyphenol extracted by olive mill wastewater, which are natural antioxidants and in some cases also antimicrobials, have been confined into the host structure of a ZnAl-LDH and employed as an integrative filler for the preparation of poly(butylene succinate) (PBS) composites by in situ polymerization [154]. The antibacterial properties were assessed against _Staphylococcus aureus_ and _Escherichia coli_ as representatives of potential agents of foodborne illnesses. Similarly, [PERSON] et al. [155] intercalated olive mill wastewater into ZnAl-LDH with the aim of enhancing the durability of polypropylene and PBS melt-blended composites. More recently a few of us reported the preparation of antibacterial host guest systems by intercalation of mono-deprotonated rosmarinic and salicylic acid into a nitrate-intercalated MgAl LDH via anion exchange [156].