## 2 Applications of Chiral Nanoparticles
### Asymmetric Catalysis
investigated the use of chiral oxovanadium (+)-pseudooephedrine complex sustained on Fe\({}_{3}\)O\({}_{4}\) magnetic nanoparticles (VO(pseudooephedrine)@MNPs) as an innovative nanocatalyst for the chemoselective oxidation of sulfides to sulfoxides (Figure 4) [56]. By using hydrogen peroxide as a green oxidant, the reaction proceeded with high yields and enantiomeric excesses ranging between 20 and 27% at room temperature under solvent-free conditions. The catalyst was also recycled up to 20 times with minimal loss of action and enantioselectivity. \begin{table}
\begin{tabular}{c c c c} \hline \hline
**NPs** & **Surface Functionalization** & **Catalyzed Reaction** & **Reference** \\ \hline \hline \multirow{3}{*}{Ni} & \multirow{3}{*}{(\(R\),\(R\))-tartaric acid} & carbonyl & \multirow{3}{*}{[53]} \\  & & hydrogenation of & \\  & & \(\beta\)-ketoesters and & \\  & & \(\beta\)-diketoesters & \\ \hline Pt & CIL\({}_{\text{PEG-CD}}\) & hydrogenation of & \\  & & activated ketones & \\ \hline ZnCl\({}_{2}\)/SiO\({}_{2}\) & \(N\)-myristoyl-L-alanine & hydroamination & \\ \hline Fe\({}_{3}\)O\({}_{4}\) & oxovanadium (+)-pseudooephedrine & oxidation of sulfides & \\ \hline Fe\({}_{3}\)O\({}_{4}\) & oxovanadium (+)-pseudooephedrine & carbonyl & \\  & & cyanosilylation & \\ \hline \(N\)-oleoyl-D/L-proline & - & aldol reaction & \\ \hline Fe\({}_{3}\)O\({}_{4}\)/SiO\({}_{2}\) & cyclohexyl-1,2-diamine & aldol reaction & \\ \hline SiO\({}_{2}\) &
\begin{tabular}{c} (\(P\))-1,12-dimethyl-8-methoxycarbonylbenzo \\ \([c]\)phenanthrene \\ \end{tabular} & Rh-catalyzed & [60] \\ \hline Au & triazacyclononane-Zn\({}^{\text{II}}\) & RNA hydrolysis & [61] \\ \hline \hline \end{tabular}
\end{table} 
Table 2: Main applications of chiral NPs for the asymmetric catalysis and their principal characteristics. The same VO (pseudoephedrine)@MNPs catalyst was also able to catalyze, again at room temperature and under solvent-free conditions, the cyanosilylation of carbonyl compounds using trimethylsilyl cyanide with 8-25% enantiomeric excesses. Again, the catalyst was reused up to 15 times with minimal loss of activity and enantioselectivity [57]. Chiral proline-based polymeric nanoparticles were able to catalyze asymmetric aldol reaction both in organic and aqueous solvents [58]. The NPs, prepared by miniemulsion polymerization and with an average diameter of 160 nm, possessed high surface area, and the whole particle, not just the surface, was shown to be chiral. Although the enantioselectivity obtained with the nanoparticle catalyst was lower than that obtained with the free amino acid, the NPs have the advantage of being easily recovered and recycled. Moreover, this approach could be used to prepare a variety of polymeric NPs with different sizes, architectures, and chemical functionalities as new nanotechnology-based organocatalysts. The same type of reaction, as well others, has been shown to be influenced by chiral amines and their byproducts. Silica-coated Fe\({}_{3}\)O\({}_{4}\) MNPs were also functionalized with chiral bis-amine organocatalysts, such as glutamate, Pro-Glu dipeptide, or cyclohexyl-1,2-diamine, for catalyzing asymmetric aldol reaction [59]. Among the investigated amines, the NPs functionalized with the stiff cyclohexyl-1,2-diamine gave the best yield (up to 08%) and enantioselectivity (up to 96%), also showing good recyclability by keeping these values high even after three cycles (Figure 5). Figure 4: Chemoselective oxidation of sulfides to sulfoxides by means of VO(pseudoephedrine)-functionalized MNPs. Reprinted with permission from [56], Copyright Elsevier, 2015. Figure 5: Mechanism of purification of asymmetric aldol reaction products by means of chiral MNPs. Reprinted with permission from [59], Copyright Elsevier, 2019. In an alternative approach, chiral silica NPs loaded with (_P_)-1,12-dimethyl-8-methoxycarbonyl benzo[_c_]phenanthrene were able to selectively adsorb, collect, and precipitate a diol disulfide from solution favoring its reaction with the rhodium catalyst in solution among other disulfides [60].