## 3 Results and Discussion  
### Preparation and Characterization of Chiral PMO NPs  
The preparation of chiral PMO nanoparticles was initiated by synthesizing a small library of chiral-bridged organosilane monomers that could serve as chiral building blocks of the periodic mesoporous organosilica nanoparticles. These chiral ligands were synthesized by reacting to different chiral amines and amino acids with a silane compound in a molar ratio of 1:2 under an inert atmosphere as illustrated in Scheme 1.  
After the chiral building blocks were prepared, the chiral PMO NPs were prepared by emulsifying the oil phase containing the chiral-bridged silane precursor in an ethanol/water mixture containing cetyltrimethylammonium bromide (CTAB) or a cetyltrimethylammonium chloride (CTAC) surfactant as a structure-directing agent. Under these conditions, the chiral ligands 1-3 yielded in the presence of CTAB or CTAC either aggregates or fused nanoparticles as was observed by scanning electron microscopy (SEM) analysis (Figures 1-3). On the other hand,1,1'-((1,2R)-1,2-diphenylethane-1,2-diyl)bis(3-(3-(triethoxysil)propyl)urea) chiral ligand (**4**) was the best chiral candidate for preparing chiral PMO nanoparticles, which afforded chiral PMO NPs with uniform shape and size as shown in the SEM images (Figure 4). In addition, a representative transmission electron microscopy (TEM) image of this system exhibited very well-ordered spherical nanoparticles with a very low resolution of their mesoporous texture (Figure 4).  
Figure 4: SEM (**a,b**) and TEM (**c**) images of a chiral PMO system prepared from ligand (**4**) with CTAB surfactant.  
Figure 3: SEM images of a chiral PMO system prepared from ligand (**3**) with (**a,b**) CTAB and (**c,d**) CTAC surfactants.  
Figure 2: SEM images of a chiral PMO system prepared from ligand (**2**) with (**a,b**) CTAB and (**c,d**) CTAC surfactants.  
In addition to the cationic surfactants, the contribution of other polymeric surfactants to the system was tested with a ligand (**4**). Apparently, non-ionic and polymeric surfactants were not highly favored in these systems and according to the obtained results, it was concluded that a cationic CTAB surfactant was the best candidate for preparing chiral PMO nanoparticles. The resulting SEM images of different systems that were prepared by utilizing different surfactants are summarized in Table 1. As seen in entries 1-3, when Triton X-100, Ieppal CO-520, and Pluronic P123 surfactants were used, nanometric sized PMO NPs were obtained, but they were highly fused and some aggregates were observed. The use of Brij 78 surfactant (Table 1, entry 4) yielded very smooth submicron PMO particles but they were also fused. However, the utilization of a cationic surfactant was much favored because it yields smooth and spherical nanoparticles.  
\begin{table}
\begin{tabular}{c c c} \hline \hline
**Entry** & **Surfactant** & **Structure** & **SEM Images** \\ \hline
1. & Triton X-100 & \(\text{H}\text{C}\) \\
2. & Ieppal CO-520 & \(\text{C}\text{g}\text{H}_{19}\) \\ \hline
3. & Pluronic P123 & \(\text{H}\text{C}\text{g}\text{H}_{19}\) \\
4. & Brij 78 & \(\text{H}\text{C}\text{g}\text{H}_{19}\) \\
5. & Genamin & \(\text{H}\text{C}\text{g}\text{H}_{19}\) \\
6. & CTAC 25\% & \(\text