# F127/Cisplatin Microemulsions: _In Vitro_, _In Vivo_ and Computational Studies
## 3 Results and Discussion
### Computational Results: The Interplay between Cis and Surfactant F127  
As said, the clinical use of free Cis is limited due to cruel organ toxicity. Moreover, insolubility and uncontrolled release of Cis limit the anti-cancer strength of the drug. This study showed that Cis-loaded microemulsions induce less toxicity than free Cis against normal HUVEC cells. Therefore, we tried to investigate mutual interactions between Cis and F127 to understand the molecular parameters that change after interactions of this drug with surfactant. We depicted a Molecular Electrostatic Potential (MEP) map of a unit of the polymeric chain of F127 to study the interactions of Cis with surfactant. This map helps to find electron-rich positions that are capable of hydrogen bonding (HB) interactions with Cis. As displayed in Figure 7, red positions are located on atoms O\({}_{2}\), O\({}_{6}\), and O\({}_{7}\) of F127. Thus, we focused on these positions for HB interactions with Cis. Binary complexes formed via HB interactions of Cis with atoms O\({}_{2}\), O\({}_{6}\), and O\({}_{7}\) of F127 are named **A**, **B**, and **C**. Results show that ammonia groups of Cis have more tendencies for HB interactions with F127 than chlorine atoms. In fact, we surveyed HB interactions between chlorine atoms of Cis and F127, but no stable complex was formed. Results indicate that the binding energy of complexes **A**, **B**, and **C**, calculated at the B3 LYP/Lanl2 dz level of theory, is 17.21, 19.75, and 15.29 kcal mol\({}^{-1}\), respectively. The hydrogen bond length (d\({}_{\text{NH}}\)) in complex **A** and **B** is 1.77 and 1.74 A, respectively. On the other hand, Cis interacts through both its ammonia groups with atom O\({}_{7}\) of F127 in the complex **C**, and the average d\({}_{\text{NH}}\) value, in this case, is 2.17 A. As can be seen, the increase of HB strength in the above-mentioned complexes is accompanied by the decrease of d\({}_{\text{NH}}\) values. This result shows that ammonia groups of Cis are good HB donors that interact with atoms O\({}_{2}\), O\({}_{6}\), and O\({}_{7}\) of F127 as HB acceptors. It seems that such interplays influence the function of Cis. Therefore, we performed further computations to better understand the nature of the mentioned interplays. The electronic properties of Cis and F127 change during the formation of the complexes. Therefore, the highest occupied molecular orbital (HOMO) and lowest unoccupied molecular orbital (LUMO) energies, and energy gap (EG) values of all geometries were calculated and are shown in Table 2. \begin{table}
\begin{tabular}{c c c c c c c} \hline \hline  & **EHOMO** & **ELUMO** & **EG** & **q0** & **qH** & **qN** \\ \hline Cis & \(-6.272\) & \(-1.901\) & \(4.372\) & - & \(0.363\) & \(-0.883\) \\ F127 & \(-6.990\) & \(1.288\) & \(8.278\) & * & - & - \\ complex **A** & \(-6.225\) & \(-1.739\) & \(4.486\) & \(-0.567\) & \(0.457\) & \(-0.916\) \\ complex **B** & \(-6.383\) & \(-1.927\) & \(4.455\) & \(-0.413\) & \(0.463\) & \(-0.918\) \\ complex **C** & \(-6.166\) & \(-1.711\) & \(4.455\) & \(-0.548\) & \(0.391\) & \(-0.890\) \\ \hline \hline \end{tabular}  
* Charge of atoms O\({}_{2}\), O\({}_{6}\), and O\({}_{7}\) in F127 is \(-0.494\), \(-0.343\), and \(-0.458\) e, respectively.  
\end{table} 
Table 2: Energies of HOMO and LUMO, EG values (in eV), and charge of atoms involved in HB interaction (in e). Figure 7: MEP maps of Cis (**left**) and F127 (**right**) together with numbers of important atoms. As can be seen, the EG value of free F127 is higher than the complexes. Results indicate that a decrease of HOMO and LUMO energies is followed by the increase of the HB strength of the complexes. The lowest E\({}_{\text{HOMO}}\) and E\({}_{\text{LUMO}}\) values correspond to complex **B**, with the largest binding energy value. Therefore, we have represented the distribution of HOMO and LUMO on the complexes in Figure 8. As can be observed, HOMO lays on Cis in all complexes, and there is only an extension on atom O\({}_{6}\) of F127 in complex **B**.