# Boron Nitride Nanotubes for Curcumin Delivery as an Anticancer Drug: A DFT Investigation
## 3 Results and Discussion
### Electronic Properties  
In this section, we study the effect of the electronic properties of BNNT on curcumin adsorption. In Table 4, the calculated HOMO and the LUMO energies and energy gap (the difference between the HOMO and LUMO energies for the pristine curcumin molecule, BNNT, and the curcumin-BNNT complexes at the theoretical level of LDA + DFT) have been reported. The energy gap (Eg) is an important element in chemical reactivity determination and charge transfer. The energy gap was determined to track the stability of the complexes. Lower LUMO energy molecules are more likely to accept electrons and have higher electrophilicity. Electrons from molecules of higher LUMO energy values can be accepted by the molecules. Higher HOMO energy values contribute to nucleophilicity. The HOMO-LUMO energy band gap of a system is associated with a decrease or increase in chemical reactivity and chemical stability. Since the HOMO-LUMO energy gap (Eg) of the curcumin drug inside the BNNTs complex has an increase in the molecular energy gap, it is then associated with a decrease in chemical reactivity and an increase in stability. This means overcoming the barriers to adequate curcumin delivery, thus improving its bioavailability.  
The value of the HOMO-LUMO energy gap (Eg) for pristine (5,5) BNNT was found to be 4.71 (Table 4). After the adsorption process of curcumin molecules on the (outside and inside) surfaces of (5,5) BNNT, Eg values were found to be 3.62 and 3.65 eV, respectively. For both complexes, HOMO and LUMO energies are adjusted to higher and lower energies, respectively, which results in a decrease in the Eg value of the complex (Table 4). The Eg of the adsorbed molecule on the inner surface of the (5,5) BNNT is higher than the Eg adsorbed molecule on the outer surface of the (5,5) BNNT. The drug molecule has better adsorption and more stability inside than outside for (5,5) BNNT. All these findings agree and accept the results of previous results seen in this review, so drug molecules are better adsorbed inside the (5,5) BNNT surface according to the adsorption energy (Table 4). Increased electrical conductivity of the complexes is predicted by the comparisons between the Eg of the drug molecule and the pristine BNNT of the complexes. Density of states (DOS) diagrams for curcumin drug, (5,5) BNNT, and curcumin drug complexes with (5,5) BNNT are shown in Figure 3. The energy level and peaks of the panel (c) are compared with those of panel (b) to show the adsorption of the nanotubes studied. As seen in Figure 3, a slight change is observed near the valence band after adsorption of drug molecules within (5,5) BNNT compared to that of the pristine (5,5) BNNT.  
\begin{table}
\begin{tabular}{c c c c c c} \hline \hline \multirow{2}{*}{**System**} & \multirow{2}{*}{**Position**} & **Eads** & \multirow{2}{*}{**EHOMO**} & **ELMO** & \multirow{2}{*}{**Eg (eV)**} \\  & & **(kcal/mol)** & & **(eV)** & & \\ \hline Curcumin & & & \(-\)5.03 & \(-\)1.22 & 3.81 \\ \hline (5,5) BNNT & & & \(-\)5.68 & \(-\)0.96 & 4.71 \\ \hline Curcumin-(5,5) BNNT & outside & \(-\)15.15 & \(-\)4.84 & \(-\)1.22 & 3.62 \\ \hline Curcumin-(5,5) BNNT & inside & \(-\)16.91 & \(-\)4.94 & \(-\)1.29 & 3.65 \\ \hline \hline \end{tabular}
\end{table}
Table 4: The adsorption energies and the geometric parameters of curcumin drug adsorbed on the BNNTs.