Adsorption of Si6O12 on CNTs in View Point of NMR Shielding Tensors and NBO Analysis: A Novel Material for Drug Delivery

The interaction of the Si6O12 molecule over the CNTs have been investigated with density functional theory using HF and B3LYP method and 6-31G, 6-31G** and 6-311G** basis sets. We also analyze the electronic structure and charge Mulliken population for the energetically most favorable complexes. Our results indicate Si6O12 can form stable bindings with CNTs via the Oxygen. The NMR shielding tensors have been investigated. The same Study performed for Si7O14 and we found that this molecule can form stable bindings with CNTs via the Silicon site. Thus, we arrive at the prediction that the even number (Si6O6) has a different mechanism for adding to CNTs compare to add number such as Si7O14.

Although it is a commonplace material using in pencil leads, its unique structure causes it to present characteristics that had not found with any other materials. CNT can be classified into single-wall CNT, double-wall CNT and multi-wall CNT according to the number of layers of the rolled graphite  .
The type attracting most attention is the single-wall CNT, which has a diameter deserving the name of "nanotube" of 0.4 to 2 nanometers. The length is usually in the order of microns, but singlewall CNT with a length in the order of centimeters has recently released [42][43][44][45][46][47][48][49][50] .
The carbon nanotube (CNT) is a representative nano-material. CNT is a cylindrically shaped carbon material with a nano-metric-level diameter 94-98 . In the NBO analysis, the interaction arising from electron delocalization are analyzed by selecting a number of natural bonding and antibonding orbitals that distort from the idealized Lewis structure, caused by interactions among them through hyper-conjugative or electrostatic interactions. In NBO analysis, the input atomic orbital basis set is transformed via natural atomic orbitals (NAOs) and natural hybrid orbital (NHOs) into NBO. In the present theoretical study, particular attention has been paid to the structural properties of The Si6O12-CNTs and Si7O14-CNTs systems. So, the NBO analysis gives supplementary information of the relative structural properties. It should be noted that conjugated systems, such as benzene and pconjugated linear molecules, have been well studied with NBO analysis.
The NMR isotropic shielding constants were calculated using the standard GIAO (Gauge-Independent Atomic Orbital) approach of Gaussian 03 program package.
a) The isotropic value σ iso of the shielding tensor which can be defined as:

RESULTS AND DISCUSSION
We studied about Si 6 O 12 and Si 7 O 14 molecules as the novel material for drug delivery.
Before and after connecting to the CNTs. NMR and NBO calculations were performed in electric field of charges. NMR and NBO parameters are listed in tables 1-5 in different levels and different basis sets. The situation of Si 6 O 12 adsorption over  Considering the optimized structure, the NMR shielding tensors were calculated then these parameters were used to show active sites in this structure. The results of σ iso , σ aniso, σ, Δδ and η for this nano-cone in the same methods and basis sets are shown in table 2. Finally the charts of σ iso , σ aniso, σ and η for the atoms of Si 6 O 12 Si7O14 in 6-31G, 6-311G**, level of theory and B3LYP method. We can obtain the interesting results from the NMR charts. Comparison of these charts (σ iso , σ aniso , σ and η) shows that some of peaks in these charts are similar to each other. If these peaks are reviewed, we can understand which similar atoms are situated in the same peaks of different charts. The comparison of these peaks shows that three atoms are exactly repeated in σ iso , σ aniso , σ and η charts. These three atoms are the active sites in these structures. In general, the chart of electronic charge in different methods and basis sets is similar to the charts of NMR parameters Silicon atoms have more electrons than oxygen atoms.
So we can find that most chemical shielding. The concavity points are created due to the change of negative charge into a positive charge.
The electron density figure show that the mechanism of positive charge is different from negative charge. Positive and negative areas are completely different.
The results show that the heterocycle drugs connect to Si 6 O 12 is stronger than Si 7 O 14 .
NBO analysis of the Si6O12 and Si7O14 system at the level of B3LYP/6-31g theory with different has been given in Table 3 Table 3.Natural electron configuration of Valance and core electrons is listed in table 4. Occupancy, geminal, vicinal, energy, NBO, Principal delocalization is listed in Table 6.