RESUMO
First principles calculations have been performed for C60@C180 carbon double-layer endofullerenes with up to: three diatomic radioiodine molecules (131I2), two potassium radio-iodide (K131I), and three sodium radio-iodide (Na131I) inside. The plane-wave pseudopotential (PP) method within the general gradient approximation (GGA) in the framework of the density functional theory (DFT) and time-dependent DFT (TD-DFT) was used to perform geometric optimizations (GOs) and molecular dynamics (MD) at 310 K and atmospheric pressure. We found that the double-layer carbon nanocapsules formed by two concentric fullerenes (C180 surrounding C60) are very stable and may contain a radiodosis, without altering their configuration; that is, the 3(131I2)@C60@C180, 2(K131I)@C60@C180, and 3(Na131I)@C60@C180 systems constitute stable nanocapsules. We analyzed the interaction of double-layer endofullerene with radioactive content with some calcium, phosphorus, and strontium atoms, [n(X131I)@C60@C180 + mY], for X = I, K, Na; Y = Ca, P, Sr; n = 1, 2, 3; m = 1, , 20. Our calculations show that up to m = 20 calcium atoms can easily be physisorbed by the outer surface of the double-layer endofullerene, maintaining their integrity and shielding the radiodosis of any interaction that can proceed from the outside. It is thus concluded that these double-layer endofullerenes can be functionalized as vectors to deliver radiodosis with structural advantages over the single layer systems; as they are more robust, stable, and possess a larger surface to functionalize with some atoms serving as molecular recognizers. Graphical abstract Double-layer carbon nanocapsules with radioiodine content and its interaction with calcium, phosphorus and strontium.
RESUMO
We report first-principles calculations carried out to analyze the adsorption of calcium on the outer surface of the fullerene C60, yielding [C60 + mCa]. Geometric optimization (GO) and molecular dynamics (MD) simulation were performed using the plane-wave pseudopotential method within the framework of density functional theory (DFT) and time-dependent DFT (TD-DFT) to investigate the configurations, the associated energies in the ground state, and the stabilities of fullerenes and endofullerenes doped with radioactive sodium iodide when they interact with calcium atoms on the outer fullerene surface (i.e., [nNa131I@C60 + mCa]). The reason for investigating these calcium-functionalized (endo)fullerene systems was to gauge their potential stability when used as vectors to deliver radioiodine to cancerous tissue in the human body. In the simulations, we found that the geometric limit on the number of calcium atoms that can be physisorbed on the outer surface of an empty fullerene while maintaining its structural stability is 28 calcium atoms, which also takes into account the proportional expansion of the fullerene as the number of absorbed calcium atoms increases. However, the stability of a fullerene system during calcium adsorption also strongly depends on whether any atoms or molecules are being encapsulated by the fullerene, as these encapsulated atoms/molecules can also interact with the fullerene and influence its stability. A Mulliken electronegativity analysis revealed that, when atoms inside and/or outside the fullerene donate charge (electrons) to the fullerene, the fullerene expands. The excess charge on the carbon atoms of the fullerene weakens some of the carbon-carbon bonds, potentially causing them to break, in which case the fullerene loses its ability to encapsulate molecules and releases them. Graphical Abstract DFT simulation of a endo fullerene doped with radioactive sodium iodide interacting with 28 calcium atoms in a geometric arrangement.
RESUMO
This paper inquires the C60 capabilities to contain radio-iodide ((131)I2) molecules. The encapsulation conditions are investigated applying first principles method to simulate with geometric optimizations and molecular dynamics at 310 K and atmospheric pressure. We find that the n(131)I2@C60 system, where n = 1, 2, 3 , is stable if the content does not exceed three molecules of radio-iodide. The application of density functional theory allows us to determine that, the nanocapsules content limit is related with the amount of charge that is transferred from the iodine (131)I2 molecules to the carbon atoms in the fullerene surface. The Mulliken population analysis reveals that the excess of charge increases the repulsive forces between atoms and the bond length average in the C60 structure. The weakened bonds easily break and will critically damage the encapsulation properties. Additionally, we test the interaction nanocapsules with different amounts of radioactive iodine diatomic molecules content with calcium atoms, and find that only the fullerene containing one radioactive iodine diatomic molecule was able to interact with up to nine atoms of calcium without disrupting or cracking. Other fullerenes with two and three radio iodine diatomic molecules cannot resist the interaction with a single calcium atom without cracking or being broken.
