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.

In this work we have studied the well-known "Buckminsterfullerene" C₆₀ containing different amounts, from one to four molecules, of sodium radio-iodide (Na(131)I), with density functional theory geometrical optimizations and molecular dynamics at 310 K and atmospheric pressure. We found that nanocapsules with the radioactive content Na¹³¹I@C₆₀, 2Na¹³¹I@C₆₀ and 3Na¹³¹I@C₆₀ are stable. Furthermore, the C₆₀ fullerene undergoes expansion when the number of sodium radio-iodide molecules inside increases. Utilizing the Mulliken charge distribution analysis it was shown that a small charge transfer occurs from iodine to fullerene's carbon atoms. This produces repulsion which increases bond lengths thus the structure is weakened while the binding energy per atom decreases. For the case in which the fullerene initially contains four sodium radio-iodide molecules the expansion is greater than that which the structure can withstand. So the fullerene breaks and releases its contents. This result leads us to conclude that the fullerene can encapsulate up to three molecules of sodium radio-iodide.

We report first-principles calculations carried out to analyze the adsorption of calcium on the outer surface of the fullerene C, yielding [C + 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., [nNaI@C + 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.