Valderrama Alejandro, Reynoso Radamés, Gómez Raúl W, Marquina Vivianne, Romero Martín
Facultad de Ciencias, Universidad Nacional Autónoma de México, Avenida Universidad No. 3000, Ciudad Universitaria, Delegación Coyoacán, C. P. 04510., Ciudad de México, México.
J Mol Model. 2017 Jan;23(1):15. doi: 10.1007/s00894-016-3187-6. Epub 2016 Dec 29.
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.
我们报告了通过第一性原理计算来分析钙在富勒烯C外表面的吸附情况，生成了[C + mCa]。在密度泛函理论（DFT）和含时密度泛函理论（TD-DFT）框架内，使用平面波赝势方法进行了几何优化（GO）和分子动力学（MD）模拟，以研究富勒烯和掺杂放射性碘化钠的内嵌富勒烯在与富勒烯外表面的钙原子相互作用时（即[nNaI@C + mCa]）的构型、基态相关能量以及稳定性。研究这些钙功能化（内嵌）富勒烯体系的原因是评估它们作为向人体癌组织输送放射性碘的载体时的潜在稳定性。在模拟中，我们发现，在保持空富勒烯结构稳定性的情况下，能够物理吸附在其外表面的钙原子数量的几何极限是28个钙原子，这也考虑到了随着吸附钙原子数量增加富勒烯的比例膨胀。然而，富勒烯体系在钙吸附过程中的稳定性还强烈取决于富勒烯是否包裹了任何原子或分子，因为这些被包裹的原子/分子也会与富勒烯相互作用并影响其稳定性。 Mulliken电负性分析表明，当富勒烯内部和/或外部的原子向富勒烯提供电荷（电子）时，富勒烯会膨胀。富勒烯碳原子上的多余电荷会削弱一些碳 - 碳键，有可能导致它们断裂，在这种情况下，富勒烯失去包裹分子的能力并将其释放。图形摘要：掺杂放射性碘化钠的内嵌富勒烯与28个钙原子以几何排列相互作用的DFT模拟。
