Systematic study of foreign-atom-doped fullerenes by using a nuclear recoil method and their MD simulation

Heterofullerene MC59 (M = B, Si, Al) as Potential Carriers for Hydroxyurea Drug Delivery

As a representative nanomaterial, C₆₀ and its derivatives have drawn much attention in the field of drug delivery over the past years, due to their unique geometric and electronic structures. Herein, the interactions of hydroxyurea (HU) drug with the pristine C₆₀ and heterofullerene MC₅₉ (M = B, Si, Al) were investigated using the density functional theory calculations. The geometric and electronic properties in terms of adsorption configuration, adsorption energy, Hirshfeld charge, frontier molecular orbitals, and charge density difference are calculated. In contrast to pristine C₆₀, it is found that HU molecule is chemisorbed on the BC₅₉, SiC₅₉, and AlC₅₉ molecules with moderate adsorption energy and apparent charge transfer. Therefore, heterofullerene BC₅₉, SiC₅₉, and AlC₅₉ are expected to be promising carriers for hydroxyurea drug delivery.

Synthesis and Stability of Actinium-225 Endohedral Fullerenes, 225Ac@C60

We report the first synthesis of ²²⁵Ac (t _1/2 = 10 days) endohedral fullerenes,²²⁵Ac@C₆₀. The ²²⁵Ac@C₆₀ was produced with a 12 ± 2% efficiency by applying an electrical arc discharge between a source of α-particle emitter ²²⁵Ac (∼1 mCi, electroplated on a Pt disk) and a thin coat of "preformed" C₆₀ on an Al disk (C₆₀ thickness of ∼0.25 mg/cm²). After formation by electrical arc discharge, the resulting radiofullerenes on the Al disk were dissolved in toluene under anaerobic conditions and converted to a malonate derivative using the Bingel reaction. Subsequent to repeated washings of the organic phase with dilute acidic solutions to remove exohedral ²²⁵Ac, ∼45% of ²²⁵Ac activity was retained in the organic phase, which resisted extraction into the aqueous phase. Failure to extract the ²²⁵Ac from the organic phase provided definitive evidence that the ²²⁵Ac is located inside of the fullerene. The formation of ²²⁵Ac@C₆₀ was further confirmed using a classical hot-atom chemistry technique in which the organic phase containing purified endohedral ²²⁵Ac@C₆₀ malonate was contacted with fresh dilute acid to repeatedly extract the ionic 4.8 m ²²¹Fr and 45.6 m ²¹³Bi activities (decay daughters of ²²⁵Ac), which were released by molecular disruption due to nuclear recoil. The result from the extraction experiments was further supported by a series of thin-layer chromatography and high-pressure liquid chromatography analysis of the organic phase containing ²²⁵Ac@C₆₀ or ²²⁵Ac@C₆₀ malonate. Taken together, studies show that, like polydentate chelators, single-wall fullerenes are not capable of retaining the ²²⁵Ac decay daughters.

Doping induced anisotropic growth in C60

Using density functional theory with generalized gradient approximation for exchange and correlation energy, we show that substitution of a Si atom at one of the C sites in C(60) not only allows C(59)Si to have a hydrophobic head with a hydrophilic tail but also the Si atom acts as a seed for anisotropic growth of the heterofullerene. This is demonstrated by interacting C(59)Si with N(7)Sc and B(8)Si. The resulting complex structures exhibit enhanced electric dipole moments and anisotropy. Thus, doping induced anisotropic growth of nanostructures provides a novel route for the synthesis of bifunctional particles with atomic-level control on selectivity and diversity. These particles may have important applications in biomedical, solar, and display industry.

Radioactive decay speedup at T=5 K: electron-capture decay rate of (7)Be encapsulated in C(60)

The electron-capture (EC) decay rate of (7)Be in C(60) at the temperature of liquid helium (T=5 K) was measured and compared with the rate in Be metal at T=293 K. We found that the half-life of (7)Be in endohedral C(60) ((7)Be@C(60)) at a temperature close to T=5 K is 52.47+/-0.04 d, a value that is 0.34% faster than that at T=293 K. In this environment, the half-life of (7)Be is nearly 1.5% faster than that inside Be metal at room temperature (T=293 K). We then interpreted our observations in terms of calculations of the electron density at the (7)Be nucleus position inside the C(60); further, we estimate theoretically the temperature dependence (at T=0 K and 293 K) of the electron density at the Be nucleus position in the stable center inside C(60). The theoretical estimates were almost in agreement with the experimental observations.

212Pb@C60 and Its Water-Soluble Derivatives: Synthesis, Stability, and Suitability for Radioimmunotherapy

Fullerenes could potentially play a valuable role in radioimmunotherapy by more stably encapsulating radionuclides, especially where conventional chelation chemistry is inadequate due to the physical and/or chemical properties of the radionuclide. One of the therapeutically useful radionuclides that requires improved containment in vivo is 212Pb (tau1/2 = 10.6 h), the beta-emitting parent to alpha-emitting 212Bi (tau1/2 = 60.6 min). Myelotoxicity resulting from the accumulation of 212Pb in the bone marrow has limited the use of this radionuclide despite its favorable decay characteristics. In this work, 212Pb@C60 and its malonic ester derivatives were prepared for the first time by allowing the 212Pb to recoil into C60 following alpha-decay from its parent, 0.15-s 216Po, generated in situ from the decay of 224Ra (tau1/2 = 15 days). Repeated washing of the organic phase containing the 212Pb@C60 malonic esters with challenge solutions containing cold Pb2+ ions demonstrated that some of the 212Pb could not be exchanged and was apparently inside of the fullerenes. Malonic esters of endohedral alpha-emitting 213Bi (tau1/2 = 45 min) fullerenes were prepared by an analogous procedure. Following acidification of the esters, a preliminary biodistribution study in mice was performed with the untargeted water-soluble radiofullerenes. It was found that 212Pb did not accumulate in bone after being administered as an endohedral fullerene, in contrast to results with polyhydroxylated radiofullerenes and conventional polyaminocarboxylate chelators for 212Pb. The results indicate that 212Pb is held more tightly in the fullerene than in other methods and suggest that fullerenes may have an important role in the targeted delivery of 212Pb.

[5,6]-Heterofullerene-like C58Ge: odd atoms assembling a cage

Density functional calculations and structural minimization techniques have been employed to characterize the structural and electronic properties of [5,6]-heterofullerene-like C(58)Ge. The heterofullerene molecule has an odd number of atoms on the skeleton of the cage and is a novel molecule. The vibrational frequencies of the molecule have been calculated at the B3LYP/3-21G level of theory. The absence of imaginary vibrational frequency confirms that the molecule corresponds to a true minimum on the potential energy hypersurface. Its heat of formation was estimated in this study. Since the symmetry of the molecule of [5,6]-heterofullerene-like C(58)Ge is C(2), it is a chiral molecule.

Structural and electronic properties of S-doped fullerene C58: Where is the S atom situated?

Structural and electronic properties of S-doped fullerene C58 were calculated systematically via Hartree-Fock self-consistent field (SCF) and density functional B3LYP levels of theory with 6-31G(d) basis set. The most stable C58S represents an open cage structure with a nine-member ring orifice, which provides a large hole for large atoms or small molecules to pass through into the cage. The most stable endohedral S@C58 has the S atom seated near the center of the C58 cage. The calculated highest occupied molecular orbital-lowest unoccupied molecular orbital energy gaps of the isomers lie in the range of 1.42-2.50 eV. The electron affinity and the ionization potential were also presented as an indicator of the kinetic stability. Our results may aid in the design of experimental methods for controlling the nature of fullerene cages (for example, doping, opening, and reclosing them).

Enhanced electron-capture decay rate of 7Be encapsulated in C60 cages

The decay rate of 7Be electron capture was measured in C60 and Be metal with a reference method. The half-life of 7Be endohedral C60 ((7)Be@C(60)) and 7Be in Be metal (Be metal (7Be)) is found to be 52.68+/-0.05 and 53.12+/-0.05 days, respectively. This amounts to a 0.83% difference in electron-capture decay half-life between (7)Be@C(60) and Be metal (7Be). Our result is a reflection of the different electron wave functions for (7)Be@C(60) inside C60 compared to the situation when 7Be is in a Be metal.