Search

A study uses density functional theory calculations to demonstrate that C38N12, just as C48N12, could be a stable N-dopant of C70. Results reveal that the chemical stability of C48N12 and C58N12, with respect to oxygenation, is not significantly different from that of C70, thereby indicating that the N-dopant would not easily be oxygenated in air under normal conditions by considering many different isomers of the product.

Density functional theory (DFT) calculations are used to investigate the relative stabilities of all isomers of [Sc.sub.3]N@[C.sub.67]B and [Sc.sub.3]N@[C.sub.67]N as well as those of stable isomers of [Sc.sub.3]N@[C.sub.66]BN. It is concluded that the relative stabilities of various isomers of the BN-substituted fullerenes are understood in terms of the combined electrostatic effects in the B- and N-substitutions of [Sc.sub.3]N@[C.sub.68] complemented by a specific local preference in the N-substitution and the formation of a B-N bond.

Multiwalled boron carbonitride (BCN) nanotubes with two different structures are synthesized. Results suggest that there is negligible binding between the C and B/N atoms, indicating the segregation of the C layers from the BN nanotubes.

G-quadruplexes are higher-order DNA and RNA structures formed from guanine-rich sequences, and they are attractive anticancer drug targets. Understanding the three-dimensional interactions between a G-quadruplex and its ligand in solution is the key to discovering a drug lead. Hence, from crystallographic or NMR structures, molecular dynamics studies have been performed on six ligand−quadruplex complexes. BRACO-19, BSU6039, daunomycin, RHPS4, MMQ1, and TMPyP4 are the six ligands that bind to the G-quadruplex structures in the studies. Based on molecular dynamics simulations and a series of computational analyses, the results suggest that ions move away from the external G-quartet to let the ligand bind to the quadruplex in aqueous solution. The ligand binding can increase the stability of the Hoogseen hydrogen bonds within the G-quartet. However, the G-quartet binding site can only fit one ligand molecule. The ligand can form hydrogen bonds at the loop or flank of the quadruplex. However, not all the interactions will stabilize the ligand−quadruplex complex in aqueous solution. These findings can assist in the design of selective and potent G-quadruplex ligands. [ABSTRACT FROM AUTHOR]

On the basis of calculations using density functional theory, we show that C58N12, just as C48N12, can be a stable N-dopant of C70. By considering many different isomers of the product, we find that the chemical stability of C48N12and C58N12, with respect to oxygenation, is not significantly different from that of C70, thereby indicating that the N-dopant would not easily be oxygenated in air under normal conditions. In both C48N12O and C58N12O, many different isomers are expected, in which oxygenation occurs at different C-N bonds as well as at C-C bonds, among which specific C-N bonds are the most amenable to the reaction. Investigation of their hydrogenations shows that C48N12is slightly more easily hydrogenated than C60, while C58N12is less easily hydrogenated. In addition, we expect a regiospecificity in the hydrogenated products of C58N12, which prefers to react at equatorial sites, while C70prefers reaction at polar sites. Meanwhile, comparison of the encapsulation energy of a nitrogen atom (Nen) in C60, C48N12, C70, and C58N12shows that the N-doped fullerenes, particularly C58N12, can encase the atom much better than the undoped ones, allowing us to expect the existence of NC48N12and NC58N12. Spin multiplicities are doublet for most of their stable structures. These observations correlate with the formation of Nen-C bonds, which are not found in NC60and NC70. Various isomers of the N-encapsulating fullerenes were identified. The relative stability of these isomers heavily depends on the number of substitutional nitrogen atoms around Nen-C bonds. [ABSTRACT FROM AUTHOR]

Multiwalled boron carbonitride (BCN) nanotubes with two different structures were synthesized via thermal chemical vapor deposition; one has 10% C atoms homogeneously doped into BN nanotubes (B0.45C0.1N0.45 NTs), and the other has BN layers sheathed with 5-nm-thick C outerlayers (BN-C NTs). The electronic structures of the B, C, and N atoms were thoroughly probed by synchrotron X-ray photoelectron spectroscopy and the X-ray absorption near-edge structure method. The B0.45C0.1N0.45 NTs contain a significant amount of BC and CN bonding with a pyridine-like structure (hole structure), which reduces the π bonding states of the B and N atoms. From the XPS valence band spectrum, the band gap was estimated to be about 2.8 eV. In the BN-C NTs, the C and BN domains are separated without forming the pyridine-like structure. Using the first principles method, we investigated the relative stabilities and electronic structures of the various isomers of the double-walled (12,0) @ (20,0) BCN NTs. The C-outerlayer BN nanotube structure is the most stable isomer, when there exist no defects in the tubes with B/N = 1.0 (i.e., graphite-like structure). In addition, a reasonable model, which is characterized by the motives consisted of three pyridine-like rings around a hollow site, is presented for the local structure of C atoms in the B0.45N0.45C0.1 NTs. A considerable decrease of the band gap due to the 10% C doping was predicted, which was consistent with the experimental results. [ABSTRACT FROM AUTHOR]