Jia-Jia Zheng

The inhibition of migration and invasion of cancer cells by graphene via the impairment of mitochondrial respiration.

Graphene and its derivatives have become important nanomaterials worldwide and have potential medical applications including in vivo diagnosis, drug delivery, and photothermal therapy of cancer. However, little is known about their effect on the metastasis of cancer cells, which is the cause of over 90% of patient deaths. In the present investigation, we provide direct evidence that low concentrations of pristine graphene and graphene oxide show no apparent influence on the viability of MDA-MB-231 human breast cancer cells, PC3 human prostate cancer cells, as well as B16F10 mouse melanoma cells. However, both pristine graphene and graphene oxide can effectively inhibit the migration and invasion of these cancer cells. Further studies indicate that exposure of cells to graphene led to the direct inhibition of the electron transfer chain complexes I, II, III and IV, most likely by disrupting electron transfer between iron-sulfur centers, which is due to its stronger ability to accept electrons compared to iron-sulfur clusters through theoretical calculations. The decreased electron transfer chain activity caused a reduction in the production of ATP and subsequent impairment of F-actin cytoskeleton assembly, which is crucial for the migration and invasion of metastatic cancer cells. The inhibition of cancer cell metastasis by graphene and graphene oxide might provide new insights into specific cancer treatment.

Density Gradation of Open Metal Sites in the Mesospace of Porous Coordination Polymers

The prevalence of the condensed phase, interpenetration, and fragility of mesoporous coordination polymers (meso-PCPs) featuring dense open metal sites (OMSs) place strict limitations on their preparation, as revealed by experimental and theoretical reticular chemistry investigations. Herein, we propose a rational design of stabilized high-porosity meso-PCPs, employing a low-symmetry ligand in combination with the shortest linker, formic acid. The resulting dimeric clusters (PCP-31 and PCP-32) exhibit high surface areas, ultrahigh porosities, and high OMS densities (3.76 and 3.29 mmol g-1, respectively), enabling highly selective and effective separation of C2H2 from C2H2/CO2 mixtures at 298 K, as verified by binding energy (BE) and electrostatic potentials (ESP) calculations.

Two-Dimensional Carbon Compounds Derived from Graphyne with Chemical Properties Superior to Those of Graphene

Computational studies considering both thermodynamic and kinetic aspects revealed that graphyne, a carbon material that has recently been of increasing interest, favours unprecedented homogeneous “in-plane” addition reactions. The addition of dichlorocarbene to the C(sp)-C(sp) bond, a site with outstanding regioselectivity in graphyne, proceeds via a stepwise mechanism. Due to their homogeneous nature, additions occurring at C(sp)-C(sp) bonds yield structurally ordered two-dimensional carbon compounds (2DCCs). 2DCCs have electronic band structures near the Fermi level that are similar to those of graphene and are either electrically semi-conductive or metallic depending on whether the reactions break the hexagonal symmetry. Notably, 2DCCs can be further functionalised through substitution reactions with little damage to the extended π-electron conjugation system. These results suggest that 2DCCs derived from graphyne have physical properties comparable to those of graphene and chemical properties superior to those of graphene. Therefore, 2DCCs are expected to be better suited to practical applications.

Violating the isolated pentagon rule (IPR): endohedral non-IPR C98 cages of Gd2@C98.

The geometric, electronic structure, and thermodynamic stability of large gadolinium-containing endohedral metallofullerenes, Gd(2)@C(98), have been systematically investigated by comprehensive density functional theory calculations combined with statistical mechanics treatments. The Gd(2)@C(2)(230924)-C(98) structure, which satisfies the isolated-pentagon rule (IPR), is determined to possess the lowest energy followed with some stable non-IPR isomers. In order to clarify the relative stabilities at elevated temperatures, entropy contributions are taken into account on the basis of the Gibbs energy at the B3LYP level for the first time. Interestingly, a novel non-IPR Gd(2)@C(1)(168785)-C(98) isomer which has one pair of pentagon adjacency is more thermodynamically stable than the lowest energy IPR species within a wide temperature interval related to fullerene formation. Therefore, the Gd(2)@C(1)(168785)-C(98) is predicted to be the most proper isomer obtained experimentally, which is the largest non-IPR carbon cage found so far. Our findings demonstrate that interaction between metals and carbon cages could stabilize the fused pentagons effectively, and thus, the non-IPR isomers should not be ignored in some cases of endohedral metallofullerenes. The IR features of Gd(2)@C(98) are simulated to assist its future experimental characterization.

Open-Shell Triplet Character of #6094C68: Spherical Aromaticity, Thermodynamic Stability, and Regioselective Chlorination

The recently captured fullerene (#6094)C68 was found to exhibit a more aromatic character than originally assumed via density functional theory calculations. Such an inconsistency was attributed to the unexpected triplet ground state of pristine (#6094)C68. The equilibrium concentrations of C68 isomeric system reveal that (#6094)C68 is thermodynamically favorable at elevated temperatures with respect to the fullerene formation. The regioselective chlorination process of the open-shell C68 was discussed as well to elucidate the formation of octachlorinated derivative C68Cl8 experimentally.

Metal-promoted restoration of defective graphene

A novel metal-participating rearrangement mechanism of graphene is elucidated via density functional calculations. Results show that the barrier for the elimination of Stone–Wales defects can be decreased by the adsorbed transition metal atoms. Molecular orbital composition analysis shows that the contribution from the metal atom to the frontier orbital in the transition state is a key factor for the distinct metal catalytic properties. Among the chosen elements (Cu, Ni, Fe, Cr, Mo, and W), tungsten can reduce the activation energy remarkably from 6.2 to 2.9 eV, and 1000 K is regarded as a favorable temperature to yield perfect hexagonal nanographene. In contrast to curved network structures in fullerenes and carbon nanotubes, the open and planar structure of graphene helped to accommodate kinetic transformations of the carbon skeleton and metal atoms in favorable pathways.

Van Der Waals heterogeneous layer‐layer carbon nanostructures involving π···H‐C‐C‐H···π···H‐C‐C‐H stacking based on graphene and graphane sheets

Noncovalent interactions involving aromatic rings, such as π···π stacking, CH···π are very essential for supramolecular carbon nanostructures. Graphite is a typical homogenous carbon matter based on π···π stacking of graphene sheets. Even in systems not involving aromatic groups, the stability of diamondoid dimer and layer‐layer graphane dimer originates from C − H···H − C noncovalent interaction. In this article, the structures and properties of novel heterogeneous layer‐layer carbon‐nanostructures involving π···H‐C‐C‐H···π···H‐C‐C‐H stacking based on [n]‐graphane and [n]‐graphene and their derivatives are theoretically investigated for n = 16–54 using dispersion corrected density functional theory B3LYP‐D3 method. Energy decomposition analysis shows that dispersion interaction is the most important for the stabilization of both double‐ and multi‐layer‐layer [n]‐graphane@graphene. Binding energy between graphane and graphene sheets shows that there is a distinct additive nature of CH···π interaction. For comparison and simplicity, the concept of H‐H bond energy equivalent number of carbon atoms (noted as NHEQ), is used to describe the strength of these noncovalent interactions. The NHEQ of the graphene dimers, graphane dimers, and double‐layered graphane@graphene are 103, 143, and 110, indicating that the strength of C‐H···π interaction is close to that of π···π and much stronger than that of C‐H···H‐C in large size systems. Additionally, frontier molecular orbital, electron density difference and visualized noncovalent interaction regions are discussed for deeply understanding the nature of the C‐H···π stacking interaction in construction of heterogeneous layer‐layer graphane@graphene structures. We hope that the present study would be helpful for creations of new functional supramolecular materials based on graphane and graphene carbon nano‐structures.

Finely Controlled Stepwise Engineering of Pore Environments and Mechanistic Elucidation of Water-Stable, Flexible 2D Porous Coordination Polymers

Two porous coordination polymers (PCPs) with different topologies (NTU-19: sql and NTU-20: dia) underwent finely controlled, stepwise crystal conversions to yield a common water-stable, flexible 2D framework (NTU-22: kgm). The crystal conversions occurred directly at higher temperature via the 3D intermediate (NTU-21: nbo), which could be observed at lower temperature. The successful isolation of the intermediate product of NTU-21, characterization with in situ PXRD and UV/Vis spectra were combined with DFT calculations to allow an understanding of the dynamic processes at the atomic level. Remarkably, breakthrough experiments demonstrate NTU-22 with integral structural properties allowed significant CO2 /CH4 mixture separation.

Fused-Pentagon-Configuration-Dependent Electron Transfer of Monotitanium-Encapsulated Fullerenes

We introduce monotitanium-based endohedral metallofullerenes (EMFs) using density functional theory calculations. Isomeric C64 fullerenes are initially employed as hosts, and Ti@C64 species show novel features on the electronic structures. Energetically, the preference of titanium residing on triple-fused-pentagon subunits is proposed in theory. More importantly, different from current knowledge on mono-EMFs, electron transfer between titanium and carbon cages is not unified but is essentially dependent on the pentagon distribution of the binding sites, giving rise to variations of the cationic titanium of Ti@C64. Such selective electron-transfer character is extended to the study of the encapsulation of other neighboring metal atoms (i.e., calcium and scandium). Because of their different capabilities to accept d electrons, fullerene cages with distinct fused-pentagon motifs show selective metal encapsulation characters. In addition, some other fullerenes (C44-C48 and C82) are selected as hosts to study the electron-transfer behavior of titanium in smaller fullerenes and larger systems without pentagon adjacency.

Boosting Activation of Oxygen Molecules on C60 Fullerene by Boron Doping

The activation of oxygen molecules on boron-doped C60 fullerene (C59 B) and the subsequent water formation reaction are systematically investigated by using hybrid density functional calculations. Results indicate that C59 B shows a favorable ability to activate oxygen molecules both kinetically and thermodynamically. The oxygen molecule is first adsorbed on the boron atom, which is identified to be the most reactive site in C59 B for O2 adsorption because of its high positive charge and spin density. The adsorption structure C59 BO2 can further isomerize to form two products with small reaction barriers. Water formation reactions upon these two structures are energetically favorable and suggest a four-electron mechanism for the oxygen reduction reaction catalyzed by C59 B. This work provides a reliable theoretical insight into the catalytic properties of boron-doped fullerene, which is believed to be helpful to explore fullerene catalysts.