164 research outputs found

    Theoretical Insights into Monometallofullerene Th@C<sub>76</sub>: Strong Covalent Interaction between Thorium and the Carbon Cage

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    Th@C<sub>76</sub> has been studied by density functional theory combined with statistical mechanics calculations. The results reveal that Th@<i>T</i><sub><i>d</i></sub>(19151)-C<sub>76</sub> satisfying the isolated pentagon rule possesses the lowest energy. Nevertheless, considering the enthalpy–entropy interplay, Th@<i>C</i><sub>1</sub>(17418)-C<sub>76</sub> with one pair of adjacent pentagons is thermodynamically favorable at elevated temperatures, which is reported for the first time. The bonding critical points in both isomers were analyzed to disclose covalent interactions between the inner Th and cages. In addition, the Wiberg bond orders of M–C bonding in different endohedral metallofullerenes (EMFs) were investigated to prove stronger covalent interactions of Th–C in Th-based EMFs

    Theoretical Insight into Sc<sub>2</sub>C<sub>76</sub>: Carbide Clusterfullerene Sc<sub>2</sub>C<sub>2</sub>@C<sub>74</sub> versus Dimetallofullerene Sc<sub>2</sub>@C<sub>76</sub>

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    In terms of density functional theory in combination with a statistical thermodynamic method, we have investigated the Sc<sub>2</sub>C<sub>76</sub> species including dimetallofullerenes Sc<sub>2</sub>@C<sub>76</sub> and carbide clusterfullerenes Sc<sub>2</sub>C<sub>2</sub>@C<sub>74</sub>. Two dimetallofullerenes, Sc<sub>2</sub>@<i>C</i><sub><i>s</i></sub>(17490)-C<sub>76</sub> and Sc<sub>2</sub>@<i>T</i><sub><i>d</i></sub>(19151)-C<sub>76</sub>, possess the lowest relative energies but exhibit poor thermodynamic stability within the fullerene-formation region (500–3000 K). In contrast, four carbide clusterfullerene isomers, Sc<sub>2</sub>C<sub>2</sub>@<i>D</i><sub>3<i>h</i></sub>(14246)-C<sub>74</sub>, Sc<sub>2</sub>C<sub>2</sub>@<i>C</i><sub>2<i>v</i></sub>(14239)-C<sub>74</sub>, Sc<sub>2</sub>C<sub>2</sub>@<i>C</i><sub>2</sub>(13333)-C<sub>74</sub>, and Sc<sub>2</sub>C<sub>2</sub>@<i>C</i><sub>1</sub>(13334)-C<sub>74</sub>, have excellent thermodynamic stability when considering the temperature effect. The Sc<sub>2</sub>C<sub>2</sub>@<i>D</i><sub>3<i>h</i></sub>(14246)-C<sub>74</sub> isomer, which satisfies the isolated-pentagon rule (IPR), was characterized by its crystallographic structure; however, the other three non-IPR structures with two pairs of pentagon adjacencies are predicted for the first time. In particular, Sc<sub>2</sub>C<sub>2</sub>@<i>C</i><sub>2</sub>(13333)-C<sub>74</sub> and Sc<sub>2</sub>C<sub>2</sub>@<i>C</i><sub>1</sub>(13334)-C<sub>74</sub> are linked by a single Stone–Wales transformation. Meanwhile, bonding critical points and Mayer bond orders in the four isomers were analyzed to disclose the unique interactions between the inner clusters and cages. Additionally, the structural characteristics, <sup>13</sup>C and <sup>45</sup>Sc NMR chemical shifts, and IR spectra of the four stable isomers are introduced to assist experimental identification and characterization in the future

    Regioselectivity of Sc<sub>2</sub>C<sub>2</sub>@<i>C</i><sub>3<i>v</i></sub>(8)‑C<sub>82</sub>: Role of the Sumanene-Type Hexagon in Diels–Alder Reaction

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    Recently, several experiments have demonstrated high chemical reactivity of the sumanene-type hexagon in Sc<sub>2</sub>C<sub>2</sub>@C<sub>82</sub>. To further uncover its reactivity, the Diels–Alder reaction to all the nonequivalent C–C bonds of C<sub>82</sub> and Sc<sub>2</sub>C<sub>2</sub>@C<sub>82</sub> has been investigated by density functional theory calculations. For the free fullerene, the [5,6] bond 7 is the thermodynamically most favored, whereas the addition on the [6,6] bond 3 has the lowest activation energy. Diels–Alder reaction has no preference for addition sites in the sumanene-type hexagon. However, in the case of the endohedral fullerene, the [6,6] bond 19 in the special hexagon becomes the most reactive site according to both kinetic and thermodynamic considerations. Further analyses reveal that bond 19 in Sc<sub>2</sub>C<sub>2</sub>@C<sub>82</sub> exhibits the shortest bond length and third largest π-orbital axis vector. In addition, the LUMOs of bond 19 are also symmetry-allowed to interact with butadiene

    Cycloaddition of Benzyne to Armchair Single-Walled Carbon Nanotubes: [2 + 2] or [4 + 2]?

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    The reaction mechanism and regioselectivity of cycloaddition reactions of benzyne to armchair single-walled carbon nanotubes were investigated with quantum chemical methods. The [2 + 2] cycloaddition reaction follows the diradical mechanism, whereas the [4 + 2] cycloaddition reaction adopts the concerted mechanism. More importantly, the [2 + 2] product is always more stable thermodynamically than the [4 + 2] ones, regardless of the diameter, while the [4 + 2] cycloaddition becomes kinetically more favored as the diameter goes up

    Theoretical Insight into the Mechanism of Gold(I)-Catalyzed Rearrangement of 2‑Propargyl 2<i>H</i>‑Azirines to Pyridines

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    The title reaction is investigated in detail theoretically using density functional theory. After 5-<i>endo</i>-dig cyclization by nucleophilic attack, five possible pathways are taken into account in this work: direct ring expansion followed or accompanied by proton-transfer (paths A and B, respectively), 1,3-cationic migration (path C), proton-transfer before ring expansion (path D), and processing via a gold-nitrene (path E). Results indicate that the reaction would undergo the favored sequential pathway (path A) rather than other pathways. Moreover, the concerted mechanism (path B), which is designed to account for the selectivity of product in the experiment, would be unlikely in the reaction. The selectivity of product could be explained by the hindrance of ligand (<i>t</i>-BuXPhos) and the stability of the carbocation. Moreover, the binding energy of product complexes could account for the observed reaction rate

    Quantum Chemical Insight into La<sub>2</sub>C<sub>96</sub>: Metal Carbide Fullerene La<sub>2</sub>C<sub>2</sub>@C<sub>94</sub> versus Dimetallofullerene La<sub>2</sub>@C<sub>96</sub>

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    A family of dilanthanum-containing endohedral metallofullerene La<sub>2</sub>C<sub>2<i>n</i></sub> (<i>n</i> = 46–51) was synthesized recently. In the present work, a systematical investigation on La<sub>2</sub>C<sub>96</sub> series including the carbide clusterfullerene form La<sub>2</sub>C<sub>2</sub>@C<sub>94</sub> and the conventional dimetallofullerene form La<sub>2</sub>@C<sub>96</sub> was implemented by density functional theory, combined with statistical mechanics. Three isomers, i.e., La<sub>2</sub>@D<sub>2</sub>(191838)-C<sub>96</sub>, La<sub>2</sub>C<sub>2</sub>@C<sub>s</sub>(153479)-C<sub>94</sub>, and La<sub>2</sub>C<sub>2</sub>@C<sub>1</sub>(153491)-C<sub>94</sub> were disclosed to be thermodynamically stable at the temperature region of endohedral metallofullerene formation. La<sub>2</sub>@D<sub>2</sub>(191838)-C<sub>96</sub> is the prevailing isomer at low temperature, while La<sub>2</sub>C<sub>2</sub>@C<sub>s</sub>(153479)-C<sub>94</sub> and La<sub>2</sub>C<sub>2</sub>@C<sub>1</sub>(153491)-C<sub>94</sub> are the most and second-most abundant isomers at high temperature. Interestingly, the highest occupied molecular orbital (HOMO) of La<sub>2</sub>C<sub>2</sub>@C<sub>1</sub>(153491)-C<sub>94</sub> is distributed on one pole of the cage, and the lowest unoccupied molecular orbital (LUMO) of this isomer is mainly located on the equator of the cage, which can facilitate synthesis of regioselective derivatives. This work will provide useful information for further experimental identification and application of La<sub>2</sub>C<sub>96</sub>

    Theoretical Insights into the Metal–Nonmetal Interaction Inside M<sub>2</sub>O@<i>C</i><sub>2<i>v</i></sub>(31922)‑C<sub>80</sub> (M = Sc or Gd)

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    The metal–nonmetal interaction is complicated but significant in organometallic chemistry and metallic catalysis and is susceptible to the coordination surroundings. Endohedral metallofullerene is considered to be an excellent model for studying metal–nonmetal interactions with the shielding effect of fullerenes. Herein, with the detection of ScGdO@C80 in a previous mass spectrum, we studied the effects of metal atoms (Sc and Gd) on the metal–nonmetal interactions of the thermodynamically stable molecules M2O@C2v(31922)-C80 (M = Sc and Gd), where metal atoms M can be the same or different, using density functional theory calculations. The inner metal atom and the fullerene cage show mainly ionic interactions with some covalent character. The Sc atom with higher electronegativity plays a greater important role in the metal–nonmetal interactions than the Gd atom. This study would be useful for the further study of the metal–nonmetal interaction

    Table_1_The relationship between achievement motivation and college students’ general self-efficacy: A moderated mediation model.xlsx

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    ObjectiveThis study focused on the relationship between achievement motivation and college students’ general self-efficacy, and aimed to explore the mechanism of action between achievement motivation and general self-efficacy.MethodsThrough convenience sampling, 1,076 college students were investigated from Anhui Province in China. Achievement motivation, general self-efficacy, perceived social support, and sports participation were evaluated using standard scales. For data analysis, Pearson’s correlation analysis, structural equation model test, and bias-corrected percentile Bootstrap method were carried out.ResultsCommon method biases can be accepted in this study. (1) Achievement motivation can directly affect general self-efficacy and make a positive prediction; (2) Perceived social support plays a mediating role between achievement motivation and general self-efficacy, that is, achievement motivation can indirectly affect general self-efficacy through perceived social support; (3) Sports participation plays a moderating role in the first half of the mediating path of “achievement motivation → perceived social support → general self-efficacy.” The interaction between achievement motivation and sports participation affects perceived social support, and then indirectly affects general self-efficacy. In this moderated mediation model, The predictive effect of achievement motivation on perceived social support is significantly different among individuals with different levels of sports participation.ConclusionPerceived social support plays a part of mediating role between achievement motivation and college students’ general self-efficacy, which is moderated by sports participation.</p

    Bingel–Hirsch Reaction on Sc<sub>2</sub>@C<sub>66</sub>: A Highly Regioselective Bond Neighboring to Unsaturated Linear Triquinanes

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    The dispersion-corrected density functional theory (M06-2X) was adopted to investigate the kinetically driven Bingel–Hirsch and thermodynamically controlled Prato reactions on Sc<sub>2</sub>@<i>C</i><sub>2<i>v</i></sub>(4059)-C<sub>66</sub> which possesses the unconventional unsaturated linear triquinanes (ULTs), respectively. The mechanism differences of these two reactions on Sc<sub>2</sub>@C<sub>66</sub> could lead to their different functionalization performances. The investigations on Bingel–Hirsch addition suggest that this process prefers to occur on the C–C bond (9–8) next to other than those (such as 9–10) on the ULT moieties, resulting in a highly regioselective product. The most favorable addition site (atom C<sub>9</sub>) for the bromomalonate anion is the only one that connects two equivalent [5,5] C–C bonds (10–11 and 31–30) among all possible atoms. In addition, solvent effect for this reaction was evaluated, and the results suggest that <i>ortho</i>-dichlorobenzene (ODCB) is more feasible than toluene for Sc<sub>2</sub>@C<sub>66</sub>. However, the Prato reaction for this system turned out to show poor regioselectivity to the best reactive bond 10–11

    A Hybrid Chalcone Combining the Trimethoxyphenyl and Isatinyl Groups Targets Multiple Oncogenic Proteins and Pathways in Hepatocellular Carcinoma Cells

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    <div><p>Small molecule inhibitors that can simultaneously inhibit multiple oncogenic proteins in essential pathways are promising therapeutic chemicals for hepatocellular carcinoma (HCC). To combine the anticancer effects of combretastatins, chalcones and isatins, we synthesized a novel hybrid molecule 3’,4’,5’-trimethoxy-5-chloro-isatinylchalcone (3MCIC). 3MCIC inhibited proliferation of cultured HepG2 cells, causing rounding-up of the cells and massive vacuole accumulation in the cytoplasm. Paxillin and focal adhesion plaques were downregulated by 3MCIC. Surprisingly, unlike the microtubule (MT)-targeting agent CA-4 that inhibits tubulin polymerization, 3MCIC stabilized tubulin polymers both in living cells and in cell lysates. 3MCIC treatment reduced cyclin B1, CDK1, p-CDK1/2, and Rb, but increased p53 and p21. Moreover, 3MCIC caused GSK3β degradation by promoting GSK3β-Ser9 phosphorylation. Nevertheless, 3MCIC inhibited the Wnt/β-catenin pathway by downregulating β-catenin, c-Myc, cyclin D1 and E2F1. 3MCIC treatment not only activated the caspase-3-dependent apoptotic pathway, but also caused massive autophagy evidenced by rapid and drastic changes of LC3 and p62. 3MCIC also promoted cleavage and maturation of the lysosomal protease cathepsin D. Using ligand-affinity chromatography (LAC), target proteins captured onto the Sephacryl S1000-C<sub>12</sub>-3MCIC resins were isolated and analyzed by mass spectrometry (MS). Some of the LAC-MS identified targets, i.e., septin-2, vimentin, pan-cytokeratin, nucleolin, EF1α1/2, EBP1 (PA2G4), cyclin B1 and GSK3β, were further detected by Western blotting. Moreover, both septin-2 and HIF-1α decreased drastically in 3MCIC-treated HepG2 cells. Our data suggest that 3MCIC is a promising anticancer lead compound with novel targeting mechanisms, and also demonstrate the efficiency of LAC-MS based target identification in anticancer drug development.</p></div
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