Two-fold addition reaction of silylene to C60: structural and electronic properties of a bis-adduct.

The addition reaction of C60 with silylene 1, a silicon analog of carbene, yielded the corresponding bis-adduct 3. The structure of 3 was determined by single-crystal X-ray structure analysis, representing the first example of a crystal structure of a silirane (silacyclopropane) derivative of fullerenes. Electrochemical measurements confirmed that the redox potentials of 3 are shifted cathodically compared to those of the parent mono-adduct 2. Density functional theory (DFT) calculations provided the basis for the electronic properties of compound 3.

Element effects in endohedral metal-metal-bonding fullerenes M2@C82 (M = Sc, Y, La, Lu).

Endohedral metal-metal-bonding fullerenes have recently emerged, in which encapsulated metals form a metal-metal bond. However, the physical reasons why some metal elements prefer to form metal-metal bonds inside fullerene are still unclear. Herein, we reported first-principles calculations on electronic structures, bonding properties, dynamics, and thermodynamic stabilities of endohedral metallofullerenes M2@C82 (M = Sc, Y, La, Lu). Multiple bonding analysis approaches unambiguously reveal the existence of one two-center two-electron σ covalent metal-metal bond in M2@C82 (M = Sc, Y, Lu); however, the La-La bonding interaction in La2@C82 is weaker and could not be categorized as one metal-metal covalent bond. The energy decomposition analysis on bonding interactions between an encapsulated metal dimer and fullerene cages suggested that there exist two electron-sharing bonds between a metal dimer and fullerene cages. The reasons why La2 prefers to donate electrons to fullerene cages rather than form a standard σ covalent metal-metal bond are mainly attributed to two following facts: La2 has a lower ionization potential, while the hybridization of ns, (n - 1)d, and np atomic orbitals in La2 is higher. Ab initio molecular dynamic simulations reveal that the M-M bond length at room temperature follows the trend of Sc < Lu < Y. The statistical thermodynamics calculations at different temperatures reveal that the experimentally observed endohedral metal-metal-bonding fullerenes M2@C82 have high concentrations in the endohedral fullerene formation temperature range.

Controlling the reactivity of La@C82 by reduction: reaction of the La@C82 anion with alkyl halide with high regioselectivity.

Endohedral metallofullerenes have excellent redox properties, which can be used to vary their reactivity to certain classes of molecules, such as alkyl halides. In this study, the thermal reaction of the La@C2v-C82 anion with benzyl bromide derivatives 1 at 110 °C afforded single-bonded adducts 2-5 with high regioselectivity. The products were characterized by matrix-assisted laser desorption/ionization time-of-flight mass spectrometry and visible-near infrared spectroscopy. The reaction of La@C2v-C82 with alkyl halides using the same conditions showed no consumption of La@C2v-C82, indicating that the reactivity of La@C2v-C82 toward alkyl halides was effectively increased by one-electron reduction. Single-crystal X-ray diffraction analysis of the single-bonded adduct 3a revealed the addition site of the p-methoxybenzyl group on La@C2v-C82. Theoretical calculations indicated that the addition site carbons in neutral La@C2v-C82 have high spin density, whereas those in the La@C2v-C82 anion do not have high charge densities. Thus, the reaction is believed to occur via electron transfer, followed by the radical coupling of La@C2v-C82 and benzyl radicals, rather than by bimolecular nucleophilic substitution reaction of La@C2v-C82 anion with 1.

Cluster-Geometry-Associated Metal-Metal Bonding in Trimetallic Carbide Clusterfullerenes.

Geometry configurations of the metallic clusters play a significant role in the involved bonding nature. Herein, we report the crystallographic characterization of unprecedented erbium-based trimetallic clusterfullerenes, namely, Er3C2@Ih(7)-C80, in which the inner Er3C2 cluster presents a lifted bat ray configuration with the C2 unit elevated by ∼1.62 Å above the Er3 plane. Within the plane, the Er···Er distances for Er1···Er2, Er1···Er2A, and Er2···Er2A are 3.4051(15), 3.4051(15), and 3.3178(15) Å, respectively, falling into the range of the metal-metal bonding. Density functional theory calculations unveil the three-center-one-electron Er-Er-Er bond in Er3C2@Ih(7)-C80 with one electron shared by three metals, and thus, its exceptional electronic structure can be expressed as (Er3)8+(C2)2-@C806-. Interestingly, with the further observation on the geometry configurations of the encapsulated clusters in M3C2@C2n (M = Sc, Y, and Lu) series, we find that the lifted bat ray configuration of the inner cluster is explicitly associated with the formation of the bonding interactions between the inner metals. This finding provides insights into the nature of metal-metal bonding and gives guidelines for the design of the single-molecule magnet.

Morphology Engineering of Fullerene[C70 ] Microcrystals: From Perfect Cubes, Defective Hoppers to Novel Cruciform-Pillars.

Controlled crystallization of fullerene molecules into ordered molecular assemblies is important for their applications. However, the morphology engineering of fullerene[C70 ] assemblies is challenging, and complicated architectures have rarely been reported due to the low molecular symmetry of C70 molecules, which makes their crystallization difficult to control and the low production yield as well. Herein, with the assistance of solvent intercalation, a general reprecipitation approach is reported to prepare morphologically controllable C70 microcrystals with mesitylene as a good solvent and n-propanol as a poor solvent in one solvent system without replacing specific solvents. A series of C70 microcrystals with high uniformity from perfect cubes and defective hoppers to novel cruciform-pillars are obtained by intentionally tuning C70 concentration and the volume ratio of mesitylene to n-propanol. Among them, novel cruciform-pillar-shaped microcrystals are obtained for the first time by further decreasing the amount of mesitylene in the solvent-intercalated microcrystals. Notably, the C70 concentration is a key parameter for the selective growth of C70 hopper, rather than the volume ratio of mesitylene to n-propanol. Interestingly, the hopper-shaped microcrystals exhibit excellent photoluminescence properties relative to those of cubes and cruciform-pillars owing to the enhanced light absorption, proving their potential applications in optoelectronic devices. This study offers new insights into the morphology-controlled synthesis of other micro/nanostructured organic microcrystals and the fine tuning of photoluminescence properties of organic crystals.

Crystallographic Characterization of Er2C2@C80-88: Cluster Stretching with Cage Elongation.

Six dierbium carbide endohedral metallofullerenes have been synthesized and chromatographically isolated. Single-crystal X-ray diffractometry unambiguously ascertains their structures as Er2C2@C2v(5)-C80, Er2C2@Cs(6)-C82, Er2C2@Cs(15)-C84, Er2C2@C2v(9)-C86, Er2C2@Cs(15)-C86, and Er2C2@Cs(32)-C88, respectively. The Er···Er distances of the major erbium sites inside the Cs(6)-C82, C2v(5)-C80, Cs(15)-C84, Cs(15)-C86, C2v(9)-C86, and Cs(32)-C88 cages are 3.801, 3.860, 4.062, 4.066, 4.307, and 4.372 Å, respectively, which show a linear tendency with an increase in the major axis of the fullerene cages (8.064, 8.238, 8.508, 8.582, 8.815, and 8.953 Å, respectively). Furthermore, the electrochemical and molecular orbital analyses reveal that the redox chemistry of the Er2C2@C80-88 isomers is associated with the carbon cage, which is different from the situations found for typical dimetallofullerenes, such as Y2@C82, Er2@C82-84, and Lu2@C82,86 isomers, which show metal-dependent oxidation processes, indicating the importance of C2 insertion in carbide cluster metallofullerenes.

Crystallographic Characterization of Ti2C2@D3h(5)-C78, Ti2C2@C3v(8)-C82, and Ti2C2@Cs(6)-C82: Identification of Unsupported Ti2C2 Cluster with Cage-Dependent Configurations.

Fullerene cages are ideal hosts to encapsulate otherwise unstable metallic clusters to form endohedral metallofullerenes (EMFs). Herein, a novel Ti2C2 cluster with two titanium atoms bridged by a C2-unit has been stabilized by three different fullerene cages to form Ti2C2@D3h(5)-C78, Ti2C2@C3v(8)-C82, and Ti2C2@Cs(6)-C82, representing the first examples of unsupported titanium carbide clusters. Crystallographic results show that the configuration of the Ti2C2 cluster changes upon cage variation. In detail, the Ti2C2 cluster adopts a butterfly shape in Ti2C2@C3v(8)-C82 and Ti2C2@Cs(6)-C82 with Ti-C2-Ti dihedral angles of 156.35 and 147.52° and Ti-Ti distances of 3.633 and 3.860 Å, respectively. In sharp contrast, a stretched planar geometry of Ti2C2 is observed in Ti2C2@D3h(5)-C78, where a Ti-C2-Ti angle of 176.87° and a long Ti-Ti distance of 5.000 Å are presented. Consistently, theoretical calculations reveal that the cluster configuration is very sensitive to the cage shape which eventually determines the electronic structures of the hybrid EMF-molecules, thus adding new insights into modern coordination chemistry.

Age-dependent electrical and morphological remodeling of the Drosophila heart caused by hERG/seizure mutations.

Understanding the cellular-molecular substrates of heart disease is key to the development of cardiac specific therapies and to the prevention of off-target effects by non-cardiac targeted drugs. One of the primary targets for therapeutic intervention has been the human ether a go-go (hERG) K+ channel that, together with the KCNQ channel, controls the rate and efficiency of repolarization in human myocardial cells. Neither of these channels plays a major role in adult mouse heart function; however, we show here that the hERG homolog seizure (sei), along with KCNQ, both contribute significantly to adult heart function as they do in humans. In Drosophila, mutations in or cardiac knockdown of sei channels cause arrhythmias that become progressively more severe with age. Intracellular recordings of semi-intact heart preparations revealed that these perturbations also cause electrical remodeling that is reminiscent of the early afterdepolarizations seen in human myocardial cells defective in these channels. In contrast to KCNQ, however, mutations in sei also cause extensive structural remodeling of the myofibrillar organization, which suggests that hERG channel function has a novel link to sarcomeric and myofibrillar integrity. We conclude that deficiency of ion channels with similar electrical functions in cardiomyocytes can lead to different types or extents of electrical and/or structural remodeling impacting cardiac output.

New Horizons in Chemical Functionalization of Endohedral Metallofullerenes.

This overview explains some new aspects of chemical functionalization of endohedral metallofullerenes (EMFs) that have been unveiled in recent years. After differences in chemical reactivity between EMFs and the corresponding empty fullerenes are discussed, cage-opening reactions of EMFs are examined. Then, the selective bisfunctionalization of EMFs is explained. Finally, single-bonding derivatization of EMFs is addressed. The diversity and applicability of the chemical functionalization of endohedral metallofullerenes are presented to readers worldwide.

Crystallographic and Theoretical Investigations of Er2 @C2 n (2 n=82, 84, 86): Indication of Distance-Dependent Metal-Metal Bonding Nature.

Successful isolation and characterization of a series of Er-based dimetallofullerenes present valuable insights into the realm of metal-metal bonding. These species are crystallographically identified as Er2 @Cs (6)-C82 , Er2 @C3v (8)-C82 , Er2 @C1 (12)-C84 , and Er2 @C2v (9)-C86 , in which the structure of the C1 (12)-C84 cage is unambiguously characterized for the first time by single-crystal X-ray diffraction. Interestingly, natural bond orbital analysis demonstrates that the two Er atoms in Er2 @Cs (6)-C82 , Er2 @C3v (8)-C82 , and Er2 @C2v (9)-C86 form a two-electron-two-center Er-Er bond. However, for Er2 @C1 (12)-C84 , with the longest Er⋅⋅⋅Er distance, a one-electron-two-center Er-Er bond may exist. Thus, the difference in the Er⋅⋅⋅Er separation indicates distinct metal bonding natures, suggesting a distance-dependent bonding behavior for the internal dimetallic cluster. Additionally, electrochemical studies suggest that Er2 @C82-86 are good electron donors instead of electron acceptors. Hence, this finding initiates a connection between metal-metal bonding chemistry and fullerene chemistry.

Isolation and Structural Characterization of Er@ C2 v(9)-C82 and Er@ C s(6)-C82: Regioselective Dimerization of a Pristine Endohedral Metallofullerene Induced by Cage Symmetry.

Two Er@C82 isomers have been isolated and unambiguously characterized as Er@ C2 v(9)-C82 and Er@ C s(6)-C82, respectively, by single-crystal X-ray diffraction. Er@ C s(6)-C82 is identified as a dimeric structure in the crystalline state, but dimerization does not occur for Er@ C2 v(9)-C82 under identical crystallization conditions, indicating a cage-symmetry-induced dimerization process. Density functional theory calculations reveal that the major unpaired spin resides on a special C atom of Er@ C s(6)-C82, which leads to regioselective dimerization. Calculations also found that the dimeric structure of Er@ C s(6)-C82·Ni(OEP) is much more stable than the two monomers, suggesting a thermodynamically favorable dimerization process. Vis-near-IR spectrometric and electrochemical results demonstrate that the electronic structure of Er@C82 isomers is Er3+@C823-, instead of the theoretically proposed Er2+@C822-.

APJ acts as a dual receptor in cardiac hypertrophy.

Cardiac hypertrophy is initiated as an adaptive response to sustained overload but progresses pathologically as heart failure ensues. Here we report that genetic loss of APJ, a G-protein-coupled receptor, confers resistance to chronic pressure overload by markedly reducing myocardial hypertrophy and heart failure. In contrast, mice lacking apelin (the endogenous APJ ligand) remain sensitive, suggesting an apelin-independent function of APJ. Freshly isolated APJ-null cardiomyocytes exhibit an attenuated response to stretch, indicating that APJ is a mechanosensor. Activation of APJ by stretch increases cardiomyocyte cell size and induces molecular markers of hypertrophy. Whereas apelin stimulates APJ to activate Gαi and elicits a protective response, stretch signals in an APJ-dependent, G-protein-independent fashion to induce hypertrophy. Stretch-mediated hypertrophy is prevented by knockdown of ß-arrestins or by pharmacological doses of apelin acting through Gαi. Taken together, our data indicate that APJ is a bifunctional receptor for both mechanical stretch and the endogenous peptide apelin. By sensing the balance between these stimuli, APJ occupies a pivotal point linking sustained overload to cardiomyocyte hypertrophy.

Salvaging Reactive Fullerenes from Soot by Exohedral Derivatization.

The awesome allotropy of carbon yields innumerable topologically possible cage structures of molecular carbon. This field is also related to endohedral metallofullerenes constructed by metal-atom encapsulation. Stable and soluble empty fullerenes and endohedral metallofullerenes are available in pure form in macroscopic amounts from carbon arc production or other physical processes followed by extraction and subsequent chromatographic separation. However, many other unidentified fullerene species, which must be reactive and insoluble in their pristine forms, remain in soot. These "missing" species must have extremely small HOMO-LUMO gaps and may have unconventional cage structures. Recent progress in this field has demonstrated that reactive fullerenes can be salvaged by exohedral derivatization, which can stabilize the reactive carbon cages. This concept provides a means of preparing macroscopic amounts of unconventional fullerenes as their derivatives.

Adamantylidene Addition to M3 N@Ih -C80 (M=Sc, Lu) and Sc3 N@D5h -C80 : Synthesis and Crystallographic Characterization of the [5,6]-Open and [6,6]-Open Adducts.

Additions of adamantylidene (Ad) to M3 N@Ih -C80 (M=Sc, Lu) and Sc3 N@D5h -C80 have been accomplished by photochemical reactions with 2-adamantyl-2,3'-[3H]-diazirine (1). In M3 N@Ih -C80 , the addition led to rupture of the [6,6]- or [5,6]-bonds of the Ih -C80 cage, forming the [6,6]-open fulleroid as the major isomer and the [5,6]-open fulleroid as the minor isomer. In Sc3 N@D5h -C80 , the addition also proceeded regioselectively to yield three major isomeric Ad mono-adducts, despite the fact that there are nine types of C-C bonds in the D5h -C80 cage. The molecular structures of the seven Ad mono-adducts, including the positions of the encaged trimetallic nitride clusters, have been unambiguously determined through single-crystal XRD analyses. Furthermore, results have shown that stepwise addition of Ad to Lu3 N@Ih -C80 affords several Ad bis-adducts, two of which have been isolated and characterized. The X-ray structure of one bis-adduct clearly revealed that the second Ad addition took place at a [6,6]-bond close to an endohedral metal atom. Theoretical calculations have also been performed to rationalize the regioselectivity.

Initial and Long-Term Results of a Microcatheter-Based Retrograde Approach for the Endovascular Treatment of Chronic Total Occlusion in Iliac or Femoropopliteal Arteries.

BACKGROUND: Initial and long-term outcomes of the retrograde endovascular approach using a microcatheter for the treatment of chronic total occlusion (CTO) in the iliac or femoropopliteal (FP) arteries have not been fully elucidated. METHODS: From 2012 to 2014, 20 consecutive patients (21 limbs) underwent endovascular therapy (EVT) for CTO in the iliac or FP arteries using the microcatheter-based retrograde approach. An analysis of the initial and long-term outcomes was conducted. RESULTS: All procedures were successful. The mean follow-up duration was 27.4 ± 11.3 months. The mean patient age was 75.8 ± 9.1 years. Eighteen (85.7%) target lesions were located in the superficial femoral artery, 1 (4.8%) in the popliteal artery, and 2 (9.5%) in the iliac artery. All lesions were de novo. The mean occlusion length was 183.3 ± 95.4 mm. A stent was used in 19 (94.5%) lesions and balloon angioplasty was performed for 2 (5.5%) lesions. Retrograde puncture site complication (hematoma in popliteal artery) was reported in 1 (4.8%) patient. Postprocedure primary patency rates at 1, 2, and 3 years were 89.5%, 72.0%, and 41.2%, respectively, and the secondary patency rates at the corresponding time points were 100%, 77.2%, and 48.6%, respectively. CONCLUSIONS: Initial and long-term outcomes of EVT for CTO in iliac and FP arteries using the microcatheter-based retrograde approach are promising.

Functionalization of Endohedral Metallofullerenes with Reactive Silicon and Germanium Compounds.

Exohedral derivatization of endohedral metallofullerenes (EMFs) has been exploited as a useful method for characterizing the structural and chemical properties of EMFs, and for functionalizing them for potential applications. The introduction of heteroatoms, such as electropositive silicon atoms, to fullerene cages is a novel functionalization method that remarkably affects the electronic characteristics of fullerenes. This review comprehensively describes the results of the reactions of monometallofullerene, dimetallofullerene, and trimetallic nitride template EMFs with disilirane, silirane, silylene, and digermirane, which afforded the corresponding silylated and germylated fullerenes. Several examples emphasize that exohedral functionalization regulates the dynamic behaviors of the encapsulated metal atoms and clusters in the fullerene cages. The electronic effects of silyl and germyl groups are represented by comparing the redox properties of silylated and germylated EMFs with those of other EMFs derivatized with carbon-atom-based functional groups.

Eu@C72: Computed Comparable Populations of Two Non-IPR Isomers.

Relative concentrations of six isomeric Eu@C 72 -one based on the IPR C 72 cage (i.e., obeying the isolated-pentagon rule, IPR), two cages with a pentagon-pentagon junction (symmetries C 2 and C 2 v ), a cage with one heptagon, a cage with two heptagons, and a cage with two pentagon-pentagon fusions-are DFT computed using the Gibbs energy in a broad temperature interval. It is shown that the two non-IPR isomers with one pentagon-pentagon junction prevail at any relevant temperature and exhibit comparable populations. The IPR-satisfying structure is disfavored by both energy and entropy.

Photoreactions of Endohedral Metallofullerene with Siliranes: Electronic Properties of Carbosilylated Lu3N@Ih-C80.

Photochemical carbosilylation of Lu3N@Ih-C80 was performed using siliranes (silacyclopropanes) to afford the corresponding [5,6]- and [6,6]-adducts. Electrochemical studies indicated that the redox potentials of the carbosilylated derivatives were shifted cathodically in comparison with those of the [5,6]-pyrrolidino adducts. The electronic effect of the silirane addends on Lu3N@Ih-C80 was verified on the basis of density functional theory calculations.

Fullerene C70 as a Nanoflask that Reveals the Chemical Reactivity of Atomic Nitrogen.

To investigate the intrinsic reactivity of atomic nitrogen, which had previously been accomplished only by examining its decay in the gas phase using special equipment, a nitrogen atom was inserted into a series of molecule-encapsulating C60 and C70 fullerenes. Among the studied endofullerenes, H2 @C70 was able to encapsulate an additional nitrogen atom within the fullerene cage under radiofrequency plasma conditions. The product was analyzed by ESR spectroscopy and mass spectrometry in solution, which revealed that the nitrogen atom with a quartet ground state does not react but weakly interact with the H2 molecule, thus demonstrating the utility of such fullerenes as "nanoflasks".

Molecular Location Sensing Approach by Anisotropic Magnetism of an Endohedral Metallofullerene.

Location recognition at the molecular scale provides valuable information about the nature of functional molecular materials. This study presents a novel location sensing approach based on an endohedral metallofullerene, Ce@C82, using its anisotropic magnetic properties, which lead to temperature-dependent paramagnetic shifts in (1)H NMR spectra. Five site-isomers of Ce@C82CH2-3,5-C6H3Me2 were synthesized to demonstrate the spatial sensing ability of Ce@C82. Single-crystal structures, absorption spectra, and density functional theory calculations were used to select the plausible addition positions in the radical coupling reaction, which preferentially happens on the carbon atoms with high electron density of the singly occupied molecular orbital (SOMO) and positive charge. Temperature-dependent NMR measurements demonstrated unique paramagnetic shifts of the (1)H peaks, which were derived from the anisotropic magnetism of the f-electron in the Ce atom of the isomers. It was found that the magnetic anisotropy axes can be easily predicted by theoretical calculations using the Gaussian 09 package. Further analysis revealed that the temperature-dependent trend in the shifts is clearly predictable from the distance and relative position of the proton from the Ce atom. Hence, the Ce-encapsulated metallofullerene Ce@C82 can provide spatial location information about nearby atoms through the temperature-dependent paramagnetic shifts of its NMR signals. It can act as a molecular probe for location sensing by utilizing the anisotropic magnetism of the encapsulated Ce atom. The potentially low toxicity and stability of the endohedral fullerene would make Ce@C82 suitable for applications in biology and material science.