Electrocatalytic Oxidation of Nitric Oxide on an Electrode Modified with Fullerene Films

Fullerene was immobilized on the surface of a glassy carbon electrode and reduced by an electrochemical method to form a partially reduced fullerene film. The films on the electrode showed stable electrocatalytic activity towards the oxidation of nitric oxide (NO). The catalytic current was proportional to the concentration of nitric oxide. Based on this property, a method for the detection of nitric oxide in aqueous solution is proposed. The detection conditions, such as supporting electrolyte, scan rate and thickness of the film were optimized. Under the optimized conditions, the catalytic currents increase linearly with the concentration of NO in the range of 3×10^–71.0×10^–4M, and the detection limit is 7.4×10^–8M. In addition, the modified electrode is very selective with respect to interferences including ascorbic acid, dopamine, and nitrite when further modified by a Nafion film on the surface of the electrode. The experimental results indicate that the partially reduced fullerene can act as an NO sensor featuring fast response and high stability.     

New Lower Bound on the Number of Perfect Matchings in Fullerene Graphs

A fullerene graph is a cubic and 3-connected plane graph (or spherical map) that has exactly 12 faces of size 5 and other faces of size 6, which can be regarded as the molecular graph of a fullerene. T. Doli [3] obtained that a fullerene graph with p vertices has at least (p+2)/2 perfect matchings by applying the recently developed decomposition techniques in matching theory of graphs. This note gets a better lower bound 3(p+2)/4 of the number of perfect matchings of a fullerene graph by finding its 2-extendability. This property further implies a chemical consequence that every derivative of a fullerene by substituting any two pairs of adjacent carbon atoms permits a Kekulé structure.     

Synthesis and spectroscopic investigation of trifluoroethoxy-coated phthalocyanine linked with fullerene

Synthesis and spectroscopic investigation of trifluoroethoxy-coated phthalocyanine-fullerene dyad 2 has been described. While nonfluorinated phthalocyanine-fullerene dyad 1 showed an efficient property of intramolecular photoinduced electron transfer, dyad 2, regardless of its covalently linked dyad system, appears not to show any electronic communication between fullerene and phthalocyanine. This observation is presumably due to the strong electron withdrawing nature of 12 trifluoroethoxy groups; fluorine leads phthalocyanine to become an acceptor whose electronic accepting property is equivalent to that of fullerene. This is a unique example that fluorine can terminate electronic communication in the covalently fullerene-phthalocyanine dyad system.     

Fabrication of Monodisperse Toroidal Particles by Polymer Solidification in Microfluidics

Microdoughnuts: Polymer toroidal particles such as the one shown in the left picture have been prepared by a capillary microfluidic technique. Droplets of polymer solution undergo non‐uniform solidification to form the anisotropic polymer particles. By incorporating functional materials inside the polymer network, functional toroidal particles (center and right images) can be tailor‐made for specific applications such as magnetic actuation.

     

Polymer‐Fullerene Network Formation via Light‐Induced Crosslinking

A facile and efficient methodology for the formation of polymer‐fullerene networks via a light‐induced reaction is reported. The photochemical crosslinking is based on a nitrile imine‐mediated tetrazole‐ene cycloaddition reaction, which proceeds catalyst‐free under UV‐light irradiation (λ_max = 320 nm) at ambient temperature. A tetrazole‐functionalized polymer (M_n = 6500 g mol⁻¹, Ð = 1.3) and fullerene C₆₀ are employed for the formation of the hybrid networks. The tetrazole‐functionalized polymer as well as the fullerene‐containing networks are carefully characterized by NMR spectrometry, size exclusion chromatography, infrared spectroscopy, and elemental analysis. Furthermore, thermal analysis of the fullerene networks and their precursors is carried out. The current contribution thus induces an efficient platform technology for fullerene‐based network formation.

     

Pentamethylated derivatives of [60]fullerene: X-ray structure of the C60Me5H and ESR spectroscopy evidence for the stable radical C60Me5

Single-crystal X-ray study of 6,9,12,15,18-pentamethyl-1,6,9,12,15,18-hexahydro(C₆₀-I_h)[5,6]fullerene (C₆₀Me₅H) has been reported. In crystal packing, the stacking self-organization of molecules is realized. It is concluded that the formation of such polar columns is a general rule for crystals of C₆₀R₅H independent of the nature of the R group. An ESR spectrum of the stable fullerenyl radical of the cyclopentadienyl-type, C₆₀Me₅, was observed in a sample of the pentamethylated[60]fullerene. Rotation of methyl groups around C-C bonds is restricted on the ESR scale time and therefore protons within each methyl group are non-equivalent.     

First syntheses and electronic properties of (oligo)phenothiazine-C60 dyads

(Oligo)phenothiazine-C₆₀ dyads 3 can be readily synthesized by a three-component condensation-cycloaddition of the corresponding (oligo)phenothiazinyl carbaldehydes 1, N-hexyl glycine (2), and C₆₀. Cyclic voltammetry of 3 and reference compounds 4 shows that the phenothiazinyl moiety (donor) and the fullerene fragment (acceptor) are electronically decoupled in ground state. However, upon UV excitation the phenothiazinyl fluorescence is considerably quenched, presumably as a consequence of a charge separation by an intramolecular photo-induced electron transfer from phenothiazine to fullerene.     

From the “Brazuca” ball to octahedral fullerenes: their construction and classification

A simple cut-and-patch method is presented for the construction and classification for fullerenes belonging to the octahedral point groups, O or \(O_h\). In order to satisfy the symmetry requirement of the octahedral group, suitable numbers of four- and eight-member rings, in addition to the hexagons and pentagons, have to be introduced. An index consisting of four integers is introduced to specify an octahedral fullerenes. However, to specify an octahedral fullerene uniquely, we also found certain symmetry rules for these indices. Based on the transformation properties under the symmetry operations that an octahedral fullerene belongs to, we can identify four structural types of octahedral fullerenes.     

Magnetic Silicon Fullerenes: Experimental Exploration and Theoretical Insight

The present article summarizes progress in research on silicon clusters with encapsulated metal atoms, and specifically focuses on the recent identification of magnetic silicon fullerenes. Considering that C\(_{20}\) forms the smallest known fullerene, the Si\(_{20}\) cluster is of particular interest in this context. While the pure hollow Si\(_{20}\) cage is unstable due to the lack of \(sp^2\) hybridization, endohedral doping with a range of metal atoms has been considered to be an effective way to stabilize the cage structure. In order to seek out suitable embedded atoms for stabilizing Si\(_{20}\), a broad search has been made across elements with relatively large atomic radius. The rare earth elements have been found to be able to stabilize the Si\(_{20}\) cage in the neutral state by forming R@Si\(_{20}\) fullerene cages. Among these atoms, Eu@Si\(_{20}\) has been reported to yield a stable magnetic silicon fullerene. The central europium atom has a large magnetic moment of nearly 7.0 Bohr magnetons. In addition, based on a stable Eu\(_2\)Si\(_{30}\) tube, a magnetic silicon nanotube has been constructed and discussed. These magnetic silicon fullerenes and nanotubes may have potential applications in the fields of spintronics and high-density magnetic storage.     

Solvent free mechanochemical oxygenation of fullerene under oxygen atmosphere

Oxygenation of fullerene took place under mechanical stressing by a simple vibration mill in an oxygen atmosphere at 1 atm. Milled products were mixtures of poly-oxidized fullerene, C₆₀O_n, containing C-O-C and CO bonds. We observed a concurrent reaction as well, that is, polymerization of C₆₀ and C₆₀O. The average number of oxygen, n, of the overall products obtained by milling for 5 h was 8.6 per molecule of C₆₀. We confirmed generation of singlet oxygen during the present mechanochemical reaction by an ESR spin trapping method. Trapping of ¹O₂ was completely inhibited the oxygenation of fullerene. Formation of ¹O₂ is attributed to the energy transfer from mechanically excited state of fullerene and plays a decisive role on the present oxygenation of fullerene under mechanical stressing in O₂. In contrast, no ¹O₂ was observed by mechanically stressing the conventional photo-sensitizer, rosebengal. The difference in the behavior of C₆₀ and rosebengal is interpreted in terms of molecular deformation, being much easier for a 3D molecule, C₆₀, than a planar molecule, in line with the concept of inverse Jahn-Teller effects.     

Shell Structures in Molecular Orbital Energy Diagrams for “Small” Fullerene Cages: Free-Electron Versus Generator Orbital Models

The nearly spherical nature of small fullerene cages C _N (N<70) suggests that their molecular orbital (MO) energy diagrams should show a shell structure. Although group theoretical analysis of the Hückel-type energies for icosahedral and other highly symmetric cages confirms this assumption, this has not been established for fullerene cages in general. This work presents a simple computational algorithm based upon the canonical orthogonalization of generator orbitals (GOs) to analyze the -MO energy diagrams for any fullerene cage C _N , and demonstrates the validity of a shell structure in these diagrams. Results are compared to simple central force (spherical) models for the calculations of -MO energies in fullerene cages. The GO approach provides a ready assignment of the -MOs to individual spherical harmonics and allows valuable interpretations of various physical phenomena.     

k-resonant toroidal polyhexes

A toroidal polyhex H(p, q, t) is a cubic bipartite graph embedded on the torus such that each face is a hexagon, which can be described by a string (p, q, t) of three integers (p≥ 1, q≥ 1, 0≤ t≤ p−1). A set of mutually disjoint hexagons of H(p, q, t) is called a resonant pattern if H(p, q, t) has a prefect matching M such that all haxgons in are M-alternating. A toroidal polyhex H(p, q, t) is k-resonant if any i (1 ≤ i ≤ k) mutually disjoint hexagons form a resonant pattern. In [16], Shiu, Lam and Zhang characterized 1, 2 and 3-resonant toroidal polyhexes H(p, q, t) for min(p, q)≥ 2. In this paper, we characterize k-resonant toroidal polyhexes H(p, 1, t). Furthermore, we show that a toroidal polyhex H(p, q, t) is k-resonant (k≥ 3) if and only if it is 3-resonant.      

Complex formation between water-soluble sulfonated calixarenes and C60 fullerene

The inclusion complexes of sulfonated thiacalix[4]arene 1 and calix[6]arene 2 sodium salts with C₆₀ fullerene were investigated by photoluminescence (PL) and quantum-chemical methods. The stoichiometries of calixarene/C₆₀ complexes were found to be 2:1 for 1 and 1:1 for 2. Related quantum-chemical investigations show that C₆₀ fullerene is included in a cavity composed of two half-bowl molecules of 1. The C₆₀ fullerene ball is located deep within the cavity of 2 and the negatively charged sulfonate arms probably inhibit the formation of the bowl-shaped capsule that was observed in the case of 1.     

Synthesis and electronic properties of (oligo)phenothiazine-ethynyl-hydro-C60 dyads

Ethynyl bridged (oligo)phenothiazine-C₆₀ dyads 2 can be readily synthesized by addition of the corresponding (oligo)phenothiazinyl lithium acetylides 1 to C₆₀ followed by protonation with acetic acid. Cyclovoltammetric data of 1 and 2 reveal that the (oligo)phenothiazinyl moieties (donor) and the fullerene fragment (acceptor) are electronically decoupled in ground state, yet, each additional phenothiazine lowers the HOMO-LUMO gap by 100 mV. Upon UV excitation the phenothiazinyl fluorescence is considerably quenched, presumably as a consequence of a charge separation by an intramolecular photo-induced electron transfer from phenothiazine to fullerene.     

Distance-restricted matching extendability of fullerene graphs

A fullerene graph is a 3-connected cubic plane graph whose all faces are bounded by 5- or 6-cycles. In this paper, we show that a matching M of a fullerene graph can be extended to a perfect matching if the following hold: (i) three faces around each vertex in \(\{x,y:xy\in M\}\) are bounded by 6-cycles and (ii) the edges in M lie at distance at least 13 pairwise.     

Syntheses and crystal structures of azafulleroid and aziridinofullerene bearing silyl or germyl benzene

Addition of silyl and germylmethyl azides (1) to fullerene C₆₀ at 50 °C through [2+3] cycloaddition led to the formation of the triazoline adducts (2). Subsequently, heating 2 at 100 °C in the solid state, caused N₂ extrusion producing two different isomers, [5,6]-azafulleroid (3) and [6,6]-aziridinofullerene (4). The ¹³C NMR spectrum of 3 had an absence of resonances in the aliphatic region for the fullerene C₆₀ cage, showing a fulleroid with C_S symmetry. In contrast, 4 exhibited one sp³ resonance in the aliphatic region for the fullerene C₆₀ cage, indicative of an aziridinofullerene with C_2V symmetry. However, MALDI-TOF mass characterization was hampered because ion peaks corresponding to the bis-adduct are detected in positive ion mode measurements, whereas the ion peaks [M−N₂]⁻ for 2a as well as [M]⁻ for 3a and 4a are observed in negative ion measurements. In an effort to obtain X-ray data, silyl and germylphenyl groups were introduced to form intermolecular complexes with fullerene C₆₀. The X-ray structures of 3c and 3d revealed a strong enhancement of homoconjugation in the bridged annulene moiety based on POAV analysis. The X-ray structures of 3c,d and 4c were confirmed with the detection of silyl and germylphenyl-C₆₀ interactions, similar to dimethoxyphenyl-C₆₀ interactions.     

Formation of new hybrid structures: Fullerene C<Subscript>60</Subscript>–amphiphilic copolymer of <Emphasis Type="Italic">N</Emphasis>-vinylpyrrolidone with (di)methacrylates in isopropyl alcohol

New hybrid structures of fullerene C₆₀ and an amphiphilic copolymer of N-vinylpyrrolidone with lauryl methacrylate and triethylene glycol dimethacrylate have been obtained via solubilization of fullerene by individual macromolecules and their micelle-like aggregates that form in isopropyl alcohol. The volume ratios of copolymer and C₆₀ solutions in toluene at which there is suppression of aggregation of fullerene and fullerene–polymer particles and the existence of stable hybrid structures in solution have been found. With the use of absorption electron spectroscopy, it has been shown that, with time, fullerene undergoes binding to donor groups of the copolymer and forms a donor–acceptor complex. According to the data of optical microscopy, fullerene is homogeneously distributed as spherical aggregates in the solid polymer matrix.     

Novel addition in trifluoromethylation of [70]fullerene

Pyrolytic trifluoromethylation of [70]fullerene with CF₃CO₂Ag at 300 °C results in the addition of up to 12 CF₃ groups to the fullerene cage. Forty-six C₇₀(CF₃)_n derivatives (numbers in parentheses) were separated by two-stage high pressure liquid chromatography (HPLC) as follows: n = 2(2), 4(16), 6(9), 8(14) 10(5), some being characterised by NMR. The range of derivatives is much greater than for other [70]fullerene reactions, and as with [60]fullerene trifluoromethylation, no single derivative is dominant, indicating that kinetic stability mainly controls product formation. NMR spectra show most derivatives to be unsymmetrical, with combinations of quartets and septets (overlapping quartets) due to contiguous (‘linear’) addend arrays, having significantly different coupling constants of the ‘terminal’ quartets of between 9.1 and 17.7 Hz. These differences, together with those observed previously in trifluoromethylation of [60]fullerene are consistent with addition across both 6:6- and 5:6-ring junctions. Of the two C₇₀(CF₃)₂ isomers, one has either C_s or C₂ symmetry, the other has C₁ symmetry, whilst the C₇₀(CF₃)₄ derivatives fall into four categories: (i) symmetrical compounds (one gives only two singlets in the NMR); (ii) unsymmetrical compounds that show a ‘linear’ coupling sequence; (iii) unsymmetrical compounds having a remote pairs of adjacent groups; (iv) compounds having a coupled array of three CF₃ groups, together with a remote group suggesting sterically-driven migration. The first evaluation of differential NMR couplings across 6:6- and 5:6-bonds in a fullerene has been made using C₆₀F₆ as a model.     

The toroidal unit cell of a quasicrystal

The problem of finding the toroidal unit cell of a quasicrystal is formulated in terms of a matrix (graph) divisor. Such a unit cell is an analog of the crystal’s unit cell with cyclic boundary conditions, but is not a crystal approximant of the latter. The proposed approach may be used for calculating the energy-band structure of quasicrystals.     

The complexity of the Clar number problem and an exact algorithm

The Clar number of a (hydro)carbon molecule, introduced by Clar (The aromatic sextet, 1972), is the maximum number of mutually disjoint resonant hexagons in the molecule. Calculating the Clar number can be formulated as an optimization problem on 2-connected plane graphs. Namely, it is the maximum number of mutually disjoint even faces a perfect matching can simultaneously alternate on. It was proved by Abeledo and Atkinson (Linear Algebra Appl 420(2):441–448, 2007) that the Clar number can be computed in polynomial time if the plane graph has even faces only. We prove that calculating the Clar number in general 2-connected plane graphs is \(\mathsf {NP}\)-hard. We also prove \(\mathsf {NP}\)-hardness of the maximum independent set problem for 2-connected plane graphs with odd faces only, which may be of independent interest. Finally, we give an exact algorithm that determines the Clar number of a given 2-connected plane graph. The algorithm has a polynomial running time if the length of the shortest odd join in the planar dual graph is fixed, which gives an efficient algorithm for some fullerene classes, such as carbon nanotubes.