Luis Echegoyen

The preparation and electrochemical properties of a novel type of composite made of small carbon nano-onions (CNOs) with poly(diallyldimethylammonium chloride) (PDDA) or chitosan (Chit) were investigated by cyclic voltammetry and electrochemical impedance spectroscopy. Composite films on glassy carbon electrode surfaces were deposited by a coating method, applying a drop of solution containing the suspended CNOs and filler, PDDA or Chit. Composites form relatively porous structures on the electrode surface and exhibit typical capacitive behavior, as well as excellent mechanical and electrochemical stability over a wide potential window, from +600 to −600 mV. The capacitance of the films is primarily related to the amount of CNOs incorporated into the layer of the filler. The capacitance ranges between 20 and 30 F g⁻¹ of incorporated CNOs. The composites also show a low relaxation time from resistive to capacitive behavior, therefore indicating that they can operate as capacitors in short time windows.

By introducing SO₂ as the sulfur source, the synthesis of an extensive family of cluster endohedral fullerenes Sc₂S@C_2n (n = 40–50) was demonstrated and a new isomer of Sc₂S@C₈₂ (C_s : 6) was isolated and characterized by spectroscopic and electrochemical methods for the first time.

An (e,e,e,e)-tetrakis-adduct of C₆₀fullerene with two pyridylpyrrolidino addends (trans-1 position relative to each other) and two (ethoxycarbonyl)methano addends (trans-1 position relative to each to other) compound 4, was obtained selectively by controlled potential electrolysis of the D_2h-hexakis-adduct 3.

Small carbon nano‐onions (CNOs, 6–8 shells) were prepared in high yield and functionalized with carboxylic groups by chemical oxidation. After functionalization these nanostructures were soluble in aqueous solutions. 3‐(4,5‐dimethylthiazol‐2‐yl)‐5‐(3‐carboxymethoxyphenyl)‐2‐(4‐sulfophenyl)‐2 tetrazolium (MTS) tests showed excellent cytocompatibility of all CNOs analyzed at 30 and 300 μg mL⁻¹, so these carbon nanostructures can be safely used for biological applications. The first covalent functionalization of oxidized CNOs (ox‐CNOs) with biomolecules, by using biotin–avidin interactions is reported here. Multilayers were prepared on a gold surface by layer‐by‐layer assembly and the process was monitored by surface plasmon resonance (SPR) spectroscopy and atomic force microscopy (AFM). Covalent binding of molecules to the short amine‐terminated organosulfur monolayers was assessed by Fourier transform infrared spectroscopy using total attenuated reflactance mode (FT‐IR/HATR).

Bingel–Hirsch derivatives of the trimetallic nitride template endohedral metallofullerenes (TNT‐EMFs) Sc₃N@I_h‐C₈₀ and Lu₃N@I_h‐C₈₀ were prepared by reacting these compounds with 2‐bromodiethyl malonate, 2‐bromo‐1,3‐dipyrrolidin‐1‐ylpropane‐1,3‐dionate bromide, and 9‐bromo fluorene. The mono‐adducts were isolated and their ¹H NMR spectra showed that the addition occurred with high regioselectivity at the [6,6] bonds of the I_h‐C₈₀ fullerene cage. Electrochemical analysis showed that the reductive electrochemistry behavior of these derivatives is irreversible at a scan rate of 100 mV s⁻¹, which is comparable to the behavior of the pristine fullerene species. The first reduction potential of each derivative is either cathodically or anodically shifted by a different value, depending on the attached addend. Bis‐adducts containing EtOOC‐C‐COOEt and HC‐COOEt addends were isolated by HPLC and in the case of Sc₃N@I_h‐C₈₀ the first reduction potential exhibits a larger shift towards negative potentials when compared to the mono‐adduct. This observation is important for designing acceptor materials for the construction of bulk heterojunction (BHJ) organic solar cells, since the polyfunctionalization not only increases the solubility of the fullerene species but also offers a promising approach for bringing the LUMO energy levels closer for the donor and the acceptor materials.

Seit dem ersten Fund von endohedralen Metallofullerenen (EMFs) hat sich die Suche nach Kohlenstoffkäfigen mit eingeschlossenen Metallen oder kleinen Molekülen rasch zu einem sehr aktiven Forschungsgebiet entwickelt. EMFs weisen besondere elektronische und Struktureigenschaften auf und finden vielfache Anwendungsmöglichkeiten. Noch mehr Potenzial bieten funktionalisierte EMFs, die besser löslich sind und durch Röntgenkristallographie und andere Techniken leicht charakterisiert werden können. Wir geben hier eine Übersicht über das allgemeine Gebiet der EMFs und insbesondere der funktionalisierten EMFs. Wir befassen uns in diesem Aufsatz mit der Struktur und den (elektrochemischen) Eigenschaften dieser faszinierenden Verbindungen und werden auch auf Anwendungen eingehen.

Ever since the first experimental evidence of the existence of endohedral metallofullerenes (EMFs) was obtained, the search for carbon cages with encapsulated metals and small molecules has become a very active field of research. EMFs exhibit unique electronic and structural features, with potential applications in many fields. Furthermore, functionalized EMFs offer additional potential applications because of their higher solubility and their ease of characterization by X‐ray crystallography and other techniques. Herein we review the general field of EMFs, particularly of functionalized EMFs. We also address their structures and their (electrochemical) properties, as well as applications of these fascinating compounds.

An isomerically pure sample of Gd₃N@C₇₈ has been extracted from the carbon soot formed in the electric-arc generation of fullerenes using hollow graphite rods packed with Gd₂O₃ and graphite powder under an atmosphere of helium and dinitrogen. Purification has been achieved by chromatographic methods and the product has been characterized by mass spectrometry, UV/vis absorption spectroscopy, and cyclic voltammetry. Although a number of endohedral fullerenes have been found to utilize the D_3h(5)-C₇₈ cage, comparison of the spectroscopic and electrochemical properties of the previously characterized Sc₃N@D_3h(5)-C₇₈ with those of Gd₃N@C₇₈ reveals significant differences that indicate that these two endohedrals do not possess the same cage structure. A single crystal X-ray diffraction study indicates that the fullerene cage does not follow the isolated pentagon rule (IPR) but has two equivalent sites where two pentagons abut. The endohedral has been identified as Gd₃N@C₂(22010)-C₇₈. Two of the gadolinium atoms of the planar Gd₃N unit are located within the pentalene folds formed by the adjacent pentagons. The third gadolinium atom resides at the center of a hexagonal face of the fullerene.

The regioselectivity of 1,3‐dipolar cycloaddition reactions between N‐(4‐thiocyanatophenyl)glycine and tetrakis[bis(ethoxycarbonyl)methylene]‐C₆₀ (7) was studied. The mono‐addition resulted in two penta‐adduct isomers (8 and 9) in a 1:1 ratio. A second addition to each compound led to, in the case of 8, two hexa‐adduct isomer products (10 and 11), whereas addition to 9 led to 11 and 12. Finally, reaction of 11 and the glycine afforded a third addition, giving rise to hepta‐adduct isomers 13 and 14. Preparative TLC and column chromatography were used to separate and purify these compounds. The structures were assigned based on their molecular symmetries as analyzed by ¹H, ¹³C, and 2D NMR spectra and MALDI‐TOF MS.(© Wiley‐VCH Verlag GmbH & Co. KGaA, 69451 Weinheim, Germany, 2009)