Irradiation fullerenes

Key Words—Graphite, fullerenes, HREM, nanostructures, electron irradiation. 

High-resolution transmission electron microscopy (HREM) is the technique best suited for the structural characterization of nanometer-sized graphitic particles. In-situ processing of fullerene-related structures may be performed, and it has been shown that carbonaceous materials transform themselves into quasi-spherical onion-like graphitic particles under the effect of intense electron irradiation[l 1],... 

Fullerene epoxide, C )0, is formed by the UV irradiation of an oxygenated benzene solution of Cfio The O atom bridges a 6 6 bond of the closed fullerene structure. The same compound is also formed as one of the products of the reaction of Cgo with dimethyldioxirane, Mc2COO (see later). ... 

Almena I., Carrillo J. R., De la Cruz P., Diaz-Ortiz A., Gomez-Escalonilla M. J., De la Hoz A., Langa F., Prieto P., Sanchez-Migallon A. Application of Microwave Irradiation to Heterocyclic Chemistry Targets Heterocyclic Systems-Chemistry and Properties 1998 2 281-308, Eds. Attanasi O. A. and Spinelli D., Pb. Soc. Chim. Ital. Keywords Diels-Alder reactions, [60]-fullerene... 

In 2000, it was proposed that the regioselectivity of the [3 + 2] cycloaddition of fullerenes could be modified under microwave irradiation. Under conventional heating, N-methylazomethine yhde and fullerene-(C7o) gave three different isomeric cycloadducts because of the low symmetry of C70 vs. Ceo. Using microwave irradiation and o-dichlorobenzene as a solvent, only two isomers were obtained, the major cycloadduct 114 being kinetically favored (Scheme 39) [75]. The same authors had previously reported the 1,3-dipolar cyclo addition of pyrazole nitrile oxides, generated in situ, to Geo under either conventional heating or microwave irradiation. The electrochemical characteristics of the cycloadduct obtained with this method made this product a candidate for photophysical apphcations [76]. 

Of all the fullerene forms, the nearly spherical properties of C o have attracted the greatest attention, especially in the field of bioconjugation. In addition to its physical properties, C o fullerenes have unique photo-optical and electro-chemical properties, which make them useful as carriers for biomedical research applications. For instance, upon exposure to light C o will generate singlet oxygen, which can be used in vivo to cleave biological molecules, particularly DNA and RNA. Studies indicate that irradiation of Cgo in solution can be used to destroy virus contamination (Kasermann and Kempf, 1997). Solutions of Buckminsterfullerene are a deep purple color, whereas other sizes of fullerenes display a variety of other colors. 

Langa et al. [26, 59, 60], while conducting the cycloaddition of N-methylazo-methine ylide with C70 fullerene, proposed a rather similar approach. Theoretical calculations predict an asynchronous mechanism, suggesting that this phenomenon can be explained by considering that, under kinetic control, microwave irradiation will favor the more polar path corresponding to the hardest transition state . 

For instance, cycloadditions of [60]fullerene (4) under the action of microwave irradiation usually require the use of this technique, because reactions are performed on a very small scale and C60. in common with many dienophiles, does not absorb microwaves efficiently [19]. 

The scope of the reaction has been demonstrated by the preparation of a series of isoxazolo[60]fullerenes 198 (Scheme 9.61) [109]. The nitrile oxides were prepared from the corresponding oximes by reaction with NBS or NCS and subsequent treatment of the mixture with triethylamine under microwave irradiation. 

Electroactive 3-(N-phenylpyrazolyl)fullereno[l,2-r/]isoxazolines have been synthesized by using 1,3-dipolar cycloaddition of pyrazole nitrile oxides, generated in situ, to Cgo at elevated temperature or microwave irradiation. The cyclic voltammetry measurements show a strong donor pyrazole ring, and a better acceptor ability of the fullerene moiety than the parent C60 (538). Treating fullerene Cgo with mesitonitrile oxide in toluene gives fullerene-nitrile oxide adduct, which is supposed to be useful for electrical and optical components (539). 

Radical polymerization of maleic anhydride and fullerene was used to obtain a new material, the photodynamic properties of which have been studied in vitro and in vivo. HeLa and bone tumor cell growth were inhibited by treatment with fullerene and light, so the polymer was tested on mice affected by bone tumor. After injection and irradiation, tumor size and weight were reduced and the mouse survival time was extended (Jiang and Li, 2007). The photodynamic properties of a supramolecular cucurbit[8]uril-fullerene complex have been studied by the same authors (Jiang and Li, 2006) who attributed HeLa cell death mainly to the damage of membrane phosphohpids and proteins. 

Both type I and II mechanisms are involved in the lipidic peroxidation of erythrocytes caused by irradiation of anionic fullerene derivatives (bearing carboxylic or phosphonate residues) (Yang et al., 2007e), with a significant activity at 10pM concentration and 30 min of irradiation, or at half concentration and double exposure time. The bis-methanophosphonate fullerene is the most effective, but no structure-activity correlations were reported. 

Xiao L, Takada H, Gan XH, Miwa N (2006) The water-soluble fullerene derivative Radical Sponge exerts cytoprotective action against UVA irradiation but not visible-light-catalyzed cytotoxicity in human skin keratinocytes. Bioorg. Med. Chem. Lett. 16 1590-1595. 

The cytotoxic and photocytotoxic effects of two water-soluble fullerene derivatives, a dendritic CL mono-adduct and the malonic acid CL tris-adduct were tested on Jurkat cells when irradiated with UVA or UVB light (Rancan et al., 2002). The cell death was mainly caused by membrane damage and it was UV dose-dependent. Tris-malonic acid fullerene was found to be more phototoxic than the dendritic derivative. This result is in contrast to the singlet oxygen quantum yields determined for the two compounds. 

The infectious titers of influenza vims were determined in the irradiated specimen at different time points. The kinetics of the vims activity in saline and allantoic fluid in the presence of fullerene and oxygen are presented in Fig. 5.1. 

Units and methods are developed to study the effect of active forms of oxygen on fullerene-based photosensitizers. The kinetics of the inactivation of influenza vims in saline and allantoic fluid during the course of photodynamic treatment using fullerene preparations is studied. Optimization of conditions has been conducted for viral inactivation (irradiation, doses, concentration of fullerene, and intensity of oxygen flow). Experiments are performed for inactivation of vims in blood semm. 

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