J1i1 1 I I

35 40 45

Time of Flight /ps

Fig. 5.13. Electron paramagnetic resonance (EPR) spectra of [email protected]: (A) normal aerobically prepared [email protected] sample dissolved in toluene at 220 K, and (B) an anaerobic-ally prepared [email protected] sample showing the octet EPR pattern clearly. The chromatography was performed using an ethanol-deactivated silica gel column with a 100% toluene elutant. The deactivation was done using an ethanol-hexane (1:1) mixed solution [5.83], uid chromatography using two polystyrene chromatographic columns in series has been shown to lead to more efficient separation of [email protected]„c and [email protected]„c metallofullerenes (m = 1,2,3) [5.100].

To monitor the synthesis process, two characterization techniques have normally been used. The first is mass spectroscopy (see Figs. 5.10 and 5.12 and §5.3.2), which provides information on the various species present in the sample and their relative abundances (see §6.2). The second method is electron paramagnetic resonance, which measures the hyperfine interaction (~ I • J) and therefore provides a sensitive measure of the angular momentum J and charge state of the dopant ion. Strong evidence for a charge transfer of three electrons from La to these higher-mass fullerene shells is provided by the octet EPR hyperfine spectrum shown in trace B of Fig. 5.13 [5.83] (see §16.2.1). In the EPR spectrum for [email protected], the spin of 139La is 7/2, and the electron g-value is 2.0010 for an unpaired electron associated with the LUMO level (see §12.1). The spectra shown in Fig. 5.13 demonstrate the importance of anaerobic sample preparation and chromatography (see §5.2.1). In trace A of Fig. 5.13 the spectrum is for an [email protected] sample handled in air and then dissolved in toluene, while the spectrum in trace B is for an anaerobically prepared and chro-matographed sample. An ethanol-deactivated silica gel column with 100% toluene elutant was used for the chromatography (see §5.2.1). EPR de

tection has also been used to provide feedback to greatly enhance the isolation capability of EPR-active endohedral metallofullerenes (such as [email protected] and [email protected]) using a chromatographic system with on-line EPR detection [5.100,101].

5.5. Health and Safety Issues

There are as yet no reports of adverse health affects resulting from exposure to fullerenes or fullerene-containing material. Nevertheless, the health effects of fullerenes have not yet been extensively studied. Early work [5.102] suggests the absence of genotoxicity of C60 as demonstrated by somatic mutation and recombination tests.

Even if fullerenes and fullerene-derived materials turn out to be benign, a number of safety issues concerning the handling of fullerenes are identified below [5.11]. Since the inhalation of airborne fullerene soot particles may pose a potential health problem for lungs, the use of fume hoods is recommended. Appropriate gloves, masks, and clothing changes are recommended to avoid skin contact with fullerene soot. Of course, proper laboratory procedures should be used to contain the soot in appropriate vessels, minimizing the possibility of airborne soot in the workspace. Adequate design protection should be provided in the event of the failure of a glass reaction vessel used for soot generation. Suitable protection should be used to avoid eye damage and potential skin cancer when exposed to radiation from the carbon arc. Impurities in the arc rods may lead to polyaromatic hydrocarbon (PAH) generation; these chemicals are known carcinogens. The usual laboratory and safety precautions regarding solvents should be exercised in their use, storage, and disposal, since the solvents can be toxic, inflammable, or explosive. Because of the limited present knowledge of fullerenes and fullerene-containing materials, they should be treated with the respect given to chemical unknowns, and care should be taken to avoid ingestion, inhalation, and skin contact [5.9],

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