Solubility endohedral fullerenes

While there are no studies of the toxicity of endohedral fullerenes in general, or gadofullerenes in particular, there are several preliminary studies regarding empty fullerenes and their derivatives. In initial steps toward characterizing the safety of water-soluble fullerene derivatives, a cytotoxicity study of various fullerene materials, including underivatized C60, C60[C(COOH)2]3, and two C.0(OH)r species, was conducted (Sayes et al., 2004). The results clearly showed that water-soluble derivatives were significantly less toxic than underivatized C60, and the trend was one of... 

Zhang S, Sun D, Li X, Pei F, Liu S (1997) Synthesis and solvent enhanced relaxation property of water-soluble endohedral metallofullerenes. Fullerene Sci. Tech. 5 1635-1643. 

The major products formed by DC arc discharge are empty fullerenes, with the endohedral fullerenes composing only about 1% of the raw soot. For this reason, better extraction methods are always being sought. Sublimation is a fairly efficient metiiod for extraction and is a solventless technique. Nevertheless, file most popular method for extraction of endohedral fiiUerenes is solvent extraction. Some popular solvents for extraction are xylene, carbon disulfide, and toluene. The efficiency of this method is not great because about half of the endohedral fiillerenes remain in the extracted residue, which needs further processing with other solvents. Extraction of trimetallic nitride endohedral fiillerenes has a higher efficiency because of increased solubility in common solvents. 

It is therefore the right time to give a first comprehensive overview of fullerene chemistry, which is the aim of this book. This summary addresses chemists, material scientists and a broad readership in industry and the scientific community. The number of publications in this field meanwhile gains such dimensions that for nonspecialists it is very difficult to obtain a facile access to the topics of interest. In this book, which contains the complete important literature, the reader will find all aspects of fullerene chemistry as well as the properties of fullerene derivatives. After a short description of the discovery of the fullerenes all methods of the production and isolation of the parent fullerenes and endohedrals are discussed in detail (Chapter 1). In this first chapter the mechanism of the fullerene formation, the physical properties, for example the molecular structure, the thermodynamic, electronic and spectroscopic properties as well as solubilities are also summarized. This knowledge is necessary to understand the chemical behavior of the fullerenes. 

The purification of endohedral metallofullerenes via HPLC had been difficulf, mainly because fhe content of metallofullerenes in raw soot is normally very limited and, furthermore, the solubility in normal HPLC solvents is generally lower than that of various empty higher fullerenes. It took almost two years for mefallofullerenes to be completely isolated by the HPLC method (Kikuchi et al., 1993 Shinohara et al., 1993a) after the first extraction of La Cg2 by the Rice group (Chai et al., 1991). Following these first isolations of metallofullerenes, isolation with different HPLC columns was also reported (Savina et al., 1994 Yamamoto et al., 1994a). The success of the purification/isolation was a real breakthrough for further characterization of the endohedral metallofullerenes. 

Endohedral metallofullerenes were presented as a new family of Gd complexes, in which Gd + cations are nicely encapsnlated inside fullerene cages. Since the Gd cation is protected from chemical attack, the Gd +-fullerenes are chemically stable and less toxic (Wilson, 1999). Water-soluble Gd + endohedral metallofullerene 99 (scheme 20), was characterized as an MRI contrast agent (Kato et al., 2003). Its water proton relaxivity r was estimated as being... 

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