Novel properties and applications of polyhydroxylated fullerenes

Fullerenes have gained considerable attention since their discovery and their potential applications have been widely studied in various fields of science. The unique electronic properties of fullerenes are attributed to the large numbers of conjugated double π- bonds. Due to the low energy of its lowest unoccupied molecular orbital (LUMO), fullerenes react with various reactive oxygen species (ROS), such as free radicals.1 However, the poor solubility of fullerenes in polar solvents (such as water) has impeded their potential uses in biological applications. Therefore, improving the solubility of fullerenes in polar solvents has been explored.

Unique properties of polyhydroxylated fullerenes

Fullerenes with various numbers of hydroxyl groups have been reported previously. Fullerenes with fewer than 12 hydroxyl groups have poor water solubility.2 Increasing the number of hydroxyl groups of polyhydroxylated fullerenes [fullerenols, (Product No. 793248 and 707481)] can improve their water solubility. Polyhydroxylated fullerene [C60(OH)n•mH2O (n > 40, m > 8), Product No. 793248] comprises a fullerene C60 with more than 40 hydroxyl groups on the fullerene cage and more than eight secondary bound water molecules as shown in Figure 1. Kokubo et al.3,4 reported that C60(OH)40•9H2O exhibits a high water solubility of up to 58.9 mg/mL under neutral pH conditions, which is much higher than that of C60(OH)36•8H2O (17.5 mg/mL) and fullerene C60 (1.3 × 10-11mg/mL).

Polyhydroxylated fullerene structure

Figure 1. The structure of a polyhydroxylated fullerene.


Due to the presence of free radical scavengers, polyhydroxy fullerenes exhibit unique properties such as high antioxidant activity. Saitoh et al.5 demonstrated the scavenging ability of polyhydroxy fullerenes against free radicals, which was evaluated by the β-carotene bleaching assay. C60(OH)44•8H2O showed scavenging activity for lipid peroxyl radicals or lipid radicals. It also suppressed UV-induced intracellular ROS generation in keratinocytes and scavenged hydroxyl radicals to a greater extent than ascorbic acid, a well-known antioxidant.6

Potential biological and industrial applications of polyhydroxylated fullerenes

Oxidative stress has been implicated in the pathogenesis of various diseases. Oxidative damage also plays a role in acne vulgaris, which is a common dermatological disease; therefore, the application of antioxidants has been considered for the treatment for acne vulgaris. Inui et al.7 demonstrated that polyhydroxylated fullerenes exert a suppressive effect on sebum secretion in hamster sebocytes and shows inhibitory activity against Propionibacterium acnes lipase. These findings suggest that polyhydroxylated fullerenes can be utilized as novel agents in the skincare treatment for acne vulgaris due to their potent antioxidant properties.

Oxidative stress is also known to be one of the key factors associated with the development of obesity-associated metabolic syndrome. Saitoh et al.5,8 reported that C60(OH)44•8H2O markedly quenched intracellular superoxide anion generation and lipid accumulation during the differentiation of OP9 preadipocytes into adipocytes. These findings suggest that polyhydroxylated fullerenes could be useful for controlling obesity and metabolic syndromes.

Polyhydroxylated fullerenes show antimicrobial activity as well. As reported by Aoshima et al.9, C60(OH)44•9H2O showed significant antimicrobial activity against Propionibacterium acnes, Staphylococcus epidermidis, Candida albicans, and Malassezia furfur, which suggests that polyhydroxylated fullerenes show antimicrobial activity via the inhibition of microbial cell growth.

Polyhydroxy fullerenes have also been investigated for their potential application as surface polishing agents. Takaya et al.10 developed the chemical mechanical polishing (CMP) technology for the planarization of the patterned copper wafer surface using the C60(OH)44•8H2O slurry. They found that the use of a polyhydroxylated fullerene as a polishing agent afforded better polishing performance compared to that achieved by using other polishing agents.




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