Fullerenols Revisited as Stable Radical Anions

Abstract

The first exhaustive purification and characterization of the much-studied "fullerenols", prepared by reaction of C(60) in toluene with an oxygenated, aqueous NaOH solution using tetrabutylammonium hydroxide as a phase transfer catalyst, has been performed. The resulting fullerenol is not simply polyhydroxylated C(60) but rather is a structurally and electronically complex C(60) radical anion with a molecular formula of Na(+)(n)[C(60)O(x)(OH)(y)](n)(-) (where n = 2-3, x = 7-9, and y = 12-15) for three different, but identical, preparations. Surprisingly, Na(+)-fullerenol is paramagnetic, exhibiting mu(B) values in aqueous solution of 1.9-2.1 B.M. at 0.5 T and 300 K and R(1) proton relaxivities of 0.55-0.77 mM(-1)s(-1) at 20 MHz and 40 degrees C, values both slightly higher than those expected for a pure S = 1/2 spin system. ESR studies (ESE-FS and 2D nutation) of frozen aqueous solutions at 1.5 and 5.0 K establish that Na(+)-fullerenol is mainly S = 1/2 with a minor, but significant, component of S = 1. Thus, this is the first report to characterize these widely studied, water-soluble fullerenols as stable radical anions. The stability of the S = 1/2 Na(+)-fullerenol radical is likely due to a highly derivatized C(60) surface that protects a cyclopentadienyl radical center on the fullerene.

A highly efficient and tumor vascular-targeting therapeutic technique with size-expansible gadofullerene nanocrystals

“…As shown in Fig. S2 and Table S1, the composition of the materials was found to contain mainly C, O, Gd, as well as a little Na that is possibly from the reactant NaOH to form a week complex with poly-ion Na + salt [24].…”

Water-Soluble Single-Nano Carbon Particles: Fullerenol and Its Derivatives

“…Although a fullerenol seems to completely dissolve in a solution, it may be aggregated in the nano-size region, as seen for many fullerene derivatives and some fullerenols (Mohan et al, 1998;Husebo et al, 2004;Brant et al, 2007;Chae et al, 2009;Su et al, 2010). The particle size of medium-degree fullerenol C 60 (OH) 24 in aqueous solution is reported as between ca.…”

“…The fullerenol has also been known to have many bioactivities, including antioxidant activity similar to pristine C 60 (Bosi et al, 2003;Bakry et al, 2007;Partha & Conyers, 2009). However, the practical use of these types of fullerenols might be restricted because of their unfavorable contamination by Na + ions, which are inevitably introduced during treatment with NaOH, and the purification is rather difficult except when done by repeated gel column chromatography (Husebo et al, 2004). The relatively higher water solubility than that expected, given the number of hydroxyl groups, is reasonably explained by the corrected chemical formula Na + n [C 60 Ox(OH) y ] n-.…”

“…For the reaction using NaOH, the attack of -OH to C 60 followed by the oxidation with molecular oxygen via one electron transfer from the C 60 anion gives the hydroxylated C 60 . The successive attack of -OH and repeated oxidation finally gives the medium-degree fullerenol (Scheme 3) (Husebo et al, 2004). …”

“…The solubility of a fullerene molecule is dependent on the number of hydroxyl groups introduced; i.e., the low-degree hydroxylated fullerenols C 60 (OH) [10][11][12] (Chiang et al, 1994) can dissolve in some polar solvents, e.g., THF, dimethylformamide (DMF), and dimethyl sulfoxide (DMSO), and the medium-degree fullerenols C 60 (OH) 16 (Wang et al, 2005) and C 60 (OH) [20][21][22][23][24] (Li et al, 1993) are reported to dissolve even in water. However, these later fullerenols may be contaminated with Na salt because of the reagents used in synthesis, resulting in compositions with the formula Na + n [C 60 Ox(OH) y ] n-and exhibiting high water solubility in spite of their small number of hydroxyl groups (Husebo et al, 2004). In contrast, the high-degree hydroxylated fullerenols C 60 (OH) 36 and C 60 (OH) 44 , which are synthesized without using any Na salt, are completely water soluble by as much as 17 and 65 mg/mL, respectively (Kokubo et al, 2008;Kokubo et al, 2010).…”