Fullerene radical scavenger

There are, indeed, many biological implications that have been triggered by the advent of fullerenes. They range from potential inhibition of HIV-1 protease, synthesis of dmgs for photodynamic therapy and free radical scavenging (antioxidants), to participation in photo-induced DNA scission processes [156, 157, 158, 159, 160, 161, 162 and 163]. These examples unequivocally demonstrate the particular importance of water-soluble fullerenes and are summarized in a few excellent reviews [141, 1751. 

Chi Y, Bhonsle JB, Canteenwala T, Huang J-P, Shiea J, Chen B-J, Chiang LY (1998) Novel water-soluble hexakis(4-sulfobutyl)fullerenes as potent free radical scavengers. Chem. Lett. 465 166. 

Chi Y, Canteenwala T, Chen HHC, Jeng US, Lin T-L, Chiang LY (2002) Free radical scavenging and photodynamic functions of micelle-like hydrophilic hexa(sulfobutyl)fullerene (FC4S). Perspect. Fullerene Nanotechnol. 165-183. 

Jeng US, Lin TL, Chang TS, Lee HY, Hsu CH, Hsieh YW, Canteenwala T, Chiang LY (2001) Comparison of the aggregation behavior of water-soluble hexa(sulfobutyl)fullerenes and polyhydroxylated fullerenes for their free-radical scavenging activity. Prog. Colloid Polym. Sci. 118 232-237. 

A water-soluble Cj-symmetrical trisadduct of Cjq showed excellent radical scavenging properties in vitro and in vivo and exhibits remarkable neuro-pro tective properties [7,8]. It is a drug candidate for the prevention of ALS and Parldnsoris disease. Concerning the reaction mechanism, nucleophilic additions and radical additions are closely related and in some cases it is difficult to decide which mechanism actually operates [92]. For example, the first step in the reaction of f-eo with amines is a single electron transfer (SET) from the amine to the fullerene. The resulting amines are finally formed via a complex sequence of radical recombinations, deprotonations and redox reactions [36]. 

Kronholm et al. (5) prepared water-soluble fullerenes, (I), which was effective as free radical scavengers. 

Cso and its derivatives are also easily excited by low-energy light [x]. Thus, a rational combination of electronic properties with chemical reactivity and/or photoactivity has resulted in the preparation of numerous fullerene-derived materials, including low temperature superconducting salts [xi], radical scavengers [xii], materials for - photovoltaic devices and -> conducting polymers [xiii]. 

Enes et al. (2006) recently presented new fulleropyrrolidines bearing one or two 3,5-di-tert-bvAy 1-4-hydroxyphcny 1 units, the EPR studies of which demonstrated that these derivatives are antioxidants. In this case, the presence of the fullerene unit seems to play a marginal role in the reaction with peroxyl radicals, which is governed by the phenol portion. Despite this, the presence of C60 should contribute to scavenge radicals in hypoxic conditions, where alkyl radicals could be the main oxidative products to be removed. 

As the AO with a direct nonspecific mechanism of action we have chosen Hypoxene - sodium poly(2,5-dihydroxiphenyl)-4-thiosulfonate. Besides a direct AO effect as a scavenger of free radicals it exerts an anti-hypoxic effect shunting I and II complexes of mitochondrial respiratory chain, which are inhibited as a consequence of hypoxia (Eropkin et al., 2007). Hypoxene was introduced into cell incubation media before illumination and left during cells further incubation. Hypoxene in the concentration of 40pg/ml, comparable to doses applied in vivo, completely blocked C60-induced phototoxicity (Table 7.3). Cellular viability has completely recovered to control level, which is a convincing evidence of free radical nature of cellular damage in photodynamic effect of fullerene. 

Irradiation of phenyliodonium salts lead to the formation of phenyl radicals. In the presence of C60 these radicals are efficiently trapped under formation of pheny-lated C6o derivatives, mainly the monoadduct. In reaction mixtures of C6o, phenyliodonium salts and spin traps like nitroso-tert-butane ( BuNO) or nitroso-durene (ND) no phenyl adducts with the spin traps could be observed after irradiation. This suggests that C6o is a more efficient scavenger for phenyl radicals than the spin traps [177], Other investigations yielded similar results, e.g., the photolysis of organomercury compounds in the presence of fullerenes leads to fullerene-derived radical adducts. These radical adducts can combine to form dimers that are thermally stable and accumulate in the samples [Eq. (7)] [178],... 

Accordingly, a concept was developed, that involves one of the organic compounds, e.g., toluene as a fullerene-dissolving medium (12,13). The systematic fullerene reduction was then obtained via addition of adequate co-solvents, namely, acetone and 2-propanol. Acetone was chosen as an efficient electron scavenger to hinder a reaction between solvated electrons and toluene. Followed by a fast protonation a radical species with a reducing character is formed. In addition, the (CH3)2 COH species is identical with the main product of the radiolysis of the second co-solvent, 2-propanol. 

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