Original Contribution
REACTIONS OF e
-
aq
, CO
2
•-
, HO
•
,O
2
•-
AND O
2
(
1
g
) WITH A
DENDRO[60]FULLERENE AND C
60
[C(COOH)
2
]
n
(n = 2– 6)
R. V. BENSASSON,* M. BRETTREICH,
†
J. FREDERIKSEN,
‡
H. G¨ OTTINGER,* A. HIRSCH,
†
E. J. LAND,
§,1
S. LEACH,
D. J. MCGARVEY,
‡
and H. SCH ¨ ONBERGER
†
*Laboratoires de Biophysique et de Photobiologie, Muse ´um National d’Histoire Naturelle, CNRS UMR 8646, INSERM U201,
Paris Cedex, France;
†
Institut fu ¨r Organische Chemie der Universita ¨t Erlangen-Nurnberg, Erlangen, Germany;
‡
School of
Chemistry and Physics, Lennard-Jones Laboratories, Keele University, Keele, Staffordshire, UK;
§
CRC Drug Development Group,
Paterson Institute for Cancer Research, Christie Hospital NHS Trust, Manchester, UK; and
DAMAP, Observatoire de
Paris-Meudon, CNRS UMR 8588, Meudon, France
(Received 28 February 2000; Revised 30 March 2000; Accepted 13 April 2000)
Abstract—Using pulse radiolysis and laser flash photolysis, we have investigated the reactions of the deleterious
species, e
-
aq
, HO
•
,O
2
•-
and O
2
(
1
g
) with 10 water-soluble cyclopropyl-fused C
60
derivatives including a mono-adduct
dendro[60]fullerene (d) and C
60
derivatives based on C
60
[C(COOH)
2
]
n=2–6
, some of which are known to be neuro-
protective in vivo. The rate constants for reactions of e
-
aq
and HO
•
lie in the range 0.5–3.3 10
10
M
-1
s
-1
. The d and
bis-adduct monoanion radicals display sharp absorption peaks around 1000 nm ( = 7 000–11 500 M
-1
cm
-1
); the
anions of the tris-, tetra-, and penta-adduct derivatives have broader, weaker absorptions. The monohydroxylated
radicals have their most intense absorption maxima around 390 – 440 nm ( = 1000 –3000 M
-1
cm
-1
). The anion and
hydroxylated radical absorption spectra display a blue-shift as the number of addends increases. The radical anions react
with oxygen (k 10
7
–10
9
M
-1
s
-1
). The reaction of O
2
•-
with the C
60
derivatives does not occur via an electron
transfer. The rate constants for singlet oxygen reaction with the dendrofullerene and eee-derivative in D
2
O at pH 7.4 are
k 7 10
7
and 2 10
7
M
-1
s
-1
respectively, in contrast to 1.2 10
5
M
-1
s
-1
for the reaction with C
60
in
C
6
D
6
. The large acceleration of the rates for electron reduction and singlet oxygen reactions in water is due to a
solvophobic process. © 2000 Elsevier Science Inc.
Keywords—Pulse radiolysis, Laser flash photolysis, Water-soluble fullerenes, dendro[60]fullerene, C
60
malonic acid
derivatives, Hydrated electron, Oxyradicals, Singlet oxygen, Free radicals
INTRODUCTION
C
60
fullerenes, with their 30 carbon-carbon double
bonds, are able to scavenge a large number of radicals
per molecule [1,2]. For the addition of radicals such as
the benzyl radical, the rate constants are larger, by three
to four orders of magnitude [3], for C
60
than those
observed for simple alkenes. Such properties have in-
spired an interest in potential biological applications of
fullerenes [4], including the inhibition of radical-initiated
lipid peroxidation [5] and the interception of deleterious
reactive oxygen species [6]. Dugan et al. have observed
the efficiency of water-soluble malonic acid derivatives,
C
60
[C(COOH)
2
]
3
, as neuroprotective agents in living
systems and assessed their ability to scavenge O
2
•-
and
HO
•
oxyradicals in solution by EPR analysis [6].
Using pulse radiolysis, we have now measured in
aqueous solution the rate constants for the reactions of
hydrated electrons (e
-
aq
), CO
2
•-
,O
2
•-
, and HO
•
radicals
with a dendritic monoadduct (d) of C
60
with 18 carbox-
ylic groups and a series of nine malonic acid C
60
deriv-
atives based on C
60
[C(COOH)
2
]
n
(n = 2– 6). The bis-
adducts studied were trans-2-, trans-3-, trans-4-, and
e-C
60
[C(COOH)
2
]
2
. The tris-adducts were e,e,e- and
t333-C
60
[C(COOH)
2
]
3
, the tetra-, penta-, and hexa-ad-
ducts being the all-e-regioisomers. The structures, sym-
metries and abbreviated names of the fullerene deriva-
tives under study are shown in Fig. 1.
We have determined in water at pH 7.4 (i) the spectra
Address correspondence to: R. V. Bensasson, Laboratoires de Bio-
physique et de Photobiologie, Muse ´um National d’Histoire Naturelle,
CNRS UMR 8646, INSERM U201, 43 rue Cuvier, 75231 Paris Cedex
05, France; Fax: +33 (1) 40 79 37 05; E-Mail: rvb@mnhn.fr.
1
Senior Research Fellow in Chemistry, Keele University.
Free Radical Biology & Medicine, Vol. 29, No. 1, pp. 26 –33, 2000
Copyright © 2000 Elsevier Science Inc.
Printed in the USA. All rights reserved
0891-5849/00/$–see front matter
PII S0891-5849(00)00287-2
26