Full text of DOI:10.1070/MC2001v011n05ABEH001459

, 2001, 11(5), 193–194
Water-soluble [60]fullerene compositions with carbohydrates
Larissa S. Litvinova,* Veniamin G. Ivanov, Maxim V. Mokeev and Vladimir N. Zgonnik
Institute of Macromolecular Compounds, Russian Academy of Sciences, 199004 St. Petersburg, Russian Federation.
Fax: +7 812 328 6869; e-mail: LitvinLS@hq.macro.ru
10.1070/MC2001v011n05ABEH001459
Water-soluble compositions of [60]fullerene with carbohydrates were mechanochemically synthesised and investigated by UV-VIS
and solid-state high-resolution 13C NMR spectroscopy.
For using fullerenes in biology and medicine, they should be con-
verted into a water-soluble state by means of complexing agents.
At present, several water-soluble fullerene-containing compounds
1
0.8
have been obtained. These are [60]fullerene complexes with
γ -cyclodextrin,1,2 polyvinylpyrrolidone3,4 water-soluble calix[n]-
arenes,5,6 poly(vinyl alcohol)7 and tetraphenylporphine with poly-
0.6
vinylpyrrolidone.8 Moreover, the preparation of stable colloid
aqueous solutions of [60]fullerene with no stabilizing agents has
also been described.9,10
0.4
However, no information is available on the products of ful-
lerene interaction with low- and high molecular weight carbo-
hydrates such as dextran, which is known in medicine as an
effective blood plasma substitute. The probable reason is the
absence of common solvents for fullerene and carbohydrates,
making it possible to mix the components homogeneously and
to investigate the products of their interaction.
The aim of this work was to obtain water-soluble [60]fullerene
compositions with oligosaccharides and polysaccharides (dextran
with a molecular weight of 40 kDa), to study the state of ful-
lerene, and to find optimal conditions for the formation of a
water-soluble product with carbohydrates characterised by dif-
ferent molecular weights.
To obtain fullerene compositions with carbohydrates, a modi-
fied mechanochemical method7 was used. A carbohydrate was
suspended in a fixed volume of [60]fullerene solution in CCl4
at a concentration of 0.1 mg ml–1. After evaporating the solvent
in air, the mixture was ground in an agate mortar and then dried
in a vacuum at 40 °C for 48 h to remove CCl4 traces. The
[60]fullerene content of the dry mixture with the carbohydrate
ranged from 0.1 to 30%. A known volume of water was added
to the finally dispersed powder; the mixture was stirred for
1 min and centrifuged; then, the solution was separated from
the precipitate by decantation.
2
0.2
0.125 0.25 0.5
1
2
4
8
16
32
[60]Fullerene/Carbohydrate (wt%)
Figure 2 Absorbance (330 nm) of [60]fullerene in an aqueous solution as
a function of [60]fullerene concentration in solid-phase compositions with
(1) sucrose and (2) dextran (40 kDa).
The concentration and the molar absorption coefficient of
water-soluble [60]fullerene were determined photometrically by
isolating fullerene from aqueous solutions by TLC on silica gel
plates prewashed with MeOH using CHCl3 as an eluent. Under
these conditions, carbohydrate complexes were decomposed and
the fullerene remained entirely at the solvent front. Subse-
quently, the part of the silica gel layer containing fullerene was
transported to a Schott filter, [60]fullerene was desorbed from
silica gel wih CCl4, the solution obtained was photometrically
examined at l = 328 nm. The concentration (C) and molar ab-
sorption coefficient (e) of fullerene passed into water were deter-
mined. The RSD for C and e was better than 15%.
The water-soluble part of the composition was investigated
by UV-VIS spectroscopy on a Specord M40 spectrophotometer.
High resolution solid-state 13C NMR spectra were obtained
at room temperature on a Bruker CPX-100 spectrometer using
magic angle spinning (MAS), and cross-polarisation (CP MAS)
techniques. The working frequency of 13C NMR was 25.18 MHz,
and the sample spin rate was 3–4 kHz. Tetramethylsilane (TMS)
was used as reference.
Figure 1 shows the electronic spectra of a [60]fullerene solu-
tion in hexane, the spectra of its films on a quartz support and
the spectra of an aqueous solution of a [60]fullerene composi-
tion with sucrose. The spectra of the composition and the film
are similar and greatly differ from that of fullerene. The bands
are wider, the bathochromic shifts of band maxima is observed,
the ratio of their intensities change and new spectral features in
the long-wave region appear. A similar bathochromic shift and
band widening in the spectra of solutions of the products of
[60]fullerene interaction with γ -cyclodextrin and liposomes was
attributed previously8 to the presence of [60]fullerene aggre-
gates in solutions. Similar results were obtained for [60]fullerene–
pyridine–water mixtures,9 which were explained by the formation
of monodisperse, spherical, and chemically inert [60]fullerene
nanocapsules.
1.0
0.8
0.6
The absorbance of solutions depends on the fullerene content
of the initial composition (Figure 2). The solutions obtained from
a composition with a high fullerene content (10% or higher)
and, correspondingly, with a lower carbohydrate content, are
characterised by low absorbance. This is probably due to a low
concentration of fullerene passed into solution (for sucrose, less
than 1×10–5 mol dm–3). The increasing carbohydrate fraction in
the composition at a fixed quantity of [60]fullerene leads, first,
to a drastic and then to a gradual increase in absorbance. When
the sucrose content of the solid-phase composition is higher
than 99.7 wt%, the fullerene concentration in water increases
×2.5
0.4
2
×0.5
0.2
1
3
210
250
300
400
500 600
l/nm
Figure 1 Absorption spectra of (1) a [60]fullerene solution in hexane (2) a
[60]fullerene film on quartz and (3) an aqueous solution of sucrose–[60]ful-
lerene composition (solid-phase [60]fullerene concentration is 2 wt%).
– 193 –

, 2001, 11(5), 193–194
with dextran contains a signal characteristic of [60]fullerene
(143.6 ppm). The half-width of the line increased to 1.2 ppm,
whereas for pure fullerene it is 0.16 ppm. The spectrum of the
same composition obtained by a CP MAS technique also
contains a [60]fullerene signal, which indicates that proton-
containing groups are located near the fullerene surface.
In the spectra of the composition with sucrose, the [60]ful-
lerene line in the MAS spectrum is broadened (1.2 ppm) and
shifted upfield (dMAS 141.3 ppm). Moreover, in the CP MAS
spectrum, a new low-intensity peak appeared at the higher mag-
netic field (dCP MAS 139.2 ppm). The line splitting and upfield
shift of the [60]fullerene signal in CP MAS can be interpreted
by the interaction of fullerene with hydroxyl groups in the
carbohydrate. This suggestion is consistent with published data,2
according to which the interaction in the [60]fullerene complex
with γ -cyclodextrine takes place via oxygen atoms including
those in hydroxyl groups. This interaction is of the donor–acceptor
character.2 It was found13,14 that when [60]fullerene is included
in capsule-like cage molecules (palladium-linked bis-porphyrins
and homooxacalix[3]arene dimeric capsules) the 13C NMR
spectra also exhibit an additional upfield line of encapsulated
[60]fullerene. The NMR data confirm the fullerene interaction
with the carbohydrate in the composite.
4
3
2
1
0.0
0.4
0.8
1.2
1.6
[C60]/104 mol dm–3
Figure 3 The concentration dependence of the molar absorption coefficient
(e) of water-soluble fullerene in aqueous solutions of a [60]fullerene–
sucrose composition (l = 440 nm).
up to (1–2)×10–4 mol dm–3. The absorbance and hence concen-
tration are lower for dextrans than for sucrose.
In conclusion, water-soluble compositions of [60]fullerene with
sucrose and dextran (40 kDa) were prepared mechanochemically.
Sucrose is a better solubilising agent for [60]fullerene than
dextran.
Two types of interactions occurred in the test samples: ful-
lerene–carbohydrate (complexation) and fullerene–fullerene (ag-
gregation). The stability of an aqueous solution of fullerene with
respect to [60]fullerene extraction by such solvents as toluene
and chloroform suggests that fullerene passes into solution in
the form of aggregates in a carbohydrate shell. Moreover, the
surface carbohydrate layer forms a van der Waals complex with
fullerene.
To better understand the properties of the products, the con-
centration dependence of the molar absorption coefficient of
water-soluble fullerene was studied using the above technique
(Figure 3). The molar absorption coefficient increases with de-
creasing the concentration of fullerene passed into water. This
indicates that the ratio of components passed into solution from
the compositions with different carbohydrate contents is not
constant. A maximal concentration of fullerene in water at its
concentration of 4% in the solid-phase composition was attained
with the use of sucrose, and it was 5×10–4 mol dm–3.
The concentration dependence of absorption, the UV-VIS
spectra of water-soluble fractions (broadening and shift of ful-
lerene bands in the UV region and new spectral features in the
long-wave range) show that fullerene passes into water as aggre-
gates. They exhibit high stability and do not form smaller frag-
ments when the solution is diluted. It is impossible to extract
fullerene from aqueous solutions by organic solvents.
This work was supported by the Russian Research and De-
velopment Programme ‘Fullerenes and Atomic Clusters’ (grant
no. 94053).
The solid-state 13C MAS NMR spectrum of a composition
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Figure 4 High-resolution solid-state 13C NMR spectra of (a) [60]fullerene,
(b) and (c) sucrose–[60]fullerene composition (20 wt%) in MAS (a), (b)
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Received: 3rd April 2001; Com. 01/1785
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