Autoxidation of linoleic acid in a strong magnetic field (9.4 T)

Article abstract of DOI:10.1016/S0040-4039(01)01571-4

Autoxidation of linoleic acid in a strong magnetic field (9.4 T) has been studied. Formation of the hydroperoxides has been monitored by the Fe(SCN)₃ method, showing that the magnetic field accelerates the autoxidation of linoleic acid.

Full text of DOI:10.1016/S0040-4039(01)01571-4

TETRAHEDRON
LETTERS
Pergamon
Tetrahedron Letters 42 (2001) 7451–7452
Autoxidation of linoleic acid in a strong magnetic field (9.4 T)
Masahiro Inotani, Shuichi Fukuyoshi and Takenori Kusumi*
Faculty of Pharmaceutical Sciences, Tokushima University, Tokushima 770-8505, Japan
Received 7 June 2001; revised 20 August 2001; accepted 24 August 2001
Abstract—Autoxidation of linoleic acid in a strong magnetic field (9.4 T) has been studied. Formation of the hydroperoxides has
been monitored by the Fe(SCN)3 method, showing that the magnetic field accelerates the autoxidation of linoleic acid. © 2001
Elsevier Science Ltd. All rights reserved.
Concerns about magnetic effects on biological systems
are growing since the chances for mankind to be
exposed to moderate or strong magnetic fields, e.g.
linear motor cars and MRI, are increasing. Living
organisms are functioned by a series of chemical reac-
tions and, therefore, basic knowledge of the magnetic
effects on fundamental chemical reactions may be
required for understanding the effect of a magnetic field
on human health.
Scheme 1.2 The hydroperoxides are formed by abstrac-
tion of a hydrogen atom from the doubly allylic meth-
ylene group and addition of oxygen to the allyl radical,
followed by addition of a hydrogen to the peroxide
radical. The present report deals with a comparative
study of linoleic acid autoxidation in the presence or
absence of a 9.4 T magnetic field.
Linoleic acid (250 mmol) was dissolved in ethanol (2.5
mL) and the solution was added to 0.1 M phosphate
buffer (pH 7.0). The total volume of the mixture was
adjusted to 25.0 mL. A 0.5 mL portion of this mixture
(1.00×10−2 M for linoleic acid) was placed in a 0.5 mm
NMR tube (this sample was designated S9.4T), which
was then set in the probe of a 400 MHz NMR spec-
trometer (Bruker ARX-400). Prior to insertion of the
sample tube, the temperature (37°C) of the probe was
In our studies on the effects of a magnetic field on
chemical reactions, superconductive NMR instruments
(400 MHz) have been used. They can produce a strong
and extremely stable magnetic field (9.4 T). We have
recently reported that a butyltin hydride reduction of
halides, supposedly a radical reaction, is accelerated by
a strong magnetic field (9.4 T).1
measured by
a thermocouple (Yokogawa 2455).
We were interested to see if autoxidation of linoleic
acid, an essential constituent of mammalian lipids,
would be affected by the magnetic field, because the
oxidation is known to proceed via radical reactions.
The autoxidation course of linoleic acid is shown in
Throughout the reaction, the spinner and transmitter
for a lock signal were turned off to avoid effects other
than that of the magnetic field. The other four 0.5 mL
portions of the mixture (S0T) were put in NMR tubes,
Scheme 1.
Keywords: autoxidation; linoleic acid; unsaturated fatty acid; magnetic field.
* Corresponding author. Tel./fax: +81 88 633 7288; e-mail: tkusumi@ph2.tokushima-u.ac.jp
0040-4039/01/$ - see front matter © 2001 Elsevier Science Ltd. All rights reserved.
PII: S0040-4039(01)01571-4

7452
M. Inotani et al. / Tetrahedron Letters 42 (2001) 7451–7452
Table 1. Autoxidationa of linoleic acid in the presence and absence of 9.4 T magnetic field
Exp. no.
1
2
3
4
5
6
7
8
9
10
LAb (mM)
A (9.4 T)c
A% (0 T)d
A/A%
9.90
0.56
0.53
1.06
10.0
0.69
0.56
1.23
10.4
0.63
0.56
1.13
10.0
0.67
0.53
1.26
10.5
0.58
0.55
1.05
10.0
0.65
0.58
1.12
10.4
0.56
0.54
1.04
10.5
0.70
0.63
1.11
9.90
0.65
0.54
1.20
9.80
0.72
0.59
1.22
a For the experimental conditions, see text. Autoxidation (at 37°C) was stopped at 10 h, and the concentration of the peroxides was expressed as
the absorbance at 500 nm after Fe(SCN)3 coloration.
b LA, linoleic acid.
c Absorbance of the sample in a 9.4 T magnetic field.
d Absorbance of the sample without a magnetic field. The average value of four experiments. Standard deviations were from 0.01 to 0.02.
Fe(SCN)3 coloration was determined for S9.4T and S0T.
The results are summarized in Table 1.
which were covered with aluminum foil to shield them
from light, and they were immersed in a water bath, the
temperature of which had been set at 37°C by use of
the same thermocouple. After 3 h, the reaction mixtures
(S9.4T and S0T) were taken out of the tubes, and 100 mL
portions of the respective mixtures were added to 75%
ethanol containing a mixture of 30% aqueous NH4SCN
(100 mL) and 20 mM FeCl2 in 3.5% hydrochloric acid
(100 mL). The concentration of Fe(SCN)3, which is
proportional to the amount of the hydroperoxides,3 was
expressed as the absorbance at 500 nm on a spec-
trophotometer. The same procedure was carried out
using a freshly prepared mixture until the reaction time
reached 5 h, and the hydroperoxide concentration was
determined. These operations were repeated, changing
the reaction times from 3 to 20 h. The results are
summarized in Fig. 1.
In all the experiments, the concentration of the
hydroperoxides determined by the Fe(SCN)3 method
was larger for the 9.4 T sample than for the 0 T one,
supporting the experimental results shown in Fig. 1.
The average ratio of A (9.4 T) versus A% (0 T) was
1.14 0.08, indicating that the autoxidation ratio of
linoleic acid (10 mM) at 37°C was increased by 14 8%
after 10 h.
The same (concentration, temperature, and reaction
time) experiments were repeated on another 400 MHz
NMR instrument (JEOL AL400). Again, the increased
ratio under the 9.4 T magnetic field was observed: A
(9.4 T)/A% (0 T)=1.15 0.09 (ten experiments).
Difference in the reaction rates between S9.4T and S0T
was, however, not observed in 1.4 T (JEOL PMX-60)
and 0.4 T (a neodymium magnet) magnetic fields.
It is obvious that the autoxidation rate of S9.4T is
greater than that of S0T. The 9.4 T magnetic field
apparently accelerates the autoxidation of linoleic acid.
It is also noticeable that the difference between S0T and
S9.4T becomes distinct after 10 h reaction time. There-
fore, in further experiments, autoxidation was inter-
rupted after 10 h, and the absorbance at 500 nm after
Interpretation of the increased rate of the autoxidation
in a 9.4 T magnetic field has been difficult so far. There
are three possible substitution positions for the
hydroperoxy group (C-10, -12, and -14: see Scheme 1),
and cis and trans isomers are feasible for the respective
hydroperoxides. The hydroperoxides are unstable and
they tend to decompose into complex mixtures includ-
ing short-chain aldehydes.
We are presuming that one of the radical reactions
(steps a–c in Scheme 1) is activated by a 9.4 T magnetic
field on the basis of our finding that the tributyltin
hydride reduction of phenylalkyl halides is accelerated
by the magnetic field,1 although the mechanism of the
acceleration is not clear.
References
1. Fukuyoshi, S.; Kusumi, T. Chem. Lett. 2001, 230–231.
2. (a) Porter, N. A.; Wujek, D. G. J. Am. Chem. Soc. 1984,
106, 2626–2629; (b) Henderson, D. E.; Slickman, A. M.;
Henderson, S. K. J. Agric. Chem. 1999, 47, 2563–2570.
3. Koch, R. B.; Stern, B.; Ferrari, C. G. Arch. Biochem.
Biophys. 1958, 78, 165–179.
Figure 1. The reaction course of the autoxidation of linoleic
acid in the presence (ꢀ) (S9.4T) and absence (ꢁ) (S0T) of a 9.4
T magnetic field. The absorbance at 500 nm of S0T is an
average of four experiments performed at 37°C.