Formation of ATP by photochemical excitation of benzoquinones in dimethylacetamide solution

Article abstract of DOI:10.1002/jccs.200200136

A new method of adenosine triphosphate production is described which involves photo-excitation of p-benzoquinones under the presence of adenosine diphosphate and inorganic phosphate in N,N-dimethylacetamide solution. A possible mechanism for the reaction is presented.

Full text of DOI:10.1002/jccs.200200136

Journal of the Chinese Chemical Society, 2002, 49, 961-963
961
Communication
Formation of ATP by Photochemical Excitation of Benzoquinones in
Dimethylacetamide Solution
Hung-Wen Lee (
) and Kunpo Huang* (
)
Department of Chemistry, Chung-Yuen Christian University, Chung-Li, Taiwan, R.O.C.
A new method of adenosine triphosphate production is described which involves photo-excitation of
p-benzoquinones under the presence of adenosine diphosphate and inorganic phosphate in N,N-dimethylacet-
amide solution. A possible mechanism for the reaction is presented.
INTRODUCTION
The molecule adenosine triphosphate (ATP) is known
possess rather strong spin-orbit coupling which facilitates
inter-system crossings, the photo-activated benzoquinones
3
can relax efficiently into their lowe s t (n- *) state. In add i -
as a common energy currency in all prese n t day living sys-
tems. It must have existed on the primitive earth in the early
stages of pre-biological evolution of life. Formation of ATP
from inorganic phosphate (Pi) and adenosine diphosphate
(ADP) is a condensation-dehydration reaction which requires
energy input either by physical1 or chemical method.2,3,4,5,6 In
the present note we demonstrate a new method in which ATP
is generated photochemically in N,N-dimethylacetamide
(DMAC) solution containing a benzoquinone, ADP and Pi.
tion, this excited state has a much longer lifetime due to mul-
tiplicities involved in this and the ground state. In order to
prove this point, commonly used energy transf e r quenchers
such as anthracene and naphthalene are separately added to
the reaction systems and their ATP yields are compared.
Anthracene is known as an efficient energy-transfer quencher
for the lowest triplet excited states of benzoquinones. The en-
ergy level of the lowest triplet excited state of anthracene lies
below that of benzoquinones (176 kJ mol-1 vs. 220 kJ mol-1,
or 682 nm vs. 539 nm). In contrast with this, naphthalene has
the corresponding triplet state energy level higher than that of
benzoquinones; hence it cannot act as energy-quencher for
the quinone triplet excited state (255 kJ mol-1 vs. 220 kJ
mol-1). The different effects of those quenchers on the
quinone triplet excited states are reflected by the different
yields of ATP, as shown in Figs. 1 and 2. The order of ATP
yields for the benzoquinones is the same as that of the life-
RESULTS AND DISCUSSION
ATP is produced when a series of benzoquinones in-
cluding p-benzoquinone, methyl benzoquinone, 2,5-dimeth-
ylbenzoquinone, trimethyl-benzoquinone are photo-excited
with wavelengths > 400 nm in the presence of ADP and Pi in
DMAC solution. Under the same conditions, duroquinone
does not produce ATP. However, if duroquinone is irradiated
by sunlight or by a light source of wavelengths shorter than
400 nm, it also generates ATP but in lesser amounts. For ex-
ample, under irradiation by bright sunlight for three hours,
the ratio of ATP yields in duroquinone and 2,5-dimethylben-
zoquinone systems is approximately 1:10.
3
time of the (n- *) state for the quinones obtained by the
works shown in references.11,12
Usually the ground state of a carbonyl group has its
electron density higher on the electronegative oxy g e n side. In
the (n- *) excited state, one of the non-bonding electrons is
brought to the more delocalized *-orbital. Therefore in this
state, the carbonyl group becomes electron-deficient and
radical-like, and is expected to behave as a strong oxi-
dant.16,17,18,19,20
Quinones are carbonyl compounds. The photo-excita-
tion by the light sources mentioned above will generate
(n- *) and ( - *) excited states of those compounds.7,8,9,10,11,12
It is generally accepted that the lowest excited states of
p-benzoquinone, methylbenzoquinone, 2,5-dimethylbenzo-
quinone and tri-methylbenzoquinone are the (n- *) state,
while the lowe s t excited state of duroquinone is the ( - *)
state.11,12,13,14 Since carbonyl groups in the benzoquinones
Unpublished works in our laboratory indicate that a
mixture solution of ADP and inorganic phosphate generated
ATP by adding proper oxidants with its redox potential higher
than 0.8 V. ATP generation was also demonstrated by the
electro-chemical anodic oxidation. Therefore, the photo-
chemical ATP formation observed in the present system is

962 J. Chin. Chem. Soc., Vol. 49, No. 6, 2002
Lee and Huang
system is likely due to be initiated by the highly oxidative
Determination of ATP concentration in each sample is
achieved by using ATP Bioluminescence assay kit CLSII
(from Roche products) in a medium containing 25 mM of
tricine (pH 7.75) and 2 mM of MgCl2.
3
character of the (n- *) state of the carbonyl group of the
benzoquinones, probably by activating the phosphate group
prior to the phosphorylation process. Investigation of the de-
tailed mechanism of the reaction is in progress.
Chemicals
Benzoquinones are obtained from Sigma Chemicals
and purified by recrystalization in tetrahydrofuran (THF) so-
lutions, followed by vacuum sublimation. Methyl- and tri-
methylbenzoquinone are prepared by mild oxidation of their
corresponding hydroquinones (from Sigma Chemicals) by
silver acetate und e r nitrogen atmosphere. The reaction is car-
ried out in THF for five days under constant stirring. The par-
ticles and precipitates are then filtered off and the solvent is
removed from the filtrate vacuum evaporation. The solid res-
idues are extracted and washed five times with n-hexane-H2O
(5:25, by volume) in order to remove CH3COOH produced.
Finally the n-hexane layer is separated out and the solvent is
removed by vacuum evaporation. Yellowish solid products
are the desired benzoquinones which are further purified by
vacuum sublimation.
EXPERIMENTAL SECTION
Light Sources
Most of the photo-excitation of benzoquinones is car-
ried out by irradiating the reaction mixtures for twenty-four
hours by four 60 watt Toa incandescent lamps (BFG 17D EX).
A light filter is used to cut off undesirable region of wave-
lengths, preserving the region long e r than 400 nm. For the re-
gion of wavelengths shorter than 400 nm, a 200 watt Hg-(Xe)
Arc Lamp (Oriel Corporation U.S.A.) is used. Some irradia-
tion is also carried und e r bright sunlight for three hours.
ATP Analy s i s
Luciferin-luciferace bioluminescence method is used.
Fig. 2. ATP yields for irradiation of various p-benzo-
quinones under the presence of anthracene.
PBQ: p-benzoquinone; MBQ: 1- methylbenzo-
quinone; DBQ: 2,5-dimethylbenzoquinone;
TBQ: trimethylbenzoquinone. Concentrations
in DMAC under Argon atmosphere: all qui-
nones, 5 mM; ortho-phosphonc acid, 4 mM;
ADP, 1 mM. Irradiation by a light source with
wavelengths > 400 nm is continued for 24
hours.
Fig. 1. ATP yields for irradiation of various benz o -
quinones under the presence of naphthalene.
PBQ: p-benzoquinone; MBQ: 1-methylbenzo-
quinone; DBQ: 2,5-dimethylbenzoquinone;
TBQ: trimethylbenzoquinone. Concentrations
in DMAC under Argon atmosphere: all qui-
nones, 5 mM; ortho-phosphoric acid, 4 mM;
ADP, 1 mM. Irradiation by a light source with
wavelengths > 400 nm is continued for 24
hours.

Photo-excited Benzoquinones and ATP Formation
Received April 22, 2002.
J. Chin. Chem. Soc., Vol. 49, No. 6, 2002 963
8. Berger, S.; Hertl, P.; Rieker, A. In The Chemistry of the
Quinonoid Compounds; Patai, S.; Rappoport, Z., Eds.; John
Wiley and Sons, 1988; p 29.
9. Trommsdorff, H. P. J. Chem. Phys. 1972, 56, 5358.
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13. Sebti, M.; Dupuy, F.; Mégel, J.; Nouchi, G. Compt. Rend.
1971, 272B, 123.
Key Words
ATP; Benzoquinones; Photochemical;
N,N-Dimethylacetamide.
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