1154
Chemistry Letters Vol.35, No.10 (2006)
A New Chemical Oscillator with a Macrocyclic Copper(II) Complex
as Catalyst and Lactic Acid as the Substrate
Gang Hu1;2 and Zude Zhangꢀ1
1Department of Chemistry, University of Science and Technology of China, Hefei 230026, P. R. China
2Department of Chemistry, Anhui University, Hefei 230039, P. R. China
(Received May 2, 2006; CL-060515; E-mail: zzd@ustc.edu.cn)
The oscillatory features of a new type Belousov–Zhabotin-
thermostat. The volume of the reaction was 40 mL. The redox
potential and instantaneous bromide concentration were moni-
tored by a platinum electrode and bromide-selective electrode,
respectively. The reference electrode was a saturated calomel
electrode connected via a salt bridge containing 10% KNO3.
Potentials of these two electrode as a function of time were
measured and recorded by using two digital voltmeters (DVM)
connected to a x–t recorder (Model XWT-264); a x–y recorder
(Model LZ-3) was introduced to investigate the oscillation
trajectories of the potentials of platinum electrode vs these of
bromide-selective electrode.
When catalytic quantities of [CuL](ClO4)2 was added to the
homogeneous solution containing NaBrO3, H2SO4, and lactic
acid (Lac), strongly damped concentration oscillations of plati-
num electrode and bromide selective electrode were observed
(Figures 2a and 2b). During the oscillations, the solution color
changed periodically between red and orange, showing the
oscillations between [CuL]2þ and [CuL]3þ. Present oscillator
could give oscillations only within the concentration range of
[NaBrO3] = 0.0210–0.0875 M, [H2SO4] = 0.45–1.0 M, [Lac] =
0.2–0.994 M, [[CuL]2þ] > 0:00167 M. When several aliquots of
solution of [CuL](ClO4)2 were successively added to the reac-
tion in which the oscillation had ceased, oscillations took place
again and the period remained the same. Addition of solution
of lactic acid could also revive the oscillation but addition of
solution of NaBrO3 failed to do so. These phenomena show that
the damping of the oscillations is not due to the depletion of the
NaBrO3 but owing to the depletion of the catalyst and lactic
acid.
To NaBrO3–H2SO4–Lac–[CuL](ClO4)2 oscillator, varia-
tions in initial concentration of reactants resulted in obvious
variation of period of oscillation (tp). The period of oscillation
decrease when the concentration of H2SO4 increase while the
concentration of NaBrO3, Lac, and [CuL](ClO4)2 fixed.
Smoes14 reported a ferroin-catalyzed oscillator in which pe-
riod of oscillation depends on initial concentration. We observed
that the dependence of the period of oscillation on the initial
concentrations of H2SO4 and lactic acid is similar to that of
ferroin-catalyzed one. However, different from ferroin-catalyzed
oscillator, with the increase in concentrations of NaBrO3, there
is a decrease in frequency.
skii oscillator with a macrocyclic copper(II) complex [CuL]-
(ClO4)2 as catalyst and lactic acid as the substrate have been
reported. This complex contains the ligand 5,7,12,14-tetra-
ethyl-7,14-dimethyl-1,4,8,11-tetraazacyclotetradeca-4,11-diene.
A tentative mechanism based on FKN has been suggested.
Oscillatory chemical reactions have been of interest for
decades.1 The most extensively studied reaction is the classical
Belousov–Zhabotinskii (BZ) oscillator, which involves the
oxidation of an organic substrate by acid bromate in the presence
of a metal ion catalyst2–5 (usually Ce4þ, Mn2þ, Fe(phen)32þ, or
Ru(bipy)32þ). Recently, oscillators involving tetraazamacrocy-
clic complexes as catalysts have been discussed in literatures.6–12
In these oscillators, the organic substrates were malonic acid,
malic acid, or pyruvic acid. In order to search for the possibil-
ities that other organic substrate species may participate in
these kinds of oscillators, we investigated the behavior of lactic
acid (lac).
We reported in this letter the discovery of a new oscillator,
NaBrO3–H2SO4–Lac–[CuL](ClO4)2, where L is 5,7,12,14-tetra-
ethyl-7,14-dimethyl-1,4,8,11-tetraazacyclotetradeca-4,11-diene.
The structure of [CuL]2þ is shown in Figure 1. Because of the
fact that lactic acid is an important intermediate in the energy
metabolism of animal and that tetraazamacrocyclic complexes
have similar structure to some enzymes, present oscillator is of
biochemical importance in that it could be regarded as a good
man-made mimic for some observed biochemical oscillators.
The catalyst [CuL](ClO4)2 was prepared according to liter-
ature13 and was identified by its IR spectra and elemental analy-
ses. All materials were of analytical grade except for lactic acid.
Lactic acid is biochemical. All materials were used without fur-
ther purification except for NaBrO3. NaBrO3 was recrystallized
in hot water three times to remove Brꢁ and other impurities. All
oscillation experiments were performed in a closed glass
container with a magnetic stirrer at 10 ꢂ 0:5 ꢃC regulated by a
If the concentration of Agþ present in the oscillating system
exceeds 6:25 ꢄ 10ꢁ5 M, the potential of bromide selective
electrode decreased temporarily due to the formation of AgBr.
Apparently Brꢁ is a control intermediate.15 The variation of
concentration of Brꢁ can ‘‘turn on’’ and ‘‘turn off’’ certain chemi-
cal processes in the oscillatory reactions.
HN
N
Cu2+
NH
N
A x–y recorder showed that the oscillation trajectories of
potentials of platinum electrode vs those of bromide selective
electrode are spirals instead of limit cycles.16
Figure 1. The structure of [CuL]2þ
.
Copyright Ó 2006 The Chemical Society of Japan
Hu, Gang
