1
672 Jiao et al.
Asian J. Chem.
J&K Scientific Ltd. and were used without further purification.
ADA-Te-ADA was synthesized according to the previous
than traditional PhSeSePh. Additionally, the highest catalytic
rates were observed when different co-solvents were used,
which were given in Table-1.
10
reported . The structure ofADA-Te-ADA was determined as:
1
H NMR (300 MHz, CDCl
3
) δ (ppm) 4.09 (t, 2 H, -COOCH
2
),
2
.66 (t, 2 H, -TeCH ), 2.07 (m, 2 H, -CH
2
2
-), 2.01 (s, 3 H, adaman-
tane), 1.88 (s, 6 H, adamantane), 1.71 (s, 6 H, adamantane).
UV-visible spectra were obtained using a Pgeneral T6 UV-
visible spectrophotometer. The buffer pH values were
determined with a METTLER TOLEDO 320 pH meter.
Determination of glutathione peroxidase activity in
solvent mixture of PBS and co-solvents: The catalytic activity
was assayed according to a modified method reported by Wu
11
and Hilvert . The typical assay process of glutathione peroxi-
dase activity in solvent mixture of PBS and ethanol was shown
as follows: The reaction was carried out at 25 °C in a 1 mL
quartz cuvette, 700 µL solvent mixture of PBS, ethanol and
Fig. 1. Determination of glutathione peroxidase catalytic rates of ADA-
Te-ADA for the reduction of CUOOH using NBT as substrate
TABLE-1
1
00 µL of the catalyst (ADA-Te-ADA) (0.025 mM) were added
INITIAL RATES (ν ) AND ACTIVITIES FOR THE REDUCTION
0
and then 100 µL of the 4-nitrobenzenethiol solution (1 mM)
was added. The mixture in the quartz cuvette was pre-incubated
at 25 °C for 3 min. Finally, the reaction was initiated by the
addition of 100 mL of cumene hydroperoxide (2 mM) and the
OF CUMENE HYDROPEROXIDE (2 mM) BY 4-NITRO-
BENZENETHIOL (1 mM) IN THE PRESENCE OF
ADA-Te-ADA (0.025 mM) AT pH 7 and 25 °C
-
1 a
Co-solvent
C H OH
DMSO
DMF
PBS:co-solvent (v:v)
ν (mM min )
0
6:4
6:4
5:5
6:4
4.21 ± 0.35
2.71 ± 0.22
2.55 ± 0.13
3.22 ± 0.28
2
5
absorption decrease of 4-nitrobenzenethiol at 410 nm (ε410
=
-1
-1
13600M cm . pH = 7) was monitored using a Pgeneral T6
UV-visible spectrophotometer. Appropriate control of the non-
enzymatic reaction was performed and was subtracted from
the catalyzed reaction. The glutathione peroxidase activities
in solvent mixture of PBS and other co-solvents were assayed
similarly except ethanol was replaced by other co-solvents.
Determination of the glutathione peroxidase catalytic
rates influenced by co-solvents: The volume ratios of PBS:
ethanol used in the determination of the glutathione peroxidase
catalytic rate were considered as: 9:1; 8:2; 7:3; 6:4; 5:5; 4:6;
CH CN
3
a
Initial rate of reaction was corrected for the spontaneous oxidation.
The concentration of catalyst is 0.025 mM and assuming one molecule
catalytic center (tellurium moiety) as one active site of enzyme
Determination of the glutathione peroxidase catalytic
rate influenced by co-solvent: Herein, the solvent mixture
consisted of PBS and co-solvent was employed as assay solu-
tion to determine the glutathione peroxidase catalytic rate. The
ratio of PBS to co-solvent was fixed to 9:1; 8:2; 7:3; 6:4; 5:5;
3:7; 2:8. The catalytic activities influenced by other co-solvents
4
:6; 3:7; 2:8, respectively. Typically, glutathione peroxidase
were assayed similarly except ethanol was replaced by other
co-solvents.
catalytic rate influenced by increasing added ethanol was
investigated. By plotting the catalytic reaction rate against the
volume ratio of PBS to co-solvent (Fig. 2). From Fig. 2a, we
noted that the catalytic rate ofADA-Te-ADA increased to some
extent with ethanol increasing added. And the highest value
RESULTS AND DISCUSSION
Determination of the glutathione peroxidase catalytic
activity of ADA-Te-ADA: Herein, to reveal the relation bet-
ween the catalytic rate of artificial glutathione peroxidase and
the property of solvent mixture, ADA-Te-ADA was selected
as the typical hydrophobic artificial glutathione peroxidase
-1
(4.21 µM × min ) was obtained when the volume ratio was
6:4. However, the catalytic reaction rate largely decreased when
the volume ratio increased further. Additionally, the similarly
catalytic behaviours were also observed when DMSO, DMF
(Fig. 1). It was clear that several hydrophobic groups presented
and CH CN were used as co-solvents (Fig. 2b-d).
3
in ADA-Te-ADA, such as adamantane, -TeCH -, -CH - and
so on. Therefore, the solubility ofADA-Te-ADA in water was
poor. Thus, the catalytic property ofADA-Te-ADA was inves-
2
2
Considering that ADA-Te-ADA consisted of several
hydrophobic groups, it is speculated that the interesting pheno-
mena of catalytic rate increasing to some extent with the
volume ratio going up was derived from the change of solubi-
lity ofADA-Te-ADA in solvent mixture. Therefore, the better
solubility of ADA-Te-ADA was favorable for the homo-
geneous phase system consistedADA-Te-ADA and substrates.
And the highest value was exhibited when the appropriate
solubility of ADA-Te-ADA and substrates was achieved.
Furthermore, the possible reason for the decreased catalytic
reaction rate might be endowed from the hydrophobic driving
force. It was noted that the hydrophobic driving force might
result in the conformation change of hydrophobic dendrimer-
tigated using ethanol, DMSO, DMF, CH CN, as co-solvents,
3
respectively. Typically, the catalytic activity ofADA-Te-ADA
for the reduction of cumene hydroperoxide by 4-nitro-
benzenethiol was evaluated according to the modified method
11
reported by Wu and Hilvert using 4-nitrobenzenethiol as a
glutathione (GSH) alternative (Fig. 1). Compared with the
traditional small molecule artificial glutathione peroxidase
-1
PhSeSePh (ν = 0.019 µM × min ), a remarkable rate enhance-
0
ment was observed when ADA-Te-ADA was functioned as
artificial glutathione peroxidase under the conditions of
different solvent mixture (Table-1). This observation proved
that ADA-Te-ADA exhibited more excellent catalytic ability
8
based artificial glutathione peroxidase . Thus, the change of
conformation could alter the substrate selectivity of artificial
Jiao
