Transition Met Chem
been studied [19, 20]. Moreover, these Pt(IV) complexes
can oxidize DODT to form a cyclic intramolecular
disulfide bond [19, 20].
Pittsburgh, PA). Standard buffers of pH 4.00, 7.00 and
10.00 were used to calibrate the electrode.
DL-Dithiothreitol (DTT, a well-known reducing agent in
biological sciences) is usually oxidized to form an
intramolecular disulfide bond [21–23]. However, the oxi-
dation of DTT by Pt(IV) complexes has not yet been
reported. In this work, we have synthesized a Pt(IV)
complex [PtCl2(en)(heda)]Cl2 (heda = N-(2-hydroxyethyl)
ethylenediamine) in order to increase the variety of Pt(IV)
complexes used in such chemistry. In addition, the kinetics
and mechanism of the oxidations of DODT and DTT by
[PtCl2(en)(heda)]Cl2 have been studied in detail.
Solutions for kinetic experiments
Combinations of NaOAc/HOAc, Na2HPO4/NaH2PO4 were
used to prepare the buffer solutions, which contained 0.1 M
NaCl and 2.0 mM Na2EDTA. NaCl in the buffer solutions
was used to suppress the hydrolysis of Pt(IV) complex,
while Na2EDTA was used to eliminate the possible cat-
alytic effect of trace metal ions such as Cu(II) and Fe(III)
during the thiol autooxidation processes [24–26]. All the
buffer solutions were adjusted to 1.0 M ionic strength
(l = 1.0 M) by adding NaClO4. A stock solution of
1.0 mM trans-[PtCl2(en)(heda)]2? was prepared by dis-
solving the appropriate amount of [PtCl2(en)(heda)]Cl2 in a
solution containing 0.90 M NaClO4, 0.09 M NaCl and
0.01 M HCl. Stock solutions of 20.0 mM dithiol (DODT or
DTT) were prepared by dissolving the required amount of
dithiol in a buffer solution. All stock solutions were pre-
pared afresh each day, using doubly distilled water.
Experimental
Materials
Standard buffers of pH 4.00, 7.00 and 10.00, K2PtCl4,
KMnO4,
N-(2-hydroxyethyl)ethylenediamine
(heda),
sodium perchlorate, perchloric acid, sodium acetate, acetic
acid, sodium dihydrogen phosphate, disodium hydrogen
phosphate, sodium chloride, and Na2EDTA were pur-
chased from Alfa Aesar and used as obtained. DODT and
DTT were obtained from Sigma-Aldrich. Ethylenediamine
2-hydrochloride (enÁ2HCl), concentrated HCl, diethyl
ether, and acetone were purchased from Shanghai Chemi-
cal Reagent Company (Shanghai, China). D2O was pur-
chased from Beijing Boya Dabei Technology Development
Co. (Beijing, China).
Synthesis of Pt(en)Cl2
Pt(en)Cl2 was synthesized according to the literature
method [27]. Generally, ethylenediamine 2-hydrochloride
(0.64 g, 4.82 mmol) was added to an aqueous solution of
K2PtCl4 (2.0 g, 4.82 mmol in 50 mL water). The resulting
solution was boiled under reflux for 4 h with stirring,
followed by dropwise addition of 10 mM KOH until the
pH of the solution was constant at pH 5. The fine yellow
precipitate of Pt(en)Cl2 was collected and washed with
water and ethanol, and then dried at 50 °C under vacuum
for 5 h. The product was characterized as Pt(en)Cl2ÁH2O
(65 % yield) by elemental analysis; Calc. for C2H10Cl2-
N2OPt: C, 6.98; H, 2.93; N, 8.14. Found: C, 6.88; H,
3.12; N, 8.35 %.
Instrumentation
1H NMR spectra were obtained on a Bruker Advance III
600 MHz digital NMR spectrometer (Bruker Daltonics
Inc., Billerica, MA); D2O was used as the solvent. The
signal from the water residue in the D2O was used as a
reference. Mass spectra were recorded on a Bruker Apex
Ultra electrospray mass spectrometer (Bruker Daltonics
Inc., Billerica, MA). X-ray crystallography data were col-
lected on a Bruker Smart Apex II CCD diffractometer
(Bruker Daltonics Inc., Billerica, MA). Elemental analyses
for C, H, and N were obtained on a CE-440 elemental
analyzer (Exeter Analytical Inc., North Chelmsford, MA).
UV–Vis spectra were recorded on a TU-1950 spectropho-
tometer (Beijing Puxi Inc., Beijing, China) using 1.00 cm
quartz cells. Kinetic runs and time-resolved spectra were
recorded on an Applied Photophysics SX-20 stopped-flow
spectrometer (Applied Photophysics Ltd., Leatherhead,
UK). The pH values of buffer solutions were measured
with an Accumet Basic AB15 Plus pH meter equipped with
an Accumet combination pH electrode (Fisher Scientific,
Synthesis of [Pt(en)(heda)]Cl2
Pt(en)Cl2ÁH2O (1.0 g, 2.91 mmol) was added to a solution
of heda (1.51 g, 14.5 mmol) in water (20 mL). The reac-
tion mixture was heated at 100 °C until the Pt(en)Cl2 was
totally dissolved, generating a pale yellow solution. This
was cooled to room temperature and then filtered through a
G4 sintered glass filter. The filtrate was concentrated to
about 2 mL on a rotary evaporator under reduced pressure
and then treated with ethanol and diethyl ether, resulting in
a precipitate. This was filtered off, washed with ethanol and
dried under vacuum at 50 °C for 5 h. The pale yellow
product, [Pt(en)(heda)]Cl2 (88 % yield), was characterized
by elemental analysis, ESI–MS and NMR. Calc. for C6-
H20Cl2N4OPt: C, 16.75; H, 4.69; N, 13.02. Found: C,
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