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Electronic Supporting Information (ESI)
[RuIII(edta)(H2O)]- mediated oxidation of hydroxyurea with H2O2. Kinetic and
mechanistic investigation
Debabrata Chatterjee, Kalyan Asis Nayak, Erika Ember and Rudi van Eldik
Experimental
Materials. K[RuIII(Hedta)Cl].2H2O was prepared by following the published
procedure,30 and characterized by elemental analysis and spectral data which were in
agreement with data reported in the literature. Anal. Calculated for
K[RuIII(Hedta)Cl].2H2O: C 24.0, H 3.42, N 5.59; Found. C 23.8, H 3.45, N 5.63. IR,
ν/cm-1: 1720 (free -COOH), 1650 (coordinated -COO-). UV-VIS in H2O: λmax/nm
(εmax/M-1 cm-1): 283 (2800 ± 50), 350 sh (680 ± 10). The complex rapidly hydrolyses to
the aqua complex when dissolved in water, and thus exists predominantly in its most
labile form [RuIII(edta)(H2O)]- (1) in the pH range 4 to 6. Hydrogen peroxide solutions
were prepared by dilution of reagent-grade 35 % (Fluka) hydrogen peroxide and stored at
4 °C prior to use. The concentration of hydrogen peroxide was periodically determined
by titration with potassium permanganate. All other chemicals used were of AR grade,
and doubly distilled H2O was used to prepare all solutions.
Instrumentation. UV-visible spectra were collected as a function of time by the use of a
rapid-scanning, dual beam spectrophotometer (Specord S 600) coupled with Alalytikjena
temperature controller. The measurements were made in tandem quartz cuvettes. Either a
SF-61SX2 (HI-TECH) stopped-flow spectrophotometer coupled to a (KinetaScan) rapid
scan spectral attachment or an Applied Photophysics SX 18.MV stopped-flow instrument
coupled to an J&M rapid scan detector, and on-line data acquisition systems were used
for all kinetic measurements. Kinetic measurements at high pressure were carried out
using a homemade, high pressure stopped-flow system. Kinetic traces were analyzed with
the OLIS KINFIT program (Bogart, GA). All the instruments were thermostated at the
desired temperature (± 0.1 °C). The pH of the solutions was measured with a Mettler
Delta 350 pH meter. Acetic acid-acetate buffer was used to adjust the pH of the
Electronic Supplementary Information for Dalton TransactionsThis journal is © The Royal Society of Chemistry 2010
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experimental solutions. Observed pseudo-first order rate constants (kobs) are presented as
an average of several kinetic runs (at least 10 to 12) and were reproducible within ± 4%.
Estimation of nitrite and nitrate was performed on a Dionex DX 120 chromatograph. The
release of NO resulting form addition of H2O2 to a solution of Ru-edta and HU was
monitored with isolated nitric oxide meter (WP Instruments, model ISO-NO Mark II).
Electronic Supplementary Information for Dalton TransactionsThis journal is © The Royal Society of Chemistry 2010
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A. Typical kinetic traces recorded at 370 nm for the reaction between [Ru(edta)H2O]-
(1.0 x 10-4 M) and HOU at 25 °C, pH = 5.0 (acetate buffer), [HOU] = 2.0 x 10-3 M
(A), [HOU] = 4.0 x 10-3 M (B), [HOU] = 5.0 x 10-3 M (C) and [HOU] = 6.0 x 10-3
M (D).
0 200 400 600 800 1000
0,05
0,10
0,15
0,20
0,25
0,30
0,35
0,40
0,45
Abs
t, s
(A)
0 100 200 300 400 500
0,1
0,2
0,3
0,4
0,5
(B)
Abs
t, s
0 100 200 300 400 500
0,1
0,2
0,3
0,4
0,5
(C)
Abs
t, s
0 100 200 300 400 500
0,1
0,2
0,3
0,4
0,5
(D)
Abs
t, s
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B. Effect of [HOU] on the observed rate constant for the reaction of 1 x 10-4 M [RuIII(edta)(H2O]- with HOU at 25 °C and pH = 5.0.
[HOU], M
kobs, s-1 k, M-1 s-1
1 x 10-3 0.0065 2 x 10-3 0.014 3 x 10-3 0.018 4 x 10-3 0.028 5 x 10-3 0.035 6 x 10-3 0.040 7 x 10-2 0.048
6.8 ± 0.4
0,000 0,002 0,004 0,0060,00
0,01
0,02
0,03
0,04
0,05
k obs, s
-1
[HOU], M
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C. Effect of temperature on the second-order rate constant for the reaction of 1 x 10-4
M [RuIII(edta)(H2O]- with HOU at pH = 5.0.
0,0033 0,0034 0,0035
-4,8
-4,4
-4,0
-3,6
-3,2
ln(k
/T)
1/T
ΔH≠ = 52 ± 2 kJ mol−1
ΔS≠ = -53 ± 6 J K-1 mol−1
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D. Effect of pressure on the second-order rate constant for the reaction of 1 x 10-4 M [RuIII(edta)(H2O]- with HOU at 25 °C and pH = 5.0.
0 200 400 600 800 1000 1200 14001.6
1.8
2.0
2.2
2.4
2.6
lnk
P, atm
ΔV≠ = -16.0 ± 0.6 cm3 mol−1
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E. Spectral changes that occur during the reaction of [RuIII(edta)(OU)]2- with H2O2 in the presence of an excess of HOU.
300 400 500 6000,00
0,05
0,10
0,15
0,20
0,25
0,30
0,35
abs
wavelength, nm
0 500 1000 1500 2000 25000,26
0,28
0,30
0,32
0,34
0,36
abs
t, s
370 nm
Electronic Supplementary Information for Dalton TransactionsThis journal is © The Royal Society of Chemistry 2010
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