1

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

2

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

3

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

Electronic Supplementary Information for Dalton TransactionsThis journal is © The Royal Society of Chemistry 2010

4

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

Electronic Supplementary Information for Dalton TransactionsThis journal is © The Royal Society of Chemistry 2010

5

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

Electronic Supplementary Information for Dalton TransactionsThis journal is © The Royal Society of Chemistry 2010

6

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

Electronic Supplementary Information for Dalton TransactionsThis journal is © The Royal Society of Chemistry 2010

7

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