Kinetics and mechanism of the interaction of nitric oxide with pentacyanoferrate(II). Formation and dissociation of [Fe(CN)5NO]3-
The interaction of NO with [Fe(CN)5H2O]3- (generated by aquation of the corresponding ammine complex) to produce [Fe(CN)5NO]3- was studied by UV-vis spectrophotometry. The reaction product is the well characterized nitrosyl complex, described as a low-spin Fe(II) bound to the NO radical. The experim...
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2003
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paper:paper_00201669_v42_n13_p4179_Roncaroli2023-06-08T14:40:31Z Kinetics and mechanism of the interaction of nitric oxide with pentacyanoferrate(II). Formation and dissociation of [Fe(CN)5NO]3- iron derivative nitric oxide nitroprusside sodium pentacyanoferric acid unclassified drug article chemical reaction kinetics complex formation concentration response decomposition dissociation molecular interaction pH spectrophotometry The interaction of NO with [Fe(CN)5H2O]3- (generated by aquation of the corresponding ammine complex) to produce [Fe(CN)5NO]3- was studied by UV-vis spectrophotometry. The reaction product is the well characterized nitrosyl complex, described as a low-spin Fe(II) bound to the NO radical. The experiments were performed in the pH range 4-10, at different concentrations of NO, temperatures and pressures. The rate law was first-order in each of the reactants, with the specific complex-formation rate constant, kf = 250 ± 10 M-1 s-1 (25.4 °C, I = 0.1 M, pH 7.0), ΔHf‡ = 70 ± 1 kJ mol-1, ΔSf‡ = +34 ± 4 J K-1 mol-1, and ΔVf‡ = +17.4 ± 0.3 cm3 mol-1. These values support a dissociative mechanism, with rate-controlling dissociation of coordinated water, and subsequent fast coordination of NO. The complex-formation process depends on pH, indicating that the initial product [Fe(CN)5NO]3- is unstable, with a faster decomposition rate at lower pH. The decomposition process is associated with release of cyanide, further reaction of NO with [Fe(CN)4NO]2-, and formation of nitroprusside and other unknown products. The decomposition can be prevented by addition of free cyanide to the solutions, enabling a study of the dissociation process of NO from [Fe(CN)5NO]3-. Cyanide also acts as a scavenger for the [Fe(CN)5]3- intermediate, giving [Fe(CN)6]4- as a final product. From the first-order behavior, the dissociation rate constant was obtained as kd = (1.58 ± 0.06) × 10-5 s-1 at 25.0 °C, I = 0.1 M, and pH 10.2. Activation parameters were found to be ΔHd‡ = 106.4 ± 0.8 kJ mol-1, ΔSd‡ = +20 ± 2 J K-1 mol-1, and ΔVd‡ = +7.1 ± 0.2 cm3 mol-1, which are all in line with a dissociative mechanism. The low value of kd as compared to values for the release of other ligands L from [FeII(CN)5L]n- suggests a moderate to strong σ-π interaction of NO with the iron(II) center. It is concluded that the release of NO from nitroprusside in biological media does not originate from [Fe(CN)5NO]3- produced on reduction of nitroprusside but probably proceeds through the release of cyanide and further reactions of the [Fe(CN)4NO]2- ion. 2003 https://bibliotecadigital.exactas.uba.ar/collection/paper/document/paper_00201669_v42_n13_p4179_Roncaroli http://hdl.handle.net/20.500.12110/paper_00201669_v42_n13_p4179_Roncaroli |
| institution |
Universidad de Buenos Aires |
| institution_str |
I-28 |
| repository_str |
R-134 |
| collection |
Biblioteca Digital - Facultad de Ciencias Exactas y Naturales (UBA) |
| topic |
iron derivative nitric oxide nitroprusside sodium pentacyanoferric acid unclassified drug article chemical reaction kinetics complex formation concentration response decomposition dissociation molecular interaction pH spectrophotometry |
| spellingShingle |
iron derivative nitric oxide nitroprusside sodium pentacyanoferric acid unclassified drug article chemical reaction kinetics complex formation concentration response decomposition dissociation molecular interaction pH spectrophotometry Kinetics and mechanism of the interaction of nitric oxide with pentacyanoferrate(II). Formation and dissociation of [Fe(CN)5NO]3- |
| topic_facet |
iron derivative nitric oxide nitroprusside sodium pentacyanoferric acid unclassified drug article chemical reaction kinetics complex formation concentration response decomposition dissociation molecular interaction pH spectrophotometry |
| description |
The interaction of NO with [Fe(CN)5H2O]3- (generated by aquation of the corresponding ammine complex) to produce [Fe(CN)5NO]3- was studied by UV-vis spectrophotometry. The reaction product is the well characterized nitrosyl complex, described as a low-spin Fe(II) bound to the NO radical. The experiments were performed in the pH range 4-10, at different concentrations of NO, temperatures and pressures. The rate law was first-order in each of the reactants, with the specific complex-formation rate constant, kf = 250 ± 10 M-1 s-1 (25.4 °C, I = 0.1 M, pH 7.0), ΔHf‡ = 70 ± 1 kJ mol-1, ΔSf‡ = +34 ± 4 J K-1 mol-1, and ΔVf‡ = +17.4 ± 0.3 cm3 mol-1. These values support a dissociative mechanism, with rate-controlling dissociation of coordinated water, and subsequent fast coordination of NO. The complex-formation process depends on pH, indicating that the initial product [Fe(CN)5NO]3- is unstable, with a faster decomposition rate at lower pH. The decomposition process is associated with release of cyanide, further reaction of NO with [Fe(CN)4NO]2-, and formation of nitroprusside and other unknown products. The decomposition can be prevented by addition of free cyanide to the solutions, enabling a study of the dissociation process of NO from [Fe(CN)5NO]3-. Cyanide also acts as a scavenger for the [Fe(CN)5]3- intermediate, giving [Fe(CN)6]4- as a final product. From the first-order behavior, the dissociation rate constant was obtained as kd = (1.58 ± 0.06) × 10-5 s-1 at 25.0 °C, I = 0.1 M, and pH 10.2. Activation parameters were found to be ΔHd‡ = 106.4 ± 0.8 kJ mol-1, ΔSd‡ = +20 ± 2 J K-1 mol-1, and ΔVd‡ = +7.1 ± 0.2 cm3 mol-1, which are all in line with a dissociative mechanism. The low value of kd as compared to values for the release of other ligands L from [FeII(CN)5L]n- suggests a moderate to strong σ-π interaction of NO with the iron(II) center. It is concluded that the release of NO from nitroprusside in biological media does not originate from [Fe(CN)5NO]3- produced on reduction of nitroprusside but probably proceeds through the release of cyanide and further reactions of the [Fe(CN)4NO]2- ion. |
| title |
Kinetics and mechanism of the interaction of nitric oxide with pentacyanoferrate(II). Formation and dissociation of [Fe(CN)5NO]3- |
| title_short |
Kinetics and mechanism of the interaction of nitric oxide with pentacyanoferrate(II). Formation and dissociation of [Fe(CN)5NO]3- |
| title_full |
Kinetics and mechanism of the interaction of nitric oxide with pentacyanoferrate(II). Formation and dissociation of [Fe(CN)5NO]3- |
| title_fullStr |
Kinetics and mechanism of the interaction of nitric oxide with pentacyanoferrate(II). Formation and dissociation of [Fe(CN)5NO]3- |
| title_full_unstemmed |
Kinetics and mechanism of the interaction of nitric oxide with pentacyanoferrate(II). Formation and dissociation of [Fe(CN)5NO]3- |
| title_sort |
kinetics and mechanism of the interaction of nitric oxide with pentacyanoferrate(ii). formation and dissociation of [fe(cn)5no]3- |
| publishDate |
2003 |
| url |
https://bibliotecadigital.exactas.uba.ar/collection/paper/document/paper_00201669_v42_n13_p4179_Roncaroli http://hdl.handle.net/20.500.12110/paper_00201669_v42_n13_p4179_Roncaroli |
| _version_ |
1768541781887025152 |