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Sodium nitroprusside

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Sodium nitroprusside
Sample of sodium nitroprusside
Sodium nitroprusside
Names
IUPAC name
Sodium pentacyanonitrosylferrate(II)
Other names
Sodium nitroprusside
Sodium nitroferricyanide
Sodium pentacyanonitrosylferrate
SNP
Identifiers
ChEMBL
DrugBank
ECHA InfoCard 100.119.126 Edit this at Wikidata
EC Number
  • 238-373-9
RTECS number
  • LJ8750000
Properties
Na2[Fe(CN)5NO]
Molar mass 261.92 g/mol (anhydrous)
297.95 g/mol (dihydrate)
Appearance red powder
Density 1.72
good
Solubility in ethanol soluble
Structure
octahedral at Fe
Pharmacology
Intravenous
Pharmacokinetics:
Circulatory
2 minutes (metabolites: several days)
Renal
Legal status
  • In general: ℞ (Prescription only)
Hazards
NFPA 704 (fire diamond)
NFPA 704 four-colored diamondHealth 1: Exposure would cause irritation but only minor residual injury. E.g. turpentineFlammability 0: Will not burn. E.g. waterInstability 0: Normally stable, even under fire exposure conditions, and is not reactive with water. E.g. liquid nitrogenSpecial hazards (white): no code
1
0
0
Flash point Non-flammable
Except where otherwise noted, data are given for materials in their standard state (at 25 °C [77 °F], 100 kPa).
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Sodium nitroprusside is the inorganic compound with the formula Na2[Fe(CN)5NO]·2H2O.[1] This red-coloured salt, which is often abbreviated SNP, is a potent vasodilator. The sodium salt dissolves in water and to a lesser extent in ethanol to give solutions containing the dianion [Fe(CN)5NO]2−.

Preparation

Sodium nitroprusside can be synthesized by boiling potassium ferrocyanide in concentrated nitric acid:[2]

K4[Fe(CN)6] + 6 HNO3 → H2[Fe(CN)5(NO)] + CO2 + NH4NO3 + 4 NaNO3
H2[Fe(CN)5NO] + Na2CO3 → Na2[Fe(CN)5(SO)] + NO2 + H2O

Or with nitrites:[3]

[Fe(CN)6]4- + H2O + NO2- → [Fe(CN)5(NO)]2- + CN- + 2 OH-

Structure and properties

Nitroprusside is a complex anion that features an octahedral ferrous centre surrounded by five tightly bound cyanide ligands and one linear nitric oxide ligand. The molecular symmetry is C4v. Linear nitrosyl ligands are assigned a single positive charge, thus the iron is assigned an oxidation state of 2+. As such it has a low-spin d6 electron configuration and is diamagnetic; together with the relatively short N-O distance of 113pm and the relatively high stretching wavenumber of 1947 cm−1, the complex is formulated as containing an [NO]+ ligand.[3]

The chemical reactions of sodium nitroprusside are mainly associated with the NO ligand.[4] For example, addition of S2- ion to [Fe(CN)5(NO)]2- produces the red [Fe(CN)5(NOS)]4- ion, which is the basis for a sensitive test for S2- ions. An analogous reaction also exists with OH- ions, giving [Fe(CN)5(NO2)]4-.[3]

Ball-and-stick model of part of the crystal structure of sodium nitroprusside dihydrate
Ball-and-stick model of part of the crystal structure of sodium nitroprusside dihydrate[5]

Medical pharmacology

Sodium nitroprusside (Abbreviated SNP, brand name: Nitropress) has potent vasodilating effects in arterioles and venules (venules more than arterioles, but this selectivity is much less marked than that of nitroglycerin).[6] It is administered intravenously in cases of acute hypertensive emergency. SNP breaks down in circulation to release nitric oxide (NO). NO activates guanylate cyclase in vascular smooth muscle and increases intracellular production of cGMP. cGMP activates Protein Kinase G which activates phosphatases which inactivate Myosin light chains. Myosin light chains are involved in muscle contraction. The end result is vascular smooth muscle relaxation, which allow vessels to dilate.

In the human heart, nitric oxide reduces both total peripheral resistance as well as venous return, thus decreasing both preload and afterload. For this reason, it can be used in severe cardiogenic heart failure where this combination of effects can act to increase cardiac output. In situations where cardiac output is normal, the effect is to reduce blood pressure.

Metabolism and toxicity

Sodium nitroprusside slowly breaks down to release 5 cyanide ions, especially upon exposure to UV light. Despite the toxic potential of cyanide, nitroprusside remains an effective drug in certain clinical circumstances such as malignant hypertension or for rapid control of blood pressure during vascular surgery and neurosurgery. The cyanide can be detoxified by reaction with a sulfur-donor such as thiosulfate, catalysed by the enzyme rhodanese. In the absence of sufficient thiosulfate, cyanide ions can quickly reach toxic levels.[7] The half-life of nitroprusside is 1–2 minutes, but the metabolite thiocyanate has an excretion half-life of several days.

Use in research

In physiology research, sodium nitroprusside is frequently used to test endothelium-independent vasodilation. Iontophoresis, for example, allows local administration of the drug, preventing the systemic effects listed above but still inducing local microvascular vasodilation.

Sodium nitroprusside is also used in the presence of buffers as a reagent for ketone strips, which test the ketone levels in the urine of a diabetic. Colour change on the strip indicates the relative concentration of ketones.

Sodium nitroprusside spectrum is used to calibrate Mössbauer spectrometers

Sodium nitroprusside is often used as a reference compound for the calibration of Mössbauer spectrometer. It is also used as an analytical reagent in qualitative organic analysis.

In combination with acetaldehyde it is also used as a colour reagent in the development of thin layer chromatography plates, particularly for N-heterocyclic compounds.

Sodium nitroprusside is also used in a urinalysis test, called the cyanide nitroprusside test, also known as Brand's test. In this test sodium cyanide is added first to urine and let stand for approximately 10 minutes. In this time disulfide bonds will be broken by the released cyanide. The destruction of disulfide bonds liberates cysteine from cystine and homocysteine from homocystine. Next sodium nitroprusside is added to the solution and it reacts with the newly freed sulfhydryl groups. The test will turn a red/purple colour if the test is positive indicating that there was significant amounts of amino acid in the urine (aminoaciduria). Cysteine, cystine, homocysteine and homocystine all react when present in the urine when this test is performed. This test can indicate inborn errors of amino acid transporters such as cystinuria, which results from pathology in the transport of dibasic amino acids.

SNP is also used in microbiology, where it has been linked with the dispersal of Pseudomonas aeruginosa biofilms by acting as a nitric oxide donor.[8]

Use in forensic science

Sodium nitroprusside is used by forensic chemists in a preliminary test in the identification of illicit substances.[9] The test, called Simon's test, is performed by adding 1 volume of a solution of SNP and acetaldehyde in deionized water to a suspected drug, followed by the addition of 2 volumes of an aqueous sodium carbonate solution. The test turns blue for some secondary amines. The most common secondary amines encountered in forensic chemistry include 3,4-methylenedioxymethamphetamine (MDMA, the main component in Ecstasy) and phenethylamines such as methamphetamine.

References

  1. ^ A. R. Butler, I. L. Megson (2002). "Non-Heme Iron Nitrosyls in Biology". Chemical Reviews. 102 (4): 1155–1165. doi:10.1021/cr000076d.
  2. ^ "Sodium Nitrosyl Cyanoferrate" in Handbook of Preparative Inorganic Chemistry, 2nd Ed. Edited by G. Brauer, Academic Press, 1963, NY. Vol. 1. p. 1768.
  3. ^ a b c Catherine E. Housecroft; Alan G. Sharpe (2008). "Chapter 22: d-Block metal chemistry: the first row metals". Inorganic Chemistry, 3rd Edition. Pearson. p. 721. ISBN 978-0-13-175553-6.
  4. ^ Coppens, P.; Novozhilova, I.; Kovalevsky, A. (2002). "Photoinduced Linkage Isomers of Transition-Metal Nitrosyl Compounds and Related Complexes". Chem. Rev. 102 (4): 861–883. doi:10.1021/cr000031c.{{cite journal}}: CS1 maint: multiple names: authors list (link)
  5. ^ A. Navaza, G. Chevrier, P. M. Alzari, P. J. Aymonino (1989). "Single-crystal neutron diffraction structure of sodium pentacyanonitrosylferrate(2−) (sodium nitroprusside) dihydrate". Acta Cryst. 45 (6): 839–841. doi:10.1107/S0108270188013691.{{cite journal}}: CS1 maint: multiple names: authors list (link)
  6. ^ http://dailymed.nlm.nih.gov/dailymed/archives/fdaDrugInfo.cfm?archiveid=2402
  7. ^ Nitropress (Nitroprusside Sodium) Drug Information: User Reviews, Side Effects, Drug Interactions and Dosage at RxList. Rxlist.com. Retrieved on 2010-12-11.
  8. ^ Barraud, N; Hassett, DJ; Hwang, SH; Rice, SA; Kjelleberg, S; Webb, JS (2006). "Involvement of nitric oxide in biofilm dispersal of Pseudomonas aeruginosa". Journal of bacteriology. 188 (21): 7344–53. doi:10.1128/JB.00779-06. PMC 1636254. PMID 17050922.
  9. ^ Carol L. O’Neala, Dennis J. Croucha, Alim A. Fatahb (2000). "Validation of twelve chemical spot tests for the detection of drugs of abuse". Forensic Science International. 109: 189–201. doi:10.1016/S0379-0738(99)00235-2. PMID 10725655.{{cite journal}}: CS1 maint: multiple names: authors list (link)
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