Guanidine

Not to be confused with Guanine, Guanosine, or Guanfacine.
Guanidine
Names
IUPAC names
Guanidine[1]
Iminomethanediamine
Identifiers
113-00-8 YesY
506044
ChEBI CHEBI:42820 YesY
ChEMBL ChEMBL821 YesY
ChemSpider 3400 YesY
DrugBank DB00536 YesY
EC Number 204-021-8
100679
4783
Jmol interactive 3D Image
Image
MeSH Guanidine
PubChem 3520
UNII JU58VJ6Y3B YesY
Properties
CH5N3
Molar mass 59.07 g·mol−1
Melting point 50 °C (122 °F; 323 K)
log P −1.251
Acidity (pKa) 13.6
Thermochemistry
−57–−55 kJ mol−1
−1.0511–−1.0531 MJ mol−1
Pharmacology
Pharmacokinetics:
7–8 hours
Hazards
Lethal dose or concentration (LD, LC):
475 mg/kg (oral, rat)[2]
Related compounds
Related compounds
Except where otherwise noted, data are given for materials in their standard state (at 25 °C [77 °F], 100 kPa).
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Infobox references

Guanidine is the compound with the formula HNC(NH2)2. It is a colourless solid that dissolves in polar solvents. It is a strong base that is used in the production of plastics and explosives. It is found in urine as a normal product of protein metabolism. Guanidine is the functional group on the side chain of arginine.

Structure

Guanidine can be thought of as a nitrogenous analogue of the carbonic acid functional group. That is, the C=O group in carbonic acid is replaced by a C=NH group, and each OH is replaced by a NH2 group.[3] A detailed crystallographic analysis of guanidine was elucidated 148 years after its first synthesis, despite the simplicity of the molecule.[4] In 2013, the positions of the hydrogen atoms and their displacement parameters were accurately determined using single-crystal neutron diffraction.[5]

Production

Guanidine can be obtained from natural sources, being first isolated by Adolph Strecker via the degradation of guanine.[6]

The compound was first synthesized in 1861 by the oxidative degradation of an aromatic natural product, guanine, isolated from Peruvian guano.[7] The commercial route involves a two step process starting with the reaction of dicyandiamide with ammonium salts. Via the intermediacy of biguanidine, this ammonolysis step affords salts of the guanidinium cation (see below). In the second step, the salt is treated with base, such as sodium methoxide.[6]

Guanidinium salts

With a pKb of 0.4, guanidine is a strong base. In neutral water, it exists exclusively as guanidinium [C(NH2)3]+). Most guanidine derivatives are in fact such salts.

Industry

The main salt of commercial interest is the nitrate [C(NH2)3]NO3. It is used as a propellant, for example in air bags.

Biochemistry

Guanidine is protonated in physiological conditions. This conjugate acid is called the guanidinium cation, [CH6N3]+. It is a highly stable +1 cation in aqueous solution due to the efficient resonance stabilization of the charge and efficient solvation by water molecules. As a result, its pKa is 13.6[8] meaning that guanidine is a very strong base in water.

Guanidinium chloride has chaotropic properties and is used to denature proteins. Guanidine hydrochloride is known to denature proteins with a linear relationship between concentration and free energy of unfolding. In aqueous solutions containing 6 M guanidinium chloride, almost all proteins lose their entire secondary structure and become randomly coiled peptide chains. Guanidinium thiocyanate is also used for its denaturing effect on various biological samples. Guanidine hydrochloride[9] is used as an adjuvant in treatment of botulism, introduced in 1968,[10] but now its role is considered controversial[11] - because in some patients there was no improvement after this drug administration.

Other

Guanidinium hydroxide is the active ingredient in some non-lye hair relaxers.

Guanidine derivatives

The general structure of a guanidine

Guanidines are a group of organic compounds sharing a common functional group with the general structure (R1R2N)(R3R4N)C=N-R5. The central bond within this group is that of an imine, and the group is related structurally to amidines and ureas. Examples of guanidines are arginine, triazabicyclodecene, saxitoxin, and creatine.

See also

References

  1. ↑ "Guanidine - Compound Summary". PubChem Compound. USA: National Center for Biotechnology Information. 16 September 2004. Identification. Retrieved 29 February 2012.
  2. ↑ http://chem.sis.nlm.nih.gov/chemidplus/rn/50-01-1
  3. ↑ M. Goebel, T.M. Klapoetke (2007). "First structural characterization of guanidine". Chem. Commun. 43 (30): 3180–2. doi:10.1039/B705100J.
  4. ↑ T. Yamada, X. Liu, U. Englert, H. Yamane, R. Dronskowski (2009). "Solid-state structure of free base guanidine achieved at last". Chem. Eur. J. 15 (23): 5651–5. doi:10.1002/chem.200900508. PMID 19388036.
  5. ↑ P. K. Sawinski, M. Meven, U. Englert, R. Dronskowski (2013). "Single-Crystal Neutron Diffraction Study on Guanidine, CN3H5". Cryst. Growth Des. 13: 1730–5. doi:10.1021/cg400054k.
  6. 1 2 Thomas Güthner, Bernd Mertschenk and Bernd Schulz "Guanidine and Derivatives" in Ullmann's Encyclopedia of Industrial Chemistry, 2006, Wiley-VCH, Weinheim. doi:10.1002/14356007.a12_545.pub2
  7. ↑ Strecker, A (1861). "Untersuchungen über die chemischen Beziehungen zwischen Guanin, Xanthin, Theobromin, Caffeïn und Kreatinin". Liebigs Ann. Chem. 118 (2): 151–177. doi:10.1002/jlac.18611180203.
  8. ↑ Perrin, D.D., Dissociation Constants of Organic Bases in Aqueous Solution, Butterworths, London, 1965; Supplement, 1972.
  9. ↑ Kaplan, J. E.; Davis, L. E.; Narayan, V; Koster, J; Katzenstein, D (1979). "Botulism, type A, and treatment with guanidine". Annals of Neurology 6 (1): 69–71. doi:10.1002/ana.410060117. PMID 389150.
  10. ↑ http://jama.ama-assn.org/content/240/21/2276.abstract
  11. ↑ Pediatric anaerobic infections: diagnosis and management, p.529
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