Isotope effect, mechanism, and origin of catalysis in the decarboxylation of mandelylthiamin. Academic Article

abstract

• The mechanism of decarboxylations in water and the catalysis of mandelylthiamin (MTh) decarboxylation by pyridinium ions is explored. It has been recently proposed that a decarboxylation step forming an intermediate molecule/CO(2) pair is reversible and that pyridinium ions catalyze the MTh decarboxylation by trapping the intermediate, preventing reversion to MTh. A calculation of the barrier for the back reaction goes against this proposal, as the diffusional separation of CO(2) would be on the order of 10,000 times faster. A comparison of predicted and experimental isotope effects for a series of decarboxylations including the MTh reaction shows in each case the absence of significant reversibility of the decarboxylation step. An alternative origin of the pyridinium catalysis of decarboxylation is proposed, based on the formal binding of the pyridinium ions to the decarboxylation transition state.

authors

• Singleton, Daniel

author list (cited authors)

• Gonzalez-James, O. M., & Singleton, D. A

citation count

• 29

complete list of authors

• Gonzalez-James, Ollie M||Singleton, Daniel A

publication date

• January 2010

publisher

• American Chemical Society (ACS)  Publisher

published in

• Journal of the American Chemical Society  Journal

keywords

• Carboxylic Acids
• Catalysis
• Isotopes
• Mandelic Acids
• Models, Molecular
• Molecular Conformation
• Thiamine
• Water

PubMed Central ID

• 20433168

Digital Object Identifier (DOI)

• 10.1021/ja101775s

start page

• 6896

end page

• 6897

volume

• 132

issue

• 20

URL

• http%3A%2F%2Fdx.doi.org%2F10.1021%2Fja101775s