Hydrolysis of Phosphotriesters: Determination of Transition States in Parallel Reactions by Heavy-Atom Isotope Effects
| Autor: | Mark Anderson, Frank M. Raushel, Hyunbo Shim, W. W. Cleland |
|---|---|
| Rok vydání: | 2001 |
| Předmět: |
Phosphorylcholine
Inorganic chemistry Iodide Oxygen Isotopes Biochemistry Catalysis Choline Reaction coordinate Hydrolysis Organophosphorus Compounds Colloid and Surface Chemistry Kinetic isotope effect Isotope-ratio mass spectrometry Alkaline hydrolysis chemistry.chemical_classification Ethanol Nitrogen Isotopes Chemistry Leaving group Esters General Chemistry Nitro Compounds Transition state Kinetics Isotope Labeling |
| Zdroj: | Journal of the American Chemical Society. 123:9246-9253 |
| ISSN: | 1520-5126 0002-7863 |
| DOI: | 10.1021/ja011025g |
| Popis: | The remote label method was used to measure primary and secondary (18)O isotope effects in the alkaline hydrolysis of O,O-diethylphosphorylcholine iodide (DEPC) and the primary (18)O effect in the alkaline hydrolysis of O,O-diethyl-m-nitrobenzyl phosphate (DEmNBP). Both the leaving group of interest (choline or m-nitrobenzyl alcohol) and ethanol can be ejected during hydrolysis due to the similarity of their pK values. The heavy-atom isotope effects were measured by isotope ratio mass spectrometry. Parallel reaction and incomplete labeling corrections were made for both systems. DEPC has a primary (18)O isotope effect of 1.041 +/- 0.003 and a secondary (18)O isotope effect of 1.033 +/- 0.002. The primary (18)O isotope effect for DEmNBP was 1.052 +/- 0.003. These large effects suggest a highly associative transition state in which the nucleophile approaches very close to the phosphorus atom to eject the leaving group. The large values are also indicative of a large compression, or general movement, on the reaction coordinate. |
| Databáze: | OpenAIRE |
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