Journal
JOURNAL OF THE AMERICAN CHEMICAL SOCIETY
Volume 131, Issue 43, Pages 15815-15824Publisher
AMER CHEMICAL SOC
DOI: 10.1021/ja906230n
Keywords
-
Categories
Funding
- Ministerio de Educacion y Ciencia
- European Regional Development Fund (ERDF) [CTQ2004-06594]
- U.S. National Institutes of Health [GM39754]
Ask authors/readers for more resources
Equilibrium constants for addition of glycine to substituted benzaldehydes to form the corresponding imines and pK(a)'s for ionization of the iminium ions were determined by H-1 NMR analysis in D2O. The introduction of a phenoxide anion substituent into the aromatic ring of benzaldehyde leads to a substantial increase in the pK(a) of the iminium ion from 6.3 to 10.2 for p-hydroxybenzaldehyde and to 12.1 for salicylaldehyde. An analysis of the differential effect of ortho- versus para-substitution shows that the iminium ion to salicylaldehyde is stabilized by an intramolecular hydrogen bond in aqueous solution, with an estimated energy ca. 3 kcal/mol larger than can be accounted for by a simple electrostatic interaction. A comparison of the o-O- substituent effect on the acidity of the iminium ions of glycine to benzaldehyde and 4-pyridine-carboxaldehyde provides evidence for the existence of an internal hydrogen bond of similar strength in pyridoxal 5'-phosphate (PLP) iminium ions in water. The effects of other ring substituents on the stability of PLP iminium ions are discussed.
Authors
I am an author on this paper
Click your name to claim this paper and add it to your profile.
Reviews
Recommended
No Data Available