Evidence on internal return from isotope effects in the hydrogen-deuterium exchange of benzyl sulfoxides. A caveat re-interpretation of isotopic exchange rates

1976 ◽  
Vol 98 (14) ◽  
pp. 4334-4336 ◽  
Author(s):  
Robert R. Fraser ◽  
L. K. Ng
Keyword(s):  
Exchange Rates ◽  
Isotopic Exchange ◽  
Isotope Effects ◽  
Deuterium Exchange ◽  
Hydrogen Deuterium Exchange ◽  
Hydrogen Deuterium

2,4-Diazapentadienes. II. A Carbanion Cyclization

1972 ◽  
Vol 50 (5) ◽  
pp. 678-689 ◽  
Author(s):  
D. H. Hunter ◽  
S. K. Sim
Keyword(s):  
Isotope Effect ◽  
Solvent Effects ◽  
Isotope Effects ◽  
Substituent Effects ◽  
Deuterium Exchange ◽  
Hydrogen Deuterium Exchange ◽  
Deuterium Isotope Effect ◽  
Potassium Methoxide ◽  
Proton Shift ◽  
Hydrogen Deuterium

The mechanism of the cyclization and 1,3-proton shift of 1,3,5-triaryl-2,4-diaza-1,3-pentadienes (1) catalyzed by phenyllithium and by potassium methoxide–methanol has been studied. On the basis of substituent effects, hydrogen–deuterium exchange, isotope effects, and solvent effects, it was deduced that both the cyclization and prototropy involve a common W-shaped carbanion which rapidly cyclizes. A kinetic deuterium isotope effect of 2 was calculated for protonation of this intermediate carbanion in methanol.

scholarly journals The stereospecificity and catalytic efficiency of the tryptophan synthase-catalysed exchange of the α-protons of amino acids

2004 ◽  
Vol 381 (3) ◽  
pp. 847-852 ◽  
Author(s):  
Máire E. NíBEILLIÚ ◽  
J. Paul G. MALTHOUSE
Keyword(s):  
Amino Acids ◽  
Exchange Rates ◽  
Catalytic Efficiency ◽  
Deuterium Exchange ◽  
Proton Exchange ◽  
Tryptophan Synthase ◽  
Hydrogen Deuterium Exchange ◽  
Pka Values ◽  
First Order ◽  
Hydrogen Deuterium

13C-NMR has been used to follow the tryptophan synthase (EC 4.2.1.20) catalysed hydrogen–deuterium exchange of the pro-2R and pro-2S protons of [2-13C]glycine at pH 7.8. 1H-NMR has also been used to follow the tryptophan-synthase-catalysed hydrogen–deuterium exchange of the α-protons of a range of L- and D-amino acids at pH 7.8. The pKa values of the α-protons of these amino acids have been estimated and we have determined whether or not their exchange rates can be predicted from their pKa values. With the exception of tryptophan and norleucine, the stereospecificities of the first-order α-proton exchange rates are independent of the size and electronegativity of the amino acid R-group. Similar results are obtained with the second-order α-proton exchange rates, except that both L-tryptophan and L-serine have much higher stereospecificities than all the other amino acids studied.

pH and Urea Dependence of Amide Hydrogen−Deuterium Exchange Rates in the β-Trefoil Protein Hisactophilin†

Biochemistry ◽  
2002 ◽  
Vol 41 (4) ◽  
pp. 1182-1194 ◽  
Author(s):  
R. Scott Houliston ◽  
Chengsong Liu ◽  
Laila M. R. Singh ◽  
Elizabeth M. Meiering
Keyword(s):  
Exchange Rates ◽  
Deuterium Exchange ◽  
Hydrogen Deuterium Exchange ◽  
Amide Hydrogen ◽  
Hydrogen Deuterium
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