Journal ArticleDOI
Kinetic hydrogen isotope effects in the concerted mechanism for the hydrolysis of acetals, ketals, and ortho esters
TLDR
In this paper, it was shown that the reaction coordinate is primarily a reorganization of heavy atoms since proton transfer from one oxygen to another has been shown to generate strongly curved Bronsted plots.Abstract:
The hydrolysis of many ortho esters, and some acetals and ketals, is general acid catalyzed, and in some examples these generate linear Bronsted plots over substantial ranges of catalyst acidity. This suggests that the reaction coordinate is primarily a reorganization of heavy atoms since proton transfer from one oxygen to another has been shown to generate strongly curved Bronsted plots. However, the isotopic fractionation factor for the catalytically active proton in these transition states is substantially less than 1.0; in several examples it is less than 0.5. Such values have been thought to require that the reaction coordinate be largely a motion of the hydrogen giving the low fractionation factor. This dilemma has been resolved by the observation and rationalization of fractionation factors as low as 0.28 for stable, hydrogen bridge-bonded complexes, AHA/sup -/. A similar, bounded coordinate is now suggested for the catalytically active protons in question. This permits the reaction coordinate to be pictured. 3 figures, 2 tables.read more
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Journal ArticleDOI
Proton-Coupled Electron Transfer
David R. Weinberg,Christopher J. Gagliardi,Jonathan F. Hull,Christine Fecenko Murphy,Caleb A. Kent,Brittany C. Westlake,Amit Paul,Daniel H. Ess,Dewey G. McCafferty,Thomas J. Meyer +9 more
TL;DR: Proton-coupled electron transfer is an important mechanism for charge transfer in a wide variety of systems including biology- and materials-oriented venues and several are reviewed.
Journal ArticleDOI
The proton inventory technique.
TL;DR: The proton inventory technique uses the dependence of enzymic reaction rate on the atom fraction of deuterium present in mixtures of protium oxide and deuterIUM oxide to deduce for simple cases the number of exchangeable hydrogenic sites that produce isotope effects, and the magnitude of the isotope effect generated at each site.
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Solid State15N NMR and Theoretical Studies of Primary and Secondary Geometric H/D Isotope Effects on Low-Barrier NHN−Hydrogen Bonds
Hans Benedict,Hans-Heinrich Limbach,Martin Wehlan,‡ Wolf-Peter Fehlhammer,and Nicolai S. Golubev,Rudolf Janoschek +5 more
TL;DR: In this article, a combination of high resolution and dipolar solid state 15N NMR was used to determine H/D isotope effects on the nitrogen-hydron (L = H, D) distances and 15N chemical shielding tensors of strongly hydrogen-bonded bisisocyanide salts of the type [(CO)5Cr−C⋮N···L−L-N ⋮C−Cr(CO) 5]- X+, where X+ = AsPh4++ (2) and X+= NPr4+
Journal ArticleDOI
Photophysics and Biological Applications of 7-Azaindole and Its Analogs
Alexandre V. Smirnov,Douglas S. English,R. L. Rich,J. Lane,Luc Teyton,A. W. Schwabacher,S. Luo,R. W. Thornburg,Jacob W. Petrich +8 more
TL;DR: The sensitivity of 7-azaindole to its environment is demonstrated and then exploited by studying it and its analogs in peptides and in complexes with larger proteins containing many tryptophan residues.
Journal ArticleDOI
Hydrogen bonds and proton transfer in general-catalytic transition-state stabilization in enzyme catalysis.
TL;DR: The question of the nature of the proton bridge involved in general acid-base catalysis in both enzymic and non-enzymic systems is considered, and rough estimates of the degree to which theProton will respond to structural changes in its bonding partners are given.