Hydrogen bonds low barrier

CS indicated that the enolate of acetyl-CoA is significantly more stable than the enol or a proton-sharing enolic form and thus do not support the proposal that a low barrier hydrogen bond is involved in catalysis in CS. This study demonstrates the practial application of high level QM-MM studies to the elucidation of mechanistic details of an enzymatic reaction that are otherwise unclear. 

Garcia-Viloca, M., Gelabert, R., Gonzalez-Lafont, A., Moreno, M., Lluch, J. M., 1998, Temperature Dependence of Proton NMR Chemical Shift as a Criterion to Identify Low-Barrier Hydrogen Bonds , J. Am. Chem. Soc., 120, 10203. 

Smallwood, C. J., McAllister, M. A., 1997, Characterization of Low-Barrier Hydrogen Bonds. 7. Relationship Between Strength and Geometry of Short-Strong Hydrogen Bonds. The Formic Acid-Formate Anion Model System. An Ab Initio and DFT Investigation , J. Am. Chem. Soc., 119, 11277. 

Warshel, A., A. Papazyan, and P. Kollman. 1985. On Low-barrier Hydrogen Bonds and Enzyme Catalysis. Science 269, 102. 

Fig. 2.8 The low-barrier hydrogen bond between Lysl6 and an oxygen atom of GTP /1-phosphate group. The electron localization function (ELF) is projected on the plane containing the three atoms involved in the LBHB. The red and yellow areas located between the... 

The topologically defined region(s) on an enzyme responsible for the binding of substrate(s), coenzymes, metal ions, and protons that directly participate in the chemical transformation catalyzed by an enzyme, ribo-zyme, or catalytic antibody. Active sites need not be part of the same protein subunit, and covalently bound intermediates may interact with several regions on different subunits of a multisubunit enzyme complex. See Lambda (A) Isomers of Metal Ion-Nucleotide Complexes Lock and Key Model of Enzyme Action Low-Barrier Hydrogen Bonds Role in Catalysis Yaga-Ozav /a Plot Yonetani-Theorell Plot Induced-Fit Model Allosteric Interaction... 

LOW-BARRIER HYDROGEN BONDS (Potential Role In Catalysis)... 

Low-barrier hydrogen bonds (abbreviated LBHBs) are short, very strong hydrogen bonds formed when the electron-pair donors (most commonly oxygen or nitrogen atoms in proteins) sharing the hydrogen have comparable pXa values. 

More recently, Cassidy et aid conducted additional H NMR experiments to evaluate the basicities of the dyad H57-D102 in the tetrahedral complexes of chymotrypsin with the peptidyl trifluoromethyl ketones (TFKs) N-acetyl-L-Leu-DL-Phe-CFs and A-acetyl-oL-Phe-CFs. The proton bridging His-57 and Asp-102 is part of a low-barrier hydrogen bond (LBHBs). In H NMR spectra at pH 7.0, these protons appear at 8 18.9 and 18.6 ppm. 

SOLVENT-SEPARATED ION PAIR SOLVENT-SHARED ION PAIR TIGHT ION PAIR LOSSEN REARRANGEMENT LOW-BARRIER HYDROGEN BONDS (Potential Role in Catalysis)... 

NUCLEAR MAGNETIC RESONANCE LARMOR PRECESSION LIGAND BINDING ANALYSIS LINE-SHAPE ANALYSIS LOW-BARRIER HYDROGEN BONDS ROLE IN CATALYSIS MAGNESIUM ION (INTRACELLULAR) MAGNETIZATION TRANSFER Nuclear pores,... 

In the third transition state (TS3), the neutral catalyst is recovered by transferring the proton back from the catalyst to the substrate. In other words, the (former) azlactone ether oxygen atom deprotonates the tertiary ammonium ion. For proton transfer, again a low-barrier hydrogen bond is formed (N—O distance 2.479A, <(0,H,N) = 166.2°). In the product complex, the catalyst is neutral and the N-acylamino acid ester is bound in its iminol form to the catalyst (Product [iminol]). Finally, an additional 66.6kJ/mol are gained by the subsequent iminol-amide tautomerization (Product [amide]). 

Scheme 4.2 Bond energy as a function of hydrogen position (black solid line), assuming identical pff, values for the donor and acceptor, relative to the lowest vibrational energy level of the hydrogen atom (highlighted by a dotted line), (a) A standard, symmetric hydrogen bond (b) the corresponding low-barrier hydrogen bond (LBHB). The red line represents the probability density function [27, 28].

In protonated l,8-bis(dimethylamino)-naphthalene [9a] 2hJ(N j,N g) = + 8.7 Hz, which is mediated by the proton since in the unprotonated compound [9b] the corresponding J(N 1,N 8) coupling was not detected. In [9a] the (N-H-N)+ interaction corresponds to a classical low-barrier hydrogen bond with a symmetric configuration. 

Does the "low-barrier hydrogen bond" in the catalytic triad play any special role in catalysis ... 

Lou Gehrig s disease 884 Low barrier hydrogen bond 614 Lowry method 102 Luciferase 795 Lungfish, genome 12... 

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