1H/2H NMR Studies of Geometric H/D Isotope Effects on the Coupled Hydrogen Bonds in Porphycene Derivatives

2007 ◽  
Vol 129 (2) ◽  
pp. 296-304 ◽  
Author(s):  
Mariusz Pietrzak ◽  
Mohamed F. Shibl ◽  
Martin Bröring ◽  
Oliver Kühn ◽  
Hans-Heinrich Limbach
Keyword(s):  
Hydrogen Bonds ◽  
Isotope Effects ◽  
2H Nmr ◽  
Nmr Studies

NMR Studies of Solid Pentachlorophenol-4-Methylpyridine Complexes Exhibiting Strong OHN Hydrogen Bonds: Geometric H/D Isotope Effects and Hydrogen Bond Coupling Cause Isotopic Polymorphism

2012 ◽  
Vol 116 (46) ◽  
pp. 11370-11387 ◽  
Author(s):  
Brenda C. K. Ip ◽  
Ilya G. Shenderovich ◽  
Peter M. Tolstoy ◽  
Jaroslaw Frydel ◽  
Gleb S. Denisov ◽  
...  
Keyword(s):  
Hydrogen Bond ◽  
Hydrogen Bonds ◽  
Isotope Effects ◽  
Nmr Studies

Hydrogen Bonds in Ionic Liquids Revisited: 35/37Cl NMR Studies of Deuterium Isotope Effects in 1-n-Butyl-3-Methylimidazolium Chloride

2007 ◽  
Vol 111 (40) ◽  
pp. 11619-11621 ◽  
Author(s):  
Richard C. Remsing ◽  
Jayme L. Wildin ◽  
Ashleigh L. Rapp ◽  
Guillermo Moyna
Keyword(s):  
Ionic Liquids ◽  
Hydrogen Bonds ◽  
Isotope Effects ◽  
Nmr Studies ◽  
Deuterium Isotope Effects

Isotopic Perturbation of Intramolecular Hydrogen Bonds in Rigid 1,3-Diols:  NMR Studies Reveal Unusually Large Equilibrium Isotope Effects

1996 ◽  
Vol 61 (26) ◽  
pp. 9610-9613 ◽  
Author(s):  
Bridgette N. Craig ◽  
Matthew U. Janssen ◽  
Brian M. Wickersham ◽  
David M. Rabb ◽  
Peter S. Chang ◽  
...  
Keyword(s):  
Hydrogen Bonds ◽  
Isotope Effects ◽  
Nmr Studies ◽  
Intramolecular Hydrogen Bonds ◽  
Intramolecular Hydrogen

1H and 2H NMR Studies of Water in Work-Free Wheat Flour Doughs

1990 ◽  
pp. 391-414 ◽  
Author(s):  
D. André d’Avignon ◽  
Chi-Cheng Hung ◽  
Mark T. L. Pagel ◽  
Bradley Hart ◽  
G. Larry Bretthorst ◽  
...  
Keyword(s):  
Wheat Flour ◽  
2H Nmr ◽  
Nmr Studies

The syntheses of 6-C-alkyl derivatives of methyl α-isomaltoside for a study of the mechanism of hydrolysis by amyloglucosidase

2001 ◽  
Vol 79 (2) ◽  
pp. 238-255 ◽  
Author(s):  
Ulrike Spohr ◽  
Nghia Le ◽  
Chang-Chun Ling ◽  
Raymond U Lemieux
Keyword(s):  
Hydrogen Bonds ◽  
Molecular Model ◽  
Aromatic Amino Acids ◽  
Hydroxyl Group ◽  
Bulk Solution ◽  
Anomeric Effect ◽  
Nmr Studies ◽  
Intermolecular Hydrogen Bonds ◽  
Model Calculations ◽  
Derivatives Of

The epimeric (6aR)- and (6aS)-C-alkyl (methyl, ethyl and isopropyl) derivatives of methyl α-isomaltoside (1) were synthesized in order to examine the effects of introducing alkyl groups of increasing bulk on the rate of catalysis for the hydrolysis of the interunit α-glycosidic bond by the enzyme amyloglucosidase, EC 3.2.1.3, commonly termed glucoamylase (AMG). It was previously established that methyl (6aR)-C-methyl α-isomaltoside is hydrolysed about 2 times faster than methyl α-isomaltoside and about 8 times faster than its S-isomer. The kinetics for the hydrolyses of the ethyl and isopropyl analogs were also recently published. As was expected from molecular model calculations, all the R-epimers are good substrates. A rationale is presented for the catalysis based on conventional mechanistic theories that includes the assistance for the decomposition of the activated complex to products by the presence of a hydrogen bond, which connects the 4a-hydroxyl group to the tryptophane and arginine units. It is proposed that activation of the initially formed complex to the transition state is assisted by the energy released as a result of both of the displacement of perturbed water molecules of hydration at the surfaces of both the polyamphiphilic substrate and the combining site and the establishment of intermolecular hydrogen bonds, i.e., micro-thermodynamics. The dissipation of the heat to the bulk solution is impeded by a shell of aromatic amino acids that surround the combining site. Such shields are known to be located around the combining sites of lectins and carbohydrate specific antibodies and are considered necessary to prevent the disruption of the intermolecular hydrogen bonds, which are of key importance for the stability of the complex. These features together with the exquisite stereoelectronic dispositions of the reacting molecules within the combining site offer a rationalization for the catalysis at ambient temperatures and near neutral pH. The syntheses involved the addition of alkyl Grignard reagents to methyl 6-aldehydo-α-D-glucopyranoside. The addition favoured formation of the S-epimers by over 90%. Useful amounts of the active R-isomers were obtained by epimerization of the chiral centers using conventional methods. Glycosylation of the resulting alcohols under conditions for bromide-ion catalysis, provided methyl (6aS)- and (6aR)-C-alkyl-hepta-O-benzyl-α-isomaltosides. Catalytic hydrogenolysis of the benzyl groups afforded the desired disaccharides. 1H NMR studies established the absolute configurations and provided evidence for conformational preferences.Key words: amyloglucosidase (AMG), exo-anomeric effect, 6-C-alkyl-α-D-glucopyranosides and isomaltosides, mechanism of enzyme catalysis.

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