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H/D Exchange Reactions (d + exchange_reaction)

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Chemistry100%

Selected Abstracts

H/D exchange reactions;

CHEMPHYSCHEM, Issue 6 2003
sigma-bond metathesis;
The mechanism of the H/D exchange reaction in alkane/hydrogen mixtures on silica-supported zirconium hydride was investigated by a modelling study using density functional theory (DFT) calculations. The electronic activation enthalpy (,H) for the CH bond activation step (TS3) was calculated to be around 92 kJ,mol,1, whereas it would be 258 kJ,mol,1for a direct exchange process (TS1, also called the kite TS). These data clearly speak in favour of the former as a mechanism for CH bond scrambling. Moreover, the calculated enthalpy of activation (,H) for H/D exchange in H2/D2mixtures (TS2) is 33.5 kJ,mol,1, which shows that this reaction is much faster than the H/D scrambling in alkane/H2mixtures, as shown experimentally. Additionally, the calculated activation entropies (For TS1,4,,S ranges between ,129 and ,174 J,mol,1,K,1) are very negative. Although the calculated activation entropies are also in full agreement with experimental data (,S=,113 J,mol,1,K,1), overall, the calculated activation enthalpies are much higher than the experimental ones. This suggests that the actual catalyst is probably more electrophilic than the model chosen for the calculations. [source]

Hydrogen/deuterium exchange on protein solutions containing nucleic acids: utility of protamine sulfate

RAPID COMMUNICATIONS IN MASS SPECTROMETRY, Issue 16 2008
Anton Poliakov
Obtaining global hydrogen/deuterium (H/D) exchange data on proteins is an important first step in amide proton exchange experiments. Important information such as the mode of exchange, the cooperativity of folding/unfolding reactions, and the effects of ligand binding can be readily obtained in global exchange experiments. Many interesting biological systems are complexes containing both proteins and nucleic acids. The low pH conditions required to quench H/D exchange reactions result in the formation of stable protein/nucleic acid precipitates which interfere with the liquid chromatography step of the experiment and preclude obtaining mass spectrometric data. In this work we show that the precipitation of proteins and nucleic acids is electrostatic in nature and can be prevented by high ionic strength and by removing nucleic acids by protamine sulfate. Using protamine sulfate in quenching solution, we were able to obtain global H/D data with protein samples containing large amounts of DNA or RNA. Copyright © 2008 John Wiley & Sons, Ltd. [source]

Glycerol-induced folding of unstructured disulfide-deficient lysozyme into a native-like conformation

BIOPOLYMERS, Issue 8 2009
Keiko Sakamoto
Abstract 2SS[6-127,64-80] variant of lysozyme which has two disulfide bridges, Cys6-Cys127 and Cys64-Cys80, and lacks the other two disulfide bridges, Cys30-Cys115 and Cys76-Cys94, was quite unstructured in water, but a part of the polypeptide chain was gradually frozen into a native-like conformation with increasing glycerol concentration. It was monitored from the protection factors of amide hydrogens against H/D exchange. In solution containing various concentrations of glycerol, H/D exchange reactions were carried out at pH* 3.0 and 4°C. Then, 1H- 15N-HSQC spectra of partially deuterated protein were measured in a quenching buffer for H/D exchange (95% DMSO/5% D2O mixture at pH* 5.5 adjusted with dichloroacetate). In a solution of 10% glycerol, the protection factors were nearly equal to 10 at most of residues. With increasing glycerol concentration, some selected regions were further protected, and their protection factors reached about a 1000 in 30% glycerol solution. The highly protected residues were included in A-, B-, and C-helices and ,3-strand, and especially centered on Ile 55 and Leu 56. In 2SS[6-127,64-80], long-range interactions were recovered due to the preferential hydration by glycerol in the hydrophobic box of the ,-domain. Glycerol-induced recovering of the native-like structure is discussed from the viewpoint of molten globules growing with the protein folding. © 2009 Wiley Periodicals, Inc. Biopolymers 91: 665,675, 2009. This article was originally published online as an accepted preprint. The "Published Online" date corresponds to the preprint version. You can request a copy of the preprint by emailing the Biopolymers editorial office at biopolymers@wiley.com [source]

H/D exchange reactions;

CHEMPHYSCHEM, Issue 6 2003
sigma-bond metathesis;
The mechanism of the H/D exchange reaction in alkane/hydrogen mixtures on silica-supported zirconium hydride was investigated by a modelling study using density functional theory (DFT) calculations. The electronic activation enthalpy (,H) for the CH bond activation step (TS3) was calculated to be around 92 kJ,mol,1, whereas it would be 258 kJ,mol,1for a direct exchange process (TS1, also called the kite TS). These data clearly speak in favour of the former as a mechanism for CH bond scrambling. Moreover, the calculated enthalpy of activation (,H) for H/D exchange in H2/D2mixtures (TS2) is 33.5 kJ,mol,1, which shows that this reaction is much faster than the H/D scrambling in alkane/H2mixtures, as shown experimentally. Additionally, the calculated activation entropies (For TS1,4,,S ranges between ,129 and ,174 J,mol,1,K,1) are very negative. Although the calculated activation entropies are also in full agreement with experimental data (,S=,113 J,mol,1,K,1), overall, the calculated activation enthalpies are much higher than the experimental ones. This suggests that the actual catalyst is probably more electrophilic than the model chosen for the calculations. [source]