H/D Exchange: Why Minimum at pH 3?

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In summary: H or pD, the lower the relative concentration. According to the site, this is due to the differences in mass between deuterium and hydrogen, with deuterium being heavier and therefore requiring a higher activation energy for bond breakage. This is explained by kinetic collision theory, which states that atoms collide and supply the energy for bond breakage. Additionally, subtle differences in electronegativity between the two isotopes may also contribute to the kinetic isotope effect.
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For a hydrogen/deuterium exchange experiment, the protein of interest is first incubated at pD = 7, after which it is quenched at pH = 2-3.

Why it the exchange done at a neutral pD and why has the exchange of hydrogen atoms a minimum at pH 3?
 
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This site pretty much explains the gist of it, there's probably a better explanation... nevertheless, here's the kinetic isotope effect

http://www.answers.com/topic/kinetic-isotope-effect

The lower the pH or pD the lower the relative concentration. According to the site, the activation energy for the breakage of a deuterium bond will be higher than the corresponding bond with hydrogen...due to the differences in mass of each, deuterium being heavier. Kinetic collision theory basically states that atoms collide, and this collision supplies the energy for the breakage of bonds (among other things), you can imagine that it'll be a bit more difficult to break the deterium bond.

Activation energy relates to the rate, the higher the energy, the slower the rate. If you wish to replace deuterium with hydrogen you'll need to increase the rate of formation of hydrogen; note that deuterium is not exactly stuck, it's in equilibrium.

The site also mentions subtle differences in electronegativity between the two in accounting for the kinetic isotope effect.

Probably not the best explanation, but hope it helps.
 
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increase the rate of formation of hydrogen

the hydrogen analog (compounds), in replacing deuterium with hydrogen
 

What is H/D exchange and why is it important?

H/D exchange is a process where hydrogen atoms in a molecule are replaced with deuterium atoms. This exchange can occur in various environments, such as in solution or in a gas phase. It is important because it provides valuable information about the structure and dynamics of molecules, which can be used for various research purposes, such as drug discovery and biomolecular studies.

Why is the minimum at pH 3 significant in H/D exchange?

The minimum at pH 3 is significant because it indicates the presence of a specific type of hydrogen bonding in the molecule. At this pH, the exchange of hydrogens is suppressed due to strong hydrogen bonding interactions, resulting in a decrease in the rate of exchange. This information can be used to understand the structure and properties of the molecule.

How is the minimum at pH 3 determined in H/D exchange experiments?

The minimum at pH 3 is determined by conducting H/D exchange experiments at different pH levels and monitoring the rate of exchange. The point where the rate of exchange reaches its lowest value is identified as the minimum at pH 3. This can be done using various techniques, such as mass spectrometry, NMR spectroscopy, and infrared spectroscopy.

What factors can affect the minimum at pH 3 in H/D exchange?

The type and strength of hydrogen bonding, the solvent environment, and the presence of other functional groups in the molecule can affect the minimum at pH 3 in H/D exchange. Additionally, temperature, pressure, and concentration of the molecule can also play a role in determining the minimum at pH 3.

How can the information obtained from H/D exchange experiments at pH 3 be used in research?

The information obtained from H/D exchange experiments at pH 3 can be used to study the structure and dynamics of molecules, as well as to understand the interactions between different molecules. This information can be applied in various fields, such as drug design, protein folding, and understanding enzyme mechanisms.

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